JP2011108796A - Surface-emitting laser element, surface-emitting laser array, optical scanner, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-emitting laser element stabilizing a polarization direction while suppressing oscillation of high-order lateral modes. <P>SOLUTION: In an emission region, a mode filter which is a transparent dielectric film having shape anisotropy in an X-axis direction and a Y-axis direction and allowing reflectivity to be lower than that of a center portion is formed with an optical thickness of λ/4. The mode filter is formed into shape having cut portions at portions of the emission region on a +Y side and a -Y side respectively in a ring shape surrounding the center portion of the emission region. Then the cut portions are each set to be smaller on a side near the center portion of the emission region than on a far side. <P>COPYRIGHT: (C)2011,JPO&INPIT

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.

  In a surface emitting laser element (Vertical Cavity Surface Emitting Laser: VCSEL), it is important for applications to suppress high-order transverse mode oscillation and to define the polarization direction in a desired direction. Has been made.

  For example, in Patent Document 1, a layer structure of a semiconductor material in which a light emitting layer is disposed between an upper reflector layer structure and a lower reflector layer structure is formed on a substrate, and above the upper reflector layer structure, An upper electrode having a circular shape in plan view is formed, and the inside of the upper electrode is an opening, and covers a part of the surface of the opening and is transparent to the oscillation wavelength of the oscillation laser light. A surface-emitting semiconductor laser device in which a simple layer is formed is disclosed.

  Further, in Patent Document 2, the main body is configured in the main body of the laser device at a position outside the opening for emitting laser light in a plane perpendicular to the laser light emitting direction and at a distance from the edge of the opening. A discontinuous portion of the semiconductor material formed by an elongated gap filled with a material different from the semiconductor material to be formed, and the side wall on the opening side of the elongated gap constituting the discontinuous portion is perpendicular to the radiation direction of the laser beam A vertical cavity surface emitting laser device is disclosed that is formed to extend in a direction aligned with a desired polarization direction of light emitted from the laser device when viewed in a flat plane.

  Patent Document 3 includes a laser structure in which a first multilayer film reflector, an active layer having a light emission center region, a second multilayer film reflector, and a transverse mode adjustment layer are stacked in this order on a substrate. Either one of the first multilayer mirror and the second multilayer mirror has a quadrilateral current injection region in which the intersection of the diagonal lines corresponds to the light emission center region, and the second multilayer mirror reflects the current injection region The light output port provided in a region corresponding to one of the diagonal lines and a pair of grooves provided with the light output port interposed therebetween, and the transverse mode adjustment layer is provided corresponding to the light output port. At the same time, a surface emitting semiconductor laser is disclosed in which the reflectance of the peripheral region excluding the central region corresponding to the light emission central region in the light exit is lower than that of the central region.

  Patent Document 4 includes a first multilayer reflective film, a first multilayer reflective film, an active layer formed on the first multilayer reflective film, and a second multilayer reflective film formed on the active layer. And at least one of the second multilayer reflective films is located in at least a part of the region corresponding to the active layer and has a thickness of substantially λ / 4n (λ: oscillation wavelength, n: refractive index). A surface-emitting type semiconductor laser device is disclosed that includes one region and a second region located in a region other than the first region and having a thickness substantially other than λ / 4n.

  However, in the laser device disclosed in Patent Document 2, the lateral confinement action of the laser light changes depending on the groove depth, and it is difficult to suppress higher-order transverse modes even though the polarization direction can be defined. there were.

  Further, in the surface emitting semiconductor laser disclosed in Patent Document 3, if the interval between the grooves is made narrower than the current confinement region in order to define the polarization direction, the current passing region is substantially narrowed. There is a disadvantage that the electrical resistance of the device increases or the current density increases, and the life of the laser device decreases.

  In the surface-emitting type semiconductor laser device disclosed in Patent Document 4, after crystal growth is performed up to a layer adjacent to the active layer, the crystal growth is interrupted, and after resist patterning and film etching, It is necessary to perform crystal growth. In this case, when the crystal growth is performed again, the surface state of the etched film affects the crystal growth, resulting in variations in the characteristics of the laser element and the control characteristics of the transverse mode, and in the process of mass production as a device. Was not suitable.

  By the way, the inventors of the present application have conducted various experiments and examinations, and when an annular low reflectance part is provided in the emission region as in the surface emitting semiconductor laser element disclosed in Patent Document 1, It has been found that the polarization suppression ratio PMSR may be reduced as compared with the case where the reflectance in the region is uniform. The polarization suppression ratio PMSR is a ratio between the light intensity in a desired polarization direction and the light intensity in a direction orthogonal thereto.

  In addition, even when the polarization direction is restricted to a desired direction by utilizing the gain anisotropy of the active layer generated by using a so-called tilted substrate, an annular low reflectance in the emission region If the portion is provided, the polarization direction may become unstable.

  The inventors of the present application made a number of samples with respect to the shape of the low reflectance portion provided in the emission region, and conducted experiments and studies. As a result, the shape of the low reflectance portion was improved in polarization stability. I found a new effect.

  The present invention has been made on the basis of the novel knowledge obtained by the inventors described above, and has the following configuration.

  According to a first aspect of the present invention, a resonator structure including an active layer, a semiconductor multilayer reflector provided with the resonator structure interposed therebetween, and an emission surface on which laser light is emitted are emitted. In a surface emitting laser element comprising an electrode provided so as to surround a region, the surface emitting laser device is formed so as to surround a central portion in the emission region, has shape anisotropy in two directions orthogonal to each other, and has the reflectance described above. The dielectric film further includes a transparent dielectric film lower than the reflectance of the central portion, and the dielectric film has at least one cut portion, and the width of the cut portion is closer to the side closer to the central portion than the far side. It is a surface emitting laser element characterized by being small.

  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.

  From a third aspect, the present invention is an optical scanning device that scans a surface to be scanned with light, the light source having the surface-emitting laser element of the present invention; a deflector that deflects the light from the light source; A scanning optical system that condenses the light deflected by the deflector onto the surface to be scanned.

  According to this, since the light source has the surface emitting laser element of the present invention, 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 deflector that deflects light from the light source; A scanning optical system that condenses the light deflected by the deflector onto the surface to be scanned.

  According to this, since the light source has the surface emitting laser array of the present invention, 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 for scanning the at least one image carrier with light modulated in accordance with image information. And an image forming apparatus.

  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. FIGS. 5A and 5B are views (No. 1) for describing a method of manufacturing a surface emitting laser element, respectively. FIGS. 6A and 6B are views (No. 2) for describing the method of manufacturing the surface emitting laser element, respectively. It is FIG. (3) for demonstrating the manufacturing method of a surface emitting laser element. It is the figure which took out and expanded the mesa upper surface in FIG. FIGS. 9A and 9B are views (No. 4) for describing the method of manufacturing the surface emitting laser element. It is FIG. (5) for demonstrating the manufacturing method of a surface emitting laser element. It is the figure which took out and expanded the mesa upper surface in FIG. It is FIG. (6) for demonstrating the manufacturing method 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 L1 of a small area | region, and Q value in a high-order transverse mode. It is a figure for demonstrating the relationship between the internal diameter L1 of a small area | region, and the optical confinement coefficient of the horizontal direction of a fundamental transverse mode. It is a figure for demonstrating the surface emitting laser element A as a comparative example. FIGS. 17A to 17C are diagrams for explaining Modifications 1 to 3 of the low reflectance region, respectively. FIGS. 18A to 18C are diagrams for describing modified examples 4 to 6 of the low reflectance region, respectively. FIG. 19A and FIG. 19B are diagrams for explaining modifications of the surface emitting laser element. 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 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, and a printer control device 1060 that comprehensively controls the above-described units 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, and a cylindrical lens 17. , A reflection mirror 18, a scanning control device (not shown), and the like. These are assembled at predetermined positions of the optical 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 cylindrical lens 17 forms an image of the light flux that has passed through the opening of the aperture plate 16 in the vicinity of the deflection reflection surface of the polygon mirror 13 via the reflection mirror 18 in the sub-scanning corresponding direction.

  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, a cylindrical 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, a p-side electrode 113, an n-side electrode 114, a mode filter 115, and 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.

  Returning to FIG. 3A, the buffer layer 102 is laminated on the surface of the substrate 101 on the + Z side 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 electrical resistance, a composition gradient layer (not shown) 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. 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 laminated on the + Z side of the lower spacer layer 104 and is an active layer having a GaInAsP / GaInP triplet well structure. Each quantum well layer is made of GaInAsP that has a composition that induces 0.7% compressive strain, and each barrier layer is made of GaInP that has a composition that induces 0.6% tensile strain.

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 be an optical thickness of one wavelength. 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 includes a first upper semiconductor DBR 107 ₁ and a second upper semiconductor DBR 107 _2.

The first upper semiconductor DBR 107 ₁ is stacked on the + Z side of the upper spacer layer 106, and includes a low refractive index layer made of p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P and 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 (not shown) in which the composition is gradually changed from one composition to the other composition is provided. 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 DBR 107 ₂ is stacked on the + Z side of the _first upper semiconductor DBR 107 ₁ , and has 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 (not shown) in which the composition is gradually changed from one composition to the other composition is provided. 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 107 _2, the selective oxidation layer made of p-AlAs is inserted in thickness 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.

  The mode filter 115 is provided on the + Z side of the contact layer 109 and in a portion deviated from the central portion in the emission region, and a transparent dielectric film that makes the reflectance of the portion lower than the reflectance of the central portion. Consists of.

  Next, a method for manufacturing the surface emitting laser element 100 will be briefly described. Note that a structure in which a plurality of semiconductor layers are stacked over the substrate 101 as described above is also referred to as a “stacked body” for convenience in the following.

(1) The stacked body is formed by crystal growth by metal organic vapor phase epitaxy (MOCVD) or molecular beam epitaxy (MBE) (see FIG. 5A).

Here, in the case of 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.

(2) A square resist pattern is formed on the surface of the laminate. Here, as an example, a substantially square shape having a side length of about 25 μm is used.

(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. 5B).

(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. 6A). 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 way, a square current passing region is formed. Here, a substantially square current passing region having a side length of about 5 μm was formed.

(6) A protective layer 111 made of SiN is formed on the entire surface by vapor phase chemical deposition (CVD) (see FIG. 6B). 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 shown in FIG. 7 as an example, parallel to a desired polarization direction P (here, the X-axis direction) across the periphery of the mesa, the side surface of the mesa, the periphery of the mesa upper surface, and the center of the mesa upper surface. A mask M is formed so that two small regions (first small region and second small region) that are opposed to each other are not etched. Specifically, only the top surface of the mesa in FIG. 7 is taken out and enlarged, the code L1 in FIG. 8 is 4.5 μm, the code L2 is 4 μm, the code d is 0.4 μm, and the code e is 2.1 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). The protective layer 111 remaining in the first small region becomes the mode filter 115A, and the protective layer 111 remaining in the second small region becomes the mode filter 115B. Note that FIG. 9B is an enlarged plan view of the mesa upper surface in FIG.

  That is, the mode filter 115 includes a mode filter 115A and a mode filter 115B. In other words, the mode filter 115 has a shape in which cut portions are respectively provided in portions on the + Y side and the −Y side of the center of the emission region in an annular shape surrounding the center portion of the emission region.

  The two cut portions of the mode filter 115 are both smaller on the side closer to the center of the emission region than on the far side.

  Here, as a method for forming the mode filter 115, an etching mask having a desired shape is formed on an SiN film formed on the entire surface by a vapor phase chemical deposition method (CVD method), and an unnecessary SiN film is etched. Although the method of removing is used, it is not limited to this. For example, a so-called lift-off method may be used in which a resist pattern serving as a mask is formed in advance, an SiN film is formed by a vapor chemical deposition method (CVD method), and then unnecessary resist patterns are removed.

(10) A square resist pattern having a side of 14 μm is formed in a region to be a light emitting portion on the upper part of the mesa, and a 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) Lift off the electrode material deposited in the region (emission region) to be the light emitting part to form the p-side electrode 113 (see FIG. 10). A region surrounded by the p-side electrode 113 is an emission region. FIG. 11 shows an enlarged plan view of the mesa upper surface in FIG. The shape of the injection region is a square having a side length of L4 (here, 14 μm). In this embodiment, the mode filter 115A is formed as a transparent dielectric film made of SiN having an optical thickness of λ / 4 on two small regions (first small region and second small region) in the emission region. A mode filter 115B 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. 12). 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.

  Then, the surface emitting laser element 100 is obtained through several post-processes.

  Here, a plurality of semiconductor layers are stacked similarly to the surface emitting laser element 100, and as shown in FIG. 13 as an example, one circular small region surrounding the central portion is set in the circular emission region, For a surface-emitting laser element (calculated surface-emitting laser element) in which a transparent dielectric film having an optical thickness of λ / 4 is formed in the small region, the small region width L2 is fixed to 3 μm. The oscillation mode distribution was obtained by calculation while changing the inner diameter L1 of the region. In the calculation, the diameter of the current passage region is 4.5 μm.

  FIG. 14 shows the relationship between the inner diameter L1 of the small region and the Q value in the high-order transverse mode obtained from the above calculation results. Here, the Q value is a dimensionless numerical value indicating the performance of the resonator for each mode, and is inversely proportional to the oscillation wavelength and the loss factor of the resonator. That is, when the oscillation wavelength is λ [m] and the loss factor of the resonator is α [1 / m], Q∝1 / λα. Incidentally, since the oscillation wavelength λ is constant, the Q value is determined by the resonator loss. Therefore, the larger the Q value for each mode, the smaller the resonator loss, and the mode is more likely to oscillate.

  According to this, it can be seen that when the value of L1 is in the range of 4 μm to 9 μm, the Q value of the high-order transverse mode is significantly reduced. The Q value corresponds to the magnitude of light confinement in the vertical direction. The higher this value, the smaller the threshold current. Therefore, when the value of L1 is within the above range, the distribution of the high-order transverse mode overlaps the low-reflectance region and the high-order transverse mode oscillation is suppressed. On the other hand, when L1 is out of the above range, the Q value increases, so that high-order transverse mode light is likely to oscillate.

  That is, in order to obtain a high effect of suppressing the high-order transverse mode, it can be said that it is desirable to reduce the reflectance of the annular region located slightly outside the current passage region when viewed from the Z-axis direction. .

  Further, FIG. 15 shows the relationship between the inner diameter L1 of the small region and the lateral optical confinement factor of the fundamental transverse mode obtained from the calculation result. According to this, the light confinement action in the lateral direction tends to increase when the inner diameter L1 of the small region is reduced, and is highest when the inner diameter L1 is reduced to about 5 μm. This is a calculation result in the case of central symmetry and isotropic. However, in the case of a shape having anisotropy in two orthogonal directions, the magnitude of the optical confinement action may be different in the two orthogonal directions. At this time, the polarization component in the direction of strong confinement becomes easier to oscillate than the polarization component in the direction of weak confinement, and it is considered that the action of controlling the polarization direction to the direction of strong confinement occurs.

  Next, the single mode output was calculated | required about the surface emitting laser element 100 manufactured as mentioned above. Here, the optical output at which the output ratio SMSR (Side Mode Suppression Ratio) between the basic transverse mode and the higher order transverse mode is 20 dB is defined as a single mode output. As a comparative example, as shown in FIG. 16, a single mode output is also obtained for a surface emitting laser element in which the low reflectance region is an annular shape without a cut portion (referred to as “surface emitting laser element A” for convenience). Asked. As a result, the surface-emitting laser element 100 was able to obtain a high output substantially equivalent to that of the surface-emitting laser element A.

  In the surface emitting laser element 100, in order to make the low reflectance region have anisotropy in two orthogonal directions, a cut portion is provided and a part of the annular region is omitted. Since the width closer to the center (here, about 5 to 9 mm from the center) is narrower than the peripheral side where the effect of suppressing the next transverse mode is low (here, 9 mm or more from the center), It is thought that the inhibitory effect could be maintained.

  Further, for the surface-emitting laser element 100, the intensity ratio PMSR (Polarization Mode Suppression Ratio) of polarization components orthogonal to each other was obtained. As a comparative example, PMSR was also obtained for the surface emitting laser element A.

  As a result, in the surface emitting laser element 100, the polarization direction was aligned in the X-axis direction, and a high PMSR of 20 dB or more was obtained. This is a value higher than that of the surface emitting laser element A, and it is considered that the stability of the polarization direction is improved by providing a cut portion in a part of the low reflectance region.

  As described above, according to the surface emitting laser device 100 according to the present embodiment, the resonator structure including the buffer layer 102, the lower semiconductor DBR 103, and the active layer 105, the upper semiconductor DBR 107, and the contact layer 109 are stacked on the substrate 101. Has been. A p-side electrode 113 is provided on the emission surface from which the laser beam is emitted so as to surround the emission region. 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. The mode filter 115A and the mode filter 115B, which are optically transparent dielectric films that are lower than the reflectance at the center of the optical filter, are formed with an optical thickness of λ / 4.

  The mode filter 115 composed of the mode filter 115A and the mode filter 115B has a cut-out portion at the + Y side and the −Y side of the center of the emission region in an annular shape surrounding the center portion in the emission region. The shape is provided. Each cut portion is set so that the side closer to the center of the emission region is smaller than the far side.

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

  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, an effect of defining the polarization direction by using the inclined substrate is added, and the stability of the polarization direction can be further improved.

  According to the optical scanning device 1010 according to the present embodiment, since the light source 14 includes the surface emitting laser element 100, a substantially circular and minute laser spot can be easily and stably formed on the surface of the photosensitive drum 1030. Can do. Therefore, it is possible to perform optical scanning with high accuracy.

  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-described embodiment, the case where the protective layer 111 is SiN has been described. However, the present invention is not limited to this. For example, any of SiN _x , SiO _x , TiO _x, and SiON may be used. By designing the film thickness according to the refractive index of each material, it is possible to obtain the same effect as in the above embodiment.

  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 mode filter 115A and the mode filter 115B 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 shape of the mode filter 115 was a shape which provided the cutting part in the annular | circular shape, it is not limited to this (FIG. 17 (A)-FIG. 18 (C) )reference).

  Moreover, although the said embodiment demonstrated the case where the shape of the electric current passage area | region was rectangular shape, it is not limited to this, Shapes other than a rectangle (for example, circular shape and polygonal shape) may be sufficient.

  In the above embodiment, the case where the optical thickness of each mode filter is λ / 4 has been described. However, the present invention is not limited to this. As an example, the optical thickness of each mode filter may be 3λ / 4 as in the surface emitting laser element 100B shown in FIGS. 19 (A) and 19 (B). In short, if the optical thickness of each mode filter is an odd multiple of λ / 4, the transverse mode suppression effect similar to that of the surface emitting laser element 100 of the above embodiment can be obtained. FIG. 19A is a view showing a cut surface when the surface emitting laser element 100B is cut in parallel to the XZ plane, and FIG. 19B is a view showing the surface emitting laser element 100B in parallel to the YZ plane. It is a figure which shows a cut surface when cut | disconnecting.

  In this case, after forming the p-side electrode 113 in the same manner as in the above embodiment, the protective layer 116 made of SiN is formed to have an optical thickness of 2λ / 4 by using a chemical vapor deposition method (CVD method). It forms so that it may become. 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.

  Alternatively, after forming the protective layer 116 on the entire surface of the emission region so that the optical thickness becomes 2λ / 4, the protective layer 116 having the optical thickness of λ / 4 may be formed on each small region. good.

  At this time, the central portion of the emission region is covered with a protective layer 116 (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) around the emission region is also covered with a protective layer 116 (dielectric film) having an optical thickness of 2λ / 4. The Rukoto.

  Further, in the surface emitting laser element 100B, since the entire emission surface is covered with the protective layer 116 (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 116 (dielectric film), since the optical thickness is an even multiple of λ / 2, the protective layer does not decrease the reflectance. Optical characteristics equivalent to those without 116 (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 effect as in the above embodiment is obtained. Obtainable.

  At this time, the manufacturing cost can be reduced by using the same material for the part of the dielectric film whose reflectance is to be reduced and the part of the dielectric film for the other part.

  In the above embodiment, the light source 14 may include a surface emitting laser array 100C shown in FIG. 20 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. 20 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 such that the intervals between the light emitting units are equal to 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. 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 stably 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 stably form 21 minute light spots having a circular shape and a high light density on the photosensitive drum 1030 at the same time.

  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.

  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 a board | substrate was an inclination board | substrate, it is not limited to this, A board | substrate may be a non-inclination board | substrate.

  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. 22, 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. 22, 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 uses a light source including any one of a surface-emitting laser element similar to the surface-emitting laser element 100 or the surface-emitting laser element 100B and a surface-emitting laser array similar to the surface-emitting laser array 100C for each color. Have. 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: 100B: Surface emitting laser element, 100C: Surface emitting laser array, 101: Substrate, 103: Lower semiconductor DBR (part of semiconductor multilayer reflector), 104: Lower spacer layer (part of resonator structure) , 105 ... active layer, 106 ... upper spacer layer (part of the resonator structure), 107 ... upper semiconductor DBR (part of the semiconductor multilayer reflector), 108 ... selective oxidation layer, 113 ... p-side electrode ( Electrode), 115A ... mode filter (part of dielectric film), 115B ... mode filter (part of dielectric film), 1000 ... laser printer (image forming apparatus), 1010 ... optical scanning device, 1030 ... photosensitive. Drum (image bearing member), 2000 ... color printer (image forming apparatus), 2010 ... optical scanning device, K1, C1, M1, Y1 ... photosensitive drum (image bearing member).

JP 2001-156395 A Japanese Patent No. 3955925 JP 2007-201398 A JP 2004-289033 A

Claims (13)

A resonator structure including an active layer, a semiconductor multilayer reflector provided with the resonator structure interposed therebetween, and an electrode provided so as to surround an emission region on an emission surface from which laser light is emitted In surface emitting laser elements,
A transparent dielectric film is formed so as to surround the central portion in the emission region, has a shape anisotropy in two directions orthogonal to each other, and has a reflectance lower than the reflectance of the central portion. ,
The surface emitting laser device according to claim 1, wherein the dielectric film has at least one cut portion, and the width of the cut portion is smaller on the side closer to the central portion than on the far side. The laser beam is linearly polarized light,
2. The surface emitting laser element according to claim 1, wherein the at least one cut-out portion is provided in a direction orthogonal to a polarization direction of the laser light when viewed from the center portion. The at least one excision is two excisions;
The surface emitting laser element according to claim 2, wherein the two cut portions are opposed to each other with the central portion interposed therebetween in a direction orthogonal 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 1, wherein the surface emitting laser element is characterized in that   5. The surface-emitting laser element according to claim 1, wherein the optical thickness of the dielectric film is an odd multiple of “oscillation wavelength / 4”. The surface emitting laser element according to claim 1, wherein the dielectric film is a film of any one of SiN _x , SiO _x , TiO _x, and SiON.   The region having a relatively high reflectance in the emission region is covered with a transparent dielectric film having an optical thickness that is an even multiple of “oscillation wavelength / 4”. The surface emitting laser element according to claim 6.   8. The dielectric film covering the region having a relatively high reflectance is formed of the same material as the dielectric film that is formed so as to surround a central portion in the emission region and lowers the reflectance. The surface emitting laser element according to 1.   A surface emitting laser array in which the surface emitting laser elements according to any one of claims 1 to 8 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 claim 1;
Deflection means for deflecting light from the light source;
A scanning optical system for condensing the light deflected by the deflecting means 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 9;
Deflection means for deflecting light from the light source;
A scanning optical system for condensing the light deflected by the deflecting means 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 10 or 11 that scans the at least one image carrier with light modulated according to image information.   The image forming apparatus according to claim 12, wherein the image information is multicolor color image information.

Images