Abstract:
A light source device includes: a semiconductor laser; a coupling lens; a holder; and a photopolymerizable resin. The coupling lens converts laser light from the semiconductor laser to a light flux, the coupling lens having a first side and a second side opposite to the first side, the coupling lens having an outer peripheral surface connecting the first side and the second side. The holder holds the semiconductor laser and the coupling lens in a manner that the first side of the coupling lens confronts the semiconductor laser. A part of the photopolymerizable resin is provided between the outer peripheral surface of the coupling lens and the holder and another remaining part of the photopolymerizable resin protrudes from between the outer peripheral surface of the coupling lens and the holder in a direction defined from the first side to the second side, the photopolymerizable resin being cured to fix the coupling lens on the holder.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2006-227130 filed Aug. 23, 2006. The entire content of this priority application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a light source device and a manufacturing method thereof, as well as an exposure device and an image forming device using the light source device. 
     BACKGROUND 
     In an image forming device such as a laser printer and a digital copier, a laser beam scans a photosensitive body in correspondence with data of an image to be printed. Thereby an electrostatic latent image is formed on the photosensitive body. Then, the image forming device forms an image by supplying developer to the electrostatic latent image, transferring the image to a recording sheet and fixing the image on the sheet. 
     The image forming device is required to be downsized and low-priced in recent years. In accordance therewith, a light source device that irradiates the laser beam for forming the electrostatic latent image is also required to have a small size and a simple structure, while high accuracy in a product is also required. 
     The light source device includes a semiconductor laser and a coupling lens (or also called a collimating lens) that gathers the laser light emitted from the semiconductor laser and converts the laser light to a light flux. These two members are positioned with their optical axes being aligned with each other with high accuracy. 
     Japanese Patent Application Laid-Open Publication No. Hei-11-231237 (which will be referred to as Document 1 hereinafter) discloses, in its  FIG. 1 , a light source device in which a laser holder that holds a semiconductor laser and a lens holder that holds a coupling lens are prepared separately. The semiconductor laser and the coupling lens are fixed on the respective holders, and the holders are fixed after being positioned corresponding to each other. The lens holder is formed in a cylindrical shape so as to surround the whole circumference of the lens. 
     Japanese Patent Application Laid-Open Publication No. 2002-31773 (which will be referred to as Document 2 hereinafter) discloses, in its  FIG. 2 , another light source device that has a more simplified configuration in comparison with the configuration described above. The light source device described in Document 2 uses a holder (holding member) that is formed by integrating a part (main part) for holding the semiconductor laser and a part for holding the coupling lens. The part for holding the coupling lens is in a base shape that protrudes from the main part of the holder in front thereof. After the semiconductor laser is fixed on the holder, the coupling lens is fixed with photopolymerizable or light-curing resin on the base portion of the holder in front of the semiconductor laser. It is noted that the photopolymerizable resin is provided not only between the coupling lens and the base, but also a part of the photopolymerizable resin protrudes outside from between the coupling lens and the base both on the front and rear sides of the coupling lens. Japanese Patent Application Laid-Open Publication No. Hei-9-218368 (which will be referred to as Document 3 hereinafter) discloses, in its  FIG. 1 , a case where the photopolymerizable resin is provided only between the coupling lens and the base. 
     SUMMARY 
     When the coupling lens is relatively thick, the lens can be sufficiently fixed by a method in which the photopolymerizable resin is provided only between the coupling lens and the holder as proposed in Document 3. 
     In addition, when the coupling lens is relatively thin, the lens can be fixed firmly by bonding the lens with the base not only at an outer peripheral surface of the lens, but also at the front and rear surfaces of the lens in a manner that a part of the photopolymerizable resin protrudes out from between the peripheral surface of the lens and the holder to the front and rear sides of the lens. It is noted that the front surface of the lens is defined as the surface of the lens from which the laser light exits, while the rear surface of the lens is defined as the other surface of the lens into which the laser light enters. 
     When the coupling lens is fixed on the base-shaped part of the holder as described in Document 2, the lens needs to be held in air by a robot hand with respect to the base. Therefore, irradiating an a curing light, such as an ultraviolet ray, for curing the photopolymerizable resin from directly above the coupling lens is difficult. However, if the ultraviolet ray is irradiated from the front (a side where the laser light exits) of the coupling lens, the ultraviolet ray does not strike on the part of the photopolymerizable resin that protrudes to the rear side of the coupling lens due to refraction of the light at the lens. For this reason, there is a problem that the photopolymerizable resin is not cured, or a large amount of time is required for the curing. 
     In such a case where the photopolymerizable resin cannot be cured evenly at a time, there is a possibility that the coupling lens moves due to contraction of the photopolymerizable resin while the photopolymerizable resin cures. Thereby, accuracy of the light source device may be lowered. 
     In view of the above, an object of the present invention is to provide a light source device with simple structure and high accuracy and a manufacturing method thereof, and an exposure device and an image forming device that employ the light source device. 
     In order to attain the above and other objects, the invention provides a light source device, including: a semiconductor laser; a coupling lens; a holder; and a photopolymerizable resin. The coupling lens converts laser light from the semiconductor laser to a light flux, the coupling lens having a first side and a second side opposite to the first side, the coupling lens having an outer peripheral surface connecting the first side and the second side. The holder holds the semiconductor laser and the coupling lens in a manner that the first side of the coupling lens confronts the semiconductor laser. A part of the photopolymerizable resin is provided between the outer peripheral surface of the coupling lens and the holder and another remaining part of the photopolymerizable resin protrudes from between the outer peripheral surface of the coupling lens and the holder in a direction defined from the first side to the second side, the photopolymerizable resin being cured to fix the coupling lens on the holder. 
     According to another aspect, the present invention provides an exposure device for forming an electrostatic latent image by scanning light on a photosensitive body, the exposure device including: a light source device that emits laser light; a cylindrical lens that focuses the laser light emitted from the light source device; a deflector that reflects the laser light that has passed through the cylindrical lens, thereby deflecting the laser light to scan in a main scanning direction; and a scanning lens that images on the photosensitive body the laser light that has been deflected to scan by the deflector. The light source device includes: a semiconductor laser; a coupling lens that converts laser light from the semiconductor laser to a light flux, the coupling lens having a first side and a second side opposite to the first side, the coupling lens having an outer peripheral surface connecting the first side and the second side; a holder that holds the semiconductor laser and the coupling lens in a manner that the first side of the coupling lens confronts the semiconductor laser; and a photopolymerizable resin, a part of the photopolymerizable resin being provided between the outer peripheral surface of the coupling lens and the holder and another remaining part of the photopolymerizable resin protruding from between the outer peripheral surface of the coupling lens and the holder in a direction defined from the first side to the second side, the photopolymerizable resin being cured to fix the coupling lens on the holder. 
     According to another aspect, the present invention provides an image forming device for forming an image on a recording sheet, the image forming device including: an exposure device that forms an electrostatic latent image by scanning light on a photosensitive body; the photosensitive body on which the electrostatic latent image is formed by the exposure device; a developing unit that supplies developer on the photosensitive body; and a transfer mender that transfers an image formed by the developer onto a recording sheet. The exposure device includes: a light source device that emits laser light; a cylindrical lens that focuses the laser light emitted from the light source device; a deflector that reflects the laser light that has passed through the cylindrical lens, thereby deflecting the laser light to scan in a main scanning direction, and a scanning lens that images on the photosensitive body the laser light that has been deflected to scan by the deflector, thereby forming an electrostatic latent image on the photosensitive body. The light source device includes: a semiconductor laser; a coupling lens that converts laser light from the semiconductor laser to a light flux, the coupling lens having a first side and a second side opposite to the first side, the coupling lens having an outer peripheral surface connecting the first side and the second side; a holder that holds the semiconductor laser and the coupling lens in a manner that the first side of the coupling lens confronts the semiconductor laser; and a photopolymerizable resin, a part of the photopolymerizable resin being provided between the outer peripheral surface of the coupling lens and the holder and another remaining part of the photopolymerizable resin protruding from between the outer peripheral surface of the coupling lens and the holder in a direction defined from the first side to the second side, the photopolymerizable resin being cured to fix the coupling lens on the holder. 
     According to another aspect, the present invention provides a method for manufacturing a light source device that includes a semiconductor laser, a coupling lens that converts laser light from the semiconductor laser to a light flux, the coupling lens having a first side and a second side opposite to the first side, a holder that holds the semiconductor laser and the coupling lens in a manner that the first side of the coupling lens confronts the semiconductor laser, and a photopolymerizable resin that fixes the coupling lens on the holder, the method including: providing the photopolymerizable resin on a holder at its area that extends from a first position to a second position; locating a coupling lens, which has a first side and a second side opposite to the first side and an outer peripheral surface connecting the first side and the second side, on the photopolymerizable resin to allow the first position to be located between the holder and either one of the first side of the coupling lens and the outer peripheral surface of the coupling lens and to allow the second position to be located away from the second side of the coupling lens in a direction defined from the first side to the second side; and irradiating the photopolymerizable resin with a curing light for curing the photopolymerizable resin from a position that is away from the second side of the coupling lens in the direction defined from the first side to the second side. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional side view of a laser printer according to an embodiment of the present invention; 
         FIG. 2  is a plan view of a scanner unit provided in the laser printer of  FIG. 1 ; 
         FIG. 3  is a perspective view of a light source device provided in the scanner unit of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view of the light source device of  FIG. 3 ; 
         FIG. 5  is a perspective view of a light source device according to a modification; and 
         FIG. 6  is a cross-sectional view of the light source device of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     A light source device, an exposure device and an image forming device according to an embodiment of the invention will be described while referring to the accompanying drawings wherein like parts and components are designated by the same reference numerals to avoid duplicating description. 
       FIG. 1  is a cross-sectional side view of a laser printer  1  according to the embodiment.  FIG. 2  is a plan view of a scanner unit  16  provided in the laser printer  1 . 
     The laser printer  1  includes a main casing  2 . The laser printer  1  further includes: a feeder section  4  and an image forming section  5 . The feeder section  4  and the image forming section  5  are housed in the main casing  2 . The feeder section  4  supplies sheets  3  (recording medium) one sheet at a time to the image forming section  5 . The image forming section  5  forms a desired image on the supplied sheet  3  based on print data. 
     The feeder section  4  includes: a paper supply tray  6 , a paper pressing plate  7 , a sheet supply roller  8 , a separating pad  9 , paper dust removing rollers  10  and  11 , and registration rollers  12 . The paper supply tray  6  is detachably mounted in the bottom section of the main casing  2 . The paper pressing plate  7  is disposed inside the paper supply tray  6 . 
     In the feeder section  4 , a stack of sheets  3  mounted in the paper supply tray  6  are pressed against the sheet supply roller  8  by the paper pressing plate  7 . One sheet at a time is separated from the sheet stack by the sheet supply roller  8  and the separating pad  9 , and passes the various rollers  10 - 12 , before being conveyed to the image forming section  5 . 
     The image forming section  5  includes: the scanner unit  16 , a process cartridge  17 , and a fixing section  18 . 
     The scanner unit  16  is provided in an upper part of the main body casing  2 . As shown in  FIG. 2 , the scanner unit  16  includes a light source device  100 , a cylindrical lens  25 , a polygon mirror  19 , an fθ lens  20 , and a reflecting mirror  22 . The light source device  100  is for emitting laser light modulated according to print data. The cylindrical lens  25  gathers or focuses laser light emitted from the light source device  100  in a sub-scanning direction, while guiding the laser light to fall incident on the polygon mirror  19 , thereby correcting an optical face tangle error of the polygon mirror  19 . The polygon mirror  19  has a mirror formed on each side of a hexagon. While rotating, the polygon mirror  19  reflects the laser light which has passed through the cylindrical lens  25 . Thereby, the mirror  19  deflects and scans the laser light in a main scanning direction. The fθ lens  20  converts the laser light which has been made to scan at an equal angular velocity by the polygon mirror  19  so that the laser light scans at a uniform velocity, while imaging the laser light on a surface of a photosensitive drum  27  to be described later. 
     In addition, the scanner unit  16  includes a correction lens  21 , reflecting mirrors  23  and  24 , as shown in  FIG. 1 , that serve to direct the laser light, which has been directed toward a lower direction by the reflecting mirror  22 , to the photosensitive drum  27 . 
     Each of the members described above is appropriately mounted in a case  101 . 
     The configuration of the light source device  100  will be described more in detail later. 
     The process cartridge  17  is disposed below the scanner unit  16  in the main casing  2 , and can be detached from the main casing  2 . The process cartridge  17  includes a casing  51 , in which the process cartridge  17  has a development cartridge  28 , the photosensitive drum  27 , a scorotron charge unit  29 , and a transfer roller  30 . 
     The development cartridge  28  is detachable from the casing  51 , and is provided with a developing roller  31 , a layer thickness regulating blade  32 , a supply roller  33 , and a toner box  34 . 
     The toner box  34  is filled with toner with a positively charging nature. Rotation of the supply roller  33  supplies the developing roller  31  with toner from the toner box  34 . At this time, the toner is triboelectrically charged to a positive charge between the supply roller  33  and the developing roller  31 . Then, as the developing roller  31  rotates, the toner supplied onto the developing roller  31  moves between the developing roller  31  and the layer thickness regulating blade  32 . This further triboelectrically charges the toner, and reduces thickness of the toner on the surface of the developing roller  31  down to a thin layer of uniform thickness. 
     The photosensitive drum  27  is disposed in confrontation with the developing roller  31 . The photosensitive drum  27  is supported rotatably in the casing  51 . The photosensitive drum  27  includes a drum-shaped member and a surface layer. The drum-shaped member is electrically grounded. The surface layer is formed from a photosensitive layer that is made from polycarbonate and that has a positively charging nature. 
     The scorotoron charge unit  29  is disposed above the photosensitive drum  27  and is spaced away from the photosensitive drum  27  by a predetermined space so as to avoid direct contact with the photosensitive drum  27 . The scorotron charge unit  29  is a positive-charge scorotron type charge unit for generating a corona discharge from a charge wire made from, for example, tungsten. The scorotoron charge unit  29  forms a blanket of positive-polarity charge on the surface of the photosensitive drum  27 . 
     The transfer roller  30  is rotatably supported at a position below and in confrontation with the photosensitive drum  27 . The transfer roller  30  is rotatably supported in the casing  51 . The transfer roller  30  includes a metal roller shaft and a roller portion covering the roller shaft. The roller portion is made from conductive rubber material. In order to perform a transfer operation, the transfer roller  30  is applied with a transfer bias according to a constant current control. 
     As the photosensitive drum  27  rotates, the scorotoron charge unit  29  first forms a blanket of positive charge on the surface of the photosensitive drum  27 , and then the surface of the photosensitive drum  27  is exposed to high speed scan of the laser beam from the scanner unit  16 . The electric potential of the positively charged surface of the photosensitive drum  27  drops at positions exposed to the laser beam. As a result, an electrostatic latent image is formed on the photosensitive drum  27  based on print data. 
     Next, an inverse developing process is performed. That is, as the developing roller  31  rotates, the positively-charged toner borne on the surface of the developing roller  31  is brought into contact with the photosensitive drum  27 . Because a developing bias voltage is applied to the developing roller  31 , the toner on the developing roller  31  is supplied to lower-potential areas of is the electrostatic latent image on the photosensitive drum  27 . As a result, the toner is selectively borne on the photosensitive drum  27  so that the electrostatic latent image is developed into a visible toner image. 
     The visible toner image borne on the surface of the photosensitive drum  27  confronts the transfer roller  30  and is transferred onto a sheet  3  as the sheet  3  passes between the photosensitive drum  27  and the transfer roller  30 . 
     The fixing section  18  includes a heating roller  41 , a pressure roller  42  applying pressure to the heating roller  41 , and transport rollers  43 . In the fixing section  18 , the toner, which has been transferred to the sheet  3  by the process cartridge  17 , is thermally transferred onto the sheet  3  while the sheet  3  passes through between the heating roller  41  and the pressure roller  42 . Thereafter, the sheet  3  is transferred to a sheet discharging path  44  by the transport rollers  43 . The sheet  3  transported to the sheet discharging path  44  is conveyed to discharge rollers  45 . When the discharge rollers  45  rotate forwardly, the discharge rollers  45  discharge the sheet  3  onto a discharge tray  46 . When the discharge rollers  45  rotate in reverse and a flapper  49  is swung from the orientation shown in solid line to the orientation shown in broken line in  FIG. 3 , the sheet  3  is fed back to the inside of the main casing  2  and is fed back to the upstream side of the image forming section  5  by a plurality of inversion transport rollers  50 . At this time, the upper and lower surfaces of the sheet  3  are reversed from the first time that an image has been formed on the sheet  3  so that an image can be formed on the other side as well. In this way, images are formed on both sides of the sheet  3 . 
       FIG. 3  is a perspective view of the light source device  100 .  FIG. 4  is a cross-sectional view of the light source device  100 . 
     As shown in  FIG. 3 , the light source device  100  includes a holder  110 . A semiconductor laser  120  and a coupling lens  130  are fixed on the holder  110 . The semiconductor laser  120  is for emitting light that is modulated according to the print data. 
     The holder  110  is obtained by carrying out a sheet-metal processing on a plate material made of aluminum alloy or aluminum. 
     The holder  110  includes a laser holding wall  111 , a lens holding part  112 , and a connecting part  113 . The semiconductor laser  120  is fixed on the laser holding wall  111 . The lens holding part  112  is of a base shape, and the coupling lens  130  is fixed on the base-shaped lens holding part  112 . The connecting part  113  connects the laser holding wall  111  and the lens holding part  112  with each other. 
     The laser holding wall  111  has a mounting through-hole  111   a  having a circular shape. The mounting through-hole  111   a  is formed on the center of the laser holding wall  111 . The mounting through-hole  111   a  is formed by penetrating the laser holding wall  111  so that the semiconductor laser  120  can fit therein (refer to  FIG. 4 ). An edging  114  projecting toward a front side (direction in which the laser light of the semiconductor laser  120  is emitted) is formed on an edge of the mounting through-hole  111   a . The edging  114  forms a tube part, in which the semiconductor laser  120  fits. In addition, the laser holding wall  111  has two screw through-holes  115  provided thereon. The screw through-holes  115  are used for fixing the semiconductor laser  120  (refer to  FIG. 3 ) on the laser holding wall  111 . 
     The lens holding part  112  is located distant from the laser holding wall  111  for a predetermined distance in a front direction. A groove  112   a  extending in a front-back direction is formed on a top surface of the lens holding part  112 , that is, a surface on which the coupling lens  130  is mounted. Photopolymerizable or light-curing resin  135  that serves as adhesive for fixing the coupling lens  130  on the lens holding part  112  is provided in the groove  112   a . That is, by applying the photopolymerizable resin  135  in the groove  112   a  in a manner that the resin  135  stays in the groove  112   a , the resin is prevented from flowing away from the lens  130  in a direction perpendicular to the front-back direction. The groove  112   a  can also serve as a reference position, on which the photopolymerizable resin  135  is to be applied. 
     The holder  110  is preferably made of metal. For example, the holder  110  is made of aluminum or aluminum alloy. In this manner, a top surface of the lens holding part  112  is capable of reflecting light for curing the photopolymerizable resin  135 . By reflecting light on the surface of the lens holding part  112 , the curing of the photopolymerizable resin  135  can be accelerated. The holder  110  may be made of other material that can reflect off light. 
     The connection part  113  includes a bottom wall part  113   a  and a front wall part  113   b . The bottom wall part  113   a  extends in a front direction from a bottom edge of the laser holding wall  111 . The front wall part  113   b  extends vertically so as to connect a front edge of the bottom wall part  113   a  and a rear edge of the lens holding part  112 . The bottom wall part  113   a  has a screw through-hole  116  formed thereon. The screw through-hole  116  is used for fixing the holder  110  on the case  101  of the scanner unit  16 . 
     The semiconductor laser  120  is a known device including a package  121  as an outer packaging and an aperture  122  formed on the package  121 . A light emitting element (not shown) is provided in the inside of the package  121 . The laser light is emitted from the semiconductor laser  120  through the aperture  122 . As shown in  FIG. 4 , the semiconductor laser  120  is pressed and fixed in the mounting through-hole  111   a . The semiconductor laser  120  has terminals  123 . The terminals  123  pass through through-holes formed in a printed circuit board  125  and are connected to a circuit (not shown). The print circuit board  125  is fixed to the laser holding wall  111  by fastening screws  12 B in the screw through-holes  115 . 
     The coupling lens  130  is for gathering the laser light emitted from the semiconductor laser  120  and converts the laser light to a light flux (bundle of light). The coupling lens  130  is located distant from the semiconductor laser  120  by a distance that is determined dependently on a focal length of the lens  130 . The coupling lens  130  is bonded with and fixed on the lens holding part  112  by the photopolymerizable resin  135 . 
     The photopolymerizable resin  135  is provided between the coupling lens  130  and the holder  110 , or more particularly, between the coupling lens  130  and the lens holding part  112 . A part of the photopolymerizable resin  135  protrudes from between the coupling lens  130  and the lens holding part  112  to the front side of the coupling lens  130 . However, no part of the photopolymerizable resin  130  protrudes from between the coupling lens  130  and the lens holding part  112  to a rear side of the coupling lens  130 . That is, no photopolymerizable resin  130  is provided on the rear side of a rear surface  132  of the coupling lens  130 . 
     In other words, the photopolymerizable resin  135  is provided on the lens holding part  112  so that the photopolymerizable resin  135  has a main part  135   a  that is located between the coupling lens  130  and the lens holding part  112  and a front protruding part  135   b  that protrudes forwardly from the main part  135   a.    
     More specifically, the coupling lens  130  has a pair of optical surfaces  132  and  133  and an outer peripheral surface  131 . The pair of optical surfaces  132  and  133  includes: the rear surface  132  and a front surface  133 . The laser light from the semiconductor laser  120  passes through the pair of optical surfaces  132  and  133 . The outer peripheral surface  131  connects the pair of optical surfaces  132  and  133 . In this example, the outer peripheral surface  131  has: a main part  3131   a  that extends parallel to the optical axis of the coupling lens  130  and an additional part  131   b  that extends from the main part  131   a  toward the rear surface  132  obliquely rearwardly with respect to the optical axis of the coupling lens  130 . The rear surface  132  is flat and is perpendicular to the optical axis of the coupling lens  130 , while the front surface  133  is curved around the optical axis of the coupling lens  130   
     In the photopolymerizable resin  135 , the main part  135   a  is located between the outer peripheral surface  131  of the coupling lens  130  and the lens holding part  112 , while the front protruding part  135   b  protrudes forwardly from the main part  135   a . No part of the photopolymerizable resin  130  protrudes rearwardly from the main part  135   a.    
     As apparent from  FIG. 4 , the coupling lens  130  is fixed at a position away from the lens holding part  112  in the vertical direction (x direction). In this manner, the coupling lens  130  can be fixed on the holder  110  after the position of the lens  130  is adjusted relative to the semiconductor laser  120 . 
     The coupling lens  130  can be made of glass or resin. A material having a thermal expansion coefficient, which is in a range of (½)×C to C, wherein C is the thermal expansion coefficient of a member constituting the holder  110  is preferably selected. By selecting a material having the thermal expansion coefficient close to that of the holder  110  as described above, a change in an optical characteristic of the light source device  100  can be made small even when there is a temperature change. 
     For example, in a case where aluminum having a thermal expansion coefficient αH of 2.30×10 −5 /K is selected as the material of the holder  110  and glass having a thermal expansion coefficient αL of 1.15×10 −5 /K is selected as the material of the coupling lens  130 , a tilt α a of an optical axis due to a temperature rise of 25 degrees Celsius (=ΔT) is calculated as:
 
Δ a=a  tan((α H−αL ) ×R×ΔT/f )=0.47′
 
     wherein R indicates a radius R of the lens  130  (3 mm, for example), and f indicates a focal length of the lens  130  (6.25 mm, for example). 
     It is noted that generally, adjustment accuracy of the lens of the light source device  100  is required to be ±5′ Therefore, by selecting glass with material as described above, influence of a temperature rise can be restricted to be sufficiently small. An example of the glass, whose thermal expansion coefficient is in a range between a half of that of aluminum and that of aluminum, is “Super Vidron” (trade name) that has thermal expansion coefficient αL=11.8×10 −5 /K and that is a molded glass manufactured by Sumita optical glass, Inc. 
     In addition, the outer peripheral surface  131  of the coupling lens  130  is roughened. So, when the coupling lens  130  is made of glass, the outer peripheral surface  131  is in a ground glass form. When the coupling lens  130  is made of resin, the outer peripheral surface  131  is in a ground resin form. Since the outer peripheral surface  131  is roughened, curing light (ultraviolet ray in the present embodiment) entering inside the coupling lens  130  diffuses adequately on the outer peripheral surface  131 . In this manner, the ultraviolet ray falls on the photopolymerizable resin  135  evenly below the coupling lens  130  (between the coupling lens  130  and the holder  110 ). 
     The holder  110  is fixed on the case  101  in a manner that a screw  129  is put into the screw through-hole  116  and screwed in the case  101 . 
     With the above-described structure, the coupling lens  130  is fixed on the holder  110  by irradiating an ultraviolet ray UV from the front side of the coupling lens  130 . Therefore, the light source device  100  can be manufactured at low cost. 
     The photopolymerizable resin  135  is entirely cured at a time. In this manner, the coupling lens  130  can be positioned with high accuracy. 
     In addition, the photopolymerizable resin  135  is cured not only at a position between the outer peripheral surface of the coupling lens  130  and the lens holding part  112  but also at a position between the front side of the coupling lens  130  and the lens holding part  112 . In this manner, even in a case where the coupling lens  130  is relatively thin, the lens  130  can be fixed on the holder  110  firmly. 
     The light source device  100  can be configured at extremely low cost by configuring the holder  110  by carrying out the sheet metal processing on a metal plate. In particular, by adopting aluminum or aluminum alloy as the material of the holder  110 , heat dissipation of the holder  110  becomes higher. Thereby, the holder  110  can be made to have a function also as a cooling plate of the semiconductor laser  120 . 
     Next, a manufacturing method of the light source device  100  will be described. 
     First, the semiconductor laser  120  is pressed and fixed in the laser holding wall  111 . Then, the print circuit board  125  is fixed on the laser holding wall  111  with the screws  128 . 
     Then, the holder  110  is fixed on the case  101  of the scanner unit  16  with the screw  129 . 
     Next, the photopolymerizable resin  135  is applied on the groove  112   a  of the lens holding part  112 . The photopolymerizable resin  135  is applied to spread from a position, directly below a position where the coupling lens  130  is assumed to be located, to a slightly front side thereof. In this manner, when the coupling lens  130  is located on the lens holding part  112 , the photopolymerizable resin  135  is prevented from protruding out from the position between the coupling lens  130  and the lens holding part  112  to the rear side (side closer to the semiconductor laser  120 ) of the coupling lens  130 . In this state, the photopolymerizable resin  135  is located between the coupling lens  130  and the lens holding part  112 , with partly protruding to the front side (exit side of the laser light) of the coupling lens  130 . 
     More specifically, the photopolymerizable resin  135  is applied to spread from a position, directly below a position where the outer peripheral surface  131  of the coupling lens  130  is assumed to be located, to a slightly front side thereof. In this manner, when the coupling lens  130  is located on the lens holding part  112 , the photopolymerizable resin  135  is prevented from protruding out from the position between the outer peripheral surface  131  of the coupling lens  130  and the lens holding part  112  to the rear side of the coupling lens  130 . In this state, the photopolymerizable resin  135  is located between the outer peripheral surface of the coupling lens  130  and the lens holding part  112 , with partly protruding to the front side of the coupling lens  130 . 
     Next, the coupling lens  130  is held by a robot hand (not shown) having multiple spindles. The coupling lens  130  may be held by the robot hand in a manner that the outer peripheral surface  131  of the coupling lens  130  is held or nipped by the robot hand, or the outer peripheral surface  131  or a rim of the front or rear side surface (optical surface)  133 ,  132  of the coupling lens  130  is vacuum-absorbed by the robot hand. Then, the laser light is emitted from the semiconductor laser  120 . While tilt and a focus of the laser light which has passed through the coupling lens  130  are checked by a measuring unit or visual observation, the robot hand is operated to adjust orientation and a position in the x-y direction shown in  FIG. 3  or  FIG. 4  of the coupling lens  130 . Further, in a similar manner, a position in the z direction shown in  FIG. 3  or  FIG. 4  of the coupling lens  130  is adjusted. 
     Then, after the position of the coupling lens  130  is fixed, an ultraviolet ray lamp UVL is provided in the front side of the coupling lens  130 . By irradiating the ultraviolet ray UV on the photopolymerizable resin  135  from the front side, the photopolymerizable resin  135  is cured. The ultraviolet ray UV is irradiated from the front side of the coupling lens  130 . Or, the ultraviolet ray UV may be irradiated obliquely from an upper front side of the coupling lens  130  so that the ultraviolet ray UV strikes on the photopolymerizable resin  135  entirely. 
     By the operation described above, the coupling lens  130  can be fixed on an ideal position with respect to the semiconductor laser  120 . In particular, the photopolymerizable resin  135  is entirely cured by the ultraviolet ray UV that is entirely struck on the photopolymerizable resin  135  even when the ultraviolet ray UV is irradiated from the front side of the coupling lens  130 . This is because the photopolymerizable resin  135  is provided between the coupling lens  135  and the holder  110  and partly protrudes on the front side of the coupling lens  130 . In addition, as described above, the ultraviolet ray UV which has entered inside the coupling lens  130  is diffused on the outer peripheral surface  131 . Then, the ultraviolet ray UV also strikes on the photopolymerizable resin  135  between the coupling lens  130  and the holder  110  evenly. In this manner, an uncured part can be eliminated. Further, the ultraviolet ray UV which has passed through the photopolymerizable resin  135  reflects off the surface of the holder  110 , or more particularly, the lens holding part  112 , and contributes to the curing of the photopolymerizable resin  135  again. Therefore, the photopolymerizable resin  135  can be prevented from being uncured. 
     Thus, the coupling lens  130  is firmly fixed on the holder  110 . In addition, the photopolymerizable resin  135  is cured at a time. So, accuracy of positioning of the coupling lens  130  can be improved. 
     Irradiating the ultraviolet ray from the rear side of the coupling lens  130  is difficult due to existence of the laser holding wall  111 . However, according to the manufacturing method of the present embodiment, the ultraviolet ray does not need to be irradiated from the rear side of the coupling lens  130 , and the light source device  100  can be manufactured easily. By irradiating the ultraviolet ray from the front side of the coupling lens  130 , the ultraviolet ray can be irradiated on the photopolymerizable resin  135  entirely without the coupling lens  130  blocking the light. 
     &lt;Modifications&gt; 
     For example,  FIG. 5  is a perspective view of a light source device  100 ′ according to a modification.  FIG. 6  is a cross-sectional view of the light source device  100 ′. 
     As shown in  FIG. 5 , a light source device  100 ′ has a groove  112   b  formed on the lens holding part  112  of the holder  110  along a direction (y direction in  FIG. 5  or  FIG. 6 ) perpendicular to the front-back direction of the coupling lens  130 . The groove  112   b  has an edge part  112   c  as a rear edge thereof which is positioned at the same position or slightly in front of the rear surface  132  of the coupling lens  130  along the front-back direction (z direction). 
     By providing the transverse groove  112   b  as described above on the lens holding part  112 , the photopolymerizable resin  135  is prevented from protruding out to the rear side of the coupling lens  130  when the photopolymerizable resin  135  is applied on the groove  112   b . For this reason, the photopolymerizable resin  135  can be applied between the coupling lens  130  and the holder  110 , and easily protrudes out only to the front side of the coupling lens  130 . 
     In addition, in the embodiment described above, the robot hand is used to adjust the position and the orientation of the coupling lens  130 . However, the position and the orientation of the coupling lens  130  may be adjusted manually while the coupling lens  130  is held by a goniometer. 
     While the invention has been described in detail with reference to the embodiment and modification thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention. 
     For example, he laser printer  1  in the embodiment described above may be modified to other various types of image forming device, such as a copier and a multi-function machine. 
     The transfer roller  30  in the above embodiment may be modified into a non-contact type transfer roller. 
     In the above embodiment, the paper  3  such as a cardboard, a postcard, and a thin paper, is used as the recording sheet. However, the laser printer  1  may be modified to print on other various types of recording medium, such as an OHP sheet. 
     In the embodiment described above, the toner, the developing cartridge  28 , the polygon mirror  19 , the fθ lens  20 , the scanner unit  16 , and the photosensitive drum  27  are used as a developer, a developing unit, a deflector, a scanning lens, an exposure device, and a photosensitive body, respectively. However, the materials and the structure of the laser printer  1 , such as the developing cartridge  28 , the polygon mirror  19 , the fθ lens  20 , the scanner unit  16 , and the photosensitive drum  27 , can be appropriately modified.