JP2005310236A - Wavelength selective polarization hologram element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact and inexpensive optical element by utilizing a wavelength plate of a phase difference film being thinner than a wavelength plate of a single crystal substrate since thinning the substrate is hard in mass production by an optical element utilizing the wavelength plate of a single crystal substrate in miniaturization of an optical pickup. <P>SOLUTION: A wavelength selective opening limit element is formed at a side plane of a single crystal substrate having high double diffraction, a polarization hologram element is formed at the opposite plane so that a pattern is overlapped. Thereby, an optical element of two substrate constitution having three functions is obtained by making one substrate have functions of wavelength selective opening limit and polarization hologram and sticking it with thin phase difference film wavelength plate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wavelength-selective aperture element, a phase difference element, a diffraction element, and an optical head device suitable for being mounted on an optical head device that records and reproduces information by irradiating light onto an optical recording medium. It is.

An optical head device is used to perform recording / reproduction on an optical disc such as a CD (compact disc) and a DVD (digital video disc). For optical head devices, in the middle of the optical path from the laser light source to the photodetector, a polarization hologram with high light utilization efficiency using polarized light, or wavelength selection that transmits or diffracts light of different wavelengths according to the wavelength There are optical pickups composed of optical elements such as directional aperture limiting elements and 1 / 4λ or 5 / 4λ wavelength plates. As the wave plate, in addition to a single crystal substrate such as quartz or LiNbO 3 (hereinafter abbreviated as LN substrate), a retardation film 402 obtained by stretching a synthetic resin sheet as shown in FIG. 4 is used to maintain optical flatness and shape. There is a wave plate sandwiched between two transparent substrates 401. (For example, see Patent Document 1)
A diffractive element having a wavelength-selective aperture limiting function using a single crystal substrate having birefringence, for example, a polarizing plate having a wavelength-selective aperture film 506 formed on a quartz wavelength plate 508 as shown in FIG. A wavelength-selective hologram element in which the LN substrate 508 constituting the layer 505 is bonded has been announced (see, for example, Non-Patent Document 1), but the crystal 508 and the LN are used to reduce the size and thickness of the optical pickup. If the thickness of the substrate 508 is reduced, the processing yield such as polishing is lowered, which is disadvantageous in cost.

On the other hand, the single-function, single-element type optical pickup requires a large number of parts and complicated adjustments, so that it is necessary to combine functions in order to reduce the size and simplify the optical pickup. A wavelength-selective aperture limiting element using a retardation film wave plate as shown in FIG. 6 has been introduced to reduce the thickness and function (see, for example, Patent Document 2). Since it is easily deformed or dissolved by a solvent, it is difficult to directly configure the aperture limiting element and the polarizing diffraction element on the retardation film. The aperture limiting element and the polarization hologram element are formed on different substrates, A configuration in which the substrate is bonded to the retardation film and the other optical element substrate is disposed so that the optical axes thereof coincide with each other (for example, as shown in FIG. 7, the polarization hologram layer 705 and the wave plate 704 are bonded to each other to form the aperture limiting element 714 An optical pickup (located in front) is being introduced. (For example, see Patent Document 3)
Further, as shown in FIG. 8, an optical element integrated with a substrate on which an aperture limiting element 807 is formed, a substrate on which a polarization hologram layer 803 is formed, and a wave plate 802 is also introduced. (For example, see Patent Document 3)
However, the conventional optical element configuration requires at least two substrates and a retardation film, and it has been difficult to reduce the size and thickness of the optical element.
JP 2000-31078 A (6th page, FIG. 1) JP 2001-126294 A (Section 6, FIG. 2) JP 2002-40257 (Section 7, FIG. 4, FIG. 7) National Technical Report Vol. 43 No. 3 Jun. 1997, p. 59

  As described above, it is difficult to reduce the thickness of the optical element using the wave plate of the single crystal substrate in mass production, and at least an optical element using the wave plate of the retardation film that is thinner than the wave plate of the single crystal substrate is used. Since it is composed of two or more substrates, there are problems in thinning and cost reduction.

  An object of the present invention is to inexpensively supply a wavelength plate having a thin wavelength selective aperture function and a polarization hologram element suitable for downsizing an optical pickup.

  In the present invention, a polarization hologram element is produced on one side of a single crystal substrate having birefringence, and a wavelength selective aperture limiting element is formed on the opposite side so that the patterns on both sides overlap, By laminating with an adhesive, a thin wave plate having a wavelength-selective polarization hologram function composed of two members is supplied.

  The wavelength-selective polarization hologram element using the retardation film wave plate of the present invention has a combined function and a reduced number of components compared to a conventional wavelength plate having a wavelength-selective aperture limiting function and a polarization hologram function. Thin and inexpensive.

  A wave plate made of a retardation film that is thinner and cheaper than a single crystal substrate is used as a wave plate, and a wavelength selective aperture limiting element and a polarization hologram element are respectively formed on both surfaces of a single crystal substrate having birefringence. It can be reduced, and by bonding them together, a small and thin wavelength plate having a wavelength selective polarization hologram function can be obtained.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 shows a wavelength-selective polarization hologram element using a retardation film in the first embodiment, wherein (a) is a plan view of the optical element viewed from the upper side in the figure, and (b) is an optical element. Sectional drawing which shows one structural example, (c) is sectional drawing which shows the other structural example of an optical element. As shown in FIG. 1, a polarization hologram layer 107 is formed on the opposite surface of a single-crystal substrate 108 having birefringence, in which a wavelength-selective multilayer film opening limiting layer 106 is formed on one surface, and is adhered to the retardation film 105. Bonding with the agent 104. A single crystal substrate 108 having a wavelength-selective aperture limiting function has a first region 101 that forms a central portion and a second region 102 that surrounds the central portion, and the second region 102 has a concentric circular cross section. Can be made to transmit or diffract light of a specific wavelength. This wavelength-selective aperture limiting function can also be achieved by forming a multilayer aperture limiting layer 109 in the second region 102 as shown in FIG. For this wavelength-selective aperture limiting function, there is no functional problem with either the flat multilayer aperture limiting layer 109 or the concave / convex type (grating type) 106 using the diffraction principle, but the concave / convex type (grating type) with high transmittance. 106 is desirable.

  A polarization hologram layer 107 is formed in a pattern in a lattice shape by proton exchange and phase compensation groove etching on the surface opposite to the surface of the single crystal substrate 108 having the birefringence that constitutes the wavelength selective aperture limiting function. . At this time, the pattern having the wavelength-selective aperture limiting function and the polarization hologram element are formed so as to overlap at the same position. The wavelength plate 105 of the retardation film and the wavelength selective aperture limiting element side of the single crystal substrate 108 having birefringence are bonded together with an adhesive. In order to prevent reflection loss at the adhesive interface between the adhesive 104 and the retardation film 105, it is desirable to use the adhesive 104 having a refractive index substantially the same as the refractive index of the retardation film 105. Further, it is desirable to provide an antireflection film 103 on the surface of the retardation film 105 in contact with the air layer in order to prevent reflection loss. In order to prevent reflection loss at the adhesive interface, it is desirable to design the film so that the refractive index of the adhesive is the same as the final layer of the multilayer film 106 or 108 of the wavelength selective aperture limiting element.

  When the multilayer film 106 exists only in the second region 102 described above, a step is generated between the first region 101 and the retardation film 105 near the boundary between the first region 101 and the second region 102 is not flat and distorted. As a result, the transmitted wavefront aberration is deteriorated, so that it is desirable to form a multilayer film in the first region 101 so as to obtain a predetermined transmittance so as to reduce the unevenness on the bonding surface side as much as possible. As the wave plate, a retardation film having a phase difference by stretching birefringence of a polymer resin such as polyolefin, polycarbonate, polyimide, polyarylate or the like can be used.

  Acrylic, epoxy, urethane, polyester, and polyimide materials can be used as the adhesive material, but it is thermosetting to relieve and suppress internal stress due to expansion and contraction of the retardation film during curing. The UV curable type is more preferable than that.

  By forming the optical element as described above, a thin optical element having the three functions of wavelength selective aperture limiting function, polarization hologram function, and phase difference generation can be configured. In the present embodiment, the number of components of the optical element can be reduced and the size can be reduced by a total of two component configurations including a single crystal substrate having birefringence and a retardation film.

(Embodiment 2)
FIG. 2 shows a wavelength-selective polarization hologram element using the retardation film in the second embodiment, wherein (a) is a plan view of the optical element viewed from the upper side in the figure, and (b) is optical. Sectional drawing which shows one structural example of an element, (c) is sectional drawing which shows the other structural example of an optical element. In FIG. 2, the same components as those in FIG. In FIG. 2, the adhesive surface of a single crystal substrate having birefringence is bonded with a retardation film 105 and an adhesive 104 as a polarization hologram element layer 107 opposite to that in FIG. With the two component configurations of the single crystal substrate 108 having the birefringence and the retardation film 105, the number of components of the optical element can be reduced and the size can be reduced as in the first embodiment.

  The head device shown in FIG. 3 is obtained by incorporating the optical element of Embodiment 1 shown in FIG. 1 into an optical system. In the optical head device of FIG. 3, light is emitted to the wavelength selective prism 306 from a semiconductor laser 309 having a wavelength of 650 nm for DVD discs and a semiconductor laser 308 having a wavelength of 780 nm for CD optical discs. The light emitted from the DVD semiconductor laser 309 passes through the wavelength selective prism 306, becomes parallel light by the condenser lens 305, passes through the polarization hologram layer 107, and passes through the entire wavelength selective multilayer film aperture limiting layer 106. In the retardation film 105, the linearly polarized light is changed to circularly polarized light. Further, a light spot suitable for reproduction of the DVD disk 302 having a substrate thickness of 0.6 mm is formed by the objective lens 303 and reflected from the DVD disk 302 by the circularly polarized light that is reversely rotated by the incident circularly polarized light. The reflected light again passes through the objective lens 303, the circularly polarized light is changed to linearly polarized light by the retardation film 105, the entire surface is transmitted through the wavelength selective multilayer film aperture limiting layer 106, and is diffracted by the polarization hologram layer 107. The light becomes convergent light, passes through the wavelength selective prism 306, and is condensed on the DVD photodetector 310.

  The light emitted from the semiconductor laser 308 for CD is reflected by the wavelength selective prism 306, becomes slightly divergent light by the condenser lens 305, passes through the polarization hologram layer 107, and is opened by the wavelength selective multilayer opening restriction layer 106. The retardation film 105 passes through the restriction. Further, a light spot suitable for reproduction of the CD disk 301 having a substrate thickness of 1.2 mm is formed by the objective lens 303 and reflected by the DVD disk 301. The reflected light again passes through the objective lens 303, passes through the retardation film and the wavelength-selective multilayer opening limiting layer 106, becomes diffracted light at the polarization hologram layer 107, becomes convergent light at the condenser lens 305, and is a wavelength-selective prism. The light passes through 306 and is collected on the CD photodetector 308.

  This example is a specific example of the wavelength selective polarization hologram element (FIG. 1) using the wave plate of the retardation film 105 in the first embodiment. The members, materials, and production methods constituting the optical element will be described below. As the single crystal substrate 108 having a high birefringence, an LN substrate having a thickness of 0.3 mm whose both surfaces were optically polished was used. After patterning into a predetermined shape using photolithography technology on one side of the LN substrate, a polarization hologram layer 107 was formed in a lattice shape by proton exchange and phase compensation groove etching, and an antireflection film 103 was formed on the final surface . The pattern of the polarization hologram layer 107 was determined by the positional relationship (arrangement) between the optical system of the optical head device and the photodetectors 308 and 310. The wavelength selective multilayer film aperture limiting element is patterned using a photolithography technique so as to overlap the pattern of the polarization hologram layer 107 on the LN substrate, and concentric circles having a concavo-convex cross section are formed in the second region 102 as a multilayer film. 106. The thickness of the multilayer film was designed so that light with a wavelength of 650 nm was transmitted and light with a wavelength of 780 nm was diffracted, and the final layer of the multilayer film 106 and the refractive index of the adhesive 104 were the same. As the retardation film, a retardation film having a thickness of 0.12 mm in which an antireflection film 103 was applied on one side of a polyolefin film obtained by stretching a resin sheet was used. The film is formed so as to generate a phase difference of any one of λ / 4, 5 / 4λ, and λ / 2 with respect to transmitted light such as semiconductor laser light. The retardation film 105 and the LN substrate were bonded together with an adhesive 104 so that the surfaces without the antireflection film (the LN substrate was the wavelength-selective aperture limiting element side) became an adhesive surface. An acrylic UV curing type was used as the adhesive, and in order to suppress erosion of the retardation film surface by the adhesive 104, the adhesive was applied and UV irradiation was performed immediately after adjusting the optical axes of both substrates. Finally, the bonded substrate was cut into squares with a dicer so as to have a predetermined size.

  The wavelength-selective polarization separation element using the retardation film wave plate according to the present invention is useful as an optical element used in an optical head device for recording and reproducing information by irradiating light onto an optical recording medium. It is.

1 shows a wavelength-selective polarization hologram element using a retardation film according to Embodiment 1 of the present invention, where (a) is a plan view of the optical element viewed from the upper side in the figure, and (b) is one of the optical elements. Sectional drawing which shows structural example, (c) is sectional drawing which shows the other structural example of an optical element. 1 shows a wavelength-selective polarization hologram element using a retardation film according to Embodiment 2 of the present invention, where (a) is a plan view of the optical element viewed from the upper side in the figure, and (b) is an optical element. Sectional drawing which shows structural example, (c) is sectional drawing which shows the other structural example of an optical element. The figure which shows the example which incorporated the structural example of the optical element of this invention in the optical head apparatus. Sectional drawing which shows one structural example of retardation film The wavelength selective polarization hologram element using the conventional quartz wavelength plate is shown, (a) is the top view which looked at the optical element from the upper side in the figure, (b) is sectional drawing which shows one structural example of an optical element The wavelength selective aperture limiting element using the conventional phase difference film is shown, (a) is sectional drawing which shows one structural example of an optical element, (b) is sectional drawing which shows the other structural example of an optical element. The figure which shows an example which incorporated the optical element using the conventional phase difference film in the optical head apparatus Sectional drawing which shows one structural example of the optical element using the conventional phase difference film

Explanation of symbols

101 First region 102 Second region 103, 503, 604 Antireflection film 104, 403, 504, 602, 805 Adhesive 105, 402, 603, 704, 802 Retardation film 106, 506 Lattice type multilayer film opening restriction layer 107 , 505, 705, 803 Polarization hologram layer 108 Single crystal substrate having birefringence 109 Flat multilayer opening restriction layer 301 CD disc 302 DVD disc 303, 702 Objective lens 304 Wavelength selective polarization using the retardation film of the present invention Hologram element 305 Condensing lens 306 Wavelength selective prism 307 Semiconductor laser for CD 308 Photodetector for CD 309 Semiconductor laser for DVD 310 Photodetector for DVD 401 Fixed transparent substrate 507 LiNbO3 substrate 508 Crystal substrate 601 Has aperture limiting function Transparent substrate 605,703,707,709,710,801,806 transparent substrate 701 the optical disk 708 polarization grating layer 711,804 retarder layer 712 isotropic medium 713 polarizing hologram element 714,807 aperture limit element

Claims (3)

A wavelength-selective aperture limiting element is formed on one surface of a single crystal substrate having high birefringence, and a polarization hologram element is formed on the opposite surface so that the pattern overlaps the element, and a retardation film wave plate is bonded to the retardation film A wavelength-selective polarization hologram element characterized by having a structure bonded together. The wavelength-selective polarization hologram element according to claim 1, wherein the retardation film includes at least one selected from the group consisting of polycarbonate, polyimide, polyarylate, polyethersulfone, polyolefin, polyacrylate, polyetherimide, and polymer liquid crystal. . 2. An optical head device for guiding emitted light from a semiconductor laser to an optical recording medium and guiding reflected light from the optical recording medium to a photodetector, wherein the optical element of claim 1 is an optical path from the semiconductor laser to the optical recording medium. Or an optical head device installed in an optical path from the optical recording medium to the photodetector.

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