JPH10123442A - Scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a scanning optical device capable of reducing spot diameter and increasing the depth of focus without causing any loss of light quantity. SOLUTION: In this device, a luminous flux optically modulated and emitted from a light source means 1 in accordance with a picture signal is made a nearly parallel luminous flux by a collimating lens 2, and is guided to a deflecting means 6 through a cylindrical lens 5, and the luminous flux deflected by the deflecting means is guided on a surface to be scanned 8 through an image-formation means 7, so that the scanning of the surface to be scanned is performed. In this case, a beam shaping means 4 is provided in an optical path between the light source means 1 and the deflecting means 6, and shapes the luminous flux to a zonal luminous flux where the light intensity distribution of the luminous flux emitted from the beam shaping means is made dense at a peripheral part as compared with the vicinity of an optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical apparatus, and more particularly to a beam shaping means comprising a diffractive optical element, which effectively shapes a light beam (laser light beam) emitted from a light source means to reduce a spot diameter. Laser beam printer (LBP) with, for example, an electrophotographic process that can increase the depth of focus
The present invention relates to a scanning optical device suitable for an apparatus such as a digital copier and a digital copier.

[0002]

2. Description of the Related Art Conventionally, in a scanning optical apparatus used in a laser beam printer, a digital copying machine, or the like, a light beam (laser light beam) which is light-modulated from a light source means in accordance with an image signal and emitted therefrom is deflected by, for example, a polygon mirror. The light is periodically deflected by an imager, focused on a photosensitive recording medium (photosensitive drum) surface in the form of a spot by an imaging optical system having f-θ characteristics, and the surface is optically scanned to record an image. I have.

FIG. 13 is a schematic view of a main part of this type of scanning optical device.

In FIG. 1, a light beam emitted from a laser unit 111 is converted into a substantially parallel light beam by a collimator lens provided inside the laser unit 111, and is incident on a cylindrical lens 112. Of the parallel light beams incident on the cylindrical lens 112, they are emitted as they are on the main scanning cross section. In the sub-scan section, the light converges and is formed as an almost linear image on the deflection surface (reflection surface) 113a of the optical deflector 113. The light beam deflected by the deflecting surface 113a is condensed on the surface of the photosensitive drum 116 via an imaging optical system (fθ lens system) 120 having a spherical lens 114 and a toric lens 115,
By rotating the optical deflector 113 in the direction of arrow A in the figure, the surface of the photosensitive drum 116 is optically scanned in the direction of arrow B in the figure (main scanning direction). Thus, an image is recorded on the surface of the photosensitive drum 116 as a recording medium.

FIG. 14 shows the laser unit 1 shown in FIG.
FIG. 11 is an enlarged explanatory view of FIG.

In FIG. 1, reference numeral 101 denotes a semiconductor laser as a light source, 102 denotes a base, 103 denotes a holder, 104 denotes a lens barrel, 105 denotes a collimator lens, and 106 denotes an aperture stop.

In FIG. 1, a light beam emitted from a semiconductor laser 101 controlled by a drive signal containing image information is converted into a parallel light beam by a collimator lens 105, and the size of the cross section of the light beam is determined by an aperture stop 106. Injected from 111.

[0008]

In recent years, high resolution and high image quality have been demanded for laser beam printers, digital copiers and the like, and particularly, high resolution and rich gradation in halftone (intermediate gradation). In order to respond to reproduction, it is required that the spot diameter on the surface of the photosensitive drum, which is the surface to be scanned, be reduced.

The spot diameter d is represented by the following equation.

D = αFλ ‥‥‥‥ (a) In the equation (a), F: F number of the imaging beam (optical system) λ: wavelength of the laser beam α: constant Therefore, in order to make the spot diameter d smaller, Is to reduce the F-number of the imaging beam as seen from equation (a),
Alternatively, it is necessary to shorten the wavelength λ of the laser beam.
However, when the F-number of the image forming beam is reduced, the beam width of the laser beam emitted from the collimator lens is increased, and therefore, it is necessary to increase the effective diameter of the collimator lens. Such a collimator lens uses a large number of lenses for this,
There is a problem in that the manufacturing cost increases because the adjustment accuracy becomes strict.

Further, since the width of the light beam incident on the deflecting surface (reflection surface) of the optical deflector also increases, the effective area of the deflecting surface must be increased. Such an optical deflector not only increases the manufacturing cost but also increases the weight of the optical deflector itself, so that the load of a motor for rotating the optical deflector becomes very large, and as a result, Various problems such as an increase in cost of the motor and an increase in power consumption occur.

Regarding shortening the wavelength λ of the laser beam, visible lasers are still generally expensive,
Although used for some high-end machines, it is not suitable for low-cost printers.

On the other hand, the depth of focus D of the laser beam formed in a spot on the photosensitive drum surface is expressed by the following equation.

D = βF ² λ ‥‥‥‥ (b) In the equation (b), F: F number of the imaging beam (optical system) λ: wavelength of the laser beam β: constant As can be seen from the equation (b). If the F-number of the imaging beam is reduced or the wavelength λ of the laser beam is shortened in order to reduce the spot diameter, the depth of focus D becomes smaller (shallower) accordingly. For this reason, the field curvature of the fθ lens (imaging optical system) must be reduced. As a result, the design becomes complicated and the processing accuracy of the fθ lens itself needs to be high. Further, there is a problem that the assembling accuracy of each optical component becomes severe, which results in a large increase in cost.

In order to solve this problem, as described in, for example, JP-A-5-307151 and JP-A-6-148545, a first-order zero-order Bessel beam is generated to reduce the spot diameter. In addition, a method of increasing the depth of focus and a method of shielding a sub-maximum (side lobe) of an eccentric Bessel beam with a slit member have been proposed.

However, in order to generate a Bessel beam, for example, a conical prism, a phase / amplitude filter, or the like must be used, so that the entire apparatus tends to be complicated. Adjustment of the method of shielding the side lobe portion of the eccentric vessel beam by the slit member tends to be complicated.

As a means for reducing the spot diameter at a low cost, minimizing the influence of the sub-local maximum of the beam, and increasing the depth of focus, for example, a collimator lens converts the beam into a parallel light beam as shown in FIG. A scanning optical device has been proposed in which a light beam in the vicinity of the optical axis of the parallel light beam is shielded by a light shielding unit, and the beam shape is shaped into an annular shape (ring shape).

However, when the above-described scanning optical device is applied to, for example, a laser printer (especially a color laser printer) which requires high definition, loss of light amount due to blocking of the central portion of the laser beam cannot be tolerated. Problem arises.

According to the present invention, a beam shaping means having a diffractive optical element is arranged in an optical path between a light source means and a deflecting means, and a light flux emitted from the light source means is effectively shaped into a beam, thereby reducing a light amount loss. Another object of the present invention is to provide a scanning optical device capable of obtaining a high-quality image by reducing the spot diameter and increasing the depth of focus.

[0020]

The scanning optical apparatus according to the present invention comprises: (1) a light beam modulated and emitted from a light source means in accordance with an image signal, converted into a substantially parallel light beam by a collimator lens, and guided to a deflection means through a cylindrical lens; A scanning optical device for irradiating the light beam deflected by the deflecting means onto the surface to be scanned through the imaging means and scanning the surface to be scanned; Beam shaping means is provided in the optical path, and the beam shaping means shapes the light flux emitted from the beam shaping means into a ring-shaped light flux that is stronger at the periphery than at the vicinity of the optical axis. Features.

In particular, (1-1) the beam shaping means comprises: a first diffractive optical element for deflecting the incident parallel light beam from the collimator lens at a predetermined angle around the optical axis; And (1-2) the first and second diffractive optical elements are manufactured from a substrate made of the same type of material. (1-3) The first and second diffractive optical elements are manufactured on both sides of the same substrate, respectively, (1-3)
-4) an aperture stop for restricting a light beam on the outer periphery is provided on a part of the element surface of the first diffractive optical element, and (1-5) an incident light beam is reduced by the first and second diffractive optical elements. The first and second diffractive optical elements are arranged such that the luminous flux density of the parallel luminous flux emitted when converting into the zonal parallel luminous flux becomes denser from the optical axis toward the periphery inside the zonal bright part. What you ’ve configured,
(1-6) The first diffractive optical element changes the angle of deflecting the incident parallel light beam from the collimator lens in the main scanning direction and the sub-scanning direction, and the second diffractive optical element By converting the light beam deflected by the first diffractive optical element into a parallel light beam having a ring shape, the shape of the light beam having a ring shape and / or the shape of the light beam near the optical axis whose light intensity distribution is weaker than that of the peripheral portion is arbitrary. Or (1-7) that the beam shaping means is held by a beam shaping barrel, and that the beam shaping barrel is incorporated in a lens barrel. (1-8) an annular stop member provided in the optical path behind the beam shaping means, and (1-9) a material having a high expansion coefficient between the first and second diffractive optical elements. It is characterized by providing a spacer.

[0022]

FIG. 1 is a schematic view of a main part of an optical system of a scanning optical device according to a first embodiment of the present invention. FIG. 2 is a schematic view of a main part of a main part from the light source means to the beam shaping means shown in FIG. FIGS. 3A and 3B are enlarged explanatory views showing the shapes of the first and second diffractive optical elements shown in FIG. 2 in order.

In FIG. 1, reference numeral 1 denotes a light source means, which is composed of, for example, a semiconductor laser. A collimator lens 2 converts a light beam (laser light beam) emitted from the light source 1 into a substantially parallel light beam. Reference numeral 3 denotes an aperture member (aperture stop) for shaping the size of the cross section of the light beam.

Numeral 4 denotes a beam shaping means, which is a first diffractive optical element 9 for deflecting the incident parallel light beam converted by the collimator lens 2 to a predetermined angle around the optical axis, and re-lighting the deflected light beam again. A second diffractive optical element 10 for deflecting the light into a parallel light flux around the axis, wherein the light intensity distribution of the light flux emitted from the beam shaping means 4 becomes stronger at the periphery than at the vicinity of the optical axis. Beam shaping. Numerals 11 and 12 denote first and second diffraction gratings of the first and second diffractive optical elements 9 and 10, respectively.

Reference numeral 5 denotes a cylindrical lens having a predetermined refractive power only in the sub-scanning direction. Reference numeral 6 denotes an optical deflector, which is formed of, for example, a polygon mirror, and is rotated at a constant speed in the direction of arrow A by driving means (not shown) such as a motor. Reference numeral 7 denotes an imaging optical system (fθ lens system) having f-θ characteristics as imaging means, which is formed of a single toric lens, and which uses a light beam deflected by the optical deflector 6 as a surface to be scanned. An image is formed on the surface of the photosensitive drum 8.

In the present embodiment, a light beam (laser light beam) which is light-modulated and emitted from the light source means 1 in accordance with an image signal is converted into a substantially parallel light beam by a collimator lens 2, and the light beam cross section is formed by a stop member (aperture stop) 3. Is shaped into a beam and is incident on the beam shaping means 4. Then, the first and second diffractive optical elements 9 and 10 beam-shape the light beam emitted from the beam shaping means 4 into a ring-shaped (ring-shaped) light beam in which the light intensity distribution becomes stronger in the peripheral portion than in the vicinity of the optical axis. Then, the light enters the cylindrical lens 5. Of the parallel light beams incident on the cylindrical lens 5, the light beams are emitted as parallel light beams in the main scanning section as they are. In the sub-scan section, the light converges on the deflection surface (reflection surface) of the optical deflector 6.
An image is formed substantially as a line image on 6a. The light beam deflected and reflected by the deflecting surface 6a is condensed on the surface of the photosensitive drum 8 via the image forming optical system 7, and the light deflector 6 is rotated in the direction of arrow A in the figure, whereby the surface of the photosensitive drum 8 is rotated. The top is scanned at a constant speed in the direction of arrow B (main scanning direction) in the figure. Thus, an image is recorded on the surface of the photosensitive drum 8 as a recording medium.

Next, the beam shaping means for beam shaping the light beam emitted from the light source means into an annular light beam will be described with reference to FIG.

FIG. 2 shows the semiconductor laser 1 as described above.
The light beam emitted from the light source is converted into a substantially parallel light beam by the collimator lens 2, and the size of the light beam cross section (outer diameter of the light beam) is regulated by the diaphragm member 3. The aperture member 3 suppresses variation in the spot diameter due to variation in the radiation angle of the light beam, and obtains a stable spot diameter.
After that, the light enters the first diffractive optical element 9 constituting the beam shaping means 4, and the first diffractive optical element 9 spreads the incident parallel light beam radially around the optical axis while maintaining a predetermined angle. Become. Then, the radiated light beam enters the second diffractive optical element 10 and is converted again into a parallel light beam parallel to the optical axis. As a result, the light intensity distribution of the light beam emitted from the beam shaping means 4 becomes a ring-shaped (ring-shaped) light beam that is stronger at the periphery than at the vicinity of the optical axis. Note that the light flux near the optical axis, where the light intensity distribution becomes weaker than the peripheral part, is also referred to as “dark part light flux”.

Here, the grating surface 11 of the first diffractive optical element 9
The ring shape can be arbitrarily shaped by arbitrarily selecting the distance between the first and second diffraction optical elements 10 and the grating surface 12 and the respective grating pitches.

The beam shaping means 4 in this embodiment has a function of bending the incident light beam to a desired angle in both the first diffractive optical element 9 and the second diffractive optical element 10. Has no kinetic effect. Therefore, FIG.
As shown in (A) and (B), the grating pitch of each of the diffraction gratings 11 and 12 in both the first and second diffractive optical elements 9 and 10 is a concentric circle centered on a uniform pitch optical axis. FIG.
In (A) and (B), the first and second diffractive optical elements 9,
Each of the 10 grating shapes is a step-like grating, but this is not particularly limited. For example, the present invention can be sufficiently applied to a sawtooth diffraction grating.

Next, a specific example will be described. In FIG. 2, let us consider a case where the beam shape of the light beam after beam shaping in an annular shape is, for example, a concentric circle with an outer shape b of φ6 mm and a dark portion a of φ2 mm. Here, the interval between the first and second diffractive optical elements 9 and 10 constituting the beam shaping means 4 is represented by t. Since b = 6 mm and a = 2 mm, b
−a = 4 mm, and the light beam incident on the beam shaping means 4 needs to be a φ4 mm beam. Therefore, a circular opening of φ4 mm is provided as the diaphragm member 3.

Next, when the interval t is 10.0 mm, the diffraction angle θ of the diffraction grating is

[0033]

(Equation 1) Becomes Assuming that the laser wavelength is λ = 675 nm, the grating pitch P is given by P = mλ / sin θ = 1.0675 / sin (5.7) from Psin θ = mλ (m is an integer, m = 1 in this embodiment).
1) = 6.78 μm The grating thickness d is (n-1) d = Lλ, and n = 1.
If 51633, L = 1, then d = 1.313 μm.

As described above, in the present embodiment, the beam shaping means 4 composed of a diffractive optical element is provided in the optical path between the semiconductor laser 1 and the optical deflector 6 as described above, and the light beam emitted from the semiconductor laser 1 is effectively used. Beam shaping,
A high quality image is obtained by reducing the spot diameter and increasing the depth of focus with an inexpensive configuration without loss of light quantity.

FIG. 4 is a schematic view of a main part of the beam shaping means according to the second embodiment of the present invention. 2, the same elements as those shown in FIG. 2 are denoted by the same reference numerals.

The present embodiment is different from the first embodiment in that the diffraction gratings of the first and second diffractive optical elements constituting the beam shaping means are provided on both surfaces of the same substrate and are integrated. It is. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

That is, in the figure, reference numeral 44 denotes a beam shaping means, on which the first and second diffraction gratings 11 and 12 of the first and second diffractive optical elements are provided on both surfaces of the same substrate. By configuring the beam shaping means 44 in this manner, in the present embodiment, the optical axes of the first and second diffraction gratings 11 and 12 can be adjusted with high precision, and the number of parts is reduced, so that a holding member or the like is used. Therefore, the number of mechanical parts is also reduced, thereby reducing the size and cost of the entire apparatus.

FIG. 5 is a schematic view of a main part of a beam shaping means according to a third embodiment of the present invention. 4, the same elements as those shown in FIG. 4 are denoted by the same reference numerals.

This embodiment differs from the second embodiment in that an aperture stop (opening) is provided on the incident surface side of the substrate, that is, a part of the element surface (diffraction grating surface) of the first diffractive optical element. That is, it is integrated with the beam shaping means. Other configurations and optical functions are substantially the same as those of the above-described second embodiment, and thus the same effects are obtained.

That is, in the figure, 54 is a beam shaping means, 53 is an aperture stop provided on a part of the element surface of the first diffractive optical element, and is formed on the substrate by means of vapor deposition or the like. Regulates the luminous flux.

As described above, in this embodiment, since the aperture stop 53 is provided on a part of the element surface of the first diffractive optical element, the number of components can be further reduced, and the single diffractive optical element can be manufactured with high accuracy. Thus, an inexpensive and high-performance scanning optical device is obtained.

FIG. 6 is a schematic view of a main part when the beam shaping means according to the fourth embodiment of the present invention is incorporated in a laser unit. 2, the same elements as those shown in FIG. 2 are denoted by the same reference numerals.

The present embodiment differs from the first embodiment in that the beam shaping means is held by a beam shaping lens barrel and that the beam shaping lens barrel is incorporated in a lens barrel. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

That is, in the figure, reference numeral 60 denotes a laser unit, 31 denotes a beam shaping barrel, and 32 denotes a lens barrel. In the present embodiment, by holding the beam shaping means 4 with the beam shaping lens barrel 31, the positions of the first and second diffractive optical elements 9, 10 can be accurately arranged, and the beam shaping can be performed. By incorporating the lens barrel 31 into the lens barrel 32, the position of each element of the light source unit 1, the collimator lens 2, and the beam shaping unit 4 can be adjusted with high accuracy.

FIG. 7 is a schematic view of a main part of a main part from the light source means to the periphery of the beam shaping means according to the fifth embodiment of the present invention. 2, the same elements as those shown in FIG. 2 are denoted by the same reference numerals.

The present embodiment differs from the first embodiment in that an annular diaphragm member is provided in the optical path behind the beam shaping means. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

That is, in the drawing, reference numeral 28 denotes a ring-shaped diaphragm member, which prevents diffracted light having a diffraction order other than the designed diffraction order as shown by a broken line 22 in the drawing from affecting the image as flare light. In this embodiment, the auxiliary throttle member 28 is
In the optical path behind the beam shaping means 4,
A good spot without flare light can be obtained on the surface to be scanned.

FIG. 8 is a schematic view of a main part of a main part from the light source means to the beam shaping means according to the sixth embodiment of the present invention. 2, the same elements as those shown in FIG. 2 are denoted by the same reference numerals.

The present embodiment is different from the first embodiment in that the first diffractive optical element and the second diffractive optical element are manufactured using the same material (material) for the substrate. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

That is, in the figure, reference numerals 13 and 14 denote first and second diffractive optical elements, respectively, which are manufactured from substrates made of the same kind of material. By manufacturing the first and second diffractive optical elements 13 and 14 from substrates made of the same material in this manner, the first and second diffraction gratings 11 and 1 are manufactured.
2 can be manufactured with the same grating thickness. For example, when manufacturing the shape of a diffraction grating using a mold or the like, the number of steps for manufacturing the mold can be reduced by half. In addition, the first and second
When the pitch of the diffraction grating is changed due to expansion of the substrates of the diffractive optical elements 13 and 14, the adverse effects can be minimized.

Here, means for alleviating the influence on the temperature rise will be described.

In the figure, a solid line 21 is a light beam at the time of design, and a broken line 22 is a light beam at the time of temperature rise. The substrate expands by increasing the temperature, and the lattice pitch increases. Therefore, the deflection angle becomes smaller. However, when the materials of the substrates are the same, the first diffractive optical element 13 and the second diffractive optical element 14 can be disposed very close to each other, so that the degree of temperature rise is considered to be the same, so that The degree of expansion and, consequently, the amount of change in deflection angle are equal. As a result, the light beam emitted from the beam shaping means 64 is affected with respect to the light beam width, but the direction of the light beam does not change as a light beam parallel to the optical axis. No adverse effects occur. Here, the second diffractive optical element 14 is preferably manufactured with a slightly wider grating width because the incident position of the light beam changes depending on the temperature rise.

FIGS. 9A and 9B are main part configuration diagrams showing the configuration of the beam shaping means according to the seventh embodiment of the present invention.
2, the same elements as those shown in FIG. 2 are denoted by the same reference numerals.

This embodiment differs from the first embodiment in that a spacer having a high expansion coefficient is used for the spacer for determining the distance between the first and second diffractive optical elements. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

That is, in FIG. 9A, reference numeral 25 denotes a spacer, which is a material having a high expansion coefficient (for example, PC (polycarbonate) expansion coefficient = 4 × 10 ⁻⁵ or Noryl expansion coefficient = 8.25 × 1).
Is made from 0 ^-5 etc.). In the present embodiment, for example, as shown in FIG. 2B, when the temperature rises, the interval between the first and second diffractive optical elements 9 and 10 is widened, and the light flux incident on the second diffractive optical element 10 is increased. The incident position becomes higher. Therefore, in this embodiment, if the expansion rate of the material of the spacer 25 is selected so as to cancel out the effect of reducing the deflection angle due to the temperature rise as described in the above-described embodiment 6, even if the temperature rise occurs, A good scanning optical system without changing the exit beam diameter can be obtained.

FIG. 10 is a block diagram showing a main part of the beam shaping means according to the eighth embodiment of the present invention.

The difference of the present embodiment from the first embodiment is that the emitted light flux becomes denser from the optical axis to the periphery inside the annular bright portion with respect to the incident light flux incident on the beam shaping means. That is, the beam shaping means is configured to emit light. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

That is, in the drawing, reference numeral 74 denotes a beam shaping means, which includes a first diffractive optical element 16 for deflecting a parallel light beam incident from a collimator lens (not shown) at a predetermined angle around an optical axis; A second diffractive optical element 17 for re-deflecting the deflected light beam into a parallel light beam around the optical axis. The luminous flux density is increased from the point toward the periphery and the light is emitted.

Usually, a light beam diverged from a laser light source and collimated by a collimator lens has a Gaussian distribution as a light amount distribution. Therefore, the amount of light near the optical axis is large, and decreases toward the periphery.

Therefore, in this embodiment, the beam shaping means 74
Is configured as described above, the beam shaping means 7
The light amount of the light beam emitted from the light source 4 can be made to be a substantially uniform light amount distribution, and a finer spot diameter can be obtained.

FIG. 11 is a schematic view of a main part of a main part from the light source means to the beam shaping means according to the ninth embodiment of the present invention.
2, the same elements as those shown in FIG. 2 are denoted by the same reference numerals.

This embodiment is different from the first embodiment in that the shape of the orbicular light beam emitted from the beam shaping means (orbicular shape) or / and the vicinity of the optical axis where the light intensity distribution is weaker than the peripheral portion. That is, the shape of the luminous flux in the (dark portion) is an elliptical shape. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

That is, in the drawing, reference numeral 84 denotes a beam shaping means, which has a first diffractive optical element 18 and a second diffractive optical element 19, and the first diffractive optical element 18 is Are deflected at different angles in the main scanning direction and the sub-scanning direction.
The diffractive optical element of (1) converts the light beam deflected by the first diffractive optical element into an annular parallel light beam. By configuring the beam shaping means in this manner, in the present embodiment, the shape of the annular light beam and / or the shape of the light beam near the optical axis (dark portion) where the light intensity distribution is weaker than the peripheral portion is changed to a shape other than the circular shape. It is shaped.

That is, in each of the above-described embodiments, the shape of the light beam is all rotationally symmetric, and is composed of a circular orbicular portion and a dark portion. However, the present invention is not limited to this. As shown, the shape of the light beam on the input side may be a circular shape, and the shape of the light beam on the output side may be an elliptical orbicular opening.

In this embodiment, unlike a normal optical system,
By arbitrarily changing the grating pitch of the first and second diffractive optical elements 18 and 19, the shape of the light beam is converted from a circle to an ellipse. By shaping the shape of the light beam into an elliptical orbicular shape in this manner, the present invention can obtain substantially the same effects as those of the above-described embodiments.

Naturally, various combinations other than those shown in FIG. 11, such as a light flux shape, such as an elliptical light incident side and a circular light emitting side, a circular ring zone and an elliptical dark part, are also conceivable.
Here, all combinations are not described. For these parameters, an optimal configuration can be selected from the radiation angle of the laser beam and its variation, the imaging magnification of the optical system in the main scanning direction and the sub-scanning direction, the desired spot diameter, and the like.

[0067]

According to the present invention, as described above, a beam shaping means having a diffractive optical element is provided in the optical path between the light source means and the deflecting means, and the light intensity distribution of the light beam emitted from the beam shaping means is light. Beam shaping into a ring-shaped (ring-shaped) light beam that is stronger at the periphery than at the vicinity of the axis reduces the spot diameter and increases the depth of focus without loss of light amount to obtain a high-quality image. Scanning optics that can be achieved.

Further, according to the present invention, by manufacturing a diffractive optical element on a substrate made of the same kind of material,
An element configuration in which a diffraction grating having the same pitch is combined can be used, whereby a scanning optical device that can greatly reduce the influence on temperature rise can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is a schematic diagram of a main part of a main part according to the first embodiment of the present invention.

FIG. 3 is an enlarged explanatory view of first and second diffractive optical elements according to the first embodiment of the present invention.

FIG. 4 is a schematic diagram of a main part of a beam shaping unit according to a second embodiment of the present invention.

FIG. 5 is a schematic diagram of a main part of a beam shaping unit according to a third embodiment of the present invention.

FIG. 6 is a schematic view of a main part when the beam shaping means according to the fourth embodiment of the present invention is incorporated in a laser unit.

FIG. 7 is a schematic diagram of a main part of a main part of a fifth embodiment of the present invention.

FIG. 8 is a schematic view of a main part of a main part according to a sixth embodiment of the present invention.

FIG. 9 is a configuration diagram of a main part of a beam shaping unit according to a seventh embodiment of the present invention.

FIG. 10 is a main part configuration diagram of a beam shaping unit according to an eighth embodiment of the present invention.

FIG. 11 is a schematic view of a main part of a main part of a ninth embodiment of the present invention.

FIG. 12 is a schematic view of a main part of a main part of a conventional scanning optical device.

FIG. 13 is a schematic diagram of a main part of an optical system of a conventional scanning optical device.

FIG. 14 is a schematic view of a main part of the laser unit shown in FIG. 13;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source means 2 Collimator lens 3 Aperture stop 4,44,54 Beam shaping means 64,74,84 Beam shaping means 5 Cylindrical lens 6 Deflection means 7 Imaging means 8 Scanning surface 9,13,16,18 First Diffractive optical element 10, 14, 17, 19 Second diffractive optical element 11 First diffraction grating 12 Second diffraction grating 31 Beam shaping barrel 32 Lens barrel 25 Spacer 28 Aperture member 53 Aperture stop 60 Lens unit

Claims (10)

[Claims] 1. A light beam modulated and emitted from a light source means in accordance with an image signal and converted into a substantially parallel light beam by a collimator lens, guided to a deflecting means through a cylindrical lens, and formed into an image of the light beam deflected by the deflecting means. A scanning optical device that guides light onto a surface to be scanned through a unit and scans the surface to be scanned, wherein a beam shaping unit is provided in an optical path between the light source unit and the deflecting unit; A scanning optical apparatus characterized in that a light intensity distribution of a light beam emitted from the beam shaping means is shaped into a ring-shaped light beam that becomes stronger at the peripheral portion as compared with the vicinity of the optical axis. A first diffractive optical element for deflecting the incident parallel light beam from the collimator lens at a predetermined angle around the optical axis; and The scanning optical device according to claim 1, further comprising a second diffractive optical element that deflects the light beam. 3. The scanning optical device according to claim 2, wherein the first and second diffractive optical elements are manufactured from substrates made of the same kind of material. 4. The scanning optical device according to claim 2, wherein the first and second diffractive optical elements are respectively manufactured on both surfaces of the same substrate. 5. The scanning optical apparatus according to claim 4, wherein an aperture stop for restricting a light beam on an outer periphery is provided on a part of an element surface of said first diffractive optical element. 6. The luminous flux density of the parallel luminous flux emitted when the incident luminous flux is converted into an orbicular parallel luminous flux by the first and second diffractive optical elements has a luminous flux density from an optical axis inside the orbicular bright portion. 3. The scanning optical device according to claim 2, wherein the first and second diffractive optical elements are configured so as to be denser as going toward. 7. The first diffractive optical element makes the angle of deflecting the incident parallel light beam from the collimator lens different from each other in the main scanning direction and the sub-scanning direction, and the second diffractive optical element makes the second diffractive optical element By converting the light beam deflected by the first diffractive optical element into a parallel light beam having a ring shape, the shape of the light beam having a ring shape and / or the shape of the light beam near the optical axis whose light intensity distribution is weaker than that of the peripheral portion is arbitrary. The scanning optical device according to claim 2, wherein the scanning optical device is shaped into a shape as described above. 8. The scanning optical apparatus according to claim 2, wherein said beam shaping means is held by a beam shaping barrel, and said beam shaping barrel is incorporated in a lens barrel. . 9. The scanning optical apparatus according to claim 2, wherein an annular stop member is provided in an optical path behind said beam shaping means. 10. The scanning optical apparatus according to claim 2, wherein a spacer made of a material having a high expansion coefficient is provided between said first and second diffractive optical elements.