Abstract:
Disclosed is an optical element wherein a fine shape is transferred precisely to the outer edge side of a lens while increase in cycle time is prevented. In the optical element, the outermost periphery of the fine shape is covered with a protrusion section provided at a flange part. Accordingly, in injection molding, with the resin introduced into the molding cavity formed in the mold, the molding cavity section corresponding to the resin inflow port side of the protrusion section provided at the flange part is filled first, and thereafter the molding cavity section corresponding to the fine shape adjacent to the protrusion section is filled. Preheating a mold surface section, for transferring the fine shape, of a movable mold with the resin accumulated in the molding cavity corresponding to the protrusion section suppresses the temperature reduction of the mold surface section corresponding to the fine shape.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an optical element which has fine shape in an optical surface, especially an object lens and other optical elements which are included in an optical pickup device. 
       BACKGROUND ART 
       [0002]    There exists a heat cycle system for injection molding as a production method of an optical element, the system is provided with a temperature sensor near a cavity surface and the system controls the molding temperature of an optical element with a cooling device which sends a coolant to the channel near the cavity and a heating device which uses the heater for heating a coolant (refer to patent literature 1). 
         [0003]    Moreover, there exists an optical element made of resin having: an optically functional part provided with fine shape on one side of the optical element fabricated by the movable die; and a flange part around the optically functional part, and the heat contraction prevention part is provided in the flange part, the heat contraction prevention part prevents the heat contraction in a direction perpendicular to a direction of an optical axis (refer to patent literature 2). An internal surface of the flange part, for example, serves as the heat contraction prevention part. 
       PRIOR ART DOCUMENT 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: Japanese Unexamined Patent Application Publication No. H6-328538 
         Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2005-132002 
       
     
       SUMMARY OF HE INVENTION 
     Problems to be Solved by the Invention 
       [0006]    In the case of a heat cycle system described in the patent literature 1, transferability can be improved, but since time is spent on heating and cooling of a metallic mold, there is a problem that cycle time increases, productivity falls and manufacture cost increases. 
         [0007]    Moreover, when fine shape is prepared in an optically functional part like the patent literature 2, resin becomes difficult to enter into the mold surface portion corresponding to fine structure, and transferability may deteriorate. Among the optical surfaces of a lens, especially the fine shape by the side of an outer edge is provided in the outer perimeter of the bush for transfer. Accordingly, temperature falls easily by heat dissipation, the resin viscosity at the time of filling may rise, and it may become remarkable deteriorating. 
         [0008]    Then, this invention aims providing an optical element in which the outer edge side of a lens having the transferred fine shape with high precision, while preventing the increase in the cycle time at the time of manufacture. 
       Means for Solving the Problems 
       [0009]    To achieve the above-mentioned object, an optical element according to the present invention comprising: an optically functional part provided with a fine shape on an optical surface of the optical element; and a flange part provided on a periphery of the optically functional part, wherein the optical element is formed by injection molding of a resin introduced into a cavity of a molding die through a portion corresponding to an outer peripheral edge of the flange part, wherein the flange part includes a heat insulation keep-warm part which projects in an optical surface side, and the heat insulation keep-warm part covers an outermost circumference of the fine shape provided on the optical surface from outside in a direction perpendicular to an optical axis. 
         [0010]    The heat insulation keep-warm part prepared in the flange part covers the outermost circumference of the fine shape prepared in the optical surface from the outside in a direction perpendicular to an optical axis in the above-mentioned optical element. Therefore, the cavity portion corresponding to the resin inlet side among the heat insulation keep-warm part prepared in the flange part is filled up with the resin introduced in the cavity formed in the mold at the time of injection molding at first, and then the cavity portion corresponding to the fine shape which adjoins the heat insulation keep-warm part is filled up with the resin introduced in the cavity. After filling up with the resin, the entire outermost circumference of the fine shape is surrounded by the insulation keep-warm part. 
         [0011]    Thus, the temperature fall of the mold surface portion corresponding to this fine shape is controlled by heating beforehand the mold surface portion for transfer of fine shape in the mold with resin collected on the cavity corresponding to a heat insulation keep-warm part. As a result, since the resin introduced into the mold surface portion corresponding to the fine shape where it got warm by preheating among in the mold enters into the concave portion of the fine transfer structure of a mold surface portion easily, the transferability can be improved and it can offer a highly precise optical element. 
         [0012]    In a specific aspect of the present invention, the heat insulation keep-warm part is provided circularly along the flange part. In this case, the mold surface portion corresponding to the fine shape of the mold is preheated as a whole by the circular heat insulation keep-warm part. 
         [0013]    In another aspect of the present invention, the flange part includes a constricted portion formed in a boundary with the optically functional part, and a ratio of A/B is 0.25 or more and 0.85 or less, where A represents a distance in a direction of the optical axis from a bottom of the constricted portion to a distal end vertex of the fine shape that is covered by the heat insulation keep-warm part and B represents a distance in the direction of the optical axis from the bottom of the constricted portion to a top of the heat insulation keep-warm part. 
         [0014]    In this case, by setting the ration A/B to be 0.85 or less, it is possible to cover the mold surface portion corresponding to the entire top portion of the outermost circumference of the fine shape by the melted resin to form the heat insulation keep-warm part with sufficient margin from outside perpendicular to the optical axis. And by setting the ratio A/B to be 0.25 or more, it is not necessary to bring a fine shape position extremely close to a part for a constricted portion. For this reason, the work of machining fine transfer structure on the mold bush corresponding to the optically functional part becomes easy, or it becomes possible to make it hard to damage the top of the mold bush at the time of machining fine transfer shape structure. 
         [0015]    In still another aspect of the present invention, C and D satisfy a relationship of C&lt;D, where C represents a distance from a distal end vertex of the outermost circumference of the fine shape that is covered by the heat insulation keep-warm part to a first intersection at which a line extending in a radial direction perpendicular to the optical axis intersects with a bore surface of the heat insulation keep-warm part and D represents a distance from the first intersection to a second intersection at which the line extending in a radial direction perpendicular to the optical axis interests with an outer surface of the heat insulation keep-warm part. 
         [0016]    In this case, the fine shape on the optical surface surrounded by the heat insulation warm-keep part is effectively heat insulated from the circumference and concurrently warmed by quantity of heat of the melted resin collected on the portion corresponding to the heat insulation keep-warm part in the cavity of the mold. Thus the transferability is further improved. 
         [0017]    In still another aspect of the present invention, D and E satisfy a relationship of E&lt;D, where D represents a distance from a first intersection at which a line extending in a radial direction perpendicular to an optical axis intersects with a bore surface of the heat insulation keep-warm part from a distal end vertex of the fine shape that is covered by the heat insulation keep warm part to a second intersection at which the line interests with an outer surface of the heat insulation keep-warm part and E represents a thickness in a direction of the optical axis of a constricted portion of the flange part formed in a boundary with the optically functional part. 
         [0018]    In this case, the melted resin which reached the portion of the fine shape of the optical surface surrounded by the heat insulation keep-warm part is effectively heat insulated from the circumference by the quantity of heat of the melted resin collected on the portion corresponding to the heat insulation keep-warm part in the cavity of the mold. Thus the transferability is further improved. 
         [0019]    In still another aspect of the present invention, a ratio E/D is 0.65 or more and 0.85 or less. In this case, because the ratio E/D is 0.85 or less, the melted resin is filled in the cavity of the molding die corresponding to the heat insulation keep-warm part prior to the cavity of the molding die corresponding to the fine shape. And because the ratio E/D is 0.65 or more, after the cavity of the molding die corresponding to the heat insulation keep-warm part is filled up with the melted resin, the cavity of the molding die corresponding to the fine shape is quickly filled while controlling the tendency in which melted resin carries out cooling solidification and which carries out sealing at the constricted portion. 
         [0020]    In still another aspect of the present invention, an angle θ between a bore surface of the heat insulation keep-warm part and an optical axis is 5° or more and 45° or less. By setting the angle θ 5° or more, it is possible to make the resistance at a time of demolding small. And by decreasing the resistance at a time of demolding, inclination of an optical element can be controlled and deformation of the fine shape caused by demolding with inclination can be prevented. And by setting the angle θ 45° or less, it is possible to prevent the distance C from being too long. Thus the optical element can be prevented from having big diameter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a partial sectional side elevation view of a lens of an embodiment. 
           [0022]      FIG. 2  is a partial sectional side elevation view for explaining a mold for forming a lens shown in  FIG. 1 . 
           [0023]      FIG. 3  is a view for explaining the flow channel space for supplying resin and the cavity for molding a lens. 
           [0024]      FIG. 4  is a view for explaining the optical pickup device incorporating the lens of  FIG. 1 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0025]    Hereafter, the objective lens for optical pickup device which is one embodiment of the optical element relating to the present invention is explained. 
         [0026]    The objective lens  10  shown in  FIG. 1  is a product made from a plastic, and is equipped with the circular optically functional part  11  which has an optical function, and the circular flange part  12  prepared in the radial outside from the outer edge of the optically functional part  11 . Since the objective lens  10  has a shape symmetrical about the optical axis OA, it is illustrating only the half and is omitting the remaining illustration. 
         [0027]    This objective lens  10  is an objective lens having NA of 0.75 or more. Specifically, the objective lens  10  shall be a two-wavelength compatible type single objective lens, for example. In this case, the objective lens  10  enables reading or writing of optical information corresponding to the standard of BD (Blu-Ray Disc) of NA 0.85 on the wavelength of 405 nm, and also enables, for example, reading or the writing of optical information corresponding to one standard of the DVD (Digital Versatile Disc) standard of NA 0.65 on the wavelength of 655 nm and CD standard of NA 0.53 on the wavelength of 780 nm. 
         [0028]    The optically functional part  11  of the objective lens  10  has 1st optical surface OS 1  having a large convex curvature on the front side, and has 2nd optical surface OS 2  slightly convex on the back side. Among these, when the objective lens  10  is built in the optical pickup device and it operates, the 1st optical surface OS 1  is arranged at a side near the laser light source for reading or writing. Moreover, when the objective lens  10  is built in the optical pickup device and it operates, the 2nd optical surface OS 2  is arranged so as to oppose BD which is an optical information recording medium. Moreover, the fine shape FS which is diffractive structure is formed in 1st optical surface OS 1 . This fine shape FS is formed of ring-shaped concentric zones and outermost circumference of the fine shape FS extends to a position near the outer edge of the optically functional part  11 . The peak Pa of the projection P of the outermost circumference of the fine shape FS is arranged on a side of the optical recording-medium side with respect to the top surface  12   a  of the flange part  12  in the direction of optic-axis OA, i.e., 2nd optical surface OS 2  side. 
         [0029]    The flange part  12  of the objective lens  10  is equipped with the annular constricted portion  13  provided in the boundary with the optically functional part  11  and the annular projection portion  14  provided in the radial outside of the constricted portion  13 . The constricted portion  13  provided in the inner side is a relatively thin portion, and the projection portion  14  provided in the outside is a relatively thick portion. The projection portion  14  provided in the outside projects from the constricted portion  13  in the laser light source side, i.e., 1st optical surface OS 1 , side, and when it carries out injection molding of the objective lens  10 , it functions as a heat insulation keeping-warm part which suppresses cooling of the transfer surface of the optically functional part  11 . Ring-shaped plane EP is formed on the laser light source side, i.e., 1st optical surface OS 1  side of the constricted portion  13 . 
         [0030]    In addition to the top surface  12   a  that is perpendicular to the optical axis OA, the projection portion  14  has the bore surface  14   a  which opposes the fine shape FS of the optically functional part  11  and the outer surface  14   b  arranged on both sides of the top surface  12   a  at the opposite side of the bore surface  14   a . The bore surface  14   a  is extended with inclination to the optical axis OA, and it has the tapered shape which spreads in the laser light source side. The outer surface  14   b  is extended in parallel to optical axis OA, and has cylindrical configuration. In addition, the optical information recording-medium side, i.e., 2nd optical surface OS 2  side of the flange part  12  whole is the flat field  12   b  which extends at right angles to the optical axis OA. This field  12   b  has a domain which consists of a flat side which carries out mirror reflection of the collimated light, for example, and when aligning the objective lens  10 , it is used. 
         [0031]    The molding die for manufacturing the objective lens  10  shown in  FIG. 1  is hereafter explained with reference to  FIG. 2 . The molding die  40  of illustration is equipped with the movable mold  41  as the 1st mold, and the fixed mold  42  as the 2nd mold. The movable mold  41  is driven by the mold open/close drive apparatus  51  and can move back-and forth in the AB direction and opening-and-closing operation is attained between the fixed metallic molds  42 . By matching the both molds  41  and  42  at parting surfaces PS 1  and PS 2  and clamping the both molds, the cavity for injection molding can be formed as explained in full detail below. 
         [0032]    As shown in  FIG. 3 , the cavity of a molding die CV for fabricating the objective lens  10  and the flow channel space FC for supplying resin to the cavity of a molding die CV are formed by a mold clamp of the movable mold  41  and the fixed mold  42 . Among these, the cavity of a molding die CV corresponds to the form of the objective lens  10  shown in  FIG. 1 . Moreover, the flow channel space FC is the space corresponding to the runner RP of the molded article before separating the objective lens  10 , and the gate portion GS is the space corresponding to the gate GP of this molded article. In addition, in the objective lens  10  shown in  FIG. 1 , the gate portion GS is completely removed by finish machining. 
         [0033]    The cavity of a molding die CV includes the main body cavity CV 1 , and a flange cavity CV 2 . Here, the 1st transfer surface S 1  and the 2nd transfer surface S 2  which define the main body cavity CV 1  are for forming the 1st optical surface OS 1  and the 2nd optical surface OS 2  of the central main optically functional part  11  in the objective lens  10 , respectively, and they correspond to the edge surfaces of the core dies  64   a  and  74   a  mentioned later. In this case, the 1st transfer surface S 1  is deeper than the 2nd transfer surface S 2  and the curvature of 1st transfer surface S 1  is larger than that of the 2nd transfer surface S 2 . Moreover, the mold surface portion S 11  corresponding to the fine shape FS of the objective lens  10  is formed in the 1st transfer surface S 1 . 
         [0034]    Referring back to  FIG. 2 , the movable mold  41  on a movable side is provided with: the template  61  which forms parting surface PS 1 ; the backup plate  62  which supports the template  61  from behind; the attachment plate  63  which supports the backup plate  62  from behind; the core die  64   a  as a mold bush which forms the cavity of a molding die CV (especially the main body cavity CV 1 ) shown in  FIG. 3 ; and the outer circumferential die  64   b  as a peripheral part which forms the cavity of a molding die CV (especially the flange cavity CV 2 ). Furthermore, the movable mold  41  is provided with: the pushing-out pin  65  which projects and pushes out the runner RA of the molded article before separating the objective lens  10 ; the movable rod  67   a  which pushes the core die  64   a  from behind; the movable rod  67   b  which pushes the pushing-out pin  65  from behind; and the back-and forth member  68  which moves the movable rods  67   a  and  67   b  back and forth. 
         [0035]    Here, the core die  64   a  is driven by the advancing movable rod  67   a  and moves forward to the fixed mold  42  side, and moves back automatically with back away of the movable rod  67   a , and returns to the original position. Moreover, the back-and forth member  68  is driven by the back-and-forth drive apparatus—and moves back-and forth in the AB direction with suitable timing and quantity. 
         [0036]    In the movable mold  41 , the template  61 , which is the mold part on the side of mold surface, is provided with: the runner concave portion  61   b  which forms the runner RP shown in  FIG. 1 ; the gate concave portion  61   c  which forms the gate GP; and the penetration holes  61   e  and  61   f  prepared in order to insert the outer circumferential die  64   b  and the pushing-out pins  65  and  66 . 
         [0037]    The fixed mold  42  on the fixing side is provided with: the template  71  for forming the parting surface PS 2 ; fixation forms parting side PS 2 ; the attachment plate  72  for supporting the template  71  from behind; the core die  74   a  as a mold bush which forms the cavity of a molding die CV (especially the main body cavity CV 1 ) shown in  FIG. 3 ; and the outer circumferential die  74   b  as a peripheral part which forms the cavity of a molding die CV (especially the flange cavity CV 2 ). 
         [0038]    In the movable mold  42 , the template  71 , which is the mold part on the side of mold surface, is provided with: the runner concave portion  71   b  which forms the runner RP shown in  FIG. 1 ; the gate concave portion  71   c  which forms the gate GP; and the penetration hole  761   e  prepared in order to insert the outer circumferential die  74   b.    
         [0039]    Hereafter, the conditions about the size of the flange part  12  of the objective lens  10  etc. are explained. First, we think about a relationship between the distance A representing a distance in a direction of the optical axis from the flat surface EP of the bottom of the constricted portion  13  to the peak Pa of the projection P on the outermost of the fine shape FS and the distance B representing a distance in the direction of the optical axis from the flat surface EP of the bottom of the constricted portion  13  to a top surface  12   a  of the projection portion  14  which corresponds to the top portion of the heat insulation keep-warm part. 
         [0040]    In the present embodiment, the ratio A/B is made to be 0.25 or more and 0.85 or less. By setting the ration A/B to be 0.85 or less, it is possible to cover the mold surface portion corresponding to the projection P on the outermost of the fine shape FS among the mold surface S 11  by the melted resin for forming the projection portion  14  with sufficient margin from outside perpendicular to the optical axis. Moreover, by setting the ration A/B to be 0.25 or less, it is not necessary to bring the position of the projection P on the outermost of the fine shape FS extremely close to a part for the constricted portion  13 . 
         [0041]    For this reason, the work which processes the fine transfer structure FT corresponding to the fine shape FS into the mold surface portion S 11  of the core die  64   a  becomes easy, or the tip of the core die  64   a  can be made hard to be damaged at the time of processing of the fine transfer structure FT corresponding to the fine shape FS. 
         [0042]    Nest, we think about a relationship between the distance C representing a distance from the top portion Pa of the projection P on the outermost of the fine shape FS to a first intersection I 1  at which a line extending in a radial direction perpendicular to the optical axis OA intersects with a bore surface  14   a  of the projection portion  14  and the distance D representing a distance from the first intersection I 1  to a second intersection I 2  at which the line extending in a radial direction perpendicular to the optical axis OA interests with the outer surface  14   b  of the projection portion  14 . 
         [0043]    In the present embodiment, these size relationship shall be C&lt;D. With this relationship, on the occasion of injection molding, the melted resin reached the portion of fine shape FS surrounded by the projection portion  14  is effectively insulated from the circumference and concurrently warmed by quantity of heat of the melted resin collected on the recess R 2  of the flange cavity CV 2  which corresponds to the projection portion  14  of the cavity of a molding die CV. Thus the transferability is further improved. 
         [0044]    Next, a relationship between the distance D representing a distance from the first intersection I 1  to the second intersection I 2  and a thickness E representing a thickness in a direction of the optical axis OA of the constricted portion  13  is considered. In addition, this thickness E is equivalent to what obtained by subtracting the distance B which is the amount of protrusion compared with the constricted portion  13  from the total thickness F of the projection portion  14 . 
         [0045]    In the present embodiment, these size relationship shall be E&lt;D. With this relationship, on the occasion of injection molding, the melted resin reached the portion of fine shape FS surrounded by the projection portion  14  is effectively insulated from the circumference and concurrently warmed by quantity of heat of the melted resin collected on the recess R 2  of the flange cavity CV 2  which corresponds to the projection portion  14  of the cavity of a molding die CV. Thus the transferability is further improved. 
         [0046]    In the present embodiment, the ratio E/D is made to be 0.65 or more and 0.85 or less. By setting the ration E/D to be 0.85 or less, on the occasion of injection molding, it is possible to fill the recess R 2  of the flange cavity CV 2  which corresponds to the projection portion  14  with the melted resin ahead of the cavity portion of the molding die corresponding to the fine shape FS among the main body cavity CV 1 , and the transfer surface S 11  is effectively preheated. And by setting the ration E/D to be 0.65 or more, after the recess R 2  of the flange cavity CV 2  corresponding to the projection portion  14  is filled up with the melted resin, the cavity portion of the molding die corresponding to the fine shape FS among the main body cavity CV 1  is quickly filled while controlling the tendency in which melted resin carries out cooling solidification and which carries out sealing at the constricted portion  13 . 
         [0047]    Next, about the angle θ between the bore surface  14   a  of the projection portion  14  and the optical axis OA, the angle θ is set to be 5° or more and 45° or less, in the present embodiment. By setting the angle θ is set to be 5° or more, it is possible to make the resistance at a time of demolding the objective lens  10  small. And by decreasing the resistance at a time of demolding inclination of the objective lens  10  can be controlled and deformation of the fine shape FS caused by demolding with inclination can be prevented. And by setting the angle θ 45° or less, it is possible to prevent the distance C from being too long. Thus the objective lens  10  can be prevented from having big diameter. 
         [0048]    Hereafter, the production method of the objective lens  10  is explained briefly. First, the movable mold  41  and the fixed mold  42  are suitably heated with a non-illustrated tool temperature regulation machine. Thereby, the temperature of the mold portion which forms the cavity of a molding die CV in both the molds  41  and  42  is changed into the temperature state of being suitable for molding. Next, by operating the mold open/close drive apparatus  51 , advancing the movable mold  41  to the fixed mold  42  side to keep the molds in mold closing state, and continuing further closing operation of the mold open/closing drive apparatus  51 , the movable mold  41  and the fixed mold  42  are clamped with necessary pressure. 
         [0049]    Next, non-illustrated injection equipment is operated to execute an injection of melted resin through the gate portion GS with required pressure into the cavity of a mold die CV between the clamped movable mold  41  and the fixed die  42 . Since melted resin in the cavity of a mold die CV is gradually cooled by heat dissipation after introducing melted resin into the cavity of a mold die CV, it waits for melted resin to solidify with this cooling and to complete molding. 
         [0050]    Next, the mold open/close drive apparatus  51  is operated, the movable mold  41  is moved backward, and a mold opening operation in which the movable mold  41  is removed from the fixed mold  42  is performed. As a result, the objective lens  10  which is a molded article is demolded from the fixed mold  42  while being carried by the movable mold  41 . 
         [0051]    Next, the back-and-forth drive apparatus  52  is operated and the objective lens  10  is pushed out by the core die  64   a  and the pushing-out pin  65  through the movable rods  67   a  and  67   b . As a result, the objective lens  10  is pushed by the movable rod  67   a  etc., it is pushed out to the fixed mold  42  side, and the objective lens  10  is demolded from the movable mold  41 . In addition, the objective lens  10  demolded from the both molds  41  and  42  is carried out to the exterior of the molding equipment by clamping the sprue portion extending from the runner RP. Furthermore, the objective lens  10  after taking out is given outside processing of removal of gate GP etc., and prepared to be a product for shipment. 
         [0052]      FIG. 4  is a figure showing roughly the construction of the optical system of the optical pickup device incorporating the objective lens  10  of  FIG. 1 . 
         [0053]    In the optical pickup device of illustration, the laser light from each laser diodes  81 A and  81 B is irradiated to the optical disc DB and DD (or DC) which are optical information recording media using the compatibility type objective lens  10 , and, the reflected light from each optical disc DB and DD (or DC) are led to each optical power detectors  87 A and  87 B through the compatibility type objective lens  10 . 
         [0054]    In addition to the laser diodes  81 A and  81 B and the optical power detectors  87 A and  87 B, the optical system including: the collimator systems  82 A and  82 B; Grating  83 A and  838 ; the polarization beam splitters  84 A and  84 B; the beam expander  84 G; the servo lenses  85 A and  85 B; ¼ wavelength plates  88 A and  88 B; the dichroic prism  84 C; the prism mirror  84 D; and etc. functions as an optical device for performing recording and reproducing of information to each optical disc DB and DD (DC). 
         [0055]    Here, the 1st laser diode  81 A generates the laser light for information reproducing of the 1st optical disc DB (specifically wavelength of 405 nm for BD), this laser light is condensed with the objective lens  10 , and a light spot equivalent to NA 0.85 is formed on the information recording surface MB. The 2nd laser diode  81 B generates the laser light for information reproducing of the 2nd optical disc DD or DC (specifically wavelength of 655 nm for DVD or wavelength of 780 nm for CD), thereafter the laser light is condensed by the objective lens  10 , and a light spot equivalent to NA 0.65 (or NA 0.53) is formed on the information recording surface MD (MC). 
         [0056]    On the other hand, the 1st optical power detector  87 A detects the information recorded on the 1st optical disc DB (specifically BD) as a light signal, and the 2nd optical power detector  87 A detects the information recorded on the 2nd optical disc DD or DC (specifically DVD or CD) as a light signal. 
         [0057]    Hereafter, a detailed structure of the optical pickup device of  FIG. 4  and specific operation are explained. When playing the 1st optical disc DB first, laser light with a wavelength of 405 nm, for example, is emitted from the first laser diode  81 A and the emitted light flux turns into a parallel light flux by the collimator system  82 A which consists of beam shaper or a collimating lens. This light flux passes through the grating  83 A, the polarization beam splitter  84 A, ¼ wavelength plate  88 A, etc. then passes through the dichroic prism  84 C and the prism mirror  84 D. Then the light flux is condensed by the objective lens  10  on the information recording surface MB of the 1st optical disc DB. 
         [0058]    The light flux which was modulated on the information recording surface MB by the information bit and was reflected, passes through the objective lens  10  again and it enters into the polarization beam splitter  84 A through the dichroic prism  84 C etc. The light flux is reflected at the dichroic prism  84 C and astigmatism is given by the servo lens  85 A. The light flux then enters on the 1st optical power detector  87 A, and the reading signal of the information recorded on the 1st optical disc DB is acquired using the output signal. 
         [0059]    Moreover, focus detection and track detection are performed by detecting the change of the light volume of the spot on the 1st optical power detector  87 A caused by the position change and/or shape change of the spot. An actuator  91  moves the objective lens  10  in the direction of an optical axis based on this detection so that the light flux from the 1st laser diode  81 A may form an image on the information recording surface MB of the 1st optical disc DB. And the actuator  91  moves the objective lens  10  in the direction perpendicular to an optic axis so that image formation of the light flux from this 1st laser diode  81 A may be carried out on a predetermined track. 
         [0060]    Next, when playing the 2nd optical disc DD or DC, laser light with a wavelength of 655 nm is emitted from the 2nd laser diode  81 B and the emitted light flux turns into a parallel light flux by the collimator system  82 B. The light flux passes through the grating  83 B, the polarization beam splitter  84 B, and ¼ wavelength plate  88 B and then after passing through the dichroic prism  84 C and the prism mirror  84 D, the light flux is condensed on the information recording surface MD of the 2nd optical disc DD, or MC of the 2nd optical disc DD, by the objective lens  10 . 
         [0061]    The light flux which was modulated on the information recording surface MD or MC by the information bit and was reflected, passes through the objective lens  10  again and it enters into the polarization beam splitter  84 B through the dichroic prism  84 C etc. The light flux is reflected at the dichroic prism  84 C and astigmatism is given by the servo lens  85 B. The light flux then enters on the 1st optical power detector  87 A, and the reading signal of the information recorded on the 2nd optical disc DD or DC is acquired using the output signal. 
         [0062]    In addition, like the case of the 1st optical disc D 13 , focus detection and track detection are performed by detecting the change of the light volume of the spot on the 2nd optical power detector  87 B caused by the position change and/or shape change of the spot and the objective lens  10  is moved for the focusing and the tracking. 
         [0063]    In addition, although the above was explanation in the case of reproducing information from the optical disc DB and DD (or DC), it is also possible to record information on the optical disc DB and DD (or DC) by adjusting the output of the semiconductor lasers  81 A and  81 B etc. 
         [0064]    Moreover, if the 2nd laser diode  81 B is a two-wave type laser diode and the objective lens  10  is a three-wave compatible type, the optical pickup device can also be used as a three-wave compatible type optical pickup device. 
         [0065]    Apparent from the above explanation, in the objective lens  10  of the present embodiment, the projection portion  14  provided in the flange part  12  covers the outermost circumference of the line shape FS from the outside in a direction perpendicular to an optical axis OA. Therefore, the cavity portion corresponding to the resin inlet side among the projection portion  14  prepared in the flange part is filled up with the resin introduced in the cavity CV formed in the mold at the time of injection molding at first, and then the cavity portion corresponding to the fine shape FS which adjoins the projection portion  14  is filled up with the resin introduced in the cavity. After filling up with the resin, the entire outermost circumference of the fine shape FS is surrounded by the projection portion  14 . 
         [0066]    Thus, the temperature fall of the mold surface portion S 11  corresponding to this fine shape FS is controlled by heating beforehand the mold surface portion for transfer of fine shape FS in the mold with resin collected on the cavity corresponding to the projection portion  14 . As a result, since the resin introduced into the mold surface portion corresponding to the fine shape (specifically, the recess R 2 ) where it got warm by preheating among in the mold enters into the concave portion of the fine transfer structure of a mold surface portion which corresponds to the fine shape FS easily, the transferability can be improved and it can offer a highly precise optical element. 
         [0067]    Although the present invention was explained based on the embodiment, present invention is not limited to the above-mentioned embodiment, and various modification is possible for it. For example, the shape of the cavity of a molding die CV established in the injection-molding die which is constituted of a fixed mold  42  and a movable mold  41  can be made not only into the shape of illustration but into various shape if the whole outermost circumference of the fine shape FS is surrounded by the projection portion  14 . That is, the shape of the cavity of a molding die CV formed by the core dies  64   a  and  74   a  etc. is mere illustration, and can be suitably changed according to the use of objective lens  10  and other optical elements etc. In addition, the use of the objective lens  10  can also be made BD exclusive use not only in compatibility, for example. Moreover, the use of the objective lens  10  can also be used not only as optical pickup device but as the lens for an image pick-up etc. 
         [0068]    Moreover, the shape of the projection portion  14  prepared in the flange part  12  of the objective lens  10  does not need to be symmetrical with the surroundings of optical axis OA, for example, thickness F of the projection portion  14  may change partially. 
         [0069]    Fine shape FS formed in the optically functional part  11  of the objective lens  10  can also be made into various diffractive structures not only according to the shape of illustration but a shape accorded with use etc. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               10  Objective lens 
               11  Optically functional part 
               12  Flange part 
               12   a  Top surface 
               13  Constricted portion 
               14  Projection portion 
               14   a  Bore surface 
               14   b  Outer surface 
               40  Molding die 
               41  Movable mold 
               42  Fixed mold 
               51  Mold open/close drive apparatus 
               52  Back-and-forth drive apparatus 
               61 ,  71  Template 
               63 ,  72  Attachment plate 
               64   a ,  74   a  Core die 
               68  Back-and forth member 
               81 A,  81 B Laser diode 
               84 A,  84 B Polarization beam splitter 
               84 C Dichroic prism 
               87 A,  87 B light detector 
               91  Actuator 
             CV Cavity of a molding die 
             CV 1  Main body cavity 
             CV 2  Flange cavity 
             FC Flow channel space 
             FS Fine shape 
             GP Gate 
             I 1  First intersection 
             I 2  Second intersection 
             OA Optical axis 
             OS 1 , OS 2  Optical surface 
             P Projection 
             Pa Peak 
             PS 1 , PS 2  Parting surface 
             S 1 , S 2  Transfer surface 
             S 11  Mold surface portion