Patent Publication Number: US-2016223727-A1

Title: Optical unit, optical element and method for manufacturing the same

Description:
TECHNICAL FIELD 
     The present invention relates to an optical unit which forms an optical image by an optical element that includes a plurality of reflective surfaces, an optical element and a method for manufacturing the same. 
     BACKGROUND ART 
     When an optical element, which is made by press-molding a metal or glass or by plating, is to be attached to a substrate, it is necessary to provide a positioning reference surface in the optical element for the positioning regarding optical design. 
     An exemplary method for providing such a positioning reference surface in an optical element includes providing a surface that regulates an outer portion of the optical element in a mold with which the optical element is molded, and forming a positioning reference surface in the optical element. Further, a method for machining an outer portion of an optical element after molding and then forming a positioning reference surface is common. 
     PTL 1 discloses a method for forming positioning; holes in flat portions of an optical element as illustrated in  FIG. 6 . 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Patent Laid-Open No. 2004-264656 
     SUMMARY OF INVENTION 
     Technical Problem 
     A method for press-molding an optical element including a plurality of reflective surfaces while bending a molding material into a roof shape, however, has the following problem during formation of a positioning reference surface. 
     In a case in which a reference surface which regulates an outer portion of the optical element is to be provided, it is necessary to provide reference surface which regulates the outer portion of the optical element in a mold with which the optical element is molded, and to transfer the reference surface to a molding material with high accuracy. 
     Therefore, a volume of a cavity to be formed by the mold and a volume of the molding material are coincident with each other, the cavity is filled with the molding material, and the reference surface is transferred to the molding material. 
     However, in a case in which the volume of the molding material is smaller than the volume of the cavity, the filling amount of the molding material in the cavity becomes insufficient and thus it is difficult to transfer the reference surface to the molding material with high accuracy. 
     Further, in a case in which the volume of the molding material is larger than the volume of the cavity, the filling amount of the molding material in the cavity becomes excessive and flowability of the molding material decreases, whereby distortion, wrinkles and burrs that may cause deterioration in accuracy are created in the optical element. For this reason, precise weight control for the molding material is required, which is a cause of an increase in cost. 
     Further, in the method of PTL 1, since it is necessary to machine the positioning holes in the molding material in advance or to machine the positioning holes in the optical element after molding, the number of process steps increases, which becomes a cause of an increase in cost. 
     In view of the above mentioned problems, an object of the present invention is to provide an optical unit that is easy in molding and mold processing and is capable of positioning during attachment to a substrate with high accuracy without affecting optical performance, an optical element and a method for manufacturing the same. 
     An optical unit of the present invention includes: an optical element which includes a plurality of reflecting portions and a connecting portion configured to connect the plurality of reflecting portions; a holding member configured to hold the optical element; and a positioning portion provided in the holding member and configured to guide a light beam that has been reflected by the plurality of reflecting portions to a predetermined position, wherein a positioning reference portion configured to be in contact with the positioning portion is provided in the connecting portion. 
     An optical element of the present invention includes: a plurality of reflecting portions; and a connecting portion configured to connect the plurality of reflecting portions; wherein planar portions are provided on side surfaces of the reflecting portions in a longitudinal direction, and planes disposed at 90 degrees with respect to the planar portions are formed in the connecting portion. 
     A method for manufacturing an optical element of the present invention comprises manufacturing the optical element by bending a single plate-shaped member by press-molding. 
     Advantageous Effects of Invention 
     According to the present invention, an optical unit that is easy in molding and mold processing and is capable of positioning during attachment to a substrate with high accuracy without affecting optical performance, an optical element and a method for manufacturing the same can be implemented. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of an optical element of an embodiment of the present invention seen from the side of reflective surfaces. 
         FIG. 2A  is a perspective view of an optical element of an embodiment of the present invention seen from a back side. 
         FIG. 2B  is an enlarged view of a positioning reference portion. 
         FIG. 2C  is an enlarged view of a positioning reference portion. 
         FIG. 3A  is a diagram illustrating a method for manufacturing an optical element of an embodiment of the present invention, illustrating a process of molding an optical element. 
         FIG. 3B  is a diagram illustrating a method for manufacturing an optical element of an embodiment of the present invention, illustrating a process of molding an optical element. 
         FIG. 3C  is a diagram illustrating a method for manufacturing an optical element of an embodiment of the present invention, illustrating a process of molding an optical element. 
         FIG. 4A  is a perspective view of a mold used in an embodiment of the present invention, illustrating a core mold. 
         FIG. 4B  is a perspective view of a mold used in an embodiment of the present invention, illustrating a cavity mold. 
         FIG. 5A  is a perspective view illustrating a holding member of an optical unit of an embodiment of the present invention. 
         FIG. 5B  is a perspective view illustrating a state in which an optical element is attached to a holding member in an optical unit of an embodiment of the present invention. 
         FIG. 6  is a perspective view of an optical element to which a related art is applied. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an optical element which includes a plurality of reflection members in an embodiment of the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  illustrates a perspective view of an optical element  10  according to an embodiment of the present invention seen from the side of reflective surfaces (which are surfaces on which light is reflected). 
       FIG. 2A  is a perspective view of the optical element  10  according to an embodiment of the present invention seen from a back side (i.e., a reverse side) of the reflective surfaces (which are the surfaces on which light is reflected). 
     The optical element  10  will be described with reference to  FIGS. 1 and 2A  with the side having the reflective surfaces being referred to as a front side and the side opposite to the reflective surfaces being referred to as a back side (i.e., a reverse side). 
     The optical element  10  is formed from a single plate-shaped member which includes a plurality of reflecting portions (in  FIG. 1 , two reflecting portions  10 A and  10 B) and a connecting portion connecting the plurality of reflecting portions. The connecting portion includes a positioning reference portion. 
     First, the reflecting portions will be described. 
     The reflecting portion  10 A includes a reflective surface  12 A and the reflecting portion  10 B includes a reflective surface  12 B. An optically-designed optical curved surface portion  11 A is formed on the reflective surface  12 A and an optically-designed optical curved surface portion  11 B is formed on the reflective surface  12 B so as to fulfill optical functions as optical elements. 
     The reflective surface  12 A is designed to include the optically-designed optical curved surface portion  11 A and a portion smoothly continued from the optical curved surface portion  11 A. The reflective surface  12 B is designed to include the optically-designed optical curved surface portion  11 B and a portion smoothly continued from the optical curved surface portion  11 B. Planar portions  15 L and  15 R may be formed at both end portions of the reflective surface  12 A in a longitudinal direction. Planar portions  16 L and  16 R may be formed at both end portions of the reflective surface  12 B in a longitudinal direction. 
     In the reflecting portion, a surface  21 A and a surface  21 B are formed on the back sides (i.e., the reverse sides) of the reflective surfaces  12 A and  12 B, respectively. 
     The surface  21 A and the surface  21 B are formed in the shape in which a thickness of the optical element  10  is reduced from those of surfaces formed by the reflective surfaces  12 A and  12 B. 
     Planar portions  25 L and  25 R are formed at both end portions of the surface  21 A in the longitudinal direction. Planar portions  26 L and  26 R are formed at both end portions of the surface  21 B in the longitudinal direction. Although an example in which the planar portions are formed at both end portions of the surface  21 A and at both end portions of the surface  21 B in the longitudinal direction is illustrated in the present embodiment, the planar portions  25 L and  25 R may be formed at both end portions of either of the surface  21 A or the surface  21 B. The planar portion  25 L, and the planar portion  25 R are used as the positioning reference portion for positioning a bottom surface (in a height direction) of the optical element  10  (i.e., for regulating parallel eccentricity). Therefore, the planar portion  25 L and the planar portion  25 R are desirably formed on the same plane. 
     A planar portion  17  formed as a plane is provided on the at least one side surface in the longitudinal direction of at least either one of the reflecting portion  10 A or the reflecting portion  10 B. The planar portion  17  is formed to be at 90 degrees with respect to the planar portion  25 L and the planar portion  25 R. Although it is sufficient to provide at least one planar portion in the present embodiment, this configuration is not restrictive: a plurality of planar portions may be provided. 
     The planar portion  17  is used as a positioning reference portion for positioning a side surface (in the longitudinal direction) of the optical element  10  (i.e., for regulating parallel eccentricity). 
     Next, the connecting portion will be described. 
     The connecting portion which connects a plurality of the reflecting portions is formed by a connecting surface  13  which connects the reflective surface  12 A and the reflective surface  12 B, and a connecting surface  23  which connects the surface  21 A and the surface  21 B. The connecting surface is desirably formed by a curved surface R. 
     Next, the positioning reference portion will be described, 
     The positioning reference portion will be described with reference to  FIGS. 2B and 2C . 
     The positioning reference portion is formed in the connecting portion.  FIGS. 2B and 2C  illustrate an example of the positioning reference portion in which a recessed portion  24 L is formed between the planar portion  25 L and the planar portion  26 L and a recessed portion  24 R is formed between the planar portion  25 R and the planar portion  26 R. Therefore, a projection  14 L and a projection  14 R (see  FIG. 1 ) may be formed on corresponding surfaces. 
     Next, the recessed portion  24 L and the recessed portion  24 R which are an example of the positioning reference portion will be described. 
     A planar portion  244  is formed in the recessed portion  24 L. A planar portion  246  is formed in the recessed portion  24 R. 
     The planar portion  244  is designed to be 90 degrees with respect to the planar portion  25 L and the planar portion  17 . The planar portion  246  is designed to be 90 degrees with respect to the planar portion  25 R and the planar portion  17 . 
     Since the planar portion  244  and the planar portion  246  are used as the positioning reference portion for positioning the central portion (in a width direction) of the optical element  10  (i.e., for regulating parallel eccentricity), the planar portion  244  and the planar portion  246  are desirably formed on the same plane. Although an example in which two planar portions, i.e., the planar portion  244  and the planar portion  246  are used for the positioning is described here, any one of the planar portions may be formed and positioning is executed using that plane may also be possible. 
     As described above, the optical element  10  may be positioned with high accuracy by regulating parallel eccentricity in the height direction, the longitudinal direction and the width direction of the optical element  10  by using the planar portion  17 , the planar portion  25 L, the planar portion  25 R, the planar portion  244  and the planar portion  246  as the positioning reference portions. 
     Although an example in which the positioning reference portion for attaching the optical element to the connecting surface on the back side of reflective surfaces is formed has been mainly described above, this is not restrictive: for example, the positioning reference portion may be formed on the connecting surface of the reflective surfaces. The planar portion  25 L and the planar portion  244  are disposed at 90 degrees with respect to each other and the planar portion  25 R and the planar portion  246  are disposed at 90 degrees with respect to each other to provide the positioning reference portions in the present embodiment. However, the planar portion  26 L and the planar portion  245  may be disposed at 90 degrees with respect to each other and the planar portion  26 R and the planar portion  247  disposed at 90 degrees with respect to each other to provide the positioning reference portion. 
     Further, the positioning reference portion may be provided on the front side. In a case in which the positioning reference portion is provided on the front side, a positioning planar portion is provided in the projection  14 L and the projection  14 R in  FIG. 1 . In particular, a planar portion of the projection  14 L may be formed at 90 degrees with respect to the planar portion  15 L and a planar portion of the projection  14 R may be formed at 90 degrees with respect to the planar portion  15 R. 
     Next, the optical unit according to an embodiment of the present invention wil be described with reference to  FIGS. 5A and 5B . 
       FIG. 5A  illustrates a holding member  70  to which the optical element according to an embodiment of the present invention is attached. A positioning portion is formed in the holding member  70 . By bringing the optical element into contact with the positioning portion, it is possible to guide a light beam reflected on optical curved surfaces of a plurality of reflective surfaces formed in the optical element to a predetermined position. The illustrated holding member  70  of the present embodiment is an example in which three cylindrical pins as positioning portions are press-fit in a plate member  71 . 
     These pins  72 ,  73  and  74  which are the positioning portions are used for positioning of the optical element  10 . If the shape of the positioning portions is cylindrical, a contact area between the positioning portions and the plane of the positioning reference portion is small, whereby it is possible to position the optical element  10  at a correct position without considering the form accuracy of the positioning portion very seriously. However, the shape of the positioning; portions is not limited to the same: a polygonal prism shape or other shapes may also be employed. Further, the press-fit of the pins is not restrictive: integral molding or any other forming methods may also be employed. A recessed portion  75  is formed near the center of the plate member  71 . This recessed portion  75  avoids interference between the surface  21 A on the back side of the optical element  10  and a surface  76  of the plate member  71  when the optical element  10  is attached to the holding member  70 . 
     Next, a state in which the optical element  10  in the embodiment of the present invention is attached to the holding member  70  will be described with reference to  FIGS. 2A to 2C and 5B . 
     The planar portion  246  of the optical element  10  is brought into contact with the pin  72 , the planar portion  244  of the optical element  10  is brought into contact with the pin  73 , and the planar portion  17  of the optical element  10  is brought into contact with the pin  74  of the holding member  70 . The optical element  10  is disposed so that the planar portions  25 L and  25 R of the optical element  10  are simultaneously brought into contact with the surface  76  of the plate member  71  of the holding member  70 . 
     Although an example in which the pin  72  and the pin  73  are brought into contact with the planar portions  246  and  244  of the optical element  10  is described in the present embodiment, this configuration is not restrictive and various other forms may be employed. For example, positioning may be executed only by the planar portion  246  and the pin  72 . Although an example in which the planar portion  17  of the optical element  10  is brought into contact with the pin  74  is illustrated, two pins may be brought into contact with the planar portion  17  or, alternatively, two planar portions may be provided each of which may be brought into contact with a pin. 
     Next, the optical element  10  is fixed to the holding member  70 . This fixation may be performed by a well-known technique. For example, the optical element  10  is fixed to the holding member  70  with an epoxy adhesive  77  applied to a boundary portion of the planar portions  25 L and  25 R of the optical element  10  and the surface  76  of the plate material  71 . 
     With such an attaching method, the optical element  10  may be attached to a designed position and thus desired optical performance may be obtained. 
     As described above, the optical unit according to an embodiment of the present invention is capable of positioning the optical element with high accuracy in a configuration in which molding and mold processing is easy without the need of complicated structure in the mold or the need of executing additional processing to the optical element after molding. 
     This optical unit may be suitably used, for example as an optical system of an image reading apparatus, such as a copier. Therefore, the optical unit may be reduced in size and weight and, at the same time, is capable of reading with high accuracy. 
     Next, a method for manufacturing the optical element  10  according to an embodiment of the present invention will be described. 
       FIG. 3A  is a schematic diagram of a mold  700  used to mold the optical element  10  in an embodiment of the present invention. 
     An upper mold core  30  which is a piece for forming the front side of the optical element  10  and a lower mold cavity  40  which is apiece for forming the back side are inserted in a pocket  51  of a drum mold  50 . The drum mold  50  is used to guide the upper mold core  30 . The lower mold cavity  40  is fixed to a bottom plate  52  with an unillustrated bolt. 
     The upper mold core  30  is fixed to a shaft, which is moved up and down, of a molding machine by an unillustrated bolt, clamp or the like. When the shaft is moved up and down, the upper mold core  30  is moved up and down inside the pocket  51  while being guided by the drum mold  50 . 
     Therefore, relative positions of the front side and the back side of the optical element  10  is kept to the accuracy that is equal to or smaller than clearance between the upper mold core  30  and the lower mold cavity  40 , and the drum mold  50 . 
     The drum mold  50  includes, on both sides thereof, windows  53  through which the molding material is introduced into the mold  70 . 
     The windows  53  are provided on both sides of the drum mold  50  so that a temperature distribution becomes symmetrical when the mold  70  is heated during the molding process. 
     Next, configurations of the upper mold core  30  and the lower mold cavity  40  used to mold the optical element  10  in the example of the present invention will be described. 
     The upper mold core  30  will be described with reference to  FIG. 4A . The upper mold core  30  is used to form the front side of the optical element  10 . 
     On the upper mold core  30 , the inverted shape of the reflective surface of the optical element  10  is formed. Especially, an optical surface  31 A and an optical surface  31 B for forming the optical curved surface  11 A and the optical curved surface  11 B of the optical element  10  are processed with high accuracy. 
     Next, the lower mold cavity  40  will be described with reference to  FIG. 4B . 
     The lower mold cavity  40  is used to form the back side of the optical element  10 . A planar portion  41 , a planar portion  42 , a planar portion  43  and a planar portion  44  are used to support the molding material introduced into the mold during the molding process, Other shapes are the inverted shapes of the back side of the optical element  10 . 
     Next, a process of press-molding the optical element according to an embodiment of the present invention will be described with reference to  FIGS. 3A to 3C . 
     The molding material may be a metallic material. Amorphous metallic material, such as Zr-based metallic glass, may be desirably used. 
     Desirably, the mold  700  and the molding machine are disposed in an unillustrated chamber and a space surrounding the mold  700  is substituted with nitrogen. 
     The bottom plate  52  is fixed to the molding machine by an unillustrated bolt or clamp. Next, a molding material  60  formed by a plate member is held by an unillustrated automatic hand and is disposed on the lower mold cavity  40  through the window  53  of the drum mold  50 . 
     Next, it is desirable to heat the drum mold  50  to a glass transition temperature of the molding material  60  by using an unillustrated cartridge heater and an infrared lamp that are built in the drum mold  50 . For example, since the glass transition temperature of Zr-based metallic glass is 450 degrees (celsius), the drum mold  50  is heated to 450 degrees (celsius). 
     The temperature is measured by, for example, the following manner: an unillustrated hole is formed at a bottom surface of the upper mold core  30  to reach near a surface that acts in molding and an unillustrated hole is formed at a bottom surface of the lower mold cavity  40  to reach near a surface that acts in molding, and a thermocouple is inserted in each hole to measure the temperature of the upper mold core  30  and the lower mold cavity  40 . 
     When the temperature of the upper mold core  30  and the lower mold cavity  40  reach the glass transition temperature of the molding material  60 , the upper mold core  30  is made to lower by the molding machine and let the molding material  60  further deform. For example, the pressure to be applied to the upper mold core  30  is set to 20 MPa and pressurizing time is set to 60 seconds, and control is made by the molding machine. 
     When the set pressure and the set pressurizing time are applied, the molding material  60  is molded into a shape in accordance with the upper mold core  30  and the lower mold cavity  40 . 
     Nitrogen gas is injected into the pressurized mold from an unillustrated valve and the mold is cooled to 300 degrees (celsius) in, for example, 100 seconds. Then, the upper mold core  30  is moved up and the molding material  60  is taken out by using an automatic hand to obtain the optical element  10 . Therefore, it is possible to form, for example, an optical element in which a plate-shaped member is bent to form an angled portion having the interior angle smaller than 180 degrees about a connecting surface and includes a reflective surface on the side which has the interior angle. Since a bent portion  61  formed by a recessed portion  32  of the upper mold core  30  and a projection  47  of the lower mold cavity  40  is designed not to regulate extension of the material, neither distortion nor wrinkles is produced in the optical element  10  by forming the bent portion  61 . 
     Further, since the bent portion  61  is deformed first by the recessed portion  32  of the upper mold core  30 , it is easy to concentrate the pressure applied by the upper mold core  30 , whereby the shape of the recessed portion  32  of the upper mold core  30  and the shape of the projection  47  of the lower mold cavity  40  may be reliably transferred with high accuracy. 
     EXAMPLE 
     Next, Example of the present invention will be described. 
     In this Example, an example in which 2-mm thick metal optical element is manufactured by press-molding using the mold illustrated in  FIGS. 3A to 3C  will be described. 
     In this example, Zr-based metallic glass which is an amorphous metallic material is used as a molding material. 
     The glass transition temperature of the material is 450 degrees (celsius). The mold  70  and the molding machine were disposed in an unillustrated chamber and a space surrounding the mold  70  was substituted with nitrogen. 
     The bottom plate  52  was fixed to the molding machine by an unillustrated bolt or clamp. Next, a molding material  60  formed by a plate member was held by an unillustrated automatic hand and was disposed on the lower mold cavity  40  through the window  53  of the drum mold  50 . 
     Next, the drum mold  50  was heated to a glass transition temperature of the molding material  60  by using an unillustrated cartridge heater and an infrared lamp that were built in the drum mold  50 . 
     The temperature is measured by the following manner: an unillustrated hole is formed at a bottom surface of the upper mold core  30  to reach near a surface that acts in molding and an unillustrated hole is formed at a bottom surface of the lower mold cavity  40  to reach near a surface that acts in molding, and a thermocouple is inserted in each hole to measure the temperature of the upper mold core  30  and the lower mold cavity  40 . 
     When the temperature of the upper mold core  30  and the lower mold cavity  40  reached the glass transition temperature of the molding material  60 , the upper mold core  30  was made to lower by the molding machine and let the molding material  60  further deform. The pressure to be applied to the upper mold core  30  was set to 20 MPa and pressurizing time was set to 60 seconds, and control was made by the molding machine. 
     When the set pressure and the set pressurizing time were applied, the molding material  60  was molded into a shape in accordance with the upper mold core  30  and the lower mold cavity  40 . 
     Nitrogen gas was injected into the pressurized mold from an unillustrated valve and the mold was cooled to 300 degrees (celsius) in 100 seconds. Then, the upper mold core  30  was moved up and the molding material  60  was taken out by using an automatic hand to obtain the optical element  10 . Therefore, it is possible to form, for example, an optical element in which a plate-shaped member is bent to form an angled portion having the interior angle smaller than 180 degrees about a connecting surface and includes a reflective surface on the side which has the interior angle. Since a bent portion  61  formed by a recessed portion  32  of the upper mold core  30  and a projection  47  of the lower mold cavity  40  is designed not to regulate extension of the material, neither distortion nor wrinkles is produced in the optical element  10  by forming the bent portion  61 . 
     Further, since the bent portion  61  is deformed first by the recessed portion  32  of the upper mold core  30 , it is easy to concentrate the pressure applied by the upper mold core  30 , whereby the shape of the recessed portion  32  of the upper mold core  30  and the shape of the projection  47  of the lower mold cavity  40  were reliably transferred with high accuracy. 
     The manufactured optical element  10  includes two reflective surfaces  12 A and  12 B as illustrated in  FIG. 1  and the size of the two reflective surfaces was 10 min×30 mm. The size of the optical curved surface portion  11 A included in the reflective surface  12 A was 8 mm×25 mm and the size of the optical curved surface portion  11 B included in the reflective surface  12 B was 5 mm×22 mm. 
     R of the connecting surface  13  which connects the curved surface  12 A and the curved surface  12 B was R0.5. 
     Regarding the back side, the surface  21 A and the surface  211 B illustrated in  FIG. 2A  are formed in the shape in which the thickness of the optical element  10 , 2 mm, is reduced from that of the reflective surface  12 A including the optical curved surface portion  11 A and the reflective surface  12 B including the optical curved surface portion  11 B on the front side. 
     R of the connecting surface  23  between the surface  21 A and the surface  21 B was R2.5. Planar portions  25 L and  25 R are formed at both end portions of the surface  21 A in the longitudinal direction. Planar portions  26 L and  26 R are formed at both end portions of the surface  21 B in the longitudinal direction. 
     An open angle made by the planar portions  25 L and  26 L, and an open angle made by the planar portions  25 R and  26 R were 100 degrees and the size thereof was set to 10 mm×5 mm, respectively. The planar portion  25 L and the planar portion  25 R were formed on the same plane. 
     The planar portion  17  formed on the side surface of the optical element  10  in longitudinal direction was formed to be 90 degrees with respect to the planar portion  25 L and the planar portion  25 R. 
     The recessed portion  24 L was formed between the planar portions  25 L and  26 L and the recessed portion  24 R was formed between the planar portions  25 R and  26 R. 
     The planar portion  244  was formed in the recessed portion  24 L, illustrated in  FIG. 2B  and the planar portion  246  was formed in the recessed portion  24 R illustrated in  FIG. 2C . The planar portion  244  and the planar portion  246  were set to be 90 degrees with respect to the planar portion  25 L, the planar portion  25 R and the planar portion  17 , and the size thereof was 1 mm×3 mm, respectively. 
     The planar portion  244  and the planar portion  246  were formed on the same plane. 
     The planar portion  245  and the planar portion  247  were provided at positions facing the planar portion  244  and the planar portion  246 . 
     The angle between the planar portion  245  and the planar portion  244  was 100 degrees and the angle between the planar portion  247  and the planar portion  246  was 100 degrees. 
     These angles were set to 100 degrees in order to avoid interference between the planar portion  245  or the planar portion  247  with their counterparts when the planar portion  244  and the planar portion  246  are used as the positioning reference portions. 
     A connecting surface  241  which connects the planar portion  244  and the planar portion  245  at R0.5 and a connecting surface  248  which connects the planar portion  246  and the planar portion  247  at R0.5 were formed. 
     Further, a connecting surface  242  which connects the planar portion  244  and the planar portion  25 L at R2.5 and a connecting surface  249  which connects the planar portion  246  and the planar portion  25 R at R2.5 were formed. 
     Further, a connecting surface  243  which connects the planar portion  245  and the planar portion  26 L at R2.5 and a connecting surface  250  which connects the planar portion  247  and the planar portion  26 R at R2.5 were formed. 
     The projection  14 L and the projection  14 R were formed on the front side and were formed in the shape in which the thickness of the optical element  10 , 2 mm, was reduced from those of the recessed portion  24 L and the recessed portion  24 R. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2013-192616, filed Sep. 18, 2013, which is hereby incorporated by reference herein in its entirety.