JP6743369B2 - Surface emitting laser, surface emitting laser array, optical scanning device, and image forming apparatus - Google Patents

Description

The present invention relates to a surface emitting laser, a surface emitting laser array, an optical scanning device, and an image forming apparatus.

In an electrophotographic image forming apparatus such as a copying machine or a printer, a surface emitting laser array is used as a light source,
The number of parts of the light source is reduced by separating the light emitted from the light source having different polarization directions and writing to a plurality of photosensitive drums without reducing the light amount.
When manufacturing surface emitting lasers having different polarization directions, it is necessary to control the polarization direction of the surface emitting laser.
Known methods for controlling the polarization direction of the surface emitting laser include a method using an inclined substrate (Patent Document 1) and a method of forming anisotropic strain inside the mesa structure (Patent Document 2).

However, the conventional method is not easy to process, which also affects the manufacturing cost.

The present invention has been made in view of such a current situation, and its main object is to provide a surface emitting laser that can obtain high polarization characteristics by easy processing and contribute to cost reduction.

In order to achieve the above object, the present invention comprises an active layer and two reflecting mirrors located on both sides of the active layer so as to be parallel to the arrangement direction of the active layer and the two reflecting mirrors. a surface emitting laser that emits light in the direction, said at least one of the two reflectors, relatively to the upper distributed Bragg reflector layer and a low refractive index layer and the high refractive index layer alternately laminated A multilayer film reflecting mirror having a fine structure including flat plates in which periodic grooves are formed in a direction parallel to a stacking direction and arranged at a period smaller than 1/2 of an oscillation wavelength λ. optical thickness of the refractive index layers and the high refractive index layer, and a case for the first polarization direction of the light, unlike in the case for the second polarization direction orthogonal to the first polarization direction, When the wavelength of the light emitted by the surface emitting laser is λ, the optical thicknesses of the low refractive index layer and the high refractive index layer of the multilayer-film reflective mirror in the central portion of the region where the light is emitted are: (2n-1)λ/4 (n is a natural number) for light in the first polarization direction, and (2n-1)λ/4 (n is a natural number) for light in the second polarization direction. And the optical thicknesses of the low refractive index layer and the high refractive index layer in the peripheral portion located outside the central portion are equal to the light in the first polarization direction and the light in the second polarization direction. for any (2n-1) λ / 4 (n is a natural number) Ru different and.
Further, the present invention includes an active layer and two reflecting mirrors located on both sides of the active layer, and emits light in a direction parallel to the arrangement direction of the active layer and the two reflecting mirrors. In the surface emitting laser, at least one of the two reflecting mirrors has a direction in which a relatively low refractive index layer and a relatively high refractive index layer are alternately laminated on an upper distributed Bragg reflecting mirror layer. in a direction parallel, to form a periodic groove, a multilayer-film reflective mirror having a microstructure consisting of flat plates arranged in period smaller than 1/2 of the oscillation wavelength lambda, the multilayer reflector, the the first direction periodic structure arranged in a second direction in which the plurality of the flat plate is orthogonal to the first direction with a plane parallel to a stacking direction of the high refractive index layer and the low refractive index layer Yes, and when the surface emitting laser and a wavelength of light emitted lambda, a second width of the flat is greater than lambda / 4.

According to the present invention, high polarization characteristics can be obtained by easy processing, which can contribute to cost reduction.

It is a top view of the surface emitting laser array which concerns on the 1st Embodiment of this invention. 2A and 2B are enlarged plan views of individual surface-emitting lasers in the surface-emitting laser array, in which FIG. 1A is a diagram showing a first surface-emitting laser, and FIG. It is a figure which shows a light emitting laser. It is sectional drawing in the A-A' line of FIG.2(a) of a 1st surface emitting laser. It is a perspective view which shows a periodic fine structure. It is a figure which shows the manufacturing process of a surface emitting laser array. FIG. 3 is an enlarged plan view of an individual surface emitting laser in the surface emitting laser array according to the second embodiment, (a) showing the first surface emitting laser, and (b) polarized with the first surface emitting laser. It is a figure which shows the 2nd surface emitting laser from which a direction differs. It is sectional drawing in the A-A' line of FIG.6(a) of a 1st surface emitting laser. It is a perspective view which shows a periodic fine structure. It is a schematic perspective view of the optical scanning device which concerns on 3rd Embodiment. It is a schematic block diagram of the color laser printer as an image forming apparatus which concerns on 4th Embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
A surface emitting laser and a surface emitting laser array as a first embodiment will be described with reference to FIGS. 1 to 5.
FIG. 1 is a plan view of a surface emitting laser array 2 according to this embodiment.
The surface emitting laser array 2 includes a first surface emitting laser 6 on a GaAs (gallium arsenide) substrate 4, and a second surface emitting laser having a polarization direction of emitted light different from that of the first surface emitting laser 6. It has a construction in which a plurality of 8 and 8 are respectively built.
Here, the term “fabrication” means fabrication by a micromachining technique to which a semiconductor manufacturing technique is applied.
Four first surface emitting lasers 6 are arranged in one row to form a first surface emitting laser group 10. Similarly, four second surface emitting lasers 8 are also arranged in one row to form a second surface emitting laser 8. The surface emitting laser group 12 of FIG.

The first surface emitting laser group 10 and the second surface emitting laser group 12 are alternately arranged in a direction orthogonal to the column direction.
Electrode pads 14 are individually arranged corresponding to the plurality of first surface emitting lasers 6 and second surface emitting lasers 8, respectively, and wiring 16 electrically connects between the respective surface emitting lasers and electrode pads 14. It is connected to the.

As shown in FIG. 2A, in the first surface-emitting laser 6, a portion of the upper DBR (distributed Bragg reflector) layer 34 as a reflector, which is surrounded by the electrode 40 above the mesa, is periodically arranged. It has a fine microstructure 18.
As shown in FIG. 2B, in the second surface emitting laser 8 as well, the periodic fine structure 22 is similarly formed in the portion of the upper DBR layer 34 as a reflecting mirror, which is surrounded by the electrode 40 above the mesa. Have
The portion where the periodic fine structure is formed may be the whole or a part of the upper DBR layer 34.

In the fine structure 18 of the first surface-emitting laser 6, flat plates having a plane parallel to the first direction (Z direction) are periodically arrayed in a second direction (X direction) orthogonal to the first direction. It has a structure.
In the fine structure 22 of the second surface emitting laser 8, flat plates having a plane parallel to the first direction (Z direction) are periodically arranged in the second direction (Y direction) orthogonal to the first direction. It has a structure.
That is, in the first surface emitting laser 6 and the second surface emitting laser 8, the arrangement directions of the flat plate structures in the microstructure are orthogonal to each other and the cycle directions are different.

FIG. 3 is a cross-sectional view of the first surface emitting laser 6 taken along the line AA′ in FIG.
The first surface emitting laser 6 includes a buffer layer 20, a lower DBR layer 24 as a reflecting mirror, a lower spacer layer 26, an active layer 28, an upper spacer layer 30, a selective oxidation layer 32, and a reflecting mirror on the substrate 4. The upper DBR layer 34, the contact layer 36, the protective layer 38, and the electrode 40 provided so as to contact the contact layer 36 with the protective layer 38 interposed therebetween.
The upper DBR layer 34 and the lower DBR layer 24 are located on both sides of the active layer 28 in the arrangement direction with the active layer 28 in between.
In FIG. 3, reference numeral 42 indicates an electrode arranged below the substrate 4.

The upper DBR layer 34 has a structure of a multilayer film reflecting mirror in which low refractive index layers 34a and high refractive index layers 34b are alternately laminated in the first direction (Z direction).
Similarly, the lower DBR layer 24 also has a structure of a multilayer film mirror in which low-refractive index layers 24a and high-refractive index layers 24b are relatively alternately laminated in the first direction (Z direction). There is.
The second surface emitting laser 8 has the same configuration as the first surface emitting laser 6 except for the difference in the periodic direction of the fine structure.

The microstructure 18 formed in the upper DBR layer 34 of the first surface emitting laser 6 will be described.
As shown in FIG. 4, a fine structure in which flat plates 44 having different refractive indexes, which originally do not have birefringence characteristics, are arranged sufficiently smaller than the wavelength (λ) of light, that is, a period smaller than λ/2 has a birefringence characteristic. Is known to occur (Principle of Optics, Max Born and Emil Wolf, PERGAMON PRESS LTD.).
The refractive index n _{// of the} light whose polarization direction is parallel to the flat plate 44 and the refractive index n _{⊥ of the} light perpendicular _thereto are expressed by the equations (1) and (2), respectively.

In formula (1) and formula (2), n ₁ and n ₂ are the refractive index of the flat plate and the refractive index of the substance filling the space between the flat plates, respectively.
t is the duty ratio of the fine structure and is represented by the equation (3).

As described above, the flat plate material (refractive index), the material filling the space between the flat plates (refractive index), the duty ratio of the fine structure, and the refractive index n _{// of the} light whose polarization direction is parallel to the flat plate and the vertical direction to the flat plate. The refractive index _{n⊥ of} light can be controlled.
Therefore, the light whose polarization direction is parallel to the flat plate and the light perpendicular to the flat plate have different optical lengths and can be controlled to arbitrary values.
The microstructures 18 and 20 are also formed based on this principle.

In the first surface emitting laser 6, the fine structure 18 of the upper DBR layer 34 is provided with the low refractive index layer 34a and the high refractive index layer 34b for the light of the first polarization direction in which the polarization direction is parallel to the flat plate. The optical thickness is configured to be ¼ of the oscillation wavelength λ.
Further, the fine structure 18 of the upper DBR layer 34 is provided with the optical thicknesses of the low refractive index layer 34a and the high refractive index layer 34b for the light of the other second polarization direction in which the polarization direction is perpendicular to the flat plate. Is smaller than 1/4 of the oscillation wavelength.
Further, for light in the second polarization direction, the difference in refractive index between the low-refractive index layer 34a and the high-refractive index layer 34b results in low refraction for light in the first polarization direction in which the polarization direction is parallel to the flat plate. The refractive index layer 34a and the high refractive index layer 34b are configured to have a smaller refractive index difference.
The same applies to the second surface emitting laser 8.

As a result, in the first surface-emitting laser 6, the upper DBR layer 34 functions as a reflecting mirror with respect to light in the first polarization direction in which the polarization direction is parallel to the flat plate, so that laser oscillation occurs and laser light is emitted. Is ejected.
On the other hand, the upper DBR layer 34 hardly reflects the light in the second polarization direction whose polarization direction is perpendicular to the flat plate, so that laser oscillation does not occur and laser light is not emitted.

The optical thicknesses of the low refractive index layer 34a and the high refractive index layer 34b for the light of the first polarization direction and the light of the second polarization direction are not limited to the above.
That is, the optical thicknesses of the low-refractive index layer 34a and the high-refractive index layer 34b are (2n-1)λ/4 (n is a natural number) for the light in the first polarization direction, and For the light in the polarization direction, it may be different from (2n−1)λ/4 (n is a natural number).

As described above, the first surface-emission laser diode 6 and the second surface-emission laser diode 8 are formed so that the periodic directions of the fine structures are different from each other, and thus the first surface-emission laser group 10 is formed. It is possible to emit laser light whose polarization directions are orthogonal to each other by the surface emitting laser group 12 of 2 and 2.

In the surface emitting laser array 2 in the present embodiment, the low refractive index layer 34a is formed of a material (Al0.9Ga0.1As) and has a thickness of 72.2 nm.
The high refractive index layer 34b is made of a material (Al0.3Ga0.7As) and has a thickness of 64.1 nm.
As shown in FIG. 4, a groove having a width w2 of 75 nm is formed at a cycle of 300 nm on the upper DBR layer 34 in which 40 layers of the low refractive index layer 34a and the high refractive index layer 34b are alternately laminated, and the width w1 of the flat plate 44 is formed. Form a fine structure of 225 nm.
The height d of the flat plate 44 in FIG. 4 corresponds to the height of the upper DBR layer 34.

The optical thickness is obtained by multiplying the thickness of a certain layer of the multilayer film forming the DBR by the refractive index of the material forming the layer.
Since the oscillation wavelength of the surface-emission laser of this embodiment is 780 nm, the first surface-emission laser 6 has the low-refractive index layer 34a for the light in the first polarization direction in which the polarization direction is parallel to the flat plate. The values of the refractive index of the high refractive index layer 34b are 2.70 and 3.04, respectively, and the optical thicknesses of the low refractive index layer and the high refractive index layer are 1/4 of the oscillation wavelength.
Therefore, the upper DBR layer 34 functions as a reflection layer, and laser oscillation is performed to emit laser light whose polarization direction is parallel to that of the flat plate.

On the other hand, for light in the second polarization direction in which the polarization direction is perpendicular to the flat plate, the refractive index values of the low refractive index layer 34a and the high refractive index layer 34b are 1.74 and 1.79, respectively. The thickness is smaller than 1/4 of the oscillation wavelength.
The difference in refractive index between the low refractive index layer 34a and the high refractive index layer 34b is 0.05, which is smaller than 0.34 when the polarization direction is parallel to the flat plate.
Therefore, since the upper DBR layer 34 does not function as a reflection layer, laser oscillation does not occur and laser light whose polarization direction is perpendicular to the flat plate is not emitted.

In the second surface-emission laser 8, the periodic direction of the fine structure is orthogonal to that of the first surface-emission laser 6, so that the polarization direction is orthogonal to the light emitted from the first surface-emission laser 6. The light is emitted.

The manufacturing process of the surface emitting laser array 2 in the present embodiment will be described with reference to FIG.
First, the buffer layer 20, the lower DBR layer 24, the lower spacer layer 26, the active layer 28, the upper spacer layer 30, the selective oxidation layer 32, and the upper DBR are formed on the GaAs substrate 4 by, for example, the MOCVD method or the MBE method. The layer 34 and the contact layer 36 are crystal-grown (a).
Using the square resist pattern formed by the photolithography process as a mask, the lower spacer layer 26 is etched halfway by dry etching to form a square mesa shape (b).
A heat treatment is performed in water vapor to oxidize the selectively oxidized layer 32 from around the mesa to form an oxidized confinement structure (c).
A line & space pattern is formed on the upper surface of the mesa by, for example, an EB drawing method or an imprint method, in which straight lines (lines) having a certain width are continuously arranged at regular intervals (spaces). Here, a line and space pattern having a cycle of 300 nm is formed of resin.

At this time, the first surface emitting laser group 10 and the second surface emitting laser group 12 shown in FIG. 1 are formed by changing the cycle direction of the line & space pattern by 90°.
Next, using the line & space pattern as a mask, the periodic fine structures 18 and 22 are formed on the upper surface of the mesa by a dry etching method (d).
For example, a protective layer 38 of SiN film is formed on the entire surface by the CVD method, a window pattern is formed on the upper portion of the mesa, and the window is opened by etching by wet etching (e).
An electrode pattern is formed by a photolithography process, an electrode material is vapor-deposited, lift-off is performed to form an electrode 40, then the back surface of the GaAs substrate 4 is polished to thin the substrate 4, and an electrode on the back surface is deposited by vapor deposition. 42 is formed and heat-treated (f).

Through the above steps, the surface emitting laser array 2 according to this embodiment can be manufactured.
In FIG. 5, only one surface emitting laser of the surface emitting laser array 2 is shown, but other surface emitting lasers (not shown) are also formed at the same time.
That is, the first surface emitting laser group 10 and the second surface emitting laser group 12 are also formed at the same time.

With the above configuration, the specific polarization direction of the laser light that is randomly polarized can be easily processed by general micromachining technology without utilizing the anisotropic properties of the material itself such as the tilt direction of the substrate. It is possible to realize a surface emitting laser that reflects, amplifies and emits only the above light.
That is, a surface emitting laser having high polarization characteristics can be obtained by easy processing.

The method using the tilted substrate described in Patent Document 1 is relatively easy to manufacture and has a high orthogonal polarization suppression ratio. However, the polarization directions of all surface emitting lasers are the same on one substrate, and the planes having different polarization directions are used. It is difficult to build a light emitting laser.
For this reason, it is necessary to combine a surface emitting laser array having a plurality of surface emitting lasers having the same polarization direction with a surface emitting laser array having a plurality of surface emitting lasers having different polarization directions from the surface emitting laser. However, the accuracy of the combination of the two substrates is required.
In the method of forming anisotropic strain inside the mesa structure described in Patent Document 2, it is relatively easy to form surface emitting lasers having different polarization directions on the same substrate, but the orthogonal polarization suppression ratio There is a problem of being low.

Since the surface emitting laser according to the present embodiment does not utilize the anisotropic characteristics of the material itself such as the tilt direction of the substrate, a plurality of polarized lights having a high orthogonal polarization suppression ratio are emitted from the same substrate. be able to.
It is not necessary to form a surface emitting laser array in which two substrates are combined, and the problem of combination accuracy can be solved.

A second embodiment will be described based on FIGS. 6 to 8. The same parts as those in the above-described embodiment are denoted by the same reference numerals, and the description of the already-explained configuration and function will be appropriately omitted.
As shown in FIG. 6A, the first surface emitting laser 6′ according to the present embodiment has a periodic fine structure 18′ in the portion of the upper DBR layer 34 surrounded by the electrode 40 above the mesa. Have As shown in FIG. 6B, similarly, the second surface emitting laser 8′ also has a periodic fine structure 22′ in a portion of the upper DBR layer 34 surrounded by the electrode 40 above the mesa. ing.
In the first surface-emitting laser 6′, the portion surrounded by the electrode 40 on the upper side of the mesa is a region from which light of the multilayer film reflecting mirror is emitted, and the circular central portion 18a and the outside of the central portion 18a in the region. As shown in FIG. 7, the peripheral portion 18b located at is different in thickness of the flat plate.

The width of the flat plate 44 of the central portion 18a in the second direction is larger than λ/4 as shown in FIG. 4, and the width of the flat plate 44 of the peripheral portion 18b in the second direction is as shown in FIG. Is smaller than λ/4.
Specifically, in the central portion 18a, grooves having a width of 75 nm are formed in a cycle of 300 nm, and the flat plate 44 has a fine structure having a width of 225 nm.
In the peripheral portion 18b, grooves having a width of 225 nm are formed at a cycle of 300 nm, and the flat plate 44 has a fine structure having a width of 75 nm.

Since the oscillation wavelength of the surface emitting laser of the present embodiment is 780 nm, the central portion 18a has a low refractive index layer 34a and a high refractive index layer for the light of the first polarization direction in which the polarization direction is parallel to the flat plate. The values of the refractive index of 34b are 2.70 and 3.04, respectively, and the optical thicknesses of the low refractive index layer 34a and the high refractive index layer 34b are 1/4 of the oscillation wavelength.
Therefore, the upper DBR layer 34 functions as a reflection layer, and laser oscillation is performed to emit laser light whose polarization direction is parallel to that of the flat plate.
For light in the second polarization direction in which the polarization direction is perpendicular to the flat plate, the values of the refractive indices of the low refractive index layer 34a and the high refractive index layer 34b are 1.74 and 1.79, respectively, and the optical thickness Is less than 1/6 of the oscillation wavelength.
The difference in refractive index between the low refractive index layer 34a and the high refractive index layer 34b is 0.05, which is smaller than 0.34 when the polarization direction is perpendicular to the flat plate. Therefore, the upper DBR layer 34 does not function as a reflection layer, laser oscillation does not occur, and a flat laser beam having a polarization direction and a vertical laser beam are not emitted.

In the peripheral portion 18b, the values of the refractive indices of the low-refractive index layer 34a and the high-refractive index layer 34b are 1.76 and 1.93, respectively, for light in the first polarization direction in which the polarization direction is parallel to the flat plate. , The optical thickness is smaller than 1/6 of the oscillation wavelength.
The difference in refractive index between the low refractive index layer 34a and the high refractive index layer 34b is 0.17, which is smaller than 0.34 when the polarization direction is perpendicular to the flat plate.

Further, in the peripheral portion 18b, the values of the refractive indices of the low refractive index layer 34a and the high refractive index layer 34b are 1.13 and 1. 14, the optical thickness is smaller than 1/9 of the oscillation wavelength. The difference in refractive index between the low refractive index layer 34a and the high refractive index layer 34b is 0.01, which is smaller than 0.34 when the polarization direction is perpendicular to the flat plate.
Therefore, the peripheral portion 18b does not function as a reflection layer for both the light of the first polarization direction in which the polarization direction is parallel to the flat plate and the light of the second polarization direction in the vertical direction. Is not fired.

As a result, the light emitted from the surface-emission laser can be high-quality laser light with a single transverse mode, a constant polarization direction, and a circular cross-sectional shape.

As described above, in the present embodiment, the optical thicknesses of the low refractive index layer 34a and the high refractive index layer 34b in the central portion 18a are (2n-1) for the light in the first polarization direction. λ/4 (n is a natural number), which is different from (2n−1)λ/4 (n is a natural number) for light in the second polarization direction.

The optical thicknesses of the low-refractive index layer 34a and the high-refractive index layer 34b in the peripheral portion 18b are (2n−1)λ for both the light of the first polarization direction and the light of the second polarization direction. /4 (n is a natural number).
Further, the difference in the refractive index between the high refractive index layer 34b and the low refractive index layer 34a of the central portion 18a for the light of the second polarization direction is the difference between the high refractive index layer 34b of the central portion 18a for the light of the first polarization direction. Is smaller than the difference in refractive index between the low refractive index layer 34a and the low refractive index layer 34a.
Furthermore, the difference in the refractive index between the high refractive index layer 34b and the low refractive index layer 34a of the peripheral portion 18b with respect to the light of the first polarization direction is the difference between the high refractive index layer of the central portion 18a with respect to the light of the first polarization direction. It is smaller than the difference in refractive index between 34b and the low refractive index layer 34a.
In addition, the difference in refractive index between the high refractive index layer 34b and the low refractive index layer 34a of the peripheral portion 18b with respect to the light of the second polarization direction is the high refractive index layer of the central portion 18a with respect to the light of the first polarization direction. It is smaller than the difference in refractive index between 34b and the low refractive index layer 34a.

The second surface-emitting laser 8'has the same configuration as the first surface-emitting laser 6', except for the difference in the period direction of the fine structure.

In each of the above embodiments, at least one of the two reflecting mirrors of the lower DBR layer 24 and the upper DBR layer 34 reflects, amplifies and emits only light in a specific polarization direction (hereinafter, “specific configuration”). That is).
In contrast to the reflecting mirror having a specific structure, the other reflecting mirror does not have to have the DBR structure and may have only the external resonator. In this case, the external resonator is arranged at an external position facing the reflecting mirror having a specific structure with the active layer interposed therebetween.
Further, the other reflecting mirror may have a combination structure of a DBR structure and an external resonator. In short, it is only necessary to form an optical resonator with a reflecting mirror having a specific structure.
Further, in each of the above-described embodiments, in the upper DBR layer 34, which is a reflecting mirror having a specific structure, the microstructures 18, 20, and 45 have a structure in which grooves are present over the entire stacking direction, but the present invention is not limited to this.
That is, it can be appropriately set within a range in which the function of the specific configuration is obtained.

An optical scanning device as a third embodiment will be described with reference to FIG.
The optical scanning device 50 has a light source unit 52. The light source unit 52 has a configuration in which the surface emitting laser array 2 as the light source described in the first embodiment and the driver 54 that drives the surface emitting laser array 2 are mounted on the support substrate 56.
Laser light emitted from the surface-emission laser array 2 based on image information passes through a coupling lens mounted on the support substrate 56 together with the surface-emission laser array 2 and enters a polarization beam splitter 58 as a polarization separation element.
The polarization beam splitter 58 has a structure for separating the light according to the polarization direction of the light, and the laser light emitted from the first surface emitting laser 6 of the surface emitting laser array 2 and the second surface emitting laser 8 are provided. The optical path is separated from the laser light emitted from the.
The laser beam that has passed through the polarization beam splitter 58 passes through a polygon mirror 60 as a light deflector, a first scanning lens 62, a mirror 64, a second scanning lens 66, and a mirror 64, and is exposed as a surface to be scanned on the image carrier. It is incident on the body drums K1 and C1.

Therefore, writing can be performed from one surface emitting laser array to two different photosensitive drums.
Unlike the method of separating the light with the half mirror prism, the amount of light is not halved, so it is possible to use the light amount twice as compared with the method of separating the light with the half mirror prism.
Further, since it is not necessary to increase the interval between the surface emitting lasers that scan different photosensitive drums, the number of surface emitting lasers in the light source unit 52 can be increased.

In the present embodiment, a polygon mirror 60 having a two-stage structure in which the phases of two polygon mirrors are shifted and overlapped is used, and a first surface emitting laser group 10 and a second surface emitting laser group 12 of the surface emitting laser array 2 are used. Are alternately emitted to write on different photosensitive drums.
It is also possible to use a normal one-stage polygon mirror to simultaneously emit light from the first surface-emission laser group 10 and the second surface-emission laser group 12 and simultaneously write on different photosensitive drums. ..
By alternately emitting the first surface-emission laser group 10 and the second surface-emission laser group 12 of the surface-emission laser array 2, the drivers 54 can be alternately switched and used, and the driver 54 is halved. Therefore, the cost can be reduced.

In the present embodiment, the polarization beam splitter 58 that separates the laser light according to the polarization state of the laser light is arranged in front of the polygon mirror 60 to separate the laser light. Alternatively, it may be arranged at the rear stage of the scanning lens or the like.
However, it is necessary to change the optical system and the driving method (lighting method) according to the arrangement position of the polarization beam splitter 58.

FIG. 10 shows a schematic configuration of a color laser printer as an image forming apparatus according to the fourth embodiment.
The color laser printer has a tandem structure including a plurality of photosensitive drums.
The color laser printer includes a photoconductor drum K1 for black (K), a charger K2, a developing device K4, a cleaning unit K5, and a charging unit K6 for transfer, and a photoconductor drum C1 and a charger C2 for cyan (C). , A developing device C4, a cleaning means C5, and a transfer charging means C6.
Further, the color laser printer includes a photosensitive drum M1 for magenta (M), a charger M2, a developing device M4, a cleaning unit M5, a transfer charging unit M6, a photosensitive drum Y1 for yellow (Y), and a charging unit. The apparatus Y2, the developing unit Y4, the cleaning unit Y5, the transfer charging unit Y6, the optical scanning device 65, the transfer belt 68, and the fixing unit 70 are provided.

Light from the surface emitting laser for black is applied to the photosensitive drum K1 via the scanning optical system for black, and light from the surface emitting laser for cyan is passed through the scanning optical system for cyan to the photosensitive drum C1. Is irradiated.
Further, the light from the surface emitting laser for magenta is applied to the photoconductor drum M1 through the scanning optical system for magenta, and the light from the surface emitting laser for yellow is passed through the scanning optical system for yellow to the photoconductor. The drum Y1 is irradiated.

The optical scanning device 65 includes the optical scanning device 50 described in the second embodiment for each two colors, and also includes the surface emitting laser array 2 described in the first embodiment for each two colors. ..
The polygon mirror and the lens may be shared by the two optical scanning devices.
Each photoconductor drum rotates in the direction of the arrow in FIG. 10, and a charger, a developing device, a transfer charging unit, and a cleaning unit are sequentially arranged around the photoconductor drum in the rotational direction.
Each charger uniformly charges the surface of the corresponding photoconductor drum. The surface of the photoconductor drum charged by the charger is irradiated with a beam by the optical scanning device 65, and an electrostatic latent image is formed on the photoconductor drum.

Then, a toner image is formed on the surface of the photosensitive drum by the corresponding developing device. Further, the corresponding transfer charging means transfers the toner image of each color onto the recording paper, and finally the fixing means 70 fixes the image on the recording paper.
In a tandem type color machine, color misregistration of each color may occur due to mechanical accuracy or the like, but since the optical scanning device 65 has a two-dimensional array of high-density light emitting units, the light emitting unit (surface It is possible to improve the correction accuracy of the color misregistration of each color by selecting (light emitting laser).

Further, the image carrier may be an image forming apparatus using a silver salt film. In this case, a latent image is formed on the silver salt film by optical scanning, and this latent image can be visualized by a process equivalent to the developing process in a normal silver salt photographic process.
Then, the image can be transferred onto the photographic paper by a process similar to the printing process in the normal silver salt photographic process. Such an image forming apparatus can be implemented as an optical plate making apparatus or an optical drawing apparatus for drawing a CT scan image or the like.
Further, the image carrier may be an image forming apparatus using a coloring medium (positive photographic paper) that develops color by the thermal energy of the beam spot.
In this case, a visible image can be directly formed on the image carrier by optical scanning.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the specific embodiment, and unless otherwise specified in the above description, the invention described in the claims is not limited thereto. Various modifications and changes are possible within the scope of the purpose.
The effects described in the embodiments of the present invention merely exemplify the most suitable effects that arise from the present invention, and the effects according to the present invention are limited to those described in the embodiments of the present invention. is not.

2 surface emitting laser array 6, 6'first surface emitting laser as surface emitting laser 8, 8'second surface emitting laser as surface emitting laser 10 first surface emitting laser group 12 second surface emitting laser Group 18, 22, 18', 22' Periodic fine structure as a periodic structure 18a, 22a Central part 18b, 22b Peripheral part 24 Lower DBR layer as a reflector 28 Active layer 34 Upper DBR layer as a reflector 34a Low Refractive Index Layer 34b High Refractive Index Layer 44 Flat Plate 50, 65 Optical Scanning Device 58 Polarization Beam Splitter as Polarization Separation Element 60 Polygon Mirror as Optical Deflector 62 First Scan Lens as Scanning Optical System 66 Scanning Optical System Second scanning lens K1, C1, M1, Y1 Photoreceptor drum as image carrier

JP 2001-60739 A Japanese Patent No. 4752201

Claims (12)

An active layer,
Two reflectors located on both sides of the active layer,
Equipped with
A surface emitting laser which emits light in a direction parallel to the arrangement direction of the active layer and the two reflecting mirrors,
At least one of the two reflecting mirrors is periodically arranged in a direction parallel to an upper distributed Bragg reflecting mirror layer in which a relatively low refractive index layer and a relatively high refractive index layer are alternately laminated. A multi-layered film mirror having a fine structure made of flat plates in which various grooves are formed and arranged at a cycle smaller than 1/2 of the oscillation wavelength λ ,
The optical thicknesses of the low-refractive index layer and the high-refractive index layer differ depending on the case of light in the first polarization direction and the case of light in the second polarization direction orthogonal to the first polarization direction. ,
When the wavelength of the light emitted by the surface emitting laser is λ, the optical thicknesses of the low refractive index layer and the high refractive index layer of the multilayer-film reflective mirror in the central portion of the region where the light is emitted are: (2n-1)λ/4 (n is a natural number) for light in the first polarization direction, and (2n-1)λ/4 (n is a natural number) for light in the second polarization direction. And the optical thicknesses of the low refractive index layer and the high refractive index layer in the peripheral portion located outside the central portion are equal to the light in the first polarization direction and the light in the second polarization direction. also for any (2n-1) λ / 4 (n is a natural number) the surface emitting laser that different from the. The surface emitting laser according to claim 1,
When the wavelength of the light emitted from the surface emitting laser is λ, the optical thicknesses of the low refractive index layer and the high refractive index layer are (2n−1)λ with respect to the light of the first polarization direction. /4 (n is a natural number), which is different from (2n-1)?/4 (n is a natural number) for light in the second polarization direction. The surface emitting laser according to claim 2,
The difference in the refractive index between the high refractive index layer and the low refractive index layer with respect to the light in the second polarization direction is the refractive index between the high refractive index layer and the low refractive index layer with respect to the light in the first polarization direction. Surface-emitting laser smaller than the difference of. The surface emitting laser according to claim 1,
The difference in refractive index between the high refractive index layer and the low refractive index layer in the central portion with respect to light in the second polarization direction is the difference between the high refractive index layer in the central portion and light with respect to the light in the first polarization direction. Smaller than the difference in refractive index from the low refractive index layer, and
The difference in refractive index between the high refractive index layer and the low refractive index layer in the peripheral portion with respect to the light in the first polarization direction is equal to the high refractive index layer in the central portion with respect to the light in the first polarization direction. Smaller than the difference in refractive index from the low refractive index layer, and
The difference in the refractive index between the high refractive index layer and the low refractive index layer in the peripheral portion with respect to the light in the second polarization direction is the difference between the high refractive index layer in the central portion and the light with respect to the light in the first polarization direction. A surface emitting laser having a refractive index smaller than that of the low refractive index layer . An active layer,
Two reflectors located on both sides of the active layer,
A surface emitting laser which emits light in a direction parallel to the arrangement direction of the active layer and the two reflecting mirrors,
At least one of the two reflecting mirrors is arranged on the upper distributed Bragg reflecting mirror layer in which relatively low refractive index layers and high refractive index layers are alternately laminated in a direction parallel to the laminating direction. A multilayer-film reflective mirror having a fine structure made of flat plates in which grooves are formed and arranged at a cycle smaller than 1/2 of the oscillation wavelength λ,
In the multilayer-film reflective mirror, a plurality of flat plates having a plane parallel to a first direction, which is a stacking direction of the low refractive index layer and the high refractive index layer, are arranged in a second direction orthogonal to the first direction. It has an arrayed periodic structure,
If the wavelength of the light emitted from the surface emitting laser is λ,
A surface emitting laser in which the width of the flat plate in the second direction is larger than λ/4 . The surface emitting laser according to claim 5,
A surface emitting laser which emits light polarized in a first polarization direction parallel to the flat plate . The surface emitting laser according to claim 5 or 6,
If the wavelength of the light emitted from the surface emitting laser is λ,
The surface emitting laser , wherein the periodic structure has a period smaller than λ/2 . The surface emitting laser according to claim 5 ,
A surface emitting laser in which a thickness of the flat plate in a central portion of a region of the multilayer film reflecting mirror where light is emitted is different from a thickness of the flat plate in a peripheral portion of a region of the multilayer film reflecting mirror where light is emitted . The surface emitting laser according to claim 8 ,
If the wavelength of the light emitted from the surface emitting laser is λ,
A surface emitting laser in which the width of the flat plate in the central portion in the second direction is larger than λ/4 and the width of the flat plate in the peripheral portion in the second direction is smaller than λ/4 . A plurality of surface emitting lasers according to any one of claims 1 to 9 ,
These surface emitting lasers are surface emitting laser arrays in which the emitted light has different polarization directions . A light source,
A polarization separation element for separating the optical path of the light from the light source,
An optical deflector for deflecting the light separated by the polarization separation element,
A scanning optical system for irradiating the surface to be scanned with the light deflected by the optical deflector,
Have
An optical scanning device in which the light source is the surface emitting laser array according to claim 10 . A plurality of image carriers,
An optical scanning device that optically scans the plurality of image carriers based on image information,
Equipped with
An image forming apparatus, wherein the optical scanning device is the optical scanning device according to claim 11 .

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