JP2008185959A - Optical scanning device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make it possible to scan a surface to be scanned with a beam in a stable manner, and form a high-quality image at high speed. <P>SOLUTION: A scanning device comprises a light source 14 having a plurality of surface emitting lasers, a polygon mirror 13 for deflecting a beam from the light source 14, a first optical system disposed on an optical path between the light source 14 and the polygon mirror 13 for guiding the beam from the light source 14 to the polygon mirror 13, a second optical system for guiding the beam deflected by the polygon mirror 13 to a photosensitive drum 901, and a monitor device for monitoring light amounts of beams projected from each light emitting part. The optical axis of a coupling lens 15 and a cylindrical lens 17 is arranged tilted with respect to the normal direction of the deflection/reflection surface with respect to the sub-scanning direction. Thereby, it is made possible to restrain the beam projected from the light source and reflected by the polygon mirror 13 from returning to the light source side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical scanning apparatus and an image forming apparatus, and more particularly to an optical scanning apparatus that scans a surface to be scanned with a light beam and an image forming apparatus including the optical scanning apparatus.

  In electrophotographic image recording, an image forming apparatus using a laser is widely used. In this case, the image forming apparatus includes an optical scanning device, and forms a latent image by rotating the drum while scanning laser light using a polygon scanner (for example, a polygon mirror) in the axial direction of the photosensitive drum. Is common. In the field of electrophotography, an image forming apparatus is required to increase image density in order to improve image quality and to increase image output speed in order to improve operability.

  One way to achieve both high density and high speed is to rotate the polygon scanner at high speed, but this method increases noise, increases power consumption, and decreases durability in the polygon scanner. It will occur.

  Further, as another method for achieving both high density and high speed, there is a method of making a light beam emitted from a light source into a multi-beam. As a method for realizing this multi-beam, (1) a method of combining a plurality of edge emitting lasers, (2) a method using a one-dimensional array of edge emitting lasers, and (3) a vertical cavity surface emitting laser (VCSEL). ) Using a two-dimensional array (see, for example, Patent Document 1 and Patent Document 2).

  The method (1) is inexpensive because a general-purpose laser can be used, but it is difficult to stably maintain the relative positional relationship between the laser and the coupling lens with a plurality of beams. There is a possibility that the interval between two adjacent scan lines in a plurality of scan lines formed on the surface to be scanned (hereinafter abbreviated as “scan line interval” for convenience) becomes non-uniform. In the method (1), the number of light sources is practically limited, and the density and speed are limited. In the method (2), the scanning line interval can be made uniform, but there is a disadvantage that the power consumption of the element is increased. Further, if the number of light sources is extremely increased, the amount of beam deviation from the optical axis of the optical system increases, and so-called beam quality may be deteriorated.

  On the other hand, in the method (3), the power consumption is about an order of magnitude smaller than that of the edge-emitting laser, and more light sources can be easily integrated two-dimensionally.

  In Patent Document 1, a plurality of combinations each including a light source in which a plurality of light-emitting points that can be independently modulated are two-dimensionally arranged and a coupling lens that couples a divergent light beam emitted from the light source are combined. A light source device configured, an optical scanning device equipped with the light source device, and an image forming device equipped with the optical scanning device are disclosed.

  Patent Document 2 discloses an optical scanning device using a surface emitting laser array, and an image forming apparatus equipped with the optical scanning device.

JP-A-2005-250319 JP 2004-287292 A

  By the way, in an optical scanning device, the amount of light emitted from a light source is usually detected by a detector such as a photodiode in order to prevent the amount of light from changing due to temperature variation or temporal variation and causing uneven density on the image. And APC (Auto Power Control) for controlling the output level based on the result. In this case, in the edge emitting laser, since the light beam is emitted in two directions, the light beam emitted forward is used for scanning, and the light beam emitted backward is used for monitoring. Even if it returns, there is little influence on the monitor result. However, in the surface emitting laser, since the light beam is emitted only in one direction, it is necessary to divide or branch the emitted light beam and use one for scanning and the other for monitoring. At this time, there is a possibility that the return light flux to the light source may affect the monitor result.

  The present invention has been made under such circumstances, and a first object thereof is to provide an optical scanning device capable of stably scanning a surface to be scanned with a light beam.

  A second object of the present invention is to provide an image forming apparatus capable of forming a high quality image at high speed.

  According to a first aspect of the present invention, there is provided an optical scanning device that scans a surface to be scanned with a light beam, and includes a light source having a plurality of surface emitting lasers; and a deflecting reflection surface for deflecting the light beam from the light source. A deflector; an aperture plate disposed on an optical path of a light beam from the light source between the light source and the deflector and having an opening that defines at least a beam diameter of the light beam toward the deflector in the sub-scanning direction; A first optical system for guiding the light beam from the light source to the deflector; a second optical system for guiding the light beam deflected by the deflector to the surface to be scanned; and emitting from the surface emitting laser of the light source A monitor optical system for monitoring the amount of light of the light flux to be emitted, and the light flux directed from the deflector toward the second optical system is inclined with respect to the normal direction of the deflection reflection surface with respect to the sub-scanning direction. An optical scanning device characterized by .

  In the present specification, regarding the sub-scanning direction, even if the tilting direction with respect to the normal direction of the deflecting reflection surface of the light incident on the deflector is the same, it is different if the tilt direction with respect to the normal direction is different. It shall be an inclination angle.

  According to this, the light beam traveling from the deflector toward the second optical system is inclined with respect to the normal direction of the deflecting reflection surface with respect to the sub-scanning direction. In this case, the light beam emitted from the light source and reflected by the deflecting reflection surface can be prevented from returning to the light source side, and the light amount of the light beam emitted from the surface emitting laser of the light source can be accurately monitored. As a result, the surface to be scanned can be stably scanned with the light flux.

  According to a second 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 a light beam including image information on the at least one image carrier. 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 formed at high speed.

  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 of the present invention.

  A laser printer 500 shown in FIG. 1 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, and a registration roller pair 908. A transfer charger 911, a fixing roller 909, a paper discharge roller 912, a paper discharge tray 910, and the like.

  A photosensitive layer is formed on the surface of the photosensitive drum 901. That is, the surface of the photoconductive drum 901 is the surface to be scanned. Here, it is assumed that the photosensitive drum 901 rotates in the direction of the arrow in FIG.

  The charging charger 902, the developing roller 903, the transfer charger 911, and the cleaning blade 905 are disposed in the vicinity of the surface of the photosensitive drum 901, respectively. Then, with respect to the rotation direction of the photosensitive drum 901, the charging charger 902, the developing roller 903, the transfer charger 911, and the cleaning blade 905 are arranged in this order.

  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, on the surface of the photosensitive drum 901, the charge is lost only in the portion irradiated with light, and a latent image corresponding to the image information is formed 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 amount of toner in the toner cartridge 904 is checked when the power is turned on or when printing is completed. When the remaining amount is low, a message prompting replacement of the toner cartridge 904 is displayed on a display unit (not shown).

  As the developing roller 903 rotates, the toner supplied from the toner cartridge 904 is charged and thinly and uniformly attached to the surface thereof. Further, the developing roller 903 has an electric field in the opposite direction between a charged portion (a portion not irradiated with light) and an uncharged portion (a portion irradiated with light) in the photosensitive drum 901. A voltage is generated to generate. By this voltage, the toner adhering to the surface of the developing roller 903 adheres only to the portion irradiated with light on the surface of the photosensitive drum 901. That is, the developing roller 903 causes the toner to adhere to the latent image formed on the surface of the photosensitive drum 901 and visualizes the image information. Here, the latent image to which the toner is attached (hereinafter referred to as “toner image” for convenience) 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 roller 911, temporarily holds the recording paper 913 taken out by the paper feed roller 907, and the recording paper 913 is synchronized 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 toner 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 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 of the optical scanning device 900 will be described.

  As shown in FIG. 2, the optical scanning device 900 includes a light source 14, a coupling lens 15, an aperture plate 16, a cylindrical lens 17, a reflection mirror 18, a polygon mirror 13, and a polygon (not shown) that rotates the polygon mirror 13. A motor, a deflector side scanning lens 11a, an image plane side scanning lens 11b, a half mirror 23, an imaging lens 24, a photodiode 25, and the like are provided. In this specification, the main scanning direction will be described as the Y-axis direction, the sub-scanning direction as the Z-axis direction, and the direction orthogonal to these will be described as the X-axis direction.

  As shown in FIG. 3, the light source 14 includes a two-dimensional array 100 in which 40 light emitting units 101 are formed on one substrate as an example. The two-dimensional array 100 is inclined from a direction corresponding to the main scanning direction (hereinafter also referred to as “M direction” for convenience) toward a direction corresponding to the sub scanning direction (hereinafter also referred to as “S direction” for convenience). There are four light emitting element rows in which ten light emitting parts are arranged at equal intervals along a direction forming the angle α (hereinafter referred to as “T direction” for convenience). These four light emitting unit rows are arranged at equal intervals in the S direction. That is, the 40 light emitting units are two-dimensionally arranged along the T direction and the S direction, respectively.

  As an example, the spacing between adjacent light emitting section rows in the S direction (reference symbol d in FIG. 3) is 44.0 μm, the spacing between the light emitting portions in the T direction in each light emitting portion row (reference symbol X in FIG. 3) is 30.0 μm, The interval between the light emitting portions when the respective light emitting portions are orthogonally projected on a virtual line extending in the S direction (reference symbol c in FIG. 3) is 4.4 μm. In the present specification, the “light emitting portion interval” refers to the distance between the centers of two light emitting portions.

  Each light emitting portion is a 780 nm band VCSEL. As shown in FIG. 4 as an example, a lower reflector 112, a spacer layer 113, an active layer 114, a spacer layer 115, an upper reflector on an n-GaAs substrate 111. 117 and a semiconductor layer such as a p-contact layer 118 are sequentially stacked. Hereinafter, a structure in which a plurality of these semiconductor layers are stacked is also referred to as a “stacked body” for convenience. An enlarged view of the vicinity of the active layer 114 is shown in FIG.

The lower reflecting mirror 112 includes a low refractive index layer (referred to as a low refractive index layer 112a) 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. 40.5 pairs are provided as a pair (with a high refractive index layer 112b). Each refractive index layer is set to have an optical thickness of λ / 4 when the oscillation wavelength is λ. Note that a composition gradient layer (not shown) in which the composition is gradually changed from one composition to the other composition between the low refractive index layer 112a and the high refractive index layer 112b in order to reduce electrical resistance. Is provided.

The spacer layer 113 is a layer made of Al _0.6 Ga _0.4 As.

As shown in FIG. 5, the active layer 114 has a quantum well layer 114 a made of Al _0.12 Ga _0.88 As and a barrier layer 114 b made of Al _0.3 Ga _0.7 As.

The spacer layer 115 is a layer made of Al _0.6 Ga _0.4 As.

  The portion composed of the spacer layer 113, the active layer 114, and the spacer layer 115 is also called a resonator structure, and is set so that its thickness is an optical thickness of one wavelength (here, wavelength λ = 780 nm). (See FIG. 5).

The upper reflecting mirror 117 includes a low refractive index layer (referred to as a low refractive index layer 117a) 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 (with high refractive index layer 117b). Each refractive index layer is set to have an optical thickness of λ / 4. A composition gradient layer (not shown) in which the composition is gradually changed from one composition to the other composition in order to reduce electric resistance between the low refractive index layer 117a and the high refractive index layer 117b. Is provided.

  A selective oxidation layer 116 made of AlAs is provided at a position away from the resonator structure in the upper reflecting mirror 117 by λ / 4.

  Next, a method for manufacturing the two-dimensional array 100 will be briefly described.

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

(2) Grooves are formed by dry etching around each of a plurality of regions, each of which serves as a light emitting portion, to form a so-called mesa portion. Here, the bottom surface of the etching is set so as to reach the lower reflecting mirror 112. Note that the bottom surface of the etching may be at least beyond the selective oxidation layer 116. As a result, the selectively oxidized layer 116 appears on the sidewall of the trench. In addition, the size (diameter) of the mesa portion is preferably 10 μm or more. This is because if it is too small, heat will be trapped during device operation, which may adversely affect the light emission characteristics. Furthermore, the width of the groove is preferably 5 μm or more. This is because if the groove width is too narrow, it becomes difficult to control the etching.

(3) The laminated body in which the groove is formed is heat-treated in water vapor, and selectively oxidizes a part of the selectively oxidized layer 116 in the mesa portion to change to an Al _x O _y insulator layer. At this time, an unoxidized AlAs region in the selectively oxidized layer 116 remains in the central portion of the mesa portion. As a result, a so-called current confinement structure is formed in which the drive current path of the light emitting part is limited to only the central part of the mesa part.

(4) Except for the region where the upper electrode 103 of each mesa part is formed and the light emitting part 102, for example, a 150 nm thick SiO ₂ protective layer 120 is provided, and polyimide 119 is buried in each groove and planarized.

(5) The upper electrode 103 is formed in each mesa portion on the p contact layer 118 except for the light emitting portion 102, and each bonding pad (not shown) is formed around the laminated body. And each wiring (not shown) which connects each upper electrode 103 and the bonding pad corresponding to each is formed.

(6) A lower electrode (n-side common electrode) 110 is formed on the back surface of the laminate.

(7) The laminate is cut into a plurality of chips.

  Returning to FIG. 2, the coupling lens 15 is disposed on the optical path of the light beam emitted from the light source 14, and makes the light beam emitted from the light source 14 substantially parallel light. Here, as an example, the coupling lens 15 is disposed at a position where the optical path length from the light source 14 (symbol d1 in FIG. 6) is 39.305 mm. And the thickness (code | symbol d2 in FIG. 6) of the coupling lens 15 is 3.8 mm as an example. The focal length of the coupling lens 15 is 42.0 mm.

  The light source 14 and the coupling lens 15 are held by a holding member made of aluminum. A cover glass having a refractive index of 1.5112 and a thickness of 0.3 mm is disposed between the light source 14 and the coupling lens 15.

  The aperture plate 16 is disposed on the optical path between the coupling lens 15 and the cylindrical lens 17 and has an aperture that defines at least the beam diameter of the light beam passing through the coupling lens 15 in the sub-scanning direction. The aperture plate 16 is disposed so as to be inclined with respect to a virtual plane perpendicular to the traveling direction of the light beam traveling from the light source 14 toward the polygon mirror 13. Thereby, it is possible to prevent the light reflected around the opening from returning to the light source 14 side. The aperture plate 16 is disposed so as to block the light beam reflected by the polygon mirror 13 and traveling toward the light source.

  The half mirror 23 is disposed on the optical path between the aperture plate 16 and the cylindrical lens 17 and reflects a part of the light beam that has passed through the aperture of the aperture plate 16. The ratio of the amount of transmitted light and reflected light in the half mirror 23 is set to any of 9: 1, 8: 2, and 7: 3.

  The cylindrical lens 17 is disposed on the optical path between the half mirror 23 and the reflection mirror 18, and the light beam that has passed through the half mirror 23 is passed through the reflection mirror 18 in the vicinity of the deflection reflection surface of the polygon mirror 13 in the sub-scanning direction. Form an image. Here, as an example, the cylindrical lens 17 is disposed at a position where the optical path length from the second surface of the coupling lens 15 (symbol d3 in FIG. 6) is 79.3 mm. The thickness of the cylindrical lens 17 (symbol d4 in FIG. 6) is 3.0 mm as an example.

  Further, a soundproof glass 21 having a wall thickness of 1.9 mm and a refractive index of 1.5112 is disposed between the cylindrical lens 17 and the polygon mirror 13 and between the polygon mirror 13 and the deflector side scanning lens 11a. (See FIG. 2).

  As an example, the polygon mirror 13 is a four-sided mirror having a radius of an inscribed circle of 7 mm, and each mirror serves as a deflection reflection surface. The polygon mirror 13 rotates at a constant speed around a rotation axis parallel to the sub-scanning direction. Here, as an example, the polygon mirror 13 is disposed at a position where the optical path length from the second surface of the cylindrical lens 17 to the rotation axis is 51.8 mm.

  The deflector-side scanning lens 11 a is disposed on the optical path of the light beam deflected by the polygon mirror 13. Here, as an example, the deflector-side scanning lens 11a is disposed at a position where the optical path length (symbol d6 in FIG. 6) from the rotation axis of the polygon mirror 13 to the first surface of the deflector-side scanning lens 11a is 46.3 mm. Has been. The center (on the optical axis) thickness (reference numeral d7 in FIG. 6) of the deflector-side scanning lens 11a is 13.5 mm.

  The image plane side scanning lens 11b is disposed on the optical path of the light beam via the deflector side scanning lens 11a. Here, as an example, the image side scanning lens 11b has an optical path length (symbol d8 in FIG. 6) from the second surface of the deflector side scanning lens 11a to the first surface of the image side scanning lens 11b of 89.7 mm. It is arranged at the position. The center (on the optical axis) thickness (symbol d9 in FIG. 6) of the image plane side scanning lens 11b is 3.5 mm.

  As an example, the optical scanning device 900 is arranged so that the optical path length (reference numeral d10 in FIG. 6) from the second surface of the image side scanning lens 11b to the photosensitive drum 901 is 142.5 mm. A dustproof glass 22 (see FIG. 2) having a refractive index of 1.5112 and a thickness of 1.9 mm is disposed between the image side scanning lens 11b and the photosensitive drum 901.

  As an example, as shown in FIG. 7, the optical axes of the coupling lens 15 and the cylindrical lens 17 are arranged so as to be inclined with respect to the normal direction of the deflection reflection surface of the polygon mirror 13 with respect to the sub-scanning direction. Yes. As a result, as shown in FIG. 8A as an example, the light beam emitted from the light source 14 is incident on the deflection reflection surface with an inclination with respect to the normal direction of the deflection reflection surface with respect to the sub-scanning direction. In this case, it is possible to suppress the light beam reflected by the deflecting reflection surface from returning to the light source side. FIG. 8B shows a case where the optical axes of the coupling lens 15 and the cylindrical lens 17 are arranged so as to coincide with the normal direction of the deflection reflection surface. In this case, the light beam emitted from the light source 14 is incident in parallel to the normal direction of the deflecting / reflecting surface, and the light beam reflected by the deflecting / reflecting surface may return to the light source side.

  As an example, as shown in FIG. 9, the light beam traveling from the polygon mirror 13 toward the deflector-side scanning lens 11a is inclined with respect to the normal direction of the deflecting reflection surface with respect to the sub-scanning direction.

  Returning to FIG. 2, the imaging lens 24 condenses the light beam reflected by the half mirror 23. A photodiode 25 is disposed in the vicinity of the condensing position, and a signal (photoelectric conversion signal) corresponding to the amount of received light is output. The output signal of the photodiode 25 is used to monitor the light amount of the light beam emitted from each light emitting unit, and the drive current of each light emitting unit is corrected based on the monitoring result.

  As is clear from the above description, in the optical scanning device 900 according to this embodiment, the coupling lens 15, the aperture plate 16, the cylindrical lens 17, and the reflection mirror 18 constitute a first optical system.

  The deflector side scanning lens 11a and the image plane side scanning lens 11b constitute a second optical system.

  The half mirror 23, the imaging lens 24, and the photodiode 25 constitute a monitor device.

  As described above, according to the optical scanning device 900 according to the present embodiment, the light source 14 having a plurality of surface emitting lasers, the polygon mirror 13 that deflects the light beam from the light source 14, and the light source 14 and the polygon mirror 13. A first optical system that is disposed on the optical path between the light source 14 and guides the light beam from the light source 14 to the polygon mirror 13; a second optical system that guides the light beam deflected by the polygon mirror 13 to the photosensitive drum 901; And a monitor device for monitoring the amount of light emitted from the unit. The optical axes of the coupling lens 15 and the cylindrical lens 17 are arranged to be inclined with respect to the normal direction of the deflection reflection surface with respect to the sub-scanning direction. Thereby, the light beam emitted from the light source 14 is inclined with respect to the normal direction of the deflecting / reflecting surface with respect to the sub-scanning direction and is incident on the deflecting / reflecting surface. It can suppress returning to. Therefore, it is possible to accurately monitor the amount of light emitted from each light emitting portion of the light source, and as a result, it is possible to stably scan the surface to be scanned with the light.

  In the present embodiment, the aperture plate 16 is inclined with respect to a virtual plane perpendicular to the traveling direction of the light beam traveling from the light source 14 toward the polygon mirror 13, so that the light reflected around the aperture is reflected. Can be prevented from returning to the light source 14 side. Thereby, the light quantity of the light beam emitted from each light emitting portion of the light source can be monitored with higher accuracy.

  In the present embodiment, the aperture plate 16 blocks the light beam reflected by the polygon mirror 13 and traveling toward the light source side, so that the light beam reflected by the polygon mirror 13 can be further prevented from returning to the light source side. . Further, when the light beam enters the light emitting portion, the resonance characteristics change and the amount of emitted light itself changes, but this can also be prevented.

  In the present embodiment, the plurality of light emitting units are two-dimensionally arranged, and the interval between the two light emitting units located at both ends with respect to the direction corresponding to the main scanning direction is located at both ends with respect to the direction corresponding to the sub scanning direction. It is larger than the interval between the two light emitting units. Thereby, compared with the reverse case (for example, FIG. 10), the inclination of the optical axis of the coupling lens 15 and the cylindrical lens 17 can be freely set to some extent.

  By the way, in the method of increasing the writing density in the sub-scanning direction using the multi-beam light source, (1) reducing the lateral magnification in the sub-scanning direction of the optical system composed of the first optical system and the second optical system. And (2) a method of reducing the interval between the light emitting sections in the sub-scanning direction (reference symbol c in FIG. 3). However, in the method (1), it is necessary to reduce the width of the opening in the sub-scanning direction in the aperture plate that defines the beam diameter on the surface to be scanned, resulting in insufficient light quantity. On the other hand, in the method (2), it is difficult to secure the space necessary for the influence of thermal interference between the light emitting units and the wiring from each light emitting unit.

  In the present embodiment, the plurality of light emitting units are two-dimensionally arranged, and the interval between the two light emitting units located at both ends with respect to the direction corresponding to the main scanning direction is 2 located at both ends with respect to the direction corresponding to the sub scanning direction. Since it is larger than the interval between two light emitting units, it is possible to reduce the effect of thermal interference between the respective light emitting units and to reduce the interval between the light emitting units in the sub-scanning direction while securing the space necessary for passing the wiring of each light emitting unit. Can do.

  In addition, the laser printer 500 according to the present embodiment includes the optical scanning device 900 that can stably scan the surface to be scanned with a light beam, and as a result, a high-quality image can be formed at high speed. Is possible.

  In the above-described embodiment, the case where the shape of each mesa portion of the two-dimensional array 100 is circular has been described. However, the shape is not limited to this, and may be any shape such as an elliptical shape, a square shape, or a rectangular shape. .

  Moreover, although the said embodiment demonstrated the case where the number of the light emission parts which comprise one light emission part row | line was 10 pieces, and the number of the light emission part row | line | columns, this invention is not limited to this. In this case, a plurality of light emitting units are two-dimensionally arranged, and an interval between two light emitting units located at both ends with respect to the direction corresponding to the main scanning direction is set at two intervals located at both ends with respect to the direction corresponding to the sub scanning direction. It is preferably larger than the interval between the light emitting portions.

  Moreover, although the said embodiment demonstrated the case where the said light emission part space | interval c was 4.4 micrometers, it is not limited to this.

  Moreover, although the said embodiment demonstrated the case where the said light emission part space | interval d was 44.0 micrometers and the said light emission part space | interval X was 30.0 micrometers, it is not limited to this.

  Moreover, in the said embodiment, as shown in FIGS. 11-13 as an example, it replaces with the said two-dimensional array 100, and the material of the one part semiconductor layer of the said some semiconductor layers of the two-dimensional array 100 is used. A modified two-dimensional array (referred to as a two-dimensional array 200) may be used. In the two-dimensional array 200, the spacer layer 113 in the two-dimensional array 100 is changed to a spacer layer 213, the active layer 114 is changed to an active layer 214, and the spacer layer 115 is changed to a spacer layer 215. is there.

The spacer layer 213 is a layer made of (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P having a wide band gap.

As shown in FIG. 12, the active layer 214 has a composition in which compressive strain remains and has a Ga ₀ having a tensile strain of four layers lattice-matched with the three GaInPAs quantum well layers 214a having a band gap wavelength of 780 nm. _.6 In _0.4 P barrier layer 214b.

The spacer layer 215 is a layer made of (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P having a wide band gap.

  A portion composed of the spacer layer 213, the active layer 214, and the spacer layer 215 is called a resonator structure, and the thickness thereof is set to be one wavelength optical thickness (see FIG. 12).

  Since the two-dimensional array 200 uses an AlGaInP-based material for the spacer layer, the band gap difference between the spacer layer and the active layer can be extremely large compared to the two-dimensional array 100 in the above embodiment. it can.

  In FIG. 13, the spacer layer / quantum well layer material is an AlGaAs / AlGaAs-based VCSEL with a wavelength of 780 nm (hereinafter referred to as “VCSEL_A” for convenience), and the spacer layer / quantum well layer material is AlGaInP / GaInPAs. In this system, a VCSEL having a wavelength of 780 nm band (hereinafter referred to as “VCSEL_B” for convenience) and a spacer layer / quantum well layer material is an AlGaAs / GaAs system and a VCSEL having a wavelength of 850 nm band (hereinafter referred to as “ For VCSEL_C "), the band gap difference between the spacer layer and the quantum well layer and the band gap difference between the barrier layer and the quantum well layer in a typical material composition are shown. Note that VCSEL_A corresponds to the VCSEL 101 of the two-dimensional array 100, and VCSEL_B of x = 0.7 corresponds to the VCSEL (referred to as VCSEL 201) in the two-dimensional array 200.

  According to this, it can be seen that VCSEL_B can take a larger band gap difference than VCSEL_C as well as VCSEL_A. Specifically, the band gap difference between the spacer layer and the quantum well layer in VCSEL_B is 767.3 meV, which is extremely larger than 465.9 meV in VCSEL_A. Similarly, the difference in the band gap between the barrier layer and the quantum well layer is superior to VCSEL_B, and better carrier confinement is possible.

  Further, in the VCSEL 201, since the quantum well layer has a compressive strain, the gain increase is large due to the band separation of the heavy hole and the light hole, and the gain becomes high, so that high output is possible with a low threshold. For this reason, the reflectance of the reflecting mirror on the light extraction side (here, the upper reflecting mirror 117) can be reduced, and a further increase in output can be achieved. Furthermore, since the gain can be increased, it is possible to suppress a decrease in light output due to a temperature rise, and it is possible to narrow the interval between the VCSELs in the two-dimensional array.

  In the VCSEL 201, since both the quantum well layer 214a and the barrier layer 214b are made of a material not containing aluminum (Al), the incorporation of oxygen into the active layer 214 is reduced. As a result, formation of a non-radiative recombination center can be suppressed, and the life can be further extended.

  By the way, for example, when a VCSEL two-dimensional array is used for a so-called writing optical unit, the writing optical unit is disposable when the life of the VCSEL is short. However, since the VCSEL 201 has a long life as described above, the writing optical unit using the two-dimensional array 200 can be reused. Therefore, promotion of resource protection and reduction of environmental load can be achieved. This also applies to other devices using a two-dimensional array of VCSELs.

  In the above-described embodiment, the case where the wavelength of the laser light emitted from each light emitting unit is in the 780 nm band has been described. However, the wavelength is not limited to this and may be any wavelength according to the sensitivity characteristic of the photosensitive drum 901. In this case, at least a part of the material constituting each light emitting part or at least a part of the structure of each light emitting part is changed according to the oscillation wavelength.

  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, an image forming apparatus including the optical scanning device 900 can form a high-quality image at high speed as a result.

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

  In this case, as shown in FIG. 14 as an example, a tandem color machine including a plurality of photosensitive drums may be used. The tandem color machine includes a black (K) photosensitive drum K1, a charger K2, a developing device K4, a cleaning unit K5, a transfer charging unit K6, a cyan (C) photosensitive drum C1, and a charger. C2, developing unit C4, cleaning unit C5, transfer charging unit C6, magenta (M) photosensitive drum M1, charging unit M2, developing unit M4, cleaning unit M5, transfer charging unit M6, yellow A photosensitive drum Y1 for (Y), a charger Y2, a developing device Y4, a cleaning unit Y5, a transfer charging unit Y6, an optical scanning device 1010, a transfer belt 80, a fixing unit 30 and the like are provided.

  As shown in FIG. 15 as an example, the optical scanning device 1010 includes two light source units (200a, 200b), two aperture plates (201a, 201b), two light beam splitting prisms (202a, 202b), Four cylindrical lenses (204a, 204b, 204c, 204d), polygon mirror 104, four fθ lenses (105a, 105b, 105c, 105d), eight folding mirrors (106a, 106b, 106c, 106d, 108a, 108b, 108c, 108d), four toroidal lenses (107a, 107b, 107c, 107d), two converging lenses (156a, 156b), and two light receiving elements (157a, 157b).

  Each of the light source units includes a light source having the two-dimensional array 100 or the two-dimensional array 200 and a coupling lens.

  The aperture plate 201a has an aperture and defines the beam diameter of light from the light source unit 200a. The aperture plate 201b has an aperture and defines the beam diameter of light from the light source unit 200b. Each of the aperture plates is disposed to be inclined with respect to the corresponding light source unit in order to use the light reflected around the aperture for monitoring. In addition, this can prevent light reflected around the opening from returning to the light source unit.

  The light beam splitting prism 202a splits light that has passed through the opening of the aperture plate 201a into two light beams that are parallel to each other at a predetermined interval in the Z-axis direction. The beam splitting prism 202b splits the light that has passed through the opening of the aperture plate 201b into two lights that are parallel to each other at a predetermined interval in the Z-axis direction.

  The cylinder lens 204 a is disposed on the optical path of the −Z side light (hereinafter also referred to as “black light” for convenience) of the two lights from the light beam splitting prism 202 a, and the black light is deflected and reflected by the polygon mirror 104. Converge in the sub-scanning direction in the vicinity.

  The cylinder lens 204 b is disposed on the optical path of + Z side light (hereinafter also referred to as “cyan light” for convenience) of the two lights from the light beam splitting prism 202 a, and the cyan light is disposed in the vicinity of the deflection reflection surface of the polygon mirror 104. Thus, the sub-scanning direction converges.

  The cylinder lens 204 c is arranged on the optical path of + Z side light (hereinafter also referred to as “magenta light” for convenience) of the two lights from the light beam splitting prism 202 b, and the magenta light is near the deflecting reflection surface of the polygon mirror 104. Thus, the sub-scanning direction converges.

  The cylinder lens 204d is disposed on the optical path of light on the −Z side (hereinafter also referred to as “yellow light” for convenience) out of the two lights from the light beam splitting prism 202b, and the yellow light is deflected and reflected by the polygon mirror 104. Converge in the sub-scanning direction in the vicinity.

  The polygon mirror 104 has a four-stage mirror having a two-stage structure, and each mirror serves as a deflection reflection surface. The light from the cylinder lens 204a and the light from the cylinder lens 204d are respectively deflected on the first (lower) deflecting / reflecting surface, and the light and cylinder from the cylinder lens 204b are deflected on the second (upper) deflecting / reflecting surface. It arrange | positions so that the light from the lens 204c may be deflected, respectively. Further, the first-stage deflecting / reflecting surface and the second-stage deflecting / reflecting surface rotate with a phase shift of 45 °, and light scanning is alternately performed in the first and second stages.

  The fθ lens 105 a and the fθ lens 105 b are disposed on the −X side of the polygon mirror 104, and the fθ lens 105 c and the fθ lens 105 d are disposed on the + X side of the polygon mirror 104.

  The fθ lens 105a and the fθ lens 105b are stacked in the Z-axis direction, the fθ lens 105a faces the first-stage deflection / reflection surface, and the fθ lens 105b faces the second-stage deflection / reflection surface. Further, the fθ lens 105c and the fθ lens 105d are stacked in the Z-axis direction, the fθ lens 105c faces the second-stage deflection reflection surface, and the fθ lens 105d faces the first-stage deflection reflection surface.

  Therefore, the black light deflected by the polygon mirror 104 enters the fθ lens 105a, the yellow light enters the fθ lens 105d, the cyan light enters the fθ lens 105b, and the magenta light enters the fθ lens 105c.

  In this optical scanning device 1010, as shown in FIG. 16A as an example, the light beam traveling from the polygon mirror 104 to the fθ lens 105a or the fθ lens 105b is the method of the deflection reflection surface of the polygon mirror 104 in the sub-scanning direction. A light beam that is inclined to the + Z side with respect to the linear direction and travels from the polygon mirror 104 toward the fθ lens 105c or the fθ lens 105d is on the −Z side with respect to the normal direction of the deflecting reflection surface of the polygon mirror 104 in the sub-scanning direction. Inclined. As an example, as shown in FIG. 16B, the light beam traveling from the polygon mirror 104 toward the fθ lens 105c or the fθ lens 105d is in the sub-scanning direction with respect to the normal direction of the deflecting reflection surface of the polygon mirror 104. When tilted to the + Z side, or as shown in FIG. 16C as an example, all the light beams traveling from the polygon mirror 104 to each fθ lens are reflected on the deflection reflection surface of the polygon mirror 104 in the sub-scanning direction. In the case where it coincides with the normal direction, as shown in FIG. 16D as an example, the reflected light from one fθ lens arranged with the polygon mirror 104 interposed therebetween is flare light and the other fθ lens. There is a risk of entering.

  The black light transmitted through the fθ lens 105a is imaged in a spot shape on the photosensitive drum K1 via the folding mirror 106a, the toroidal lens 107a, and the folding mirror 108a.

  The cyan light transmitted through the fθ lens 105b forms a spot image on the photosensitive drum C1 via the folding mirror 106b, the toroidal lens 107b, and the folding mirror 108b.

  The magenta light transmitted through the fθ lens 105c forms a spot image on the photosensitive drum M1 via the folding mirror 106c, the toroidal lens 107c, and the folding mirror 108c.

  The yellow light transmitted through the fθ lens 105d forms a spot image on the photosensitive drum Y1 via the folding mirror 106d, the toroidal lens 107d, and the folding mirror 108d.

  In this optical scanning device 1010, the number of folding mirrors that bend the optical path of the light beam toward the photosensitive drum K1, the number of folding mirrors that bend the optical path of the light beam toward the photosensitive drum C1, and the optical path of the light beam toward the photosensitive drum M1. The number of folding mirrors that bend and the number of folding mirrors that bend the optical path of the light beam toward the photosensitive drum Y1 is two. That is, the difference in the number of folding mirrors provided corresponding to each photosensitive drum is an even number. Thereby, as shown in FIG. 17A as an example, the bending direction of the scanning line in each photosensitive drum becomes the same direction, and the color misregistration can be easily reduced. Assuming that the difference between the number of folding mirrors provided corresponding to the photosensitive drum Y1 and the number of folding mirrors provided corresponding to the other three photosensitive drums is one, FIG. As shown in FIG. 17B, the scanning line bending direction in each photosensitive drum is reversed, and there is a possibility that the color shift is increased.

  The converging lens 156a is disposed on the optical path of the light reflected by the aperture plate 201a, and condenses the light reflected by the aperture plate 201a. The converging lens 156b is disposed on the optical path of the light reflected by the aperture plate 201b, and condenses the light reflected by the aperture plate 201b.

  The light receiving element 157a is disposed at the light condensing position via the converging lens 156a, and receives the light via the converging lens 156a. The light receiving element 157b is disposed at a light condensing position via the converging lens 156b, and receives light via the converging lens 156b.

  Each light receiving element outputs a signal (photoelectric conversion signal) corresponding to the amount of received light.

  As is clear from the above description, in this optical scanning device 1010, each coupling lens, each aperture plate, and each cylindrical lens 17 constitute a first optical system.

  Each fθ lens, each toroidal lens, and each folding mirror constitute a second optical system.

  Each aperture plate, each converging lens, and each light receiving element constitute a monitor device.

  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.

  Further, an image forming apparatus using a color developing medium (positive photographic paper) that develops color by the heat energy of a beam spot as an image carrier may be used. In this case, a visible image can be directly formed on the image carrier by optical scanning.

  As described above, the optical scanning device of the present invention is suitable for stably scanning the surface to be scanned with a light beam. The image forming apparatus of the present invention is suitable for forming a high quality image at high speed.

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 two-dimensional array of VCSEL contained in the light source in FIG. It is a figure for demonstrating the structure of each VCSEL in the two-dimensional array of FIG. It is the figure which expanded a part of VCSEL of FIG. It is a figure for demonstrating the position of each optical element in the optical scanning device of FIG. It is a figure for demonstrating the relationship between the incident direction of the light beam which injects into a polygon mirror, and the normal line direction of the deflection | deviation reflective surface of a polygon mirror regarding a subscanning direction. FIGS. 8A and 8B are diagrams for explaining the relationship between the incident direction of the light beam incident on the polygon mirror and the return light from the polygon mirror, respectively. It is a figure for demonstrating the light beam which goes to a deflector side scanning lens from a polygon mirror regarding a subscanning direction. It is a figure for demonstrating the two-dimensional array of a comparison object. It is a figure for demonstrating the modification of VCSEL. It is the figure which expanded a part of VCSEL of FIG. It is a figure for demonstrating the characteristic of VCSEL of FIG. It is a figure for demonstrating schematic structure of a tandem color machine. It is the schematic which shows the optical scanning device in FIG. FIGS. 16A to 16D are diagrams for explaining the light fluxes directed from the polygon mirror to the fθ lenses. FIG. 17A and FIG. 17B are diagrams for explaining the bending of the scanning line.

Explanation of symbols

  11a: Scanning lens (part of the second optical system), 11b ... Scanning lens (part of the second optical system), 13 ... Polygon mirror (deflector), 14 ... Light source, 15 ... Coupling lens (first 1 ... a part of the first optical system), 16 ... aperture plate (a part of the first optical system), 17 ... a cylindrical lens (a part of the first optical system), 18 ... a reflection mirror (of the first optical system) Part), 23 ... half mirror (part of monitor device), 24 ... imaging lens (part of monitor device), 25 ... photodiode (part of monitor device), 101 ... VCSEL (surface emitting laser), 104 ... polygon mirror (deflector), 105a, 105b, 105c, 105d ... fθ lens (part of the second optical system), 106a, 106b, 106c, 106d ... folding mirror (part of the second optical system) 107a, 1067, 07c, 107d ... toroidal lens (part of the second optical system), 108a, 108b, 108c, 108d ... folding mirror (part of the second optical system), 156a, 156b ... converging lens (part of the monitor device) ) 157a, 157b... Light receiving element (part of the monitor device), 201... VCSEL (surface emitting laser), 201a, 201b... Aperture plate (part of the first optical system), 202a, 202b. Part of the first optical system), 204a, 204b, 204c, 204d ... cylindrical lens (part of the first optical system), 500 ... laser printer (image forming apparatus), 900 ... optical scanning device, 901 ... photosensitive Body drum (image carrier), 1010... Optical scanning device, K1, C1, M1, Y1... Photosensitive drum (image carrier).

Claims (8)

An optical scanning device that scans a surface to be scanned with a light beam,
A light source having a plurality of surface emitting lasers;
A deflector having a deflecting reflecting surface for deflecting a light beam from the light source;
An aperture plate disposed on an optical path of a light beam from the light source between the light source and the deflector and having an opening that defines at least a beam diameter in a sub-scanning direction of the light beam toward the deflector; A first optical system for guiding a light beam from the deflector to the deflector;
A second optical system for guiding the light beam deflected by the deflector to the surface to be scanned;
A monitor device for monitoring the amount of light emitted from the surface emitting laser of the light source;
An optical scanning device characterized in that a light beam traveling from the deflector toward the second optical system is inclined with respect to a normal direction of the deflection reflection surface with respect to a sub-scanning direction.   The optical scanning device according to claim 1, wherein the aperture plate is disposed to be inclined with respect to a virtual plane perpendicular to a traveling direction of a light beam traveling from the light source toward the deflector.   3. The optical scanning device according to claim 1, wherein the aperture plate blocks a light beam reflected by the deflector and directed toward the light source. 4.   The plurality of surface emitting lasers are two-dimensionally arranged, and an interval between two surface emitting lasers positioned at both ends with respect to a direction corresponding to the main scanning direction is set at two positions positioned at both ends with respect to a direction corresponding to the sub scanning direction. The optical scanning device according to claim 1, wherein the optical scanning device is larger than an interval between the surface emitting lasers. The second optical system includes a first scanning optical system disposed on one side of the deflector, and a second scanning optical system disposed on the other side of the deflector,
The light beam traveling from the deflector to the first scanning optical system and the light beam traveling from the deflector to the second scanning optical system are inclined in opposite directions with respect to the normal direction of the deflection reflecting surface with respect to the sub-scanning direction. The optical scanning device according to claim 1, wherein the optical scanning device is provided.   Each of the first scanning optical system and the second scanning optical includes at least one reflecting mirror that bends the optical path of the light beam, and the difference in the number of reflecting mirrors in each scanning optical system is an even number. The optical scanning device according to claim 5. At least one image carrier;
An image forming apparatus comprising: at least one optical scanning device according to any one of claims 1 to 6 that scans a light beam including image information with respect to the at least one image carrier.   The image forming apparatus according to claim 7, wherein the image information is multicolor image information.

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