JP2001004942A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of performing high-speed and high-resolution laser beam scanning. SOLUTION: This device is provided with a laser beam scanner 53 scanning the surface of an electrified image carrier 5 with a laser beam. The scanner 53 is provided with a semiconductor laser array 21 provided with plural light emitting parts 21a and a rotary polygon mirror 3 deflecting the laser beam from the light emitting part 21a to the image carrier 5. The light emitting parts 21a are two-dimensionally arranged on the surface of the array 21. The lighting and the light quantity of the light emitting part 21a are individually controlled by a controller 60.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus for forming a latent image on an image carrier by scanning with a laser beam.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus which forms an electrostatic latent image on an image carrier by a laser beam and prints on paper at a high speed by an electrophotographic process has been used in an output of a computer, a facsimile, a multifunctional copying machine, or the like. It has been widely used as a device. In recent years, further improvement in output speed has been desired, and the improvement has been progressing.

For example, in an image forming apparatus using a rotating polygon mirror-type deflecting device, one scanning line is drawn by deflecting one laser beam for each small surface of the mirror surface. In order to increase the number, when the number of facets of the rotary polygon mirror is constant, the number of rotations increases. Conversely, when the rotation speed is constant, the number of surfaces of the rotating polygon mirror increases. In order to increase the number of rotations of the rotating polygon mirror, bearings using gas or liquid dynamic pressure or static pressure are required, but these bearings are expensive, difficult to handle, and cannot be used for general laser beam printers. It was difficult. Conversely, when the number of faces of the polygon mirror is increased, the deflection angle becomes smaller, and the optical path length after the deflection device becomes longer. Also, the collimated diameter of the laser beam incident on the imaging optical system increases in proportion to the optical path length, and the size of the lens and the rotating polygon mirror also increases. In particular,
When high resolution is required, the number of scanning lines increases, so that a higher rotation speed and a longer optical path length are required. This is the same phenomenon even when a device other than the rotary polygon mirror is used as the deflecting device, which causes an increase in the scanning frequency and an increase in the optical path length after the deflecting device. Therefore, an exposure method of writing a plurality of scanning lines using a plurality of laser beams in one scan (so-called multi-beam) has been developed.

In order to obtain a plurality of laser beams, a plurality of gas laser (for example, He—Ne) oscillators are used as a light source, and a laser beam of one oscillator is time-divisionally divided by an acousto-optic modulator (AOM) or the like. Although a method of distributing the laser beam to a plurality of light emitting devices has been developed, as a simpler and more compact method, for example, as shown in Japanese Patent Application Laid-Open No. 54-7328, a plurality of light emitting units for emitting laser beams are provided on one element. Integrated semiconductor laser arrays have been used as light sources.

[0005]

An image forming apparatus using a semiconductor laser array will be described below. The image forming apparatus uses a laser array integrated on one substrate as a light source, and a beam emission point of each light emitting unit is located at an end surface of a semiconductor element substrate. The plurality of laser beams are collimated by a common collimator lens into laser beams each having a substantially constant diameter, and are incident on one small surface of a rotating polygon mirror (deflecting device). Here, with the rotation of the facet, the laser beam is deflected, focused on the spot via the imaging lens, and exposes the image carrier to form an electrostatic latent image. The formed electrostatic latent image is developed and transferred on paper according to an electrophotographic process, and finally fixed. Also, as disclosed in Japanese Patent Application Laid-Open No. 54-158251, the light emitting portion of the laser array is arranged at a certain angle with respect to the scanning surface in order to reduce the interval between scanning lines that are simultaneously scanned on the image carrier. Have been.

On the other hand, there has been a demand for an image forming apparatus using such a semiconductor laser array which can perform high-speed and high-resolution scanning. However, the conventional image forming apparatus cannot sufficiently realize high-speed and high-resolution scanning.

The present invention has been made in view of the above points, and has as its object to provide a compact image forming apparatus capable of performing high-speed and high-resolution laser beam scanning.

[0008]

A first feature of the present invention is as follows.
An image carrier on which an electrostatic latent image is formed, a charger for charging the surface of the image carrier, and a laser beam scanning device for scanning a plurality of laser beams on the charged surface of the image carrier And a developing device for applying a developer to the surface of the image carrier on which the laser beam has been scanned, wherein the laser beam scanning device is a semiconductor laser array in which a plurality of laser beam emitting portions are formed on an element substrate. ,
A deflecting device for deflecting the laser beam from the light emitting unit to the surface of the image carrier, wherein the light emitting units are two-dimensionally arranged on the surface of the semiconductor laser array, and each light emitting unit is individually An image forming apparatus characterized in that lighting and light amount can be controlled.

According to a second feature of the present invention, there is provided a semiconductor laser array having a plurality of light emitting portions for laser beams formed on an element substrate, and a deflecting device for deflecting a laser beam from the light emitting portions. The laser beam scanning device is characterized in that the units are two-dimensionally arranged on the surface of the semiconductor array, and that each light emitting unit is individually controllable in lighting and light quantity.

A third feature of the present invention is that an image carrier having an electrostatic latent image formed on the surface thereof, a charger for charging the surface of the image carrier, and a charging device for charging the surface of the image carrier are provided. A laser beam scanning device for scanning a plurality of laser beams, and a developing device for applying a developer to the surface of the image carrier on which the laser beam has been scanned, wherein the laser beam scanning device has a laser beam on an element substrate. And a deflecting device for deflecting the laser beam from the light emitting portion to the surface of the image carrier, wherein the light emitting portion has an optical axis substantially perpendicular to the element substrate surface. An image forming apparatus comprising:

According to a fourth feature of the present invention, there is provided a semiconductor laser having a light emitting portion of a laser beam formed on an element substrate, and a deflecting device for deflecting the laser beam from the light emitting portion. A laser beam scanning device having an optical axis substantially perpendicular to the element substrate surface.

A fifth feature of the present invention is that an image carrier on which an electrostatic latent image is formed, a charger for charging the surface of the image carrier, and a charging device for charging the surface of the image carrier are provided. A laser beam scanning device that scans a plurality of laser beams; and a developing device that attaches a developer to a surface of the image carrier on which the laser beams have been scanned, wherein the laser beam scanning device emits a plurality of laser beams. A laser array, a collimator lens for collimating each of the plurality of laser beams, a deflecting device for periodically deflecting the directions of the plurality of laser beams collimated by the collimator lens, A scanning lens for forming an image of the laser beam on the image carrier, and the deflecting device is a rotating mirror having one reflecting surface. A forming apparatus.

A sixth feature of the present invention is that a semiconductor laser array for emitting a plurality of laser beams, a collimator lens for collimating each of the plurality of laser beams,
A deflecting device that periodically deflects the directions of the plurality of laser beams collimated by the collimator lens, and a scanning lens that forms the laser beam deflected by the deflecting device on an image carrier, The deflecting device is a rotary mirror having one reflecting surface, and is a laser beam scanning device.

A seventh feature of the present invention is that an image carrier on which an electrostatic latent image is formed, a charger for charging the surface of the image carrier, and a charging device for charging the surface of the image carrier are provided. A laser beam scanning device that scans a plurality of laser beams, and a developing device that attaches a developer to the surface of the image carrier on which the laser beams have been scanned, the laser beam scanning device includes a light emitting unit that emits a laser beam. A plurality of semiconductor laser arrays, a collimator lens for collimating each of the plurality of laser beams, a deflecting device for periodically deflecting the directions of the plurality of laser beams collimated by the collimator lens, and the deflecting device A scanning lens for forming an image of the deflected laser beam on the image carrier, wherein the focal length of the collimator lens is fc, Among the plurality of light emitting portions on Zaarei, Derutama apart farthest two light emitting portion of the mutual distance
The image forming apparatus is characterized in that fc / δmax> 25 where x is satisfied.

An eighth feature of the present invention is that a semiconductor laser array having a plurality of light emitting units for emitting a laser beam,
A collimator lens for collimating each of the plurality of laser beams; a deflecting device for periodically deflecting the directions of the plurality of laser beams collimated by the collimator lens; and a laser beam deflected by the deflecting device. A scanning lens that forms an image on a carrier, wherein the focal position of the collimator lens is fc, and a distance between two light-emitting portions of the plurality of light-emitting portions on the semiconductor laser array that is farthest from each other is δmax. Then, the laser beam scanning device is characterized in that fc / δmax> 25.

A ninth feature of the present invention is that an image carrier on which an electrostatic latent image is formed, a charger for charging the surface of the image carrier, and a charging device for charging the surface of the image carrier are provided. A laser beam scanning device that scans a plurality of laser beams, and a developing device that adheres a developer to the surface of the image carrier on which the laser beam has been scanned, the laser beam scanning device includes a plurality of laser beam emitting devices. The light emitting unit has a semiconductor laser array provided on an element substrate, and a deflecting device that deflects a laser beam emitted from the light emitting unit, and a central axis of the laser beam emitted from the semiconductor laser array is At least a part of the cross section of the plurality of laser beams is substantially perpendicular to the element substrate surface and on the optical path between the semiconductor laser array and the deflecting device. An aperture stop is provided at a position where a laser beam having the maximum power among a plurality of laser beams after passing through the aperture stop has a power of 1, and the power of each of the other laser beams is 0. 9. An image forming apparatus, wherein

According to a tenth feature of the present invention, there is provided a semiconductor laser array in which a plurality of light emitting units for emitting a laser beam are provided on an element substrate, and a deflecting device for deflecting the laser beam emitted from the light emitting unit. Having a central axis of a laser beam emitted from the semiconductor laser array is substantially perpendicular to the element substrate surface, in an optical path between the semiconductor laser array and the deflecting device,
When an aperture stop is provided at a position where at least a part of the cross section of the plurality of laser beams overlaps, and among the plurality of laser beams after passing through the aperture stop, the laser beam having the maximum power is set to 1 To
A laser beam scanning device characterized in that the power of each of the other laser beams is 0.9 or more.

An eleventh feature of the present invention resides in that an image carrier on which an electrostatic latent image is formed, a charging device for charging the surface of the image carrier, and a charging device for charging the surface of the image carrier. A laser beam scanning device that scans a plurality of laser beams,
A developing device for applying a developer to the surface of the image carrier on which the laser beam has been scanned, wherein the laser beam scanning device includes a semiconductor laser array having a plurality of light emitting units for emitting a laser beam; A collimator lens for converting the emitted laser beam into a parallel beam, and a deflecting device for deflecting the laser beam, wherein an aperture stop is provided on an optical path between the semiconductor laser array and the deflecting device; The focal length of the lens is f, the distance between the focal point of the collimator lens on the deflection device side and the aperture stop is s, and the distance between the light emitting unit and the optical axis disposed farthest from the optical axis of the collimator lens is When the interval is t, the diameter of the aperture stop is D, and the diameter of the parallel beam is d,

(Equation 1) An image forming apparatus which satisfies certain conditions.

A twelfth feature of the present invention is that an image carrier having an electrostatic latent image formed on its surface, a charger for charging the surface of the image carrier, and a charging device for charging the surface of the charged image carrier are provided. A laser beam scanning device that scans a plurality of laser beams,
A developing device for applying a developer to the surface of the image carrier on which the laser beam has been scanned, wherein the laser beam scanning device includes a semiconductor laser array having a plurality of light emitting units for emitting a laser beam; A collimator lens for converting the emitted laser beam into a parallel beam, and a deflecting device for deflecting the laser beam, an aperture stop is provided on an optical path between the semiconductor laser array and the deflecting device, The focal length of the collimator lens is f, the distance between the focal point of the collimator lens on the deflecting device side and the aperture stop is s, and the light emitting unit and the optical axis arranged at the position farthest from the optical axis of the collimator lens. Where t is the interval, D is the diameter of the aperture stop, and d is the diameter of the parallel beam.

(Equation 2) An image forming apparatus which satisfies certain conditions.

A thirteenth feature of the present invention is that a semiconductor laser array having a plurality of light emitting portions for emitting a laser beam, a collimator lens for converting the laser beam emitted from the light emitting portion into a parallel beam, A deflecting device for deflecting a beam, an aperture stop is provided on an optical path between the semiconductor laser array and the deflecting device, the focal length of the collimator lens is f, The distance between the focal point and the aperture stop is s, the distance between the light emitting unit disposed farthest from the optical axis of the collimator lens and the optical axis is t, the diameter of the aperture stop is D, and the diameter of the parallel beam is When the diameter is d,

(Equation 3) A laser beam scanning apparatus characterized by satisfying the following conditions.

According to a fourteenth feature of the present invention, there is provided a semiconductor laser array having a plurality of light emitting portions for emitting a laser beam, a collimator lens for converting the laser beam emitted from the light emitting portion into a parallel beam, and a laser. A deflecting device for deflecting a beam, an aperture stop is provided on an optical path between the semiconductor laser array and the deflecting device, the focal length of the collimator lens is f, The distance between the focal point and the aperture stop is s, the distance between the light emitting unit disposed farthest from the optical axis of the collimator lens and the optical axis is t, the diameter of the aperture stop is D, and the diameter of the parallel beam is When the diameter is d,

(Equation 4) A laser beam scanning apparatus characterized by satisfying the following conditions.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS §1 First Embodiment of Image Forming Apparatus
Example 1-1 Comparison with Background Art In order to better understand this embodiment, the background art will be described first.

FIG. 7 shows a general semiconductor laser array used in an image forming apparatus. As shown in FIG.
In the semiconductor laser array 1 that emits a laser beam, the divergence angle of the beam greatly differs between a plane that includes the optical axis of the laser beam and is parallel to the bonding plane and a plane that also includes the optical axis and is perpendicular to the bonding plane. In FIG. 7, the divergence angle θp in a plane parallel to the bonding plane is about 10 degrees at full width at half maximum in the case of a normal laser diode. However, on a plane perpendicular to the bonding surface, the divergence angle θt is affected by diffraction, and becomes as large as about 30 degrees at full width at half maximum. Furthermore, this spread angle θ
It is also difficult to freely set the magnitudes of t and θp and their ratios (that is, the ratio of the major axis to the minor axis of the ellipse). In addition, the beam waist position is also δ between the parallel plane and the vertical plane.
Only different. This value is generally called "astigmatic difference".

Due to this astigmatism, the beam exiting the collimator lens is not strictly parallel to the scanning plane and either or both directions perpendicular to the scanning plane. For this reason, a spot could not be accurately formed on the image carrier, and aberrations were caused. In a conventional laser beam printer,
Since the focal length of the imaging lens is long and the spot diameter is large, it did not cause much problem. However, in recent years, as the demand for a high-resolution printer has increased, this aberration has become a problem. As one solution to this problem, a beam shaping optical system that corrects astigmatism using a so-called anamorphic lens having different powers in a vertical plane and a horizontal plane by combining lenses has been proposed. However, such a beam shaping optical system is not preferable for reducing the cost and size of the apparatus, and is difficult to apply when scanning a plurality of laser beams.

Further, since the laser beam is emitted from the end face of the semiconductor laser array 1, the light emitting portion of the laser beam is necessarily arranged in a one-dimensional straight line.
When trying to obtain a plurality of laser beams more, there is a problem that the effective diameter of the optical system becomes large because the laser beams are arranged linearly.

Furthermore, because of the value of the divergence angle itself, the focal length of the collimator lens for collimating the divergence angle is inevitably reduced to about several mm. If the distance between the semiconductor laser array and the collimator lens is small (for example, several tens of μm) and fluctuates, the obtained collimated light (parallel beam) will not be parallel, and the beam diameter at the time of entering the imaging optical system will also fluctuate. The imaging spot size on the carrier changes. Therefore, there is a problem that the allowable adjustment range of the semiconductor laser and the collimator lens is very small, and the productivity is poor. Also, even if it is adjusted accurately in the beginning, the position of the collimator lens will be misaligned due to the temperature rise around the optical system during use and the deformation of the members due to aging, and the imaging spot diameter will also fluctuate. However, there is a problem that image quality is deteriorated.

Further, when a laser beam having a plurality of parallel optical axes enters this collimator lens, the optical axes spread at a large angle. For the sake of simplicity, consider a laser scanning optical system in which the number of laser beams is two and the collimator lens and the imaging lens are both convex single lenses. FIG. 8 is a cross-sectional view of the optical system on the optical path.
Are collimated by the collimator lens 2 having the focal length fc. Here, since the semiconductor laser array 1 is located at the object-side focal point of the collimator lens 2, the two laser beams intersect at the image-side focal point F. In order to form these two substantially parallel laser beams on the image plane 11, the imaging lens 4 having a focal length fi is placed so that its object-side focal point coincides with the image-side focal point F of the collimator lens 2. Since the mirror surface of the deflecting device does not have optical power, it is omitted here. For example, 100 μm on the image plane 11 (where the spot diameter and the beam diameter are
When an image is formed on a spot 6 having a beam cross-sectional intensity distribution as a Gaussian distribution and defined as a diameter having a power of 1 / e ² with respect to the peak intensity), if the fi is set to 200 mm, the light enters the image forming lens. The beam diameter (ie, collimating diameter) Wc is about 2 mm. In order to obtain this beam diameter, the focal length fc of the collimator lens 2 is about 3 mm. As is clear from FIG. 8, the distance d 'between the spots on the image plane.
Is obtained by multiplying the ratio of fc and fi by d. In the current semiconductor laser array, it is difficult to make the interval between the light emitting parts 100 μm or less in order to avoid mutual interference. Therefore, in the present example, the spot interval d ′ on the image plane is

(Equation 5) Will be.

When a so-called tilt correction optical system for correcting the difference in tilt angle of each facet of the rotary polygon mirror is provided, the angle formed by the optical axis of each laser beam depends on the relative distance between each lens and the collimator lens. It can be even larger. Therefore, there has been proposed a structure in which a lens is further added or a mutual angle of the optical axis of the laser beam is corrected by inserting a prism, for example, as disclosed in Japanese Patent Application Laid-Open No. 58-211175. However, these structures make the configuration of the optical system more complicated, expensive and difficult to adjust. In FIG. 8, the tilt correction lens is omitted for simplicity.

Next, FIG. 9 shows a relationship between a spot position and a scanning line on a conventional image carrier. In this example, writing is performed by four spots, that is, four laser beams. As described above, the laser scanning optical system becomes an enlargement optical system, and the spot interval on the semiconductor laser array is enlarged on the image carrier as indicated by d 'in the figure. Much larger. For example, in the case of a resolution of 300 dpi (dot par inch, the number of dots per inch [= 25.4 mm]), P = 2
Although 5.4 / 300 = 84.7 μm, the spot interval has a value of 6.7 mm as described above. Therefore, the angle α formed between the line 12 connecting the centers of the spots 6 and the scanning line 9 is, in this case,

(Equation 6) And will be very small. The line connecting the light-emitting portions on the semiconductor laser array 1 (that is, the end face of the bonding surface) also needs to be attached at an angle of α to the scanning surface, and as α decreases, very fine adjustment is required. .

Generally, the polarization of a laser beam emitted from a semiconductor laser is linearly polarized, and the direction of the plane of polarization of the laser beam is uniquely determined by the inclination of the bonding surface of the semiconductor laser array. However, in general, the reflectance on the reflection surface differs depending on the P-polarized light and the S-polarized light depending on the angle of incidence on the mirror surface. FIG. 10 shows the reflectances Rp and Rs of the P-polarized light and the S-polarized light of the metal mirror. Since the angle of incidence on the mirror surface changes with the rotation of the rotating polygon mirror, the light amount of the laser beam expressed as a combination of P-polarized light and S-polarized light also changes as shown in FIG. In particular, a problem arises when the deflection angle of the rotating polygon mirror is increased.
To avoid this, a method of inclining the polarization plane by 45 ° with respect to the rotation axis of the rotary polygon mirror as shown in Japanese Patent Application Laid-Open No. 58-42025 has been proposed. In this case, this inclination angle is determined due to the restriction of the scanning line interval, so that this method cannot be used. In this case, there is a problem that the plane of polarization must be rotated using a １ ／ λ plate or the like.

Further, each laser beam emitted from the semiconductor laser array 1 enters the same collimator lens 2. At this time, as shown in FIG. 8, the collimating diameter Wc of each laser beam is determined by the divergence angle θ of the laser beam and the distance fc from the semiconductor laser array 1 to the collimator lens 2, but the distance to the lens is the same for each laser beam. Therefore, it is determined only by the divergence angle θ of the laser beam. However, in the conventional edge-emitting type semiconductor laser array 1, since this spread angle varies for each light-emitting portion,
The collimation diameter Wc of each laser beam also varies. Therefore, the spot size at which the collimated laser beam is imaged also varies. FIG. 11 shows a laser scanning optical system (single beam) that uses only one laser beam that is usually used very commonly.
As shown in FIG. 8, a beam shaping such that the collimator diameter Wc is adjusted can be performed by inserting a stop 13 in front of or behind the collimator lens 2, but as shown in FIG. In such a case, the stop can be placed only at the focal position of the collimator lens.

Generally, in a semiconductor laser array,
Laser oscillation does not occur unless the current flowing through the optical resonator exceeds a certain value. This current value is called "threshold current".
Of several tens mA, and the heat causes a shift in the characteristics of the laser beam, particularly the oscillation wavelength, so that heat dissipation from the semiconductor laser array has been a problem. In particular, in a semiconductor laser array that emits a plurality of beams, the number of heat sources is equal to the number of light emitting units, which is an obstacle to integrating a large number of light emitting units.

1-2 Configuration of the Present Invention One embodiment of the present invention will be described below. FIG. 2 is a diagram showing the entire image forming apparatus of the present invention. The process of obtaining a print result on the transfer material 51 is based on a so-called electrophotographic process. As the image carrier 5, in an electrophotographic printer using a semiconductor laser as a light source, an organic photoconductor (OPC) sensitized to a longer wavelength is often used. The image carrier 5 is first charged to a constant surface potential by a charger 52, and then optical writing, that is, exposure is performed by a laser beam scanning device 53. A plurality of laser beams 54 whose light intensities are independently modulated in accordance with image information from the laser beam scanning device 53 scan the image carrier 5 in the axial direction, and generate charges for canceling the surface potential only at the exposed portions. The absolute value of the surface potential of the portion becomes smaller. As a result, a distribution of the surface potential according to the image, that is, an electrostatic latent image is formed on the image carrier 5. The electrostatic latent image is developed by the developer 55 by selectively applying a developer according to the surface potential. This developer is transferred by the transfer device 56 to the transfer material 51.
(Usually on paper). The developer on the transfer material 51 is
The heat and pressure are fixed by the fixing device 57 and discharged.

FIG. 1 is a schematic view of a laser beam scanning device 53 used in the image forming apparatus of the present invention. The laser beam scanning device 53 shown in FIG. 2 assumes that the laser beam 54 is bent and emitted downward,
Here, it is simplified for the sake of explanation.

In FIG. 1, the semiconductor laser array 21
A plurality of light emitting portions 21a are two-dimensionally arranged on an element substrate 22 (FIG. 3), and are collimated (parallelized) by a collimator lens 2 into a laser beam having a predetermined beam diameter. The lighting and the light amount of the light emitting units 21a are individually controlled by the control device 60. This laser beam is incident on one facet of the rotating polygon mirror 3 and is deflected as it rotates. The laser beam that has passed through the imaging lens 4 forms an image on a spot 6 on the image carrier 5. In FIG. 1, the tilt correction lens is omitted for simplicity.

As the semiconductor laser array 21 having such characteristics, it is preferable to use a so-called surface-emitting type semiconductor laser array. Even more preferably, II-VI
A surface emitting semiconductor laser array having a light emitting portion in which a group III compound semiconductor is embedded is used. FIG. 3 is a cross-sectional view of one of the light-emitting portions 21a of the surface-emitting type semiconductor laser array 21. In FIG. 3, one optical resonator corresponds to one light emitting unit two-dimensionally arranged on the element substrate 22.

In FIG. 3, on a GaAs substrate 22, a semiconductor multilayer reflection layer 23 is formed by laminating several tens of AlGaAs layers having different compositions from each other.
A cladding layer 24 made of GaAs, an active layer 25, a cladding layer 26, and a contact layer 27 are laminated.
_{A two-} dielectric multilayer reflective layer 28 is formed. Ga
Window-like electrodes 29 and 30 are formed on the entire back surface of the As substrate 22 and around the dielectric multilayer reflective layer on the front surface, and the whole constitutes an optical resonator.

The light generated by the active layer 25 reciprocates between the upper and lower reflective layers 27 and 23 in a direction perpendicular to the surface of the substrate 22 and oscillates. Be vertical. A group II-VI compound semiconductor is embedded as an embedded layer 32 around the optical resonator. Group II-VI compound semiconductors include Zn, Cd, and Hg as Group II elements, and O, S, Se, and Te as Group VI elements.
Are combined with 2 to 4 elements, and the lattice constant of the compound is determined by the cladding layer 24, the active layer 25, and the cladding layer 26.
It is desirable to match the lattice constant of the semiconductor layer composed of
Since the II-VI group compound semiconductor has a very high electric resistance, the current is efficiently confined in the optical resonator. The buried layer 32 is made of AlGa constituting an optical resonator.
Since there is a difference in the refractive index from the As semiconductor layer, light traveling at an angle perpendicular to or close to the surface of the element substrate 22 inside the optical resonator is totally reflected at the interface with the buried layer 32 and is efficiently confined.

Therefore, when such a semiconductor laser array 21 is used, laser oscillation starts with a very small current as compared with a conventional semiconductor laser array. That is,
Low threshold current. Therefore, even if a plurality of light emitting units 21a are arrayed and integrated on one element substrate 22, the amount of heat loss in the element substrate 22 is small and more light power or the number of light emitting units 21a can be obtained.

The surface emitting semiconductor laser array 21
Since the cross-sectional area (near-field pattern) of the laser beam emitting portion (light emitting portion) 21a can be made relatively large as compared with a conventional edge-emitting semiconductor laser, the divergence angle of the laser beam becomes small. The size of the divergence angle is determined by the area of the exit window. Since the area can be accurately controlled by etching or the like, the divergence angle can be made constant. Furthermore, the length and width of the divergence angle of the laser beam, that is, the ratio of the major axis to the minor axis of the elliptical cross-section beam can be arbitrarily set by the shape of the exit window. For example, with a perfect circular window, a laser beam with a circular cross section having an isotropic divergence angle can be obtained. Therefore, the astigmatic difference of the beam due to the cross section in the optical axis direction is also small.

However, in an ordinary laser beam printer, the shape of the spot formed by the laser beam on the image carrier is often an ellipse whose minor axis coincides with the scanning direction. This is because the spot moves in the scanning direction for the lighting time and the image is elongated, which is to be corrected. For that purpose, it is desirable that the cross-sectional shape of the laser beam incident on the imaging optical system is an ellipse having a long axis in the scanning direction. As described above, the surface emitting semiconductor laser array 21 can freely control the ellipticity of the exit beam, so that the scanning surface has a long axis without using a special optical system, and an appropriate long axis can be obtained. A laser beam having a cross section having a short axis ratio can be incident on the imaging optical system.

The surface emitting semiconductor laser array 2
1 can make the spread angle of the laser beam from each light emitting portion 21a uniform as described above. Therefore, the diameter of the beam incident on the collimator lens or the image forming optical system can be controlled to be substantially constant for each laser beam, and as a result, the size of the image forming spot on the image carrier can also be fixed.

In the surface emitting semiconductor laser array 21, when the cross-sectional area of the resonator in the surface of the element substrate 22 increases, not only the 0th mode but also the oscillation of a higher order mode starts, and the light quantity distribution of the formed spot also increases. Has several peaks,
It is extremely undesirable to form an electrostatic latent image on the image carrier 5. Therefore, by arranging a plurality of small optical resonators close to each other and oscillating them in phase synchronization, it is possible to obtain a light emitting unit 21a having a large area oscillating in the zero-order mode.

FIG. 4 is a partial cross-sectional view of one light emitting portion 21a of the phase-locked surface emitting semiconductor laser array 21. Here, a plurality of optical resonators are adjacent to each other at a very small interval, and the lower portion of the buried layer 32 does not reach the active layer 25. Therefore, the cladding layer 26 below the buried layer 32
The light leaking from adjacent optical resonators via the light sources affects each other and oscillates in phase. Therefore, the plurality of adjacent optical resonators operate as if they are one optical resonator.
Since the wavefronts of the light emitted from the optical resonators are aligned in this manner, they act as a planar laser radiation source, and the apparent area of the light emitting portion becomes large, so that the divergence angle of the laser beam is very small, and the half value It is also possible to set the angle to 2 degrees or less.

In the surface emitting semiconductor laser array 21 that performs phase synchronization as described above, the divergence angle of the laser beam is smaller than that of the conventional semiconductor laser. This will be described in comparison with the conventional embodiment. For example, if the divergence angle of the laser beam is 2 degrees at full width at half maximum and the laser beam is incident on the imaging optical system with a beam diameter of 2 mm as in the previous example, the focal length fc of the collimator lens becomes about 35 mm. Since the focal length fc of the collimator lens 2 can be lengthened in this manner, a margin for adjusting the distance of the collimator lens 2 to the semiconductor laser array 21 increases. Further, assuming that the distance d 'between the laser beams emitted from the semiconductor laser array 21 is d, the imaging spot interval d' of the laser beam on the image carrier is

(Equation 7) Assuming that the scanning line interval is also 84.7 μm, which is the same as the conventional example, the angle α of the line connecting the spot to the scanning surface is

(Equation 8) This is much larger than when a conventional semiconductor laser array is used (see equation (3)). Therefore, the mounting adjustment of the semiconductor laser array 21 around the optical axis direction can be easily performed, and depending on the processing tolerance of each component, the assembly can be performed without adjusting the angle α. In addition, it is clear from this figure that the effective diameter of the optical system can be small because the image spots and the laser beams reaching the image spots are close to each other. Further, by making the divergence angle of the laser beam extremely small, during the distance from the semiconductor laser array 21 to the rotary polygon mirror 3 and further to the imaging lens 4,
The size of the laser beam does not widen so much, and even on the entrance surface of the imaging lens 4, it can be made small enough to obtain the required imaging spot diameter. That is, a collimator lens for collimating (parallelizing) the laser beam to a required collimating diameter as in a normal laser scanning optical system becomes unnecessary. However, since the optical path length changes according to the deflection angle of the rotary polygon mirror 3, and the size of the laser beam incident on the imaging lens 4 also changes, an optical system for correcting the change is required. Moreover, since such an optical function can be easily provided to the imaging lens 4, the number of components of the entire optical system is reduced.

Further, the surface emitting type semiconductor laser array 2
In 1, the light emitting units 21 a can be placed anywhere as long as the light emitting units 21 a do not interfere with each other, so that the light emitting units 21 a can be two-dimensionally arranged on the element substrate 22. Now, consider an exposure system that performs scanning with four laser beams in the same manner as in the conventional embodiment shown in FIG.
When four laser beams are arranged as shown in FIG. 5A, the angle or distance between the laser beams can be reduced as compared with the case where they are arranged in a straight line as shown in FIG.
The size of the optical system can be reduced accordingly.

Although the above example shows the case where the number of laser beams is four, when the number of laser beams is further increased, the semiconductor laser array 21 is arranged so that the position of the spot 6 on the image carrier 5 becomes closest. Since the arrangement of the upper light emitting portion 21a can be freely selected, the effect is further enhanced. FIG. 5C shows an example of the arrangement of the imaging spots 6 with respect to the scanning lines 9 when the number of laser beams is eight.

The relationship between the relative positions of the imaging spots described above is not necessarily similar to the arrangement of the light emitting portions 21a on the semiconductor laser array 21. For example, when an optical element having optical characteristics different from the scanning direction and the orthogonal direction enters the middle of the laser beam, such as the tilt correction optical system of the rotary polygon mirror 3 already mentioned, if the laser beams are mutually The angle and the distance may differ between the scanning direction and the direction perpendicular to the scanning direction. However, even in such a case, in the conventional edge emitting semiconductor laser array, the light emitting portions arranged in a straight line cannot be formed into a linear array of image spots on the image carrier. On the other hand, in the present invention, the effect of two-dimensionally arranging the light emitting portions 21a on the element substrate 22 as described above is similarly exhibited.

Also in the surface-emitting type semiconductor laser array 21, the emitted laser beam is generally linearly polarized. The direction is determined by the planar shape of the resonator in the plane of the element substrate 22, and the polarization plane generally coincides with the longitudinal direction of the planar shape. For example, if an elliptical resonator shape is used, the major axis direction becomes the polarization plane. As described above, in the semiconductor laser array 21 of the phase-locked type, one light-emitting portion is composed of a plurality of, for example, four optical resonators that oscillate in phase synchronization. At this time, since the cross-sectional shape of the emitted laser beam is a combined shape of the laser beams emitted from the respective optical resonators, the cross-sectional shape of the emitted beam can be freely set by arranging the individual optical resonators. Also in this case, since the direction of the polarization plane is determined by the planar shape of each resonator, the long axis and the direction of the polarization plane can be set independently even when a combined elliptical laser beam is obtained.

FIG. 6A schematically shows this state, and is a plan view of one light emitting section 42 on the semiconductor laser array viewed from the beam emitting side. As shown in FIG. 6A, four optical resonators 41 having an elliptical cross section that oscillate in phase synchronization constitute one light emitting unit 42, and are emitted from the individual optical resonators 41. Polarization plane of laser beam 4
In FIG. 6A, the long axis of the laser beam 3 is 45 degrees, but the long axis of the elliptical laser beam obtained by synthesis is in the vertical direction. Also, as shown in FIG. 6B, the individual optical resonators 41
When the directions of the polarization planes 43 of the laser beam emitted from the laser beam are arranged at different angles, the combined emission laser beam becomes approximately circularly polarized.

As described above, in the ordinary laser beam printer, the shape of the image forming spot 6 of the laser beam on the image carrier is often an elliptical shape whose minor axis coincides with the scanning direction. . Therefore, as described above, the direction of the polarization plane of the laser beam from each optical resonator is inclined 45 degrees with respect to the major axis direction of the cross section of the combined elliptical laser beam so that the major axis of the combined emission beam coincides with the scanning direction. When the semiconductor laser array 21 is provided, the polarization plane of the laser beam from each optical resonator is inclined by 45 degrees with respect to the beam scanning plane. As a result, the polarization plane is also inclined by 45 degrees with respect to the rotation axis of the rotary polygon mirror 3, and is less susceptible to a difference in reflectance due to the angle of incidence on the rotary polygon mirror as shown in FIG. The same applies to a laser beam having an elliptical cross section that is substantially circularly polarized. Note that, depending on the configuration of the optical system, the short axis of the laser beam emitted from the semiconductor laser array 21 may coincide with the scanning direction, but the same effect is exerted.

The embodiment described above is only one embodiment of the present invention. For example, the same effect can be obtained by using a galvanomirror or a hologram disk instead of the rotary polygon mirror 3 as the deflecting device. Further, the effects of the present invention can be similarly exerted even if the presence / absence, configuration, and relative positional relationship of the collimator lens, the tilt correction lens, and the imaging lens are changed.

The scope of application of the image forming apparatus of the present invention has exactly the same effects not only for printing apparatuses such as printers and copiers but also for facsimile machines and displays.

1-3 Effects As described above, in the image forming apparatus of the present invention,
By adopting an exposure method that scans with multiple laser beams using a semiconductor laser array, a high-speed and high-resolution scanning device can be obtained with a low scanning frequency and a short optical path length, and the device can be reduced in size and cost. Becomes further,
By using a surface emitting semiconductor laser array as the semiconductor laser array, the divergence angle of the laser beam is reduced, and the distance between the collimator lens and the semiconductor laser array can be increased, so that the adjustment margin in the optical axis direction of the collimator lens increases.
At the same time as productivity increases, exposure can be performed with a fixed spot diameter without being affected by aging or temperature fluctuation during use, and image quality is improved.

When the light emitting units are arranged in an array,
Since there is little variation in the spread angle of the beam from each light emitting unit, the variation in the diameter of the imaging spot is also reduced, and at the same time, the angle between the beams and the interval between the imaging spots can be reduced. For this reason, the configuration of the optical system is simplified, and the effective area of each lens and deflector can be reduced, which contributes to a reduction in the cost of the apparatus.

In the surface-emitting semiconductor laser array, the light-emitting portions can be arranged two-dimensionally.
It is possible to reduce the effective area of each lens and deflector.

Since the interval between the imaging spots is not large as compared with the scanning line interval, the tolerance of the mounting angle of the semiconductor laser array around the optical axis can be made large, can be easily adjusted, and the variation of the scanning line interval can be reduced. And the image quality is improved.

In the surface emitting semiconductor laser array, the astigmatic difference is small due to its characteristics, and the elliptical shape of the beam cross section (ratio between the major axis and the minor axis) can be freely set. It is possible to perform accurate beam shaping even without using.

Further, for a surface emitting semiconductor laser array
By using a group II-VI compound semiconductor as the buried layer, laser oscillation at a low threshold current becomes possible, and the influence of the heat generation of the element on the characteristics of the laser can be reduced. Will be possible.

Next, by using a phase-locked surface-emitting semiconductor laser array in which a plurality of optical resonators emit light in phase synchronization as the surface-emitting semiconductor laser, the divergence angle of the emitted beam can be further reduced, and in some cases, the collimator The lens can be omitted, and the configuration of the optical system can be further simplified.

Further, since one light emitting portion can be constituted by a plurality of optical resonators whose polarization planes can be freely set, when a synthetic laser beam having an elliptical cross section is used, the direction of the polarization plane of each laser beam is changed. Can be controlled independently and arbitrarily from the longitudinal direction of the cross section of the synthesized laser beam, and minimizes fluctuations in the amount of light due to the position in the scanning direction of the laser beam due to the difference in reflectance caused by the difference in the angle of incidence on the rotating polygon mirror. Can be easily realized.

§2 Second Embodiment of Image Forming Apparatus 2-1 Comparison with Background Art In order to better understand this embodiment, the background art will be described first.

FIG. 17 is a sectional view of an optical path of a conventional image forming apparatus.
Shown in FIG. 17 is an optical path cross-sectional view that is perpendicular to the scanning surface of the image carrier of the image forming apparatus and that includes the optical axis of the laser beam. The optical axis is turned over the small surface 8 of the rotary polygon mirror of the image forming apparatus. In FIG. 17, a laser beam emitted from a semiconductor laser 101 has a divergence angle θ.
Radiated at This beam is shaped into a substantially parallel beam by a collimator lens 102 having a focal length fc.
Each beam is once focused by the tilt correction lens 107 on the small surface 108 of the rotating polygon mirror. The beam deflected by the rotary polygon mirror passes through the second tilt correction lens 107 ', becomes a parallel beam again, and forms a spot 106 on the image carrier by the imaging lens 104 having a focal length fi. In a plane parallel to the scanning plane, the tilt correction lens 107,
Since 107 'has no optical power, the beam remains parallel in its plane. That is, the beam forms a line image on the small surface 108 of the rotating polygon mirror.

However, as shown in the conceptual diagram of FIG. 18, the laser beam from the semiconductor laser 101 which has been used conventionally has a surface including the optical axis and parallel to the bonding surface and a surface including the optical axis and perpendicular to the bonding surface. In the plane, the divergence angle of the beam was greatly different. The divergence angle θp in a plane parallel to the bonding plane is about 10 degrees at full width at half maximum in the case of a normal semiconductor laser. However, on a plane perpendicular to the bonding surface, the divergence angle θt is affected by diffraction, and becomes as large as about 30 degrees at full width at half maximum. Further, it is also difficult to freely set the magnitudes of the spread angles θt and θp and their ratios (that is, the ratio of the major axis to the minor axis of the ellipse). Accordingly, the beam waist position differs between the parallel plane and the vertical plane by d. This value is generally called "astigmatic difference".

Strictly speaking, the beam exiting the collimator lens due to the astigmatism is not parallel to the scanning plane and either or both directions perpendicular to the scanning plane. For this reason, a spot could not be accurately formed on the image carrier, and aberrations were caused.

In the conventional image forming apparatus, since the focal length of the image forming lens is long and the spot diameter is large, this is not a problem. However, as the demand for a high-resolution printer increases in recent years, this aberration is reduced. It has been a problem. As one solution to this problem, a beam shaping optical system that corrects astigmatism using a so-called anamorphic lens having different powers in a vertical plane and a horizontal plane by combining lenses has been proposed. However, such a beam shaping optical system is not preferable for reducing the cost and size of the apparatus.

Next, the beam divergence angle is large.
The problem caused by this will be described with reference to FIG. Now
For example, 100 μm at the image plane 111 (the spot diameter,
The beam diameter is based on the Gaussian distribution
And 1 / e with respect to the peak intensity ²Diameter to be the power of
When an image is formed on the spot 106 of
Is 200 mm, the incident beam diameter (
That is, the collimating diameter Wc is about 2 mm. Fall correction
The lenses 107 and 107 'are positioned on the facet 108 of the polygon mirror.
Symmetry, the exit beam diameter of lens 107 'and lens 1
07 are equal. To get this beam diameter
The focal length fc of the collimator lens 102 is about 3 m
m.

As described above, since the focal length of the collimator lens 102 is short, in order to obtain an accurate parallel beam,
The error of the position of the collimator lens with respect to the semiconductor laser in the optical axis direction has to be adjusted very small. Further, the beam divergence angles θt and θp may also vary greatly due to semiconductor process factors, resulting in a problem that the diameter of the collimated beam also varies. It was necessary to provide an aperture stop and perform beam shaping to reduce the beam diameter. Furthermore, even if it is accurately adjusted in the beginning, the position of the collimator lens 102 is out of order due to a rise in temperature around the optical system during use and deformation of the member due to aging, and again the imaging spot diameter varies. As a result, there is a problem that image quality is deteriorated.

Generally, the polarization of a semiconductor laser is linearly polarized, and the direction of the plane of polarization of the laser beam is uniquely determined by the inclination of the bonding surface of the semiconductor laser.
However, in general, the reflectance on the reflection surface differs depending on the P-polarized light and the S-polarized light depending on the angle of incidence on the mirror surface. FIG. 19 shows the reflectance R of each of the P-polarized light and the S-polarized light of the metal mirror.
p and Rs are shown.

Since the angle of incidence on the mirror surface changes with the rotation of the rotating polygon mirror, the light quantity of the laser beam expressed as a combination of P-polarized light and S-polarized light also changes as shown in FIG. In particular, a problem arises when the deflection angle of the rotating polygon mirror is increased. To avoid this, JP-A-58-4202
As shown in FIG. 5, the polarization plane is shifted by 4 with respect to the rotation axis of the rotating polygon mirror.
Although a method of inclining by 5 ° has been proposed, this method cannot be used because the direction of the major axis of the elliptical cross section of the beam is also determined, or the polarization plane is not rotated by using a λλ plate or the like. There was a problem that must not be.

In general, in a semiconductor laser,
Laser oscillation does not occur unless the current flowing through the optical resonator exceeds a certain value. This current value is called a "threshold current", which is several tens mA in a conventional semiconductor laser, and the heat causes a shift in the laser characteristics, particularly the oscillation wavelength.

2-2 Configuration of the Present Invention One embodiment of the present invention will be described below. FIG. 13 is a diagram illustrating an image forming apparatus according to the present invention. The process of obtaining a print result on the transfer material 151 is based on a so-called electrophotographic process. As the image carrier 105, an organic photoconductor (OPC) sensitized to a longer wavelength side in an electrophotographic printer using a semiconductor laser as a light source is often used. After the image carrier 105 is charged to a constant surface potential by the charger 152, optical writing, that is, exposure is performed by the laser beam scanning device 153. A laser beam 154 whose light intensity is modulated according to image information from the laser beam scanning device 153 scans the image carrier 105 in the axial direction,
A charge that cancels the surface potential is generated only in the exposed portion, and the absolute value of the surface potential in that portion is reduced. As a result, a distribution of the surface potential according to the image, that is, an electrostatic latent image is formed on the image carrier. The electrostatic latent image is developed by the developer 155 by selectively applying a developer according to the surface potential. This developer is transferred to a transfer material 151 (usually paper) by a transfer device 156. The developer on the transfer material 151 is fixed by heat and pressure by a fixing device 157 and is discharged.

Next, a laser beam scanning device will be described with reference to FIG. In the laser beam scanning device 153 shown in FIG. 13, it is assumed that the laser beam 154 is bent and emitted downward, but is simplified here for the sake of explanation. In FIG. 12, the semiconductor laser 121 emits a laser beam from the light emitting unit 121a in a direction perpendicular to the bonding surface. The lighting and the light amount of the light emitting unit 121a are controlled by the control device 160. This beam is collimated by a collimator 102 into a laser beam having a predetermined beam diameter. This laser beam enters one small surface of the rotary polygon mirror 103 and is deflected by its rotation. The beam that has passed through the imaging lens 104 forms an image on a spot 106 on the image carrier 105.
As a semiconductor laser having such characteristics, it is preferable to use a so-called plane emission type semiconductor laser. Still more preferably, it is preferable to use a surface-emitting type semiconductor laser in which a II-VI compound semiconductor is embedded around the light emitting portion 121a. FIG. 14 is a cross-sectional view of the light emitting unit 121a of the surface emitting semiconductor laser, showing a case where one optical resonator forms one light emitting unit.
Cladding layer 124 and the first two AlGaAs layers of different composition on a GaAs substrate 122 by stacking several 10 layers 14, the active layer 125, cladding layer 126, a contact layer 127 is laminated, and finally SiO ₂ derivatives multilayer film A reflection layer 128 is formed. Further, window-like electrodes 129 and 130 are formed on the entire back surface of the GaAs substrate 122 and around the dielectric multilayer reflection layer on the front surface, and the whole constitutes an optical resonator. The light generated in the active layer 125
Since the laser beam oscillates back and forth between the upper and lower reflective layers 127 and 123 in the direction perpendicular to the surface 22, the optical axis of the laser beam 131 is substantially perpendicular to the substrate surface.

A group II-VI compound semiconductor is embedded as an embedded layer 132 around the optical resonator. II-VI
Group compound semiconductors include Zn and C as Group II elements.
d, Hg, O, S, Se, and Te as Group VI elements in 2 to 4
The combination of elements and the lattice constant of the compound are determined by the cladding layer 124, the active layer 125, and the cladding layer 126.
It is desirable to match the lattice constant of the semiconductor layer composed of
Since the II-VI compound semiconductor has a very high electric resistance, the current is efficiently confined in the optical resonator, and at the same time, the refractive index is different from that of the AlGaAs semiconductor layer forming the optical resonator. Therefore, light traveling at an angle perpendicular to or close to the substrate surface of the element inside the optical resonator is totally reflected at the interface with the buried layer 132 and is efficiently confined. Therefore, if such a semiconductor laser is used,
Laser oscillation starts with a very small current compared to a conventional semiconductor laser. That is, the threshold current is low, and the heat loss in the element substrate is small.

Further, in the surface emitting semiconductor laser, the cross-sectional area (near field pattern) of the laser beam emitting portion can be relatively large as compared with the conventional edge emitting semiconductor laser, so that the divergence angle of the laser beam is increased. Becomes smaller. The size of the divergence angle is determined by the area of the exit window. Since the area can be accurately controlled by etching or the like, the divergence angle can be made constant. Furthermore, the length and width of the divergence angle of the laser beam, that is, the ratio of the major axis to the minor axis of the elliptical cross-section beam can be arbitrarily set by the shape of the exit window. For example, with a perfect circular window, a laser beam with a circular cross section having an isotropic divergence angle can be obtained. Therefore,
The astigmatic difference of the beam due to the cross section in the optical axis direction is also small.

By the way, in a usual laser beam printer, the shape of the spot formed by the laser beam on the image carrier is often an ellipse whose minor axis coincides with the scanning direction. This is because the spot moves in the scanning direction for the lighting time and the image is elongated, which is corrected. For that purpose, it is desirable that the cross-sectional shape of the laser beam incident on the imaging optical system is an ellipse having a long axis in the scanning direction. In the case of this embodiment, the surface emitting semiconductor laser 121 can freely control the elliptic ratio of the emission beam, so that the scanning surface has a long axis without using a special optical system, and an appropriate long axis and short axis can be used. A laser beam having a cross section having a ratio of 2 can be incident on the imaging optical system.

In the surface-emitting semiconductor laser 121, when the cross-sectional area of the optical resonator in the plane of the element substrate 122 becomes large, not only the 0th mode but also the oscillation of a higher order mode starts, and the light quantity distribution of the formed spot also becomes large. Has several peaks,
It is extremely undesirable to form an electrostatic latent image on the image carrier 105. Therefore, by arranging a plurality of small optical resonators close to each other and oscillating them in phase synchronization, it is possible to obtain a light emitting section 121a oscillating in the zero-order mode and having a large area.

FIG. 1 is a partial sectional view of one light emitting portion 121a of the phase-locked surface emitting semiconductor laser 121.
It is shown in FIG. Here, a plurality of optical resonators are adjacent to each other at a very small interval, and the lower portion of the buried layer 132 is
Has not reached. Therefore, light leaking from adjacent optical resonators via the cladding layer 126 below the buried layer 132 affects each other and oscillates in phase. Therefore, the plurality of adjacent optical resonators operate as if they are one optical resonator. Since the wavefronts of the light emitted from the respective optical resonators are aligned in this manner, they act as planar laser radiation sources, and their light emitting portions 1
Since the apparent area of 21a is large, the divergence angle of the laser beam is very small, and it is possible to set the full width at half maximum to 2 degrees or less.

Therefore, in the phase-locked light-emitting semiconductor laser, the divergence angle of the laser beam is smaller than that of the conventional semiconductor laser. This will be described in comparison with the conventional embodiment. For example, if the divergence angle of the laser beam is 2 degrees at full width at half maximum and the laser beam is incident on the imaging optical system with a beam diameter of 2 mm as in the conventional embodiment, the focal length fc of the collimator lens 102 becomes about 35 mm. Since the focal length fc of the collimator lens 102 can be lengthened in this way, the margin for adjusting the distance of the collimator lens 102 to the semiconductor laser 121 increases.

When the divergence angle of the laser beam is made extremely small, the rotating polygon mirror 103 is moved from the semiconductor laser.
And the distance to the imaging lens 104, the size of the laser beam does not spread so much.
Also on the incident surface 04, it can be made small enough to obtain the required imaging spot diameter. That is, a collimator lens for collimating (parallelizing) a laser beam to a required collimating diameter as in a normal laser scanning optical system is not required. However, the optical path length changes according to the deflection angle of the rotary polygon mirror 103, and the size of the laser beam incident on the imaging lens 104 also changes, so that an optical system for correcting the change is required. However, since such an optical function can be easily provided to the imaging lens, the number of components of the entire optical system is reduced.

In general, even in a surface-emitting type semiconductor laser, an emission beam is linearly polarized. The direction is determined by the planar shape of the resonator in the plane of the element substrate, and the polarization plane generally coincides with the longitudinal direction of the planar shape. For example, if an elliptical resonator shape is used, the major axis direction becomes the polarization plane. As described above, the light-emitting portion of the phase-locked semiconductor laser is composed of a plurality of, for example, four optical resonators that oscillate in phase synchronization. At this time, since the cross-sectional shape of the emission beam is a combined shape thereof, the cross-sectional shape of the combined emission beam can be freely set by arranging the individual optical resonators. Also in this case, since the direction of the polarization plane of each laser beam is determined by the planar shape of each resonator, for example, even when a combined elliptical laser beam is obtained, the direction of the long axis and the direction of the polarization plane can be set independently.

FIG. 16A schematically shows this state, and is a plan view of the light emitting section 142 of the semiconductor laser viewed from the beam emitting side. Four optical resonators 141 having an elliptical cross section oscillating in phase synchronization constitute one light emitting unit 142, and the polarization plane 143 of the laser beam emitted from each resonator 141 is 45 degrees in the figure. Although it is inclined,
The major axis of the elliptical laser beam obtained by synthesis is in the vertical direction. Further, as shown in FIG. 16B, when the directions of the polarization planes 143 of the individual optical resonators 141 are arranged at different angles, the combined emission beam becomes approximately circularly polarized light.

As described above, in the ordinary laser beam printer, the shape of the spot formed by the laser beam on the image carrier is often an ellipse whose minor axis coincides with the scanning direction. Therefore, when the direction of the polarization plane of the laser beam is inclined by 45 degrees with respect to the major axis direction of the cross section of the combined elliptical beam as described above, if the semiconductor laser is arranged so that the major axis of the combined emission beam coincides with the scanning direction, The polarization plane is inclined at 45 degrees with respect to the beam scanning plane. As a result, the rotating polygon mirror 1
The polarization plane is also inclined by 45 degrees with respect to the rotation axis of 03, and is less susceptible to a difference in reflectance due to the angle of incidence on the rotating polygon mirror 103 as shown in FIG. The same applies to the above-mentioned laser beam having an elliptical cross section which is circularly polarized light. Note that, depending on the configuration of the optical system, the short axis of the laser beam emitted from the semiconductor laser may coincide with the scanning direction, but the same effect is exerted.

The embodiment described above is merely an embodiment of the present invention. For example, a deflector is not a rotary polygon mirror, but a deflector.
The same effect can be obtained by using a galvanomirror or a hologram disk. Further, the effects of the present invention can be similarly exerted even if the presence / absence, configuration, and relative positional relationship of the collimator lens, the tilt correction lens, and the imaging lens are changed.

Further, it goes without saying that the application range of the image forming apparatus of the present invention is not limited to printing apparatuses such as printers and copiers, but can be applied to facsimile machines and displays.

2-3 Effect As described above, in the image forming apparatus of the present invention,
By using a surface emitting semiconductor laser as the semiconductor laser, the divergence angle of the laser beam is reduced, and the distance between the collimator lens and the semiconductor laser can be increased.
The adjustment margin in the optical axis direction of the collimator lens is increased, and the productivity is increased. At the same time, exposure can be performed with a fixed spot diameter without being affected by aging or temperature fluctuation during use, and image quality is improved.

In the surface emitting semiconductor laser, the astigmatic difference is small due to its characteristics, and the elliptical shape of the beam cross section (ratio between the major axis and the minor axis) can be freely set. Accurate beam shaping becomes possible without using it.

In addition, II-VI
By using a group III compound semiconductor as a buried layer, laser oscillation at a low threshold current becomes possible, current consumption of the element can be reduced, and the influence of heat generation of the element on laser characteristics can be reduced.

Next, by using a phase-locked surface-emitting semiconductor laser in which a plurality of optical resonators emit light in phase synchronization as the surface-emitting semiconductor laser, the divergence angle of the emitted beam can be further reduced, and in some cases, the collimator lens Can be omitted, and the configuration of the optical system can be further simplified.

Further, since one light emitting portion is constituted by a plurality of optical resonators whose polarization planes can be freely set, when a laser beam having an elliptical cross section is used, the direction of the polarization plane of the laser beam is changed to the major axis of the beam cross section. The direction of the laser beam can be controlled independently and arbitrarily, and it is easy to minimize the variation in the amount of light due to the position in the scanning direction of the laser beam due to the difference in reflectance caused by the difference in the angle of incidence on the rotating polygon mirror.

§3 Third Embodiment of Image Forming Apparatus 3-1 Comparison with Background Art In order to better understand this embodiment, the background art will be described first.

FIG. 27 is a sectional view of an optical path of a conventional image forming apparatus.
Shown in FIG. 27 is a sectional view of the optical path in a plane perpendicular to the scanning plane of the image carrier of the image forming apparatus and including the optical axis, that is, in the sub-scanning plane. In addition, the optical axis is folded back with respect to the reflecting surface 208 of the rotating polygon mirror. In FIG. 27, a laser beam emitted from a semiconductor laser 201 is emitted at a divergence angle θ. This beam is shaped into a substantially parallel beam by a collimator lens 202 having a focal length fc, and each beam is once focused by a tilt correction lens 207 onto a reflecting surface 208 of a rotating polygon mirror. Rotating polygon mirror 20
The beam deflected at 8 is the second tilt correction lens 20
After exiting 7 ', the beam becomes a parallel beam again, and a spot 206 is formed on the image carrier 211 by the scanning lens 204 having a focal length fi. Since the tilt correction lenses 207 and 207 'have no optical power in a plane parallel to the scanning plane,
In that plane the beam remains parallel. That is, the beam forms a line image on the reflecting surface 208 of the rotating polygon mirror.

Next, the tilt correction lenses 207, 207 '
Explain the function of. Regardless of how precisely the inclination of each reflection surface 208 of the rotating polygon mirror with respect to the mutual rotation axis is processed,
There is an error of several tens of seconds in the angle, and therefore, the imaging position of the beam reflected on this surface is shifted in the sub-scanning direction on the surface of the image carrier due to the principle of "optical leverage", and the scanning line pitch The size cannot be ignored. Therefore, JP 4
As shown in 8-49315, a tilt correction lens 207 'is provided so that each reflection surface and the surface (image forming surface) of the image carrier 211 are at an optically conjugate position. The tilt correction lens 207 'is generally formed of a cylindrical lens or a toric lens having optical power only in the sub-scanning plane. Even if the reflecting surface is tilted, the beam always forms an image at the same position on the image forming surface.

FIG. 28 is a conceptual diagram of a so-called edge-emitting type semiconductor laser conventionally used. As shown in FIG. 28, the divergence angle of the beam is significantly different between a plane that includes the optical axis and is parallel to the bonding plane and a plane that also includes the optical axis and is perpendicular to the bonding plane. The divergence angle θp in a plane parallel to the bonding plane is about 10 degrees at full width at half maximum in the case of a normal laser diode. However, on a plane perpendicular to the bonding surface, the divergence angle θt is affected by diffraction, and becomes as large as about 30 degrees at full width at half maximum.

However, when the divergence angle of the laser beam emitted in the direction perpendicular to the bonding surface differs from that of the bonding surface,
If this is collimated (that is, collimated) by the collimator lens 202 as it is, the cross section of the collimated laser beam also becomes an elliptical shape that is greatly crushed. When a parallel beam having a significantly different ratio of the major axis to the minor axis is imaged on the image carrier 211 by the scanning lens 204, the imaged spot has an elliptical shape having a major axis / minor axis ratio opposite to that of the parallel beam. become.

On the other hand, as shown in Japanese Patent Application Laid-Open No. 52-119331, it is desirable that the image spot on the image plane, that is, on the image carrier, be an ellipse having a slightly shorter minor axis in the scanning direction. This is because, since the laser is turned on with a pulse for a certain time, it is necessary to make the spot diameter in the scanning direction smaller than that in the sub-scanning direction in order to correct the moving distance during that time.

Therefore, in order to form a beam having a remarkably different divergence angle on a spot having a desired ratio of the major axis to the minor axis as described above, the optical characteristics differ between the scanning direction and the direction perpendicular thereto. That is, the anamorphic optical system has to be provided somewhere in the path from the semiconductor laser 201 to the image carrier 211.

Therefore, the method of giving the above characteristic to the tilt correction optical system is most widely used. In FIG. 27, the tilt correction lenses 207 and 207 'are afocal in the sub-scanning direction. Therefore, if the distances from the reflection surface to the two lenses are different, the beam expander operates only in the sub-scanning direction.

However, such a tilt correction optical system is generally constituted by a long cylindrical lens, a toric lens, or the like, and is an optical component that is difficult or expensive to manufacture. Further, the optical axis adjustment of the tilt correction lens 207 located in front of the rotary polygon mirror requires precision, which is one of the factors that hinder the improvement in productivity and reliability of this type of image forming apparatus.

As described above, the main cause of the angular error of the laser beam in the sub-scanning plane, which requires the tilt correction lens, is the angular processing between the reflecting surfaces of the rotary polygon mirror. Due to the accuracy, the dynamic deflection of the rotating axis of the rotating polygon mirror is not a major problem. Therefore, if only one mirror surface is rotated instead of the rotating polygon mirror, a major cause of this problem is eliminated, and a tilt correction lens is not required for a normal image forming apparatus.

Further, since such a rotating mirror has only one reflecting surface, it can be easily processed, and the moment of inertia of the rotating portion is small, which is advantageous against vibration during rotation.

Although the idea of such a rotary single-sided mirror has existed for a long time, since only one scan can be performed per rotation,
The scanning speed was significantly lower than that of a polygon mirror, and was insufficient for use in a so-called laser beam printer.

Now, the scanning line pitch is set to 300 dpi (1
300 dots per inch [= 25.4 mm], that is, the number of scanning lines is 300), and the size of the sheet is A4. The sheet is fed in the longitudinal direction and 10 sheets are printed per minute. In the case of forming an image corresponding to the above, if a six-sided rotating polygon mirror is used, the number of rotations is about 7000 rpm (1
Rotations per minute). Generally, the upper limit of the number of revolutions of a rotating polygon mirror using ball bearings is said to be about 12000 to 14000 rpm in the current technology.
Even if one reflecting mirror rotating at 2000 rpm is used, the number of printed sheets per minute is less than three.

When the tilt correction lenses 207 and 207 'are removed, as described above, the laser beam radiated from the semiconductor laser and having a large divergence angle of the divergence angle is adjusted to the required elliptic ratio on the image carrier. The function as an anamorphic beam expander that forms an image on a spot is lost.

3-2 Configuration of the Present Invention FIG. 21 is a view showing an image forming apparatus according to the present invention. As a process for obtaining a print result on the transfer material 251, in the case of a so-called electrophotographic printer, an organic photoconductor (OPC) sensitized to a longer wavelength is often used. The image carrier 205 is first charged to a constant surface potential by the charger 252,
Optical writing, that is, exposure is performed by the laser beam scanning device 253. This laser beam scanning device 253
A plurality of laser beams 254 whose light intensities are independently modulated according to image information scan the image carrier 205 in the axial direction, and generate and discharge an electric charge to cancel the surface potential only at the exposed portion. The absolute value of the potential decreases. As a result, a distribution of the surface potential according to the image, that is, an electrostatic latent image is formed on the image carrier 205. The electrostatic latent image is developed by the developer 255 by selectively applying a developer according to the surface potential. This developer is transferred to a transfer material 251 (usually paper) by a transfer device 256. The transfer material 251 is fixed by heat and pressure by the fixing device 257 and is discharged.

FIG. 20 is a schematic view of a laser beam scanning optical device according to the present invention. In the laser beam scanning device 253 shown in FIG. 21, it is assumed that the laser beam 254 is bent and emitted downward, but in FIG. 20, it is simplified for the sake of explanation. The method of scanning with a plurality of laser beams as in the present invention is also called a “multi-beam” laser scanning method. Here, the plurality of laser beams emitted from the plurality of light emitting units 221a of the semiconductor laser array 221 are collimated (parallelized) into a laser beam having a predetermined beam diameter by the collimator lens 202. This laser beam is incident on a rotating mirror 218 having only one reflecting surface, and is deflected as it rotates. The laser beam that has passed through the scanning lens 204 forms an image on a spot 206 on the image carrier 205. The lighting and the light amount of the light emitting units 221a are individually controlled by the control device 260.

The function of the scanning lens 204 is roughly divided into two.
There are two. One is a so-called “fθ function”, which has a function of converting scanning at a constant angular speed of the rotating mirror 218 into scanning at a constant linear speed on the image carrier 205. The other is a function of correcting the field curvature, which has a function of correcting the image point to move back and forth in the optical axis direction depending on the scanning angle so that the image plane becomes flat.

Incidentally, both the collimator lens 202 and the scanning lens 204 have isotropic optical characteristics in all planes including the optical axis. That is,
In every plane including the optical axis, the collimator lens 2
02 and the scanning lens 204 have the same focal length and curvature, and are lenses that are not anamorphic.

Since the number of laser beams is four in this embodiment, if the rotation number of the rotating mirror 218 is the same, it is possible to obtain a scanning speed four times as high as that in the case of one laser beam. it can. Assuming that a rotating mirror with the highest rotational speed available at present as shown in the above conventional example is used, a printing speed of just over 10 sheets per minute in A4 paper conversion can be obtained, and a laser beam for personal use at present. It has sufficient scanning speed for printers. If the number of laser beams is further increased, it can be used for general business purposes.

Each light emitting section 2 of the semiconductor laser array 221
21a emits a modulated laser beam that is independently controlled based on image data to be written to each scanning line. For this reason, although not shown in the figure, data is transferred in parallel from the image data storage unit to the semiconductor laser array 221.

As will be described later, in order to set the scanning line interval to a predetermined value, the positions of the imaging spots of the respective beams in the scanning direction are different. For this reason, there is provided a function of delaying the modulation timing of each laser beam in accordance with the shift amount of the position.

FIG. 22 shows, for simplicity, the multi-beam laser scanning method of the present invention in which the number of laser beams is two, and the collimator lens and the scanning lens are both convex single lenses. Consider an optical system.
Two laser beams emitted from the semiconductor laser array 221 at an interval d are collimated by a collimator lens 2 having a focal length fc.
At 02 each becomes a parallel laser beam. Here, since the semiconductor laser array 221 is located at the object-side focal point of the collimator lens 202, the two laser beams intersect at the image-side focal point F. For example, the spot diameter d ₀ = 100 μm on the image plane 211 (the spot diameter and the beam diameter are defined as a diameter where the intensity distribution of the cross section of the beam is a Gaussian distribution and the power is 1 / e ² with respect to the peak intensity). When forming an image on the spot 206 of
If it is 0 mm, the diameter of the beam incident on the scanning lens (that is, the collimated diameter) Wc is expressed by the following equation (5).

[0113]

(Equation 9) Where λ is the wavelength of the laser, which is 780 nm. On the other hand, the focal length fc of the collimator lens 202 is determined by the divergence angle θ of the laser beam emitted from the semiconductor laser array 221.
And is expressed by the following equation (6).

[0114]

(Equation 10) Here, θ is defined by the full angle of 1 / e ² simultaneously with the definition of the beam diameter.

Next, from the collimator lens 202 to the reflecting surface 208 of the deflecting device, due to the arrangement of each element of the scanning device,
Assuming that a constant distance h is required, and that n laser beams are arranged in a straight line, the distance q on the reflecting surface 208 at which the n laser beams are reflected is the distance q Is, if the interval between laser beams is d,

[Equation 11] Is represented by

A case in which an edge emitting semiconductor laser which emits a laser beam from an end face of a substrate of an element, which is currently often used for a semiconductor laser array, will be described. As shown in FIG. 28 in the description of the conventional example, the emitted laser beam is affected by diffraction in the vertical direction of the substrate of the semiconductor laser array 201 and spreads at an angle of about 30 degrees at full width at half maximum. go. At this time, the focal length fc of the collimator lens 202 becomes about 3 mm. Therefore, for example, if the number n of laser beams is 4 and the distance h from the collimator lens 202 to the reflection surface 208 is 100, q = 9.7 mm. For this reason, the size of the reflection surface needs to be at least larger by the distance q. Even in such a case, since the present invention has only one reflecting surface, it is not a problem to increase the size of the reflecting surface as compared with the case of the rotary polygon mirror.

However, it is more preferable to use a so-called surface emitting semiconductor laser for the semiconductor laser array 221. Such a surface emitting semiconductor laser array 221
In this case, since the cross-sectional area of the laser beam emitting portion 221a can be made larger than that of a conventional edge-emitting semiconductor laser, the divergence angle of the laser beam becomes smaller. The size of the divergence angle is determined by the area of the exit window. Since the area can be accurately controlled by etching or the like, the divergence angle can be made constant. For example, the divergence angle is 8 at full width at half maximum.
It is also possible to obtain a laser beam of a degree.
Further, in such a surface emitting semiconductor laser, current and light can be efficiently confined in an optical resonator of the laser, so that heat generation per light emitting portion is reduced and a plurality of light emitting portions are adjacent to each other. In such a case, mutual optical, electrical, and thermal interference can be reduced. Therefore, the distance between the light emitting portions can be reduced as compared with the conventional semiconductor laser.

Using the above equation (6), the focal length fc of the collimator lens in the case of using a surface-emitting type semiconductor laser in which the divergence angle of the exit beam is 8 degrees is about 8 m.
m. Further, since the interval d between the light emitting units on the semiconductor laser array can be set to about 50 μm, similarly to the above example, when the number of beams is n = 4 and the distance h from the collimator lens 202 to the reflecting surface 208 is 100 mm. The distance q between the four beams on the reflecting surface is about 1.73 mm according to the above equation (7), which is not a significant problem compared to the collimated diameter Wc of the beam.

In particular, if the spot diameter on the image carrier is set to 50 μm in order to form a higher resolution image, the collimating diameter Wc is doubled by about 4 according to the above equation.
mm. Therefore, the focal length f of the collimator lens
c is also doubled, and the distance q between the reflection positions of the beam on the reflection surface
Is also halved.

As described above, when each beam is tracked,
At any position on the optical axis, the distance between each beam is
Since the diameter is sufficiently smaller than the collimation diameter, even if the optical system handles a plurality of laser beams, it is only necessary to carry out the optical design for one representative beam, and the design of the laser scanning optical system becomes very easy.

Further, since the focal length of the collimator lens is longer than that in the case of using the conventional edge-emitting type semiconductor laser, a larger error in the distance between the semiconductor laser and the collimator lens in the optical axis direction is allowed.

Among the surface-emitting type semiconductor laser arrays suitable for the multi-beam scanning method, more preferably, the surface-emitting type semiconductor laser array in which the II-VI group compound semiconductor is embedded around the light emitting portion. It is.

FIG. 23 shows a light emitting unit 2 arranged two-dimensionally on the element substrate of the surface emitting type semiconductor laser array 221.
FIG. 21B is a cross-sectional view of one of 21a. In FIG.
First, two types of AlGa having different compositions are formed on an aAs substrate 222.
A semiconductor multilayer reflective layer 223 in which several tens of As layers are stacked is formed, and a cladding layer 224, an active layer 225, a cladding layer 226, and a contact layer 227 made of AlGaAs are stacked thereon, and finally an SiO ₂ dielectric multilayer is formed. A film reflection layer 228 is formed. Further, window-shaped electrodes 229 and 230 are formed on the entire back surface of the GaAs substrate 222 and around the dielectric multilayer film reflection layer on the front surface, and the whole constitutes an optical resonator. Since the light generated in the active layer reciprocates between the upper and lower reflective layers 227 and 223 in the direction perpendicular to the substrate surface and oscillates, the optical axis of the laser beam 231 is substantially perpendicular to the substrate surface.

A group II-VI compound semiconductor is embedded as an embedded layer 232 around the optical resonator. II-VI
It is preferable to combine 2 to 4 elements of O, S, Se, and Te as group elements, and adjust the lattice constant of the compound to the lattice constant of the semiconductor layer including the cladding layer 224, the active layer 225, and the cladding layer 226. desirable. Since the II-VI compound semiconductor has a very high electric resistance, the current is efficiently confined in the optical resonator, and at the same time, the refractive index is different from that of the AlGaAs semiconductor layer forming the optical resonator. Therefore, light traveling at an angle perpendicular to or close to the substrate surface of the element inside the optical resonator is totally reflected at the interface with the buried layer 232 and is efficiently confined. For this reason,
When such a semiconductor laser is used, laser oscillation starts with a very small current as compared with a conventional semiconductor laser. That is, the threshold current is low, and the heat loss in the element substrate is small. In FIG. 23, a diode is formed on a GaAs substrate 222, and light generated in the active layer 225 reciprocates between the reflection layers 223 and 228 and oscillates.
The laser beam 231 is emitted perpendicularly to the substrate surface of the element from the reflective layer 228 having a slightly lower reflectance in the two reflective layers.

As mentioned in the description of the conventional example,
In a typical laser beam printer, the shape of the image spot of the laser beam on the image carrier is an ellipse whose minor axis coincides with the scanning direction. Conversely, an ellipse having a major axis in the scanning direction is desirable.

However, in the present invention, since no tilt correction optical system exists, as described above, when an edge-emitting type semiconductor laser array is used, an appropriate elliptical laser beam is made incident on the scanning lens. Therefore, it is necessary to shape the ratio of the major axis to the minor axis of the cross section of the laser beam using a collimator lens having anamorphic characteristics. Fabricating such a collimating lens is not very difficult and does not detract from the advantages of the present invention.

However, in the surface-emitting type semiconductor laser array, since the ellipticity of the cross section of the emitted laser beam can be freely controlled, the scanning surface has a long axis and an appropriate length can be obtained without using a special optical system. A laser beam having a cross section having a ratio of the axis to the minor axis can be incident on the scanning lens. That is, a surface-emitting type semiconductor laser array is optimal for obtaining an ideal elliptic ratio of an image forming spot.

In a surface-emitting type semiconductor laser, a light-emitting portion can be placed anywhere as long as it does not interfere with each other. Therefore, the light-emitting portions can be two-dimensionally arranged on an element. Now, in an exposure system that performs scanning with four laser beams, the positional relationship between a scanning line and an image spot is considered. Here, it is assumed that four scan lines adjacent to each other are drawn by one scan. When the imaging spots 206 are arranged as shown in FIG. 24A, the angle or distance between the laser beams can be reduced as compared with the case where they are arranged in a straight line as shown in FIG. The size of other optical systems can be reduced accordingly.

The above example shows the case where the number of laser beams is four. However, when the number of laser beams is further increased, the light emission on the semiconductor laser array is adjusted so that the position of the spot on the image carrier becomes closest. Because you can choose the arrangement of the part freely,
The effect is greater. As an example, FIG. 24C shows an example of the arrangement of the imaging spots with respect to the scanning lines when the number of laser beams is eight. That is, even if the number of reflecting surfaces of the rotating mirror is one, a practically sufficient printing speed can be obtained by further increasing the number of beams.

In this embodiment, since the scanning optical system has the same optical characteristics in the scanning direction and the sub-scanning direction, the arrangement of the imaging spots on the image carrier and the arrangement on the semiconductor laser array The arrangement of the light emitting units is similar.

Next, the deflection device used in the present invention will be described with reference to the plan view of FIG. Only one reflecting surface 215 is provided, which is attached to the rotating part of the motor 216, and rotates at a constant speed. As described above, in the conventional polygon mirror, the processing method and the structure are limited in order to maintain the mutual inclination accuracy of the reflection surfaces. In general, many rotating polygon mirrors have a mirror-finished mirror body made of metal such as aluminum coated. But,
When there is only one reflecting surface, the manufacturing method is not limited to the above-mentioned shaving, but can be manufactured only by sticking a metal reflective film deposited on a surface of a glass having a good flatness to a rotating portion, and the like. Can be cheaper.

The rotating portion including the reflecting surface 215 has a smaller mass than a conventional polygon mirror, and is very advantageous with respect to vibration during rotation. The rotating part is designed so as to achieve a dynamic balance with respect to the rotating shaft, or additional processing is performed as necessary.

Further, it is designed such that the center of the reflection surface 215 coincides with the rotation axis A. When the laser beam 217 is incident on the reflection surface 215 in the vicinity of the rotation axis A, even if the reflection surface 215 rotates, the laser beam
Since 7 is located at almost one point on the reflecting surface 215, the size of the reflecting surface can be very small as compared with the conventional rotary polygon mirror.

Further, when there is only one reflecting surface, the angle at which the beam can be deflected is greatly increased as compared with the case of a polygon mirror. For example, as shown in FIG. 26, in the case of a six-sided mirror, when the collimating diameter Wc of the laser beam 217 is 0, the limit of the scanning angle α is 120 degrees regardless of the size of the reflecting surface. On the other hand, in the design of the scanning optical system, the effective scanning angle is about 90 degrees when the scanning angle is large, and a detector for detecting the collimation diameter Wc of the laser beam incident on the reflecting surface and the beam scanning start position is provided. In order to allow a margin for the position, the scanning angle of the deflecting device is insufficient with the above-mentioned six-surface mirror, and the effective scanning angle of the scanning lens is narrowed.

On the other hand, when the number of the reflecting surface is one, the rotation axis is positioned on the reflecting surface as described above, or when the size of the reflecting surface is infinite, it is theoretically 360 degrees. Therefore, a scanning lens having a large scanning angle can be used,
The entire scanning optical system can be designed small.

When one reflecting surface is used, the period used for actual scanning is about 10% of the time for one rotation, and the other time does not contribute to scanning. If the laser is emitted during that period, the laser beam is irradiated on the back of the reflection surface, etc., and unintended reflected light may form on the image carrier.Therefore, a circuit that does not operate the laser during unnecessary periods Is provided.

Alternatively, by using the time not used for such scanning, the laser is turned on, the amount of light is detected, and the driving current of the laser can be set so as to obtain a predetermined amount of light. At the time of turning on the laser for this current control, as described above, in order to prevent the laser beam from reaching the image carrier due to unnecessary reflection, the angles of peripheral members of the deflection device are appropriately designed, It is desirable to perform an anti-reflection surface treatment.

The embodiment described above is only one embodiment of the present invention, and the structure of the collimator lens and the scanning lens,
Even if the relative positional relationship changes, the effect of the present invention is similarly exhibited. It is clear that the same effect can be obtained by other methods such as injection molding of plastics as to the structure and manufacturing method of the rotating mirror. Further, the effect of the present invention can be similarly exerted not only in the case where the rotating mirror rotates in one direction at a constant speed, but also in the case of a so-called galvano mirror which performs rotational vibration.

Alternatively, the structure of the element of the surface emitting laser shown in the above embodiment is one example that can be realized, and has a structure in which the characteristics such as the divergence angle of the emission beam and the interval between the light emitting portions are equivalent. If it is, the same effect is exerted even with other structures. Further, it goes without saying that the application range of the image forming apparatus of the present invention has exactly the same effects not only in printing apparatuses such as printers and copiers but also in facsimile machines and displays.

3-3 Effect As described above, in the image forming apparatus of the present invention,
By using a rotating mirror having only one flat reflecting surface as the deflector, the rotating part of the deflector becomes smaller and lighter, not only easy to manufacture, but also the dynamic vibration characteristics are improved. Further, by omitting the tilt correction optical system and not using an anamorphic optical system in particular, a scanning optical system with a very simple configuration and easy assembly adjustment can be realized. Further, by using the multi-beam system, the same scanning speed as that of the related art can be maintained.

According to the present invention, particularly when a surface-emitting type semiconductor laser array is used, a new additional optical system other than the collimator lens and the scanning lens is added.
The size of the reflection surface can be reduced, and at the same time, the elliptic ratio of the image spot on the image surface can be set freely.

§4 Fourth Embodiment of Image Forming Apparatus 4-1 Comparison with Background Art To better understand this embodiment, the background art will be described first.

FIG. 33 is a sectional view of an optical path of a conventional image forming apparatus.
Shown in

In FIG. 33, a laser beam emitted from a semiconductor laser 301 is emitted at a divergence angle θ. This beam is a collimator lens 30 having a focal length fc.
2 are shaped into substantially parallel beams, and each beam is reflected by the tilt correction lens 307 to the reflecting surface 308 of the rotating polygon mirror.
Focus on top once. The beam deflected by the rotary polygon mirror passes through the second tilt correction lens 307 ', becomes a parallel beam again, and forms a spot on the image carrier by the scanning lens 304 having a focal length fi. Since the tilt correction lenses 307 and 307 'have no optical power in a plane parallel to the scanning plane, the beam remains parallel in that plane. That is, the beam forms a line image on the reflecting surface 8 of the rotary polygon mirror.

Next, the tilt correction lenses 307, 307 '
Explain the function of. No matter how precisely the inclination of each reflection surface 308 of the rotating polygon mirror with respect to the mutual rotation axis is processed,
The angle has an error of several tens of seconds, so the image position of the beam reflected on this surface is enlarged by the principle of "optical leverage", and cannot be ignored on the surface of the image carrier with respect to the scanning line pitch. It will be large. Therefore, as disclosed in Japanese Patent Application Laid-Open No. 48-49315, the tilt correction lens 30 is arranged so that each reflecting surface and the surface of the image carrier (image forming surface) are located at optically conjugate positions.
7 'is provided. The tilt correction lens 307 'is generally formed of a cylindrical lens or toric lens having optical power only in the sub-scanning plane. For example, even if the reflecting surface is inclined as shown at 308 'in FIG. 33, the beam always forms an image at the same position on the image forming surface.

However, in recent years, with the improvement of computer utilization technology, the output speed of the image forming apparatus has been further desired to be improved, and the improvement has been progressing. However, for example, in a deflecting device using a rotating polygon mirror, one laser beam is deflected for each of the small surfaces of the mirror surface to draw one scanning line. Therefore, it is necessary to increase the number of scans per unit time. On the other hand, when the number of facets of the rotating polygon mirror is constant, the number of revolutions increases, and when the number of revolutions is constant, the number of faces of the rotating polygon mirror increases. In order to increase the number of rotations of the rotating polygon mirror, bearings using dynamic pressure or static pressure of gas or liquid are indispensable, but these bearings are difficult to handle due to their effect and cannot be used for general laser beam printers. It was difficult. Conversely, increasing the number of faces of the polygon mirror decreases the deflection angle, so that the optical path length after the deflector becomes longer and the collimated diameter of the laser beam incident on the imaging optical system also increases in proportion to it. The size of the rotating polygon mirror also increases. In particular, when high resolution is also required at the same time, the number of scanning lines increases, so that a higher rotation speed and a longer optical path length are required. The same applies to the case where a device other than the rotary polygon mirror is used as the deflecting device, which results in an increase in the scanning frequency and an increase in the optical path length after the deflecting device. Therefore, an exposure method for writing a plurality of scanning lines using a plurality of laser beams in one scan (so-called multi-beam) has been developed.

In order to obtain a plurality of laser beams, a plurality of gas laser (for example, He—Ne) oscillators are used as a light source, and the laser beam of one oscillator is time-divisionally divided by an acousto-optic modulator (AOM) or the like. Although a method of distributing the light to a plurality of light emitting devices has been developed, a simpler method for reducing the size of the device is to integrate a plurality of light emitting units on one element as disclosed in, for example, Japanese Patent Application Laid-Open No. 54-7328. (Multi-beam laser scanning method) using a semiconductor laser array as a light source has been proposed.

However, when a laser beam having a plurality of parallel optical axes is incident on the collimator lens, the optical axes are spread at a large angle with each other, and the reflection surface and the optical system of the deflecting device are disturbed. There is a problem that the size of the constituent lens becomes very large as compared with the case where scanning is performed using one laser beam.

FIG. 34 is a sectional view showing the optical path from the semiconductor laser array to the image carrier in the multi-beam laser scanning method. For simplicity, consider a laser beam scanning optical system in which the number of laser beams is two and the collimator lens and the scanning lens are both convex single lenses.
Two laser beams emitted from the semiconductor laser array 321 at an interval δ are collimated by a collimator lens 3 having a focal length fc.
At 02 each becomes a parallel laser beam. Here, since the semiconductor laser array 321 is located at the object-side focal point of the collimator lens 2, the two laser beams intersect at the image-side focal point F. For example, the spot diameter d on the image plane 311
= 100 μm (where the spot diameter and beam diameter are
The intensity distribution of the cross section of the beam is defined as a Gaussian distribution, which is defined as a diameter at which the power becomes 1 / e ² with respect to the peak intensity.)
When forming an image on the spot 306, fi is set to 200 m
If m, the diameter of the beam incident on the scanning lens (that is, the collimated diameter) Wc is expressed by the following equation (8).

[0150]

(Equation 12) Where λ is the wavelength of the laser, which is 780 nm. Therefore, in this example, the collimating diameter Wc is about 2 mm.
As shown in the conceptual diagram of FIG. 35, a so-called edge-emitting laser diode which has been used conventionally has a beam parallel to a bonding plane including an optical axis and a plane including an optical axis and perpendicular to the bonding plane. The divergence angle was very different. The divergence angle θp in a plane parallel to the bonding plane is about 10 degrees at full width at half maximum in the case of a normal semiconductor laser. However, in the plane perpendicular to the bonding plane, the spread plane θt is affected by diffraction, and becomes as large as about 30 degrees at full width at half maximum. Further, the spread angles θt, θ
It is also difficult to freely set the size of p and its ratio (that is, the ratio of the major axis to the minor axis of the ellipse). When the coupling efficiency between the semiconductor laser array and the collimator lens is increased to effectively use most of the radiation beam, the focal length fc of the collimator lens 2 must be set to obtain the collimated diameter of 2 mm as described above. It is about 3 mm. On the other hand, in the current semiconductor laser array, it is difficult to make the interval δ between the light-emitting portions 100 μm or less in order to avoid mutual interference.

From the image-side focal point F of the collimator lens 302 to the reflecting surface 308 of the deflector, a certain distance h is required due to the arrangement of the components of the scanning device. Assuming that the interval between the two light emitting units, which are farthest from each other, is δmax,
The distance q between the two beams on the reflecting surface 308 of the deflector
Is

(Equation 13) Is represented by For example, when the number of beams is four and the light emitting units are arranged in a line every 0.1 mm on the semiconductor laser array, δmax is 3 × δ = 0.3 mm. If the distance h from the image-side focal point F of the collimator lens 302 to the reflecting surface 308 is 50 mm, q = 5 mm. For this reason, the size of the reflecting surface is required at least by the distance q plus the diameter of the laser beam collimator, so that the rotating portion of the deflector becomes large, the load on the bearing is large, and the effect of imbalance during rotation is also reduced. Easier to receive. As is clear from equation (9), the value of q increases as the value of fc / δmax decreases.

Next, the above-described tilt correction lens 307,
Consider the case where 307 'is added to the scanning optical system. Since the tilt correction lens is an anamorphic optical element,
Optical characteristics are different between the scanning surface and the sub-scanning surface. As described above, since the tilt correction lens has no optical power in the scanning plane, the distance q between the two beams having the maximum distance in the scanning plane on the reflecting surface is calculated by the above equation (9). Desired. Therefore, only the sub-scanning plane needs to be newly considered. FIG. 36 is an optical path cross-sectional view in the sub-scanning plane including the tilt correction lens 307, and shows the semiconductor laser array 321.
To the reflecting surface 308 of the deflector.

As described above, when viewed in the sub-scanning plane,
Each beam forms a line image on the reflecting surface 308 of the deflector, and the position where the line image is formed on the reflecting surface has a certain distance q in the sub-scanning direction. The focal length of the tilt correction lens 307 on the front side of the beam deflector is ft, the distance from the image-side focal point F of the collimator lens 302 to the tilt correction lens 307 is t1, and the reflection surface 3 of the deflector from the tilt correction lens 307.
34 is t2, and other symbols are shown in FIG.
Assuming that the two laser beams are the same as each other, two of the plurality of laser beams, which are farthest from each other, are the tilt correction lenses 307
And the mutual distance q of the beams when entering the reflecting surface 308 are expressed by the following equations (10) and (11), respectively.

[0154]

[Equation 14] Here, in general, ft = t2 so that the collimated laser beam has a beam waist on the scanning surface.

When t1 <ft, the two beams do not intersect on the image side. Therefore, q> q ′, and q increases as t1 decreases. For example, t1 = 20m
Calculating with m, ft = 30 mm, and t2 = 30 mm, q '= 2 mm and q = 3 mm. Equation (11) includes q ', and according to equation (10), fc /
When δmax is large, q ′ is also small. Where t1 + t
Since 2 = h, it is the same as the above calculation example in the scanning plane. That is, in this example, in the sub-scanning direction,
It can be seen that the distance between the beams at both ends is reduced.

Further, the same applies to the distance between the plurality of laser beams when they enter the scanning lens 4. That is, it is the same as Expression (10) if the incident position on the tilt correction lens is regarded as the incident position on the scanning lens. Since the distance from the collimator lens to the scanning lens is greater than in the previous case, it is necessary to further increase the size of the scanning lens.

Generally, the optical power of each optical element constituting the laser beam scanning optical system is the largest for a collimator lens. That is, the focal length is the shortest. This means
It means that the angle formed by each beam when passing through a collimator lens changes the most before multiple laser beams emitted from the semiconductor laser array reach the image carrier via the optical system. ing.

In order to avoid this problem, there has been proposed a method in which a plurality of laser beams are reflected on a reflecting surface so as to be close to each other by adding many optical elements.
For example, in JP-A-56-69611, an afocal optical system is provided behind a collimator lens to collect beams on a reflection surface. However, the addition of such an optical system again undesirably complicates the structure of the scanning optical system, and is not preferable in terms of cost, ease of adjustment, and reliability.

When a plurality of laser beams follow optical paths different from each other as described above, it is necessary to design each laser beam so that each aberration and the size of an image spot are set to desired values. The design man-hours are increased, the development period of the image forming apparatus is extended, and at the same time, a design solution that satisfies the design specifications is obtained at any position within the scanning range with a plurality of laser beams. It becomes difficult. This becomes a more serious problem in an image forming apparatus having a high resolution which requires a higher design, that is, a small imaging spot diameter.

Furthermore, a laser scanning optical system designed through such difficulties is more effective than a conventional laser beam scanning optical system using a single laser beam. Not only is large, but also the configuration is advanced (that is, the number of lenses is large, and the adjustment of the lens position is required to be accurate), which makes it difficult to standardize production equipment.

4-2 Configuration of the Present Invention FIG. 30 is a diagram showing an image forming apparatus of the present invention. The process of obtaining a print result on the transfer material 351 is based on a so-called electrophotographic process. As the image carrier 305, in an electrophotographic printer using a semiconductor laser as a light source, an organic photoconductor (OPC) sensitized to a longer wavelength side is often used. The image carrier 305 is first charged to a constant surface potential by a charger 352, and then the laser beam scanning device 3
Optical writing, that is, exposure is performed by 53. A plurality of laser beams 354 whose light intensities are independently modulated according to image information from the laser beam scanning device 353.
Scans the image carrier 305 in the axial direction, generates charges that cancel the surface potential only in the exposed portion, and reduces the absolute value of the surface potential in that portion. As a result, a distribution of the surface potential according to the image, that is, an electrostatic latent image is formed on the image carrier. The electrostatic latent image is developed by a developer 355 by selectively applying a developer according to the surface potential. This developer is transferred to a transfer material 351 (usually paper) by a transfer device 356. The transfer material 351 is fixed by heat and pressure by a fixing device 357 and is discharged.

FIG. 29 is a schematic view showing a laser beam scanning optical system according to the present invention. In the laser beam scanning device 353 shown in FIG. 30, it is assumed that the laser beam 354 is bent and emitted downward, but is simplified here for the sake of explanation. Here, the laser beams emitted from the plurality of light emitting portions 341a of the monolithic semiconductor laser array 341 are collimated (parallelized) into a laser beam having a predetermined beam diameter by the collimator lens 302. These laser beams are incident on the rotary polygon mirror 303, and are deflected by the rotation. The laser beam that has passed through the scanning lens 304 forms an image on a spot 306 having a predetermined size on the image carrier 305. The lighting and the light amount of the light emitting unit 341a are individually controlled by the control device 360.

It is preferable to use a so-called surface emitting semiconductor laser for the semiconductor laser array having such characteristics. Still more desirable is a surface-emitting type semiconductor laser array in which a group II-VI compound semiconductor is embedded around a light emitting portion.

FIG. 31 is a cross-sectional view of one of the light-emitting portions two-dimensionally arranged on the element substrate of the surface-emitting type semiconductor laser array. A semiconductor multilayer reflective layer 322 formed by laminating several tens of AlGaAs layers is formed.
a cladding layer 324 made of lGaAs, an active layer 325,
A cladding layer 326 and a contact layer 327 are laminated, and finally, a SiO ₂ dielectric multilayer reflective layer 328 is formed. Further, window-like electrodes 329 and 330 are formed on the entire back surface of the GaAs substrate 322 and around the dielectric multilayer film reflection layer on the front surface.
Are formed, and the whole constitutes an optical resonator. The light generated in the active layer is applied to the upper and lower reflective layers 3 in a direction perpendicular to the substrate surface.
Since the laser beam oscillates back and forth between 27 and 323, the optical axis of the laser beam 331 is substantially perpendicular to the substrate surface.
A group II-VI compound semiconductor is embedded around the optical resonator as an embedded layer 332. Group II-VI compound semiconductors include Zn, Cd, and Hg as Group II elements, O, S, Se, and Te as Group VI elements in combination of 2 to 4 elements. 3
It is desirable to match the lattice constant of the semiconductor layer including the active layer 24, the active layer 325, and the cladding layer 326. Since the II-VI compound semiconductor has a very high electric resistance, the current is efficiently confined in the optical resonator, and at the same time, the refractive index is different from that of the AlGaAs semiconductor layer forming the optical resonator. Therefore, light traveling at an angle perpendicular to or close to the substrate surface of the element inside the optical resonator is totally reflected at the interface with the buried layer 332 and is efficiently confined. Therefore, when such a semiconductor laser is used, laser oscillation starts with a very small current as compared with a conventional semiconductor laser.
That is, the threshold current is low, and the heat loss in the element substrate is small. In FIG. 31, a diode is formed on a GaAs substrate 322, and the light generated in the active layer 325 reciprocates between the reflection layers 323 and 328 and oscillates. From the small reflective layer 328,
The laser beam 31 is emitted perpendicular to the substrate surface of the element.

In such a surface-emitting semiconductor laser, the cross-sectional area of the laser beam emitting portion can be larger than that of a conventional edge-emitting semiconductor laser, so that the divergence angle of the laser beam becomes smaller. The size of the divergence angle is determined by the area of the exit window. Since the area can be accurately controlled by etching or the like, the divergence angle can be made constant. For example, it is sufficiently possible to obtain a laser beam having a divergence angle of about 8 degrees at full width at half maximum. Further, in such a surface emitting semiconductor laser, current and light can be efficiently confined in the laser resonator, so that heat generation per light emitting portion is reduced and a plurality of light emitting portions are adjacent. The mutual optical, electrical and thermal interference in the case is greatly reduced compared to the conventional edge emitting semiconductor laser array. Therefore, the distance between the light emitting portions can be reduced as compared with the conventional semiconductor laser, and a value of about 50 μm can be realized.

As described above in the description of the conventional example,
In order to obtain a beam collimated to a beam diameter of 2 mm, the focal length fc of the collimator lens when using the above-mentioned surface emitting semiconductor laser is about 8 mm. In addition, the interval δ between the light emitting units on the semiconductor laser array 341
Can be reduced to about 50 μm, so that δmax when 150 beams are arranged in series is 150 μm. When the reflection surface of the deflector is placed at the same position (from the collimator lens) as in the conventional embodiment, the interval q between the reflection positions of the beam on the reflection surface is 1/5 or less. Here, the value of fc / δmax is about 53 in comparison with about 10 in the prior art example. Similarly, if the distance h from the collimator lens to the reflecting surface is 50 mm, the distance q between the four beams on the reflecting surface is given by the above equation (9). About 0.94
mm, which is not a significant problem compared to the collimator diameter Wc of the beam.

In particular, if the spot diameter d on the image carrier is 50 μm in order to form a higher-resolution image, the collimating diameter Wc is doubled to about 4 mm according to the above equation. Accordingly, the focal length fc of the collimator lens is doubled, and the interval q between the reflection positions of the beam on the reflection surface is further reduced by half.

As described above, when each beam is tracked,
At any position on the optical axis, the distance formed by each laser beam is not so large as compared to the collimated diameter. Therefore, even if the optical system handles multiple laser beams, only one representative beam is required. An optical design may be performed, and the design of the laser scanning system becomes very easy.
If the precision of the imaging spot is not particularly required, the conventional laser beam scanning optical system using one laser beam can be used as it is.

Next, in a surface-emitting type semiconductor laser, the light-emitting portions can be placed anywhere as long as they do not interfere with each other, so that the light-emitting portions can be two-dimensionally arranged on the element. The laser beams emitted from the light emitting portions arranged at intervals δ on the element substrate are enlarged by the optical magnification M of the scanning optical system, and are spaced δ ′ on the image plane, that is, on the image carrier.
Image at the spot. This value of M is approximately equal to the ratio of the focal length of the collimator lens to the focal length of the scanning lens.

Now, in an exposure system that performs scanning with four laser beams, the positional relationship between a scanning line and an imaging spot will be considered. Here, it is assumed that four scan lines adjacent to each other are drawn by one scan. Here, one of the four imaging spots 6 having the largest distance from each other is defined as δ′max. FIG.
When the imaging spots are arranged as shown in FIG.
Δ'max compared to the case where they are arranged in a straight line as in (b).
Can be reduced. The arrangement of the imaging spots on the image carrier is similar to the arrangement of the light emitting units on the semiconductor laser array, or when there is a tilt correction optical system,
There is a mapping relationship in which a certain magnification is further multiplied in the sub-scanning direction.
Therefore, that δ'max is small in the same optical system means that δmax is also small. Therefore, by taking the arrangement shown in FIG.
In equation (10) or equation (11), q becomes smaller,
The size of the reflecting surface of the deflecting device can be reduced accordingly, and the effect of the present invention can be further enhanced.

The above example shows a case where the number of laser beams is four. However, when the number of laser beams is further increased, the light emission on the semiconductor laser array is set so that the position of the spot on the image carrier becomes closest. Because you can choose the arrangement of the part freely,
The effect is greater. As an example, FIG. 32C shows an example of the arrangement of the imaging spots with respect to the scanning lines when the number of laser beams is eight. That is, in equation (9), when the light emitting units are arranged in a straight line, δmax = 7 × δ, but when the light emitting units are arranged as shown in FIG.
= 3 × δ, the value of q may be calculated and the size of the optical system may be designed, and the effect of the present invention may be further enhanced. Further, for example, since the imaging spots 306a and 306e are at the same position in the scanning direction, the corresponding light emitting units can be driven at the same timing.

When a surface-emitting type semiconductor laser array is used, the focal length of the collimator lens is larger than that when a conventional edge-emitting type semiconductor laser is used, so that the error in the distance between the semiconductor laser and the collimator lens in the optical axis direction is reduced. Greater tolerance is allowed. For this reason, the adjustment work at the time of manufacturing becomes easy, and it is hard to be affected by the temperature shift and the positional shift of the collimator lens due to aging.

As described above, according to the image forming apparatus of the present invention, a plurality of laser beams emitted from the semiconductor laser array are collimated by the collimator lens, deflected by the beam deflector, and deflected by the scanning lens. Optical writing is performed by forming an image of a spot on the carrier. At this time, the focal length fc of the collimator lens is longer than that of the conventional one, and the interval δ between the light emitting units on the semiconductor laser array is also small. In particular, when a surface-emitting type semiconductor laser array is used, the focal length fc of the collimator lens becomes longer because the divergence angle of the emitted laser beam is small, and the amount of heat generated in each light-emitting portion is small. Since the interference is small, the interval between the light emitting units can be reduced.

In the case where no tilt correction lens is provided, the distance q between the beams at both ends of each laser beam arranged in a line on the reflecting surface of the deflector is expressed by the above-mentioned equation (9).

When there is a tilt correction lens, the distance q 'of the beam at both ends on the sub-scanning surface in the tilt correction lens and the distance q on the reflecting surface of the deflector are expressed by the equations (10) and (11), respectively. Is represented by In Equations (9) and (10), it can be seen that q and q ′ are inversely proportional to fc / δmax. In equation (11), since q is proportional to q ′, it is also inversely proportional to fc / δmax. In this case also, equation (9) can be applied to the scanning plane.

That is, when these equations (9) to (11) are reviewed, if the reciprocal of fc / δmax is multiplied by a value corresponding to the dimension in the optical axis direction, the distance between the beams in the direction orthogonal to the optical axis is obtained. It turns out that it becomes. Generally small (here A4
In this case, the distance between the optical elements in the optical axis direction and the focal length take a value of about 50 mm. Let this value be Z. On the other hand, when converted from the resolution, the collimated diameter of the laser beam is about 2 mm. Therefore, in order to keep the maximum distance of the beam at each lens or reflecting surface to the same extent as the collimating diameter, it is desirable to set δmax / fc × Z to 2 mm or less. Therefore, the value of fc / δmax is 25
The above is desirable.

Similarly, in the case of the scanning lens, when the longest distance between a plurality of laser beams incident on the scanning lens is set to about 2 mm as described above, a value of about 100 mm should be considered. I have to. Therefore, when the same calculation is performed, fc / δmax becomes 50
It is desirable that this is the case.

As described above, if the maximum value of the distance between a plurality of beams at each lens or reflecting surface is approximately the same as the collimated diameter of the laser beam, the optical system that scans one laser beam The size of each lens and the reflecting surface does not become significantly large as compared with. Further, if the distance between the laser beams can be made smaller than the collimating diameter, a plurality of laser beams can be treated as one laser beam in optical design.

The embodiment described above is merely an embodiment of the present invention. For example, a semiconductor laser has the same effect as long as the divergence angle of the emitted beam is small and the interval between the light emitting portions is small. Further, even if the configuration of the collimator lens and the scanning lens and the relative positional relationship change, the effect of the present invention is similarly exerted. It is clear that the same effect can be obtained by using a deflector other than the rotary polygon mirror as well as a galvanomirror.

Alternatively, the structure of the surface-emitting type semiconductor laser array described in the above embodiments is such that the distance between the light-emitting portions satisfies the above-mentioned predetermined relationship with respect to the focal length of the collimator lens. The same effect can be obtained with any type.

Further, it goes without saying that the application range of the image forming apparatus of the present invention is not limited to printing apparatuses such as printers and copiers, but also has exactly the same effects in facsimile machines and displays.

4-3 Effect As described above, in the image forming apparatus of the present invention,
While taking the exposure method using multiple laser beams,
By using a semiconductor laser array that satisfies certain conditions for the focal length of the collimator lens and the distance between the light emitting portions of the semiconductor laser array, the size of the reflecting surface of the scanner and the size of each lens can be reduced without adding auxiliary optical elements. Of the scanning optical system or the entire image forming apparatus can be reduced in size and cost.

Further, since a plurality of laser beams take substantially the same optical path, the design can be performed in the same manner as a scanning optical system using one laser beam. Therefore, the number of design steps can be greatly reduced, and the development period can be shortened. At the same time, the production equipment can be used in common with the case of a scanning optical system using one laser beam, and the productivity is greatly improved.

Further, when a plurality of laser beams are incident on each optical system constituting the scanning optical system, the distance between the two laser beams is farthest from the collimated diameter of the laser beam. If smaller, the conventional scanning optical system using one laser beam can be diverted as it is. That is, without changing the scanning optical system of the image forming apparatus using one laser beam at all.
By simply increasing the number of laser beams, a high-speed image forming apparatus can be manufactured, and there are immeasurable product manufacturing benefits.

Next, since the divergence angle of the laser beam is reduced, the distance between the collimator lens and the semiconductor laser array can be increased, so that the margin for adjustment of the collimator lens in the optical axis direction is increased, and the productivity is increased, and at the same time, deterioration over time. Exposure can be performed with a constant spot diameter without being affected by temperature fluctuations during use, and image quality is improved.

§5 Fifth Embodiment of Image Forming Apparatus 5-1 Comparison of Background Art In order to better understand this embodiment, the background art will be described first.

A scanning optical system of a conventional image forming apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. 3-248114 (FIG. 4).
1). In FIG. 41, the light source uses an edge emitting semiconductor laser array 420 in which the center axis of the emitted beam is substantially parallel to the element substrate surface, and is disposed on the object-side focal plane of the collimator lens 402. An aperture stop 403 is provided at the image-side focal position of the collimator lens 402.

However, in the prior art described above, since the beam divergence angle of the edge emitting semiconductor laser and the interval between the light emitting portions are large, the position where the cross sections of a plurality of beams overlap is the image side focal position of the collimator lens. In the immediate vicinity. Especially when a large number of beams are arranged in a row, the position where the cross sections of the beams at both ends overlap is
It is more limited. Accordingly, the position where the aperture stop is arranged is also limited to a small range, and there is a problem that the degree of freedom in design is small.

In general, in an optical system, a holding frame of a lens may be used as an aperture stop, so that it is not necessary to provide a separate aperture stop. However, in the above-described related art, there is also a problem in that the cross section of the plurality of beams does not overlap at the position of the collimator lens, so that the holding frame of the collimator lens cannot be used as an aperture stop.

5-2 Configuration of the Present Invention FIG. 38 is a configuration diagram of the image forming apparatus of the present invention. The image forming process of the electrophotographic printer will be described below. A uniform charge is given to the image carrier 407 by the charger 451, and a latent image is formed by exposing and scanning the image carrier 407 with the scanning optical system 452. Next, developing unit 4
At 53, a developer is adhered on the latent image to visualize it, and the transfer device 4
At 54, the developer forming the visible image is transferred onto a transfer material 455 such as paper, and the fixing device 456 heats and melts the developer to fix it on the transfer material 455.

FIG. 37 is a configuration diagram of a scanning optical system showing an embodiment of the present invention. The light source is a surface emitting semiconductor laser array 401 in which the central axis of the emitted beam is substantially perpendicular to the surface of the element substrate 422. A plurality of beams emitted from the light emitting portion 401a of the surface emitting semiconductor laser array 401 are collimated by the collimator lens 402, pass through the aperture stop 403, and enter one deflection surface 405 of the rotary polygon mirror 404 as a deflection device. I do. The reflected beam is deflected and scanned with the rotation of the rotary polygon mirror 404, and the imaging lens 40 is rotated.
6 to form an image on the image carrier 407.

Note that the light emitting section 401a is provided with the control device 460.
The lighting and the light amount are individually controlled by.

In general, regardless of edge emission or surface emission, the divergence angle of an output beam from a semiconductor laser is
There is some variation between the light emitting units, and the beam diameter collimated by the collimator lens 402 also varies. However, if the aperture stop 403 is provided at a position where the cross-sections of the plurality of beams substantially overlap, and the diameter of the aperture stop 403 is set to be approximately equal to or smaller than the diameter of the parallel beam, the plurality of parallel beam diameters after passing through the aperture stop 403 can be obtained. Becomes uniform.
As a result, the spot diameter formed on the image carrier 407 also becomes uniform, stable and good printing quality is obtained, and there is no difference in printing quality between the apparatuses. Here, the beam divergence angle and its diameter are assumed to form a Gaussian distribution of the intensity distribution of the beam cross section, and are each 1 / cent of the central intensity.
It is a diameter representing the full angle of the angle of ² and the position of 1 / e ^{2 of the} center intensity.

The effect of making the beam diameter uniform by the aperture stop will be described. When a laser beam is stopped down by an aperture stop, diffraction, which is a property of wave optics, occurs. When the center of the aperture stop and the center of the incident beam coincide with each other, the imaging spot diameter d ₀ on the image carrier in consideration of diffraction is:

(Equation 15) It is represented by Here, k is a constant, λ is the wavelength of the laser beam, f is the focal length of the imaging lens, and D is the diameter of the aperture stop. Further, if the ratio of the diameter d of the beam incident on the aperture stop to the diameter D of the aperture stop is a cutting ratio T = d / D,
The constant k is

(Equation 16) (“Laser & Optics Guide II”
Japan Melles Griot Co., Ltd.).

As an example, let the diameter D of the aperture stop be 1,
When the diameter d of the incident beam has a variation of ± 20% around 1, the variation of the diameter of the imaging spot is +
5.9% to -3.1%. As described above, the aperture stop has an effect of suppressing the variation in the image spot diameter to the variation in the beam diameter.

The aperture stop is positioned at a position where at least a part of the cross section of the plurality of beams on the optical path overlaps, and among the plurality of beams after passing through the aperture stop, the beam having the maximum power Is set to 1, if all the beams are arranged at positions where the powers of all the other beams are 0.9 or more, the variation in the power of the beams after passing can be suppressed to 10% or less. With such a degree of variation, good print quality without uneven print density can be obtained.

Here, the position of the aperture stop 403 that satisfies the above conditions in a system as shown in FIG. 39 will be specifically described. Here, FIG. 39A is a side view of the scanning optical system.
FIG. 39B is a cross-sectional view at the position of the aperture stop 403. Due to its characteristics, the surface emitting type semiconductor laser array 401 has a spread angle of 10 degrees or less and a light emitting unit spacing of 0.05.
mm or less. In FIG. 39, the distance Δ between the light emitting unit A410 and the light emitting unit B411 is 0.05 mm.
The light emitting unit A410 is placed on the optical axis 412 of the optical system.
The beam emitted from each of the light emitting units 410 and 411 is
The beams are assumed to be a beam A413 and a beam B414, respectively. The divergence angle θ of each emission beam is 10 degrees, the focal length fc of the collimator lens 402 is 10 mm, and the distance h from the collimator lens 402 to the deflection surface 405 of the rotating polygon mirror is 100 mm. In this case, the beam diameter d is 3.0 mm. The center of the aperture stop 403 is the optical axis 412
And its diameter D is equal to the beam diameter d.

Assuming that the sectional intensity distribution of the laser beam has a Gaussian distribution, the sectional intensity I is

[Equation 17] It is represented by Here, P is the power of the entire beam, w is the radius of the beam, and x is the distance from the beam center. The power after the beam A413 has passed through the aperture stop 403 is given by

(Equation 18) It is obtained by integration as in equation (15), and its value is 86.5% of the power P before passing. Therefore, for the beam B414, the power after passing through the aperture stop 403 must be 86.5 × 0.9 = 77.9 (%) or more compared to the power before passing. Next, the power after the beam B414 has passed through the aperture stop 403 is determined. Aperture stop 4
03, the center axis of the beam B414 and the optical axis 41
Assuming that the distance from the aperture stop 403 is t, the cross-sectional intensity I immediately before passing through the aperture stop 403 is expressed by using a cylindrical coordinate system.

[Equation 19] It is expressed as Here, as shown in FIG. 39B, r is the distance from the optical axis 412 to an arbitrary point A on the aperture stop 403, and φ is the central axis 414a of the optical axis 412 and the beam B414.
Are angles formed by a plane B formed by the optical axis and a line connecting the optical axis 412 and the point A. The power of the beam B14 after passing through the aperture stop 3 is given by the above equation.

(Equation 20) When the ratio between t and the beam diameter d is 0.200, the power after passing through the aperture stop 403 is 77.9% of the power P before passing through the aperture stop 403. Will be the same. That is, if the aperture stop 403 is placed at a position where t / d is 0.200 or less, the power difference between the beams A413 and B414 after passing through the aperture stop 403 is 10% or less. Assuming that the aperture stop 403 is placed at the position of the collimator lens 402 or the position of the deflection surface 405 of the rotary polygon mirror, the distances t are 0.05 mm and 0.
45 mm, and t / d is 0.017 and 0.1, respectively.
5, which is smaller than 0.200. Therefore, the aperture stop 403 can be placed at any position between the collimator lens 402 and the deflecting surface 405 of the rotary polygon mirror, and the degree of freedom in design can be increased. Further, even when the beams are arranged in a line and the number is increased, the aperture stop 403 can be set at the position of the collimator lens 402. The aperture stop 403 is located at the position of the collimator lens 402.
Can be arranged, so that the collimator lens 402
Can be used as an aperture stop, and there is no need to provide a separate aperture stop, so that components of the scanning optical system can be reduced.

In this embodiment, the aperture stop is provided between the collimator lens and the rotary polygon mirror. However, if the above condition is satisfied, the aperture stop is provided between the surface emitting semiconductor laser array and the collimator lens. You may. Further, the optical system provided between the light source and the rotary polygon mirror need not be limited to a collimator lens for collimating a beam.

FIG. 40 is a block diagram showing a portion from a semiconductor laser to a rotary polygon mirror according to another embodiment. Aperture stop 4
Numeral 03 is provided at a position where the central axes of the plurality of beams intersect with the optical axis 412.

According to such a configuration, the aperture stop 403
, The center axes of the beams are perfectly aligned,
As compared with the previous embodiment, the uniformity of the diameter of the imaging spot and the uniformity of the power of the imaging spot are further improved.
This configuration may be adopted when higher characteristics are required for these characteristics of the imaging spot. In this embodiment, the optical system provided between the light source and the rotary polygon mirror is not limited to the collimator lens for collimating the beam.

5-3 Effects As described above, according to the present invention, by providing an aperture stop at a position on the optical path between the surface emitting semiconductor laser array and the deflector where a plurality of beam cross-sections substantially overlap. Even if the beam divergence angle varies, the imaging spot diameter can be made uniform, and there is an effect that stable and good printing quality can be obtained. In addition, an aperture stop can be provided at an arbitrary position in a wide range on the optical path between the semiconductor laser array and the deflector, or the holding frame of the collimator lens can be used as the aperture stop, which is a design problem. This also has the effect of increasing the degree of freedom.

§6 Sixth Embodiment of Image Forming Apparatus 6-1 Comparison with Background Art In order to better understand this embodiment, the background art will be described first.

Conventionally, a scanning optical system of an image forming apparatus using a semiconductor laser array is disclosed, for example, in Japanese Patent Laid-Open No. 3-24811.
No. 4 discloses the configuration as shown in FIG. The semiconductor laser array 501 is arranged on the object-side focal plane of the collimator lens 502. An aperture stop 503 is provided at the image-side focal position of the collimator lens 502.

However, in the prior art as described above, the position at which the aperture stop is arranged is limited only to the image-side focal position of the collimator lens, so that the degree of freedom in design is small. In some cases, the holding frame of the lens is used as an aperture stop, but there is a problem that such a configuration cannot be used in the related art.

6-2 Configuration of the Present Invention FIG. 48 is a configuration diagram of an image forming apparatus according to the present invention, and the image forming process will be described. A uniform charge is given to the image carrier 507 by the charger 551, and a latent image is formed by exposing and scanning the image carrier 507 by the scanning optical system 552, and a developer is applied on the latent image by the developing device 553. Attached and visualized. Next, the developer forming a visible image is transferred onto a transfer material 555 such as paper by a transfer device 554, and the developer is heated and melted by a fixing device 556 to be fixed on the transfer material 555.

FIG. 42 is a configuration diagram of a scanning optical system showing an embodiment of the present invention. A plurality of beams emitted from the semiconductor laser array 501 are collimated by the collimator lens 502, pass through the aperture stop 503, and enter one deflection surface 505 of the rotary polygon mirror 504 as a deflection device. The reflected beam is deflected and scanned as the rotating polygon mirror 504 rotates,
The light passes through the imaging lens 506 and is imaged on the image carrier 507.

In FIGS. 42 and 49, an aperture stop 503 is provided on the optical path between the semiconductor laser array 501 and the deflector 504, the focal length of the collimator lens 502 is f, and the collimator lens 502 is closer to the deflector 504. The distance between the focal point and the aperture stop 503 is s, the distance between the light-emitting portion disposed farthest from the optical axis of the collimator lens 502 and the optical axis is t, the diameter of the aperture stop 503 is D, and the diameter of the parallel beam is If d

(Equation 21) It has become.

Also, instead of equations (18) and (19),

(Equation 22) May be satisfied.

In general, the divergence angle of the output beam from the semiconductor laser 501 varies to some extent for each light emitting unit, and the beam diameter collimated by the collimator lens 502 also varies. However, the aperture stop 503 is provided at a position where the cross sections of the plurality of beams substantially overlap, and the aperture stop 503 is provided.
Is set to be approximately equal to or smaller than the parallel beam diameter d, the plurality of parallel beam diameters d after passing through the aperture stop 503 become uniform. As a result, the spot diameter formed on the image carrier 505 also becomes uniform, stable and good printing quality is obtained, and there is no difference in printing quality between apparatuses. Here, the beam divergence angle and its diameter are assumed that the intensity distribution of the beam cross section forms a Gaussian distribution,
It is a diameter that represents a full angle of an angle that is 中心 of the central intensity and a position that is 1 / e ^{2 of the} central intensity.

The effect of making the beam diameter uniform by the aperture stop 503 will be described. When the laser beam is stopped down by the aperture stop 503, diffraction, which is a property of wave optics, occurs. When the center of the aperture stop 503 coincides with the center of the incident beam, the imaging spot diameter d ₀ on the image carrier 505 in consideration of diffraction is:

(Equation 23) Is represented by

[0212] where k is a constant, lambda is the wavelength of the laser beam, f ₀ is the focal length, the diameter of D is the aperture stop of the imaging lens. Further, the diameter d of the beam incident on the aperture stop
Assuming that the ratio of the aperture stop diameter D to the cutting ratio T = d / D, the constant k is

(Equation 24) (“Laser & Optics Guide II”
Japan Melles Griot Co., Ltd.).

As an example, the diameter D of the aperture stop 503 is set to 1
When the diameter d of the incident beam has a variation of ± 20% around 1, the variation of the diameter of the imaging spot is suppressed to + 5.9% to -3.1%. As described above, the aperture stop 503 has an effect of suppressing the variation of the image spot diameter to the variation of the beam diameter.

The intensity distribution of the beam cross section collimated by the collimator lens 502 has a substantially Gaussian distribution, and as shown in FIG.
When the beam passes through, the periphery of the beam is blurred, so that the power of the beam after passing is lower than that before passing. As shown in FIG. 45, if the aperture stop 503 is arranged at the focal point of the collimator lens 502 on the deflector side, the central axes of a plurality of beams passing through the aperture stop 503 are all coincident. The rate of decrease in power due to passing is equal. However, if the position where the aperture stop 503 can be arranged is limited to only the position of the deflector-side focal point of the collimator lens 502, the degree of freedom in design becomes small.

As shown in FIG. 46, if the aperture stop 503 is arranged at a position shifted from the focal point on the deflector side of the collimator lens 502, the central axes of a plurality of beams passing through the aperture stop 503 are shifted from each other. The beam 511a along the optical axis 510 of the collimator lens and the beam 511b inclined with respect to the optical axis 510 are used for the aperture stop 5.
The way in which you pass 03 is different. FIG. 47 shows this state. FIG. 47A shows the beam 511.
47A shows a beam 511b in FIG. 47 (b), and a portion where the cross-sectional intensity distribution of the beam is shaded by the aperture stop is indicated by oblique lines. The power after passing through the aperture stop 503 differs for each beam, and the power of the beam 511a is larger than that of the beam 511b. If the difference is greater than a certain level, the density will appear uneven when printed. However, even if the power after passing through the aperture stop varies, within a certain range, substantially good print quality can be obtained. Therefore, there is an allowable range in which the aperture stop can be arranged corresponding to the allowable range.

When the condition shown in Expression (18) is satisfied, the variation in the power of the beam after passing through the aperture stop 503 becomes 20
% Or less. However, the condition of Expression (18) is an approximate expression, and is satisfied within the range of the condition of Expression (19). Also,
When the condition of Expression (20) is satisfied, the variation in the power of the beam after passing through the aperture stop 503 can be suppressed to 5% or less. However, the condition of Expression (20) is an approximate expression, and Expression (2)
The condition is satisfied within the range of 1).

According to an experiment conducted by the present inventor, in the case where only characters and lines are printed by the image forming apparatus, good printing can be obtained if the variation in the power of the imaging spot is about 20% or less. If the variation is larger than that, the print quality deteriorates. Also, when printing a halftone pattern with graphic output or printing a fine halftone dot,
Variations in the power of the imaging spot tend to appear as density unevenness, and in order to obtain good printing quality, the variations need to be about 5% or less. Therefore, equation (18)
And the condition of the expression (19) are conditions suitable for an image forming apparatus for printing only characters and lines, and the expression (2)
The condition 0) and the condition of the expression (21) are suitable for an image forming apparatus that is used for printing halftones and halftone dots in addition to printing characters.

According to the above conditions, the aperture stop 503 can be provided at an arbitrary position in a wide range on the optical path between the semiconductor laser array 511 and the deflecting device 504, and the degree of freedom in design is increased. Alternatively, the holding frame of the collimator lens 502 can be used as an aperture stop, so that there is no need to provide a separate aperture stop,
The components of the scanning optical system can be reduced.

Next, as an example, in a system as shown in FIG.
The position of the aperture stop 503 that satisfies the above conditions is specifically calculated. A case where a surface emitting semiconductor laser array is used as the semiconductor laser array 501 will be considered. A surface-emitting semiconductor laser is a semiconductor laser in which the center axis of an emitted beam is substantially perpendicular to the element substrate surface. Due to its characteristics, the surface emitting semiconductor laser array 501 has a divergence angle of 10 degrees or less and an interval between light emitting portions of 0.1 mm.
It is possible to make it equal to or less than 05 mm. Therefore, a semiconductor laser array 501 including two light emitting units is considered, and the distance t between the light emitting units 512a and 512b is set to 0.05 mm.
Then, the light emitting unit 512a is placed on the optical axis 510 of the collimator lens 502. Note that these light emitting units 512a, 512
The lighting and the light amount of b are controlled by the control device 560 (FIG. 42). The beam emitted from each light emitting unit is
These are referred to as a beam 511a and a beam 511b, respectively. The divergence angle θ of each emission beam is 10 degrees, the focal length f of the collimator lens 502 is 10 mm, and the distance h from the collimator lens 502 to the deflection surface 505 of the rotary polygon mirror is h.
Is set to 50 mm. In this case, the beam diameter d is 3.0
mm. The center of the aperture stop 503 is on the optical axis 510, and its diameter D is assumed to be equal to the beam diameter d.

Since D / d = 1, both the condition of equation (19) and the condition of equation (21) are satisfied. Equation (18)
According to the above condition, s ≦ 58 mm, and the aperture stop 503 can be placed at an arbitrary position between the collimator lens 502 and the deflection surface 505 of the rotary polygon mirror. Equation (2)
According to the condition 0), s ≦ 28 mm, and the aperture stop 50
3 is a collimator lens 502 and a collimator lens 50
28 mm from the focal point on the deflecting surface 505 side to the deflecting surface 505 side
It can be placed in any position between the positions. Also,
Even when the number of the light emitting units is arranged in a line and the number is increased, and t is increased, if the number of the light emitting units is 12 or less under the conditions of Expressions (18) and (19), the aperture stop 503 is changed. Can be set. Further, under the conditions of Expressions (20) and (21), the aperture stop 503 can be set at the position of the collimator lens 502 as long as the number of light emitting units is six or less. If the aperture stop 503 can be arranged at the position of the collimator lens 502, the holding frame of the collimator lens 502 can be used as the aperture stop. In this case, there is no need to provide a separate aperture stop. Can be reduced.

6-3 Effect As described above, according to the present invention, the aperture stop is provided on the optical path between the semiconductor laser array and the deflector.
By satisfying the conditions of Expressions (18) and (19), even if the beam divergence angle varies, the imaging spot diameter can be made uniform, and stable and good printing quality can be obtained. Having. An aperture stop can be provided at an arbitrary position in a wide range on the optical path between the semiconductor laser array and the deflector while maintaining good printing quality of characters and lines, or the holding frame of the collimator lens can be provided. It can also be used as an aperture stop, and has the effect of increasing the degree of freedom in design.

Further, an aperture stop is provided on the optical path between the semiconductor laser array and the deflector, and the beam divergence angle varies by satisfying the conditions of the expressions (20) and (21). Also, there is an effect that the imaging spot diameter can be made uniform and stable and good printing quality can be obtained. In addition to printing characters, while maintaining good printing quality such as halftones and halftone dots, it is possible to provide an aperture stop at any position in a wide range on the optical path between the semiconductor laser array and the deflector. Alternatively, the holding frame of the collimator lens can be used as an aperture stop, which has the effect of increasing the degree of freedom in design.

<Industrial Applicability> The image forming apparatus according to the present invention can perform high-speed printing on paper by an electrophotographic process. Such an image forming apparatus can be widely used as an output device of a computer, a facsimile, a multifunction copying machine, or the like.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a laser scanning optical system showing a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a side view showing the image forming apparatus.

FIG. 3 is a sectional view of an optical resonator of the surface-emitting type semiconductor laser array.

FIG. 4 is a perspective view showing a light-emitting portion of a phase-locked surface-emitting type semiconductor laser array.

FIG. 5 is a layout diagram showing a relationship between spot positions with respect to scanning lines.

FIG. 6 is a layout diagram of an optical resonator of a light emitting unit of the phase-locked surface-emitting type semiconductor laser array.

FIG. 7 is a conceptual diagram of a general edge emitting semiconductor laser array.

FIG. 8 is an optical path cross-sectional view of a general laser scanning optical system.

FIG. 9 is a layout diagram showing a relationship between spot positions with respect to scanning lines.

FIG. 10 is an explanatory diagram showing the reflectance of a general metal mirror for P deflection and S deflection.

FIG. 11 is a schematic diagram showing a method of adjusting a collimate diameter of a laser beam.

FIG. 12 is a schematic view of a laser scanning optical system showing an image forming apparatus according to a second embodiment of the present invention.

FIG. 13 is a side view showing the image forming apparatus.

FIG. 14 is a sectional view of an optical resonator of a surface emitting semiconductor laser.

FIG. 15 is a perspective view showing a light-emitting portion of a phase-locked surface-emitting type semiconductor laser array.

FIG. 16 is a layout view of an optical resonator of a light emitting unit of a phase-locked surface emitting semiconductor laser array.

FIG. 17 is a sectional view of an optical axis in a direction perpendicular to a scanning line of a general laser scanning optical system.

FIG. 18 is a schematic view of a general semiconductor laser.

FIG. 19 is an explanatory diagram showing the reflectance of a general metal mirror for P deflection and S deflection.

FIG. 20 is a schematic view of a laser scanning optical system showing a third embodiment of the image forming apparatus according to the present invention.

FIG. 21 is a side view showing the image forming apparatus.

FIG. 22 is an optical path cross-sectional view in a scanning plane.

FIG. 23 is a sectional view of an optical resonator of a surface-emitting type semiconductor laser.

FIG. 24 is a layout diagram showing the relationship between spot positions with respect to scanning lines.

FIG. 25 is a plan view of a beam deflecting device.

FIG. 26 is an operation diagram of a beam deflector using a general rotary polygon mirror.

FIG. 27 is an optical path cross-sectional view of a general laser beam scanning optical system.

FIG. 28 is a schematic view of a general edge-emitting semiconductor laser.

FIG. 29 is a schematic view of a laser scanning optical system showing a fourth embodiment of the image forming apparatus according to the present invention.

FIG. 30 is a side view showing the image forming apparatus.

FIG. 31 is a sectional view of an optical resonator of a surface-emitting type semiconductor laser.

FIG. 32 is a layout diagram showing a relationship between a scanning line and a spot position.

FIG. 33 is an optical path sectional view of a general laser beam scanning optical system.

FIG. 34 is an optical path sectional view in a general multi-beam scanning method.

FIG. 35 is a schematic view of a general edge-emitting semiconductor laser.

FIG. 36 is an optical path cross-sectional view including a general tilt correction lens.

FIG. 37 is a schematic view of a laser scanning optical system showing a fifth embodiment of the image forming apparatus according to the present invention.

FIG. 38 is a side view showing the image forming apparatus.

FIG. 39 is a configuration diagram near a light source in the scanning optical system.

FIG. 40 is a configuration diagram near a light source in a scanning optical system according to another embodiment.

FIG. 41 is a configuration diagram near a light source in a general scanning optical system.

FIG. 42 is a schematic view of a laser scanning optical system showing a sixth embodiment of the image forming apparatus according to the present invention.

FIG. 43 is a configuration diagram near a light source in a general scanning optical system.

FIG. 44 is an explanatory diagram showing that a beam is cut by an aperture stop.

FIG. 45 is a ray diagram when an aperture stop is provided at a focal position of a collimator lens.

FIG. 46 is a ray diagram when an aperture stop is provided at a position deviated from the focal position of the collimator lens.

FIG. 47 is a view showing how a beam cross-sectional intensity distribution is blurred.

FIG. 48 is a side view showing the image forming apparatus.

FIG. 49 is a configuration diagram near a light source in a scanning optical system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 3 Polarizing device 5 Image carrier 21 Semiconductor laser array 21a Light emitting part 22 Element substrate 52 Charger 53 Laser beam scanner 105 Image carrier 121 Semiconductor laser 121a Light emitting part 122 Element substrate 152 Charger 153 Laser beam scanner 155 Development Device 205 Image carrier 202 Collimator lens 204 Scan lens 218 Polarizer 221 Semiconductor laser array 253 Laser beam scanner 255 Developer 302 Collimator lens 305 Image carrier 341 Semiconductor laser array 341a Light emitting section 353 Laser beam scanner 355 Developer 401 semiconductor laser array 401a light emitting unit 404 polarizing device 407 image carrier 422 element substrate 451 charger 453 developer

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H04N 1/113 B41J 3/00 D 1/29 H04N 1/04 104A (31) Priority claim number Japanese Patent Application No. 4-33413 (32) Priority date February 20, 1992 (199.2.2.20) (33) Priority claiming country Japan (JP) (31) Priority claim number Japanese Patent Application No. 4-81044 (32) Priority date Heisei 4 April 2, 1992 (1992.4.2) (33) Priority claiming country Japan (JP) (31) Priority claim number Japanese Patent Application No. 4-81045 (32) Priority date April 2, 1992 (1992) 4.4.2) (33) Priority claiming country Japan (JP) (31) Priority claim number Japanese Patent Application No. 4-81047 (32) Priority date April 2, 1992 (1992.4.2) (33) ) Priority claiming country Japan (JP) (31) Priority claim number Japanese Patent Application No. 4-81048 (32) Priority date April 2, 1992 (1992.4.2) (33) Priority claiming country Japan ( JP) (72) Inventor Kinro Koga 3-5-5 Yamato, Suwa-shi, Nagano Pref. Seiko Epson Corporation (72) Invention Person Takada Takada 3-5-5 Yamato, Suwa City, Nagano Prefecture Inside Seiko Epson Corporation

Claims (32)

[Claims] An image carrier on which an electrostatic latent image is formed on a surface.
And a charger (5) for charging the surface of the image carrier (5).
2), a laser beam scanning device (53) for scanning a plurality of laser beams on the charged surface of the image carrier (5), and a laser beam scanning device that scans the surface of the image carrier (5) with the laser beam. A developing device (55) for applying a developer; the laser beam scanning device (53) includes a semiconductor laser array (21) in which a plurality of laser beam emitting portions (21a) are formed on an element substrate (22); A deflecting device (3) for deflecting the laser beam from the light emitting section (21a) to the surface of the image carrier (5), wherein the light emitting section (21a) is provided with the semiconductor laser array (2).
1) An image forming apparatus which is arranged two-dimensionally on a surface, and in which each of the light emitting portions (21a) can individually control the lighting and the light amount. 2. The image forming apparatus according to claim 1, wherein the light emitting portion of the semiconductor laser array has an optical axis substantially perpendicular to the surface of the element substrate. 3. A light emitting section (21a) of a semiconductor laser array.
A pair of reflecting mirrors (23, 28) having different reflectances disposed on the surface of the element substrate (22), and a columnar cladding layer disposed between the pair of reflecting mirrors (23, 28). An optical resonator having a multi-layer semiconductor layer including (26), and a group II-VI compound semiconductor epitaxial layer (32) embedded around the columnar cladding layer (26). The image forming apparatus according to claim 2. 4. The group II-VI compound semiconductor epitaxial layer (32) comprises a group II element of Zn, Cd, Hg and a group VI element of O, S, Se, Te in two, three or three elements. 4. The image forming apparatus according to claim 3, wherein the image forming apparatus is a semiconductor epitaxial layer in which four elements are combined. 5. The semiconductor layer (24, 25, 26) having a lattice constant of the II-VI compound semiconductor epitaxial layer (32).
The image forming apparatus according to claim 3, wherein the lattice constant is equal to 6. A column-shaped cladding layer (26) is formed by a separation groove provided in a semiconductor layer, and a II-VI compound semiconductor epitaxial layer (32) is buried and formed in the separation groove. 4. The image according to claim 3, wherein the plurality of semiconductor layers have an active layer (25) disposed below the separation groove, whereby the phases of light in the respective optical resonators are synchronized. Forming equipment. 7. The image forming apparatus according to claim 1, wherein the divergence angle of the laser beam from the light emitting portion (21a) of the semiconductor laser array (21) is within 20 degrees at full width at half maximum. 8. The image forming apparatus according to claim 1, wherein the laser beam emitted from the light emitting section (21a) of the semiconductor laser array (21) enters the deflection device without being collimated. 9. A laser beam emitting part (2) on an element substrate.
Semiconductor laser array (21) in which a plurality of 1a) are formed
And a deflecting device (3) for deflecting the laser beam from the light emitting section (21a), wherein the light emitting section (21a)
Is a laser beam scanning device, wherein two-dimensionally arranged on the surface of the semiconductor array (21), each light emitting part (21a) is individually controllable in lighting and light quantity. 10. An image carrier (105) on which an electrostatic latent image is formed, a charger (152) for charging the surface of the image carrier (105), and the charged image carrier (10).
5) A laser beam scanning device (153) for scanning the surface with a laser beam, and a developing device (155) for applying a developer to the surface of the image carrier (105) scanned by the laser beam. The laser beam scanning device (153) includes a semiconductor laser (121) having a laser beam light emitting portion (121a) formed on an element substrate (122), and the laser beam from the light emitting portion (121a) carrying the image. Deflection device (1) for deflecting to the surface of the body
03), wherein the light emitting section (121a) has an optical axis substantially perpendicular to the surface of the element substrate (122). 11. A light emitting section (121a) of a semiconductor laser.
Are a pair of reflecting mirrors (123, 128) having different reflectivities disposed on the surface of the element substrate (122), and a columnar cladding layer (12) disposed between the pair of reflecting mirrors.
An optical resonator having a multi-layered semiconductor layer including the above-mentioned 6), and an II− embedded around the columnar cladding layer (126).
The image forming apparatus according to claim 10, further comprising a group VI compound semiconductor epitaxial layer (132). 12. The group II-VI compound semiconductor epitaxial layer (132) comprises a group II element such as Zn, Cd, Hg and VI
The image forming apparatus according to claim 11, wherein the image forming apparatus is a semiconductor epitaxial layer in which Group 3, O, S, Se, and Te are combined with two, three, or four elements. 13. A semiconductor layer comprising a II-VI compound semiconductor epitaxial layer (132) having a lattice constant of (124, 125,
The image forming apparatus according to claim 11, wherein the lattice constant is equal to (126). 14. A cladding layer (126) formed in a columnar shape.
Is formed by a separation groove provided in the semiconductor layer, and II-VI
A group III compound semiconductor epitaxial layer (132) embedded in the isolation trench, the multilayer semiconductor layer having an active layer (125) disposed below the isolation trench;
12. The image forming apparatus according to claim 11, wherein the phases of light in the respective optical resonators are synchronized. 15. A light emitting section (1) of a semiconductor laser (121).
11. The divergence angle of the laser beam emitted from 21a) is within 20 degrees at full width at half maximum.
The image forming apparatus as described in the above. 16. A light emitting section (1) of a semiconductor laser (121).
11. The image forming apparatus according to claim 10, wherein the laser beam emitted from 21a) is incident on the deflection device (103) without being collimated. 17. A semiconductor laser (1) having a laser beam emitting portion (121a) formed on an element substrate (122).
21) and a deflecting device (103) for deflecting the laser beam from the light emitting section (121a), and the light emitting section (121a) has an optical axis substantially perpendicular to the surface of the element substrate (122). A laser beam scanning device characterized by the above-mentioned. 18. An image carrier (205) on which an electrostatic latent image is formed on a surface, a charger (252) for charging the surface of the image carrier, and a plurality of chargers for charging the surface of the image carrier. Laser beam scanning device (2
53), and a developing device (255) for applying a developer to the surface of the image carrier scanned by the laser beam, wherein the laser beam scanning device (253) emits a plurality of laser beams. 221), a collimator lens (202) for collimating each of the plurality of laser beams, and the collimator lens (20).
A deflecting device (218) for periodically deflecting the directions of the plurality of laser beams collimated in (2), and the deflecting device (2);
A scanning lens (204) for imaging the laser beam deflected by (18) on the image carrier (205), wherein the deflecting device (218) is a rotating mirror having one reflecting surface. Characteristic image forming apparatus. 19. A semiconductor laser array (221) comprising a plurality of light emitting units (221) arranged two-dimensionally on an element substrate.
a), each light emitting unit emits a laser beam having an optical axis substantially perpendicular to the element substrate surface,
19. The image forming apparatus according to claim 18, wherein each of the light emitting units (221a) is capable of individually controlling lighting and light amount. 20. The scanning lens according to claim 1, wherein the scanning lens and the collimating lens have isotropic optical characteristics in all planes including their optical axes.
9. The image forming apparatus according to 8. 21. The reflecting surface of the rotating mirror (218) is placed geometrically including the rotation axis of the rotating mirror (218), and at least one of the plurality of laser beams or the plurality of laser beams. 19. The image forming apparatus according to claim 18, wherein a central axis of the image is reflected and deflected by the reflection surface near the position of the rotation axis on the reflection surface. 22. A scanning lens (2) on an image carrier (205).
04), the imaging spot (206) formed by
The ratio of the divergence angle of the laser beam emitted from the semiconductor laser array to the scanning direction and the direction orthogonal thereto is substantially an ellipse or an ellipse having a minor axis in the scanning direction, and the major axis of the imaging spot (206). 19. The image forming apparatus according to claim 18, wherein the ratio is the reciprocal of the ratio of the minor axis. 23. A semiconductor laser array (221) for emitting a plurality of laser beams, a collimator lens (202) for collimating each of the plurality of laser beams,
A deflecting device (218) for periodically deflecting the directions of the plurality of laser beams collimated by the collimator lens;
And a scanning lens (204) for forming an image of the laser beam deflected by the deflecting device (218) on an image carrier (205). The deflecting device (218) has a rotation having one reflection surface. A laser beam scanning device, which is a mirror. 24. An image carrier (305) on which an electrostatic latent image is formed on a surface, a charger (352) for charging the surface of the image carrier, and a plurality of chargers for charging the surface of the image carrier. Laser beam scanning device (3
53) and the image carrier (30) scanned by the laser beam.
5) a developing device (355) for adhering a developer to the surface; the laser beam scanning device (353) includes a semiconductor laser array (341) having a plurality of light emitting units (341a) for emitting a laser beam; A collimator lens (302) for collimating each of the plurality of laser beams
A deflecting device (303) for periodically deflecting the direction of the plurality of laser beams collimated by the collimator lens (302); and a laser beam deflected by the deflecting device (303). 305), a scanning lens (304) for forming an image, a focal length of the collimator lens (302) is fc, and a plurality of light emitting units (341) on the semiconductor laser array (341).
a) The image forming apparatus is characterized in that fc / δmax> 25, where δmax is the distance between the two light emitting units that are farthest from each other. 25. Assuming that the focal length of the collimator lens (302) is fc, and the interval between the two light emitting units farthest from each other among the plurality of light emitting units (341a) on the semiconductor laser array (341) is δmax. 25. The image forming apparatus according to claim 24, wherein fc / δmax> 50. 26. A light emitting section (341a) of a semiconductor laser array (341) is two-dimensionally arranged on an element substrate (322), and each light emitting section (341a) has a light beam substantially perpendicular to the element substrate surface. 23. The image forming apparatus according to claim 22, wherein a laser beam having an axis is emitted, and its lighting and light amount can be individually controlled. 27. The image forming apparatus according to claim 24, wherein the deflecting device (303) is a rotary polygon mirror having a plurality of mirror surfaces arranged in a regular polygonal prism shape. 28. A tilt correction optical system (307, 3) for optically correcting a shift of a scanning line in a sub-scanning direction due to a difference in tilt angle of each reflecting surface with respect to a rotation axis of a rotary polygon mirror (303).
28. The image forming apparatus according to claim 27, wherein the image forming device (07 ') is provided on an optical path from the semiconductor laser array (341) to the image carrier (305). 29. A light emitting section (34) for emitting a laser beam.
Semiconductor laser array (341) having a plurality of 1a)
A collimator lens (302) for collimating each of the plurality of laser beams; and a collimator lens (3).
02), a deflecting device (303) for periodically deflecting the directions of the plurality of laser beams collimated, and an image of the laser beam deflected by the deflecting device (303) on the image carrier (305). Scan lens (30
4) and the focal position of the collimator lens is f
c, of the plurality of light emitting units on the semiconductor laser array, the distance between two light emitting units farthest from each other is δma
A laser beam scanning device, wherein x is fc / δmax> 25. 30. An image carrier (407) on which an electrostatic latent image is formed, a charger (451) for charging the surface of the image carrier (407), and a charging device (451) for charging the surface of the image carrier. On the other hand, a laser beam scanning device (452) for scanning a plurality of laser beams, and a developing device (4) for attaching a developer to the surface of the image carrier (407) scanned by the laser beams.
53), wherein the laser beam scanning device comprises: a semiconductor laser array (401) in which a plurality of light emitting units (401a) for emitting laser beams are provided on an element substrate (422); and the light emitting units (401a). A deflection device (404) for deflecting a laser beam emitted from the
The central axis of the laser beam emitted from the semiconductor laser array (401) is substantially perpendicular to the element substrate surface (422), and the semiconductor laser array (40)
An aperture stop (403) is provided at a position where at least a part of a cross section of a plurality of laser beams overlaps on an optical path between 1) and the deflecting device (404), and after passing through the aperture stop (403). An image forming apparatus comprising: a laser beam having a maximum power among a plurality of laser beams, wherein the power of each of the other laser beams is 0.9 or more when the power is set to 1; 31. An optical system comprising a single lens or a plurality of lenses is provided between a semiconductor laser array (401) and a deflecting device (404), and a central axis of a plurality of laser beams intersects an optical axis of the optical system. 31. The image forming apparatus according to claim 30, wherein the aperture stop (403) is provided at a position where the aperture stop is performed. 32. A semiconductor laser array (401) having a plurality of light emitting portions (401a) for emitting a laser beam provided on an element substrate (422), and said light emitting portions (401).
a) a deflecting device (404) for deflecting the laser beam emitted from the semiconductor laser array (40).
The central axis of the laser beam emitted from 1) is substantially perpendicular to the surface of the element substrate (422), and the central axis of the laser beam in the optical path between the semiconductor laser array (401) and the deflecting device (404). An aperture stop is provided at a position where at least a part of the cross section of the laser beam overlaps, and among the plurality of laser beams having passed through the aperture stop (403), the power of the laser beam having the maximum power is set to one. A laser beam scanning device wherein the power of each of the other laser beams becomes 0.9 or more when the laser beam scanning is performed.