JP4890358B2 - Surface emitting laser array, optical scanning device, image forming apparatus, optical transmission module, and optical transmission system - Google Patents

Description

  The present invention relates to a surface emitting laser array, an optical scanning device, an image forming apparatus, an optical transmission module, and an optical transmission system. More specifically, the present invention relates to a surface emitting laser array having a plurality of light emitting units, and light having the surface emitting laser array. The present invention relates to a scanning device, an image forming apparatus including the optical scanning device, an optical transmission module including the surface emitting laser array, and an optical transmission system including the optical transmission module.

  The surface emitting laser has a pair of distributed Bragg reflectors provided on a semiconductor substrate, and an active layer and a resonator spacer layer provided therebetween. Then, current is injected into the active layer by the electrodes provided in each distributed Bragg reflector, and laser oscillation is generated perpendicular to the semiconductor substrate.

Further, the surface emitting laser has a current confinement structure formed by oxidizing a semiconductor layer containing Al (aluminum) in order to reduce the threshold current and control the transverse mode, and oxidizes the semiconductor layer containing Al. In addition, the light emitting portion is generally processed into a mesa shape. The mesa-shaped structure is protected by an insulating film such as SiO ₂ .

  The surface emitting laser has the characteristics that (1) the threshold current is low, (2) a circular emission beam shape is obtained, and (3) the laser output can be extracted in a direction perpendicular to the semiconductor substrate. In particular, since a laser output can be taken out in a direction perpendicular to the semiconductor substrate, it is easy to integrate a plurality of light emitting units on one semiconductor substrate with high positional accuracy. Therefore, a surface emitting laser array having a plurality of light emitting portions has been attracting attention as a writing light source or a parallel light interconnection light source in an electrophotographic system.

By the way, since the light emitting part has a mesa shape, it is thermally insulated from the surrounding semiconductor layer, and the thermal resistance of the insulating film such as SiO ₂ is much larger than the thermal resistance of the semiconductor. Low heat dissipation. Therefore, in the surface emitting laser array, a plurality of light emitting portions cause thermal interference with each other, and an uneven temperature distribution is likely to occur in the array surface. In general, the light output characteristics of the light emitting part are greatly influenced by temperature. For example, when the temperature becomes higher than the reference temperature, the laser output decreases and the change with time is accelerated. Therefore, in the surface emitting laser array, there is a possibility that the light output characteristics of the respective light emitting units vary due to changes with time.

  Therefore, for example, Patent Document 1 includes a substrate, a plurality of laser elements arranged two-dimensionally on the substrate, and an electrode unit for supplying current to the plurality of laser elements, and includes a plurality of laser elements. Discloses a surface-emitting type semiconductor laser array arranged at least in a region excluding the central portion. This surface-emitting semiconductor laser array reduces the temperature difference between each laser element by suppressing the effect of temperature rise at the center, and makes the characteristics of the array, that is, the oscillation wavelength, light output, and average life uniform. I am trying.

  Patent Document 2 discloses a surface emitting semiconductor laser array in which a plurality of semiconductor laser elements each having an active layer and a pair of mirror layers sandwiching the active layer are arranged in an array on the same substrate, A surface-emitting type semiconductor laser array is disclosed in which a cross-sectional area of a heat conductor coupled to one semiconductor laser element is larger than a cross-sectional area of a heat conductor coupled to another semiconductor laser element. In this surface emitting semiconductor laser array, the cross-sectional area of the electrode wiring coupled to the laser element located at the center of the array can be made larger than the cross-sectional area of the electrode wiring coupled to the other laser element.

JP 2005-216925 A JP 2007-53243 A

  However, when the arrangement of the plurality of light emitting portions in the surface emitting laser array becomes higher, in the surface emitting semiconductor laser arrays disclosed in Patent Document 1 and Patent Document 2, the temperature distribution in the surface emitting laser array is uniform. It is difficult to maintain the characteristics, and there is a risk of variation in light output characteristics between the light emitting units.

  The present invention has been made under such circumstances, and a first object of the present invention is to provide a surface emitting laser array in which the light output characteristics of a plurality of light emitting sections are uniform over time.

  A second object of the present invention is to provide an optical scanning apparatus capable of stably performing simultaneous scanning with a plurality of lights.

  A third object of the present invention is to provide an image forming apparatus capable of stably forming a high quality image.

  A fourth object of the present invention is to provide an optical transmission module that can stably generate a high-quality optical signal.

  A fifth object of the present invention is to provide an optical transmission system capable of stably performing high-quality optical transmission.

  According to a first aspect of the present invention, in the surface emitting laser array having a plurality of mesa-shaped structures including a current confinement structure in which a current passage region is surrounded by an oxide, the plurality of structures are the mesa. A first structure and a second structure which are different from each other in at least one of a shape and a shape of the current passage region, and the first structure changes with time in light output characteristics as compared with the second structure. The surface emitting laser array is characterized in that the surface emitting laser array is disposed in a region where the temperature rise is smaller than that in the region where the second structure is disposed.

  Note that in this specification, two structures that are similar to each other have the same shape.

  According to this, the plurality of structures include a first structure and a second structure that are different from each other in at least one of a mesa shape and a current passage region shape, and the first structure is the second structure. The change in light output characteristics with time is smaller than that of the body, and the first structure is arranged in a region where the temperature rise is larger than the region where the second structure is arranged. In this case, even if there is a non-uniform temperature distribution in the array plane, it is possible to suppress deterioration of a structure having a large temperature rise earlier than a structure having a small temperature rise. Therefore, the light output characteristics of the plurality of light emitting units can be made uniform over time.

  According to a second aspect of the present invention, there is provided an optical scanning device for scanning a surface to be scanned with light, the light source unit having the surface emitting laser array of the present invention; and a deflector for deflecting the light from the light source unit. And a scanning optical system for condensing the light deflected by the polarizer on the surface to be scanned.

  According to this, since the light source unit has the surface emitting laser array of the present invention, as a result, simultaneous scanning with a plurality of lights can be stably performed.

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

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

  According to a fourth aspect of the present invention, there is provided an optical transmission module that generates an optical signal in accordance with an input electric signal, the surface emitting laser array of the present invention; An optical transmission module comprising: a driving device that is driven according to an electrical signal.

  According to this, since the surface emitting laser array of the present invention is provided, as a result, it is possible to stably generate a high-quality optical signal.

  According to a fifth aspect of the present invention, an optical transmission module of the present invention; an optical transmission medium that transmits an optical signal generated by the optical transmission module; and an optical signal that passes through the optical transmission medium is converted into an electrical signal. An optical transmission system comprising: a converter for converting.

  According to this, since the optical transmission module of the present invention is provided, as a result, high-quality optical transmission can be stably performed.

<Surface emitting laser array>
“First Embodiment”
Hereinafter, a surface emitting laser array 100 of a 0.78 μm band will be described as a first embodiment of the surface emitting laser array of the present invention.

  As an example, the surface-emitting laser array 100 includes 25 light-emitting portions as shown in FIG. 1A and FIG. 1B, which is a cross-sectional view taken along the line AA in FIG. . In the present specification, the laser oscillation direction in the surface emitting laser array 100 is described as a Z-axis direction, and two directions perpendicular to each other in a plane perpendicular to the Z-axis direction are described as an X-axis direction and a Y-axis direction.

  Here, the 25 light emitting units are two-dimensionally arranged at equal intervals in the X-axis direction and the Y-axis direction. The 16 light emitting portions in the peripheral part in the two-dimensional array are square, and the nine light emitting parts in the center in the two-dimensional array are circular. In the first embodiment, for the sake of convenience, the square light emitting part is also referred to as a “first light emitting part”, and the circular light emitting part is also referred to as a “second light emitting part”.

  Each light emitting unit is formed on a substrate 101 with an n-GaAs buffer layer 102, a lower reflecting mirror 103, a lower spacer layer 104, an active layer 105, an upper spacer layer 106, a selective oxidation layer 107, an upper reflecting mirror 108, and a GaAs contact layer. Semiconductor layers such as (not shown) are sequentially stacked. Hereinafter, a structure in which a plurality of these semiconductor layers are stacked is also referred to as a “semiconductor stacked body” for convenience.

  The substrate 101 is an n-GaAs (100) plane substrate.

The lower reflecting mirror 103 is a pair of a low refractive index layer made of n-Al _0.9 Ga _0.1 As and a high refractive index layer made of n-Al _0.3 Ga _0.7 As. Have. Then, between the low refractive index layer and the high refractive index layer, a composition gradient layer having a thickness of 20 nm (illustrated) in which the composition is gradually changed from one composition to the other composition in order to reduce electrical resistance. (Omitted) is provided. Each refractive index layer includes 1/2 of the composition gradient layer, and is set to have an optical thickness of λ / 4 when the oscillation wavelength is λ.

The lower spacer layer 104 is a layer made of non-doped Al _0.3 Ga _0.7 As.

The active layer 105 is an AlGaAs / Al _0.3 Ga _0.7 As multiple quantum well active layer.

The upper spacer layer 106 is a layer made of non-doped Al _0.3 Ga _0.7 As.

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

The upper reflecting mirror 108 has 24 pairs of 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. ing. Then, between the low refractive index layer and the high refractive index layer, a composition gradient layer having a thickness of 20 nm (illustrated) in which the composition is gradually changed from one composition to the other composition in order to reduce electrical resistance. (Omitted) is provided. Each refractive index layer is set to have an optical thickness of λ / 4, including 1/2 of the composition gradient layer.

  A selective oxidation layer 107 made of p-AlAs is provided at a position away from the resonator structure in the upper reflecting mirror 108 by λ / 4.

  Next, a method for manufacturing the surface emitting laser array 100 will be briefly described.

(1) The semiconductor stacked body is formed by crystal growth using metal organic chemical vapor deposition (MOCVD) or molecular beam crystal growth (MBE) (see FIG. 2A).

Here, trimethylaluminum (TMA), trimethylgallium (TMG), and trimethylindium (TMI) are used as the Group III material, and arsine (AsH ₃ ) gas is used as the Group V material. 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.

(2) A photomask including a photomask 109 corresponding to the light-emitting portion is patterned by photolithography on the surface of the stacked body which is the surface (surface opposite to the substrate 101) in the semiconductor stacked body (see FIG. 2B). ). Here, as shown in FIG. 3 as an example, the shape of the photomask 109 corresponding to the first light emitting portion is a square shape having a side of 20 μm, and the photomask 109 corresponding to the second light emitting portion. The shape is a circular shape having a diameter of 20 μm. The gap between two adjacent photomasks is 20 μm.

(3) A mesa shape is formed by a dry etching method using a photomask as an etching mask (see FIG. 4A). Hereinafter, for convenience, a mesa-shaped portion (structure) is abbreviated as “mesa”. Here, the etching is performed until the bottom surface of the etching reaches the lower reflecting mirror 103.

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

(5) The semiconductor stacked body is heat-treated in water vapor to selectively oxidize the selectively oxidized layer 108 in the mesa. Then, an unoxidized region in the selective oxidation layer 108 remains in the central portion of the mesa. As a result, a so-called current confinement structure is formed in which the drive current path of the light emitting unit is limited to only the central part of the mesa (see FIGS. 4C and 5). The non-oxidized region (current passing region) in the first light emitting unit is a square shape having a side length of 3 μm, and the current passing region in the second light emitting unit is a circular shape having a diameter of 3 μm. It is.

(6) An insulating film 111 made of SiO ₂ is formed as a passivation film by using a chemical vapor deposition method (CVD method) (see FIG. 6A).

(7) Flatten with polyimide 112 (see FIG. 6B).

(8) Open a window for the P-side electrode contact on the top of the mesa (see FIG. 6C). Here, after masking with a photoresist, the opening at the top of the mesa is exposed to remove the photoresist at that portion, and then the polyimide 112 and the insulating film 111 are etched and opened with BHF.

(9) A square-shaped resist pattern having a side of 10 μm is formed in a region serving as a light emitting portion above the mesa in the first light emitting portion, and a diameter of 10 μm is formed in a region serving as the light emitting portion above the mesa in the second light emitting portion. A circular resist pattern is formed. Then, 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.

(10) Lift off the electrode material of the light emitting portion to form the p-side electrode 113 (see FIG. 7A).

(11) 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. 7B). Here, the n-side electrode 114 is a multilayer film made of AuGe / Ni / Au.

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

(13) The semiconductor laminate is cut for each chip.

  By the way, according to the experiments by the inventors, a result is obtained that the change in the light output characteristics with time is smaller in the circular light-emitting portion than in the square light-emitting portion at a predetermined temperature equal to or higher than the reference temperature ( (See FIG. 8). In the first embodiment, the second light emitting unit is disposed at the center of the two-dimensional array that is a region where the temperature rise is large, and the first light emitting unit is disposed at the periphery of the two-dimensional array that is the region where the temperature rise is small. A light emitting unit is arranged. Thereby, in the surface emitting laser array 100, even if there is a non-uniform temperature distribution in the array surface, the light output characteristics of the plurality of light emitting units are substantially equal to each other over time (see FIG. 9).

  FIG. 10 shows the light output characteristics when the shapes of the plurality of light emitting portions are all the same for comparison. In this case, as time elapses, the difference between the light output characteristics of the central light emitting section and the light output characteristics of the peripheral light emitting sections increases. Further, FIG. 11 shows the light output characteristics when the shape of the light emitting part in the central part is made similar to the shape of the light emitting part in the peripheral part in order to suppress the deterioration with time of the light emitting part in the central part. Has been. In this case, there is already a difference in the light output characteristics of the light emitting part in the central part and the light output characteristics of the light emitting part in the peripheral part at the initial stage.

  As described above, according to the surface emitting laser array 100 according to the first embodiment, the first light emitting units having the mesa shape and the square shape of the current passing region are arranged in the peripheral portion of the two-dimensional array, A second light-emitting portion having a mesa shape and a current-passing region having a circular shape is disposed at the center of the two-dimensional array. Since the second light-emitting portion has a smaller change in light output characteristics with time than the first light-emitting portion, the light-emitting portion where the temperature rises is large even if there is a non-uniform temperature distribution in the array surface. It is possible to suppress deterioration at an earlier stage than the light emitting portion where the increase is small. Therefore, the light output characteristics of the plurality of light emitting units can be made uniform over time.

  Note that depending on the structure of the mesa and the manufacturing method, the square-shaped light-emitting portion may have a smaller change in light output characteristics with time than the circular light-emitting portion. In this case, a square is formed at the center of the two-dimensional array. A circular light-emitting part may be arranged around the periphery of the two-dimensional array.

“Second Embodiment”
Next, a 0.78 μm band surface emitting laser array 200 will be described as a second embodiment of the surface emitting laser array of the present invention.

  As an example, the surface-emitting laser array 200 has 25 light emitting units as shown in FIG. Here, the 25 light emitting sections are all square and are two-dimensionally arranged at equal intervals in the X-axis direction and the Y-axis direction. However, the nine light emitting portions in the central part in the two-dimensional array are all rotated by 45 degrees in the XY plane with respect to the light emitting parts in the peripheral part in the two-dimensional array. In the second embodiment, for convenience, each of the 16 light emitting units in the peripheral part in the two-dimensional array is referred to as a “third light emitting part”, and each of the nine light emitting parts in the central part in the two-dimensional array is provided. Also referred to as “fourth light emitting portion”.

  As shown in FIG. 12B, which is a BB cross-sectional view of FIG. 12A, each light emitting portion is formed on the substrate 101A in the same manner as in the first embodiment described above. 102, a lower reflecting mirror 103, a spacer layer 104, an active layer 105, a spacer layer 106, a selective oxidation layer 107, an upper reflecting mirror 108, a semiconductor layer such as a GaAs contact layer (not shown) are sequentially stacked.

  The substrate 101A is an n-GaAs (311) A-plane substrate. That is, the substrate 101A is a so-called inclined substrate.

  The surface emitting laser array 200 is manufactured in the same manner as in the first embodiment described above. However, the photomask 109 is patterned according to the shape of the light emitting portion (see FIG. 13).

  By the way, when the tilted substrate is used, the symmetry of the crystal is lowered, and therefore the shape of the current passing region may differ depending on the rotation angle in the XY plane even if the shape of the mesa is the same. In the second embodiment, the current passing region in the third light emitting unit is rectangular, and the current passing region in the fourth light emitting unit is square.

  Further, according to experiments by the inventors, a result that the change in the light output characteristics with time is smaller in the fourth light emitting unit than in the third light emitting unit at a predetermined temperature equal to or higher than the reference temperature ( (See FIG. 14). In the second embodiment, the fourth light emitting unit is arranged in the center of the two-dimensional array that is a region where the temperature rise is large, and the third light emitting unit is arranged in the peripheral part of the two-dimensional array that is the region where the temperature rise is small. A light emitting unit is arranged. Thus, in the surface emitting laser array 200, even if there is a non-uniform temperature distribution in the array surface, the light output characteristics of the plurality of light emitting units are substantially equal to each other over time.

  As described above, according to the surface-emitting laser array 200 according to the second embodiment, the substrate 101A is an inclined substrate, and the third light-emitting unit whose current passing region has a rectangular shape has a peripheral shape in the two-dimensional array. A fourth light-emitting portion having a square shape in the current passing region is disposed in the central portion of the two-dimensional array. Since the fourth light emitting unit has a smaller change in light output characteristics with time than the third light emitting unit, even if there is a non-uniform temperature distribution in the array plane, the light emitting unit where the temperature rise is large It is possible to suppress deterioration at an earlier stage than the light emitting portion where the increase is small. Therefore, the light output characteristics of the plurality of light emitting units can be made uniform over time.

  In the first and second embodiments, the case where the number of light emitting units included in one chip is 25 has been described. However, the present invention is not limited to this.

“Third embodiment”
Next, a surface emitting laser array 300 of 0.78 μm band will be described as a third embodiment of the surface emitting laser array of the present invention.

  As shown in FIG. 15 as an example, the surface-emitting laser array 300 includes 35 light emitting units, and is a light emitting unit including five light emitting units arranged at equal intervals in a line along the Y-axis direction. Seven rows are arranged in the X-axis direction.

  Here, in order to distinguish each light emission part row | line | column, for convenience, the 1st light emission part row | line | column L1, the 2nd light emission part row | line | column L2, the 3rd light emission part row | line | column L3, the 4th light emission part from left to right of the paper surface of FIG. A row L4, a fifth light emitting portion row L5, a sixth light emitting portion row L6, and a seventh light emitting portion row L7 are used.

  Regarding the X-axis direction, the distance between the first element row L1 and the second element row L2 is X1, the distance between the second element row L2 and the third element row L3 is X2, and the third element row L3 and the fourth element row. The interval between the column L4 is X1, the interval between the fourth element column L4 and the fifth element column L5 is X1, the interval between the fifth element column L5 and the sixth element column L6 is X2, and the sixth element column L6 and the seventh element column L6. The distance from the element row L7 is X1, and X1> X2.

  And in each light emission part row | line | column of 1st element row | line | column L1, 4th light emission part row | line | column L4, and 7th light emission part row | line | column L7, each light emission part has a mesa shape and the shape of a current passage area | region is a square light emission part (said 1st Of the second light emitting part row L2, the third light emitting part row L3, the fifth light emitting part row L5, and the sixth light emitting part row L6, each light emitting part has a mesa shape and a current passage. The region is a circular light emitting part (second light emitting part).

  As in the first embodiment described above, each light emitting unit is formed on the substrate 101 with the n-GaAs buffer layer 102, the lower reflecting mirror 103, the spacer layer 104, the active layer 105, the spacer layer 106, and the selective oxidation layer 107. A semiconductor layer such as an upper reflecting mirror 108 and a GaAs contact layer (not shown) is sequentially stacked.

  The surface emitting laser array 300 is manufactured in the same manner as in the first embodiment described above. However, the photomask 109 is patterned according to the shape of the light emitting portion.

  As described above, according to the surface emitting laser array 300 according to the third embodiment, the first light emitting units having the mesa shape and the square shape of the current passing region are arranged in a sparse region in the two-dimensional array. The second light-emitting portions having a mesa shape and a circular current passing region are arranged in a dense region in the two-dimensional array. As described above, since the second light emitting unit has a smaller change in light output characteristics with time than the first light emitting unit, even if there is a non-uniform temperature distribution in the array plane, the temperature rise is large. It is possible to suppress deterioration of the light emitting part earlier than the light emitting part where the temperature rise is small. Therefore, the light output characteristics of the plurality of light emitting units can be made uniform over time.

  Note that depending on the structure of the mesa and the manufacturing method, the light-emitting portion having a square shape may have a smaller temporal change in light output characteristics than the light-emitting portion having a circular shape. These light emitting portions may be square light emitting portions, and a plurality of light emitting portions arranged sparsely may be circular light emitting portions.

  Moreover, although the said 3rd Embodiment demonstrated the case where the number of the light emission parts contained in one chip | tip was 35, it is not limited to this.

  Moreover, although the said embodiment demonstrated the case where the oscillation wavelength of a surface emitting laser array was a 0.78 micrometer band, it is not limited to this. For example, a wavelength band such as a 0.65 μm band, a 0.85 μm band, a 0.98 μm band, a 1.3 μm band, and a 1.5 μm band may be used. 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 0.65 μm band, an InGaAs mixed crystal semiconductor material in the 0.98 μm band, and a GaInNAs (Sb) mixed crystal semiconductor material in the 1.3 μm band and 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.

<Image forming apparatus>
Next, an embodiment of the image forming apparatus of the present invention will be described. FIG. 16 shows a schematic configuration of a laser printer 1000 as an image forming apparatus according to an embodiment of the present invention.

  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 static elimination unit 1034, a cleaning blade 1035, a toner cartridge 1036, a paper supply roller 1037, a paper supply tray 1038, A registration roller pair 1039, a fixing roller 1041, a paper discharge roller 1042, a paper discharge tray 1043, and the like are provided.

  A photosensitive layer is formed on the surface of the photosensitive drum 1030. That is, the surface of the photoconductor drum 1030 is a scanned surface. Here, 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 blade 1035 are each arranged in the vicinity of the surface of the photosensitive drum 1030. Then, with respect to the rotation direction of the photosensitive drum 1030, the charging charger 1031 → the developing roller 1032 → the transfer charger 1033 → the charge eliminating unit 1034 → the cleaning blade 1035 are arranged in this order.

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

  The optical scanning device 1010 irradiates the surface of the photosensitive drum 1030 charged by the charging charger 1031 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 1030 on the surface of the photosensitive drum 1030. 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 blade 1035 removes toner (residual toner) remaining on the surface of the photosensitive drum 1030. The removed residual toner is used again. The surface of the photosensitive drum 1030 from which the residual toner has been removed returns to the position of the charging charger 1031 again.

<Optical scanning device>
Next, the configuration of the optical scanning device 1010 will be described.

  As shown in FIG. 17, the optical scanning device 1010 includes a light source unit 10, a coupling lens 11, an aperture plate 12, a cylindrical lens 13, a polygon mirror 14, an fθ lens 15, a toroidal lens 16, and two mirrors (17, 18), and a control device (not shown) for comprehensively controlling the above-described units.

  As an example, the light source unit 10 includes a surface emitting laser array 10A in which 40 light emitting units are two-dimensionally arranged as shown in FIG. Similar to the surface-emitting laser array 100, the surface-emitting laser array 10A has a light-emitting portion whose mesa shape and current-passing region are square in the periphery of the two-dimensional array. A light emitting part having a circular shape is arranged at the center of the two-dimensional array. Note that the M direction in FIG. 18 indicates the direction corresponding to the main scanning direction, and the S direction indicates the direction corresponding to the sub scanning direction.

  In the surface emitting laser array 10 </ b> A, a light emitting unit array composed of 10 light emitting units arranged in a line at equal intervals along a direction inclined by an angle θ with respect to the M direction (hereinafter referred to as “T direction” for convenience). , Four rows are arranged at equal intervals d1 in the S direction. Further, when 40 light emitting units are orthogonally projected onto a virtual line extending in the S direction, the light emitting unit intervals are equal intervals d2. In the present specification, the “interval between the light emitting portions” refers to the distance between the centers of the two light emitting portions.

  Returning to FIG. 17, the coupling lens 11 shapes the light emitted from the light source unit 10 into substantially parallel light.

  The aperture plate 12 has an aperture and defines the beam diameter of light that passes through the coupling lens 11.

  The cylindrical lens 13 condenses the light that has passed through the opening of the aperture plate 12 in the vicinity of the deflection 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 reflection 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. 17 by a rotation mechanism (not shown). Therefore, the light emitted from the light source unit 10 and condensed near the deflection reflection 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 light from the polygon mirror 14, and moves the image plane of light deflected by the polygon mirror 14 at a constant angular velocity at a constant speed in the main scanning direction.

  The toroidal lens 16 forms an image of the light from the fθ lens 15 on the surface of the photosensitive drum 1030 via the mirror 18.

  In this case, in the surface emitting laser array 10A, since the intervals between the light emitting portions when the respective light emitting portions are orthogonally projected onto the virtual line extending in the S-axis direction are equal intervals d2, as shown in FIG. By adjusting the above, 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 direction on the photosensitive drum 1030. For example, if the distance d1 is 26.5 μm, the distance d2 is 2.65 μm. If the magnification of the optical system is doubled, writing dots can be formed on the photosensitive drum 1030 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 density can be increased by increasing the number of light emitting portions in the T direction, making the array arrangement in which the distance d1 is narrowed and the distance d2 is further reduced, or by reducing the magnification of the optical system. Printing is possible. Note that the writing interval in the main scanning direction can be easily controlled by the lighting timing of the light source.

  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.

  As described above, according to the optical scanning device 1010 according to the present embodiment, the light source unit 10 has a two-dimensional light emitting unit having a mesa shape and a square shape of the current passing region, like the surface emitting laser array 100. A surface-emitting laser array 10A is arranged in which a light emitting part arranged in the peripheral part of the array and having a circular mesa shape and a current passing region is arranged in the center part of the two-dimensional array. Accordingly, the light output characteristics of the light emitting units are uniform over time, and as a result, simultaneous scanning with a plurality of lights can be stably performed.

  In addition, the laser printer 1000 according to the present embodiment includes the optical scanning device 1010 that can stably perform simultaneous scanning with a plurality of lights. As a result, a high-quality image can be stably formed. It becomes possible.

  In the above embodiment, the case where the light source unit 10 includes the surface emitting laser array 10A equivalent to the surface emitting laser array 100 has been described. However, the surface emitting laser is used instead of the surface emitting laser array 10A. A surface emitting laser array equivalent to either one of the arrays 200 and 300 may be included.

  In the above embodiment, the case of the laser printer 1000 as the image forming apparatus has been described. However, the present invention is not limited to this. In short, an image forming apparatus including the optical scanning device 1010 can stably form a high-quality image.

  For example, an image forming apparatus that includes the optical scanning device 1010 and 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.

  Even in an image forming apparatus that forms a multicolor image, a high-definition image can be stably formed by using an optical scanning device that supports color images.

  For example, as shown in FIG. 20, a tandem color machine 1500 corresponding to a color image and including a plurality of photosensitive drums may be used. The tandem color machine 1500 includes a black (K) photosensitive drum K1, a charger K2, a developing unit K4, a cleaning unit K5, a transfer charging unit K6, a cyan (C) photosensitive drum C1, a charging unit. A developing unit C2, a developing unit C4, a cleaning unit C5, a transfer charging unit C6, a magenta (M) photosensitive drum M1, a charging unit M2, a developing unit M4, a cleaning unit M5, and a transfer charging unit M6; A yellow (Y) photosensitive drum Y1, a charger Y2, a developing unit Y4, a cleaning unit Y5, a transfer charging unit Y6, an optical scanning device 1010A, a transfer belt 80, a fixing unit 30 and the like are provided. .

  The optical scanning device 1010A includes a surface emitting laser array for black, a surface emitting laser array for cyan, a surface emitting laser array for magenta, and a surface emitting laser array for yellow. Each surface emitting laser array is a surface emitting laser array equivalent to the surface emitting laser array 10A. The light from the surface emitting laser array for black is irradiated to the photosensitive drum K1 through the scanning optical system for black, and the light from the surface emitting laser array for cyan passes through the scanning optical system for cyan. The light from the surface emitting laser array for magenta is irradiated to the photosensitive drum C1, and the light from the surface emitting laser array for yellow is irradiated to the photosensitive drum M1 through the magenta scanning optical system. The photosensitive drum Y1 is irradiated through the scanning optical system.

  Each photosensitive drum rotates in the direction of the arrow in FIG. 20, and a charger, a developer, a transfer charging unit, and a cleaning unit are arranged in the order of rotation. Each charger uniformly charges the surface of the corresponding photosensitive drum. The surface of the photosensitive drum charged by the charger is irradiated with light by the optical scanning device 1010A, and an electrostatic latent image is formed on the photosensitive drum. Then, a toner image is formed on the surface of the photosensitive drum by the corresponding developing device. Further, the toner images of the respective colors are transferred onto the recording paper by the corresponding transfer charging means, and finally the image is fixed on the recording paper by the fixing means 30.

  In a tandem color machine, color misregistration of each color may occur due to mechanical accuracy or the like. However, the correction accuracy of color misregistration of each color can be improved by selecting a light emitting unit to be lit.

  In this tandem color machine 1500, instead of the optical scanning device 1010A, a black optical scanning device, a cyan optical scanning device, a magenta optical scanning device, and a yellow optical scanning device may be used. In short, each surface emitting laser array may be any surface emitting laser array equivalent to the surface emitting laser array 10A.

<Optical transmission system>
FIG. 21 shows a schematic configuration of an optical transmission system 2000 according to an embodiment of the present invention. In this optical transmission system 2000, an optical transmission module 2001 and an optical reception module 2005 are connected by an optical fiber cable 2004, and one-way optical communication from the optical transmission module 2001 to the optical reception module 2005 is possible.

  The optical transmission module 2001 includes a light source 2002 including a surface emitting laser array equivalent to any of the surface emitting laser arrays 100 to 300, and light of laser light output from the light source 2002 in accordance with an electric signal input from the outside. And a drive circuit 2003 that modulates the intensity.

  The optical signal output from the light source 2002 is coupled to the optical fiber cable 2004, guided through the optical fiber cable 2004, and input to the optical receiving module 2005.

  The optical receiving module 2005 includes a light receiving element 2006 that converts an optical signal into an electric signal, and a receiving circuit 2007 that performs signal amplification, waveform shaping, and the like on the electric signal output from the light receiving element 2006.

  According to the optical transmission module 2001 according to the present embodiment, the light source 2002 has a surface-emitting laser array equivalent to any one of the surface-emitting laser arrays 100 to 300, and as a result, a high-quality optical signal can be stably output. Can be generated.

  In addition, the optical transmission system 2000 according to the present embodiment includes the optical transmission module 2001 that can stably generate a high-quality optical signal. As a result, high-quality optical transmission with low power consumption. Can be performed stably.

  In the present embodiment, a configuration example of unidirectional communication of a single channel is shown, but a configuration of bidirectional communication, a parallel transmission method, a wavelength division multiplex transmission method, or the like can also be adopted. In short, what is necessary is just to have the light source 2002. FIG.

  As described above, the surface emitting laser array according to the present invention is suitable for making the light output characteristics of a plurality of light emitting portions uniform over time. Further, the optical scanning device of the present invention is suitable for stably performing simultaneous scanning with a plurality of lights. The image forming apparatus of the present invention is suitable for stably forming a high quality image. The optical transmission module of the present invention is suitable for stably generating a high-quality optical signal. The optical transmission system according to the present invention is suitable for stably performing high-quality optical transmission.

FIG. 1A is a plan view of the surface emitting laser array 100 according to the first embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line AA in FIG. 2A and 2B are views (No. 1) for describing a method for manufacturing the surface emitting laser array 100, respectively. FIG. 3 is a plan view of FIG. FIGS. 4A to 4C are views (No. 2) for describing a method for manufacturing the surface emitting laser array 100, respectively. FIG. 5 is a plan view of FIG. FIGS. 6A to 6C are views (No. 3) for describing the method of manufacturing the surface emitting laser array 100, respectively. FIGS. 7A and 7B are views (No. 4) for describing the method of manufacturing the surface emitting laser array 100, respectively. It is a figure for demonstrating the time-dependent change of the light output characteristic of a circular light emission part and a square-shaped light emission part. FIG. 6 is a diagram for explaining a temporal change in light output characteristics of a light emitting part at a central part and a light emitting part at a peripheral part in the surface emitting laser array 100. It is a figure for demonstrating the time-dependent change of the light output characteristic of the light emission part of the center part in the conventional surface emitting laser array, and the light emission part of a peripheral part. It is a figure for demonstrating the time-dependent change of the light output characteristic of the light emission part of the center part in the conventional surface emitting laser array, and the light emission part of a peripheral part. FIG. 12A is a plan view of a surface emitting laser array 200 according to the second embodiment of the present invention, and FIG. 12B is a cross-sectional view taken along line BB in FIG. It is a figure for demonstrating the photomask when manufacturing the surface emitting laser array 200. FIG. It is a figure for demonstrating the time-dependent change of the light output characteristic of a 3rd light emission part and a 4th light emission part. It is a figure for demonstrating the surface emitting laser array 300 which concerns on the 3rd Embodiment of this invention. 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. It is a figure for demonstrating the surface emitting laser array contained in the light source unit in FIG. It is a figure for demonstrating a write dot. It is a figure for demonstrating schematic structure of a tandem color machine. It is a figure for demonstrating schematic structure of the optical transmission module and optical transmission system which concern on one Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Light source unit, 10A ... Surface emitting laser array, 14 ... Polygon mirror (deflector), 15 ... f (theta) lens (a part of scanning optical system), 16 ... Toroidal lens (a part of scanning optical system), 100 ... surface Light emitting laser array, 101 ... substrate, 101A ... substrate (tilted substrate), 200 ... surface emitting laser array, 300 ... surface emitting laser array, 1000 ... laser printer (image forming apparatus), 1010 ... optical scanning device, 1010A ... optical scanning Devices: 1030: photosensitive drum (image carrier), 1500: tandem color machine (image forming device), 2000: light transmission system, 2001: light transmission module (light transmission module), 2003: drive circuit (drive device), 2004 ... Optical fiber cable (light transmission medium), 2006 ... Light receiving element (part of converter), 2007 ... Reception circuit (conversion) Some of), K1, C1, M1, Y1 ... photosensitive drum (image bearing member).

Claims (9)

In a surface emitting laser array having a plurality of mesa-shaped structures including a current confinement structure in which a current passing region is surrounded by an oxide,
The plurality of structures include a first structure and a second structure in which at least one of the mesa shape and the shape of the current passage region is different from each other,
The first structure is disposed in a region where the change in light output characteristics with time is smaller than that of the second structure, and the temperature rise is larger than the region where the second structure is disposed. A surface emitting laser array characterized by the above. The plurality of structures are formed on an inclined substrate,
The shape of the current passing region in the first structure is different from the shape of the current passing region in the second structure,
The mesa shape in the first structure coincides with a shape obtained by rotating the mesa shape in the second structure by a predetermined angle in a plane orthogonal to the thickness direction. 2. The surface emitting laser array according to 1. The plurality of structures are two-dimensionally arranged,
The structure located at the center of the two-dimensional array is a structure equivalent to the first structure,
3. The surface emitting laser array according to claim 1, wherein a structure located at a peripheral portion in the two-dimensional array is a structure equivalent to the second structure. 4. The plurality of structures include a plurality of densely arranged structures and a plurality of sparsely arranged structures,
The plurality of densely arranged structures are structures equivalent to the first structure,
3. The surface emitting laser array according to claim 1, wherein the plurality of sparsely arranged structures are structures equivalent to the second structure. An optical scanning device that scans a surface to be scanned with light,
A light source unit comprising the surface emitting laser array according to any one of claims 1 to 4;
A deflector for deflecting light from the light source unit;
A scanning optical system for condensing the light deflected by the polarizer 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 5 that scans the at least one image carrier with light including image information.   The image forming apparatus according to claim 6, wherein the image information is multicolor color image information. An optical transmission module that generates an optical signal according to an input electrical signal,
A surface emitting laser array according to any one of claims 1 to 4;
An optical transmission module comprising: a driving device that drives the surface-emitting laser array in accordance with the input electric signal. An optical transmission module according to claim 8;
An optical transmission medium for transmitting an optical signal generated by the optical transmission module;
A converter for converting an optical signal through the optical transmission medium into an electric signal;

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