JP2015026637A - Surface emission laser element, surface emission laser array, optical scanner, image forming apparatus, and method for manufacturing surface emission laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface emission laser element capable of controlling a polarization direction to be constant and reducing a deviation amount of an emission direction from a direction perpendicular to a surface of an inclined substrate even when an energizing time is elongated.SOLUTION: A surface emission laser element 100 includes a lower reflection mirror 103, a resonator structure including an active layer 105, and an upper reflection mirror 107, stacked on a substrate 101 (inclined substrate) and emits laser light from an emission region enclosed by an upper electrode 111. At a time of starting energizing, an emission direction of the laser light from the emission region is tilted in an opposite direction to a direction where the emission direction drifts with time with respect to a plane orthogonal to the inclination direction of the substrate 101. By this configuration, a polarization direction can be maintained constant, and a deviation in the emission direction from the normal direction on the surface (reference plane) of the inclined substrate can be reduced even when the energizing time is elongated.

Description

  The present invention relates to a surface emitting laser element, a surface emitting laser array, an optical scanning device, and an image forming apparatus. More specifically, a lower reflecting mirror, a resonator structure including an active layer, and an upper reflecting mirror are stacked on an inclined substrate. Surface emitting laser element, surface emitting laser array including the surface emitting laser element, optical scanning device including the surface emitting laser element or the surface emitting laser array, image forming apparatus including the optical scanning device, and the surface emitting laser The present invention relates to a method for manufacturing an element.

  2. Description of the Related Art Conventionally, a surface-emitting type semiconductor laser in which a first reflection mirror layer, a spacer layer including a quantum well active layer, a second reflection mirror layer, and the like are stacked on a semiconductor substrate and emits laser light is known (for example, Patent Documents). 1).

  In this surface emitting semiconductor laser, the main surface (front surface) of the semiconductor substrate is inclined with respect to the plane including the crystal axis serving as a reference, and the polarization direction is constant.

  However, in the surface emitting semiconductor laser disclosed in Patent Document 1, when the energization time is increased, the emission direction is greatly deviated from the direction perpendicular to the main surface (front surface) of the semiconductor substrate.

  The present invention relates to a surface emitting laser element in which a lower reflecting mirror, a resonator structure including an active layer, and an upper reflecting mirror are stacked on an inclined substrate, and laser light is emitted from an emission region surrounded by electrodes. The surface emitting laser element is characterized in that an emission direction of the laser light from the emission region in is inclined to a side opposite to a direction of temporal variation of the emission direction with respect to a plane orthogonal to the inclination direction of the inclined substrate. It is.

  According to this, the polarization direction can be made constant, and even when the energization time becomes long, the deviation amount in the emission direction from the direction perpendicular to the surface of the inclined substrate can be reduced.

It is a figure for demonstrating schematic structure of the laser printer which concerns on one Embodiment of this invention. It is a figure for demonstrating the optical scanning device in FIG. It is a figure for demonstrating the arrangement | sequence of the some surface emitting laser element of a surface emitting laser array. It is FIG. (1) for demonstrating the structure of a surface emitting laser element. It is FIG. (2) for demonstrating the structure of a surface emitting laser element. It is a top view of the mesa of a surface emitting laser element. FIGS. 7A and 7B are views (No. 1 and No. 2) for explaining the inclined substrate, respectively. It is FIG. (1) for demonstrating the manufacturing method of a surface emitting laser element. It is FIG. (2) for demonstrating the manufacturing method of a surface emitting laser element. It is FIG. (3) for demonstrating the manufacturing method of a surface emitting laser element. It is a figure for demonstrating deviation | shift amount (DELTA) y from the center of the injection | emission area | region of the center of the area | region enclosed by a dielectric film. 12 (A) and 12 (B) are diagrams for explaining temporal variations in the emission direction of the conventional surface emitting laser elements A and B, respectively. FIGS. 13A and 13B are diagrams for explaining temporal variation in the emission direction of the surface emitting laser elements of Examples 1 and 2 of the present embodiment, respectively. 6 is a plan view of a mesa of a surface emitting laser element according to Modification 1. FIG. 10 is a plan view of a mesa of a surface emitting laser element according to Modification 2. FIG.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a laser printer 500 according to an embodiment.

  The laser printer 500 includes an optical scanning device 900, a photosensitive drum 901, a charging charger 902, a developing roller 903, a toner cartridge 904, a cleaning blade 905, a paper feeding tray 906, a paper feeding roller 907, a registration roller pair 908, and a transfer charger 911. , A static elimination unit 914, a fixing roller 909, a paper discharge roller 912, a paper discharge tray 910, and the like.

  The charging charger 902, the developing roller 903, the transfer charger 911, the charge removal unit 914, and the cleaning blade 905 are each disposed near the surface of the photosensitive drum 901. Then, with respect to the rotation direction of the photosensitive drum 901, the charging charger 902, the developing roller 903, the transfer charger 911, the static elimination unit 914, and the cleaning blade 905 are arranged in this order.

  A photosensitive layer is formed on the surface of the photosensitive drum 901. Here, the photosensitive drum 901 rotates in the clockwise direction (arrow direction) in the plane in FIG. The charging charger 902 uniformly charges the surface of the photosensitive drum 901.

  The optical scanning device 900 irradiates the surface of the photosensitive drum 901 charged by the charging charger 902 with light modulated based on image information from a host device (for example, a personal computer). As a result, a latent image corresponding to the image information is formed on the surface of the photosensitive drum 901 on the surface of the photosensitive drum 901. The latent image formed here moves in the direction of the developing roller 903 as the photosensitive drum 901 rotates. The configuration of the optical scanning device 900 will be described later.

  The toner cartridge 904 stores toner, and the toner is supplied to the developing roller 903. The developing roller 903 causes the toner supplied from the toner cartridge 904 to adhere to the latent image formed on the surface of the photosensitive drum 901 to visualize the image information. Here, the latent image to which the toner is attached moves in the direction of the transfer charger 911 as the photosensitive drum 901 rotates.

  Recording paper 913 is stored in the paper feed tray 906. A paper feed roller 907 is disposed in the vicinity of the paper feed tray 906, and the paper feed roller 907 takes out the recording paper 913 one by one from the paper feed tray 906 and conveys it to the registration roller pair 908. The registration roller pair 908 is disposed in the vicinity of the transfer charger 911, temporarily holds the recording paper 913 taken out by the paper feed roller 907, and the photosensitive paper drum 901 is rotated in accordance with the rotation of the photosensitive drum 901. It is sent out toward the gap between 901 and the transfer charger 911.

  A voltage having a polarity opposite to that of the toner is applied to the transfer charger 911 in order to electrically attract the toner on the surface of the photosensitive drum 901 to the recording paper 913. With this voltage, the latent image on the surface of the photosensitive drum 901 is transferred to the recording paper 913. The recording sheet 913 transferred here is sent to the fixing roller 909.

In the fixing roller 909, heat and pressure are applied to the recording paper 913, whereby the toner is fixed on the recording paper 913. The recording paper 913 fixed here is sent to the paper discharge tray 910 via the paper discharge roller 912 and sequentially stacked on the paper discharge tray 910.
The neutralization unit 914 neutralizes the surface of the photosensitive drum 901. The cleaning blade 905 removes toner remaining on the surface of the photosensitive drum 901 (residual toner). The removed residual toner is used again. The surface of the photosensitive drum 901 from which the residual toner has been removed returns to the position of the charging charger 902 again.

  Next, the configuration and operation of the optical scanning device 900 will be described with reference to FIG. The optical scanning device 900 includes a light source unit 10 including a surface emitting laser array LA, a coupling lens 11, an aperture member 12 (opening member), a cylindrical lens 13, a polygon mirror 14, an fθ lens 15, a toroidal lens 16, and two mirrors. (17, 18), and a main control device (not shown) for comprehensively controlling the above-described units.

  The coupling lens 11 shapes the light beam emitted from the light source unit 10 into substantially parallel light. The aperture member 12 defines the beam diameter of the light beam that has passed through the coupling lens 11. The cylindrical lens 13 condenses the light beam that has passed through the aperture (aperture) of the aperture member 12 on the reflection surface of the polygon mirror 14 via the mirror 17.

  The polygon mirror 14 is formed of a regular hexagonal columnar member having a low height, and six deflection surfaces are formed on the side surface. Then, it is rotated at a constant angular velocity in the direction of the arrow shown in FIG. 2 by a rotation mechanism (not shown). Therefore, the light beam emitted from the light source unit 10 and condensed on the deflection surface of the polygon mirror 14 by the cylindrical lens 13 is deflected at a constant angular velocity by the rotation of the polygon mirror 14.

  The fθ lens 15 has an image height proportional to the incident angle of the light beam from the polygon mirror 14, and moves the image surface of the light beam deflected by the polygon mirror 14 at a constant angular velocity at a constant speed in the main scanning direction. Let

  The toroidal lens 16 forms an image of the light beam from the fθ lens 15 on the surface of the photosensitive drum 901 via the mirror 18.

  In this case, when a plurality of surface emitting laser elements 100 (VCSEL: Vertical Cavity Surface Emitting Laser) included in the surface emitting laser array LA are two-dimensionally arranged as shown in FIG. 3, in the surface emitting laser array LA, Since the intervals of perpendiculars extending in a straight line extending in the direction corresponding to the sub-scanning direction (hereinafter also referred to as sub-scanning corresponding direction) from the center of each surface emitting laser element 100 are equal intervals (referred to as interval d2), By adjusting this timing, it can be considered that the configuration is similar to the case where the light sources are arranged at equal intervals in the sub-scanning corresponding direction on the photosensitive drum 901. Here, the sub-scanning corresponding direction is the y-axis direction.

  For example, if the pitch d1 of the surface emitting laser elements 100 in the sub-scanning corresponding direction is 26.5 μm, the interval d2 is 2.65 μm. If the magnification of the optical system is doubled, writing dots can be formed on the photosensitive drum 901 at intervals of 5.3 μm in the sub-scanning direction. This corresponds to 4800 dpi (dots / inch). That is, high-density writing of 4800 dpi (dot / inch) can be performed.

  Of course, the number of surface emitting lasers in the direction corresponding to the main scanning direction (hereinafter also referred to as the main scanning corresponding direction) is increased, or the array d is arranged such that the pitch d1 is reduced and the interval d2 is further reduced. If the magnification is reduced, the density can be increased and higher quality printing can be achieved. Note that the writing interval in the main scanning direction can be easily controlled by the lighting timing of the light source. Here, the main scanning corresponding direction is the x-axis direction.

  FIG. 4 shows a yz sectional view of the surface emitting laser element 100. FIG. 5 shows an xz sectional view of the surface emitting laser element 100. FIG. 6 shows a plan view of the mesa of the surface emitting laser element 100 (viewed from the + z side).

  As an example, the surface emitting laser element 100 is a surface emitting laser element having an oscillation wavelength band of 780 nm. As shown in FIGS. 4 and 5, the substrate 101, the lower reflecting mirror 103, the lower spacer layer 104, and the active layer 105 are used. , An upper spacer layer 106, an upper reflecting mirror 107, and the like.

  The main surface (front surface) of the substrate 101 is a mirror-polished surface, and as shown in FIG. 7A, the normal direction of the mirror-polished surface (the direction parallel to the z-axis) is the crystal orientation [1 0 0. ] Is an n-GaAs single crystal substrate tilted by θ (= 15 °) toward the crystal orientation [1 1 1] A direction. That is, the substrate 101 is a so-called inclined substrate. Here, as shown in FIG. 7B, 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. Therefore, the tilt axis of the tilted substrate is parallel to the x axis. The −y direction is also referred to as “the tilt direction of the tilted substrate”. That is, the “inclination direction of the inclined substrate” is orthogonal to both the normal line and the inclined axis of the surface (mirror polished surface) of the inclined substrate.

  Thus, by using an inclined substrate as the substrate 101, the crystal structure becomes asymmetric with respect to the main surface of the substrate 101, and anisotropy can be imparted to the optical gain. As a result, the polarization direction can be aligned with a specific direction in which the optical gain is increased.

  4 and 5, a lower electrode 113 (n-side electrode) is formed on the back surface of the substrate 101. Here, the lower electrode 113 is a multilayer film made of AuGe / Ni / Au.

The lower reflecting mirror 103 is stacked on the surface of the substrate 101 via the buffer layer 102, and includes a low refractive index layer made of n-Al _0.9 Ga _0.1 As and n-Al _0.3 Ga _0.7 As. 37.5 pairs of high refractive index layers made of 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. 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 laminated on the lower reflecting mirror 103, and is non-doped Al _0.6 Ga _0.4 As.

The active layer 105 is stacked on the lower spacer layer 104 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 Al _0.12 Ga _0.88 As, and each barrier layer is made of Al _0.3 Ga _0.7 As.

The upper spacer layer 106 is laminated on the active layer 105 and is made of non-doped Al _0.6 Ga _0.4 As.

  A portion including the lower spacer layer 104, the active layer 105, and the upper spacer layer 106 is also called a resonator structure, and includes an optical thickness of one wavelength including one half of the adjacent composition gradient layer. It is set to be. 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 reflecting mirror 107 is laminated on the upper spacer layer 106, and includes a low refractive index layer made of p-Al _0.9 Ga _0.1 As and a high refractive index layer made of p-Al _0.3 Ga _0.7 As. There are 24 pairs. 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. 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 resonator structure in the upper reflecting mirror 107 includes a selective oxide layer 108 including an oxide 108a (oxidized region) and a current passing region 108b surrounded by the oxide 108a. The current flowing through the upper reflector is confined by the selective oxide layer and efficiently injected into the active layer. Here, the planar shape (the shape seen from the + z side) of the current passage region 108b is a square (see FIG. 6).

  A contact layer 109 made of p-GaAs is laminated on the upper reflecting mirror 107. Then, an optically transparent protective film 110 made of p-SiN is formed so as to cover the resonator structure, and an upper electrode 111 (p-side electrode) is provided on the protective film 110. It has been. The upper electrode 111 is in ohmic conduction with the upper reflecting mirror 107 through the contact layer 109. Therefore, by applying a predetermined voltage between the upper electrode 111 and the lower electrode 113 (by energizing the surface emitting laser element 100), current can be injected into the active layer 105 to cause laser oscillation. The upper electrode 111 has, for example, a square opening on the contact layer 109 (see FIG. 6).

  The optical thickness of the protective film 110 is preferably (2n−1) λ / 4 (n is a natural number), and here is λ / 4.

  For example, a square area (opening) surrounded by the upper electrode 111 is referred to as an “emission area”. A dielectric film 112 is provided in the emission region. Here, the xy position (position in the xy plane) of the center of the emission region coincides with the xy position of the center of the current passing region. That is, the center of the emission region and the center of the current passage region are located on the same straight line perpendicular to the surface (mirror polished surface) of the substrate 101.

  As will be described later in detail, the dielectric film 112 is a part of a p-SiN layer that is stacked on the contact layer 109 when the protective film 110 is formed.

  As an example, as shown in FIG. 6, the dielectric film 112 has a donut-shaped planar shape in which the center of the inner diameter is eccentric. Specifically, in the dielectric film 112, the center of the outer diameter coincides with the center of the injection region, and the center of the inner diameter is shifted from the center of the injection region in the + y direction (see FIG. 11). That is, the center of the predetermined region surrounded by the dielectric film 112 is shifted in the + y direction with respect to the center of the emission region.

  In this case, a reflectance distribution in the xy plane is generated during laser oscillation. That is, in the surface emitting laser element 100, the reflectance is lower at the xy position where the dielectric film 112 is provided than at the xy position where the dielectric film 112 is not provided.

  The optical thickness of the dielectric film 112 is (2n−1) λ / 4 (n is a natural number) (here, λ / 4), like the protective film 110. In this case, the reflectance of the peripheral part of the emission region can be sufficiently reduced, and higher-order mode oscillation can be sufficiently suppressed.

  As a result, the output of the higher-order mode light emitted from the peripheral portion of the emission region where the dielectric film 112 is present without lowering the output of the fundamental mode light emitted from the central portion of the emission region where the dielectric film 112 is absent. Can be sufficiently reduced.

  Next, a manufacturing method of the surface emitting laser array LA including the plurality of surface emitting laser elements 100 will be described.

  First, each semiconductor layer is sequentially stacked on the substrate 101 by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

Here, an example using the MOCVD method will be described. Trimethylaluminum (TMA), trimethylgallium (TMG), and trimethylindium (TMI) are used as Group III materials, and arsine (AsH ₃ ) is used as Group V materials. Further, carbon tetrabromide (CBr ₄ ) is used as a p-type dopant material, and hydrogen selenide (H ₂ Se) is used as an n-type dopant material.

  Specifically, the buffer layer 102, the lower reflecting mirror 103, the lower spacer layer 104, the active layer 105, the upper spacer layer 106, the upper reflecting mirror 107, and the contact layer 109 are sequentially grown on the substrate 101 to obtain a stacked body. (See FIG. 8). Note that. A selective oxidation layer 108 made of p-AlAs having a thickness of 30 nm is provided at a position 3 pairs away from the upper spacer layer of the upper reflecting mirror 107.

Next, a square resist pattern having a side length of 20 μm is formed using a known photolithography technique, and the laminate is dry-etched by an ECR etching method using Cl ₂ gas, so that at least the selective oxide layer 108 is formed. A square mesa having a planar shape of 20 um square is formed so as to be exposed (see FIG. 9). Here, the etching bottom surface is the upper surface of the lower spacer layer 104. In FIG. 9 and FIG. 10, only one mesa is shown for convenience. Actually, 40 mesas are formed for one surface emitting laser array LA.

  Next, the laminate on which the mesa is formed is heat-treated in water vapor. Thereby, Al (aluminum) in the selective oxidation layer 108 is selectively oxidized from the outer peripheral portion of the mesa, and an unoxidized region 108b surrounded by the Al oxide 108a remains in the central portion of the mesa ( (See FIG. 10). 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, for example, a square current passing area of 4.5 um square is formed.

  Next, an optically transparent p-SiN layer made of p-SiN is formed using a p-CVD method. Here, the optical thickness of the p-SiN layer was set to λ / 4.

  Next, using a photolithographic technique, the p-SiN layer is wet etched using BHF (buffered hydrofluoric acid) as an etchant to form the protective film 110 and the dielectric film 112, and the deposition of the p-side electrode material is performed. I do. Here, the p-SiN layer is etched so that an opening (contact hole) for taking out the p-side electrode is formed and a part of the dielectric film 112 remains in the emission region (FIGS. 4 to 5). 6).

  As the p-side electrode material, a multilayer electrode made of Ti / Pt / Au is used. The p-side electrode material is patterned so as to form a square-shaped emission region having a side length of 10 μm in the center of the mesa to form the upper electrode 111 (p-side electrode). The p-SiN film remaining in the emission region surrounded by the upper electrode 111 is the dielectric film 112. Here, the center of the inner diameter of the dielectric film 112 is shifted by Δy (for example, 0.2 μm) in the + y direction from the center of the emission region (see FIG. 11).

  Next, after polishing the back side of the substrate 101 to a predetermined thickness (for example, about 100 μm), the lower electrode 113 (n-side electrode) is formed. Here, the lower electrode 113 is a multilayer film made of AuGe / Ni / Au.

  Then, through a plurality of processes including, for example, a cleaving process, a surface emitting laser array LA including a plurality of two-dimensionally arranged surface emitting laser elements 100 is manufactured.

  The surface emitting laser element (VCSEL) configured and manufactured as described above has features such as low power consumption, a circular beam shape, and easy two-dimensional array. From these features, the surface emitting laser element is preferably used as a light source in the optical writing field and the optical communication field as in the present embodiment.

  In such a field, in particular, it is required that the polarization direction of the laser light emitted from the surface emitting laser element is constant and the laser light is emitted perpendicularly to the reference surface (substrate surface). The

  By the way, a surface emitting laser element made of a semiconductor material exhibits temporal changes in various characteristics due to energization. The injection direction is one such characteristic. Here, the “emission direction” means a direction in which the intensity of the laser light emitted from the surface emitting laser element is maximized.

  The inventors have found that in a surface emitting laser element using a tilted substrate, the emission direction varies along the tilt direction of the tilted substrate (in the tilt direction or in the opposite direction) as the energization time increases. It was.

  Then, the spread of the laser beam radiation angle in the direction in which the dielectric film is arranged closer to the straight line that is orthogonal to the surface of the inclined substrate and passes through the center of the current passage region and the center of the emission region is suppressed. It has been found by the inventors' investigation.

  Based on the knowledge based on this study, by shifting the center of the inner diameter of the dielectric film 112 from the center of the emission region, the laser beam emission direction can be changed in the direction opposite to the direction of the deviation.

  Therefore, in the surface emitting laser element 100 of the present embodiment, the emission direction at the initial stage of energization including the time of energization is parallel to the zx plane (the plane including the normal line and the tilt axis of the mirror-polished surface of the substrate 101). The reflectance distribution by the dielectric film 112 is given in advance (at the time of design) so as to be slightly shifted to the −y side (tilt direction side).

  Actually, the emission direction at the start of energization of the surface emitting laser element 100 was measured. As a result, the direction perpendicular to the reference plane (xy plane) including the tilt direction and the tilt axis of the tilted substrate (the method of the mirror polished surface) Line direction), that is, 0.05 deg in the -y direction with respect to the plane orthogonal to the inclination direction.

  When the surface emitting laser element 100 was energized for 300 hours under an APC condition of 1.5 mW at a temperature of 70 ° C., the emission direction was measured again. As a result, the emission direction was 0. 0 in the + y direction from the direction perpendicular to the reference plane. It was tilted by 05deg. As a result, the injection direction is inclined (varied) by 0.1 deg in the + y direction.

  Therefore, the injection direction is inclined by 0.03 deg or more in the opposite direction (−y direction) to the direction (+ y direction) in which the injection direction fluctuates with respect to the plane orthogonal to the tilt direction in the initial period of energization including the start of energization. Preferably it is. In this case, the inclination of the injection direction after energization for a long time from the direction orthogonal to the reference plane can be minimized. However, considering the allowable range of the emission direction required for the surface emitting laser element 100, the inclination of the emission direction from the direction orthogonal to the reference plane is preferably 0.5 deg or less, for example, in the initial stage of energization.

  That is, in the surface emitting laser element of the present embodiment, the direction from the direction orthogonal to the reference plane of the emission direction is optimized so as to be optimal with respect to the energization time required for the element and the amount of change in the inclination of the emission direction within that time. A higher effect can be obtained by setting an initial value of inclination (a value at the start of energization).

  A conventional surface emitting laser element (surface emitting laser element designed so that the emission direction is in a direction perpendicular to the reference plane that is the surface of the tilted substrate) was energized in the same manner, and the emission direction was measured. The injection direction fluctuated by 0.1 deg in the + y direction, and as a result, tilted by 0.1 deg in the + y direction from the direction orthogonal to the reference plane.

  When the deviation in the emission direction from the direction orthogonal to the reference plane is evaluated in terms of absolute value, the conventional surface emitting laser element has fluctuated in the range of 0 deg to 0.1 deg, whereas the surface emitting laser element of this embodiment is Thus, the fluctuation was in the range of 0 deg to 0.05 deg, and the amount of inclination deviation from the direction perpendicular to the reference plane in the injection direction within the same time could be reduced to half.

  In FIGS. 12A and 12B, the emission directions of conventional surface emitting laser elements A and B each using an inclined substrate are two-dimensionally shown. In FIGS. 12A and 12B, the origin O indicates the direction orthogonal to the reference plane, and the two crosses indicate the laser light emission direction at the start of energization and after long-time energization, respectively. Yes. In the reference plane (surface of the inclined substrate), the direction orthogonal to the inclination direction of the inclined substrate is the x-axis direction, and the parallel direction is the y-axis direction. A circle (broken line) centered on the origin O indicates the allowable range in the emission direction required for the surface emitting laser element.

  In the conventional surface emitting laser elements A and B, in the initial energization state, the emission direction is in a direction orthogonal to the reference plane or a direction close thereto. However, the injection direction varies along the tilt direction of the substrate due to the variation over time. Here, a case is shown in which the variation with time occurs in the opposite direction (+ y direction) to the tilt direction (−y direction). As a result, in the surface emitting laser elements A and B, the emission direction is out of the allowable range.

  FIGS. 13A and 13B two-dimensionally show the emission directions of the surface emitting laser elements of Examples 1 and 2 of the present embodiment.

  In the surface emitting laser elements of Examples 1 and 2, the emission direction in the initial energization state is within the allowable range, and the inclination direction side (−y side) with respect to the plane orthogonal to the inclination direction, that is, the emission direction varies with time. It is facing the opposite direction. Then, after energization for a long time, the injection direction is directed to the opposite side (+ y side) to the plane orthogonal to the tilt direction within the allowable range.

  In this case, it is possible to compensate (cancel) the temporal variation in the injection direction and keep the injection direction after the temporal variation within an allowable range.

  As described so far, it is desirable to use an inclined substrate in order to provide a surface emitting laser element having a constant polarization direction. However, by using the tilted substrate, the emission direction of the surface emitting laser element changes along the tilt direction of the tilted substrate as the energization time increases.

  That is, in a surface-emitting laser element using an inclined substrate, even if the emission direction is designed to be perpendicular to the reference plane, the emission direction becomes the reference plane (the surface of the inclined substrate) as the energization time increases. ) Gradually from the direction perpendicular to the inclination direction of the inclined substrate.

  In the surface emitting laser element of the present embodiment described above, the lower reflecting mirror 103, the resonator structure including the active layer 105, and the upper reflecting mirror 107 are laminated on the substrate 101 which is an inclined substrate, and is surrounded by the upper electrode 111. This is a surface emitting laser element that emits laser light from the emission region, and the direction of emission of the laser light from the emission region at the start of energization (the direction in which the intensity of the laser light is maximum) is orthogonal to the inclination direction of the inclined substrate It is inclined to the opposite side to the direction of temporal variation of the injection direction with respect to the surface to be moved.

  In this case, it is possible to obtain the anisotropy of the gain in the tilt direction by the tilted substrate and to compensate (cancel) the variation with time in the injection direction.

  As a result, the polarization direction can be made constant, and the amount of deviation in the emission direction from the direction perpendicular to the surface of the inclined substrate can be reduced even when the energization time is increased.

  In addition, since the injection direction at the start of energization is inclined by 0.03 deg to 0.1 deg with respect to the plane orthogonal to the tilt direction of the substrate 101, the variation in the injection direction over time can be caused even for a long time energization. Compensation (cancellation) makes it possible to keep the injection direction within an allowable range regardless of the energization time.

  Further, the upper reflecting mirror 107 has an oxide constriction structure that forms a current passage region with an oxide, and a dielectric film 112 surrounding at least a part of a predetermined region including the center of the emission region is formed in the emission region. The center of the current passing area and the center of the emission area are located on the same straight line perpendicular to the surface of the substrate 101, and the center of the predetermined area is shifted in the tilt direction with respect to the center of the emission area. ing. In this case, the emission direction of the laser beam can be adjusted with high accuracy, and a surface emitting laser element in which the emission direction is offset in a direction that changes with time can be easily produced.

  The optical thickness of the dielectric film 112 is (2n−1) λ / 4 (n is a natural number) when the oscillation wavelength of the laser beam is λ. Therefore, the reflectance at the periphery of the emission region is Can be sufficiently reduced, and high-order mode oscillation can be sufficiently suppressed.

  The normal direction of the main surface of the substrate 101 is inclined toward the crystal orientation [1 1 1] A direction with respect to the crystal orientation [1 0 0] direction, and the emission direction is the normal line. Since it is inclined toward the inclination direction with respect to the direction, it is possible to surely cancel out the deviation in the injection direction with respect to the direction parallel to the inclination direction.

  Further, the surface emitting laser array LA includes a plurality of surface emitting laser elements of the present embodiment that are two-dimensionally arranged.

  In this case, it is possible to provide a surface emitting semiconductor laser array in which all the surface emitting laser elements 100 in the array face a direction close to a direction orthogonal to the reference plane (the surface of the substrate 101).

  At this time, all the surface emitting laser elements in the array do not have to have the same shape, and the emission directions of all the surface emitting laser elements in the array do not have to be the same. For example, when the driving time and load conditions required for each element differ depending on the use of the surface emitting laser array, the shape and the emission direction may be adjusted for each element according to the conditions.

  The optical scanning device 900 includes a light source unit 10 having a surface emitting laser array LA, a polygon mirror 14 for deflecting light from the light source unit 10, and light deflected by the polygon mirror 14 on a photosensitive drum 901. And a scanning optical system for condensing light on the surface (scanned surface).

  In this case, the surface of the photosensitive drum 901 can be scanned stably and accurately at high speed.

  In the optical scanning device 900, the number of the surface emitting laser elements 100 included in the surface emitting laser array LA is not limited to 40, and may be plural.

  The light source unit 10 may have only one surface emitting laser element having the same configuration as each surface emitting laser element of the surface emitting laser array LA, instead of the surface emitting laser array LA.

  The laser printer 500 also includes a photosensitive drum 901 and an optical scanning device 900 that scans the surface of the photosensitive drum 901 with light modulated based on image information.

  In this case, a high-definition image can be formed on the surface of the photosensitive drum 901 at a high speed.

  The shape and arrangement of the dielectric film of the surface emitting laser element 100 of the above embodiment can be changed as appropriate. In short, the dielectric film may be formed so as to surround at least a part of a predetermined region including the center of the emission region.

  For example, as in Modification 1 shown in FIG. 14, two dielectric films 212 having a substantially U shape in plan view are formed, a pair of free ends (open ends) are opposed to each other in the x-axis direction, and each dielectric You may arrange | position so that the center position of a pair of free end of the film | membrane 212 may shift | deviate to + y direction from the center of an injection | emission area | region. That is, each dielectric film 212 may be disposed so as to surround a part of a predetermined region including the center of the emission region.

  Further, for example, as shown in FIG. 15, the center of the dielectric film 312 having a donut shape (a concentric outer shape and an inner shape) is shifted in the + y direction from the center of the emission region. It may be arranged. The dielectric film 312 may be disposed so as to surround the entire predetermined region including the center of the emission region.

  In the above embodiment, the case of the laser printer 500 as the image forming apparatus has been described. However, the present invention is not limited to this. In short, any surface-emitting laser element having the same configuration as each surface-emitting laser element of the surface-emitting laser array LA of the above embodiment, or an image forming apparatus such as a printer or a copier having the surface-emitting laser array LA. High-definition images can be formed at high speed.

  In addition, when an image forming apparatus that forms a color image is used as the image forming apparatus, a high-definition image can be formed at high speed by using an optical scanning device corresponding to the color image.

  As an image forming apparatus for forming a color image, for example, a photosensitive drum for black (K), a photosensitive drum for cyan (C), a photosensitive drum for magenta (M), and a photosensitive drum for yellow (Y). As described above, a tandem color machine including a plurality of photosensitive drums may be used.

  By the way, in an image forming apparatus that forms a color image, a color shift may occur due to a manufacturing error or a position error of each component. Even in such a case, color misregistration can be reduced by selecting a VCSEL to be lit.

  Moreover, although the said embodiment demonstrated the case where the oscillation wavelength of the surface emitting laser element 100 was a 780 nm band, it is not limited to this. By appropriately selecting the material, for example, VCSELs in the wavelength bands of 650 nm band, 850 nm band, 980 nm band, 1.3 um band, and 1.5 um band can be produced in the same manner as in the above embodiment. In this case, the oscillation wavelength of the VCSEL may be changed according to the characteristics of the photoreceptor. The VCSEL can be used for applications other than the image forming apparatus in any wavelength band.

  Moreover, in the said embodiment, although AlGaAs is used as a material of the surface emitting laser element 100, it is not limited to this. For example, the same effect can be obtained even when AlGaInAs or GaInPAs is used. Further, the composition of each element is not limited.

  In particular, 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, the substrate may be made of a material other than GaAs.

  Moreover, in the said embodiment, although the planar shape (shape seen from + z side) of the mesa of each surface emitting laser element is a square, it is not limited to this. The planar shape of the mesa may be a rectangle, a circle, an ellipse, or the like, for example.

  Further, the arrangement of the plurality of VCSELs in the surface emitting laser array LA is not limited to that described in the above embodiment (see FIG. 3). In short, it is preferable that the plurality of VCSELs of the surface emitting laser array are two-dimensionally arranged so that the positions in the sub-scanning corresponding direction (y-axis direction) are different from each other. For example, a surface emitting laser array having a plurality of VCSELs arranged in a matrix may be rotated around the emission direction (z-axis direction).

  Further, as the image forming apparatus, 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 employed.

  For example, the medium may be a printing plate known as CTP (Computer to Plate). That is, the optical scanning device 900 is also suitable for an image forming apparatus that directly forms an image on a printing plate material by laser ablation to form a printing plate.

  For example, the medium may be so-called rewritable paper. For example, a material described below is applied as a recording layer on a support such as paper or a resin film. Then, reversibility is imparted to color development by thermal energy control by laser light, and display / erasure is performed reversibly.

  There are a transparent cloudy type rewritable marking method and a color developing / erasing type rewritable marking method using a leuco dye, both of which can be applied.

  The transparent cloudy type is a polymer thin film in which fine particles of fatty acid are dispersed. When heated to 110 ° C. or higher, the resin expands due to melting of the fatty acid. Thereafter, when cooled, the fatty acid becomes supercooled and remains in a liquid state, and the expanded resin solidifies. Thereafter, the fatty acid solidifies and shrinks to become polycrystalline fine particles, and voids are formed between the resin and the fine particles. Light is scattered by this gap and appears white. Next, when heated to an erasing temperature range of 80 ° C. to 110 ° C., the fatty acid partially melts, and the resin thermally expands to fill the voids. If it cools in this state, it will be in a transparent state and an image will be erased.

  The rewritable marking method using a leuco dye utilizes a reversible color development and decoloration reaction between a colorless leuco dye and a developer / decolorant having a long-chain alkyl group. When heated by laser light, the leuco dye and the developer / decolorant react to develop color, and when rapidly cooled, the colored state is maintained. Then, when it is slowly cooled after heating, phase separation occurs due to the self-aggregating action of the long-chain alkyl group of the developer / decolorant, and the leuco dye and developer / decolorizer are physically separated and decolored.

  In addition, when the medium is exposed to ultraviolet light, it develops in C (cyan) and is decolored by visible R (red) light, and when exposed to ultraviolet light, it develops in M (magenta). A photochromic compound that is decolored by G (green) light, a photochromic compound that develops color when exposed to ultraviolet light (Y) and is decolored by visible B (blue) light. So-called color rewritable paper provided on the body may be used.

  This is a method of expressing full color by controlling the color density of the three types of materials that develop color in Y, M, and C by the time and intensity of applying R, G, and B light once it is made black by applying ultraviolet light. However, if the strong light of R, G, and B is continuously applied, all three types can be decolored to become pure white.

  A device that imparts reversibility to color development by such light energy control can also be realized as an image forming apparatus including an optical scanning device similar to the above-described embodiment.

  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.

  DESCRIPTION OF SYMBOLS 10 ... Light source unit (light source device), 14 ... Polygon mirror (deflector), 100 ... Surface emitting laser element, 101 ... Inclined substrate, 103 ... Lower reflecting mirror, 105 ... Active layer, 107 ... Upper reflecting mirror, 108a ... Oxidation 111, upper electrode (electrode), 112, dielectric film, 500, laser printer, 900, optical scanning device, 901, photosensitive drum (image carrier), LA, surface emitting laser array.

JP 2001-168461 A

Claims (10)

In a surface-emitting laser element in which a lower reflecting mirror, a resonator structure including an active layer, and an upper reflecting mirror are stacked on an inclined substrate, and laser light is emitted from an emission region surrounded by electrodes,
A surface in which an emission direction of laser light from the emission region at the start of energization is inclined to a side opposite to a direction of temporal variation of the emission direction with respect to a surface orthogonal to the inclination direction of the inclined substrate. Light emitting laser element.   2. The surface emitting laser element according to claim 1, wherein the emission direction at the start of energization is tilted by 0.03 deg to 0.5 deg with respect to a plane orthogonal to the tilt direction. The upper reflecting mirror has an oxide constriction structure that forms a current passage region with an oxide,
The emission region is provided with a dielectric film surrounding at least a part of a predetermined region including the center of the emission region,
The center of the current passage region and the center of the emission region are located on the same straight line perpendicular to the surface of the inclined substrate,
The surface emitting laser element according to claim 1, wherein the center of the predetermined region is shifted in the tilt direction with respect to the center of the emission region.   4. The optical thickness of the dielectric film is (2n−1) λ / 4, where λ is an oscillation wavelength of a laser beam. 5. Surface emitting laser element. The normal direction of the main surface of the substrate is inclined toward the crystal orientation [1 1 1] A direction with respect to the crystal orientation [1 0 0] direction,
The surface emitting laser element according to claim 1, wherein the emission direction is inclined toward the inclination direction with respect to the normal direction.   The surface emitting laser array containing the surface emitting laser element as described in any one of Claims 1-5 arranged two-dimensionally. An optical scanning device that scans a surface to be scanned with light,
A light source device comprising the surface emitting laser element according to any one of claims 1 to 5 or the surface emitting laser array according to claim 6.
A deflector for deflecting light from the light source device;
A scanning optical system that condenses the light deflected by the deflector onto the surface to be scanned. At least one image carrier;
An image forming apparatus comprising: at least one optical scanning device according to claim 7 that scans a surface of the at least one image carrier with light modulated based on image information.   The image forming apparatus according to claim 8, wherein the image information is multicolor color image information. In a method of manufacturing a surface emitting laser element in which a lower reflecting mirror, a resonator structure including an active layer, and an upper reflecting mirror are stacked on an inclined substrate, and laser light is emitted from an emission region surrounded by electrodes.
In the emission region, the emission direction of the laser light from the emission region at the start of energization is inclined to the side opposite to the direction of temporal variation of the emission direction with respect to the plane orthogonal to the inclination direction of the inclined substrate. A method of manufacturing a surface emitting laser element, comprising a step of forming a dielectric film.

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