JP2013191855A - Surface emitting laser element, surface emitting laser array, optical scanner and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface emitting laser element obtaining a stable polarization direction while controlling oscillation in a high-order transverse mode.SOLUTION: A surface emitting laser element comprises: a buffer layer 102, a lower semiconductor DBR 103, a lower space layer 104, an active layer 105, an upper space layer 106, an upper semiconductor DBR 107 and a contact layer 109 which are stacked on a substrate 101; a p-side electrode 113 provided on an emission surface from which laser beams are emitted so as to surround an emission region; and an n-side electrode 114 provided on the substrate 101 side. The emission region includes a transparent layer 111A and a transparent layer 111B which are transparent dielectric films and provided in two sub-regions (first sub-region, second sub-region) provided away from a central part of the emission region, for making reflectivity of each sub region be lower than reflectivity of the central part of the emission region. Each of the transparent layer 111A and the transparent layer 111B has an optical thickness of "oscillation wavelength/4".

Description

  The present invention relates to a surface emitting laser element, a surface emitting laser array, an optical scanning apparatus, and an image forming apparatus. More specifically, the present invention relates to a surface emitting laser element that emits laser light in a direction perpendicular to a substrate, a surface emitting laser array, The present invention relates to an optical scanning device having a surface emitting laser element or a surface emitting laser array, and an image forming apparatus including the optical scanning device.

  A vertical cavity surface emitting laser (Vertical Cavity Surface Emitting Laser) emits light in a direction perpendicular to a substrate, and is an edge emitting semiconductor laser device that emits light in a direction parallel to the substrate. In recent years, it has been attracting attention because of its low price, low power consumption, small size, suitable for two-dimensional devices, and high performance.

  As an application field of the surface emitting laser element, an optical writing light source (oscillation wavelength: 780 nm band) in a printer, a writing light source (oscillation wavelength: 780 nm band, 850 nm band) in an optical disk apparatus, and a LAN (Local Area) using an optical fiber are used. And a light source (oscillation wavelength: 1.3 μm band, 1.5 μm band) of an optical transmission system such as Network). Furthermore, it is also expected as a light source for light transmission between boards, within a board, between chips of an integrated circuit (LSI: Large Scale Integrated circuit), and within a chip of an integrated circuit.

  In these application fields, the light emitted from the surface emitting laser element (hereinafter also referred to as “emitted light”) needs to have (1) a circular cross-sectional shape and (2) a constant polarization direction. It is often said.

  In order to make the cross-sectional shape of the emitted light circular, it is necessary to suppress oscillation of higher-order transverse modes, and various attempts have been made (for example, see Patent Document 1).

  Various attempts have been made to control the polarization direction of emitted light (see, for example, Patent Document 2).

  Furthermore, it has been studied to achieve both higher-order transverse mode oscillation control and polarization direction control (see, for example, Patent Document 3 and Patent Document 4).

  However, the methods disclosed in Patent Literature 1 and Patent Literature 2 have the disadvantage that it is difficult to achieve both higher-order transverse mode oscillation control and polarization direction control. Further, in the method disclosed in Patent Document 3, there is a possibility that the electric resistance of the surface emitting laser element is increased or the life is decreased due to an increase in current density. Furthermore, the method disclosed in Patent Document 4 has the disadvantage that it is difficult to stabilize the various characteristics of the surface emitting laser element and the control characteristics of the high-order transverse mode.

  According to a first aspect of the present invention, there is provided a surface emitting laser element that emits laser light in a direction perpendicular to a substrate, and is provided on a light emitting surface from which the laser light is emitted and is provided so as to surround an emission region. Nλ / 4 (where n is an odd number and λ is an odd number), which is formed in a side electrode and a portion of the emission region that is off the center of the emission region and has a lower reflectance than that of the center of the emission region. The surface emitting laser element is characterized in that the shape of the low reflectance region in the emission region has anisotropy in two directions orthogonal to each other.

  According to this, the polarization direction can be stabilized while controlling the oscillation of the high-order transverse mode.

  From a second viewpoint, the present invention is a surface emitting laser array in which the surface emitting laser elements of the present invention are integrated.

  According to this, since the surface emitting laser element of the present invention is integrated, the polarization direction can be stabilized while controlling the oscillation of the high-order transverse mode.

  According to a third aspect of the present invention, there is provided an optical scanning device that scans a surface to be scanned with light, a light source having the surface-emitting laser element of the present invention, a deflecting unit that deflects light from the light source, And a scanning optical system that condenses the light deflected by the deflecting unit on the surface to be scanned.

  According to this, since the light source has the surface emitting laser element of the present invention, as a result, stable optical scanning can be performed.

  According to a fourth aspect of the present invention, there is provided an optical scanning device that scans a surface to be scanned with light, a light source having the surface emitting laser array of the present invention, a deflection unit that deflects light from the light source, And a scanning optical system that condenses the light deflected by the deflecting unit on the surface to be scanned.

  According to this, since the light source has the surface emitting laser array of the present invention, as a result, stable optical scanning can be performed.

  According to a fifth aspect of the present invention, there is provided at least one image carrier, and at least one optical scanning device according to the invention that scans the at least one image carrier with light including image information. An image forming apparatus provided.

  According to this, since the optical scanning device of the present invention is provided, as a result, a high-quality image can be formed.

It is a figure for demonstrating schematic structure of the laser printer which concerns on one Embodiment of this invention. It is the schematic which shows the optical scanning device in FIG. FIGS. 3A and 3B are diagrams for explaining the surface emitting laser elements included in the light source in FIG. 4A and 4B are diagrams for explaining the substrate of the surface emitting laser element. It is the figure which expanded the active layer vicinity. FIGS. 6A to 6C are views (No. 1) for describing a method of manufacturing a surface emitting laser element, respectively. FIGS. 7A and 7B are views (No. 2) for describing the method for manufacturing the surface emitting laser element, respectively. It is the figure which took out and expanded the mesa upper surface in FIG.7 (B). FIGS. 9A to 9C are views (No. 3) for describing the method for manufacturing the surface emitting laser element, respectively. It is the figure which took out and expanded the mesa upper surface in FIG.9 (C). It is FIG. (4) for demonstrating the manufacturing method of a surface emitting laser element. It is a figure for demonstrating the relationship between the suppression ratio SMSR of a high-order transverse mode, and the area S of an electric current passage area | region. It is a figure for demonstrating the relationship between polarization suppression ratio PMSR and polarization angle (theta) p. It is a figure for demonstrating the modification 1 of a surface emitting laser element. It is a figure for demonstrating the comparative example of a surface emitting laser element. It is a figure for demonstrating the surface emitting laser element used in calculating an oscillation mode distribution. It is a figure for demonstrating the relationship between the internal diameter L5 of a small area | region, and the Q value in a high-order transverse mode. It is a figure for demonstrating the relationship between the internal diameter L5 of a small area | region, and the optical confinement coefficient (GA) of the horizontal direction of a fundamental transverse mode. It is a figure for demonstrating the modification 2 of a surface emitting laser element. FIGS. 20A and 20B are diagrams for explaining a third modification of the surface emitting laser element. FIG. 21A to FIG. 21C are diagrams for explaining a manufacturing method of Modification 3 of the surface emitting laser element. FIGS. 22A and 22B are diagrams for explaining a fourth modification of the surface emitting laser element. It is the figure which took out and expanded the mesa upper surface in the manufacturing process of the surface emitting laser element of the modification 4. It is the figure which took out and expanded the mesa upper surface in the surface emitting laser element of the modification 4. It is a figure for demonstrating the relationship between the presence or absence of the suppression structure of a high-order transverse mode, and the suppression ratio (SMSR) of a high-order transverse mode. It is a figure for demonstrating the relationship between R2 / R1 and a polarization suppression ratio (PMSR). FIG. 27A to FIG. 27F are diagrams for explaining the shape of the low-reflectance region, respectively. It is a figure for demonstrating a surface emitting laser array. It is AA sectional drawing of FIG. It is a figure for demonstrating schematic structure of a color printer.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a laser printer 1000 as an image forming apparatus according to an embodiment.

  The laser printer 1000 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 paper feeding 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, a printer control device 1060 that comprehensively controls the above-described units, and the like 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 of the arrow in FIG.

  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.

  The toner cartridge 1036 stores toner, and the toner is supplied to the 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, and 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 configuration of the optical scanning device 1010 will be described.

  As shown in FIG. 2 as an example, the optical scanning device 1010 includes a deflector-side scanning lens 11a, an image plane-side scanning lens 11b, a polygon mirror 13, a light source 14, a coupling lens 15, an aperture plate 16, an anamorphic. A lens 17, a reflection mirror 18, a scanning control device (not shown), and the like are provided. These are assembled at predetermined positions in the housing 30.

  In the following, for convenience, the direction corresponding to the main scanning direction is abbreviated as “main scanning corresponding direction”, and the direction corresponding to the sub scanning direction is abbreviated as “sub scanning corresponding direction”.

  The coupling lens 15 converts the light beam output from the light source 14 into substantially parallel light.

  The aperture plate 16 has an aperture and defines the beam diameter of the light beam through the coupling lens 15.

  The anamorphic lens 17 forms an image of the light beam that has passed through the opening of the aperture plate 16 in the sub-scanning corresponding direction in the vicinity of the deflection reflection surface of the polygon mirror 13 via the reflection mirror 18.

  The optical system arranged on the optical path between the light source 14 and the polygon mirror 13 is also called a pre-deflector optical system. In the present embodiment, the pre-deflector optical system includes a coupling lens 15, an aperture plate 16, an anamorphic lens 17, and a reflection mirror 18.

  As an example, the polygon mirror 13 has a hexahedral mirror having an inscribed circle radius of 18 mm, and each mirror serves as a deflecting reflection surface. The polygon mirror 13 deflects the light flux from the reflection mirror 18 while rotating at a constant speed around an axis parallel to the sub-scanning corresponding direction.

  The deflector-side scanning lens 11 a is disposed on the optical path of the light beam deflected by the polygon mirror 13.

  The image plane side scanning lens 11b is disposed on the optical path of the light beam via the deflector side scanning lens 11a. Then, the light beam that has passed through the image plane side scanning lens 11b is irradiated onto the surface of the photosensitive drum 1030, and a light spot is formed. This light spot moves in the longitudinal direction of the photosensitive drum 1030 as the polygon mirror 13 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 13 and the photosensitive drum 1030 is also called a scanning optical system. In the present embodiment, the scanning optical system includes a deflector side scanning lens 11a and an image plane side scanning lens 11b. Note that at least one folding mirror is disposed on at least one of the optical path between the deflector side scanning lens 11a and the image plane side scanning lens 11b and the optical path between the image plane side scanning lens 11b and the photosensitive drum 1030. May be.

  As an example, the light source 14 includes a surface emitting laser element 100 as shown in FIGS. 3 (A) and 3 (B). In this specification, 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. 3A is a view showing a cut surface when the surface emitting laser element 100 is cut in parallel to the XZ plane, and FIG. 3B is a view in which the surface emitting laser element 100 is cut in parallel to the YZ plane. It is a figure which shows the cut surface at the time.

  The surface emitting laser element 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 or the like.

  The surface of the substrate 101 is a mirror-polished surface, and as shown in FIG. 4A, 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. 4B, 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.

  Further, here, it is assumed that a polarization control action is performed to stabilize the polarization direction in the X-axis direction by using an inclined substrate as the substrate 101.

  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 40.5 pairs of a low refractive index layer made of n-AlAs and a high refractive index layer made of n-Al _0.3 Ga _0.7 As. Have. Between each refractive index layer, in order to reduce electric resistance, 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 (see FIG. 5). . Each refractive index layer includes 1/2 of the adjacent composition gradient layer, and is set to have an optical thickness of λ / 4 when the oscillation wavelength is λ. 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 and is an active layer having a triple quantum well structure having three quantum well layers 105a and four barrier layers 105b (see FIG. 5). 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.

  A portion composed of the lower spacer layer 104, the active layer 105, and the upper spacer layer 106 is also called a resonator structure, and the thickness thereof is set to an optical thickness of one wavelength (see FIG. 5). ). 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 that a high stimulated emission probability can be obtained.

The upper semiconductor DBR 107 is laminated on the + Z side of the upper spacer layer 106, and has a low refractive index layer made of p-Al _0.9 Ga _0.1 As and a high refractive index made of p-Al _0.3 Ga _0.7 As. It has 23 pairs of layers.

  Between the refractive index layers in the upper semiconductor DBR 107, a composition gradient layer is provided in which the composition is gradually changed from one composition to the other composition in order to reduce electrical resistance. Each refractive index layer is set to have an optical thickness of λ / 4 including 1/2 of the adjacent composition gradient layer.

  In one of the low refractive index layers in the upper semiconductor DBR 107, a selectively oxidized layer 108 made of p-AlAs is inserted with a thickness of 30 nm. The insertion position of the selectively oxidized layer 108 is a position corresponding to the third node from the active layer 105 in the standing wave distribution of the electric field.

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

  Note that a structure in which a plurality of semiconductor layers are stacked on the substrate 101 is also referred to as a “stacked body” for convenience in the following.

  Next, a method for manufacturing the surface emitting laser element 100 will be briefly described. Here, it is assumed that the desired polarization direction (referred to as the desired polarization direction P) is the X-axis direction.

(1) The above laminate is formed by crystal growth by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) (see FIG. 6A).

Here, trimethylaluminum (TMA), trimethylgallium (TMG), and trimethylindium (TMI) are used as Group III materials, and phosphine (PH ₃ ) and arsine (AsH ₃ ) are used as Group V materials. ing. 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.

(2) A square resist pattern having a side of 25 μm is formed on the surface of the laminate.

(3) A square columnar mesa structure (hereinafter abbreviated as “mesa” for convenience) is formed by ECR etching using Cl ₂ gas using the resist pattern as a photomask. Here, the bottom surface of the etching is located in the lower spacer layer 104.

(4) The photomask is removed (see FIG. 6B).

(5) The laminated body is heat-treated in water vapor. As a result, Al (aluminum) in the selectively oxidized layer 108 is selectively oxidized from the outer peripheral portion of the mesa, and an unoxidized region 108b surrounded by the Al oxide layer 108a remains in the central portion of the mesa. (See FIG. 6C). In other words, a so-called oxidized constriction structure is formed that restricts the drive current path of the light emitting part only to the central part of the mesa. The non-oxidized region 108b is a current passage region (current injection region). In this manner, a substantially square current passing region having a width of about 4 μm to 6 μm, for example, is formed.

(6) A protective layer 111 made of SiN is formed by vapor phase chemical deposition (CVD) (see FIG. 7A). Here, the optical thickness of the protective layer 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.

(7) An etching mask (referred to as a mask M) for opening a window for the P-side electrode contact is formed on the upper part of the mesa serving as a laser light emission surface. Here, as an example, as shown in FIG. 7B and FIG. 8 in which only the mesa in FIG. 7B is taken out and enlarged, the periphery of the mesa, the periphery of the top surface of the mesa, and the center portion of the top surface of the mesa are sandwiched. Then, the mask M is formed so that the two small regions (the first small region and the second small region) facing each other in the direction parallel to the desired polarization direction P (here, the X-axis direction) are not etched. . Specifically, the code L1 in FIG. 8 is 5 μm, the code L2 is 2 μm, and the code L3 is 8 μm.

(8) The protective layer 111 is etched with BHF to open a window for the P-side electrode contact.

(9) The mask M is removed (see FIGS. 9A and 9B). Hereinafter, for convenience, the protective layer 111 remaining in the first small region is referred to as “transparent layer 111A”, and the protective layer 111 remaining in the second small region is referred to as “transparent layer 111B”.

(10) A square resist pattern having a side of 10 μm is formed in a region to be a light emitting part (opening part of the metal layer) on the upper part of the mesa, and the p-side electrode material is deposited. As the electrode material on the p side, a multilayer film made of Cr / AuZn / Au or a multilayer film made of Ti / Pt / Au is used.

(11) The electrode material deposited in the region (emission region) to be the light emitting part is lifted off to form the p-side electrode 113 (see FIG. 9C). An area surrounded by the p-side electrode 113 is an emission area. FIG. 10 shows an enlarged view of only the mesa in FIG. 9C. The shape of the injection region is a square having a side length of L4 (here, 10 μm). In the present embodiment, the transparent layer 111A is formed as a transparent dielectric film made of SiN having an optical thickness of λ / 4 in two small regions (first small region and second small region) in the emission region. A transparent layer 111B is present. As a result, the reflectance of the two small regions (the first small region and the second small region) is lower than the reflectance at the center of the emission region.

(12) 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 (see FIG. 11). Here, the n-side electrode 114 is a multilayer film made of AuGe / Ni / Au.

(13) Ohmic conduction is established between the p-side electrode 113 and the n-side electrode 114 by annealing. Thereby, the mesa becomes a light emitting part.

(14) Cut for each chip.

  With respect to the surface emitting laser element 100 manufactured in this way, the relationship between the suppression ratio SMSR (Side Mode Suppression Ratio) in the high-order transverse mode and the area S of the current passing region when the optical output is 2.0 mW is obtained. It was. The result is shown in FIG. 12 together with the comparative example.

Reference sign A in FIG. 12 is the case of the surface emitting laser element 100 according to the present embodiment, and reference sign B is the case of the surface emitting laser element (comparative example) in which no dielectric film is formed in the emission region. In the case of the symbol B, as the area of the current passing region is increased, the high-order transverse mode having a light output peak at the periphery of the emission region is likely to oscillate, and the SMSR is significantly reduced. On the other hand, in the case of the code A, the SMSR is improved from 5 dB to 15 dB as compared with the case of the code B. In particular, the SMSR of about 25 dB or more is obtained in the range where the area S of the current passing region is 30 μm ² or less.

  In general, the light output of the fundamental transverse mode is the largest near the center of the emission region, and tends to decrease as it goes to the periphery. On the other hand, the light output in the high-order transverse mode is greatest at the periphery of the emission region and tends to decrease as it approaches the center. In the present embodiment, the reflectance of the two small areas (first small area and second small area) set in the periphery of the emission area is set lower than the reflectance of the central portion. The reflectance of the higher order transverse mode is lowered without lowering the reflectance of the transverse mode, and the action of suppressing the oscillation of the higher order transverse mode works.

  For the surface emitting laser element 100, the relationship between the polarization suppression ratio PMSR (Polarization Mode Suppression Ratio) and the polarization angle θp was determined. The result is shown in FIG. 13 together with the comparative example. The polarization suppression ratio is a ratio between the light intensity in a desired polarization direction and the light intensity in a direction orthogonal to the desired polarization direction, and about 20 dB is required for a copying machine or the like. Here, the Y-axis direction is the polarization angle θp = 0 degrees, and the X-axis direction is the polarization angle θp = 90 degrees.

  A symbol A in FIG. 13 is a case of the surface emitting laser element 100 according to the present embodiment. Reference symbol C in FIG. 13 is a case of a surface-emitting laser element equivalent to a surface-emitting laser element 100 rotated 90 degrees around the Z-axis (modified example of this embodiment) as shown in FIG. 14 as an example. It is. Further, as shown in FIG. 15 as an example, the symbol D in FIG. 13 is a transparent dielectric having an optical thickness of λ / 4 in which one small region surrounding the central portion is set in the emission region. This is the case of a surface emitting laser element (comparative example) on which a film is formed.

  In the case of code A, the polarization direction is stable in the X-axis direction, and in the case of code C, the polarization direction is stable in the Y-axis direction. In either case, a PMSR higher than that of the code D by about 5 dB was obtained. On the other hand, in the case of D, although the polarization direction is stable in the X-axis direction, PMSR is less than 10 dB, and the polarization direction may be unstable.

  The reason why the polarization stability is improved by making the number of small regions on which the transparent dielectric film having an optical thickness of λ / 4 is formed as a factor is that two directions orthogonal to each other (here, the X-axis direction and It is considered that anisotropy occurred in the light confinement action in the Y-axis direction). In this embodiment, the light whose polarization direction coincides with the X-axis direction has a confinement action at the center of the emission region having a higher reflectance than the periphery of the emission region, and the polarization direction coincides with the Y-axis direction. The oscillation threshold value is lower than that of light. As a result, it is considered that the polarization suppression ratio is improved.

  Here, as an example, as shown in FIG. 16, a ring-shaped small region surrounding the central portion is set in a circular emission region, and a transparent dielectric having an optical thickness of λ / 4 is set in the small region. With respect to the surface emitting laser element on which the body film is formed (calculated surface emitting laser element), the oscillation mode distribution was calculated by fixing the small region width L6 to 3 μm and changing the small region inner diameter L5. . In the calculation, the diameter of the current passage region is 4.5 μm. In FIG. 16, for convenience, the same reference numerals are used for those equivalent to the surface emitting laser element 100.

  FIG. 17 shows the relationship between the inner diameter L5 of the small region and the Q value in the high-order transverse mode obtained from the above calculation results. According to this, it can be seen that as the value of L5 is increased from 1 μm, the Q value is significantly reduced. This is presumably because the high-order transverse mode has a portion with high light intensity overlapped with a small region, and oscillation of the high-order transverse mode is suppressed. Specifically, by setting the value of L5 within the range of about 5 μm to 9 μm, it is possible to greatly suppress the oscillation of the high-order transverse mode.

  Further, FIG. 18 shows the relationship between the inner diameter L5 of the small region and the lateral optical confinement factor Γ in the basic transverse mode obtained from the calculation result. According to this, it can be seen that the lateral light confinement effect is strong when the value of L5 is 5 μm or less, and that when the value of L5 is greater than 5 μm, the lateral light confinement effect decreases as the value increases. From this, it is possible to cause anisotropy in the lateral confinement action by providing a plurality of small regions and providing anisotropy between the small regions. As a result, the polarization component having a strong confinement effect oscillates more easily than the polarization component having a weak confinement effect, and the polarization direction can be controlled to a direction having a strong confinement effect.

  As described above, according to the surface emitting laser element 100 according to the present embodiment, 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, and the contact are formed on the substrate 101. A layer 109 is stacked. On the emission surface from which the laser beam is emitted, a p-side electrode 113 provided surrounding the emission region and an n-side electrode 114 provided on the substrate 101 side are provided. In addition, in the emission area, the reflectance of each small area is set to the emission area in two small areas (a first small area and a second small area) provided in a portion off the center of the emission area. A transparent layer 111A and a transparent layer 111B, which are optically transparent dielectric films that are lower than the reflectance of the central portion, are formed with an optical thickness of λ / 4.

  In this case, due to the optically transparent film formed on the exit surface, the reflectivity at the periphery in the exit area is relatively lower than the reflectivity at the center of the exit area. High-order transverse mode oscillation can be suppressed without reducing the optical output of the mode.

  In addition, the region having a relatively high reflectivity at the center of the emission region has a shape having anisotropy in two directions perpendicular to each other, and intentionally anisotropic with respect to the lateral confinement action with respect to the laser light. The stability of the polarization direction can be improved.

  That is, it is possible to stabilize the polarization direction while controlling the oscillation of the high-order transverse mode.

  Further, it is possible to control the higher-order transverse mode and the polarization direction without reducing the area of the current passing region. As a result, the electrical resistance of the element does not increase, and the current density in the current confinement region does not increase, so that the element life is not reduced.

  In addition, two small regions (first small region and second small region) in the emission region are opposed to each other across the center of the emission region with respect to a direction parallel to the desired polarization direction P. In this case, the dielectric film can be easily and accurately provided in each small region.

  The substrate 101 is a so-called inclined substrate, and the direction in which the first small region and the second small region face each other is parallel to the inclined axis direction of the main surface of the substrate 101 (here, the X-axis direction). It is. In this case, the polarization control action by using the inclined substrate is added, and the stability of the polarization direction can be further improved.

  The side surface of the mesa is covered with a protective layer 111 that is a dielectric film. In this case, destruction of elements caused by moisture absorption is suppressed, and long-term reliability can be further improved.

  According to the optical scanning device 1010 according to the present embodiment, the light source 14 includes the surface emitting laser element 100. In this case, since a single fundamental transverse mode laser beam is obtained, a circular and minute laser spot can be easily formed on the surface of the photosensitive drum 1030. In addition, since the polarization direction is stable, it is not easily affected by distortion of the light spot or fluctuation in light quantity. Accordingly, it is possible to form an image of a small beam spot having a circular shape and a high light density on the photosensitive drum 1030 with a simple optical system. Therefore, stable optical scanning can be performed.

  Since the laser printer 1000 according to the present embodiment includes the optical scanning device 1010, a high-quality image can be formed.

  In the above embodiment, the case where a polarization control action is attempted to stabilize the polarization direction in the X-axis direction by using an inclined substrate as the substrate 101 has been described, but the polarization direction should be stabilized in the Y-axis direction. When the polarization control action is as follows, the desired polarization direction P is the Y-axis direction, and the direction in which the first small region and the second small region are opposed is the tilt axis of the main surface of the substrate 101. You may make it a direction orthogonal to a direction (here X-axis direction) (refer FIG. 14).

Further, in the above embodiment, the protective layer 111 has been described for the case of SiN, not limited to this, for _example, SiN _x, SiO x, may be any of TiO _x and SiON. The same effect can be obtained by designing the film thickness according to the refractive index of each material.

  In the above embodiment, the case where the first small region and the second small region are provided so as to be symmetric with respect to an axis passing through the center of the emission region and parallel to the Y axis is described. It is not limited to this. There may be a first small area on one side of the axis passing through the center of the injection area and parallel to the Y axis, and a second small area on the other side.

  Moreover, although the said embodiment demonstrated the case where the shape of each small area | region was a rectangle, it is not limited to this. An arbitrary shape such as an elliptical shape or a semicircular shape may be used (see FIG. 19).

  Moreover, although the said embodiment demonstrated the case where the transparent layer 111A and the transparent layer 111B were the same materials as the protective layer 111, it is not limited to this.

  Moreover, although the said embodiment demonstrated the case where the optical thickness of 111 A of transparent layers and the transparent layer 111B was (lambda) / 4, it is not limited to this. As an example, as shown in FIGS. 20A and 20B, the optical thickness of the transparent layer 111A and the transparent layer 111B may be 3λ / 4. In short, if the optical thickness of the transparent layer 111A and the transparent layer 111B is an odd multiple of λ / 4, the transverse mode suppressing effect similar to that of the surface emitting laser element 100 of the above embodiment can be obtained. 20A is a diagram showing a cut surface when the surface-emitting laser element 100A is cut in parallel to the XZ plane, and FIG. 20B is a diagram showing the surface-emitting laser element 100A in parallel to the YZ plane. It is a figure which shows a cut surface when cut | disconnecting.

  In this case, as shown in FIG. 21A as an example, after the p-side electrode 113 in the above embodiment is formed, a vapor phase chemical deposition method (CVD method) is used, and as an example, FIG. As shown in (B), the protective layer 111 made of SiN is formed so as to have an optical thickness of 2λ / 4. Specifically, 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. Then, 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 (see FIG. 21C).

  At this time, the central portion of the emission region is covered with a protective layer 111 (dielectric film) having an optical thickness of 2λ / 4. In addition, a region excluding two small regions (the first small region and the second small region) at the periphery of the emission region is also covered with a protective layer 111 (dielectric film) having an optical thickness of 2λ / 4. The Rukoto.

With respect to this surface emitting laser element 100A, when the relationship between the suppression ratio SMSR of the higher-order transverse mode when the optical output is 2.0 mW and the area of the current passage region is obtained, the area of the current passage region is 30 μm ² or less. An SMSR of about 25 dB or more was obtained in the range.

  Further, when the relationship between the polarization suppression ratio PMSR and the polarization angle θp was determined for the surface emitting laser element 100A, the polarization direction of the light emitted from the surface emitting laser element 100A is controlled in the X-axis direction, which is as high as about 20 dB. PMSR was obtained.

  Further, in the surface emitting laser element 100A, since the entire emission surface is covered with the protective layer 111 (dielectric film), oxidation and contamination of the emission surface can be suppressed. Although the central portion of the emission region is also covered with the protective layer 111 (dielectric film), the optical thickness is an even multiple of λ / 2, so that the reflectance is not lowered and the protective layer Optical characteristics equivalent to those without 111 (dielectric film) were obtained.

  That is, if the optical thickness of the portion where the reflectance is to be lowered is an odd multiple of λ / 4 and the optical thickness of the other portion is an even multiple of λ / 4, the same transverse mode suppression effect can be obtained. It is done.

  In the above embodiment, the light source 14 may include the surface emitting laser element 100B shown in FIGS. 22A and 22B as an example instead of the surface emitting laser element 100.

  The surface-emitting laser element 100B is a surface-emitting laser having an oscillation wavelength of 780 nm, and includes a substrate 201, a buffer layer 202, a lower semiconductor DBR 203, a lower spacer layer 204, an active layer 205, an upper spacer layer 206, an upper semiconductor DBR 207, and a contact. A layer 209 and the like.

  The substrate 201 is an inclined substrate similar to the substrate 101.

  The buffer layer 202 is laminated on the + Z side surface of the substrate 201 and is a layer made of n-GaAs.

The lower semiconductor DBR 203 is stacked on the + Z side of the buffer layer 202 and includes 40.5 pairs of a low refractive index layer made of n-AlAs and a high refractive index layer made of n-Al _0.3 Ga _0.7 As. Have. Between each refractive index layer, in order to reduce an electrical resistance, a composition gradient layer having a thickness of 20 nm in which the composition is gradually changed from one composition to the other composition is provided. Each refractive index layer includes 1/2 of the adjacent composition gradient layer, and is set to have an optical thickness of λ / 4 when the oscillation wavelength is λ.

The lower spacer layer 204 is laminated on the + Z side of the lower semiconductor DBR 203 and is a layer made of non-doped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P.

  The active layer 205 is stacked on the + Z side of the lower spacer layer 204 and is an active layer having a triple quantum well structure having three quantum well layers and four barrier layers. Each quantum well layer 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 is made of GaInP, which is a composition that induces a tensile strain of 0.6%.

The upper spacer layer 206 is stacked at the + Z side of the active layer 205, a layer made of non-doped _{(Al 0.1 Ga 0.9) 0.5 In} 0.5 P.

  A portion composed of the lower spacer layer 204, the active layer 205, and the upper spacer layer 206 is also called a resonator structure, and the thickness thereof is set to be an optical thickness of one wavelength. The active layer 205 is provided at the center of the resonator structure, which is a position corresponding to the antinode in the standing wave distribution of the electric field, so that a high stimulated emission probability can be obtained.

The upper semiconductor DBR 207 includes a first upper semiconductor DBR 207 ₁ and a second upper semiconductor DBR 207 _2.

The first upper semiconductor DBR 207 ₁ is stacked at the + Z side of the upper spacer layer _{206, p- (Al 0.7 Ga 0.3} ) 0.5 In 0.5 consists P low refractive index layer and the p- ( al _0.1 Ga _0.9) has a high refractive index layer 1 pairs pair consisting _0.5 in _0.5 P. Between each refractive index layer, in order to reduce electrical resistance, a composition gradient layer is provided in which the composition is gradually changed from one composition to the other composition. Each refractive index layer is set to have an optical thickness of λ / 4 including 1/2 of the adjacent composition gradient layer.

The second upper semiconductor DBR207 ₂ is stacked on the + Z side of the _first upper semiconductor DBR2071, and includes a low refractive index layer made of p-Al _0.9 Ga _0.1 As, and p-Al _0.3 Ga _{0. It} has 23 pairs of high refractive index layers made of ₇ As. Between each refractive index layer, in order to reduce electrical resistance, a composition gradient layer is provided in which the composition is gradually changed from one composition to the other composition. Each refractive index layer is set to have an optical thickness of λ / 4 including 1/2 of the adjacent composition gradient layer.

One of the low refractive index layers of the second upper semiconductor DBR 207 _2, the selective oxidation layer made of p-AlAs is inserted in thickness 30 nm. The insertion position of the selective oxidation layer is a position corresponding to the third node from the active layer 205 in the standing wave distribution of the electric field.

The contact layer 209 is a layer that is stacked on the + Z side of the _second upper semiconductor DBR 2072 and is made of p-GaAs.

  Note that a structure in which a plurality of semiconductor layers are stacked on the substrate 201 in this manner is also referred to as a “stacked body B” for convenience.

  Next, a method for manufacturing the surface emitting laser element 100B will be briefly described. Here, it is assumed that the desired polarization direction P is the X-axis direction.

(1) The laminate B is formed by crystal growth by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxial growth (MBE).

(2) A square resist pattern having a side of 25 μm is formed on the surface of the laminate B.

(3) A square columnar mesa is formed by ECR etching using Cl ₂ gas, using the resist pattern as a photomask. Here, the bottom surface of the etching is located in the lower spacer layer 204.

(4) The photomask is removed.

(5) The laminated body B is heat-treated in water vapor. As a result, Al (aluminum) in the selectively oxidized layer is selectively oxidized from the outer peripheral portion of the mesa, and an unoxidized region 208b surrounded by the Al oxide layer 208a remains in the central portion of the mesa. In other words, a so-called oxidized constriction structure is formed that restricts the drive current path of the light emitting part only to the central part of the mesa. The non-oxidized region 208b is a current passage region (current injection region). In this manner, a substantially square current passing region having a width of about 4 μm to 6 μm, for example, is formed.

(6) The protective layer 211 made of SiN is formed using a vapor phase chemical deposition method (CVD method). Here, the optical thickness of the protective layer 211 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.

(7) An etching mask (referred to as a mask M) for opening a window for the P-side electrode contact is formed on the upper part of the mesa serving as a laser light emission surface. Here, as shown in FIG. 23 in which only the mesa is taken out and enlarged as an example, the periphery of the mesa, the periphery of the mesa upper surface, and the center of the mesa upper surface are surrounded, and the minor axis direction is set to a desired polarization direction P (here, The mask M is formed so that an annular region having a direction parallel to the X-axis direction is not etched. Specifically, the code R1 in FIG. 23 is 6 μm, the code R2 is 7 μm, and the code M1 is 10 μm.

(8) The protective layer 211 is etched with BHF to open a window for the P-side electrode contact.

(9) The mask M is removed.

(10) A square resist pattern having a side of 10 μm is formed in a region to be a light emitting part (opening part of the metal layer) on the upper part of the mesa, and the p-side electrode material is deposited. As the electrode material on the p side, a multilayer film made of Cr / AuZn / Au or a multilayer film made of Ti / Pt / Au is used.

(11) The electrode material deposited in the region (emission region) to be the light emitting part is lifted off to form the p-side electrode 213. A region surrounded by the p-side electrode 213 is an emission region. FIG. 24 shows an enlarged view of only the mesa taken out. The shape of the injection region is a square whose length of one side is M1 (here, 10 μm). Here, the transparent layer 211 exists as a transparent dielectric film made of SiN having an optical thickness of λ / 4 in an annular region in the emission region. As a result, the reflectance of the annular region is lower than the reflectance of the central portion of the emission region.

(12) After polishing the back side of the substrate 201 to a predetermined thickness (for example, about 100 μm), the n-side electrode 214 is formed. Here, the n-side electrode 214 is a multilayer film made of AuGe / Ni / Au.

(13) Ohmic conduction is established between the p-side electrode 213 and the n-side electrode 214 by annealing. Thereby, the mesa becomes a light emitting part.

(14) Cut for each chip.

  In the surface-emitting laser element 100B manufactured as described above, the reflectance of the peripheral portion where the SiN film having a thickness of λ / 4n remains in the emission region is lower than the reflectance of the central portion. In general, the light output of the fundamental transverse mode is the largest near the center of the emission region, and tends to decrease as it goes to the periphery. On the other hand, the light output of the high-order transverse mode is greatest at the periphery of the emission region and tends to decrease as it approaches the center of the emission region. Therefore, in the surface emitting laser element 100B, it is possible to reduce the reflectance of the higher-order transverse mode without reducing the reflectance of the fundamental transverse mode. That is, the action of suppressing higher-order transverse mode oscillations works.

In FIG. 25, the light output is 1 for the element having the high-order transverse mode suppression structure (symbol A) and the element not having the high-order transverse mode suppression structure (symbol B) similar to the surface emitting laser element 100B. The result of comparing the suppression ratio (SMSR) of the high-order transverse mode at .4 mW is shown. Here, the horizontal axis S is the area of the current passage region. In an element that does not have a high-order transverse mode suppression structure, the high-order transverse mode having a light output peak at the periphery of the emission region is likely to oscillate, so the SMSR is significantly reduced. On the other hand, in the element having the high-order transverse mode suppression structure, the SMSR is improved by 10 dB or more and the area S of the current passing region is 30 mm ² or less compared to the element not having the high-order transverse mode control structure. An SMSR of 20 dB or more is obtained in the above range.

  FIG. 26 shows the relationship between R2 / R1 and the polarization suppression ratio (PMSR) in the annular region. In FIG. 26, point A is R1 = R2 = 5 μm, point B is R1 = 5 μm, R2 = 6 μm, point C is R1 = 5 μm, R2 = 7 μm, point D is R1 = 5 μm This is a case of dividing into two.

  Here, since the anisotropy of the gain is generated by using the inclined substrate, the polarization direction is in the X-axis direction in all four structures regardless of the shape of the low reflectance region. However, when comparing the polarization suppression ratio indicating the polarization stability, the higher the ratio of the inner diameter (R2) in the direction orthogonal to the polarization direction to the inner diameter (R1) in the direction parallel to the polarization direction, the higher the polarization suppression ratio. Results were obtained.

  As a factor for obtaining such a result, it is considered that anisotropy occurs in the light confinement action in two directions orthogonal to each other. At points B and C, the light confinement action at the center of the emission region in the X-axis direction, which is the polarization direction, is stronger than in the Y-axis direction. As a result, the polarization stability was improved as compared with the structure of point A having an isotropic inner diameter. Further, the polarization suppression ratio is most improved in the structure of the point D in which the low reflectance region is separated into a plurality of parts, which is equivalent to the surface emitting laser element 100 in the above embodiment.

  The shape of the low-reflectance region is not limited to an elliptical ring shape having a long side and a short side, and the same transverse mode suppression effect and polarization control can be achieved even in an arbitrary shape such as a rectangular shape. An effect is acquired (refer FIG. 27 (A)-FIG. 27 (F)).

  In the above embodiment, the light source 14 may include a surface emitting laser array 100C shown in FIG. 28 as an example instead of the surface emitting laser element 100.

  In the surface emitting laser array 100C, a plurality (21 in this case) of light emitting units are arranged on the same substrate. Here, the X-axis direction in FIG. 28 is a main-scanning corresponding direction, and the Y-axis direction is a sub-scanning corresponding direction. The plurality of light emitting units are arranged at equal intervals d2 when all the light emitting units are orthogonally projected onto a virtual line extending in the Y-axis direction. That is, the 21 light emitting units are two-dimensionally arranged. In this specification, the “light emitting portion interval” refers to the distance between the centers of two light emitting portions. Further, the number of light emitting units is not limited to 21.

  Each light emitting portion has the same structure as the surface emitting laser element 100 described above, as shown in FIG. 29 which is a cross-sectional view taken along the line AA of FIG. The surface emitting laser array 100C can be manufactured by a method similar to that of the surface emitting laser element 100 described above. Therefore, it is possible to obtain a plurality of laser beams in a single fundamental transverse mode having a uniform polarization direction between the light emitting units. Accordingly, it is possible to simultaneously form 21 minute light spots that are circular and have a high light density on the photosensitive drum 1030.

  In the surface emitting laser array 100C, 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 the photosensitive drum 1030 is adjusted by adjusting the lighting timing. In the above, it can be considered that the configuration is the same as the case where the light emitting units are arranged at equal intervals in the sub-scanning direction.

  For example, if the distance d2 is 2.65 μm and the magnification of the optical system of the optical scanning device 1010 is doubled, high-density writing of 4800 dpi (dots / inch) can be performed. Of course, higher density can be achieved by increasing the number of light emitting sections in the main scanning corresponding direction, or by arranging the array in which the pitch d1 in the sub scanning corresponding direction is narrowed to further reduce the interval d2, or by reducing the magnification of the optical system. And higher quality printing becomes possible. Note that the writing interval in the main scanning direction can be easily controlled by the lighting timing of the light emitting unit.

  In this case, the laser printer 1000 can perform printing without decreasing the printing speed even if the writing dot density increases. Further, when the writing dot density is the same, the printing speed can be further increased.

  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.

  By the way, it is preferable that the groove | channel between two light emission parts shall be 5 micrometers or more for the electrical and spatial separation of each light emission part. This is because if it is too narrow, it becomes difficult to control etching during production. Further, the mesa size (length of one side) 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.

  In the above embodiment, a surface emitting laser array in which light emitting units similar to the surface emitting laser element 100 are arranged one-dimensionally may be used instead of the surface emitting laser element 100.

  In the above embodiment, the case where the normal direction of the main surface of the substrate is inclined 15 degrees toward the crystal orientation [1 1 1] A direction with respect to the crystal orientation [1 0 0] direction is described. However, the present invention is not limited to this. The normal direction of the main surface of the substrate may be inclined toward one direction of crystal orientation <1 1 1> with respect to one direction of crystal orientation <1 0 0>.

  Moreover, although the said embodiment demonstrated the case where the oscillation wavelength of a light emission part was a 780 nm band, it is not limited to this. The oscillation wavelength of the light emitting unit may be changed according to the characteristics of the photoreceptor.

  Moreover, each said surface emitting laser element can be used also for uses other than an image forming apparatus. In that case, the oscillation wavelength may be a wavelength band such as a 650 nm band, an 850 nm band, a 980 nm band, a 1.3 μm band, and a 1.5 μm band depending on the application. In this case, a mixed crystal semiconductor material corresponding to the oscillation wavelength can be used as the semiconductor material constituting the active layer. For example, an AlGaInP mixed crystal semiconductor material can be used in the 650 nm band, an InGaAs mixed crystal semiconductor material can be used in the 980 nm band, and a GaInNAs (Sb) mixed crystal semiconductor material can be used in the 1.3 μm band and the 1.5 μm band.

  Further, by selecting the material and configuration of each reflecting mirror according to the oscillation wavelength, a light emitting unit corresponding to an arbitrary oscillation wavelength can be formed. For example, other than AlGaAs mixed crystal such as AlGaInP mixed crystal can be used. The low refractive index layer and the high refractive index layer are preferably a combination that is transparent with respect to the oscillation wavelength and can take a difference in refractive index as much as possible.

  In the above embodiment, the laser printer 1000 is described as the image forming apparatus. 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.

  As an example, as shown in FIG. 30, a color printer 2000 including a plurality of photosensitive drums may be used.

  The color printer 2000 is a tandem multicolor printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow). The black “photosensitive drum K1, charging device K2, "Developing device K4, cleaning unit K5, and transfer device K6", cyan "photosensitive drum C1, charging device C2, developing device C4, cleaning unit C5, and transfer device C6", and magenta "photosensitive drum" M1, charging device M2, developing device M4, cleaning unit M5, and transfer device M6 ”,“ photosensitive drum Y1, charging device Y2, developing device Y4, cleaning unit Y5, and transfer device Y6 ”for yellow, and light A scanning device 2010, a transfer belt 2080, a fixing unit 2030, and the like are provided.

  Each photoconductor drum rotates in the direction of the arrow in FIG. 30, and a charging device, a developing device, a transfer device, and a cleaning unit are arranged around each photoconductor drum along the rotation direction. 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 includes any one of a surface emitting laser element similar to the surface emitting laser element 100, the surface emitting laser element 100A, or the surface emitting laser element 100B, and a surface emitting laser array similar to the surface emitting laser array 100C. A light source is included for each color. Therefore, the same effect as that of the optical scanning device 1010 can be obtained. In addition, since the color printer 2000 includes the optical scanning device 2010, the same effect as the laser printer 1000 can be obtained.

  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, if each light source of the optical scanning device 2010 has a surface-emitting laser array similar to the surface-emitting laser array 100C, color misregistration is reduced by selecting a light-emitting unit to be lit. can do.

  As described above, the surface emitting laser element according to the present invention is suitable for stabilizing the polarization direction while controlling the oscillation of the high-order transverse mode. The surface emitting laser array according to the present invention is suitable for stabilizing the polarization direction while controlling the oscillation of the higher-order transverse mode. Further, the optical scanning device of the present invention is suitable for performing stable optical scanning. The image forming apparatus of the present invention is suitable for forming a high quality image.

  DESCRIPTION OF SYMBOLS 11a ... Deflector side scanning lens (a part of scanning optical system), 11b ... Image surface side scanning lens (a part of scanning optical system), 13 ... Polygon mirror (deflector), 14 ... Light source, 100 ... Surface emitting laser Element: 100A ... Surface emitting laser element, 100B ... Surface emitting laser element, 100C ... Surface emitting laser array, 101 ... Substrate, 111 ... Protective layer (dielectric film), 111A ... Transparent layer (dielectric film), 111B ... Transparent Layer (dielectric film), 113 ... p-side electrode (p-side electrode), 1000 ... laser printer (image forming apparatus), 1010 ... light scanning device, 1030 ... photosensitive drum (image carrier), 2000 ... color printer (Image forming apparatus), 2010... Optical scanning device, K1, C1, M1, Y1... Photosensitive drum (image carrier).

Japanese Patent No. 3565902 Japanese Patent No. 3955925 JP 2007-201398 A JP 2004-289033 A

Claims (17)

A surface emitting laser element that emits laser light in a direction perpendicular to a substrate,
A p-side electrode provided on the emission surface from which the laser beam is emitted, surrounding the emission region;
Nλ / 4 (where n is an odd number and λ is an oscillation wavelength) that is formed in a portion of the emission region that is off the center of the emission region and has a reflectance lower than that of the center of the emission region. A step structure,
The surface emitting laser element according to claim 1, wherein the shape of the low reflectance region in the emission region has anisotropy in two directions orthogonal to each other.   2. The surface emitting laser element according to claim 1, wherein the step structure is formed in a plurality of small regions provided in a portion deviating from a central portion of the emission region. The step structure is formed in an annular region provided in a portion off the center of the injection region,
The surface emitting laser element according to claim 1, wherein the annular region has different diameters in two directions orthogonal to each other. The plurality of small areas include a first small area and a second small area,
3. The surface emitting laser element according to claim 2, wherein the first small region and the second small region are opposed to each other with a central portion of the emission region interposed therebetween. The laser beam is linearly polarized light,
5. The surface emitting laser element according to claim 4, wherein the first small region and the second small region are opposed to each other with respect to a direction parallel to a polarization direction of the laser light. The laser beam is linearly polarized light,
4. The surface emitting laser element according to claim 3, wherein the minor axis direction of the annular region is a direction parallel to the polarization direction of the laser light.   The substrate is a substrate in which a normal direction of a main surface is inclined toward one direction of crystal orientation <1 1 1> with respect to one direction of crystal orientation <1 0 0>. The surface emitting laser element according to claim 4, wherein the surface emitting laser element is characterized in that   The minor axis direction of the annular region or the direction in which the first small region and the second small region face each other is parallel to the tilt axis direction of the main surface of the substrate. Item 8. The surface emitting laser element according to Item 7.   The minor axis direction of the annular region or the direction in which the first small region and the second small region face each other is orthogonal to the tilt axis direction of the main surface of the substrate. The surface emitting laser element according to claim 7.   The center of the emission region is covered with a dielectric film, and the optical thickness of the dielectric film is an even multiple of "oscillation wavelength / 4". The surface emitting laser element according to one item.   A region excluding the plurality of small regions or the annular region at the periphery of the emission region is covered with a dielectric film, and the optical thickness of the dielectric film is an even multiple of “oscillation wavelength / 4”. The surface-emitting laser element according to claim 2, wherein the surface-emitting laser element is provided. The exit surface is the top surface of the mesa structure;
The surface emitting laser element according to claim 1, wherein a side surface of the mesa structure is covered with a dielectric film.   A surface-emitting laser array in which the surface-emitting laser elements according to any one of claims 1 to 12 are integrated. An optical scanning device that scans a surface to be scanned with light,
A light source comprising the surface-emitting laser element according to any one of claims 1 to 12,
Deflecting means for deflecting light from the light source;
A scanning optical system that condenses the light deflected by the deflecting unit on the surface to be scanned. An optical scanning device that scans a surface to be scanned with light,
A light source comprising the surface emitting laser array according to claim 13;
Deflecting means for deflecting light from the light source;
A scanning optical system that condenses the light deflected by the deflecting unit on the surface to be scanned. At least one image carrier;
An image forming apparatus comprising: at least one optical scanning device according to claim 14 or 15 that scans the at least one image carrier with light modulated according to image information.   The image forming apparatus according to claim 16, wherein the image information is multicolor image information.