Abstract:
An optical scanner forms an electrostatic latent image on a photosensitive member by scanning the photosensitive member with a light beam. The optical scanner includes: an incident optical system which at least comprises: a light beam emission device configured to emit a light beam; and a cylindrical lens configured to condense the light beam emitted from the light beam emission device, and a scanning optical system which at least comprises: a light deflecting device configured to reflect the light beam having passed through the cylindrical lens to deflect the light beam in a main scanning direction for scanning the photosensitive member; and a scanning lens configured to focus the light beam deflected by the light deflecting device on the photosensitive member to form an electrostatic latent image thereon. The incident optical system and the scanning optical system are divided by a light shielding wall.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the foreign priority benefit under Title 35, United States Code, §119(a)-(d) of Japanese Patent Application No. 2007-275935 filed on Oct. 24, 2007 in the Japan Patent Office, the disclosure of which is herein incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an optical scanner configured to scan a photosensitive member with a light beam to form an electrostatic latent image on the photosensitive member. 
         [0003]    Generally, an optical scanner used for a laser printer has various optical elements, such as a semiconductor laser, a coupling lens, a reflecting mirror, and a cylindrical lens which constitute an incident optical system, and a deflecting mirror, a scanning lens, and a reflecting mirror which constitute a scanning optical system. Of these optical elements, a lens produces stray light when a light beam is reflected on its incidence surface and emission surface. If the stray light reaches a photosensitive member, a ghost image may be formed, thereby leading to deteriorated image quality. Particularly, in the case where stray light occurs in the incident optical system and reaches the photosensitive member, only little stray light becomes a problem because the optical path of the stray light beam is unchanged and the photosensitive member is continuously irradiated with the stray light at the same area. 
         [0004]    To eliminate this problem, for example, Japanese Laid-open Patent Publication No. 2003-195209 discloses an image exposure device including a limiter such as a light filter and a half mirror on an optical path of light beam emitted from a laser beam source (semiconductor laser) that emits a large amount of stray light. Because the limiter limits the amount of light emitted from the laser beam source to the required amount for exposure, this image exposure device can restrict stray light from the laser beam source. 
         [0005]    However, in this conventional image exposure device, a laser beam from the laser beam source goes around the limiter and can be incident on the reflecting mirror and the cylindrical lens that is arranged on an optical path adjacent thereto. This conventional image exposure device is therefore insufficient to restrict stray light generated in the incident optical system from reaching the photosensitive member. Further, this image exposure device is much less sufficient to restrict stray light caused by a laser beam from another laser beam source. 
         [0006]    In view of the foregoing drawbacks of the prior art, the present invention seeks to provide an optical scanner which can sufficiently restrict stray light generated in an incident optical system from reaching a photosensitive member. 
       SUMMARY OF THE INVENTION 
       [0007]    According to the present invention, there is provided an optical scanner for forming an electrostatic latent image on a photosensitive member by scanning the photosensitive member with a light beam, the optical scanner comprising: an incident optical system including: a light beam emission device configured to emit a light beam; and a cylindrical lens configured to condense the light beam emitted from the light beam emission device, and a scanning optical system including: a light deflecting device configured to reflect the light beam having passed through the cylindrical lens to deflect the light beam in a main scanning direction for scanning the photosensitive member; and a scanning lens configured to focus the light beam deflected by the light deflecting device on the photosensitive member to form an electrostatic latent image thereon. The incident optical system and the scanning optical system are divided by a light shielding wall. 
         [0008]    With this configuration of the aforementioned optical scanner, the light shielding wall divides the incident optical system including the light beam emission device and the cylindrical lens from the scanning optical system including the light deflecting device and the scanning lens. Therefore, it is possible to divide the incident optical system from the photosensitive member that is arranged downstream from the scanning optical system in a travelling direction of the light beam. 
         [0009]    Preferably, the light shielding wall is at least higher than an optical axis of the light beam that is emitted from the incident optical system. More preferably, the light shielding wall has a height to completely partition the incident optical system and the scanning optical system, for example, by extending to the ceiling of a casing for accommodating the incident optical system and the scanning optical system. Further, in the case where a gap is formed between the light shielding wall and the casing, it is further preferable that the gap is closed by a sponge member. 
         [0010]    According to the present invention, because the light shielding wall divides the incident optical system from the photosensitive member that is arranged downstream from the scanning optical system in the travelling direction of the light beam, it is possible to sufficiently restrict stray light generated in the incident optical system from reaching the photosensitive member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Other objects and aspects of the present invention will become more apparent by describing in detail illustrative, non-limiting embodiments thereof with reference to the accompanying drawings, in which: 
           [0012]      FIG. 1  is a sectional view illustrating the overall structure of a color laser printer as an embodiment of an image forming apparatus; 
           [0013]      FIG. 2  is a plan view illustrating the configuration of an optical scanner according to one preferred embodiment of the present invention; 
           [0014]      FIG. 3  is a sectional view taken along the line III-III of  FIG. 2 ; 
           [0015]      FIG. 4  is a perspective view illustrating the configuration of a laser beam source of the optical scanner as shown in  FIG. 2 ; and 
           [0016]      FIG. 5  is a perspective view illustrating optical paths of the optical scanner. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Structure of Laser Printer 
       [0017]    One preferred embodiment of the present invention will be described in detail with reference to the attached drawings. 
         [0018]    Firstly, the overall structure of a color laser printer will be described with reference to  FIG. 1 . 
         [0019]    In the following description, unless otherwise stated, directions of the color laser printer refer to the directions as seen from a user facing the color laser printer during its use. To be more specific, referring to  FIG. 1 , a left-side direction and a right-side direction of the color laser printer are referred to as a “front or near side” and a “rear or far side”, respectively. Also, a direction away from a viewer of  FIG. 1  is referred to as a “left side”, and a direction toward the viewer of  FIG. 1  as a “right side”. An upper and lower direction in  FIG. 1  is referred to as a “vertical direction” or an “upper and lower direction” as it is. 
         [0020]    As seen in  FIG. 1 , the color laser printer  1  has four photosensitive drums  3 A- 3 D as an example of a plurality of photosensitive members. The photosensitive drums  3 A- 3 D are arranged parallel in a main body  2  in a near-to-far direction (hereinafter referred to as a “front-back direction”. A surface of each photosensitive drum  3 A- 3 D is uniformly charged by a Scorotron charger  4 A- 4 D, and thereafter an optical scanner  5  scans the surface of the photosensitive drum  3 A- 3 D with a laser beam (light beam) to form an electrostatic latent image on the photosensitive drum  3 A- 3 D based on an image data. The electrostatic latent image becomes a visible image on each photosensitive drum  3 A- 3 D when toner (developer) is supplied from a corresponding development roller  6 A- 6 D carrying the toner, so that a toner image is formed on the photosensitive drum  3 A- 3 D. 
         [0021]    A stack of paper (or sheets) P is stored in a sheet cassette  7  that is received in the main body  2 . Paper P passes through various rollers provided in the sheet feeding unit  8  and a feeding direction of the paper P is changed from the near side to the far side, so that the paper P is transferred from the sheet cassette  7  to a conveyor belt  9 . The conveyor belt  9  is positioned opposite to the photosensitive drums  3 A- 3 D. Different colored toner on the photosensitive drum  3 A- 3 D is transferred one after another onto the paper P that is conveyed on the conveyor belt  9  along a paper conveyance passage while a transfer bias is being applied to the transfer rollers  10 A- 10 D. After toner images for four different colors are transferred from the photosensitive drums  3 A- 3 D onto the paper P to form a complete toner image, the paper P is conveyed to a fixing device  11  at which the toner image is thermally fixed on the paper P. The paper P then passes through various rollers, so that the feeding direction of the paper P is changed from the far side to the near side and the paper P is discharged and stacked on a sheet output tray  12 . 
         [0022]    Four process cartridges  13 A- 13 D are provided in the main body  2  between the sheet cassette  7  and the optical scanner  5 . These process cartridges  13 A- 13 D are arranged in line in the main body  2  along the front-back direction. The process cartridges  13 A- 13 D are detachably mounted to a frame  14  that is also detachably mounted to the main body  2 . The process cartridges  13 A- 13 D are thus arranged in predetermined positions in the main body  2  while being attached to the frame  14 . 
         [0023]    Each process cartridge  13 A- 13 D mainly includes a casing  15 A- 15 D forming an outer frame, the photosensitive drum  3 A- 3 D, the Scorotron charger  4 A- 4 D, and a developer cartridge  16 A- 16 D that is detachably mounted to the corresponding casing  15 A- 15 D. Further, the developer cartridge  16 A- 16 D mainly includes the development roller  6 A- 6 D, a feed roller  17 A- 17 D, and a toner hopper  18 A- 18 D. The process cartridges  13 A- 13 D have substantially the same construction except that the color of toner stocked in the toner hopper  18 A- 18 D of the developer cartridge  16 A- 16 D is different from those of the other process cartridges  13 A- 13 D. 
       Overall Structure of Optical Scanner 
       [0024]    Detailed description will be given of the structure of the optical scanner  5 . 
         [0025]    As seen in  FIG. 2 , the optical scanner  5  mainly consists of an incident optical system  30  and a scanning optical system  40 , which are positioned in a hollow casing  20 . The incident optical system  30  and the scanning optical system  40  are divided in the casing  20  by a light shielding wall  21  that is integrally formed with the casing  20 . To be more specific, the light shielding wall  21  is integrally formed with a bottom wall, a side wall (left-side side wall of  FIG. 2 ), and a ceiling or top wall (not shown) of the casing  20 , so that the internal space of the casing  20  is completely divided by the light shielding wall  21  into two spaces. The incident optical system  30  is positioned in one of the two spaces, while the scanning optical system  40  is positioned in the other space of the casing  20 . 
         [0026]    Two openings  22  are formed in the light shielding wall  21  for allowing laser beams (light beams) emitted from the incident optical system  30  to pass through the openings  22 . In other words, the light shielding wall  21  according to the present invention has only two openings  22  for allowing the laser beams to pass through the light shielding wall  21 . Namely, except for the openings  22 , the incident optical system  30  is absolutely isolated from the scanning optical system  40  in the casing  20 . An aperture member  34  to be described later is fixed at a laser beam emission side of the opening  22 . 
         [0027]    The integrally formed casing  20  and light shielding wall  21  or at least the light shielding wall  21  is made of resin, which blocks transmission of a laser beam emitted from a semiconductor laser  35  (see  FIG. 4 ) and having a specific wavelength: for example, resin of which transmissivity is equal to or less than 10%. The light shielding wall  21  may be made of resin having a lower transmissivity at a wavelength around 780 nm, so that the light shielding wall  21  can restrict transmission of near-infrared light. 
         [0028]    As shown in  FIG. 3 , a plurality of openings  23 , that is, four openings  23 A- 23 D are formed in the bottom portion of the casing  20 . A plurality of laser beams (light beams) that are emitted from the incident optical system  30  and then deflected in the scanning optical system  40  pass through the openings  23 A- 23 D so that each of the plurality of light beams is directed to the surfaces of different photosensitive drums  3 A- 3 D for scanning the photosensitive drums  3 A- 3 D. The incident optical system  30  and the scanning optical system  40  will be described in detail. 
       Structure of Incident Optical System 
       [0029]    As seen in  FIG. 2 , the incident optical system  30  mainly includes four laser beam sources  31  ( 31 A- 31 D) as an example of a plurality of light beam emission devices, two reflecting mirrors  32 , two cylindrical lenses  33 , and two aperture members  34 . 
         [0030]    In the following description, an upstream side and a downstream side of a travelling direction of the laser beam that is emitted from the laser beam source  31  will be simply referred to as an “upstream side” and a “downstream side”. 
         [0031]    As best seen in  FIG. 4 , the laser beam source  31  includes a semiconductor laser  35  as an example of a light emitting element, a coupling lens  36 , and a holder  37 . The four laser beam sources  31 A- 31 D have substantially the same construction. 
         [0032]    The coupling lens  36  is a convex lens which is made of resin or glass. The coupling lens  36  condenses the laser beam emitted from the semiconductor laser  35  and converts it into a light beam (collimated light beam). 
         [0033]    The holder  37  is formed by sheet metal working of a plate member that is made of aluminum alloy. The holder  37  consists of a laser retaining wall  37 A, a bottom wall  37 B extending downstream from the lower end of the laser retaining wall  37 A, a connecting portion extending upward from the downstream end of the bottom wall  37 B, and a lens retaining portion  37 C extending downstream from the upper end of the connecting portion. 
         [0034]    A through hole is formed in the laser retaining wall  37 A so that the semiconductor laser  35  is press fitted into the through hole. Attachment holes  37 D are formed in the laser retaining wall  37 A and the bottom wall  37 B. The holder  37  is fixed to the casing  20  or fixing portions provided in the casing  20  by screws (see  FIG. 2 ). 
         [0035]    The lens retaining portion  37 C has a groove  37 E extending along the travelling direction of the laser beam. The coupling lens  36  is bonded in the groove  37 E at a predetermined position distanced away from the semiconductor laser  35 . In this embodiment, a passage from the semiconductor laser  35  to the coupling lens  36  is open without being covered by a lens-barrel. 
         [0036]    As best seen in  FIG. 2 , the laser beam source  31 A and the laser beam source  31 B are arranged such that their optical paths of the emitted laser beams intersect orthogonally to each other. To be more specific, the laser beam source  31 A is arranged opposite to a polygon mirror  41  to be described later, and the laser beam source  31 B is arranged such that the optical path of the laser beam emitted therefrom is substantially orthogonal to the line connecting the laser beam source  31 A and the polygon mirror  41 . The laser beam sources  31 C and  31 D are arranged symmetrically to the laser beam sources  31 A,  31 B. 
         [0037]    The reflecting mirror  32  is arranged downstream of the laser beam source  31 A (or  31 C) in such a position as to tilt at approximately 45 degrees with respect to the optical paths of the laser beams emitted from the laser beam sources  31 A,  31 B (or the laser beam sources  31 C,  31 D). As best seen in  FIG. 5 , the reflecting mirror  32  deflects the laser beam from the laser beam source  31 B at approximately 90 degrees so that the direction of the laser beam from the laser beam source  31 B is changed to substantially align with that of the laser beam from the laser beam source  31 A. The laser beam from the laser beam source  31 A passes above the reflecting mirror  32 . 
         [0038]    The cylindrical lens  33  is positioned downstream from the reflecting mirror  32  and arranged in the opening  22  formed in the light shielding wall  21  at the laser beam incident side thereof. In order to correct optical face tangle errors of the polygon mirror  41 , the cylindrical lens  33  refracts the laser beams from the laser beam sources  31 A,  31 B (or the laser beam sources  31 C,  31 D) such that these laser beams are converged in the subscanning direction Y (see  FIG. 5 ) and focused on the polygon mirror  41 . The cylindrical lens  33  is made of resin or glass, and has a convex surface at a beam-incident side and a flat surface at a beam-emitting side. 
         [0039]    The aperture member  34  is made of a substantially rectangular plate member (sheet metal). The aperture member  34  is positioned downstream from the cylindrical lens  33  and fixed at a laser beam emission side of the opening  22 . As best seen in  FIG. 5 , the aperture member  34  has two aperture slits  34 A,  34 B as an example of an optical aperture. These aperture slits  34 A,  34 B are lined in the subscanning direction Y at an interval corresponding to the optical paths of the laser beam sources  31 A,  31 B (or the laser beam sources  31 C,  31 D). Each of the aperture slits  34 A,  34 B is in the shape of an oblong opening extending in the main scanning direction X. When the laser beam from the cylindrical lens  33  passes through the aperture slit  34 A or the aperture slit  34 B of the aperture member  34 , the laser beam is limited to have predetermined widths in the main scanning direction X and the subscanning direction Y. Therefore, each of the aperture slits  34 A,  34 B functions as an optical aperture. 
         [0040]    Providing the aperture member  34  in the opening  22  of the light shielding wall  21  can improve a light shielding property because the light shielding wall  21  allows transmission of the laser beam only through the aperture slits  34 A,  34 B. 
       Structure of Scanning Optical System 
       [0041]    As seen in  FIGS. 2 and 3 , the scanning optical system  40  mainly includes the polygon mirror  41  as an example of a light deflecting device, two scanning lenses  42  positioned on both sides of the polygon mirror  41  (i.e., the polygon mirror  41  is interposed between the scanning lenses  42 ), a plurality of reflecting mirrors  43 - 46 , and four toroidal lenses  47 . 
         [0042]    The polygon mirror  41  is arranged downstream from the incident optical system  30  and the aperture member  34  and is positioned substantially at a center of the scanning optical system  40  (also at a center of the casing  20 ). The polygon mirror  41  has a hexagonal cross-section and each of the six sides is provided with a reflecting mirror. As best seen in  FIG. 5 , the polygon mirror  41  spins at a high speed to reflect the laser beams on the reflecting mirrors so that the laser beams passing through the aperture slits  34 A,  34 B of the aperture member  34  are deflected in the main scanning direction Y for scanning the photosensitive drums  3 A- 3 D. The laser beams emitted from the incident optical system  30  are incident on a reflecting mirror of the polygon mirror  41  at different incident angles, and therefore the laser beams are reflected by the reflecting mirror at different angles in the subscanning direction Y. 
         [0043]    The scanning lenses  42  are arranged downstream from the polygon mirror  41 . The scanning lenses  42  convert the laser beams deflected at an equiangular speed by the polygon mirror  41  into beams for scanning the photosensitive drums  3 A- 3 D at a constant speed. As seen in  FIG. 3 , of the two laser beams passing through one scanning lens  42  (the scanning lens  42  positioned on the left side of  FIG. 3 ), the lower laser beam is reflected by the reflecting mirror  43 A and the reflecting mirror  43 B so that the travelling direction of the laser beam is changed, and thereafter the laser beam passes through the toroidal lens  47  and then through the opening  23 A. The laser beam coming from the opening  23 A is directed to and focused on the photosensitive drum  3 A for scanning the photosensitive drum  3 A. Meanwhile, the upper laser beam of the two laser beams is reflected in turn by the reflecting mirrors  44 A,  44 B, and  44 C so that the travelling direction of the laser beam is changed, and thereafter the laser beam passes through the toroidal lens  47  and then through the opening  23 B. The laser beam coming from the opening  23 B is directed to and focused on the photosensitive drum  3 B for scanning the photosensitive drum  3 B. 
         [0044]    Similarly, of the two laser beams passing through the other scanning lens  42  (the scanning lens  42  positioned on the right side of  FIG. 3 ), the lower laser beam is reflected in turn by the reflecting mirrors  45 A,  45 B, and  45 C so that the travelling direction of the laser beam is changed, and thereafter the laser beam passes through the toroidal lens  47  and then through the opening  23 C. The laser beam coming from the opening  23 C is directed to and focused on the photosensitive drum  3 C for scanning the photosensitive drum  3 C. Meanwhile, the upper laser beam of the two laser beams is reflected by the reflecting mirror  46 A and the reflecting mirror  46 B so that the travelling direction of the laser beam is changed, and thereafter the laser beam passes through the toroidal lens  47  and then through the opening  23 D. The laser beam coming from the opening  23 D is directed to and focused on the photosensitive drum  3 D for scanning the photosensitive drum  3 D. 
         [0045]    The operation of the optical scanner  5  as constructed above will be described below. 
         [0046]    As shown in  FIG. 5 , the laser beam emitted from the semiconductor laser  35  is partly reflected by the incidence surface and the emission surface of the coupling lens  36  and the cylindrical lens  33  and becomes stray light. Particularly, in the case where a plurality of laser beam sources  31  are employed as with this embodiment, the numbers of semiconductor lasers  35 , coupling lenses  36 , and cylindrical lenses  33  are increased, so that an extremely large amount of stray light is generated. 
         [0047]    Further, the laser beam emitted from the semiconductor laser  35  gradually extends from its point of emission. Especially in the case of this embodiment where the passage from the semiconductor laser  35  to the coupling lens  36  is open without being covered by a lens-barrel, part of the laser beam emitted from the semiconductor laser  35  does not go into the coupling lens  36  and becomes stray light. 
         [0048]    The extremely large amount of stray light generated as above can be shielded by the light shielding wall  21 , so that little or no stray light goes into the scanning optical system  40 . According to this embodiment, the laser beams emitted from the incident optical system  30  to the scanning optical system  40  are only allowed to pass through the aperture slits  34 A,  34 B of the aperture member  34  that is fixed in the opening  22  of the light shielding wall  21 . Therefore, the area of the opening of the light shielding wall  21  can be minimized to limit the amount of stray light going into the scanning optical system  40 . Further, according to this embodiment, because the light shielding wall  21  is integrally formed with the casing  20 , no gap is formed between the casing  20  and the light shielding wall  21 . This can restrict stray light from passing through gaps between the casing  20  and the light shielding wall  21  and going into the scanning optical system  40 . 
         [0049]    Stray light shielded and blocked by the light shielding wall  21  is reflected by the light shielding wall  21  and the walls of the casing  20 , and is gradually absorbed and removed. In this embodiment, the casing  20  and the light shielding wall  21  are made of resin which blocks transmission of the laser beam emitted from the semiconductor laser  35  and having a specific wavelength. This can prevent stray light from transmitting through the light shielding wall  21  and going into the scanning optical system  40 . 
         [0050]    As in the case of a so-called tandem color laser printer, a plurality of reflecting mirrors  43 - 46  are arranged in a complex manner and a plurality of openings  23  are formed as beam-emitting openings, so that stray light generated in the incident optical system  30  is more likely to reach the photosensitive drums  3 A- 3 D. However, as described above, in the optical scanner  5  according to this embodiment, stray light generated in the incident optical system  30  hardly reaches the photosensitive drums  3 A- 3 D. 
         [0051]    According to this embodiment, all the components making up the incident optical system  30  are arranged in one side of the light shielding wall  21  that partitions the casing  20 , and therefore stray light generated in the incident optical system  30  is reliably blocked by the light shielding wall  21  so as not to reach the photosensitive drums  3 A- 3 D. This can restrict a formation of a ghost image that would otherwise occur if the photosensitive drums  3 A- 3 D were continuously irradiated with stray light at the same area, thereby leading to improved image quality. 
         [0052]    Further, because a plurality of laser beam sources  31  are put together in a space of the casing  20  that is partitioned by the light shielding wall  21 , it is possible to simplify the construction of the casing  20 . This can reduce the cost and the size of the optical scanner  5 . Further, because the passage from the semiconductor laser  35  to the coupling lens  36  is open, it is possible to reduce the cost and the size of the laser beam source  31  as well as to improve the degree of freedom for adjustment of the distance between the semiconductor laser  35  and the coupling lens  36 . Further, because the casing  20  and the light shielding wall  21  are integrally formed, the light shielding wall  21  functions as a reinforcement member to improve the strength of the casing  20 . 
         [0053]    Although the present invention has been described in detail with reference to the above preferred embodiment, the present invention is not limited to this specific embodiment and various changes and modifications may be made without departing from the scope of the appended claims. 
         [0054]    According to the above embodiment, the internal space of the casing  20  is completely divided by the light shielding wall  21 . However, the present invention is not limited to this specific construction. As long as stray light generated in the incident optical system  30  does not go into the scanning optical system  40 , a gap may be formed between the light shielding wall (e.g., the upper end of the light shielding wall)  21  and the casing  20 . 
         [0055]    According to the above embodiment, the cylindrical lens  33  is arranged in the opening  22  formed in the light shielding wall  21  at the laser beam incident side of the opening  22 . However, the present invention is not limited to this specific construction and the cylindrical lens  33  may be arranged between the reflecting mirror  32  and the light shielding wall  21 . 
         [0056]    According to the above embodiment, the aperture slits  34 A,  34 B of the aperture member  34  fixed in the opening  22  are used as an example of an optical aperture. However, an optical aperture may be formed directly in the light shielding wall  21 . 
         [0057]    According to the above embodiment, the laser beam source  31  as an example of a light beam emission device is configured such that the passage from the semiconductor laser  35  to the coupling lens  36  is open. However, the present invention is not limited to this specific construction. For example, the passage from the semiconductor laser  35  to the coupling lens  36  may be covered by a lens-barrel. 
         [0058]    According to the above embodiment, the light shielding wall  21  is integrally formed with the casing  20 . However, the casing  20  and the light shielding wall  21  may be formed as discrete members and assembled together. 
         [0059]    Further, according to the above embodiment, the light shielding wall  21  is made of resin. However, the present invention is not limited to this specific construction, and the light shielding wall  21  may be made of metal. Providing a metallic light shielding wall can effectively restrict transmission of stray light. In particular, even if near-infrared light is used as a light beam, the transmissivity of the light beam becomes almost zero. In the case where the light shielding wall  21  is made of metal, it is preferable that the surface of the light shielding wall  21  is colored, for example, with black. This can restrict reflection of the light beam. 
         [0060]    According to the above embodiment, the polygon mirror  41  is used as an example of a light deflecting device and the semiconductor laser  35  is used as an example of a light emitting element. However, the present invention is not limited to this specific construction. Materials or configuration may be modified without departing from the scope of the present invention. For example, a galvano mirror (vibrating mirror) may be used as a light deflecting device.