JP2007185850A - Light source device, optical scanner, and image forming device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized and low cost light source device using surface emitting laser which has both a light quantity control means and a polarization control means in one light source device and in which an optical path branching means and the polarization control means are integrated with a cover glass, and to provide an optical scanner provided with the light source device and an image forming device provided with the same. <P>SOLUTION: In the light source device equipped with the surface emitting laser 1, the cover glass 3 for sealing the surface emitting laser 1, and a photo-detector 2 which receives a part of the light beam irradiated from the surface emitting laser 1, the optical path branching means which branches a part of the light beam irradiated from the surface emitting laser 1 and guides it to the photo-detector 2, and the polarization control means which controls the polarization of the light beam irradiated from the surface emitting laser 1 are integrated with the cover glass 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface emitting laser light source device or a multi-beam surface emitting laser light source device capable of controlling light quantity and polarization, an optical scanning device including the same, and an image forming apparatus including the same.

In recent years, it has been desired to improve the printing speed and the writing density of image forming apparatuses. Therefore, as one of means for achieving high-speed and high-density optical scanning in the optical scanning device constituting the image forming apparatus, there is a method of increasing the deflection speed of the optical deflector, that is, increasing the rotational speed of the polygon mirror.
However, there are problems such as noise and heat associated with high-speed rotation, and there is a limit to improving the rotation speed. On the other hand, as another means for achieving high-speed and high-density optical scanning, there is a method of scanning a plurality of light beams at a time and simultaneously scanning a plurality of lines.
As a multi-beam light source device capable of scanning a plurality of light beams, using one multi-beam light source (laser array light source having a plurality of light emitting points in one package) that generates a plurality of light beams, This can be realized by replacing the conventional optical scanning device using one light source.
On the other hand, many methods for achieving a multi-beam light source device using a plurality of conventional single beam light sources (laser light sources having one light emitting point in one package) have been proposed.
A semiconductor laser is generally used as a light source, and an edge-emitting laser has been the mainstream in the past. In recent years, however, surface emitting lasers (called VCSELs) have appeared.
Since surface emitting lasers are easier to array than edge emitting lasers, the edge emitting lasers have a limit of about 4 to 8 beams, whereas surface emitting lasers have 16 to 32 beams. In addition, further arraying is possible.
Therefore, it is expected as a light source for improving the printing speed and writing density of the image forming apparatus, and as an optical device using a surface emitting laser, for example, a light source for optical communication.

Two media having different refractive indexes (for example, one is air and the other isotropic medium) has a structure (SWS = Subwavelength Structure) having a periodic structure smaller than the wavelength of light. In an optical element, an optical anisotropy called structural birefringence appears.
Conventionally, in order to use birefringence, it has been necessary to use a birefringent crystal such as quartz or calcite, and it has been difficult to change the birefringence because it is a property specific to a substance. On the other hand, birefringence can be changed depending on the shape of a general medium without using a special crystal in structural birefringence, and can be controlled relatively easily.
Thereby, a polarizing beam splitter or the like that does not use a birefringent crystal can be realized. In addition, the antireflective structure can be formed on the optical surface by controlling the effective refractive index according to the shape of the medium.
Since it has the above-mentioned structural birefringence, the phase difference can be changed by controlling the thickness of the TE polarized light and TM polarized light, and the function of λ / 2 plate and λ / 4 plate is generated. Can be made.
If the refractive indices for TE polarized light and TM polarized light are n (TE) and n (TM), the wavelength of light to be used is λ, and the thickness of the structure is d, the generated phase difference φ is
φ = 2π {n (TE) −n (TM)} d / λ
It can be expressed as
Further, by selecting an appropriate thickness d, it is possible to realize a polarizing filter that transmits only one of the polarized light.

However, when a light source device using a surface emitting laser is applied to a conventional optical scanning device, it has various problems as described below with respect to an edge emitting laser, and is intended to solve these problems. Several techniques are known (see, for example, Patent Documents 1 to 6 and Non-Patent Document 1).
The edge-emitting laser is generally driven by applying APC (Auto Power Control) while monitoring the light emitted backward, whereas the surface-emitting laser is rearward because of its structure. Since no outgoing light is generated, it is necessary to control the amount of light by some means.
In an image output by an image forming apparatus using a light source device to which light amount control cannot be applied, a density variation due to a light output variation of the light source device occurs, resulting in a problem that a good image cannot be obtained.
Therefore, as a light amount control means when using a surface emitting laser, a part of the light beam emitted from the surface emitting laser having a certain predetermined ratio is branched and guided to a photodetector. In accordance with the output of the photodetector, a means for driving the surface emitting laser by controlling the driving current so that the light output of the surface emitting laser becomes a predetermined output in the laser light quantity control device can be considered.

FIG. 13 is a schematic diagram showing a conventional example of branching of some light beams using a beam splitter. FIG. 14 is a schematic view showing a conventional example of branching of a part of a light beam using a half mirror.
As a method for branching a part of the light beam and guiding it to the photodetector 40, in Patent Document 1, a part of the light beam is branched using a beam splitter 41 (FIG. 13). Further, in Patent Document 2, a part of a light beam is branched using a half mirror 44 as a beam separation optical element (FIG. 14).
In the light quantity control circuit 42 of the optical system 43 in FIG. 14, only the half mirror 44, the polygon mirror 48, and the two scanning imaging lenses 46 and 47 on the surface to be scanned (photosensitive drum) 45 are indicated by reference numerals.
In the edge emitting laser, the polarization direction of the emitted light beam is linearly polarized light having a direction parallel to the active layer of the edge emitting laser. FIG. 15 is a schematic diagram showing the polarization direction of the light beam emitted from the edge emitting laser.
In contrast to the linearly polarized light of the edge-emitting laser as shown in FIG. 15, the surface-emitting laser is basically random polarized light due to its structure, and thus polarization control by some means is required.
In an optical scanning device, a light beam is reflected by an optical deflector and transmitted and reflected by a number of optical elements. At this time, since transmission and reflection at the interface have polarization dependency, the polarization direction is in a plane parallel to the incident surface (P-polarized light), and the polarization direction is perpendicular to the incident surface ( In the case of (S-polarized), the transmittance and reflectance are different.
Therefore, in the multi-beam light source device, it is desirable that the polarization directions of the light beams emitted from the respective light sources are equal. In addition, if a light source device using a surface emitting laser is replaced with an optical scanning device manufactured assuming a light source device using an edge emitting laser, the polarization directions must be matched equally, and different polarization states In this case, the light quantity characteristic in one line (in one scan) is remarkably deteriorated.
Therefore, in an image output by such an image forming apparatus, a density variation due to the polarization dependency of the transmittance or reflectance of the optical deflector or optical element occurs, and a good image cannot be obtained. Cause problems.

FIG. 16 is a schematic view showing a conventional polarization control means. Because of this problem, as an example of polarization control means when a surface emitting laser is used, a structure for controlling the polarization direction can be provided in the device structure itself as shown in Patent Document 3, but the element structure is complicated. It is difficult to manufacture (FIG. 16).
Further, it is speculated that the control structure varies depending on the structure of the surface emitting laser and the manufacturing method, and it is not necessarily applicable to any surface emitting laser. As another example, it is conceivable to control the polarization of a light beam emitted from a surface emitting laser at a stage where it does not receive polarization dependency of transmission and reflection.
FIG. 17 is a schematic view showing a conventional example of the polarization control means of Patent Document 4 in which a polarization beam splitter is arranged on the emission side of the surface emitting laser. FIG. 18 is a schematic diagram showing a conventional example of the polarization control means of Patent Document 5 using a polarizer and a half mirror.
As a method using polarization control means outside the light emitting part of the surface emitting laser, in Patent Document 4, a polarizing beam splitter 50 is arranged on the emission side of the surface emitting laser 49 so that only a light beam having a desired polarization direction is transmitted. (FIG. 17). Further, in Patent Document 5, only a light beam having a desired polarization direction is transmitted by providing a polarizer 51 and a half mirror 52 in the optical path of the light beam (FIG. 18).

In these conventional technologies, the light amount control is not performed in Patent Document 1 and Patent Document 4. In Patent Document 5, a polarization control unit and a unit for branching a light beam for performing light amount control are provided, but are separated separately. In Patent Document 6, the polarization direction is controlled by a polarizing filter.
As described above, the light amount control means of Patent Document 1 branches a part of light with a beam splitter or a cover glass (parallel plate) and guides it to the photodetector. The light quantity control means of Patent Document 2 uses a beam separation optical element (half mirror).
In Patent Document 3, polarization is controlled by a resonator structure. In the polarization control means of Patent Document 4, a polarization beam splitter is disposed on the emission side of the surface emitting laser. Patent Document 5 discloses an optical scanning device in which a polarization limiting unit is provided between a light source unit and a deflecting unit, and the polarization limiting unit is formed integrally with some optical elements. Further, a light amount detection unit is provided between the polarization limiting unit and the deflection unit.
In Patent Document 6, the polarization direction is controlled by a polarizing filter. Further, Non-Patent Document 1 describes a structure having a periodic structure smaller than the wavelength of light (SWS = Subwavelength Structure).
JP-A-8-330661 JP 2003-215485 A JP-A-8-56049 Japanese Utility Model Publication No. 4-121771 JP-A-9-288244 JP-A-10-325933 Light control by fine structure, Kikuta / Iwata's paper "Optics", Vol. 27, No. 1 (1998), 12-17

However, in these conventional techniques, the polarization control of the surface emitting laser is not performed. In general, an edge-emitting laser is driven by APC (automatic power control) while monitoring the emitted light from the rear, whereas the surface-emitting laser has a structure in which the emitted light is rearward. Therefore, it is necessary to control the amount of light by some means.
In an image output by an image forming apparatus using a light source device that cannot perform light amount control, a density variation due to a light output variation of the light source device occurs, and a problem that a good image cannot be obtained occurs.
Furthermore, when a light source device using a surface-emitting laser is replaced with an optical scanning device manufactured assuming a light source device using an edge-emitting laser, the polarization directions must be matched equally, and different polarization states In this case, there is a problem that the light quantity characteristic in one line (in one scan) is remarkably deteriorated.
In view of the above situation, the object of the present invention is to have both the light quantity control means and the polarization control means in one light source device, and further, the optical path branching means and the polarization control means are integrated with the cover glass. An object of the present invention is to provide a light source device using a small-sized and low-cost surface emitting laser, an optical scanning device including the same, and an image forming apparatus including the same.

In order to solve the above-described problems, the invention described in claim 1 includes a surface emitting laser, a cover glass for sealing the surface emitting laser, and a part of a light beam emitted from the surface emitting laser. In a light source device comprising a photodetector for receiving light, an optical path branching means for branching a part of a light beam emitted from the surface emitting laser and guiding it to the photodetector, and emitting from the surface emitting laser The light source device is characterized in that polarization control means for controlling polarization of the light beam is integrated with the cover glass.
The invention according to claim 2 is characterized in that the light path branching means is provided on the surface emitting laser side of the cover glass.
According to a third aspect of the present invention, there is provided the light source device according to the second aspect, wherein the optical path branching means is a diffraction grating having a periodic structure provided on the cover glass.
According to a fourth aspect of the present invention, there is provided the light source device according to the first aspect, wherein the polarization control means is provided on a side of the cover glass opposite to the surface emitting laser.
According to a fifth aspect of the present invention, there is provided a diffraction grating according to the fourth aspect of the present invention, wherein the polarization control means is provided on the cover glass and has a periodic structure that is the same as or smaller than the wavelength of the surface emitting laser. The light source device is characterized.

The invention according to claim 6 is a polarization-dependent diffraction grating in which the optical path branching unit and the polarization control unit are provided on one surface of the cover glass and have at least two periodic structures. The light source device according to Item 1 is characterized.
The invention according to claim 7 is characterized in that the light path branching means and the polarization control means are provided on the surface emitting laser side of the cover glass.
The invention according to claim 8 is the light source device according to claim 1, wherein the surface emitting laser is a surface emitting laser array having a plurality of light emitting portions.
According to a ninth aspect of the present invention, there is provided the light source device according to any one of the first to eighth aspects and a second optical system for guiding a light beam guided from the light source device to an optical deflector. An optical deflector for deflecting and scanning the light beam guided from the second optical system, and a third for imaging the light beam deflected and scanned by the optical deflector as a light spot on the surface to be scanned. An optical scanning device having an optical system is characterized.
According to a tenth aspect of the present invention, there is provided an image forming apparatus using the optical scanning device according to the ninth aspect as an optical writing unit.

According to the present invention, means having two functions of an optical path branching means and a polarization control means are integrated, and furthermore, the function is applied to a cover glass generally possessed by a semiconductor laser (edge emitting laser or surface emitting laser) device. By concentrating, a small and low-cost light source device can be provided.
According to the present invention, the light output fluctuation of the light source device does not occur, and the density fluctuation caused by it does not occur on the image. In addition, the polarization dependency of the transmittance and reflectance of the optical deflector and optical element is prevented, and density fluctuations caused by it are prevented from occurring. By suppressing these density fluctuations, a good image can be obtained. be able to.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing a first embodiment of a light source device according to the present invention. In FIG. 1, a light source device A includes a surface emitting laser 1 and a cover glass 3 for sealing a surface emitting laser 1 by a photodetector 2 that receives a part of a light beam emitted from the surface emitting laser 1. , The holder 4 and the base 5.
FIG. 2 is a schematic view showing an example of a surface emitting laser. In the surface emitting laser 1 of FIG. 2, the active layer 1c is sandwiched between two clad layers 1a and 1b, and reflection surfaces 1d and 1e having high reflectivity are formed on upper and lower surfaces of the clad layers 1a and 1b. In contrast, the structure is formed.
A region sandwiched between the two reflecting surfaces 1d and 1e is a so-called Fabry-Perot resonator perpendicular to the substrate 6, and laser oscillation occurs in the oscillation region 1f of the active layer 1c. The light beam oscillates in the direction, that is, in the direction of arrow A shown in the figure. The surface emitting laser 1 basically has random polarization due to this structure.

In FIG. 1, a light beam emitted from the surface emitting laser 1 is incident on a cover glass 3 that is an optical element, and a part of the light beam is branched by the cover glass 3 and is incident on a photodetector 2. On the other hand, the light beam emitted from the surface emitting laser 1 is randomly polarized light, whereas the light beam after passing through the cover glass 3 is linearly polarized light having a predetermined direction.
At this time, the cover glass 3 is an optical path branching means and also has a polarization control means. Therefore, the cover glass 3 is integrated with the optical path branching means and the polarization control means. Based on the intensity signal of the light beam from the photodetector 2, the light amount control of the surface emitting laser 1 is performed.
FIG. 3 is a schematic diagram showing an example of a laser light quantity control device. In FIG. 3, a part of the light beam reflected at an angle θ from the cover glass 3 of the light source device A is incident on the photodetector 2.
The light intensity signal from the light detector 2 is sent to the laser light quantity control device 7, which controls the drive current so that the light output of the surface emitting laser 1 becomes a predetermined output. The current signal from the laser light quantity control device 7 is fed back to the surface emitting laser 1, and the surface emitting laser 1 is driven with a predetermined light output.

FIG. 4 is a schematic view showing an example of the optical path branching means. In FIG. 4, the surface emitting laser 1 of the light source device A is attached to a base 5. The optical path branching means is a half mirror surface 3 a provided on the surface emitting laser side of the cover glass 3 supported by the holder 4.
The half mirror surface 3a transmits a predetermined ratio, for example, 50% of the light beam and reflects the remaining 50%. The half mirror surface 3a can be formed of a dielectric multilayer film or the like.
Here, the ratio of the light beam transmitted or reflected by the half mirror surface 3a can be set by the following factors. In general, it is desirable that the light beam emitted from the light source device A has as high output as possible, and the transmittance should be as high as possible.
Therefore, it is desirable to reflect only the minimum light output necessary for detecting a part of the light beam by the photodetector 2. By providing the optical path branching unit on the surface emitting laser 1 side, it is possible to branch the optical path with high light intensity by branching a part of the light beam before the polarization control unit.

FIG. 5 is a schematic view showing another example of the optical path branching means. In FIG. 5, the light path branching means of the light source device A is a diffraction surface 3 b having a periodic structure provided on the surface emitting laser 1 side of the cover glass 3.
For example, it is a state that ± 1st order reflected light is detected by the photodetector 2. By setting the pitch Λ of the diffractive surface 3b to λ> λ with respect to the wavelength λ emitted from the surface emitting laser 1, ± 1st-order diffracted light is generated.
In FIG. 5, the photodetectors 2 are provided for the ± 1st order reflected light, but can be provided for either the + 1st order or the −1st order, and of course, the diffracted light other than the ± 1st order. Can also be used. The cover glass 3 can be directly processed, and it is not necessary to add another substance such as a polymer or a metal wire, and a stable polarization control means can be formed.
Further, by blazing the diffractive surface 3b, the + 1st order diffraction efficiency can be made higher than the -1st order, and vice versa. Unnecessary light emitted from the diffractive surface or the like can also be cut by an opening means (not shown) or the like inside or outside the light source device A as necessary.
FIG. 6 is a schematic view showing an example of the polarization control means. In FIG. 6, the polarization control means is a polymer polarizing filter (polarizer) 8 provided on the opposite side of the cover glass 3 from the surface emitting laser 1.
By providing the polarization control means on the side opposite to the surface emitting laser 1 in this way, the polarization control means is provided on the final surface of the light source device A, so that light can be emitted from the light source device in a state in which polarization control is well performed. .
Of the randomly polarized light emitted from the surface emitting laser 1, only the linearly polarized light component having a certain direction is transmitted. In addition, a wire grid polarizer or the like can be used as the polarization control means. Thus, it is desirable that the cover glass 3 can be thinly formed on the surface.

FIG. 7 is a schematic view showing another example of the polarization control means. In FIG. 7, the polarization control means is a diffraction surface (diffraction grating) 9 having polarization dependency due to a periodic structure provided on the opposite side of the cover glass 3 from the surface emitting laser 1.
A so-called resonance in which the pitch Λ ′ of the diffractive surface 9 is close to the wavelength λ emitted from the surface emitting laser 1 (Λ ′ = λ˜10λ) or the pitch Λ ′ is smaller than the wavelength λ (Λ ′ <λ). In a region called a region or a sub-wavelength region, the diffractive surface 9 has polarization dependency. Such a diffractive surface 9 has different behavior depending on the polarization direction of the light beam incident on the diffractive surface 9 (for example, TE wave or TM wave).
For example, a polarization-dependent diffractive surface 9 with Λ ′ = 2λ is shown in Schmitz et al. (OPTICS LETTERS, Vol. 20, No. 17, p1830). According to this, TE polarized light can be transmitted, and TM polarized light is diffracted by ± 1st order.
Even if a subwavelength structure satisfying Λ ′ <λ is used, it is possible to transmit the desired polarized light as described above by using the structural birefringence. Unnecessary light emitted from the diffractive surface 9 or the like can be cut by an opening means (not shown) or the like in the light source device A or outside as necessary.
The cover glass 3 can be processed directly, and it is not necessary to add another substance such as a multilayer film, and it is possible to form an optical path branching means that is stable in terms of heat and strength.

FIG. 8 is a schematic view showing an example in which both the optical path branching means and the polarization control means are provided on one surface of the cover glass. FIG. 9 is a schematic diagram showing the optical path branching means and the polarization control means of FIG. 8 together with TE polarized light and TM polarized light.
8 and 9, a diffraction surface 10 is provided in which both the optical path branching unit and the polarization control unit are provided on one surface of the cover glass 3 (the surface on the surface emitting laser 1 side in the drawing). On the opposite side of the diffractive surface 10, the photodetector 2 attached to the base 5 in the holder 4 is disposed.
On the cover glass 3, a diffraction grating having a pitch Λ as an optical path branching unit and a diffraction grating having a pitch Λ ′ as a polarization control unit are integrated, and a polarization-dependent diffraction grating in which two periodic structures are combined. 10 is formed. When compared in terms of pitch, Λ> Λ ′.

When exhibiting structural birefringence, the periodic structure portion having the pitch Λ ′ can be approximated as a uniform isotropic medium having an effective refractive index as represented by the following equation. The refractive indexes for TE polarized light and TM polarized light are n (TE) and n (TM), the refractive index n of the substrate (here, the refractive index of the cover glass 3), the wavelength of light λ, the pitch Λ ′, and the fill factor f ′. Then,
n (TE) = √ {fn ² + (1−f)}
n (TM) = √ [n ² / {f + (1−f) n ² }]
It becomes.
Therefore, the periodic structure portion having the pitch Λ ′ can be handled so as to have different effective refractive indexes for the TE polarized light and the TM polarized light. That is, in FIG. 9, it looks like a diffraction grating having a refractive index n (TE) with a pitch Λ for TE-polarized light and a diffraction grating having a refractive index n (TM) with a pitch Λ for TM-polarized light. looks like.
Therefore, it is possible to configure a polarization separation mirror that can exhibit different behavior with respect to TE polarized light and TM polarized light, and transmits one linearly polarized light but reflects linearly polarized light orthogonal thereto. Thereby, polarization control is possible.
Further, in order to branch the optical path, by selecting the pitch Λ for the reflected light beam, for example, ± 1st-order diffraction can be generated, so that the light beam is transmitted to the photodetector 2. Can be partly branched and behave as optical path branching means.

Furthermore, as shown in FIG. 8, the diffraction element 10 in which the optical path branching means and the polarization control means are combined can be provided on the surface emitting laser 1 side of the cover glass 3. Thus, by providing the optical path branching means and the polarization control means on one surface of the cover glass 3, it can be formed by direct processing on the cover glass 3, and it is not necessary to add another substance. There is an advantage that it is only necessary to process the surface.
Since the surface-emitting laser 1 side is packaged, it is possible to omit the protection of the surface of the non-diffractive element or the like, and it is possible to protect it from foreign matter or dust. Of course, it cannot be provided on the side opposite to the surface emitting laser 1.
In the present invention, as a component constituting the light source device, in addition to the surface emitting laser, the cover glass, and the photodetector, a base and a holder are illustrated. However, a holder in which these are integrated may be used. Alternatively, a third holding member may be provided separately.
These do not affect the present invention. Further, the method for supporting the holder and the cover glass is not described in detail, and a known method can be used.
Optical path branching means for branching the light beam from the surface emitting laser into a light beam emitted from the light source device and a light beam guided to the photodetector in the light source device, and the light beam emitted from the light source device is linearly polarized light The feature of the present invention lies in the fact that the polarization control means is integrated and integrated on the cover glass, and other configurations are not limited at all.
Surface emitting lasers are relatively easy to array compared to edge emitting lasers, and surface emitting laser arrays having several tens of light emitting points have been realized. These elements can also be applied to the light source device of the present invention.

FIG. 10 is a schematic view showing a light source device using a surface emitting laser array. In FIG. 10, a light source device A shows a surface-emitting laser array 1A and a plurality of light beams emitted from the surface-emitting laser array 1A (in the drawing, three light beams are shown for simplification). .
The photodetector 2 that receives a part of the light beam is packaged by a cover glass 3, a holder 4, and a base 5 for sealing the surface emitting laser array 1A.
As for the optical path branching means and the polarization control means, the above-described example can be applied to each light beam. Each light beam branched by the optical path branching means may be detected collectively by the photodetector 2 if the light amount of each light beam of the surface emitting laser array 1A is collectively controlled. it can.
In this case, a photodetector having a size that can be detected collectively may be prepared, or a photodetector having a size that only detects several light beams may be prepared as a representative. On the other hand, if the light amount control is separately performed for each light beam of the surface emitting laser array 1A, it is necessary to prepare a photodetector for each light beam branched by the optical path branching means.

FIG. 11 is a schematic view showing an optical scanning device according to the present invention. Referring to FIG. 11, in (a), the direction in which the light beam is deflected and scanned is referred to as a main scanning direction, and a schematic cross section thereof is shown. In (b), the direction orthogonal thereto is referred to as a sub scanning direction, A cross section is shown.
The light source unit 20 includes a light source device A and a first optical system 11 (for example, a single lens). The light beam emitted from the light source device A is shaped into a parallel light beam by the single lens 11 and guided to the second optical system 21. The second optical system 21 includes, for example, a cylindrical lens 12. The light beam is converged in one direction so as to be a linear light beam by the cylindrical lens 12, and a line image is formed on the deflection reflection surface of the optical deflector 13. To form an image.
Thereafter, the light is guided to the third optical system 22. The third optical system 22 includes, for example, two scanning imaging lenses 14 and 15, and two light beams deflected and scanned by the optical deflector 13 are converted into desired light spots by the scanning imaging lenses 14 and 15. Imaged. The formed light spot scans the scanning surface 16 at a predetermined interval.
The same applies to the case where a plurality of light beams are used for the light source device A using the surface emitting laser array 1A (FIG. 10). In this case, a plurality of light spots on the scanned surface 16 are maintained at a predetermined interval in the main scanning direction and the sub-scanning direction. Each optical element (surface emitting laser arrays 1A and 11 to 15 of light source device A) is arranged so as to obtain this predetermined interval.
Thus, the present invention can also be applied to a surface emitting laser array, which is advantageous for improving the number of beams. Furthermore, there are advantages in improving the printing speed and writing density of the image forming apparatus. In addition, since a small and low-cost light source device can be applied, the optical scanning device can also be reduced in size and cost.
In the case where there is an unnecessary light beam emitted from the light source device A (for example, a light beam of an unnecessary diffraction order by the diffraction element), light is applied to the surface to be scanned in the optical scanning device or outside the device as necessary. What is necessary is just to shield from light so as not to form a spot.

FIG. 12 is a schematic view showing an image forming apparatus equipped with an optical scanning device according to the present invention. One of image forming processes for forming an image in an image forming apparatus is an electrophotographic process. An outline of the electrophotographic process will be described below.
In the electrophotographic process, as is well known, an electric potential is applied to the image carrier (for example, photoconductor) 23 by the charging means 24 (charging process), and the light spot from the optical writing unit (exposure means) 25 is applied to the image carrier 23. A latent image is formed by irradiating on the surface (exposure process), toner is attached to the latent image by developing means 26 to form a toner image (developing process), and the toner image is copied onto recording paper P by transfer means 27 ( Transfer process), pressure or heat is applied by the fixing means 28, and the recording paper P is fused (fixing process).
The toner remaining on the image carrier 23 is cleaned by the cleaner unit 29, and the charged portion is discharged by the discharging unit 30. The optical writing unit of the present invention can also be applied to a tandem type image forming apparatus that is advantageous for high-speed color image output.
As described above, in the image forming apparatus, by controlling the light amount of the surface emitting laser, the density fluctuation caused by it does not occur on the image. Further, by controlling the polarization of the surface emitting laser 1, the polarization dependency of the transmittance and the reflectance of the optical deflector and the optical element does not occur, and the density fluctuation caused by it does not occur on the image. By suppressing these density fluctuations, a good image can be obtained even when the surface emitting laser 1 is used.
Furthermore, by applying the surface emitting laser 1, it is possible to improve the printing speed and the writing density of the image forming apparatus. On the other hand, in configuring an optical scanning device having the same printing speed and the same scanning density as when the surface emitting laser 1 is used, the rotational speed of the optical deflector can be reduced, so that the power consumption is reduced. Contributes to the reduction of noise and heat generation associated with rotational movement.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows 1st Embodiment of the light source device by this invention. Schematic which shows an example of a surface emitting laser. Schematic which shows an example of a laser light quantity control apparatus. Schematic which shows an example of an optical path branching means. Schematic which shows another example of an optical path branching means. Schematic which shows an example of a polarization control means. Schematic which shows another example of a polarization control means. Schematic which shows an example which provided both the optical-path branching means and the polarization control means on one surface of the cover glass. Schematic which shows the optical path branching means and polarization control means of FIG. 8 with TE polarization and TM polarization. Schematic which shows the light source device using a surface emitting laser array. 1 is a schematic diagram showing an optical scanning device according to the present invention. 1 is a schematic diagram showing an image forming apparatus equipped with an optical scanning device according to the present invention. Schematic which shows the prior art example of the branching of the one part light beam using a beam splitter. Schematic which shows the prior art example of the branching of the one part light beam using a half mirror. The schematic diagram which shows the polarization direction of the light beam which an end surface emitting laser radiate | emits. Schematic which shows the conventional polarization control means. Schematic which shows the prior art example of the polarization control means of patent document 4 which arrange | positions a polarization beam splitter on the output side of a surface emitting laser. Schematic which shows the prior art example of the polarization control means of the permitted literature 5 which uses a polarizer and a half mirror.

Explanation of symbols

A light source device, B image forming apparatus, 1 surface emitting laser, 1A surface emitting laser array, 2 photodetector, 3 cover glass (light path branching means, polarization control means), 3a half mirror surface (light path branching means), 3b diffraction Surface (depending on the periodic structure), 8 polarizer (polarization control means), 9 diffraction grating (diffractive surface due to periodic structure), 10 diffraction grating (combining optical path branching means and polarization control means)

Claims (10)

  A surface emitting laser comprising: a surface emitting laser; a cover glass for sealing the surface emitting laser; and a light detector that receives a part of a light beam emitted from the surface emitting laser. An optical path branching means for branching a part of the light beam emitted from the light beam and guiding it to the photodetector and a polarization control means for controlling the polarization of the light beam emitted from the surface emitting laser are integrated with the cover glass. And a light source device.   The light source device according to claim 1, wherein the optical path branching unit is provided on the surface emitting laser side of the cover glass.   3. The light source device according to claim 2, wherein the optical path branching means is a diffraction grating having a periodic structure provided on the cover glass.   The light source device according to claim 1, wherein the polarization control unit is provided on a side of the cover glass opposite to the surface emitting laser.   5. The light source device according to claim 4, wherein the polarization control means is a diffraction grating having a periodic structure that is approximately the same as or smaller than the wavelength of the surface emitting laser provided on the cover glass.   The light source device according to claim 1, wherein the optical path branching unit and the polarization control unit are polarization-dependent diffraction gratings having at least two periodic structures provided on one surface of the cover glass.   The light source device according to claim 6, wherein the optical path branching unit and the polarization control unit are provided on the surface emitting laser side of the cover glass.   The light source device according to claim 1, wherein the surface emitting laser is a surface emitting laser array having a plurality of light emitting units.   9. The light source device according to claim 1, a second optical system for guiding a light beam guided from the light source device to an optical deflector, and light guided from the second optical system. An optical deflector for deflecting and scanning the beam; and a third optical system for forming an image of the light beam deflected and scanned by the optical deflector as a light spot on the surface to be scanned. Optical scanning device. An image forming apparatus using the optical scanning device according to claim 9 as an optical writing unit.

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