JP3962914B2 - Method for manufacturing plastic optical element, mold, and optical element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an optical element such as a plastic diffractive lens in which a plurality of concentric diffraction grooves are formed, a molding die used therefor, and a plastic optical element formed by these.
[0002]
[Prior art]
For example, in an optical pickup device of an optical recording / reproducing apparatus that records or reproduces information on an optical disk, a positive lens having a chromatic aberration correction function is formed by forming concentric diffraction grooves on a convex base surface. It is known to be used as an industrial lens. Such a lens is called a chromatic aberration correction lens, and has an advantage that a single lens can easily form an imaging system having a chromatic aberration correction function. In addition, it is known that by adopting plastic as a material, it is possible to apply a plastic molding technique by a replica method represented by injection molding, and to supply a product with stable performance in a large amount at a low price.
[0003]
For the imaging lens as described above, a mold for preventing transfer failure in the diffraction groove is disclosed (for example, see Patent Document 1). The molding die is formed with a thin groove for venting gas extending from the center corresponding to the optical axis to the periphery. With such a concave groove, the gas in the cavity can be discharged to the outside during molding, and an imaging lens that does not disturb the shape of the diffraction groove can be manufactured.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-33611
[0005]
[Problems to be solved by the invention]
However, in the above 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 leading end side of the concave groove, the concave groove is blocked at the leading end side, and gas may accumulate in the cavity. Molding defects may occur due to the gas remaining inside.
[0006]
Therefore, an object of the present invention is to provide a method for manufacturing an optical element that does not cause the above 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 problems, a first plastic optical element manufacturing method according to the present invention is a plastic optical element manufacturing method having, as optical surfaces, a plurality of divided surfaces that switch the optical path in stages. And extending along the molding surface so as to intersect the molding surface having a surface shape corresponding to the optical surface of the optical element and the plurality of step portions forming the boundaries of the plurality of division surfaces, and the center of the optical element A step of preparing a molding die including a concave groove whose width changes from the side toward the peripheral side, a step of forming a cavity using the molding die, and a step of injecting molten resin into the cavity. Here, the optical element is an optical member typified 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. The flow of gas can be controlled, and an optical element with less disorder in shape can be provided at the step portion of the boundary between the plurality of divided surfaces.
[0009]
In a specific aspect of the manufacturing method, the optical element is a lens. In this case, it is possible to manufacture an imaging lens that does not disturb the shape at the step portion for diffraction, and the performance of the diffractive plastic lens can be improved.
[0010]
In another specific aspect of the above manufacturing method, the groove extends linearly from the center to the periphery of the molding surface corresponding to the refractive surface of the lens, and the groove width along the molding surface increases toward the periphery. To do. In this case, when the molten resin is injected into the cavity, the peripheral groove is less likely to be filled, so the central groove is filled first. Therefore, the gas in the cavity can be reliably discharged to the outside, and the highly accurate lens can be manufactured by reliably transferring the shape of the inner surface of the cavity.
[0011]
In another specific aspect of the above manufacturing method, the concave groove extends linearly from the center to the periphery of the molding surface corresponding to the refractive surface of the lens, and the groove width along the molding surface decreases toward the periphery. To 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 in the center, and a lens with high objectivity 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 that switch the optical path stepwise at the boundary as an optical surface, and the optical surface of the optical element. And a mold surface extending apart from each other along the molding surface so as to communicate between the molding surface having a surface shape corresponding to the first and second stepped portions forming the boundaries of the plurality of dividing surfaces adjacent to each other. 1st and 2nd ditch | groove and the 1st and 2nd ditch | groove between the 3rd level | step-difference part adjacent to a 2nd level | step-difference part and a 2nd level | step-difference part while forming the boundary of a some division surface Preparing a mold having a third concave groove extending along the molding surface so as to communicate at a position spaced from both of the mold, forming a cavity using the mold, and in the cavity And injecting a molten resin.
[0013]
In the manufacturing method, the molding die includes the first and second concave grooves that communicate between the first and second step portions, and the third concave groove that communicates between the second and third step portions. Since the third groove is arranged away from both the first and second grooves, even when the first groove is filled first when the molten resin is injected into the cavity, The second and third concave grooves spaced apart 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 straight, it is possible to provide an optical element that is less disturbed in shape at the step portion of the boundary. Further, since the concave groove does not extend straight, the influence on the characteristics of the optical element is relatively small.
[0014]
A first mold 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 dividing surfaces that switch the optical path stepwise at the boundary as an optical surface, and a plurality of dividing surfaces. And a concave groove extending along the molding surface so as to intersect with a plurality of stepped portions forming the 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, Thus, it is possible to control the flow of the flowing gas, and it is possible to provide an optical element that is less disturbed in shape at the step portion of the boundary.
[0016]
A second mold 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 that switch the optical path stepwise at the boundary as an optical surface, and a plurality of divisions. A first groove and a second groove extending apart from each other along the molding surface so as to communicate between the first and second step portions that form the boundary of the surface adjacent to each other; and A molding surface is formed so as to form a boundary and communicate between the third step portion adjacent to the second step portion and the second step portion at a position separated from both the first and second concave grooves. And a third concave groove extending along.
[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 mold are immediately formed. It is possible to provide an optical element having good optical characteristics in which the groove is switched and the gas can be discharged without being filled, and the shape is less disturbed in the step portion of the boundary.
[0018]
The first plastic optical element according to the present invention intersects an optical surface including a plurality of division surfaces that switch the optical path stepwise at a boundary and a plurality of step portions forming the boundaries of the plurality of division surfaces. And a ridge extending along the optical surface and having a width that changes from the center side toward 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 an element, it becomes possible to control the flow of gas flowing through the concave groove on the inner surface of the cavity where the ridge should be formed, and the shape is less disturbed at the stepped portion of 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 boundaries that form adjacent boundaries between the plurality of divided surfaces. First and second ridges extending apart from each other along the optical surface so as to communicate between the stepped portions, and a third adjacent to the second stepped 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 stepped portion and the second stepped portion at a position spaced from both the first and second ridges.
[0021]
In the second optical element, when an optical element is formed by injecting molten resin into a cavity having an inner surface shape corresponding to the outer shape of the optical element, a 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 spaced apart from it are not immediately formed, and the gas can be discharged by switching the grooves 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 less disturbance in shape at the step portion of the boundary between the plurality of divided surfaces.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
FIGS. 1A and 1B are views showing an example of a molding die used when manufacturing the plastic diffractive lens according to the first embodiment. 1A is a top view of the mold, FIG. 1B is a perspective view of the mold, and FIG. 1C is a partially enlarged perspective view of the mold.
[0023]
A mold member 20 that is a molding die includes a columnar protrusion 21. The end portion 22 of the projection 21 is provided with a circular and generally concave transfer portion 23 at the center thereof, and an annular flat edge portion 24 around the periphery thereof.
[0024]
A plurality of ring-shaped split surfaces 23a are formed concentrically on the transfer portion 23, and a step 23b having a sawtooth cross section is formed at the boundary between a pair of adjacent split surfaces 23a. Each dividing surface 23a is a spherical surface or an aspherical surface forming a refractive surface, and becomes a transfer surface, that is, a molding surface on which one surface of the diffractive lens is to be formed in cooperation with the step 23b.
[0025]
Further, at the end portion 22 of the protrusion 21, a single degassing groove 25 extending from the center to the periphery from the transfer portion 23 to the edge portion 24 is formed. The concave groove 25 extends linearly so as to cross the dividing surface 23a and the step 23b, and in the portion 25a provided on the transfer portion 23, the groove extends from the central root portion RC to the outer transfer end portion RP. The width is gradually increasing. The concave groove 25 has a constant groove width in a portion 25 b provided on the edge 24. The concave groove 25 has a depth substantially equal to or slightly deeper than the depth of the step 23b, that is, the height difference in each of the portions 25a and 25b, so that each step 23b arranged concentrically is completely 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 the mold member 30 facing the mold member 20 are prepared, and both the members 20 and 30 are fixed to a pair of opposed cylindrical holders 41 and 42. Thus, the upper surface and the lower surface are defined by both the members 20 and 30, and the cavity CA including the biconvex lens-like internal space whose 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 its end surface, and an annular flat edge portion 34 around the concave transfer portion 33. The former transfer portion 33 faces the transfer portion 23 of the mold member 20, but has no diffraction groove corresponding to the step 23 b formed in the transfer portion 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 and 42 align both the mold members 20 and 30 by abutting the end surfaces of the both, and separate them from each other by a predetermined distance. In addition, by bringing the holders 41 and 42 together, an injection gate 43 for injecting molten resin is formed in a part between the end surfaces of the holders 41 and 42. Further, a narrow gap 44 is formed at a position facing the injection gate 43. Thus, 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 supported on the upper mold member 20. It is in close contact with each of the split surfaces 23a formed concentrically. However, the 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 that has originally been in the cavity CA or gas that is gradually generated from the molten resin MR.
[0030]
When the molten resin MR is further pressurized and filled into the cavity CA from this state, the molten resin MR is gradually filled into the groove portion of the step 23b. At this time, a passage for venting air 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. And can be exhausted out of the cavity CA through the gap 44. Here, since the width of the concave groove 25 is gradually increased 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, an airway can be secured in the concave groove 25 until the groove portions of all the steps 23b are almost completely filled with the molten resin MR. That is, the groove portion of the step 23b can be almost completely filled with the molten resin MR, and the shape of the transfer portion 23 composed of the dividing surface 23a and the step 23b can be completely transferred to the molten resin MR and cooled and cured. .
[0031]
FIG. 3 is a perspective view illustrating the structure of a diffractive lens 50 manufactured using the manufacturing method shown in FIG. The diffractive lens 50 includes a lens body 51, a peripheral part 52, and a convex part 53.
[0032]
The lens main body 51 has a convex lens-like outer shape, and a plurality of ring-shaped split surfaces 51b are concentrically formed on an upper surface 51a constituting the optical surface thereof. Each divided surface 51b is formed of an aspherical surface or a spherical surface, and a step-shaped diffraction groove 51c is formed between a pair of adjacent divided 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 diffractive lens 50. Each divided surface 51b corresponds to each divided surface 23a formed on the transfer portion 23 of the mold member 20 shown in FIG. The diffraction groove 51c corresponds to the protrusion of each step 23b formed in the transfer portion 23 and has a shape that is inverted.
[0033]
The peripheral portion 52 is a portion for holding the diffractive lens 50 shown in FIG. 2, and is an annular shape formed by being sandwiched between the edge portion 24 of the mold member 20 and the edge portion 34 of the mold member 30. It is a member. A convex portion 53 corresponding to the injection gate 43 in FIG. 2 remains in a part of the peripheral portion 52.
[0034]
A convex strip 54 is formed from the center of the upper surface 51 a of the lens body 51 to the peripheral portion 52. The protrusion 54 is a portion 54a formed on the lens body 51 and extends linearly so as to cross each dividing surface 23a and each step 23b, and from the central base portion PC to the outer transfer end portion. The width gradually increases toward PP. Further, the ridge 54 has a certain width at a portion 54 b formed on the peripheral portion 52. The portion 54a of the ridge 54 has a height substantially equal to or slightly higher than the protrusion formed on the side of the diffraction groove 51c from the root portion PC to the transfer end PP.
[0035]
Although the back surface of the lens body 51 is not shown, it is a convex surface obtained by inverting the transfer portion 33 of the mold member 30.
[0036]
The above diffractive lens 50 is molded by the above-described method described with reference to FIG. The surface shape accurately corresponds to the step 23b. That is, the diffractive lens 50 obtained in this way is an optical element with little disturbance in shape in the diffractive groove 51c that is a boundary between the plurality of divided surfaces 51b. That is, since the dividing surface 51b and the diffraction groove 51c can be formed as designed, for example, it is possible to provide a diffraction lens 50 that 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 molding die used when manufacturing the plastic diffractive lens according to the second embodiment. A mold member 120 which is a mold according to the second embodiment is a modification of the mold according to the first embodiment, and the same portions are denoted by the same reference numerals and redundant description is omitted.
[0038]
In the case of this mold member 120, one ventilation groove 125 extending from the center to the periphery is formed from the transfer portion 23 to the edge portion 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 root portion RC on the center side to the outer transfer end portion RP in the portion 125a provided on the transfer portion 23. Is gradually decreasing. Further, the concave groove 125 has a certain width at a portion 125 b provided on the edge 24. The concave groove 125 has a depth substantially equal to or slightly deeper than the depth of the step 23b, that is, the height difference in each of the portions 125a and 125b, so that each step 23b arranged concentrically is completely It is divided.
[0039]
4 is 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 molten resin. In the final stage of filling the cavity with the molten resin, the upper surface of the injected molten resin is in close contact with the divided surfaces 23 a formed concentrically on the upper mold member 120. However, 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 pressurized and filled into the cavity formed by the mold member 120, the molten resin is gradually filled into 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 side via the portion 125a, and is accumulated in the most central step 23b. That is, the gas remaining in the cavity can be collected in the center, and a highly diffractive lens (not shown) can be manufactured. Note that the diffraction groove or edge to be formed by the most central step 23b does not necessarily have to be sharp, and 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 diffractive lens according to the third embodiment. A mold member 220 which is a mold according to the third embodiment is a modification of the mold according to the first embodiment.
[0042]
In the case of this mold member 220 as well, one concave groove 225 for gas venting extending from the center to the periphery from the transfer portion 23 to the edge portion 24 is formed. The width of the concave groove 225 gradually increases from the central base portion RC to the outer transfer end portion RP in the portion 225 a provided on the transfer portion 23. However, the width increase rate is not constant, and the width increase rate gradually increases toward the transfer end RP. The concave groove 225 has the same depth as in the case of the first embodiment in each portion 225a, 225b, and completely separates each step 23b arranged concentrically.
[0043]
Also 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 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 little disturbance in shape in the diffractive groove at the boundary between the plurality of divided surfaces.
[0044]
[Fourth Embodiment]
FIG. 6 is a top view of a mold used in manufacturing the plastic diffractive lens according to the fourth embodiment. A mold member 320 which is a mold according to the fourth embodiment is also a modification of the mold according to the first embodiment.
[0045]
Also in the case of this mold member 320, one degassing concave groove 325 extending from the center to the periphery is formed from the transfer portion 23 to the edge portion 24. The width of the concave groove 325 gradually increases from the central base portion RC to the outer transfer end portion RP in a 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 the case of 1st Embodiment in each part 325a, 325b, and has completely divided | segmented each level | step difference 23b arrange | positioned concentrically.
[0046]
Also 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 dividing surface 23a The shape of the transfer portion 23 composed of the step 23b can be completely transferred to the molten resin. In other words, the diffractive lens (not shown) obtained in this way is an optical element with little disturbance in shape in the diffractive grooves constituting the boundaries between the plurality of divided surfaces.
[0047]
[Fifth Embodiment]
FIG. 7 is a top view of a molding die used when manufacturing the plastic diffractive lens according to the fifth embodiment. A mold member 420 which is a mold according to the fifth embodiment is a modification of the mold according to the first embodiment.
[0048]
In the case of this mold member 420, in the transfer portion 23, thin concave grooves 425 for degassing are formed at two or more locations on each dividing surface 23 a. Each concave groove 425 is formed so as to cross the ring-shaped split surface 23a, but does not extend to the adjacent split surface 23a. That is, the plurality of steps 23b arranged at a predetermined interval are connected at different positions by the short concave grooves 425 having a line segment shape, and have an Amida pattern as a whole. Note that a pair of concave grooves 426 are also formed on the outer edge 24 of the transfer portion 23 so as to be appropriately separated. 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 recessed groove 426 crosses the annular edge 24.
[0049]
Each of the concave grooves 425 and 426 has a depth substantially equal to the depth of the step 23b, that is, a height difference, or is slightly deeper than that.
[0050]
The mold member 420 of FIG. 7 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 molten resin. In the final stage of filling the cavity with the molten resin, the upper surface of the injected molten resin is in close contact with the divided surfaces 23 a 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]
From this state, when the molten resin is further pressurized and filled into the cavity formed by the mold member 420, the molten resin is gradually filled into 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 out of the cavity. Here, a plurality of concave grooves 425 are formed at different positions on each dividing surface 23a, and even if one concave groove 425 is filled with a molten resin and closed on a specific dividing surface 23a, the other concave groove 425 is formed. The airway can be secured. Therefore, the groove part of each level | step difference 23b can be almost completely embedded with molten resin, and the shape of the transfer part 23 which consists of the division surface 23a and the level | step difference 23b can be completely transferred to molten resin. In other words, the diffractive lens (not shown) obtained in this way is an optical element with little disturbance in shape in the diffractive grooves constituting the boundaries between the plurality of divided surfaces.
[0052]
[Sixth Embodiment]
FIG. 8 is a top view of a molding die used when manufacturing the plastic diffractive lens according to the sixth embodiment. A mold member 520, which is a mold according to the sixth embodiment, is a modification of the mold according to the fifth embodiment.
[0053]
In the case of this mold member 520, in the transfer portion 23, thin concave grooves 525 for degassing are formed at two or more locations on each divided surface 23a. Each concave groove 525 is formed so as to cross a pair of adjacent dividing surfaces 23a in principle, but is formed at a different position with respect to a specific dividing surface 23a, and three adjacent dividing surfaces 23a. Is not supposed to cross. That is, when paying attention to a certain ring-shaped dividing surface 23a, the inner groove groove 525 traverses this dividing surface 23a and the dividing surface 23a adjacent to the inside, so that the dividing surface 23a to be noticed and the outside thereof. A groove 525 located on the outer side crosses the adjacent dividing surface 23a. Each concave groove 525 has a depth substantially equal to the depth of the step 23b, that is, the height difference, or slightly deeper than that.
[0054]
Even when the molten resin is filled in the cavity formed by the mold member 520, when attention is paid to the specific dividing surface 23a, even if one of the concave grooves 525 is filled with the molten resin and is closed, the other concave groove 525 is filled. The airway can be secured. 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 composed of the dividing surface 23a and the step 23b is completely transferred to the molten resin. be able to. In other words, the diffractive lens (not shown) obtained in this way is an optical element with little disturbance in shape in the diffractive grooves constituting the boundaries between the plurality of divided surfaces.
[0055]
[Seventh Embodiment]
FIG. 9 schematically shows a configuration of an optical pickup apparatus including an optical system for an optical pickup composed of a diffractive lens according to the first to sixth embodiments, that is, a diffractive lens formed using the mold members 50 to 520. FIG.
[0056]
This optical pickup device has a semiconductor laser 62 for information reproduction of the first optical disc 61 and a semiconductor laser 66 for information reproduction of the second optical disc 65, that is, laser beams having different wavelengths from each other. Can be injected. The laser beams from both semiconductor lasers 62 and 66 are irradiated onto the optical discs 61 and 65 using the objective lens 77 formed of the diffraction lens formed by the method of the first to sixth embodiments, and reflected from the optical discs 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 disc 61, a beam is emitted from the first semiconductor laser 62, and the emitted light beam is transmitted through the beam splitter 71, and the polarized beam splitter 72, the collimator 73, and the quarter wavelength plate 74 are passed through. The light passes through and becomes a circularly polarized parallel light beam. This light beam is focused by a diaphragm 76 and is condensed by the objective lens 77 on the information recording surface 61b via the transparent substrate 61a of the first optical disk 61.
[0058]
The light beam modulated and reflected by the information bit on the information recording surface 61b is transmitted again through the objective lens 77, the diaphragm 76, the quarter wavelength plate 74, and the collimator 73, enters the polarization beam splitter 72, and is reflected there. Astigmatism is given by the cylindrical lens 78 and incident on the photodetector 79, and a read signal of information recorded on the first optical disc 61 is obtained using the output signal.
[0059]
In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector 79. 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 flux from 62 is imaged 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 light synthesizing unit, and is combined with the light beam from the first semiconductor laser 62. Similarly, the light passes through the polarization beam splitter 72, the collimator 73, the quarter wavelength plate 74, the diaphragm 76, and the objective lens 77, and is condensed on the information recording surface 65b via the transparent substrate 65a of the second optical disk 65.
[0061]
The light beam modulated and reflected by the information bit on the information recording surface 65 b is again passed through the objective lens 77, the stop 76, the quarter wavelength plate 74, the collimator 73, the polarization beam splitter 72, and the cylindrical lens 78, and the photodetector 79. A signal for reading information recorded on the second optical disk 65 is obtained by using the output information.
[0062]
Further, as in the case of the first optical disc 61, the spot shape change on the photodetector 79 and the light quantity change due to the position change are detected, and focus detection and track detection are performed, and the two-dimensional actuator 81 is used for focusing. The objective lens 77 is moved for tracking.
[0063]
In the optical pickup device of the seventh embodiment, the objective lens 77 made of a diffractive lens with little disturbance in shape is used. Therefore, light of different wavelengths from 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 according to the embodiment, but the present invention is not limited to the above embodiment. For example, the diffractive lens to be formed by the mold members 20 to 520 is not limited to a convex lens but may be a concave lens.
[0065]
In the first to fourth embodiments, the number of the concave grooves 25 to 325 is not limited to 1 and can be 2 or more.
[0066]
In the fifth and sixth embodiments, the width, arrangement, number, and the like of the concave grooves 425 and 525 can be appropriately changed according to the specifications of the diffractive lens and molding conditions (for example, the lens material).
[0067]
In the first to sixth embodiments, the case where a diffractive lens is manufactured has been described, or the present invention is not limited to manufacturing a lens. For example, it can be used to manufacture a phase shift device.
[0068]
【The invention's effect】
As described above, according to the first invention, since the mold 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, the concave mold is formed. The flow of the gas flowing through the groove can be controlled, and an optical element with little disturbance in shape can be provided at the step portion of the boundary between the plurality of divided surfaces.
[0069]
According to the second invention, even when the first concave groove is filled first when the molten resin is injected into the cavity formed from the mold, the second and third concave grooves spaced apart from the first concave groove are formed. It is possible to provide an optical element that is not immediately filled, can be switched in the groove, and can be discharged, so that the shape is less disturbed in the step portion of the boundary.
[Brief description of the drawings]
FIGS. 1A and 1B are views showing an example of a method for producing a plastic optical element according to a first embodiment. FIGS. 1A, 1B, and 1C are a top view, a perspective view, and a perspective view of a mold member, respectively. It is a partial expansion perspective view.
2 is a diagram illustrating a method for manufacturing a diffractive lens using the mold member of FIG.
3 is a perspective view of a diffractive lens manufactured using the mold member of FIG. 1. 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 parts
23 Transfer section
23a Dividing surface
23b Step
25 groove
30 Mold parts
41, 42 holder
43 Injection gate
44 Clearance
50 Diffractive lens
51 Lens body
51b Dividing surface
51c Diffraction groove
54 Projections
CA cavity
MR Molten resin

Claims (10)

A method of manufacturing a plastic optical element having a plurality of divided surfaces that switch the optical path stepwise at the boundary as an optical surface,
The optical element extends along the molding surface so as to intersect a molding surface having a surface shape corresponding to the optical surface of the optical element and a plurality of step portions forming boundaries of the plurality of division surfaces. Preparing a molding die having a concave groove whose width changes from the center side to the peripheral side,
Forming a cavity using the mold;
And a step of injecting molten resin into the cavity. The method of manufacturing a plastic optical element according to claim 1, wherein the optical element is a lens. 3. The concave groove extends linearly from the center to the periphery of the molding surface corresponding to the refractive surface of the lens, and the groove width along the molding surface increases toward the periphery. A method for producing the plastic optical element according to the description. 3. The concave groove extends linearly from the center to the periphery of the molding surface corresponding to the refractive surface of the lens, and the groove width along the molding surface decreases toward the periphery. A method for producing the plastic optical element according to the description. A method of manufacturing a plastic optical element having a plurality of divided surfaces that switch the optical path stepwise at the boundary as an optical surface,
Along the molding surface so as to communicate between the molding surface having a surface shape corresponding to the optical surface of the optical element and the first and second stepped portions that form the boundary between the plurality of division surfaces adjacent to each other. First and second concave grooves extending apart from each other, a third step portion that forms a boundary between the plurality of dividing surfaces and is adjacent to the second step portion, and the second step portion Providing a mold having a third groove extending along the molding surface so as to communicate with each other at a position spaced from both the first and second grooves;
Forming a cavity using the mold;
And a step of injecting molten resin into the cavity. 6. The method of manufacturing a plastic optical element according to claim 5, wherein the optical element is a lens. A molding surface having a surface shape corresponding to the optical surface of a plastic optical element having a plurality of divided surfaces that switch the optical path stepwise at the boundary as an optical surface;
A concave groove extending along the molding surface so as to intersect with a plurality of stepped portions forming boundaries of the plurality of dividing surfaces and having a width changing from the center side to the peripheral side of the optical element; A mold provided. A molding surface having a surface shape corresponding to the optical surface of a plastic optical element having a plurality of divided surfaces that switch the optical path stepwise at the boundary as an optical surface;
First and second concave grooves extending apart from each other along the molding surface so as to communicate between the first and second stepped portions that form adjacent boundaries of the plurality of dividing surfaces;
The boundary between the plurality of dividing surfaces is formed, and the third step portion adjacent to the second step portion and the second step portion are separated from both the first and second grooves. A mold comprising: a third groove extending along the molding surface so as to communicate at a position. An optical surface including a plurality of divided surfaces that switch the optical path stepwise at the boundary;
A ridge that extends along the optical surface so as to intersect with a plurality of stepped portions that form boundaries of the plurality of dividing surfaces, and has a width that changes from the center side toward the peripheral side of the optical element; Provided plastic optical element. An optical surface including a plurality of divided surfaces that switch the optical path stepwise at the boundary;
First and second ridges extending away from each other along the optical surface so as to communicate between the first and second stepped portions that form adjacent boundaries of the plurality of dividing surfaces;
The boundary between the plurality of dividing surfaces is formed, and the third step portion adjacent to the second step portion and the second step portion are separated from both the first and second protrusions. A plastic optical element comprising a third ridge extending along the optical surface so as to communicate with each other at a position.

Images