JP2008158183A - Manufacturing method of optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of optical element capable of materializing a diffraction element exhibiting a satisfactory characteristic. <P>SOLUTION: When a diffraction pattern layer 20E is formed by a replica method, a first UV-curing resin 100A is irradiated with UV rays which allow curing reaction to quickly proceed, even though there is a risk of degrading the resin by long-time irradiation over a short curing time, whereby a most part of functional groups of the first UV-curable resin 100A are reacted effectively, and thereafter, the first UV-curing resin 100A is irradiated with an irradiation light, which has a low speed of curing reaction although there is a small risk of degrading the resin because of a low energy level of the resin over an irradiation time longer than the curing time, whereby the functional groups remaining in the first UV-curable resin 100A, of which the speed of curing reaction is left to be small because of disappearance of the fluidity, is made to substantially completely react taking a long time. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an optical element, and is suitable for application to, for example, a diffraction element formed using an ultraviolet curable resin.

Conventionally, in an optical pickup of an optical disc apparatus, a diffraction element is used for the purpose of correcting an aberration of a light beam. A diffraction element forms a fine groove-shaped diffraction grating on the surface of a transparent plate-shaped element substrate, and diffracts a light beam by an optical path difference when passing through the peaks and valleys of the diffraction grating (for example, , See Patent Document 1).
JP 2005-339762 A

  By the way, in the diffraction element having such a configuration, a molded product as a base is formed by injection molding, and an ultraviolet curable resin (hereinafter referred to as UV (UltraViolet ray) curable resin) applied to the base is patterned. It is considered that a diffraction pattern can be reproduced with high accuracy by providing a diffraction grating by a so-called UV replica method in which a transferred mold is pressed and cured.

  By the way, in the UV curable resin, the transparency is improved in accordance with the UV curing reaction by irradiating ultraviolet rays, and the transmittance with respect to the light beam is improved. For this reason, when manufacturing a diffraction element, it is desirable to fully advance the curing reaction of UV curable resin.

  However, since ultraviolet rays used in the UV curing reaction have a large energy, irradiation over a long period of time may cause a so-called yellowing reaction or deterioration of the UV curing resin. It is not preferable to irradiate for a long time.

  On the other hand, if the UV curable resin is irradiated with ultraviolet rays for a short time, the UV curing reaction cannot be sufficiently progressed, and there is a problem that a diffractive element having a desired transmittance cannot be manufactured. .

  The present invention has been made in consideration of the above points, and intends to propose a method of manufacturing an optical element exhibiting good characteristics.

  In order to solve such a problem, in the method of manufacturing an optical element of the present invention, an ultraviolet curable resin is applied to a first member formed of a transparent optical material, the first pressing member is pressed, and ultraviolet rays are predetermined. A second member forming step for forming a second member in close contact with the first member by irradiating and curing over the curing time of the second member, and at a wavelength longer than ultraviolet light for the second member And an irradiation step for irradiating the irradiation light over a predetermined irradiation time longer than the curing time.

  Thereby, after most of the ultraviolet curable resin is effectively cured using ultraviolet rays, the ultraviolet curable resin is almost completely cured using irradiation light with a low risk of causing deterioration of the first and second members. Can be made.

  According to the present invention, an ultraviolet curable resin is applied to a first member formed of a transparent optical material, the first pressing member is pressed, and ultraviolet rays are irradiated and cured for a predetermined curing time. A second member forming step for forming a second member in close contact with the first member, and irradiation light having a wavelength longer than the ultraviolet ray with respect to the second member for a predetermined time longer than the curing time. By providing an irradiation step of irradiating over the irradiation time, irradiation with a low risk of causing deterioration of the first and second members after effectively curing most of the ultraviolet curable resin using ultraviolet rays The ultraviolet curable resin can be almost completely cured using light, and thus a method for producing an optical element exhibiting good characteristics can be realized.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

(1) Configuration of Optical Disc Device (1-1) Overall Configuration of Optical Disc Device In FIG. 1, reference numeral 1 denotes an optical disc device using a diffractive element according to the present invention, which is a CD (Compact Disc) system or a DVD (Digital Versatile Disc) system. Alternatively, the optical disc 100 can be played back by any one of three methods such as a BD (Blu-ray Disc, registered trademark) method.

  The optical disc device 1 is configured to be controlled in an integrated manner by the control unit 2. When a reproduction instruction or the like from an external device (not shown) is received in a state where the optical disc 100 is loaded, a drive unit is received from the control unit 2. 3 and the signal processing unit 4 are controlled to read information recorded on the optical disc 100.

  In practice, the drive unit 3 rotates the optical disc 100 at a desired rotational speed by the spindle motor 5 based on the control of the control unit 2, and the sled motor 6 increases the optical pickup 7 in the tracking direction which is the radial direction of the optical disc 100. Further, the biaxial actuator 8 finely moves the objective lens unit 9 in two directions, ie, a focus direction and a tracking direction, which are directions in which the objective lens unit 9 approaches or separates from the optical disc 100.

  In parallel with this, the signal processing unit 4 irradiates the desired track of the optical disc 100 with a predetermined light beam from the objective lens unit 9 by the optical pickup 7, and generates a reproduction signal based on the detection result of the reflected light. The reproduction signal is sent to an external device (not shown) via the control unit 2.

  The optical pickup 7 is a so-called three-wavelength compatible type, and light having a wavelength of about 780 [nm] from the objective lens unit 9 to the optical disk 100 of the CD system (hereinafter referred to as the CD system disk 100c). The optical disc 100 is irradiated with a beam, and an optical beam 100 having a wavelength of about 650 [nm] is irradiated onto an optical disc 100 made of DVD (hereinafter referred to as a DVD disc 100d). This is called a BD type disc 100b) and is irradiated with a light beam having a wavelength of about 405 [nm].

  As described above, the optical disc apparatus 1 can reproduce the optical disc 100 by irradiating the optical disc 100 of the CD format, DVD format, or BD format with a light beam suitable for each format. .

(1-2) Configuration of Optical Pickup As shown in FIG. 2, the optical pickup 7 uses a light beam having a wavelength of about 780 [nm] for a CD system as a light beam light source (hereinafter referred to as a CD light beam). Lc) and a laser diode 11 capable of emitting a light beam having a wavelength of about 650 [nm] for DVD system (hereinafter referred to as a DVD light beam Ld), and a wavelength of about 405 [nm] for the BD system. ] And a laser diode 12 that can emit a light beam (hereinafter referred to as a BD light beam Lb).

  The coupling lens 13 converts the optical magnification of the light beam emitted from the laser diode 11.

  The beam splitter 14 reflects or transmits the light beam according to the wavelength at the reflection / transmission surface 14A. The light beam for CD Lc having a wavelength of about 780 [nm] is reflected on the reflection / transmission surface 14A. The DVD light beam Ld having a wavelength of about 650 [nm] is reflected, and the BD light beam Lb having a wavelength of about 405 [nm] is transmitted.

  The polarization beam splitter 15 reflects or transmits the light beam according to the polarization direction on the polarization plane 15A, transmits the light beam incident from the beam splitter 14 side, and adjusts the polarization direction. Thus, the light beam incident from the collimator lens 16 side is reflected.

  The collimator lens 16 converts the light beam incident from the polarization beam splitter 15 and made of divergent light into parallel light, and converts the light beam made incident from the rising mirror 17 and made of parallel light into convergent light. .

  The rising mirror 17 reflects the horizontal light beam incident from the collimator lens 16 and raises it in the vertical direction, that is, the direction in which the light beam is incident substantially perpendicularly to the optical disc 100. A vertically incident light beam is reflected in the horizontal direction.

  The ¼ wavelength plate 18 converts the light beam incident from the rising mirror 17 from linearly polarized light to circularly polarized light by delaying the phase of a part of the component in the light beam by ¼ wavelength, or an objective lens. The light beam incident from the unit 9 is converted from circularly polarized light to linearly polarized light.

  As shown in the perspective view of FIG. 3, the objective lens unit 9 has a flat disk-like diffraction element 20 attached to the lower part of a substantially cylindrical lens barrel portion 19 (partially cut surface is shown in FIG. 3). In addition, a spindle-shaped portion having a slightly smaller diameter than that of the disk is integrally formed on the lower surface of a flat disk-shaped portion having the same size as that of the diffraction element 20 from the upper portion to the center portion of the lens barrel portion 19. The objective lens 21 having the shape as described above is attached.

  The objective lens unit 9 converts the light beam incident from the quarter-wave plate 18 and made of parallel light into convergent light by the diffraction element 20 and the objective lens 21, and focuses it on the signal recording surface of the optical disc 100. Has been made.

  The optical pickup 7 converts the light beam reflected and diverged from the signal recording surface of the optical disc 100 into parallel light by the objective lens 21 and the diffraction element 20 of the objective lens unit 9, and is converted by the quarter wavelength plate 18. The circularly polarized light is converted into linearly polarized light, reflected by the rising mirror 17 in the horizontal direction, that is, in the direction in which the polarization beam splitter 15 is provided, and converted from parallel light to convergent light by the collimator lens 16, and then the polarization beam splitter 15. To enter.

  In this case, the polarization beam splitter 15 reflects the light beam on the polarization plane 15A in accordance with the polarization direction of the light beam and makes it incident on the conversion lens 22.

  The conversion lens 22 converts the optical magnification of the CD light beam Lc, the DVD light beam Ld, and the BD light beam Lb. The optical axis synthesizing element 23 matches the optical axes of the CD light beam Lc and DVD light beam Ld emitted from the laser diode 11 with the optical axis of the BD light beam Lb emitted from the laser diode 12. Has been made.

  A plurality of detection regions each having a predetermined shape are formed at predetermined positions on the upper surface of the photodetector 24 (that is, the surface irradiated with the light beam that has passed through the conversion lens 22 and the optical axis combining element 23). A plurality of detection signals are generated by detecting and photoelectrically converting the respective light amounts of the light beams, and supplying the detection signals to the signal processing unit 4 (FIG. 1).

  In response to this, the signal processing unit 4 generates a reproduction RF signal by performing predetermined arithmetic processing using the detection signal from the photodetector 24 (FIG. 2), and performs predetermined decoding based on the reproduction RF signal. A reproduction signal is generated through processing, demodulation processing, and the like.

  The signal processing unit 4 (FIG. 1) generates a drive control signal such as a tracking error signal and a focus error signal by performing predetermined arithmetic processing using the detection signal from the photodetector 24 (FIG. 2). These are supplied to the control unit 2. In response to this, the control unit 2 performs tracking control, focus control, and the like via the drive unit 3 and can adjust the irradiation state of the light beam to the optical disc 100 to normally generate a reproduction signal.

(1-2-1) In the case of a CD-type disc In practice, when the control unit 2 (FIG. 1) recognizes that the optical disc 100 is a CD-type disc 100c by a predetermined disc type determination method, the optical pickup 7 ( A CD light beam Lc composed of divergent light is emitted from the light emitting point 11 A of the laser diode 11 in FIG. 2) and is incident on the beam splitter 14 via the coupling lens 13.

  The optical pickup 7 reflects the CD light beam Lc at the reflection / transmission surface 14 A by the beam splitter 14, transmits the polarization beam splitter 15, converts the divergent light into parallel light by the collimator lens 16, and After rising from the horizontal direction to the vertical direction and converted from linearly polarized light to circularly polarized light by the quarter wavelength plate 18, the CD light beam Lc is incident on the objective lens unit 9.

  The objective lens unit 9 converts the CD light beam Lc incident from the quarter-wave plate 18 into convergent light by the diffraction element 20 and the objective lens 21, and focuses this on the signal recording surface of the CD disc 100c. .

  The objective lens unit 9 converts the CD light beam Lc reflected on the signal recording surface of the CD disc 100c into divergent light into parallel light by the objective lens 21 and the diffractive element 20, and the quarter-wave plate 18 is converted. To enter.

  Thereafter, the optical pickup 7 converts the CD light beam Lc incident on the quarter-wave plate 18 from circularly polarized light to linearly polarized light, reflects it in the horizontal direction by the rising mirror 18, and converges from parallel light by the collimator lens 16. After being converted into light, the light is reflected on the polarization plane 15A by the polarization beam splitter 15, and sequentially passes through the conversion lens 22 and the optical axis synthesizing element 23 to irradiate the photodetector 24.

  The photodetector 24 detects the light amount of the irradiated CD light beam Lc by a plurality of detection regions, generates a plurality of detection signals, and supplies the detection signals to the signal processing unit 4 (FIG. 1).

  In response to this, the signal processing unit 4 generates a reproduction RF signal based on a plurality of detection signals, generates a reproduction signal, and generates a drive control signal such as a tracking error signal and a focus error signal. Has been made.

(1-2-2) In the case of a DVD type disc When the controller 2 (FIG. 1) recognizes that the optical disc 100 is a DVD type disc 100d by a predetermined disc type determination method, the optical pickup 7 (FIG. 2) The DVD light beam Ld made of divergent light is emitted from the light emitting point 11B of the laser diode 11 and is incident on the beam splitter 14 via the coupling lens 13.

  Thereafter, as in the case of the CD system disc 100c, the optical pickup 7 converts the DVD light beam Ld into the coupling lens 13, the beam splitter 14, the polarization beam splitter 15, the collimator lens 16, the rising mirror 17 and the quarter wavelength plate. Then, the light beam Ld for DVD is converted into convergent light by the diffraction element 20 and the objective lens 21 in the objective lens unit 9, and is focused on the signal recording surface of the DVD type disc 100d.

  Similarly to the case of the CD disc 100c, the objective lens unit 9 converts the DVD light beam Ld, which has been reflected and diverged from the signal recording surface of the DVD disc 100d, into parallel light by the objective lens 21 and the diffraction element 20. After the conversion, the ¼ wavelength plate 18, the rising mirror 17, the collimator lens 16, the polarization beam splitter 15, the conversion lens 22, and the optical axis synthesizing element 23 are passed or reflected in this order to irradiate the photodetector 24.

  As in the case of the CD system disc 100c, the photodetector 24 generates a plurality of detection signals by detecting the amount of light of the irradiated DVD light beam Ld using a plurality of detection areas, and generates these detection signals from the signal processing unit 4 (FIG. 1). ).

  In response to this, the signal processing unit 4 generates a reproduction RF signal, generates a reproduction signal, and generates a drive control signal such as a tracking error signal and a focus error signal.

(1-2-3) In the case of a BD disc When the control unit 2 (FIG. 1) recognizes that the optical disc 100 is a BD disc 100b by a predetermined disc type determination method, the optical pickup 7 (FIG. 2) A BD light beam Lb made of divergent light is emitted from the light emitting point 12 A of the laser diode 12 and is incident on the beam splitter 14.

  In this case, the beam splitter 14 transmits the BD light beam Lb through the reflection / transmission surface 13 </ b> A and makes it incident on the polarization beam splitter 15.

  Thereafter, the optical pickup 7 passes or reflects the BD light beam Lb in the order of the polarizing beam splitter 15, the collimator lens 16, the rising mirror 17 and the quarter wavelength plate 18 in the same manner as in the case of the CD disc 100c, and the objective lens. In the unit 9, the BD light beam Lb is converted into convergent light by the objective lens 21, and this is focused on the signal recording surface of the BD disc 100b.

  Incidentally, the diffractive element 20 of the objective lens unit 9 transmits the BD light beam Lb as it is without being diffracted (details will be described later).

  Similarly to the case of the CD disc 100c, the objective lens unit 9 converts the BD light beam Lb, which is reflected from the signal recording surface of the BD disc 100b and becomes divergent light, into parallel light by the objective lens 21. The quarter-wave plate 18, the rising mirror 17, the collimator lens 16, the polarization beam splitter 15, the conversion lens 22, and the optical axis synthesizing element 23 are passed or reflected in this order, and are irradiated to the photodetector 24.

  As in the case of the CD system disc 100c, the photodetector 24 generates a plurality of detection signals by detecting the amount of light of the irradiated BD light beam Lb by a plurality of detection areas, and generates these signals as a signal processing unit 4 (FIG. 1). ).

  In response to this, the signal processing unit 4 generates a reproduction RF signal, generates a reproduction signal, and generates a drive control signal such as a tracking error signal and a focus error signal.

  As described above, the optical pickup 7 has a CD light beam Lc, a DVD light beam Ld, or a DVD light beam Ld by the objective lens unit 9 regardless of whether the optical disk 100 is a CD disk 100c, a DVD disk 100d, or a BD disk 100b. The BD light beam Lb can be focused on the signal recording surface of the optical disc 100, and the reflected light can be detected by the photodetector 24.

(1-3) Structure of Objective Lens Unit Next, FIG. 4 shows an enlarged cross-sectional view of the CD lens 100c, the DVD disk 100d, the BD disk 100b, and the objective lens unit 9.

  Incidentally, although the biaxial actuator 8 (FIG. 1) is attached to the objective lens unit 9, it is omitted in FIG.

  In general, in the CD system, DVD system, and BD system, from the viewpoint of compatibility and the like, the wavelength of the light beam for reading information, the numerical aperture for condensing the light beam, and signal recording from the lower surface of each optical disc 100 The thickness of the portion up to the surface (so-called cover layer) is defined by the standards.

  Specifically, in the CD system, the wavelength is specified to be about 780 [nm], the numerical aperture is about 0.45, and the thickness of the cover layer is 1.2 [mm]. In the DVD system, the wavelength is about 650 [nm]. nm], a numerical aperture of about 0.6, and a cover layer thickness of 0.6 [mm]. In the BD method, the wavelength is about 405 [nm], the numerical aperture is about 0.85, and the cover The thickness of the layer is defined as 0.1 [mm].

  In the objective lens unit 9, due to the characteristics of the objective lens 21, the focal lengths when the CD light beam Lc, the DVD light beam Ld, and the BD light beam Lb are respectively irradiated from the objective lens 21 are different. .

  For this reason, in the optical disc apparatus 1, the height of the objective lens unit 9 (that is, the distance from the optical disc 100) is adjusted via the biaxial actuator 8 (FIG. 1) while the height of the optical disc 100 is actually fixed. Each light beam is focused on the signal recording surface of each optical disk.

  In FIG. 4, for convenience of explanation, the objective lens unit 9 is fixed and the height of the optical disc 100 is changed. As a result, in FIG. 4, the height of the lower surface of each optical disk is different. In FIG. 4, only the cover layer is shown for the CD disc 100c, DVD disc 100d, and BD disc 100b.

  By the way, the objective lens 21 has priority over the CD light beam Lc and the DVD light beam Ld from the viewpoint of the relative intensity of the BD light beam Lb and the numerical aperture defined by the BD method. The design is optimized for the light beam Lb.

  For this reason, the objective lens 21 of the objective lens unit 9 converts the BD light beam Lb into convergent light when the BD light beam Lb is incident as parallel light from the lower side of the objective lens 21, and converts the BD light beam Lb into convergent light. It is possible to focus on the signal recording surface of 100b.

  However, since the objective lens 21 is optimized for the BD light beam Lb, if the CD light beam Lc or the DVD light beam Ld is incident as parallel light from the lower side of the objective lens 21, it is converted into convergent light. Although it can be converted, aberration is generated and the signal recording layer of the optical disc 100 cannot be correctly focused.

  Therefore, the objective lens unit 9 causes the BD light beam Lb to enter the objective lens 21 as parallel light, and selectively diffracts only the CD light beam Lc or the DVD light beam Ld by the diffraction element 20 to be non-parallel. The light is incident on the objective lens 21 as light.

  Specifically, the diffraction element 20 has a CD diffraction grating DGc formed on the upper layer portion 20A, which is a hologram that diffracts the CD light beam Lc and does not diffract the DVD light beam Ld and the BD light beam Lb. As shown in FIG. 4, the CD light beam Lc is diffracted slightly outward by the CD diffraction grating DGc.

  That is, the upper layer portion 20A of the diffraction element 20 can transmit the DVD light beam Ld and the BD light beam Lb as they are, and can selectively diffract only the CD light beam Lc, in other words, the CD light beam. It functions as a lens that corrects only the aberration of Lc.

  In response to this, as shown in FIG. 4, the objective lens 21 refracts the CD light beam Lc incident from the diffractive element 20 on its lower surface and upper surface, and converts it into convergent light. As a result, the objective lens unit 9 can correct the aberration of the CD light beam Lc, and can focus the CD light beam Lc irradiated from the objective lens 21 on the signal recording surface of the CD system disc 100c. .

  Further, the diffraction element 20 is formed with a DVD diffraction grating DGd formed of a hologram that diffracts the DVD light beam Ld and does not diffract the CD light beam Lc and the BD light beam Lb in the lower layer portion 20B. As shown in FIG. 4, the DVD light beam Ld is slightly diffracted outward by the DVD diffraction grating DGd.

  That is, the lower layer portion 20B of the diffraction element 20 can transmit the CD light beam Lc and the BD light beam Lb as they are, and can selectively diffract only the DVD light beam Ld, in other words, the DVD light beam. It functions as a lens that corrects only the Ld aberration.

  In response to this, the objective lens 21 refracts the DVD light beam Ld incident from the diffraction element 20 on the lower surface and the upper surface, respectively, and converts it into convergent light, as shown in FIG. As a result, the objective lens unit 9 can correct the aberration of the DVD light beam Ld, and can focus the DVD light beam Ld irradiated from the objective lens 21 on the signal recording surface of the DVD disc 100d. .

  In this way, the objective lens unit 9 corrects the aberration by diffracting only the CD light beam Lc by the upper layer portion 20A of the diffractive element 20, and diffracts only the DVD light beam Ld by the lower layer portion 20B of the diffractive element 20. By correcting the aberration, the CD light beam Lc, the DVD light beam Ld, and the BD light beam Lb irradiated from the objective lens 21 optimized for the BD light beam Lb are converted into the CD disk 100c and the DVD disk. Each of the signal recording surfaces of the disc 100d and the BD disc 100b can be focused.

(1-4) Configuration of Diffraction Element As shown in FIG. 5A, the diffraction element 20 is configured around a base layer 20C formed in a generally flat disk shape, as described above. A CD diffraction grating DGc is formed in the upper layer portion 20A, and a DVD diffraction grating DGd is formed in the lower layer portion 20B.

  The base layer 20C is made of a transparent synthetic resin having a predetermined refractive index, and refracts the light beam at the interface with another substance having a different refractive index or air.

  On the other hand, in the upper layer portion 20A, as shown in a partially enlarged cross-sectional view in FIG. 5B, a stepped CD diffraction pattern PTc is formed on the upper surface 20Ca of the base layer 20C, and a transparent curable resin is formed on the upper side thereof. A cover layer 20D is joined.

  The CD diffraction pattern PTc is formed in three steps, and the overall height, that is, the distance between the first step and the third step is about 12 [μm], and for each CD diffraction pattern PTc. The period is about 18 [μm] at the minimum. Further, as shown in FIG. 3, the CD diffraction pattern PTc is formed concentrically in a range from the center to about half of the outer diameter on the upper surface of the diffraction element 20.

  The cover layer 20D is made of a material having a refractive index different from that of the base layer 20C. The lower surface of the cover layer 20D is formed so as to be bonded to the CD diffraction pattern PTc as the first diffraction pattern without any gap. Is formed in a planar shape.

  In this way, the upper layer portion 20A of the diffraction element 20 is formed with the stepped CD diffraction pattern PTc on the upper surface 20Ca of the base layer 20C, and the cover layer 20D having a refractive index different from that of the base layer 20C is bonded to the upper side portion 20A. Thus, the light beam is diffracted or transmitted according to the wavelength, and as a result, functions as a CD diffraction grating DGc that diffracts only the CD light beam Lc as the light beam of the first wavelength. Has been made.

  On the other hand, the lower layer portion 20B has a diffraction pattern layer 20E in which a diffraction grating DGd for DVD is formed on a lower surface 20Cb of a base layer 20C formed in a planar shape, as shown in a partially enlarged sectional view in FIG. It is formed by bonding.

  The diffraction pattern layer 20E is made of a transparent resin having a refractive index substantially equal to that of the base layer 20C as the first member, and stepwise diffraction patterns for DVD PTd are periodically formed on the lower surface side. In addition, since the lower surface of the diffraction pattern layer 20E is not covered with other substances, it directly touches the air.

  The DVD diffraction pattern PTd is formed in a five-step staircase, and the overall height, that is, the distance between the first step and the fifth step is 6 [μm]. The period is 170 [μm] at the minimum. Further, as shown in FIG. 3, the DVD diffraction pattern PTd is formed concentrically in a range from the center to about 2/3 of the outer diameter on the lower surface of the diffraction element 20.

  In this way, the lower layer portion 20B of the diffraction element 20 is formed with a diffraction pattern PTd for DVD as a second diffraction pattern having a step shape on the diffraction pattern layer 20E bonded to the lower side of the base layer 20C. Thus, the light beam is diffracted or transmitted according to the wavelength, and as a result, functions as a DVD diffraction grating DGd that diffracts only the DVD light beam Ld as the light beam of the second wavelength.

(2) Diffraction Element Manufacturing Method (2-1) Formation of Base Layer, Diffraction Pattern Layer, and Cover Layer Next, a manufacturing method of the diffraction element 20 will be described. As described above, the diffraction element 20 is formed with the diffraction pattern layer 20E having the DVD diffraction pattern PTd and the cover layer 20D covering the CD diffraction pattern PTc.

  As a method for manufacturing a diffraction element, injection molding in which a mold is filled with an optical resin to produce a molded product is widely used. However, when a diffractive element having a deep groove and a narrow diffraction pattern, such as a base layer 20C having a CD diffraction pattern PTc (FIG. 5B), is manufactured by injection molding, the molded product has a large mold release resistance. Distortion occurs, and the manufactured diffraction element generates aberration.

  Therefore, in the diffraction element 20 of the present invention, the cover layer 20D and the diffraction pattern layer 20E provided on the upper surface and the lower surface of the base layer 20C made of an injection molded product are referred to as ultraviolet curable resin (hereinafter referred to as UV (Ultra Violet ray) curable resin). ) Using a so-called UV replica method.

  As a result, the cover layer 20D and the diffraction pattern layer 20E are formed on the base layer 20C, which is an injection-molded product, by the UV replica method capable of reproducing a pattern with higher accuracy, and thus the distortion generated in the base layer 20C is optically reduced. The optical characteristics of the diffraction element 20 are kept good by canceling out.

  That is, when manufacturing the diffractive element 20, first, as shown in FIG. 6 (A), the lower surface 20Cb of the base layer 20C by injection molding has a refractive index substantially equal to that of the injection molding resin forming the base layer 20C. The first UV curable resin 100A having is applied.

  Subsequently, as shown in FIG. 6B, a UV curable resin 100A in which a DVD diffraction grating mold 101A having a mold shape obtained by inverting the DVD diffraction pattern PTd (FIG. 5C) is applied to the lower surface 20Cb. In addition, an ultraviolet light source (not shown) is used to irradiate a resin curing ultraviolet ray of about 365 [nm], for example, over a predetermined curing time (for example, 30 seconds) from the upper surface side of the base layer 20C. Thus, the first UV curable resin 100A is cured in a state where the mold shape of the DVD diffraction grating mold 101A is transferred, and thus the DVD diffraction pattern PTd is accurately reproduced as shown in FIG. 6C. The diffraction pattern layer 20E is formed in close contact with the lower surface 20Cb of the base layer 20C.

  Note that the base layer 20C has a distortion due to the peeling resistance when taken out from the mold, and therefore, the lower surface 20Cb that should originally be flat also has a distortion. However, since the UV curable resin 100A forming the diffraction pattern layer 20E has a refractive index substantially equal to that of the base layer 20C, the diffraction pattern layer 20E and the base layer 20C are optically integrated. The distortion of the lower surface 20Cb serving as the interface between the two has no optical influence.

After the diffraction pattern layer 20E is formed in this manner, as shown in FIG. 7A, the second upper surface 20Ca of the base layer 20C has a refractive index different from that of the injection molding resin for forming the base layer 20C. (For example, the refractive index of the injection molding resin is n _BASE = 1.5, whereas the refractive index of the second UV curable resin 100B is n _UV2 = 1.6).

  Subsequently, as shown in FIG. 7B, the flat UV mold 101B having a flat mold surface is pressed against the second UV curable resin 100B, whereby the second UV curable resin 100B is applied to the base layer 20C. By adhering to the CD diffraction pattern PTc (FIG. 5C) formed on the upper surface 20Ca of the substrate, and further irradiating ultraviolet rays from the lower surface side of the base layer 20C, the second UV curable resin 100B is cured. Then, a cover layer 20D that covers the CD diffraction pattern PTc is formed (FIG. 7C).

  Then, as shown in FIG. 7D, the base layer 20C on which the diffraction pattern layer 20E and the cover layer 20D are formed is heated for a predetermined time in a heating furnace (not shown) set at a predetermined annealing temperature. By doing so, an annealing process is performed. The annealing temperature at this time is effectively as short as possible in accordance with various conditions such as the curing state of the cover layer 20D and the diffraction pattern layer 20E, the processing time, and the capability of the heating device, and the cover layer 20D and the diffraction pattern layer 20E. The base layer 20C, the cover layer 20D, and the diffraction pattern layer 20E are appropriately selected from a temperature range lower than the glass transition point so as to stabilize the physical properties.

  Thereby, residual strain and low molecular weight components of the diffraction pattern layer 20E and the cover layer 20D can be removed, and the physical properties of the diffraction pattern layer 20E and the cover layer 20D can be stabilized to some extent.

  Incidentally, the CD diffraction pattern PTc formed on the upper surface 20Ca of the base layer 20C has a distortion caused by injection molding, and this distortion causes an aberration. Since the diffraction of light by the diffraction grating is caused by the difference in refractive index between the two layers in contact with each other through the diffraction pattern, the greater the difference in refractive index, the greater the aberration due to distortion of the diffraction pattern.

In the conventional diffraction element, the diffraction pattern is formed so as to be in direct contact with air, whereas the refractive index difference between the refractive index of the material forming the diffraction element and the refractive index of air (n _AIR = 1) is large. In the diffraction element 20 of the present invention, the CD diffraction pattern PTc of the base layer 20C (refractive index n _BASE = 1.5) is covered with the cover layer 20D (refractive index n _UV2 = 1.6). The difference in refractive index between the base layer 20C and the cover layer 20D that are in contact with each other via the CD diffraction pattern PTc can be set smaller than that of the conventional diffraction element, thereby reducing the aberration caused by the distortion of the CD diffraction pattern PTc. can do.

(2-2) Post-curing treatment of UV curable resin by irradiation with light beam for BD As described above, the diffraction element 20 can proceed with a curing reaction by annealing treatment to stabilize its physical properties to a certain extent. The reaction is not fully progressing. Specifically, the diffractive element 20 after annealing has a BD light transmittance of about 84% with respect to the BD light beam Lb, which is lower than the designed value of 90%.

  The UV curable resin after UV curing already has a high degree of polymerization and no fluidity, so its reaction rate is very low, and it takes a long time to further proceed the curing reaction with the remaining functional groups. UV irradiation is required.

  However, as described above, the ultraviolet ray for resin curing has a large energy, and when irradiated for a long time, it may cause a so-called yellowing reaction or deterioration of the UV cured resin. Therefore, it is not preferable to irradiate with ultraviolet rays for a long time.

  For example, as shown in FIG. 8 (A), the light energy of ultraviolet rays at 365 [nm] is 328 [kJ / mol], and as can be seen from FIG. 8 (B) showing the representative value of the binding energy of the organic compound, The energy level is almost the same as the binding energy of the C—C bond. For this reason, if the diffraction element 20 is irradiated with ultraviolet rays for a long time, the C—C bond in the UV curable resin and the injection molding resin is dissociated, and there is a risk of causing deterioration thereof.

  On the other hand, the light energy of blue light of 405 [nm] is 295 [kJ / mol], and this value is considerably smaller than the binding energy of the C—C bond. Even when it is irradiated with blue light, it can be said that the risk of causing dissociation of the C—C bond in the UV curable resin and the injection molding resin is very small.

  Therefore, in this embodiment, the diffractive element 20 after the annealing treatment is irradiated with blue light (about 405 [nm]) as irradiation light.

  In FIG. 9, the irradiation light having a wavelength of about 405 [nm] is emitted from the laser diode at an irradiation density of 10 [mW / mm 2], and the diffractive element 20 transmits BD light with respect to the irradiation energy when the irradiation light is irradiated to the irradiation element. It shows the change in rate.

From FIG. 9, by applying 70 [mWh / mm ² ] of irradiation light to the diffraction element 20 (that is, 7 hours × 10 [mW / mm 2]), the BD light transmittance of the diffraction element 20 is as designed. It reaches about 90 [%], and after that, it can be seen that the BD light transmittance hardly changes even if irradiation of irradiation light is continued. Further, it can be seen that when the irradiation energy is around 70 [mWh / mm ² ], the BD light transmittance hardly changes.

  Therefore, in the present embodiment, irradiation light having an irradiation density of 10 [mW / mm 2] is irradiated to the diffraction element 20 after annealing for 7 hours. As a result, the diffractive element 20 can sufficiently advance the curing reaction of the UV curable resin, so that the BD light transmittance as the diffractive element 20 as a whole is improved and the variation in the BD light transmittance for each diffractive element 20 is also improved. It is made to be able to suppress.

  In addition, before and after the post-curing process using irradiation light of about 405 [nm], the light transmittance (not shown) of 600 [nm] with respect to the light beam having a wavelength of about 600 [nm] with respect to the diffraction element 20. Almost did not change, and all showed high values.

  From this, by using the irradiation light of about 405 [nm] having substantially the same wavelength as the BD light beam Lb, the activity of the functional group that absorbs this wavelength region is selectively enhanced to advance the curing reaction. It can be seen that the BD light transmittance is effectively improved.

(3) Operation and Effect In the above configuration, in the diffraction element 20, the first UV curable resin 100A is applied to the base layer 20C as the first member formed of a transparent optical material, and the first pressing member The diffraction pattern layer 20E as the second member is formed by pressing the DVD diffraction grating mold 101A as the first member and irradiating and curing ultraviolet rays over a predetermined curing time, thereby forming the diffraction pattern layer 20E as the second member. On the other hand, irradiation light having a wavelength longer than that of ultraviolet rays was irradiated for a predetermined irradiation time longer than the curing time.

  Thereby, the diffraction element 20 combines the short-time ultraviolet irradiation and the irradiation light irradiation for a long time, and after the majority of the curing reaction in the UV curable resin proceeds rapidly and effectively by the ultraviolet irradiation, The curing reaction can proceed slowly and almost completely by irradiation light with a low risk of causing photodegradation.

  The diffractive element 20 selectively uses the blue light having the same wavelength as the BD light beam Lb irradiated to the optical disc 100 as the irradiation light, so that the curing reaction that proceeds in advance by the BD light beam Lb is selectively performed. Can be terminated.

  As a result, variation in the transmittance of the diffraction element 20 in the optical pickup 7 can be suppressed, and defects in the optical pickup 7 due to variation in the transmittance of the diffraction element 20 can be reduced.

  Further, after the optical pickup 7 is assembled, various adjustment operations such as laser power can be performed using the diffraction element 20 having a stable transmittance, so that the BD light transmittance is prevented from changing after the adjustment. Therefore, the optical pickup 7 can be adjusted with higher accuracy.

  According to the above configuration, in the diffraction element 20, when the diffraction pattern layer 20 </ b> E is formed by the replica method, there is a risk that the resin may be deteriorated if irradiation is performed for a long time, but the ultraviolet ray with which the curing reaction proceeds rapidly is short. The first UV curable resin 100A is irradiated over the curing time, and after most of the functional groups of the first UV curable resin 100A are effectively reacted, the resin is deteriorated by irradiation with a low energy level. Although the danger is low, the first UV curable resin 100A is irradiated with irradiation light having a low curing reaction speed over an irradiation time longer than the curing time, and the fluidity disappears, so the curing reaction speed is originally low. Since the functional group remaining in the first UV curable resin 100A in FIG. 1 is allowed to react almost completely over a long period of time, it is effective in a state where there is no risk of causing photodegradation. One almost completely can proceed the curing reaction in the first UV resin 100A, thus possible to realize a method of manufacturing an optical element exhibiting good characteristics.

(4) Other Embodiments In the above-described embodiment, the present invention is applied to the diffraction element 20 having a three-layer structure in which the cover layer 20D and the diffraction pattern layer 20E are provided with respect to the base layer 20C. However, the present invention is not limited to this. For example, as shown in FIG. 10, the present invention is applied to a diffractive element 20Z having a two-layer structure in which a cover layer 20D is provided on a base layer 20C. You may make it apply invention. Further, the present invention may be applied not only to the diffraction element but also to other various optical elements.

  Further, in the above-described embodiment, the case where laser light having a wavelength of about 405 [nm] is used as irradiation light has been described. However, the present invention is not limited to this, and the risk of causing light degradation is low. Light having a wavelength may be used as irradiation light. For example, light emitted by a xenon lamp is cut and light having a wavelength of less than about 400 [nm] is cut by a filter, so that about 400 [nm] of the emitted light is cut. A portion having the above wavelength may be used as irradiation light. Further, the wavelength of the irradiation light is shorter than the ultraviolet ray depending on the reactivity of the UV curable resin to be used, and the wavelength at which the curing reaction of the UV curable resin proceeds (380 [nm] to 450 [nm]). ) Can be selected as appropriate.

  Further, in the above-described embodiment, the case where the irradiation light is irradiated after the annealing treatment has been described. However, the present invention is not limited to this, and the irradiation light may be irradiated before the annealing treatment. Even in this case, the effect of improving the transmittance can be obtained as in the above-described embodiment.

  The present invention can be used for various optical elements used for optical pickups, for example.

1 is a schematic diagram illustrating an overall configuration of an optical disc device. It is a basic diagram which shows the structure of an optical pick-up. It is a basic diagram which shows the structure of an objective lens unit. It is a basic diagram which shows the optical path in an objective lens unit. It is a basic diagram which shows the structure of a diffraction element. It is a basic diagram with which it uses for description of the manufacturing method of a base layer. It is a basic diagram with which it uses for description of the manufacturing method of a cover layer. It is a basic diagram which shows light energy and binding energy. It is a basic diagram which shows irradiation time and BD light transmittance. It is a basic diagram which shows the diffraction element by other embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Optical disk apparatus, 2 ... Control part, 3 ... Drive part, 4 ... Signal processing part, 7 ... Optical pick-up, 9 ... Objective lens unit, 11 ... Laser diode, 19 ... Lens-barrel part 20 …… Diffraction element, 20A …… Upper layer portion, 20B …… Lower layer portion, 20C …… Base layer, 20D …… Cover layer, 20Du …… Cover upper layer, 20Do …… Cover lower layer, 20E …… Diffraction pattern layer, 21 ... Objective lens, DGc ... Diffraction element for CD, DGd ... Diffraction element for DVD, Lb ... Light beam for BD, Ld ... Light beam for DVD, Lc ... Light beam for CD, 100A ... No. 1 UV curable resin, 100B .. Second UV curable resin.

Claims (7)

By applying an ultraviolet curable resin to the first member formed of a transparent optical material, pressing the first pressing member, and irradiating and curing ultraviolet rays over a predetermined curing time, the first member A second member forming step of forming a second member in close contact with the member;
An irradiation step of irradiating the second member with irradiation light having a wavelength longer than that of the ultraviolet rays over a predetermined irradiation time longer than the curing time. . The optical element is
Used in an optical pickup that irradiates an optical disk with a light beam,
The irradiation light is
The optical element manufacturing method according to claim 1, wherein the optical element has the same wavelength as the light beam. The irradiation light is
The method for producing an optical element according to claim 1, wherein light having a wavelength equal to or shorter than the wavelength of the ultraviolet light is cut by a filter. Before or after the irradiation step,
An annealing step of heating the optical element on which the second member is formed over a predetermined annealing time at a predetermined annealing temperature lower than the glass transition point of the second member. The manufacturing method of the optical element of Claim 1. The irradiation time is
When the irradiation light is further irradiated to the second member after the irradiation step, the transmittance of the second member with respect to the light beam is selected so as to hardly change. The method for producing an optical element according to claim 2. After the second member forming step,
A UV curable resin is applied to the surface facing the first member, the second pressing member is pressed, and UV light is irradiated for curing over a predetermined curing time to be in close contact with the first member. The method of manufacturing an optical element according to claim 1, further comprising: a third member forming step of forming a third member that is made to move. The optical element is
It consists of a diffraction element which has a diffraction grating. The manufacturing method of the optical element of Claim 1 characterized by the above-mentioned.

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