JP2004098538A - Method for manufacturing optical element made of plastic, mold for molding, and optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical element and to provide a mold for molding and the optical element made of a plastic. <P>SOLUTION: One degassing groove 25 extended from a center to a periphery is formed from a transfer part 23 to an edge 24. The groove 25 is linearly extended so as to cross a divided surface 23a and a step 23b, and is gradually increased in width from a transfer end RP of an outside from a root part RC of a central side of the part 25a provided on the part 23. Thus, a molten resin MR is gradually filled in the groove 25 from the part RC to the end RP. Accordingly, an airway can be assured at the part of the groove 25 until the resin MR is completely filled in the groove part of each step 23b. The groove part of the step 23b can be substantially completely buried with the resin MR. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of manufacturing an optical element such as a plastic diffractive lens having a plurality of concentric diffraction grooves formed therein, a mold used for the method, and a plastic optical element formed by these.
[0002]
[Prior art]
For example, in an optical pickup device or the like of an optical recording / reproducing device that records or reproduces information on an optical disk, a concentric diffraction groove is formed on a convex base surface to form a positive lens having a chromatic aberration correction function. It is known to be used as an optical lens. Such a lens is called a chromatic aberration correction lens, and has an advantage that an image forming system having a chromatic aberration correction function can be easily formed with one lens. In addition, it is known that the adoption of plastic as a material enables the application of plastic molding technology by a replica method represented by injection molding, thereby making it possible to supply inexpensive, large-volume products with stable performance.
[0003]
With respect to the imaging lens as described above, a mold for preventing transfer failure in a diffraction groove has been disclosed (for example, see Patent Document 1). In this mold, a thin groove for venting is formed extending from the center corresponding to the optical axis to the periphery. According to such a concave groove, the gas in the cavity is discharged to the outside during molding, and an imaging lens with no disorder in the shape of the diffraction groove can be manufactured.
[0004]
[Patent Document 1]
JP-A-2001-33611
[0005]
[Problems to be solved by the invention]
However, in the above-described mold, the gas in the cavity may not be sufficiently discharged to the outside. For example, when the molten resin injected into the cavity is filled first from the tip side of the groove, the groove may be closed at the tip side and gas may accumulate in the cavity. Molding failure may occur due to the gas remaining inside.
[0006]
Accordingly, an object of the present invention is to provide a method of manufacturing an optical element which does not cause the above-described problems, a mold used for the method, and an optical element made of plastic.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, a first method for manufacturing a plastic optical element according to the present invention is a method for manufacturing a plastic optical element having a plurality of divided surfaces that switch stepwise at an optical path as optical surfaces. A molding surface having a surface shape corresponding to the optical surface of the optical element, and extending along the molding surface so as to intersect with a plurality of steps forming a boundary between the plurality of divided surfaces, and a center of the optical element. The method includes the steps of preparing a mold having a concave groove whose width changes from the side toward the periphery, forming a cavity using the mold, and injecting a molten resin into the cavity. Here, the optical element is an optical member represented by a lens, and includes a phase shift device.
[0008]
In the above manufacturing method, since the mold used for this has a concave groove whose width changes from the center side to the peripheral side of the optical element, when the molten resin is injected into the cavity, it flows through the concave groove. Since the flow of gas can be controlled, it is possible to provide an optical element in which the shape is less disturbed at the step portion at the boundary between the plurality of divided surfaces.
[0009]
In a specific aspect of the above manufacturing method, the optical element is a lens. In this case, it is possible to manufacture an imaging lens in which the shape is not disturbed at the step portion for diffraction, and it is possible to enhance the performance of the plastic lens of the diffraction type.
[0010]
In another specific aspect of the above manufacturing method, the concave groove extends linearly from the center of the molding surface corresponding to the refractive surface of the lens to the periphery, and the groove width along the molding surface increases toward the periphery. I do. In this case, when the molten resin is injected into the cavity, the peripheral groove is difficult to fill, so the central groove is filled first. Therefore, the gas in the cavity can be reliably discharged to the outside, and the inner surface shape of the cavity can be reliably transferred to manufacture a high-precision lens.
[0011]
In another specific aspect of the above manufacturing method, the concave groove linearly extends from the center of the molding surface corresponding to the refractive surface of the lens to the periphery, and the groove width along the molding surface decreases toward the periphery. I do. In this case, when the molten resin is injected into the cavity, the gas remaining in the cavity at the final stage can be collected at the center, and a highly symmetric lens can be manufactured.
[0012]
A second method for manufacturing a plastic optical element according to the present invention is a method for manufacturing a plastic optical element having a plurality of divided surfaces as optical surfaces that switch the optical path stepwise at a boundary, wherein the optical surface of the optical element is A molding surface having a surface shape corresponding to the first surface and a first surface extending apart from each other along the molding surface so as to communicate between the first and second step portions which form the boundaries of the plurality of divided surfaces adjacent to each other. A first and a second groove forming a boundary between the first and second grooves and the plurality of divided surfaces and forming a boundary between the third step and the second step adjacent to the second step; Preparing a mold having a third concave groove extending along the molding surface so as to communicate at a position separated from both of them; a step of forming a cavity using the mold; Injecting the molten resin.
[0013]
In the above manufacturing method, the mold includes the first and second concave grooves communicating between the first and second step portions, and the third concave grooves communicating between the second and third step portions. Since the third groove is provided separately from both the first and second grooves, even when the first groove is first filled when the molten resin is injected into the cavity, The second and third concave grooves separated from this are not immediately filled, and the gas can be discharged by switching the grooves. That is, since the concave groove does not extend in a straight line, it is possible to provide an optical element whose shape is less disturbed at the step portion at the boundary. In addition, since the groove is configured so as not to extend straight, the influence on the characteristics of the optical element is relatively small.
[0014]
A first molding die according to the present invention includes a molding surface having a surface shape corresponding to an optical surface of a plastic optical element having a plurality of division surfaces for switching an optical path stepwise at a boundary as an optical surface, and a plurality of division surfaces. A concave groove extending along the molding surface so as to intersect with a plurality of steps forming a boundary of the surface, and having a width changing from the center side to the peripheral side of the optical element.
[0015]
Since the first molding die has a concave groove whose width changes from the center side to the peripheral side of the optical element, when the molten resin is injected into the cavity formed from the molding die, the groove is formed through the concave groove. Thus, the flow of the flowing gas can be controlled, and an optical element with less disturbance in shape at the step portion at the boundary can be provided.
[0016]
A second molding die according to the present invention includes a molding surface having a surface shape corresponding to the optical surface of a plastic optical element having a plurality of division surfaces for switching an optical path stepwise at a boundary as an optical surface, and a plurality of division surfaces. First and second concave grooves extending apart from each other along the molding surface so as to communicate between the first and second step portions formed adjacent to each other at the boundary of the surface; A molding surface is formed such that a boundary is formed and a third step portion and a second step portion adjacent to the second step portion are connected at a position separated from both the first and second grooves. And a third groove extending along the third groove.
[0017]
In the second mold, even if the first groove is filled first when the molten resin is injected into the cavity formed from the mold, the second and third grooves separated from the first groove are immediately formed. The gas can be discharged by switching the groove without being filled, and an optical element having good optical characteristics with little disturbance in shape at the step portion at the boundary can be provided.
[0018]
The first plastic optical element according to the present invention intersects with an optical surface including a plurality of divided surfaces that switch the optical path stepwise at a boundary and a plurality of step portions forming a boundary between the plurality of divided surfaces. A ridge that extends along the optical surface and changes in width from the center side to the peripheral side of the optical element.
[0019]
Since the first optical element has a ridge whose width changes from the center side to the peripheral side of the optical element, a molten resin is injected into a cavity having an inner surface shape corresponding to the outer shape of the optical element. When forming the element, it becomes possible to control the flow of the gas flowing through the concave groove on the inner surface of the cavity where the ridge is to be formed, and the shape is less disturbed at the step portion at the boundary between the plurality of divided surfaces. .
[0020]
The second plastic optical element according to the present invention includes an optical surface including a plurality of divided surfaces that switch the optical path stepwise at a boundary, and first and second optical surfaces formed adjacent to the boundaries of the plurality of divided surfaces. First and second ridges extending apart from each other along the optical surface so as to communicate between the step portions, and a third portion adjacent to the second step portion while forming a boundary between the plurality of divided surfaces. And a third ridge extending along the optical surface so as to communicate between the step portion and the second step portion at a position separated from both the first and second ridges.
[0021]
In the second optical element, when a molten resin is injected into a cavity having an inner surface shape corresponding to the outer shape of the optical element to form an optical element, a concave groove on the inner surface of the cavity corresponding to the first ridge is formed. Even if it is filled first, the second and third ridges separated therefrom are not immediately formed, and the gas can be discharged by switching the groove on the inner surface of the cavity corresponding to the second and third ridges. In addition, it is possible to provide an optical element having good optical characteristics with little disturbance in shape at a step portion at a boundary between a plurality of divided surfaces.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
[First Embodiment]
FIGS. 1A and 1B are diagrams showing an example of a mold used when manufacturing the plastic diffraction lens according to the first embodiment. FIG. 1A is a top view of a molding die, FIG. 1B is a perspective view of the molding die, and FIG. 1C is a partially enlarged perspective view of the molding die.
[0023]
The mold member 20 as a molding die includes a columnar projection 21. The end 22 of the projection 21 has a transfer portion 23 having a circular concave shape as a whole at the center thereof, and an annular flat edge 24 around the transfer portion 23.
[0024]
A plurality of ring-shaped divided surfaces 23a are formed concentrically in the transfer unit 23, and a step 23b having a sawtooth cross section is formed at the boundary between a pair of adjacent divided surfaces 23a. Each of the divided surfaces 23a is a spherical surface or an aspherical surface forming a refraction surface, and becomes a transfer surface, that is, a molding surface on which one surface of the diffractive lens is to be formed by cooperating with the step 23b.
[0025]
In addition, a single gas vent groove 25 extending from the center to the periphery from the transfer portion 23 to the edge 24 is formed at the end 22 of the projection 21. The concave groove 25 extends linearly so as to cross the dividing surface 23a and the step 23b. In the portion 25a provided on the transfer portion 23, the groove 25 extends from the root RC on the center side to the outer transfer end RP on the outside. The width is gradually increasing. The concave groove 25 has a constant groove width in a portion 25b provided on the edge 24. The concave groove 25 has a depth approximately equal to or slightly greater than the depth of the step 23b, that is, a height difference in each of the portions 25a and 25b, and completely removes the concentrically arranged steps 23b. It is divided (see FIG. 1 (c)).
[0026]
FIG. 2 is a diagram illustrating a process of manufacturing a diffractive lens using the mold member 20 shown in FIG. First, the mold member 20 of FIG. 1 and a mold member 30 facing the mold member 20 are prepared, and both members 20 and 30 are fixed to a pair of opposed cylindrical holders 41 and 42. As a result, a cavity CA including a biconvex lens-shaped internal space in which the upper and lower surfaces are defined by the members 20 and 30 and the side surfaces are defined by the holders 41 and 42 is formed.
[0027]
Here, the mold member 30 includes a concave transfer portion 33 at the center of the end face, and includes an annular flat edge portion 34 around the transfer portion 33. The former transfer section 33 faces the transfer section 23 of the mold member 20, but has no diffraction groove corresponding to the step 23 b formed in the transfer section 23 and has a smooth surface. The latter edge 34 faces the edge 24 of the mold member 20. Unlike the case of the mold member 20, the transfer portion 33 and the edge portion 34 are not formed with a groove corresponding to the groove 25 shown in FIG.
[0028]
The holders 41, 42 align the two mold members 20, 30 by abutting their end surfaces, and separate them from each other by a predetermined distance. Further, by bringing both holders 41 and 42 into contact with each other, an injection gate 43 for injecting the molten resin is formed at a part between the end faces of the holders 41 and 42. Further, a narrow gap 44 is formed at a position facing the injection gate 43. Accordingly, the molten resin MR is injected from the injection gate 43 and exhausted from the gap 44, so that the cavity CA can be completely filled with the molten resin MR.
[0029]
In the final stage of filling the cavity CA with the molten resin MR, the cavity CA is substantially filled with the molten resin MR introduced from the injection gate 43. That is, the lower surface of the injected molten resin MR is supported in close contact with the transfer portion 33 formed on the lower mold member 30, and the upper surface of the injected molten resin MR is attached to the upper mold member 20. It comes into close contact with each of the concentric divided surfaces 23a. However, gas is still accumulated in the groove portion of the step 23b formed between the divided surfaces 23a, and is not filled with the molten resin MR. Such a gas is air which is originally present in the cavity CA or gas which is gradually generated from the molten resin MR.
[0030]
From this state, when the molten resin MR is further filled into the cavity CA under pressure, the groove of the step 23b is gradually filled with the molten resin MR. At this time, an air vent passage extending from the center to the outside is formed between the concave groove 25 and the upper surface of the molten resin MR, so that the gas accumulated in each step 23b can be sent to the peripheral side through the concave groove 25. Thus, the air can be exhausted to the outside of the cavity CA through the gap 44. Here, since the width of the concave groove 25 gradually increases from the root portion RC to the transfer end portion RP, the concave groove 25 is gradually filled with the molten resin MR from the root portion RC to the transfer end portion RP. . Therefore, until the groove portions of all the steps 23b are almost completely filled with the molten resin MR, an airway can be secured in the concave groove portion 25. That is, the groove portion of the step 23b can be almost completely buried with the molten resin MR, and the shape of the transfer portion 23 including the dividing surface 23a and the step 23b can be completely transferred to the molten resin MR and cooled and hardened. .
[0031]
FIG. 3 is a perspective view illustrating the structure of the diffraction lens 50 manufactured using the manufacturing method shown in FIG. The diffraction lens 50 includes a lens body 51, a peripheral part 52, and a convex part 53.
[0032]
The lens body 51 has a convex lens-like outer shape, and a plurality of orbicular divided surfaces 51b are formed concentrically on an upper surface 51a constituting an optical surface thereof. Each division surface 51b is formed of an aspherical surface or a spherical surface, and a step-like diffraction groove 51c is formed between a pair of adjacent division surfaces 51b. The radius of curvature of each divided surface 51b, the width and radius of the annular zone, and the like are appropriately set according to the purpose of use of the diffraction lens 50. Each of the divided surfaces 51b corresponds to each of the divided surfaces 23a formed on the transfer portion 23 of the mold member 20 shown in FIG. 1, and has an inverted shape. The diffraction grooves 51c correspond to the protrusions of the steps 23b formed in the transfer portion 23, and have a shape inverted from each other.
[0033]
The peripheral portion 52 is a portion for holding the diffractive lens 50 shown in FIG. 2, and has an annular shape formed between the edge 24 of the mold member 20 and the edge 34 of the mold member 30. It is a member. In a part of the peripheral part 52, a convex part 53 corresponding to the injection gate 43 of FIG. 2 remains.
[0034]
A ridge 54 is formed from the center of the upper surface 51 a of the lens body 51 to the peripheral portion 52. The ridge 54 is a portion 54a formed on the lens body 51 and linearly extends across each of the divided surfaces 23a and each of the steps 23b, and extends outward from the central root PC. The width gradually increases toward PP. The ridge 54 has a constant width at a portion 54 b formed on the peripheral portion 52. The portion 54a of the ridge 54 has, from the root PC to the transfer end PP, a height substantially equal to or slightly higher than the protrusion formed on the side along the diffraction groove 51c.
[0035]
Although not shown, the rear surface of the lens body 51 is a convex surface obtained by inverting the transfer portion 33 of the mold member 30.
[0036]
Since the above-described diffractive lens 50 is molded by the above-described method described with reference to FIG. 2 and the like, the upper surface 51a of the lens main body 51 has the transfer portion 23 provided on the mold member 20 of FIG. The surface shape corresponds exactly to the step 23b. That is, the diffractive lens 50 obtained in this manner is an optical element with less disturbance in shape in the diffraction groove 51c which is a boundary between the plurality of divided surfaces 51b. That is, since the division surface 51b and the diffraction groove 51c can be formed as designed, it is possible to provide the diffraction lens 50 which has no spherical aberration and corrects chromatic aberration for two or more different wavelengths.
[0037]
[Second embodiment]
FIG. 4 is a top view of a mold used when manufacturing the plastic diffraction lens according to the second embodiment. A mold member 120, which is a molding die according to the second embodiment, is a modification of the molding die according to the first embodiment, and the same portions are denoted by the same reference numerals, and redundant description will be omitted.
[0038]
In the case of the mold member 120, one ventilation groove 125 extending from the center to the periphery is formed from the transfer portion 23 to the edge 24. The concave groove 125 extends linearly so as to cross the dividing surface 23a and the step 23b, and has a width from the center-side root portion RC to the outer transfer end portion RP in the portion 125a provided on the transfer portion 23. Is gradually decreasing. The concave groove 125 has a constant width in a portion 125b provided on the edge portion 24. The concave groove 125 has a depth substantially equal to or slightly greater than the depth of the step 23b, that is, a height difference in each of the portions 125a and 125b, and completely removes the concentrically arranged steps 23b. We are divided.
[0039]
The mold member 120 of FIG. 4 is also combined with members similar to the mold member 30 and the holders 41 and 42 shown in FIG. 2 to form a cavity for injecting the molten resin. In the final stage of filling the cavity with the molten resin, the upper surface of the injected molten resin substantially adheres to each of the divided surfaces 23 a formed concentrically on the upper mold member 120. However, the gas is still accumulated in the groove portion of the step 23b formed in the mold member 120 and the molten resin is not filled.
[0040]
From this state, when the molten resin is further filled into the cavity formed by the mold member 120 under pressure, the molten resin is gradually filled in the groove portion of the step 23b. At this time, since the width of the portion 125a provided with the concave groove 125 gradually decreases from the root portion RC to the transfer end portion RP, the molten resin is gradually filled from the transfer end portion RP to the root portion RC. Conceivable. In this case, the gas accumulated in each step 23b is gradually sent from the peripheral side to the center through the portion 125a, and accumulates in the center step 23b. That is, the gas remaining in the cavity can be collected at the center, and a highly symmetric diffractive lens (not shown) can be manufactured. Note that the diffraction groove or edge to be formed by the central step 23b does not necessarily need to be sharp, so that the amount of deterioration of the characteristics of the diffraction lens is almost negligible depending on the application.
[0041]
[Third embodiment]
FIG. 5 is a top view of a molding die used when manufacturing the plastic diffraction lens according to the third embodiment. A mold member 220, which is a molding die according to the third embodiment, is a modification of the molding die according to the first embodiment.
[0042]
In the case of this mold member 220 as well, a single gas vent groove 225 extending from the center to the periphery is formed from the transfer portion 23 to the edge 24. The width of the concave groove 225 gradually increases from the center RC to the outer transfer end RP in the portion 225 a provided on the transfer unit 23. However, the rate of increase in width is not constant, and the rate of increase in width gradually increases toward the transfer end RP. In addition, the concave groove 225 has the same depth as in the first embodiment in each of the portions 225a and 225b, and completely separates the concentric steps 23b.
[0043]
Even when the molten resin is filled in the cavity formed by the mold member 220, the groove portion of the step 23b can be almost completely filled with the molten resin as in the case of the first embodiment, and the dividing surface 23a And the shape of the transfer portion 23 composed of the step 23b can be completely transferred to the molten resin. That is, the diffractive lens (not shown) obtained in this way is an optical element with less disturbance in shape in the diffraction groove at the boundary between the plurality of divided surfaces.
[0044]
[Fourth embodiment]
FIG. 6 is a top view of a mold used when manufacturing the plastic diffraction lens according to the fourth embodiment. A mold member 320 that is the mold of the fourth embodiment is also a modification of the mold of the first embodiment.
[0045]
In the case of this mold member 320 as well, a single gas vent groove 325 extending from the center to the periphery is formed from the transfer portion 23 to the edge 24. The width of the concave groove 325 is gradually increased from the center RC to the outer transfer end RP in the portion 325 a provided on the transfer portion 23. However, the increase rate of the width is not constant, and the increase rate of the width gradually decreases toward the transfer end portion RP. In addition, the concave groove 325 has the same depth as in the first embodiment in each of the portions 325a and 325b, and completely separates the steps 23b arranged concentrically.
[0046]
When the molten resin is filled in the cavity formed by the mold member 320, the groove portion of the step 23b can be almost completely filled with the molten resin as in the case of the first embodiment. And the shape of the transfer portion 23 composed of the step 23b can be completely transferred to the molten resin. That is, the diffractive lens (not shown) obtained in this manner is an optical element with less disorder in shape in the diffraction groove forming the boundary between the plurality of divided surfaces.
[0047]
[Fifth Embodiment]
FIG. 7 is a top view of a mold used when manufacturing the plastic diffraction lens according to the fifth embodiment. A mold member 420, which is a molding die according to the fifth embodiment, is a modification of the molding die according to the first embodiment.
[0048]
In the case of the mold member 420, in the transfer section 23, thin concave grooves 425 for venting gas are formed at two or more locations on each of the divided surfaces 23a. Each concave groove 425 is formed so as to cross the ring-shaped divided surface 23a, but does not extend to the adjacent divided surface 23a. In other words, the plurality of steps 23b arranged at predetermined intervals are connected at different positions by the short groove 425 having a line segment shape, and have an Amitada pattern as a whole. In addition, a pair of concave grooves 426 are formed on the outer edge 24 of the transfer unit 23 at appropriate intervals. These concave grooves 426 are connected to the outermost step 23 b and extend to the outer periphery of the edge 24. That is, the concave groove 426 traverses the annular edge 24.
[0049]
Each of the concave grooves 425, 426 has a depth substantially equal to the depth of the step 23b, that is, the height difference, or is slightly deeper than that.
[0050]
The mold member 420 in FIG. 7 is also combined with the mold member 30 and members similar to the holders 41 and 42 shown in FIG. 2 to form a cavity for injecting the molten resin. In the final stage of filling the cavity with the molten resin, the upper surface of the injected molten resin is almost in close contact with each of the divided surfaces 23a formed concentrically on the upper mold member 420. However, gas is still accumulated in the groove portion of the step 23b sandwiched between them, and the molten resin is not filled.
[0051]
In this state, when the molten resin is further filled into the cavity formed by the mold member 420 with pressure, the molten resin is gradually filled in the groove portion of the step 23b. In this case, the gas accumulated in each step 23b can be sent to the peripheral side through the concave grooves 425 and 426, and can be exhausted outside the cavity. Here, a plurality of concave grooves 425 are formed at different positions on each divided surface 23a. Even if one concave groove 425 is filled with molten resin and closed on a specific divided surface 23a, the other concave groove 425 is formed. Can secure the airway. Therefore, the groove portion of each step 23b can be almost completely buried with the molten resin, and the shape of the transfer portion 23 including the dividing surface 23a and the step 23b can be completely transferred to the molten resin. That is, the diffractive lens (not shown) obtained in this manner is an optical element with less disorder in shape in the diffraction groove forming the boundary between the plurality of divided surfaces.
[0052]
[Sixth embodiment]
FIG. 8 is a top view of a molding die used when manufacturing the plastic diffraction lens according to the sixth embodiment. A mold member 520, which is a molding die according to the sixth embodiment, is a modification of the molding die according to the fifth embodiment.
[0053]
In the case of this mold member 520, in the transfer section 23, thin concave grooves 525 for venting gas are formed at two or more locations on each divided surface 23a. Each groove 525 is formed in principle so as to cross a pair of adjacent divided surfaces 23a, but is formed at a different position with respect to a specific divided surface 23a, and the three adjacent divided surfaces 23a are formed. Is not meant to cross. That is, when focusing on a certain annular zone-shaped division surface 23a, the inside groove 525 traverses this division surface 23a and the division surface 23a adjacent inside the division surface 23a. A concave groove 525 on the outer side crosses the adjacent divided surface 23a. Note that each groove 525 has a depth substantially equal to the depth of the step 23b, that is, the height difference, or is slightly deeper than that.
[0054]
Even when the cavity formed by the mold member 520 is filled with the molten resin, paying attention to the specific dividing surface 23a, even if one groove 525 is filled with the molten resin and closed, the other groove 525 is filled. Can secure the airway. Therefore, as in the case of the fifth embodiment, the groove portion of the step 23b can be almost completely filled with the molten resin, and the shape of the transfer portion 23 including the divided surface 23a and the step 23b is completely transferred to the molten resin. be able to. That is, the diffractive lens (not shown) obtained in this manner is an optical element in which the shape of the diffraction groove constituting the boundary between the plurality of divided surfaces is less disturbed.
[0055]
[Seventh embodiment]
FIG. 9 schematically shows a configuration of an optical pickup device including an optical system for an optical pickup including a diffraction lens according to the first to sixth embodiments, that is, a diffraction lens formed using mold members 50 to 520. FIG.
[0056]
This optical pickup device has a semiconductor laser 62 for reproducing information from a first optical disk 61 and a semiconductor laser 66 for reproducing information from a second optical disk 65, that is, laser beams having different wavelengths from each other. Can be injected. The laser beams from the two semiconductor lasers 62 and 66 are applied to the optical disks 61 and 65 by using the objective lens 77 composed of the diffractive lens formed by the method of the first to sixth embodiments, and are reflected from the optical disks 61 and 65. The light is collected using the objective lens 77. The thickness of one substrate of the optical disk is 0.6 ± 0.1 mm, and the thickness of the other substrate is 1.2 ± 0.1 mm, which are different from each other.
[0057]
First, when reproducing the first optical disk 61, a beam is emitted from the first semiconductor laser 62, and the emitted light flux passes through the beam splitter 71, and passes through the polarization beam splitter 72, the collimator 73, and the 波長 wavelength plate 74. The light passes through to become a circularly polarized parallel light beam. This light beam is stopped down by the stop 76 and is focused on the information recording surface 61b via the transparent substrate 61a of the first optical disc 61 by the objective lens 77.
[0058]
The light flux modulated and reflected by the information bit on the information recording surface 61b again passes through the objective lens 77, the stop 76, the quarter-wave plate 74, and the collimator 73, enters the polarization beam splitter 72, and is reflected there. Astigmatism is given by the cylindrical lens 78, the light is incident on the photodetector 79, and a read signal of information recorded on the first optical disk 61 is obtained using the output signal.
[0059]
Further, a change in the light amount due to a change in the shape and position of the spot on the photodetector 79 is detected, and focus detection and track detection are performed. Based on this detection, the two-dimensional actuator 81 moves the objective lens 77 in the optical axis direction so that the light beam from the first semiconductor laser 62 forms an image on the recording surface 61b of the first optical disk 61, and this semiconductor laser The objective lens 77 is moved in a direction perpendicular to the optical axis so that the light beam from 62 is focused on a predetermined track.
[0060]
On the other hand, when reproducing the second optical disk 65, a beam is emitted from the second semiconductor laser 66, and the emitted light beam is reflected by the beam splitter 71, which is a photosynthesis means, and is combined with the light beam from the first semiconductor laser 62. Similarly, the light passes through the polarizing beam splitter 72, the collimator 73, the quarter-wave plate 74, the stop 76, and the objective lens 77, and is condensed on the information recording surface 65b via the transparent substrate 65a of the second optical disc 65.
[0061]
The light flux modulated and reflected by the information bit on the information recording surface 65b is passed through the objective lens 77, the aperture 76, the quarter-wave plate 74, the collimator 73, the polarization beam splitter 72, and the cylindrical lens 78 again to the photodetector 79. The light is incident upward, and a read signal of information recorded on the second optical disk 65 is obtained using the output information.
[0062]
Further, as in the case of the first optical disk 61, a change in the light amount due to a change in the shape and position of the spot on the photodetector 79 is detected, and focus detection and track detection are performed. Then, the objective lens 77 is moved for tracking.
[0063]
In the optical pickup device according to the seventh embodiment, since the objective lens 77 composed of a diffractive lens with less disorder is used, light of different wavelengths from each of the semiconductor lasers 62 and 66 is condensed or imaged with low aberration. be able to.
[0064]
As described above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the above embodiments. For example, the diffraction lens to be formed by the mold members 20 to 520 is not limited to a convex lens, but may be a concave lens or the like.
[0065]
Further, in the first to fourth embodiments, the number of the concave grooves 25 to 325 is not limited to one but may be two or more.
[0066]
In the fifth and sixth embodiments, the width, arrangement, number, and the like of the concave grooves 425, 525 and the like can be appropriately changed according to the specifications of the diffractive lens and the molding conditions (for example, the material of the lens).
[0067]
In the first to sixth embodiments, the case where a diffractive lens is manufactured has been described. However, the present invention is not limited to manufacturing a lens. For example, it can be used for manufacturing a phase shift device.
[0068]
【The invention's effect】
As described above, according to the first aspect, since the mold has the concave groove whose width changes from the center side to the peripheral side of the optical element, when the molten resin is injected into the cavity, the concave is formed. The flow of the gas flowing through the groove can be controlled, and an optical element with less disturbance in shape at the step portion at the boundary between the plurality of divided surfaces can be provided.
[0069]
According to the second invention, even if the first groove is filled first when the molten resin is injected into the cavity formed from the mold, the second and third grooves separated from the first groove are formed. The gas is not immediately filled, the gas can be discharged by switching the groove, and an optical element with less disorder in shape at the step portion at the boundary can be provided.
[Brief description of the drawings]
FIG. 1 is a view showing an example of a method of manufacturing a plastic optical element according to a first embodiment, wherein (a), (b) and (c) are a top view, a perspective view, and a mold member, respectively. It is a partial expansion perspective view.
FIG. 2 is a diagram illustrating a method of manufacturing a diffraction lens using the mold member of FIG.
FIG. 3 is a perspective view of a diffractive lens manufactured using the mold member of FIG.
FIG. 4 is a top view of a mold member used for manufacturing a plastic optical element according to a second embodiment.
FIG. 5 is a top view of a mold member used for manufacturing a plastic optical element according to a third embodiment.
FIG. 6 is a top view of a mold member used for manufacturing a plastic optical element according to a fourth embodiment.
FIG. 7 is a top view of a mold member used for manufacturing a plastic optical element according to a fifth embodiment.
FIG. 8 is a top view of a mold member used for manufacturing a plastic optical element according to a sixth embodiment.
FIG. 9
[Explanation of symbols]
20 Mold members
23 Transfer unit
23a Dividing surface
23b step
25 groove
30 Mold parts
41, 42 holder
43 Injection gate
44 gap
50 Diffraction lens
51 Lens body
51b Dividing surface
51c diffraction groove
54 Ridge
CA cavity
MR molten resin

Claims (10)

A method for manufacturing a plastic optical element having a plurality of divided surfaces as optical surfaces that switch the optical path stepwise at a boundary,
A molding surface having a surface shape corresponding to the optical surface of the optical element, and extending along the molding surface so as to intersect with a plurality of steps forming a boundary between the plurality of divided surfaces, and the optical element Preparing a mold having a concave groove whose width changes from the center side to the peripheral side of the mold,
Forming a cavity using the mold,
Injecting a molten resin into the cavity. The method for manufacturing a plastic optical element according to claim 1, wherein the optical element is a lens. 3. The groove according to claim 2, wherein the groove extends linearly from the center of the molding surface corresponding to the refractive surface of the lens to the periphery, and the groove width along the molding surface increases toward the periphery. A method for producing the plastic optical element described in the above. 3. The groove according to claim 2, wherein the groove extends linearly from the center of the molding surface corresponding to the refractive surface of the lens to the periphery, and the groove width along the molding surface decreases toward the periphery. A method for producing the plastic optical element described in the above. A method for manufacturing a plastic optical element having a plurality of divided surfaces as optical surfaces that switch the optical path stepwise at a boundary,
A molding surface having a surface shape corresponding to the optical surface of the optical element, and along the molding surface so as to communicate between the first and second step portions which form the boundaries of the plurality of divided surfaces adjacent to each other. First and second concave grooves extending apart from each other, a third step portion adjacent to the second step portion and forming a boundary between the plurality of divided surfaces, and a second step portion; Preparing a mold having a third groove extending along the molding surface so as to communicate between the first and second grooves at a position separated from both the first and second grooves;
Forming a cavity using the mold,
Injecting a molten resin into the cavity. The method for manufacturing a plastic optical element according to claim 5, wherein the optical element is a lens. A molded surface having a surface shape corresponding to the optical surface of a plastic optical element having a plurality of divided surfaces as optical surfaces that are switched stepwise at an optical path boundary,
Along with extending along the molding surface so as to intersect with a plurality of steps forming a boundary between the plurality of divided surfaces, a concave groove whose width changes from a center side to a peripheral side of the optical element. Equipped mold. A molded surface having a surface shape corresponding to the optical surface of a plastic optical element having a plurality of divided surfaces as optical surfaces that are switched stepwise at an optical path boundary,
First and second concave grooves extending apart from each other along the molding surface so as to communicate between first and second step portions which form the boundaries of the plurality of divided surfaces adjacent to each other;
A third step portion adjacent to the second step portion and a second step portion forming a boundary between the plurality of divided surfaces are separated from both the first and second grooves. A third groove extending along said molding surface to communicate in position. An optical surface including a plurality of divided surfaces that switch the optical path step by step at a boundary,
While extending along the optical surface so as to intersect with the plurality of steps forming the boundary of the plurality of divided surfaces, a ridge whose width changes from the center side to the peripheral side of the optical element. An optical element made of plastic. An optical surface including a plurality of divided surfaces that switch the optical path step by step at a boundary,
First and second ridges extending apart from each other along the optical surface so as to connect between first and second step portions which form the boundaries of the plurality of divided surfaces adjacent to each other;
A third step portion adjacent to the second step portion and a boundary between the third step portion and the second step portion are separated from both the first and second ridges while forming a boundary of the plurality of divided surfaces. A third ridge extending along said optical surface so as to communicate at a location.

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