JP2013051277A - Surface emitting laser, surface emitting laser array, optical scanner and image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface emitting laser of high yield and high reliability.SOLUTION: A surface emitting laser emitting laser beams in a direction perpendicular to a substrate, includes a transparent film formed on a peripheral part around a center part of emission of the laser beams on an outgoing surface outgoing the laser beams, by a dielectric film for reducing a reflectance ratio than that of the center part. The transparent film is split into more than one portion and split transparent film portions are located with respect to the emission center of the laser beams, on both sides to become polarization direction of the laser beams, and on both sides to become a direction orthogonal to the polarization direction, respectively.

Description

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

  A surface emitting laser (VCSEL: Vertical Cavity Surface Emitting Laser) is a semiconductor laser that emits light in a direction perpendicular to a substrate, and can be easily integrated two-dimensionally. Compared with a light emitting laser, the power consumption is about an order of magnitude less, and more light sources can be integrated two-dimensionally.

  Applications of surface emitting lasers include light sources for optical writing of image forming apparatuses (such as printers), light sources for recording / reproducing optical disks, and optical transmission systems such as LAN (Local Area Network) using optical fibers. Examples include a light source, a light source for light transmission between boards, a light source for light transmission between chips, and a light source for light transmission within a chip in an optical integrated circuit. By the way, light (emitted light) emitted from a surface emitting laser for these uses is usually required to have a circular cross-sectional shape of a light spot, a constant deflection direction, and the like.

  In order to make the cross-sectional shape of the light spot of the emitted light circular, it is necessary to suppress high-order transverse mode oscillation. For example, in Patent Document 1, an emission window of a laser beam is formed by providing a dielectric film transparent to the oscillation wavelength of the laser beam in a part of the opening of the surface emitting laser, and the planar view shape of the emission window Discloses a method of suppressing the transverse mode of laser light. In addition, Patent Documents 2 to 6 disclose the control of the transverse mode of laser light, but these do not control the polarization.

  As for polarization control of emitted light, for example, Patent Document 7 discloses a method of aligning polarization by providing discontinuous portions in the body of a device. In addition, Patent Documents 8 and 9 also disclose polarization control.

  Further, as a method for achieving both higher-order transverse mode oscillation control and polarization direction control, for example, Patent Document 10 discloses that a quadrilateral current injection region provided in the lower DBR reflective layer and an upper DBR reflective layer are provided. Polarization is controlled by the light exit port and a pair of trenches provided between them, and the transverse mode adjustment layer is provided corresponding to the light exit port, and the reflectance of the peripheral region is that of the central region. A method of controlling the transverse mode by providing a transverse mode adjusting layer that is lower than the above is disclosed. In addition, Patent Documents 11 to 16 disclose a method for achieving both higher-order transverse mode oscillation control and polarization direction control.

  By the way, when a surface emitting laser is used as a writing light source of an image forming apparatus, normally, only the central light portion of the emitted laser beam is used for writing, and the outer periphery of the emitted laser beam is used for detecting the output of the laser beam. Used. For this reason, the profile (how to spread) of the laser beam changes during actual use, and there is a problem that the laser beam output at the use point cannot be converted.

  In general, when suppressing the higher-order transverse mode, the bimodality as shown in FIG. 1B (in a two-dimensional manner, a circular ring) is used for the unimodal fundamental mode as shown in FIG. However, when a surface emitting laser is used as a writing light source of an image forming apparatus, the unimodality is maintained as described above. But it can be a problem.

  In order to explain this, the beam profile of the surface emitting laser described in Patent Document 14 shown in FIG. 2 was measured after applying an energization load of 1.4 mW and 70 ° C. for a predetermined time. . The result is shown in FIG. 2 shows the top surface of the mesa of the surface emitting laser, and FIG. 2 shows the surface emitting laser in which a transparent layer 11A made of a dielectric film for lowering the reflectance inside the p-side electrode 13 and 11B is provided. The transparent layers 11A and 11B have a shape in which a ring zone (or an annulus) is divided into two, and the gap formed between the transparent layer 11A and the transparent layer 11B is the center of laser light emission. It is formed in the Y-axis direction (V direction). In the present embodiment, the interval of the gap between the transparent layer 11A and the transparent layer 11B is c. The direction perpendicular to the substrate surface is the Z axis.

  As shown in FIG. 3, it can be seen that although the beam profile is maintained unimodal, there is a difference between the beam spreading speed in the X direction and the beam spreading speed in the Y direction. That is, the beam spread in the Y direction shown in FIG. 3B is faster than that in the X direction shown in FIG. Such a difference in the spread speed of the beam profile in the X direction and the Y direction affects FFP (Far Field Pattern) -dHV which is a characteristic value indicating a difference between the vertical and horizontal directions of the far field profile. In some cases, the condition of characteristics as a light source used when writing an image is not satisfied. In addition, when the surface emitting laser is an array, it influences the characteristic (ΔFFP-V) indicating the far-field profile channel-to-channel deviation in the direction of rapid spread, and serves as a light source used when writing an image. There are cases where the characteristic conditions are not satisfied. In the present application, a change in characteristics due to energization may be described as energization aging.

  Since it is known that such a phenomenon remarkably occurs in a channel having a low single mode output, it is possible to select a surface emitting laser having such a small phenomenon based on the single mode output. Further, such a phenomenon does not always cause a serious problem due to the relationship with the life of the light source required in the image forming apparatus. However, if such a change with time of energization can be reduced, the yield can be reduced. The reliability can be improved. In the present application, the single mode output means an output value at which the strength of the fundamental mode with respect to the second mode is equal to or higher than a certain ratio, for example, 20 dB or higher.

  The present invention has been made in view of the above, and provides a surface emitting laser and a surface emitting laser array at a low cost by improving the yield of the surface emitting laser, and a highly reliable surface emitting laser and surface emitting laser. It is an object of the present invention to provide a laser array, and further to provide an optical scanning apparatus and an image forming apparatus having such a surface emitting laser or a surface emitting laser array having a high yield and high reliability. It is the purpose.

  The present invention relates to a surface emitting laser that emits laser light in a direction perpendicular to the substrate, and the center of the laser light emission center portion around the emission surface on which the laser light is emitted, A transparent film formed of a dielectric film for lowering the reflectance than the portion, the transparent film is divided into a plurality of parts, and the divided transparent film is a center of emission of the laser light On the other hand, the laser beam is present on both sides of the polarization direction of the laser beam and on both sides of the direction orthogonal to the polarization direction.

  According to the present invention, since the energization change over time, that is, the spread of the beam profile in the energized state can be reduced, the yield of the surface emitting laser can be improved, and the surface emitting laser and the surface emitting laser array can be improved. Can be provided at low cost. Therefore, a highly reliable surface emitting laser and surface emitting laser array can be provided. Further, by using such a surface emitting laser, it is possible to provide an optical scanning device and an image forming apparatus that are low in cost and high in reliability.

Explanatory drawing of fundamental mode and higher order mode of laser light emitted from surface emitting laser Top view of a conventional surface emitting laser mesa Explanatory drawing of the time-dependent change in the surface emitting laser shown in FIG. Correlation diagram between SMSR and FFP-H and FFP-V in the surface emitting laser shown in FIG. Correlation diagram between distance c between transparent films and single mode output in the surface emitting laser shown in FIG. Top view of other conventional surface emitting laser mesa Top view of surface emitting laser according to the first embodiment Structure diagram of surface emitting laser in the first embodiment Illustration of inclined substrate Structure diagram of main part of surface emitting laser according to the first embodiment Process drawing (1) of the manufacturing method of the surface emitting laser in 1st Embodiment Process drawing (2) of the manufacturing method of the surface emitting laser in 1st Embodiment Enlarged view of the top surface of the mesa in FIG. Process drawing (3) of the manufacturing method of the surface emitting laser in 1st Embodiment Process drawing (4) of the manufacturing method of the surface emitting laser in 1st Embodiment Enlarged view of the mesa upper surface in FIG. Process drawing of the manufacturing method of the surface emitting laser in 1st Embodiment (5) Process drawing of the manufacturing method of the surface emitting laser in 1st Embodiment (6) Correlation diagram between SMSR of surface emitting laser and FFP-H, FFP-V in the first embodiment Explanatory drawing (1) of the surface emitting laser array in 1st Embodiment Explanatory drawing (2) of the surface emitting laser array in 1st Embodiment Configuration diagram of laser printer in second embodiment The block diagram of the optical scanning device in 2nd Embodiment The block diagram of the color printer in 3rd Embodiment Explanatory drawing of the surface emitting laser array in 4th Embodiment Explanatory drawing of the optical transmission module in 4th Embodiment

  The form for implementing this invention is demonstrated below. In addition, about the same member etc., the same code | symbol is attached | subjected and description is abbreviate | omitted.

[First Embodiment]
As described above, in the surface emitting laser shown in FIG. 2, the energization change of the beam profile with time is different between the X direction (H direction) and the Y direction (V direction). FIG. 4 shows the SMSR (Sub-Mode Suppression Ratio), the X-direction far-field profile (FFP-H), and the Y-direction far-field profile in the surface emitting laser shown in FIG. This shows the relationship with (FFP-V). The SMSR is a logarithm of the ratio between the main wavelength peak intensity and the second wavelength peak intensity. By increasing the output, the intensity of the second peak is relatively increased and the SMSR value is decreased. As the SMSR value decreases, the beam profiles (FFP-H, FFP-V) expand. In general, since the beam shape at the second peak is wider than the beam shape at the main peak, it is considered that the beam profile widens as the second peak increases. The speed at which this beam profile spreads is faster in FFP-V than in FFP-H.

  FIG. 5 shows the result of measuring how the single mode output of the surface emitting laser shown in FIG. 2 changes from the value before the energization load after applying the energization load of 1.4 mW, 80 ° C. for 15 hours. Is shown. As shown in FIG. 2, the surface emitting laser was measured by producing a plurality of surface emitting lasers having different gaps c between the transparent film 11A and the transparent film 11B. In FIG. 5, the single mode output change rate of 1 means that the single mode output has not changed from the beginning. The value of the interval c is a value in the photomask used when the surface emitting laser is manufactured, and the distance between the patterns of the transparent film 11A and the transparent film 11B formed in the actual surface emitting laser is slightly different. In some cases, for convenience, the distance c between the patterns of the transparent film 11A and the transparent film 11B is described. As shown in FIG. 5, when the gap c between the transparent film 11A and the transparent film 11B by the photomask is narrow, the change in the single mode output is small, and when the gap c is wide, the change in the single mode output is large. There is a tendency. That is, as the interval c is wider, the energization change with time of the single mode output (and the SMSR serving as the index) is larger and tends to decrease. As described above, when the single mode output decreases, the beam profile widens, and as shown in FIG. 3 and the like, the FFP-V spreads faster than the FFP-H.

  Here, the transparent film 11A and the transparent film 11B formed on the VCSEL emission surface will be described. The transparent film 11A and the transparent film 11B are formed of a dielectric film having a predetermined film thickness so that the reflectance is relatively low, and thereby, in the central portion of the laser light emitted from the surface emitting laser. The reflectance is relatively higher than the peripheral portion. The peripheral portion is a portion around the central portion, and by forming a dielectric film having a predetermined film thickness on the peripheral portion, the central portion is more than the reflectance of the peripheral portion due to the influence of light interference. It can be formed so that the reflectance of the portion is high.

  In this way, the confinement in the peripheral portion can be weaker than the central portion of the laser beam, and the fundamental mode can be extracted preferentially. That is, the profile of the higher-order transverse mode is wider than the beam profile of the fundamental mode. Therefore, by forming the transparent film 11A and the transparent film 11B, the reflectance of the peripheral portion is lowered. It can be taken out preferentially.

  Also, as in the surface emitting laser shown in FIG. 2, by providing a gap or the like between the transparent film 11A and the transparent film 11B in a predetermined direction, the polarization direction of the surface emitting laser becomes, for example, the direction indicated by the arrow P. Can be controlled. That is, as shown in FIG. 6A, by providing a gap between the transparent film 11A and the transparent film 11B in the Y-axis direction, the polarization direction of the emitted laser light can be controlled to a predetermined direction. 6A has the same structure as that shown in FIG. Further, as shown in FIG. 6B, by providing a gap between the transparent film 11C and the transparent film 11D in the Y-axis direction, the polarization direction of the emitted laser light can be controlled to a predetermined direction. However, by providing the gap in the Y-axis direction in this way, the laser beam spreads faster in the direction in which the gap is provided, as shown in FIG. Therefore, as shown in FIG. 6C, by not providing a gap in the transparent film 11E, it is possible to prevent the laser beam from spreading quickly in either the X-axis direction or the Y-axis direction. However, in this case, the effect of aligning the polarization direction is weakened.

(Surface emitting laser)
Next, the surface emitting laser in the present embodiment will be described with reference to FIG. In the surface emitting laser according to the present embodiment, a plurality of, for example, four transparent films formed on the upper surface of the mesa have both sides in the X axis direction and the Y axis direction with reference to the emission center of the laser light of the surface emitting laser. The gaps are formed between the transparent films. The transparent film is formed of a dielectric film. After that, by further forming a protective layer made of a dielectric film, which will be described later, with a predetermined film thickness, the reflectance of the area where the transparent film is formed can be increased. It is formed to be low. In the present embodiment, the top surface of the mesa is formed in a square or rectangular shape, and the sides constituting the square or rectangle are formed along the X-axis direction or the Y-axis direction. Therefore, the X-axis direction and the Y-axis direction are orthogonal. In such a surface emitting laser, the polarization direction of the emitted laser light is the X-axis direction or the Y-axis direction.

  In the case shown in FIG. 7A, transparent films 111A and 111B are formed in the X-axis direction with respect to the laser light emission center 100A in the region surrounded by the p-side electrode 113 on the top surface of the mesa. Transparent films 111C and 111D are formed in the Y-axis direction.

  The regions where the transparent films 111A, 111B, 111C, and 111D are formed are formed with such a thickness that the reflectance is lower than the regions where the transparent films 111A, 111B, 111C, and 111D are not formed. . Further, there are gaps between the transparent film 111A and the transparent film 111C, between the transparent film 111A and the transparent film 111D, between the transparent film 111B and the transparent film 111C, and between the transparent film 111B and the transparent film 111D. It is formed, and this gap portion has a high reflectance.

  Thus, the transparent films 111A, 111B, 111C, and 111D are formed to have a shape divided into four by providing four gaps in the annular zone shape, and the transparent films 111A and 111B are It is formed long along the Y-axis direction, and the transparent films 111C and 111D are formed between the transparent film 111A and the transparent film 111B.

  As a result, the polarization direction of the surface emitting laser can be aligned in a certain direction, and the spread of the laser beam in the surface emitting laser is prevented from being accelerated in either the X-axis direction or the Y-axis direction. Can do. That is, by providing gaps between adjacent transparent films 111A, 111B, 111C, and 111D, the polarization direction can be made uniform, and the transparent films 111A, 111A, 111B can be aligned in the X-axis direction and Y-axis direction with respect to the laser emission center. By forming 111B, 111C, and 111D, it is possible to suppress the spread of the laser beam emitted from the surface emitting laser in either the X-axis direction or the Y-axis direction from being accelerated. Note that gaps formed between the transparent film 111A and the transparent film 111C, between the transparent film 111A and the transparent film 111D, between the transparent film 111B and the transparent film 111C, and between the transparent film 111B and the transparent film 111D. Are not formed in the X axis direction and the Y axis direction with respect to the laser light emission center 100A. That is, these gaps are formed in regions other than the regions in the X-axis direction and the Y-axis direction with respect to the laser light emission center 100A.

  In the case shown in FIG. 7B, transparent films 111E and 111F are formed in the Y-axis direction with respect to the laser light emission center 100A in the region surrounded by the p-side electrode 113 on the top surface of the mesa. Transparent films 111G and 111H are formed in the X-axis direction.

  The region where the transparent films 111E, 111F, 111G, and 111H are formed is formed with such a film thickness that the reflectance is lower than the region where the transparent films 111E, 111F, 111G, and 111H are not formed. . Further, there are gaps between the transparent film 111E and the transparent film 111G, between the transparent film 111E and the transparent film 111H, between the transparent film 111F and the transparent film 111G, and between the transparent film 111F and the transparent film 111H. It is formed, and this gap portion has a high reflectance.

  As described above, the transparent films 111E, 111F, 111G, and 111H are formed so as to be divided into four parts by providing four gaps in the annular shape, and the transparent films 111E and 111F are The transparent films 111G and 111H are formed long along the X-axis direction, and are formed between the transparent film 111E and the transparent film 111F.

  As a result, the polarization direction of the surface emitting laser can be aligned in a certain direction, and the spread of the laser beam in the surface emitting laser is prevented from being accelerated in either the X-axis direction or the Y-axis direction. Can do. That is, by providing gaps between the adjacent transparent films 111E, 111F, 111G, and 111H, the polarization direction can be made uniform, and the transparent films 111E, 111E, By forming 111F, 111G, and 111H, the spread of the laser beam emitted from the surface emitting laser in either the X-axis direction or the Y-axis direction can be suppressed. Note that gaps formed between the transparent film 111E and the transparent film 111G, between the transparent film 111E and the transparent film 111H, between the transparent film 111F and the transparent film 111G, and between the transparent film 111F and the transparent film 111H. Are not formed in the X axis direction and the Y axis direction with respect to the laser light emission center 100A. That is, these gaps are formed in regions other than the regions in the X-axis direction and the Y-axis direction with respect to the laser light emission center 100A.

  In the case shown in FIG. 7C, transparent films 111J and 111K are formed in the X-axis direction with respect to the laser light emission center 100A in the region surrounded by the p-side electrode 113 on the top surface of the mesa. Transparent films 111L and 111M are formed in the Y-axis direction.

  The region where the transparent films 111J, 111K, 111L, and 111M are formed is formed with such a thickness that the reflectance is lower than the region where the transparent films 111J, 111K, 111L, and 111M are not formed. . Further, there are gaps between the transparent film 111J and the transparent film 111L, between the transparent film 111J and the transparent film 111M, between the transparent film 111K and the transparent film 111L, and between the transparent film 111K and the transparent film 111M. It is formed, and this gap portion has a high reflectance.

  Thus, the transparent films 111J, 111K, 111L, and 111M have a square or rectangular shape having a square opening, that is, a shape that is divided into four by providing four gaps in the shape of a square. The transparent films 111J and 111K are formed long along the Y-axis direction, and the transparent films 111L and 111M are formed between the transparent film 111J and the transparent film 111K.

  As a result, the polarization direction of the surface emitting laser can be aligned in a certain direction, and the spread of the laser beam in the surface emitting laser is prevented from being accelerated in either the X-axis direction or the Y-axis direction. Can do. That is, by providing gaps between adjacent transparent films 111J, 111K, 111L, and 111M, the polarization direction can be made uniform, and the transparent films 111J, 111J, By forming 111K, 111L, and 111M, it is possible to suppress the spread of the laser beam emitted from the surface emitting laser in either the X-axis direction or the Y-axis direction from being accelerated. Note that gaps formed between the transparent film 111J and the transparent film 111L, between the transparent film 111J and the transparent film 111M, between the transparent film 111K and the transparent film 111L, and between the transparent film 111K and the transparent film 111M. Are not formed in the X-axis direction and the Y-axis direction with respect to the laser light emission center 100A. That is, these gaps are formed in regions other than the regions in the X-axis direction and the Y-axis direction with respect to the laser light emission center 100A.

  In the case shown in FIG. 7D, transparent films 111N and 111P are formed in the Y-axis direction with respect to the laser light emission center 100A in the region surrounded by the p-side electrode 113 on the top surface of the mesa. Transparent films 111Q and 111R are formed in the X-axis direction.

  The regions where the transparent films 111N, 111P, 111Q, and 111R are formed are formed with such a thickness that the reflectance is lower than the regions where the transparent films 111N, 111P, 111Q, and 111R are not formed. . Further, there are gaps between the transparent film 111N and the transparent film 111Q, between the transparent film 111N and the transparent film 111R, between the transparent film 111P and the transparent film 111Q, and between the transparent film 111P and the transparent film 111R. It is formed, and this gap portion has a high reflectance.

  Thus, the transparent films 111N, 111P, 111Q, and 111R have a square or rectangular shape having a square opening, that is, a shape that is divided into four by providing four gaps in a square shape. The transparent films 111N and 111P are formed long along the X-axis direction, and the transparent films 111Q and 111R are formed between the transparent film 111N and the transparent film 111P.

  As a result, the polarization direction of the surface emitting laser can be aligned in a certain direction, and the spread of the laser beam in the surface emitting laser is prevented from being accelerated in either the X-axis direction or the Y-axis direction. Can do. That is, by providing gaps between adjacent transparent films 111N, 111P, 111Q, and 111R, the polarization direction can be made uniform, and the transparent films 111N, XN and Y-axis directions can be aligned with respect to the laser emission center. By forming 111P, 111Q, and 111R, the spread of the laser beam emitted from the surface emitting laser in either the X-axis direction or the Y-axis direction can be suppressed. Note that gaps formed between the transparent film 111N and the transparent film 111Q, between the transparent film 111N and the transparent film 111R, between the transparent film 111P and the transparent film 111Q, and between the transparent film 111P and the transparent film 111R. Are not formed in the X-axis direction and the Y-axis direction with respect to the laser light emission center 100A. That is, these gaps are formed in regions other than the regions in the X-axis direction and the Y-axis direction with respect to the laser light emission center 100A.

  In the case shown in FIG. 7E, transparent films 111S and 111T are formed in the X-axis direction with respect to the laser light emission center 100A in the region surrounded by the p-side electrode 113 on the top surface of the mesa. Transparent films 111U and 111V are formed in the Y-axis direction.

  The regions where the transparent films 111S, 111T, 111U and 111V are formed are formed with such a film thickness that the reflectance is lower than the regions where the transparent films 111S, 111T, 111U and 111V are not formed. . Further, there are gaps between the transparent film 111S and the transparent film 111U, between the transparent film 111S and the transparent film 111V, between the transparent film 111T and the transparent film 111U, and between the transparent film 111T and the transparent film 111V. It is formed, and this gap portion has a high reflectance. As shown in FIG. 7A, the gap is not formed in parallel to the Y-axis direction, but is formed in a shape that extends radially from the center 100A of the laser beam issuance. Therefore, these gaps are not formed in parallel with the X-axis direction and the Y-axis direction. That is, these gaps are formed in regions other than the regions in the X-axis direction and the Y-axis direction with respect to the laser light emission center 100A.

  As described above, the transparent films 111S, 111T, 111U, and 111V are formed so as to be divided into four parts by providing four gaps in the annular shape, and the transparent films 111S and 111T are formed as follows: The transparent films 111U and 111V are formed long along the Y-axis direction, and are formed between the transparent film 111S and the transparent film 111T.

  As a result, the polarization direction of the surface emitting laser can be aligned in a certain direction, and the spread of the laser beam in the surface emitting laser is prevented from being accelerated in either the X-axis direction or the Y-axis direction. Can do. That is, by providing gaps between adjacent transparent films 111S, 111T, 111U, and 111V, the polarization direction can be made uniform, and the transparent films 111S, By forming 111T, 111U, and 111V, it is possible to suppress the spread of the laser beam emitted from the surface emitting laser in either the X-axis direction or the Y-axis direction from being accelerated.

  In the case shown in FIG. 7F, transparent films 111W and 111X are formed in the Y-axis direction with respect to the laser light emission center 100A in the region surrounded by the p-side electrode 113 on the top surface of the mesa. Transparent films 111Y and 111Z are formed in the X-axis direction.

  The region where the transparent films 111W, 111X, 111Y, and 111Z are formed is formed with such a thickness that the reflectance is lower than the region where the transparent films 111W, 111X, 111Y, and 111Z are not formed. . Further, there are gaps between the transparent film 111W and the transparent film 111Y, between the transparent film 111W and the transparent film 111Z, between the transparent film 111X and the transparent film 111Y, and between the transparent film 111X and the transparent film 111Z. It is formed, and this gap portion has a high reflectance. As shown in FIG. 7B, the gap is not formed in parallel to the Y-axis direction, but is formed in a shape that extends radially from the center 100A of the laser beam issuance. Therefore, these gaps are not formed in parallel with the X-axis direction and the Y-axis direction. That is, these gaps are formed in regions other than the regions in the X-axis direction and the Y-axis direction with respect to the laser light emission center 100A.

  As described above, the transparent films 111W, 111X, 111Y, and 111Z are formed so as to be divided into four parts by providing four gaps in the annular shape, and the transparent films 111W and 111X are formed as follows: The transparent films 111 </ b> Y and 111 </ b> Z are formed between the transparent film 111 </ b> W and the transparent film 111 </ b> X.

  As a result, the polarization direction of the surface emitting laser can be aligned in a certain direction, and the spread of the laser beam in the surface emitting laser is prevented from being accelerated in either the X-axis direction or the Y-axis direction. Can do. That is, by providing gaps between the adjacent transparent films 111W, 111X, 111Y, and 111Z, the polarization direction can be made uniform, and the transparent films 111W in the X-axis direction and the Y-axis direction with respect to the laser emission center. By forming 111X, 111Y, and 111Z, it is possible to suppress the spread of the laser beam emitted from the surface emitting laser in either the X-axis direction or the Y-axis direction from being accelerated.

(Structure of surface emitting laser)
Next, the structure of the surface emitting laser 100 in the present embodiment will be described with reference to FIG. 8A is a top view of the surface emitting laser 100, and FIG. 8B is a cross-sectional view of the surface emitting laser 100 taken along the alternate long and short dash line 8A-8B in FIG. 8A on the XZ plane. It is. In the present specification, as described above, the laser oscillation direction is defined as the Z-axis direction, and two directions perpendicular to each other in a plane perpendicular to the Z-axis direction are described as the X-axis direction and the Y-axis direction.

  The surface emitting laser 100 is a surface emitting laser having an oscillation wavelength of 780 nm, and includes a substrate 101, a buffer layer 102, a lower semiconductor DBR 103, a lower spacer layer 104, an active layer 105, an upper spacer layer 106, an upper semiconductor DBR 107, and a contact layer 109. Etc. Further, a mesa 110 is formed in part of the active layer 105, the upper spacer layer 106, the upper semiconductor DBR 107, the contact layer 109, and the lower spacer layer 104. A dielectric film 111 is formed on a part of the side surface and the upper surface of the mesa 110, and a p-side electrode 113 is formed on a part of the upper surface of the dielectric film 111 and the mesa 110. An n-side electrode 114 is formed on the back surface of the substrate 101. Further, in the region surrounded by the p-side electrode 113 on the contact layer 109 on the upper surface of the mesa 110, transparent films 111A, 111B, 111C, and 111D are formed, and the transparent films 111A, 111B, 111C, and 111D A protective layer 121 is formed on the contact layer 109. In addition, a current confinement layer 108 is formed between the upper spacer layer 106 and the upper semiconductor DBR 107 or in the upper semiconductor DBR 107, and the current confinement layer 108 is formed in the peripheral portion oxidized from the side surface of the mesa 110. It is formed by a selective oxidation region 108a and an unoxidized current confinement region 108b in the central portion.

  The surface of the substrate 101 is a mirror-polished surface, and as shown in FIG. 9A, the normal direction of the mirror-polished surface (main surface) is crystal orientation with respect to the crystal orientation [1 0 0] direction. [1 1 1] An n-GaAs single crystal substrate inclined 15 degrees (θ = 15 degrees) in the A direction. That is, the substrate 101 is a so-called inclined substrate. Here, as shown in FIG. 9B, the crystal orientation [0 −1 1] direction is arranged in the + X direction, and the crystal orientation [0 1 −1] direction is arranged in the −X direction.

  By using such a tilted substrate as the substrate 101, a polarization control action is attempted to stabilize the polarization direction in the X-axis direction.

  The buffer layer 102 is laminated on the + Z side surface of the substrate 101 and is a layer made of n-GaAs.

The lower semiconductor DBR 103 is stacked on the + Z side of the buffer layer 102, and includes a pair of a low refractive index layer 103a made of n-AlAs and a high refractive index layer 103b made of n-Al _0.3 Ga _0.7 As. It is formed by stacking 5 pairs. Between each refractive index layer, as shown in FIG. 10, a composition gradient layer having a thickness of 20 nm is provided in which the composition is gradually changed from one composition to the other composition in order to reduce the electrical resistance. It has been. Then, the thickness of each refractive index layer is set so that the thickness including ½ of the thickness of the adjacent composition gradient layer is an optical thickness of λ / 4 when the oscillation wavelength is λ. Has been. When the optical thickness is λ / 4, the actual thickness D of the layer is D = λ / 4n (where n is the refractive index of the medium of the layer).

The lower spacer layer 104 is stacked on the + Z side of the lower semiconductor DBR 103 and is a layer made of non-doped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P.

  The active layer 105 is stacked on the + Z side of the lower spacer layer 104. As shown in FIG. 10, the active layer 105 has a triple quantum well structure having three quantum well layers 105a and four barrier layers 105b. Is a layer. Each quantum well layer 105a is made of GaInAsP, which has a composition that induces 0.7% compressive strain, and has a band gap wavelength of about 780 nm. Each barrier layer 105b is made of GaInP which is a composition that induces a tensile strain of 0.6%.

The upper spacer layer 106 is laminated on the active layer 105 on the + Z side, and is a layer made of non-doped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P.

  The portion composed of the lower spacer layer 104, the active layer 105, and the upper spacer layer 106 is also called a resonator structure as shown in FIG. 10, and the thickness thereof is an optical thickness of one wavelength. Is set. The active layer 105 is provided at the center of the resonator structure at a position corresponding to the antinode in the standing wave distribution of the electric field so as to obtain a high stimulated emission probability.

The upper semiconductor DBR 107 is stacked on the + Z side of the upper spacer layer 106, and has a low refractive index layer 107a made of p-Al _0.9 Ga _0.1 As and high refraction made of p-Al _0.3 Ga _0.7 As. It is formed by laminating 25 pairs of the rate layer 107b.

  Between the refractive index layers in the upper semiconductor DBR 107, as shown in FIG. 10, there is provided a composition gradient layer in which the composition is gradually changed from one composition to the other composition in order to reduce electrical resistance. It has been. The film thickness in each refractive index layer is set so that the film thickness including ½ of the film thickness of the adjacent composition gradient layer is an optical thickness of λ / 4.

  In one of the low refractive index layers in the upper semiconductor DBR 107, a current confinement layer 108 made of p-AlAs is inserted with a thickness of 30 nm. The insertion position of the current confinement layer 108 is a position corresponding to the third node from the active layer 105 in the standing wave distribution of the electric field. In the current confinement layer 108, after the mesa 110 is formed, the selective oxidation region 108a is formed by performing thermal oxidation or the like. The current confinement layer 108 is formed by an oxidized selective oxidation region 108a and an unoxidized current confinement region 108b.

  The contact layer 109 is stacked on the + Z side of the upper semiconductor DBR 107 and is a layer made of p-GaAs.

  In addition, a structure in which the buffer layer 102, the lower semiconductor DBR 103, the lower spacer layer 104, the active layer 105, the upper spacer layer 106, the upper semiconductor DBR 107, the contact layer 109, and the like are stacked on the substrate 101 as described above is referred to as a “stacked body” for convenience. Also called.

(Method for manufacturing surface emitting laser)
Next, a method for manufacturing the surface emitting laser 100 will be described with reference to FIGS. Here, it is assumed that the desired polarization direction P (for example, P-polarized light) is the X-axis direction.

First, as shown in FIG. 11A, the stack is formed by crystal growth by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxial growth (MBE). For example, in the case of manufacturing by the MOCVD method, trimethylaluminum (TMA), trimethylgallium (TMG), and trimethylindium (TMI) are used as the group III material, and phosphine (PH ₃ ), Arsine (AsH ₃ ) is used. Further, carbon tetrabromide (CBr ₄ ) and dimethyl zinc (DMZn) are used as the raw material for the p-type dopant, and hydrogen selenide (H ₂ Se) is used as the raw material for the n-type dopant.

  Next, a square resist pattern (not shown) having a side of 25 μm is formed on the surface of the laminate. Specifically, a photoresist is applied to the surface of the produced laminate, and a resist pattern is formed by performing pre-baking, exposure using an exposure apparatus, and development.

Next, the stacked body in the region where the resist pattern is not formed is removed by ECR etching using Cl ₂ gas, using the resist pattern as a mask. In this embodiment mode, dry etching is performed until the lower spacer layer 104 is exposed.

  Next, as shown in FIG. 11B, the photomask is removed. Thereby, a quadrangular prism-shaped mesa structure (hereinafter abbreviated as “mesa” for convenience) 110 is formed.

  Next, as shown in FIG.11 (c), a laminated body is heat-processed in water vapor | steam. As a result, Al (aluminum) in the current confinement layer 108 is selectively oxidized from the outer peripheral portion serving as the side surface of the mesa 110. As a result, in the current confinement layer 108, a selectively oxidized region 108a in the peripheral portion and a non-oxidized current confinement region 108b in the central portion are formed. In this way, a so-called current confinement structure (oxidized constriction structure) is formed, and the current path flowing through the active layer can be limited only to the central portion of the mesa 110. That is, the current flows in the current confinement region 108b that is not oxidized, and the selective oxidation region 108a does not flow. Therefore, it is possible to concentrate the current on the central portion of the mesa 110. Such a current confinement region 108b is formed, for example, in a substantially square shape having a side width of about 4 μm to 6 μm.

Next, as shown in FIG. 12A, a dielectric film 111 made of SiN, which is a silicon nitride film, is formed by using a chemical vapor deposition method (CVD method). In this embodiment, the optical thickness of the dielectric film 111 is set to λ / 4. Specifically, since the refractive index n of SiN is 1.86 and the oscillation wavelength λ is 780 nm, the actual film thickness (= λ / 4n) is set to about 105 nm. The dielectric film 111 may be formed of a silicon oxide (SiO _x ) film, a titanium oxide (TiO _x ) film, or a silicon oxynitride (SiON) film in addition to SiN (SiN _x ).

  Next, as shown in FIG. 12B, an etching mask (masks M, MA, MB, MC, and MD) for opening a P-side electrode contact on the mesa 110 serving as a laser beam emission surface. Is made. Here, as an example, the mask M is fabricated so that the periphery of the mesa 110 and the periphery of the upper surface of the mesa 110 are not etched, and the transparent films 111A, 111B, 111C, and 111D are formed so as to surround the center of the upper surface of the mesa 110 in a ring shape. Masks MA, MB, MC, MD are prepared so as to be formed. For example, as shown in FIG. 13, the distance between the mask MA for forming the transparent film 111A and the masks MC and MD for forming the transparent films 111C and 111D, and the mask MB for forming the transparent film 111B, The distance L1 between the masks MC and MD for forming the transparent films 111C and 111D is 1 μm, and the width L2 in the X-axis direction of the mask MA for forming the transparent film 111A and the mask MB for forming the transparent film 111B is The mask MC for forming the transparent film 111C and the width L3 in the X-axis direction of the mask MD for forming the transparent film 111D are 2 μm, and the mask MC and the transparent film 111D for forming the transparent film 111C are formed. A mask MC for forming the transparent film 111C having a width L4 of 3.5 μm in the Y-axis direction of the mask MD for forming the transparent film 111C Interval L5 in the Y-axis direction of the mask MD for forming a transparent film 111D is formed to have a 4.5 [mu] m. FIG. 13 is an enlarged view of a portion of the mesa 110 in FIG. In the present embodiment, the masks M, MA, MB, MC, and MD are formed by resist patterns.

  Next, the dielectric film 111 in the region where the masks M, MA, MB, MC, and MD are not formed is etched with BHF (buffered hydrofluoric acid) to open a window for the P-side electrode contact.

  Next, as shown in FIG. 14, the masks M, MA, MB, MC, and MD are removed. Thus, a dielectric film 111 serving as a protective film is formed around the mesa 110 and around the top surface of the mesa 110, and the transparent films 111A, 111B, 111C, and 111D are formed on the contact layer 109 on the top surface of the mesa 110. Is formed. 14A is a top view on the XY plane in this step, and FIG. 14B is a cross-sectional view taken along the alternate long and short dash line 14A-14B in FIG. 14A. ) Is a cross-sectional view taken along the alternate long and short dash line 14C-14D in FIG.

  Next, a square resist pattern having a side of 10 μm is formed in a region serving as a light emitting portion (opening portion of the metal layer) above the mesa 110, and thereafter, p-side electrode material is deposited. As the p-side electrode material, a multilayer film made of Cr / AuZn / Au or a multilayer film made of Ti / Pt / Au is used.

  Next, as shown in FIG. 15, the p-side electrode 113 is formed by removing a part of the electrode material deposited in the region (emission region) serving as the light emitting portion by lift-off. The p-side electrode 113 is formed in a square shape on the upper surface of the mesa 110, and a region surrounded by the p-side electrode 113 is an emission region.

  FIG. 16 is an enlarged view of the upper part of the mesa 110. The shape of the emission region is a square whose side is L6 (for example, 10 μm). In the present embodiment, transparent films 111A, 111B, 111C, and 111D made of a transparent dielectric film made of SiN having an optical thickness of λ / 4 are disposed around the emission center 100A of the laser light in the emission region. The laser light emission center 100A is formed on both sides in the X-axis direction and both sides in the Y-axis direction.

Next, as shown in FIG. 17, a protective layer 121 made of SiN is formed by vapor phase chemical deposition (CVD) so as to have an optical thickness of 2λ / 4. That is, since the refractive index n of SiN is 1.86 and the oscillation wavelength λ is 780 nm, the actual film thickness (= 2λ / 4n) is set to about 210 nm. Thereby, the protective layer 121 is also formed on the transparent films 111A, 111B, 111C, and 111D. The protective layer 121 may be formed of a silicon oxide (SiO _x ) film, a titanium oxide (TiO _x ) film, or a silicon oxynitride (SiON) film in addition to SiN (SiN _x ).

  Next, as shown in FIG. 18, after polishing the back side of the substrate 101 to a predetermined thickness (for example, about 100 μm), an n-side electrode 114 is formed. Here, the n-side electrode 114 is a multilayer film made of AuGe / Ni / Au. 18A is a sectional view of the surface emitting laser 100 on the XZ plane, and FIG. 18B is a sectional view of the surface emitting laser 100 on the YZ plane.

  Next, ohmic conduction is established between the p-side electrode 113 and the n-side electrode 114 by annealing. Thereby, the surface emitting laser 100 in which the mesa 110 serves as a light emitting portion can be formed.

  Next, it cut | disconnects for every chip | tip and the surface emitting laser array chip | tip with which the surface emitting laser is arranged two-dimensionally is produced.

  In the surface emitting laser according to the present embodiment thus formed, the protective layer 121 is formed on the transparent films 111A, 111B, 111C, and 111D, and the optical film thickness of the dielectric film is as follows. The optical film thickness of the dielectric film at the center of the mesa 110 where the transparent films 111A, 111B, 111C, and 111D are not formed can be formed to be 2λ / 4.

  FIG. 19 shows the SMSR, the X-direction far field profile (FFP-H), and the surface emitting laser A in the present embodiment and the surface emitting laser B having the structure shown in FIG. The relationship with the far-field profile (FFP-V) of a Y direction is shown. As shown in FIG. 19, the surface emitting laser A in the present embodiment has a far field profile (FFP-H) in the X direction and a Y direction more than the surface emitting laser B having the structure shown in FIG. 2. The difference from the far field profile (FFP-V) can be reduced.

  In the above description, the case where the optical film thickness of the transparent films 111A, 111B, 111C, and 111D is 3λ / 4 has been described. However, the present invention is not limited to this, and the optical film thickness is 1 of the wavelength λ. It may be an odd multiple of / 4. Further, the case where the optical film thickness of the protective layer 121 is 2λ / 4 has been described. However, the present invention is not limited to this, and the optical film thickness is an even multiple of 1/4 of the wavelength λ. Good.

(Surface emitting laser array)
Next, a surface emitting laser array in which a plurality of surface emitting lasers 100 according to the present embodiment are formed will be described. Since surface emitting lasers can be easily arranged two-dimensionally, a surface emitting laser array can be easily formed by a plurality of surface emitting lasers.

  Hereinafter, the surface emitting laser array 300 will be described with reference to FIG. As shown in FIG. 20, this surface-emitting laser array 300 includes a plurality of (herein, 32 (4 × 8)) surface-emitting lasers 100 serving as light-emitting portions 200 on the same substrate in the main scanning direction. The interval c is 30 μm, and the interval d1 in the sub-scanning direction is 24 μm. The X-axis direction is the main scanning corresponding direction, and the Y-axis direction is the sub-scanning corresponding direction. The plurality of light emitting units 200 are arranged at equal intervals d2 when all the light emitting units 200 are orthogonally projected onto a virtual line extending in the Y-axis direction. Thus, the 32 light emitting units 200 are two-dimensionally arranged. In the present specification, the “light emitting part interval” means the distance between the centers of the two light emitting parts 200. 20 shows that the number of the light emitting units 200 is 32, the number of the light emitting units 200 may be plural, and for example, the number of the light emitting units 200 may be 40. . With such a surface emitting laser array 300, it is possible to simultaneously form 32 minute light spots having a circular shape and a high light density on a photosensitive drum described later.

  Further, in the surface emitting laser array 300, the intervals between the light emitting portions when the respective light emitting portions are orthogonally projected onto a virtual line extending in the sub-scanning corresponding direction are equal intervals d2, and therefore, a photosensitive later described by adjusting the lighting timing. It can be understood that the configuration is the same as the case where the light emitting units are arranged at equal intervals in the sub-scanning direction on the body drum. The writing interval in the main scanning direction can be easily controlled by the lighting timing of the light emitting unit.

  By the way, in the surface emitting laser array 300 according to the present embodiment, the groove between two adjacent light emitting units 200 is preferably 5 μm or more for electrical and spatial separation of each light emitting unit. This is because if it is too narrow, it becomes difficult to control etching during production. In addition, the size (length of one side) of the mesa constituting the light emitting unit 200 is preferably 10 μm or more. This is because if it is too small, heat will be accumulated during operation and the characteristics may be deteriorated.

  FIG. 21 shows a wiring structure in the surface emitting laser array 300. As described above, in the surface emitting laser array 300, the 32 light emitting units 200 arranged two-dimensionally and the 32 electrode pads 210 provided around the 32 light emitting units and corresponding to the light emitting units 200 are provided. Have. Each electrode pad 210 is electrically connected by the corresponding light emitting unit 200 and wiring member 220.

  The surface-emitting laser and the surface-emitting laser array in the present embodiment have little change with energization, that is, the change in the spread of the far-field profile (FFP-H) in the X direction and the far direction in the Y direction. Since the difference in change in the spread of the visual field profile (FFP-V) can be reduced, the lifetime can be extended and the reliability can be improved as compared with the conventional one.

  Further, instead of the surface emitting laser array 300 in which the surface emitting lasers are two-dimensionally arranged as described above, a surface emitting laser array in which the surface emitting lasers to be the light emitting units 200 are one-dimensionally arranged may be used.

[Second Embodiment]
Next, a second embodiment will be described. The present embodiment is a laser printer 1000 as an image forming apparatus using the surface emitting laser or the surface emitting laser array in the first embodiment.

  Based on FIG. 22, a laser printer 1000 in the present embodiment will be described. The laser printer 1000 according to this embodiment includes an optical scanning device 1010, a photosensitive drum 1030, a charging charger 1031, a developing roller 1032, a transfer charger 1033, a charge eliminating unit 1034, a cleaning unit 1035, a toner cartridge 1036, a paper feeding roller 1037, a feeding roller. A paper tray 1038, a registration roller pair 1039, a fixing roller 1041, a paper discharge roller 1042, a paper discharge tray 1043, a communication control device 1050, and a printer control device 1060 that comprehensively controls each of the above parts are provided. These are housed in predetermined positions in the printer housing 1044.

  The communication control device 1050 controls bidirectional communication with a host device (for example, a personal computer) via a network or the like.

  The photosensitive drum 1030 is a cylindrical member, and a photosensitive layer is formed on the surface thereof. That is, the surface of the photoconductor drum 1030 is a scanned surface. The photosensitive drum 1030 rotates in the direction indicated by the arrow X.

  The charging charger 1031, the developing roller 1032, the transfer charger 1033, the charge removal unit 1034, and the cleaning unit 1035 are each disposed in the vicinity of the surface of the photosensitive drum 1030. Then, along the rotation direction of the photosensitive drum 1030, the charging charger 1031 → the developing roller 1032 → the transfer charger 1033 → the discharging unit 1034 → the cleaning unit 1035 are arranged in this order.

  The charging charger 1031 uniformly charges the surface of the photosensitive drum 1030.

  The optical scanning device 1010 scans the surface of the photosensitive drum 1030 charged by the charging charger 1031 with a light beam modulated based on image information from the host device, and corresponds to the image information on the surface of the photosensitive drum 1030. A latent image is formed. The latent image formed here moves in the direction of the developing roller 1032 as the photosensitive drum 1030 rotates. The configuration of the optical scanning device 1010 will be described later.

  Toner cartridge 1036 stores toner, and this toner is supplied to developing roller 1032.

  The developing roller 1032 causes the toner supplied from the toner cartridge 1036 to adhere to the latent image formed on the surface of the photosensitive drum 1030 to visualize the image information. Here, the latent image to which the toner is attached (hereinafter also referred to as “toner image” for the sake of convenience) moves in the direction of the transfer charger 1033 as the photosensitive drum 1030 rotates.

  Recording paper 1040 is stored in the paper feed tray 1038. A paper feed roller 1037 is disposed in the vicinity of the paper feed tray 1038. The paper feed roller 1037 takes out the recording paper 1040 one by one from the paper feed tray 1038 and conveys it to the registration roller pair 1039. The registration roller pair 1039 temporarily holds the recording paper 1040 taken out by the paper supply roller 1037, and in the gap between the photosensitive drum 1030 and the transfer charger 1033 according to the rotation of the photosensitive drum 1030. Send it out.

  A voltage having a polarity opposite to that of the toner is applied to the transfer charger 1033 in order to electrically attract the toner on the surface of the photosensitive drum 1030 to the recording paper 1040. With this voltage, the toner image on the surface of the photosensitive drum 1030 is transferred to the recording paper 1040. The recording sheet 1040 transferred here is sent to the fixing roller 1041.

  In the fixing roller 1041, heat and pressure are applied to the recording paper 1040, whereby the toner is fixed on the recording paper 1040. The recording paper 1040 fixed here is sent to the paper discharge tray 1043 via the paper discharge roller 1042 and is sequentially stacked on the paper discharge tray 1043.

  The neutralization unit 1034 neutralizes the surface of the photosensitive drum 1030.

  The cleaning unit 1035 removes the toner remaining on the surface of the photosensitive drum 1030 (residual toner). The surface of the photosensitive drum 1030 from which the residual toner has been removed returns to the position facing the charging charger 1031 again.

  Next, the optical scanning device 1010 will be described with reference to FIG. The optical scanning device 1010 controls a light source unit 1100, a coupling lens and an aperture plate (not shown), a cylindrical lens 1113, a polygon mirror 1114, an fθ lens 1115, a toroidal lens 1116, two mirrors (1117, 1118), and the above-described units. A control device (not shown) for controlling the operation is provided. The light source unit 1100 includes the surface emitting laser or the surface emitting laser array in the first embodiment.

  The cylindrical lens 1113 condenses the light output from the light source unit 1100 in the vicinity of the deflection reflection surface of the polygon mirror 1114 via the mirror 1117.

  The polygon mirror 1114 is made of a regular hexagonal columnar member having a low height, and six deflection reflection surfaces are formed on the side surface. Then, it is rotated at a constant angular velocity in the direction indicated by the arrow Y by a rotation mechanism (not shown).

  Accordingly, the light emitted from the light source unit 1100 and condensed near the deflection reflection surface of the polygon mirror 1114 by the cylindrical lens 1113 is deflected at a constant angular velocity by the rotation of the polygon mirror 1114.

  The fθ lens 1115 has an image height proportional to the incident angle of light from the polygon mirror 1114, and moves the image surface of light deflected by the polygon mirror 1114 at a constant angular velocity with constant speed in the main scanning direction. The toroidal lens 1116 forms an image of the light from the fθ lens 1115 on the surface of the photosensitive drum 1030 via the mirror 1118.

  The toroidal lens 1116 is disposed on the optical path of the light beam through the fθ lens 1115. Then, the light beam that has passed through the toroidal lens 1116 is irradiated onto the surface of the photosensitive drum 1030 to form a light spot. This light spot moves in the longitudinal direction of the photosensitive drum 1030 as the polygon mirror 1114 rotates. That is, the photoconductor drum 1030 is scanned. The moving direction of the light spot at this time is the “main scanning direction”. The rotation direction of the photosensitive drum 1030 is the “sub-scanning direction”.

  The optical system arranged on the optical path between the polygon mirror 1114 and the photosensitive drum 1030 is also called a scanning optical system. In this embodiment, the scanning optical system includes an fθ lens 1115 and a toroidal lens 1116. Note that at least one folding mirror may be disposed on at least one of the optical path between the fθ lens 1115 and the toroidal lens 1116 and on the optical path between the toroidal lens 1116 and the photosensitive drum 1030.

  Since the laser printer 1000 in this embodiment uses the surface emitting laser or the surface emitting laser array in the first embodiment, the laser printer 1000 does not decrease the printing speed even if the writing dot density increases. Can be printed. Further, when the writing dot density is the same, the printing speed can be further increased.

  Further, in this case, since the polarization directions of the light beams from the respective light emitting units are stably aligned, the laser printer 1000 can stably form a high-quality image for a long period of time.

  In the description of the present embodiment, the case of the laser printer 1000 as the image forming apparatus has been described. However, the present invention is not limited to this.

  For example, an image forming apparatus that directly irradiates laser light onto a medium (for example, paper) that develops color with laser light may be used.

  Further, an image forming apparatus using a silver salt film as the image carrier may be used. 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 a developing process in a normal silver salt photographic process. Then, it can be transferred to photographic paper by a process equivalent to a printing process in a normal silver salt photographic process. Such an image forming apparatus can be implemented as an optical plate making apparatus or an optical drawing apparatus that draws a CT scan image or the like.

[Third Embodiment]
Next, a third embodiment will be described. The third embodiment is a color printer 2000 including a plurality of photosensitive drums.

  Based on FIG. 24, the color printer 2000 in this Embodiment is demonstrated. The color printer 2000 in the present embodiment is a tandem multicolor printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow). “Charging device K2, developing device K4, cleaning unit K5, and transfer device K6”, “photosensitive drum C1, charging device C2, developing device C4, cleaning unit C5, and transfer device C6” for cyan, and magenta “Photosensitive drum M1, charging device M2, developing device M4, cleaning unit M5, and transfer device M6” and yellow “photosensitive drum Y1, charging device Y2, developing device Y4, cleaning unit Y5, and transfer device Y6” ”, Optical scanning device 2010, transfer belt 2080, fixing unit 2030, and the like. It is equipped with a.

  Each photosensitive drum rotates in the direction of the arrow shown in FIG. 24, and a charging device, a developing device, a transfer device, and a cleaning unit are arranged around each photosensitive drum in the order of rotation. Each charging device uniformly charges the surface of the corresponding photosensitive drum. The surface of each photoconductive drum charged by the charging device is irradiated with light by the optical scanning device 2010, and a latent image is formed on each photoconductive drum. Then, a toner image is formed on the surface of each photosensitive drum by a corresponding developing device. Further, the toner image of each color is transferred onto the recording paper on the transfer belt 2080 by the corresponding transfer device, and finally the image is fixed on the recording paper by the fixing unit 2030.

  The optical scanning device 2010 has a light source unit including the surface emitting laser or the surface emitting laser array in the first embodiment for each color, and the optical scanning device 1010 described in the second embodiment. The same effect can be obtained. In addition, since the color printer 2000 includes the optical scanning device 2010, it is possible to obtain the same effect as the laser printer 1000 in the second embodiment.

  By the way, in the color printer 2000, color misregistration may occur due to manufacturing error or position error of each component. Even in such a case, since each light source of the optical scanning device 2010 is formed by the light source unit including the surface emitting laser or the surface emitting laser array in the first embodiment, the light emitting unit to be lit is selected. Thus, color misregistration can be reduced.

  Therefore, since the color printer 2000 according to the present embodiment uses the surface emitting laser or the surface emitting laser array according to the first embodiment, a high-quality image can be stably formed for a long period of time.

[Fourth Embodiment]
Next, a fourth embodiment will be described. This embodiment is a one-dimensional surface-emitting laser array that is a surface-emitting laser element in which surface-emitting lasers are arranged one-dimensionally.

The present embodiment will be described with reference to FIG. In this embodiment, a surface emitting laser element 3010 has a structure in which a plurality of surface emitting lasers 3100 are arranged one-dimensionally. Each surface emitting laser 3100 is provided with an electrode pad 3120. In the surface emitting laser 3100, a lower semiconductor DBR, a lower spacer layer, an active layer, an upper spacer layer, and an upper semiconductor DBR are formed on a substrate. A GaAs substrate is used as the substrate, and the lower semiconductor DBR has an n-GaAs high refractive index layer and an n-Al _0.9 Ga _0.1 As low optical film formed so as to have an optical film thickness of λ / 4. It is formed by alternately stacking 36.5 pairs of refractive index layers. The active layer is composed of three GaInNAs quantum well active layers and is formed so that the oscillation wavelength is 1.3 μm. The upper spacer layer, the lower spacer layer, and the barrier layer are made of GaAs. ing. The upper semiconductor DBR has 26 pairs of p-GaAs high-refractive index layers and p-Al _0.9 Ga _0.1 As low-refractive index layers alternately formed so that the optical film thickness is λ / 4. It is formed by forming. The current confinement layer is formed of AlAs having a thickness of 20 nm in the upper semiconductor DBR 5λ / 4 away from the resonator region constituted by the upper spacer layer, the active layer, and the lower spacer layer. In addition, the lowermost low refractive index layer of the upper semiconductor DBR is formed of p-Al _0.6 Ga _0.4 As different from other low refractive index layers, and between the current confinement layers, A p-Al _0.8 Ga _0.2 As intermediate layer having a thickness of 35 nm is provided.

  Next, an optical communication module having a structure combined with an optical fiber using the surface emitting laser element according to the present embodiment as a light source will be described. Specifically, as shown in FIG. 26, an optical fiber 3200 is provided corresponding to each surface emitting laser formed one-dimensionally on the surface emitting laser element 3010. As shown in the figure, by integrating a large number of uniform surface emitting lasers on the same substrate, for example, when applied to optical communication, data transmission by multiple beams can be easily performed simultaneously. High-speed communication can be performed. Further, since the surface emitting laser can be operated with low power consumption, even when incorporated in an apparatus such as a communication device, the surface emitting laser hardly generates heat and the temperature does not increase so much.

  In the present embodiment, the case where the surface emitting laser and the optical fiber are made to correspond to 1: 1 has been described, but a plurality of surface emitting lasers having different oscillation wavelengths are arranged in an array in one or two dimensions, By performing wavelength division multiplexing transmission, the transmission speed can be further increased.

  In this embodiment, since a highly reliable surface emitting laser element is used, a highly reliable optical transmission module can be obtained, and further, a highly reliable optical communication system can be realized. it can. This optical communication system is particularly preferably used for short-distance data communication such as home use, indoor use such as an office, and inside an apparatus.

  As mentioned above, although the form which concerns on implementation of this invention was demonstrated, the said content does not limit the content of invention.

100 Surface Emitting Laser Element 100A Laser Light Emission Center 101 Substrate 102 Buffer Layer 103 Lower Semiconductor DBR
104 Lower spacer layer 105 Active layer 106 Upper spacer layer 107 Upper semiconductor DBR
108 current confinement layer 108a selective oxidation region 108b current confinement region 109 contact layer 110 mesa 111 dielectric film 111A, 111B, 111C, 111D transparent film 121 protective layer 1000 laser printer (image forming apparatus)
1010 Optical scanning device 2000 Color printer (image forming apparatus)

Japanese Patent No. 3565902 Japanese Patent No. 4537658 JP 2005-44964 A Japanese Patent No. 4311610 JP 2009-188155 A Japanese Patent No. 3697903 Japanese Patent No. 3955925 JP-A-8-56049 JP 2008-28120 A JP 2007-201398 A Special table 2008-522388 gazette JP 2011-9963 A JP 2011-14869 A JP 2010-153768 A JP 2009-170508 A Japanese Patent No. 4621393

Claims (10)

In a surface emitting laser that emits laser light in a direction perpendicular to the substrate,
On the emission surface from which the laser beam is emitted, a peripheral portion around the central portion of the emission of the laser beam has a transparent film formed of a dielectric film for lowering the reflectance than the central portion. And
The transparent film is divided into a plurality of parts,
The divided transparent films are present on both sides of the laser light emission center on both sides of the laser light in the polarization direction and on both sides in the direction orthogonal to the polarization direction. A surface emitting laser characterized by the above.   The gap formed between the divided transparent films adjacent to each other is formed in a region other than the polarization direction of the laser beam and the direction orthogonal to the polarization direction with respect to the emission center of the laser beam. The surface emitting laser according to claim 1, wherein the surface emitting laser is provided. The transparent film is divided into four parts,
Among the divided transparent films, either a pair of transparent films existing in the polarization direction of the laser beam or a pair of transparent films existing in a direction orthogonal to the polarization direction The surface emitting laser according to claim 1, wherein the surface emitting laser is formed long in a polarization direction of the laser light or in a direction orthogonal to the polarization direction. The emission surface is an upper surface of a mesa whose upper surface is formed in a square or rectangular shape,
The surface emitting laser according to any one of claims 1 to 3, wherein the polarization direction is parallel to any one of the square and the rectangle. A protective layer formed of a dielectric film is formed on the emission surface including the transparent film,
The optical film thickness of the protective layer is an even multiple of 1/4 of the wavelength of the laser beam,
5. The surface emitting laser according to claim 1, wherein an optical film thickness of the transparent film is an odd multiple of ¼ of a wavelength of the laser beam. 6. The surface according to claim 1, wherein the protective layer and the transparent film are made of a material containing any one of SiN _x , SiO _x , TiO _x, and SiON. Light emitting laser.   A surface-emitting laser array, wherein a plurality of surface-emitting lasers according to claim 1 are formed. An optical scanning device that scans a surface to be scanned with light,
A surface-emitting laser according to any one of claims 1 to 6, or a light source having the surface-emitting laser array according to claim 7,
A light deflector for deflecting light from the light source;
A scanning optical system for condensing the light deflected by the light deflection unit on the surface to be scanned;
An optical scanning device comprising: An image carrier;
The optical scanning device according to claim 8, wherein the image carrier is scanned with light modulated according to image information;
An image forming apparatus comprising:   The image forming apparatus according to claim 9, wherein there are a plurality of the image carriers, and the image information is multicolor color information.

Images