JP2009015995A - Liquid crystal diffractive lens element and optical head device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal diffractive lens element which has high efficiency of using light incident with a predetermined wavelength and high reliability thereof, which has a high degree of flexibility in selecting a material, and of which the focal length is easily changed. <P>SOLUTION: A first birefringent material worked so as to have a Fresnel lens shape is disposed on one of mutually facing surfaces of a pair of transparent substrates 101a, 101b, a liquid crystal material 104 is injected in a gap between the transparent substrates, and a voltage is optionally applicable to the liquid crystal material via transparent electrodes 102a, 102b. A second birefringent material worked so as to have a Fresnel lens shape is disposed on one of mutually facing transparent substrates 102b, 102c and an isotropic material 106 is filled in the space therebetween. Alignment directions of the first birefringent material 103a and a surface of the transparent electrode 102b are made perpendicular to each other, and the alignment directions of the first birefringent material 103a and the second birefringent material 103b are made perpendicular to each other. The liquid crystal diffractive lens element makes the incident light travel in straight lines and be transmitted therethrough when no voltage is applied thereto, and makes it diffuse when a voltage is applied thereto so as to change the focal length with the voltage. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is used to record information on an optical recording medium such as a liquid crystal diffractive lens element and an optical disk capable of switching a focal position and / or reproduce information from the optical recording medium (hereinafter referred to as recording / reproduction). The present invention relates to an optical head device using a liquid crystal diffractive lens element.

  2. Description of the Related Art Conventionally, in an optical head device that performs recording and reproduction on an optical recording medium such as an optical disk, information is recorded and reproduced on optical disks having different cover thicknesses such as CD and DVD. In addition, the optical disc includes a single-layer optical disc having a single information recording layer and a multi-layer optical disc having a plurality of layers. For example, when recording / reproducing information with respect to a two-layer optical disc having two recording layers, the depth of the information recording surface for recording information from the optical disc surface (hereinafter simply referred to as the depth of the information recording surface) is different. . In order to perform recording and reproduction on optical discs having different information recording surface depths as described above, a light modulation element for switching the focal length is used (for example, see Patent Document 1).

  Here, the light modulation element disclosed in Patent Document 1 includes a pair of transparent substrates 501a and 501b as shown in FIG. 7, and a birefringent material 503a having a Fresnel lens shape on the opposing surfaces of these transparent substrates, respectively. Transparent electrodes 502 a and 502 b are provided so that a voltage can be applied to the liquid crystal material 504 sandwiched between these transparent substrates. By applying a voltage to the liquid crystal, the refractive index of the liquid crystal is switched to switch whether or not the birefringent material functions as a Fresnel lens.

  In a liquid crystal element used in an optical head device, light polarized in a specific direction is usually used as incident light, and the refractive index is switched by matching the alignment direction of the liquid crystal with the polarization direction of the incident light. Done. The refractive index of the liquid crystal is switched so as to be the same as or different from the refractive index of the optical member having the shape of the Fresnel lens before and after switching of the voltage applied to the liquid crystal.

International Publication No. 2006/043516 Pamphlet

  However, the liquid crystal lens diffractive element described in Patent Document 1 has a problem in the orientation of the liquid crystal because the two-sided Fresnel lens-shaped birefringent material in contact with the liquid crystal is subjected to the alignment treatment. In the configuration of Patent Document 1, it is necessary to match the ordinary light refractive index and the extraordinary light refractive index of the liquid crystal material 504 and the birefringent materials 503a and 503b. However, when a polymer liquid crystal that can be easily processed is used as the birefringent material, the combination of the materials that match the ordinary refractive index and the extraordinary refractive index with respect to the liquid crystal material is limited, resulting in a difference in refractive index. As a result, the light utilization efficiency was reduced. Further, in this liquid crystal element, twisted nematic (hereinafter referred to as TN) liquid crystal is put into a cell having a Fresnel lens structure shape on both sides, and therefore, the depth distribution of the Fresnel lens shape causes the output of incident light in the liquid crystal element. There was a problem that the light distribution was large.

  The present invention has been made to solve such problems. A liquid crystal lens diffractive element in which the orientation of liquid crystal is easy, the degree of freedom of material selection is high, and the outgoing light distribution of incident light is stable is provided. The optical head device used is provided.

In order to achieve the above object, the cross-sectional shape provided on any one of the three or more transparent substrates arranged in parallel and the opposing surfaces of the pair of transparent substrates among the transparent substrates is a Fresnel lens shape. A voltage is applied to the first liquid crystal material, the first liquid crystal material filling the space between the first birefringent material and the transparent substrate surface facing the surface of the first birefringent material. A cross-sectional shape provided on one of the opposed surfaces of the pair of transparent substrates, which is different from the opposed surfaces of the electrodes and the pair of transparent substrates having the first birefringent material, is a Fresnel lens shape. A filling material filling a space between the second birefringent material and the surface of the transparent substrate facing the surface of the second birefringent material, and an extraordinary refractive index direction of the first birefringent material; Abnormal refractive index direction of the second birefringent material Is parallel or orthogonal, the first _{n O_B1} the ordinary refractive index of the birefringent material, the extraordinary refractive index of _{n E_B1,} said first liquid crystal material ordinary refractive index of _{n o_LC, n e_LC} the extraordinary refractive index And when
_{n e_LC -n e_B1 = n e_B1 -n} o_LC> 0
_{no_B1} = _{no_LC}
A liquid crystal diffractive lens element composed of a material that substantially satisfies the following equation is provided.

  With this configuration, the function of the Fresnel lens formed of the birefringent material can be expressed or eliminated by switching the alignment direction of the liquid crystal by applying a voltage to the liquid crystal. With this function, the focal length can be switched by applying or not applying a voltage regardless of the polarization state of incident light, and a highly reliable liquid crystal diffractive lens element can be realized. Here, the expression “substantially satisfying the equation” means a value within ± 5% of the error of each refractive index equation, and so on. Further, the refractive index of the birefringent material and the liquid crystal material may be a combination of materials that match the ordinary light refractive index, which is preferable because the degree of freedom of material selection is widened.

Further, the filler material is isotropic material, the refractive index n _s of the isotropic _material, the second the ordinary refractive index of the birefringent material n _{O_B2,} the extraordinary refractive index when the n _{E_B2} ,
_n o_B2 = n _s
Or
_n e_B2 = n _s
The liquid crystal diffractive lens element described above is made of a material that substantially satisfies any of the equations.

  With this configuration, the combination of the second birefringent material and the isotropic material allows diverging light and straight transmitted light or light to be collected regardless of the polarization state of light incident upon application / non-application of voltage to the first liquid crystal material. Since the focal length can be switched between light and straight transmitted light, the degree of freedom in design is increased, which is preferable.

  Further, the first birefringent material and the second birefringent material are the same material, and a Fresnel lens shape made of the first birefringent material and a Fresnel lens shape made of the second birefringent material, The liquid crystal diffractive lens element is provided as described above, wherein

  With this configuration, since two Fresnel lenses formed of a birefringent material have the same function, it is easy to control incident light. Further, the same material and shape are preferable because productivity is improved.

The refractive index of the isotropic material and the ordinary light refractive index of the first liquid crystal material are:
n _s = _{no_LC}
The liquid crystal diffractive lens element described above is made of a material that substantially satisfies the following equation.

  With this configuration, the Fresnel lens function of the second birefringent material can exhibit the lens function or can be transmitted straight through depending on the polarization direction of incident light without applying a voltage. Further, a lens function with good control can be realized by combining the alignment state of the first birefringent material and the first liquid crystal material and the polarization state of incident light.

  The first liquid crystal material on the surface of the first birefringent material and the alignment direction of the first liquid crystal material on the surface of the transparent substrate facing the first birefringent material are orthogonal to each other. A liquid crystal diffractive lens element is provided.

  With this configuration, the alignment direction of the first liquid crystal material is twisted by 90 ° with respect to the thickness direction when no voltage is applied. As a result, the polarization state of linearly polarized light that is incident when no voltage is applied can be changed by 90 ° and emitted. On the other hand, since it is possible to emit light while maintaining the polarization state of incident linearly polarized light when a voltage is applied, control of the expression of the Fresnel lens function can be easily realized by the polarization state.

  The second birefringent material is between the first birefringent material and the second birefringent material, and is different from the opposing surfaces of the pair of transparent substrates having the first birefringent material. A second liquid crystal material that fills the space between the opposing surfaces of the pair of transparent substrates, which is different from the opposing surfaces of the pair of transparent substrates having the birefringent material, and applies a voltage to the second liquid crystal material A liquid crystal diffractive lens element as described above is provided.

  With this configuration, the polarization state of the light emitted from the Fresnel lens made of the first birefringent material is changed by applying a voltage to the second liquid crystal material or not applied to the Fresnel lens made of the second birefringent material. Therefore, the polarization state can be arbitrarily controlled.

  In addition, the optical thickness of the space in which the second liquid crystal material is uniformly aligned and filled with the second liquid crystal material is (2n + 1) · (λ / The liquid crystal diffractive lens element described above (n is an integer) is provided which is substantially equal to 2).

  With this configuration, the light incident on the second liquid crystal material can be made to function as a λ / 2 plate, so that the linearly polarized light emitted from the Fresnel lens made of the first birefringent material can be converted into different linearly polarized light. The lens function of the Fresnel lens made of the second birefringent material can be easily controlled.

  In addition, the first liquid crystal material on the surface of the first birefringent material and the first liquid crystal material on the surface of the transparent substrate facing the first birefringent material are parallel to each other, and the first birefringent material is parallel. The liquid crystal diffractive lens element according to the above, wherein the angle formed by the alignment direction of the first liquid crystal material and the alignment direction of the second liquid crystal material on the surface of the refractive material is approximately 45 °.

  With this configuration, if the light incident on the second liquid crystal material is linearly polarized light parallel to the slow axis or the fast axis, linearly polarized light orthogonal to the incident light is emitted. Therefore, a liquid crystal diffractive lens element that can easily control the polarization state can be realized.

  Furthermore, a light source that emits linearly polarized light of a specific wavelength, an objective lens that condenses the light that emits linearly polarized light on the optical recording medium, and a photodetector that detects reflected light from the optical recording medium, An optical head device for recording / reproducing information on an optical recording medium, wherein the liquid crystal diffractive lens element described above is installed in an optical path between the objective lens and the photodetector. I will provide a.

  With this configuration, by installing any one of the liquid crystal diffractive lens elements, it is possible to realize an optical head device that easily controls the focal length of incident light by applying or not applying a voltage. Recording and reproduction of a multilayered optical disk or the like can be performed with good control.

  The present invention can function the Fresnel lens formed by the first birefringent material and the Fresnel lens formed by the second birefringent material by applying a voltage to the liquid crystal and switching the alignment direction of the liquid crystal. By utilizing this function, it is possible to realize a liquid crystal diffractive lens element and an optical head device that can switch the focal length of incident light when a voltage is applied and when a voltage is not applied.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 shows a sectional view of a liquid crystal diffractive lens element according to a first embodiment of the present invention. In order to simplify the description, a portion sandwiched between the transparent substrate 101a and the transparent substrate 101b is a liquid crystal diffraction lens 11, and a portion sandwiched between the transparent substrate 101b and the transparent substrate 101c is a birefringent diffraction lens. 12

  The liquid crystal diffractive lens 11 is provided on the first liquid crystal material 104 sandwiched between the transparent substrates 101a and 101b, the transparent electrodes 102a and 102b for applying a voltage to the first liquid crystal material 104, and the transparent substrate 101a side. It is made of a first birefringent material 103 a having a Fresnel lens shape and is sealed by a sealing material 105. The transparent electrode only needs to be able to apply a voltage to the liquid crystal in the Z-axis direction, and may be provided on the Fresnel lens-shaped surface of the first birefringent material 103a. It is preferable to provide it on the surface of the transparent substrate 101a from the viewpoint of properties.

  The first liquid crystal material 104 and the first birefringent material 103a having refractive index anisotropy each have an alignment direction. In particular, the liquid crystal material 104 is aligned by an alignment film (not shown). There are liquid crystal materials in which the major axis direction of the liquid crystal molecules is the slow axis, and the major axis direction of the liquid crystal molecules is the fast axis. It demonstrates as what uses the liquid crystal material which becomes. That is, the liquid crystal molecules have a characteristic that the alignment direction of the liquid crystal molecules coincides with the slow axis. Further, even when a liquid crystal material whose major axis direction is a fast axis is used, the same characteristics can be obtained by adjusting the orientation state only by the alignment direction of liquid crystal molecules being a fast axis.

  The birefringent diffraction lens 12 is filled with a Fresnel lens-shaped second birefringent material 103b provided on the surface side of the transparent substrate 101b, which is different from the transparent electrode 102b, and is flattened with the filling material 106 and sandwiched between the transparent substrates 101b and 101c. And is sealed with a sealing material 105. The filler material 106 is described as an isotropic material below, but a birefringent material may be used. In this case, either the ordinary light refractive index or the extraordinary light refractive index of the birefringent material serving as the filling material is appropriately matched with either the ordinary light refractive index or the extraordinary light refractive index of the second birefringent material 103b. It can be realized by designing to.

  The orientation directions of the liquid crystal molecules are shown in 15a, 15b and 15c. The alignment direction of the first birefringent material 103a and the alignment direction of the first liquid crystal material 104 on the surface of the Fresnel lens shape are the X axis direction, but the alignment direction of the first liquid crystal material in contact with the transparent electrode 102b is the Y axis. Direction. That is, as shown by 15b, the first liquid crystal material 104 has a twist angle of 90 ° in the thickness direction (Z-axis). The orientation direction of the second birefringent material 103b is the Y-axis direction.

  A voltage is applied to the transparent electrodes 102a and 102b by an external signal source. FIG. 2 is a cross-sectional view of the liquid crystal diffractive lens 11 of FIG. 1 developed in the XY plane. As wiring for connecting the transparent electrodes 102a and 102b and the external signal source 17, a flexible circuit board may be used. In this case, on the liquid crystal diffraction lens 11 side, the flexible circuit board is connected to the terminal extraction portion 110a of the transparent electrodes 102a and 102b. , 110b.

  Here, for example, an acrylic resin, an epoxy resin, a vinyl chloride resin, a polycarbonate, or the like may be used as the transparent substrates 101a and 101b, but a glass substrate is preferable in terms of durability.

As the transparent electrodes 102a and 102b, a metal film made of Au, Al or the like can be used. However, using a film made of ITO, SnO ₃ or the like has better light transmission and mechanical durability than the metal film. It is suitable because of its excellent properties. An external signal source 17 is connected to the transparent electrodes 102 a and 102 b so that a predetermined signal is applied to the first liquid crystal material 104. The applied voltage signal is preferably a rectangular AC signal, and the frequency of the rectangular AC signal is preferably 10 Hz to 10 kHz. Further, it is extremely preferable to sufficiently reduce the direct current component in the rectangular alternating current signal.

  The first birefringent material 103a and the second birefringent material 103b may be made of different materials as long as the light divergence and condensing functions of the Fresnel lens described later are of the same level. These birefringent materials may be the same and are preferable from the viewpoint of productivity. Further, the position of the Fresnel lens may not be formed on the surface shown in FIG. 1, and may be formed on the transparent electrode 102b or the transparent substrate 101c. In this case, the condensing characteristic and the diverging characteristic of the incident light are emitted differently depending on the surface forming the Fresnel lens. For example, when light incident on the liquid crystal diffractive lens element 10 is linearly transmitted when no voltage is applied, the liquid crystal diffractive lens 11 diverges (condenses) and the birefringent diffractive lens 12 condenses (diverges). Can do. Also, even if the first birefringent material 103a and the second birefringent material 103b are different materials, the same divergence and condensing characteristics can be obtained by designing the Fresnel lens shape depth to match the material. Can be.

  Hereinafter, for the sake of simplicity, the first birefringent material 103a and the second birefringent material 103b will be described as the same material. The Fresnel lens shape is formed concentrically around the optical axis that is the intersection of the X axis and the Y axis in FIG. Here, as the birefringent material, an inorganic material such as lithium niobate or quartz, a polymer liquid crystal, or the like can be used. The use of a polymer liquid crystal as the above-mentioned birefringent material is preferable from the viewpoint of ease of processing, adjustment of the refractive index, and high design freedom due to many variations of the polymer liquid crystal. .

  Further, each of the above-mentioned wheels forming the Fresnel lens is blazed in order to increase the diffraction efficiency. In addition, what approximated the cross-sectional shape which makes the cross section the surface containing the center axis | shaft of said braid | blade by step shape (henceforth a pseudo blazed wheel) may be used instead of said blazed wheel. Hereinafter, the term “blazed wheel” includes a pseudo-blazed wheel.

  The blaze wheel may be a convex blaze wheel protruding from the substrate surface or a concave blaze wheel recessed from the substrate surface. Hereinafter, the shape of the Fresnel lens will be described with reference to FIG. The curves indicated by reference signs P1 and P2 in FIG. 6 include the optical axis of the difference distribution (hereinafter referred to as phase shift distribution) of the phase change amount received by the incident light after passing through the predetermined lens. In-plane. Hereinafter, a curve indicated by using symbols P1 and P2 is referred to as an optical axis phase shift curve.

  Here, the difference distribution (phase shift distribution) of the phase change amount is obtained by subtracting the phase change amount on the optical axis from the distribution of the phase change amount after passing through the lens. The phase shift distribution is substantially rotationally symmetric with respect to the optical axis and has a distribution that switches the focus of incident light. Here, the optical axis phase shift curves indicated by reference signs P1 and P2 correspond to the optical axis phase shift curves of the convex lens and the concave lens, respectively.

Here, the phase shift distribution is represented by the following power series.
φ (r) = a ₁ r ² + a ₂ r ⁴ + a ₃ r ⁶ + a ₄ r ⁸ +...
Here, r is a radial distance from the optical axis, a _i (i = 1, 2, 3, 4,...) Is a constant, and φ (r) is a phase shift distribution at the distance r. is there.

  The phase shift distribution in the plane including the optical axis of the light after passing through each Fresnel lens is an optical axis phase shift curve indicated by reference signs F1 (corresponding to P1) and F2 (corresponding to P2). Since the light does not substantially change due to the phase difference of an integral multiple of the wavelength, each Fresnel lens is equivalent to the phase shift distribution having one of the optical axis phase shift curves indicated by reference signs P1 and P2. , Change the phase of the incident light. Hereinafter, the phase shift distribution having the optical axis phase shift curve indicated by reference signs F1 and F2 is simply referred to as “phase shift distribution indicated by reference signs F1 and F2.” Since the Fresnel lens is well known, further specific description is omitted.

  Each blaze wheel constituting each Fresnel lens has a radial width and a thickness in the optical axis direction in which a phase shift distribution indicated by reference numerals F1 and F2 is obtained. The thickness of each blaze ring in the optical axis direction is determined according to the birefringent material used. In the example shown in FIG. 6, the maximum thickness of each blaze wheel in the optical axis direction is set so that the optical path difference is a maximum of one wavelength. Note that it is preferable that the first birefringent material and the second birefringent material are the same and the Fresnel lens shapes are the same because the focal length can be switched at the same magnification.

  The formation of each blaze ring may be performed by using a photolithography technique and an etching technique, by using a mold, or by another method.

  The alignment of the first liquid crystal material 104 is performed by irradiating a chemical substance having a photoreactive functional group with a surface rubbed with an alignment film such as polyimide or polyvinyl alcohol (PVA), UV light polarized in a specific direction, or the like. The liquid crystal 104 can be set by bringing a surface obtained by obliquely vapor-depositing SiO or the like, a surface obtained by irradiating diamond-like carbon or the like with an ion beam, and the like.

  Note that the first birefringent material 103a is formed using a polymer liquid crystal to form a Fresnel lens, and the first liquid crystal material 104 is aligned using the alignment of the surface molecules of the polymer liquid crystal. This is suitable because an alignment treatment using is unnecessary. In addition, it is preferable that the alignment direction of the first liquid crystal material 104 coincides with the slow axis of the first birefringent material 103 a in contact with the first liquid crystal material 104.

It is preferable to provide an insulating film between the opposing transparent electrodes 102a and 102b to prevent a short circuit. For the formation of the insulating film, a vacuum film formation method such as sputtering using an inorganic material such as SiO ₂ , ZrO ₂ , or TiO ₂ , a chemical film formation method using a sol-gel method, or the like can be used.

  The sealing material 105 is for preventing the first liquid crystal material 104 from leaking between the transparent substrates 101a and 101b, and is provided on the outer periphery of the optically effective area to be secured. As a material for the sealing material 105, a resin adhesive such as epoxy and acrylic is preferable for handling, but it may be cured by heating or irradiation with UV light. Further, in order to obtain a desired cell interval, a spacer such as glass fiber may be mixed in a few percent.

  It should be noted that providing an antireflection film on the substrate surface facing the first liquid crystal material 104 side or the isotropic material 106 out of the substrate surfaces of the transparent substrates 101a and 101c improves the light utilization efficiency. This is preferable because it will improve. As such an antireflection film, a dielectric multilayer film, a wavelength order thin film, or the like can be used, but other films may be used. These films can be formed by vapor deposition or sputtering, but may be formed by other methods.

Further, hereinafter, the Fresnel lens shape formed by using the first birefringent material 103a and the second birefringent material 103b as the same material is also assumed to be the same. Further, the first birefringent material 103a and the second birefringent material 103b of the same material are simply referred to as “birefringent materials”. As the refractive index characteristics of these materials, the ordinary refractive index of the birefringent material in the wavelength band of incident light (for example, 405 ± 20 nm) is _{no_B} , the extraordinary refractive index is _{ne_B} , and the ordinary refractive index of the first liquid crystal material. when the rate _{n o_LC,} the extraordinary refractive index _{n e_LC,} the refractive index of the isotropic material and _{n s,
n e_LC -n e_B = n e_B -n} o_LC> 0 ··· (1)
_{no_B} = _{no_LC} = n _s (2)
By substantially satisfying the above equation, the lens function described later can be effectively operated.

  Hereinafter, the operation when linearly polarized light enters the liquid crystal diffractive lens element 10 in the traveling direction of 100 in the X-axis direction or the Y-axis direction will be described with reference to FIG.

(No voltage applied, linearly polarized light incident in the X-axis direction)
At this time, as shown in 15b, the first liquid crystal material 104 is oriented along the X axis on the Fresnel lens surface, while being oriented along the Y axis on the opposing transparent electrode 102b and twisted by 90 ° in the liquid crystal material layer. . In addition, the orientation direction of the birefringent material is the direction of 15a and 15c. When X-axis linearly polarized light travels in the Z-axis direction and enters the liquid crystal diffractive lens 11 as indicated by 100, both the first liquid crystal material 104 and the birefringent material 103a are aligned in the X-axis direction. It is the direction of the optical refractive index, and the light that has entered straight on the optical axis parallel to the Z axis by the action of the Fresnel lens from the relationship of _{ne_LC} > _{ne_B} travels as condensed light.

Since the first liquid crystal material 104 is twisted by 90 ° in the liquid crystal layer, the polarization state of the incident light is rotated by 90 °, and the condensed light becomes linearly polarized light in the Y direction. Light emitted from the liquid crystal diffraction lens 11 is incident on the birefringent lens 12, birefringent material 103b is the direction of extraordinary refractive index because it is oriented to the Y-axis, Fresnel the relationship of _{n e_B>} n _s Light that is condensed and incident by the action of the lens travels as diverging light.

  Here, from the equations (1) and (2), the condensing action of the liquid crystal diffractive lens 11 and the diverging action of the birefringent lens 12 cancel each other, and as a result, linearly polarized light in the X direction when no voltage is applied. Is incident on the liquid crystal diffractive lens element 10, it passes straight through.

(Voltage applied, linearly polarized light incident in the X-axis direction)
When a voltage is applied to the first liquid crystal material 104, the first liquid crystal material 104 twisted in the alignment direction 15b is aligned substantially parallel to the Z-axis that is the electric field direction. When X-axis linearly polarized light travels in the Z-axis direction and enters the liquid crystal diffraction lens 11 as indicated by 100, the birefringent material 103a is an extraordinary refractive index in the X-axis direction, and the first liquid crystal material 104 is in the Z-axis direction. Since it is oriented, it is an ordinary refractive index, and light that has entered straight from the action of the Fresnel lens from the relationship of _{ne_B} > _{no_LC} proceeds as diverging X-axis linearly polarized light.

Light emitted from the liquid crystal diffraction lens 11, is incident with linearly polarized light of the X axis to the birefringent diffraction lens 12, birefringent material 103b is the direction of the ordinary light refractive index, Fresnel from the relationship _n o_B ₌ n _s The light is transmitted without diverging the light.

(No voltage applied, linearly polarized light incident in the Y-axis direction)
At this time, since the first liquid crystal material 104 in contact with the Fresnel lens shape made of the birefringent material 103a and the birefringent material 103a is oriented along the X axis as shown by 15b, even if light in the Y axis direction enters. It becomes an ordinary light refractive index mutually. _{Due to} the relationship of _{no_B} = _{no_LC,} the liquid crystal diffractive lens 11 passes straight without acting as a Fresnel lens, and the alignment direction of the first liquid crystal material 104 is twisted by 90 ° in the thickness direction as in 15b. Therefore, the polarization state is emitted as linearly polarized light in the X-axis direction.

The light incident on the birefringent lens 12 in the polarization state of the X axis becomes the ordinary refractive index in the birefringent material 103b of the Fresnel lens shape, isotropic material 106 also causes the Fresnel lens functions from the relationship _n o_B ₌ n _s Without going straight.

(Voltage applied, linearly polarized light incident in the Y-axis direction)
When a voltage is applied to the first liquid crystal material 104, the first liquid crystal material 104 twisted in the alignment direction 15b is aligned substantially parallel to the Z-axis that is the electric field direction. When Y-axis linearly polarized light travels in the Z-axis direction and enters the liquid crystal diffraction lens 11 as indicated by 100, the birefringent material 103a is aligned with the ordinary refractive index in the Y-axis direction, and the first liquid crystal material 104 is aligned in the Z-axis direction. Accordingly, the refractive index is ordinary light, and the liquid crystal diffractive lens 11 passes straight without acting as a Fresnel lens _because of the relationship of n _{o_B} = _{no_LC} . Further, the polarization state of the light emitted from the liquid crystal diffractive lens 11 remains in the Y-axis direction.

Light emitted from the liquid crystal diffraction lens 11, is incident with linearly polarized light of the Y-axis birefringent lens 12, birefringent material 103b is extraordinary refractive index, the relation of _{n e_B>} n _s of the Fresnel lens The incident light due to the action diverges and exits.

  As described above, in the first embodiment, the liquid crystal diffractive lens element 10 is not limited to the liquid crystal diffractive lens element 10 as long as the optical axis is Z-axis light when no voltage is applied to the first liquid crystal material 104. Go straight on. On the other hand, when a voltage is applied, Fresnel lens action is generated by the Fresnel lens-shaped birefringent materials 103a and 103b, and the light is emitted as divergent light.

(Second Embodiment)
FIG. 3A shows a cross-sectional view of a liquid crystal diffractive lens element 20 according to the second embodiment of the present invention. In order to simplify the explanation, the portion sandwiched between the transparent substrate 201a and the transparent substrate 201b is the liquid crystal diffraction lens 21, and the portion sandwiched between the transparent substrate 201b and the transparent substrate 201c is the liquid crystal phase modulation element 22. A portion sandwiched between the transparent substrate 201c and the transparent substrate 201d is referred to as a birefringent diffraction lens 23.

  The liquid crystal diffractive lens 21 is provided on the first liquid crystal material 204a sandwiched between the transparent substrates 201a and 201b, the transparent electrodes 202a and 202b for applying a voltage to the first liquid crystal material 204a, and the transparent substrate 201a side. It is made of a birefringent material 203 a having a Fresnel lens shape, and is sealed by a sealing material 205. The transparent electrode only needs to be able to apply a voltage to the first liquid crystal material 204a in the Z-axis direction, and may be provided on a Fresnel lens-shaped surface made of the birefringent material 203a. It is preferable to provide it on the surface of the transparent substrate 201a from the viewpoint of reliability and reliability.

  The first liquid crystal material 204a and the birefringent material 203a having refractive index anisotropy each have an alignment direction. In particular, the first liquid crystal material 204a is aligned by an alignment film (not shown). In the layers of the birefringent material 203a and the first liquid crystal material 204a, the alignment direction of the first liquid crystal material 204a on the Fresnel lens surface and the opposing transparent electrode 202b surface is the X-axis direction.

  The liquid crystal phase modulation element 22 includes a second liquid crystal material 204b sandwiched between the transparent substrates 201b and 201c, and transparent electrodes 202c and 202d for applying a voltage to the second liquid crystal material 204b. It is sealed. Although the orientation direction of the second liquid crystal material is also shown in FIG. 3B, it is oriented in a certain direction on the XY plane in the liquid crystal layer, and an angle of 45 ° with respect to the X-axis direction for the reason described later. I am doing. The transparent electrode only needs to be able to apply a voltage in the Z-axis direction to the first liquid crystal material 204a. The second liquid crystal material 204b may be the same as or different from the first liquid crystal material 204a. The wavelength of the incident light is λ, and the material of the liquid crystal layer and the liquid crystal layer function as a λ / 2 plate when no voltage is applied. What is necessary is just to set thickness.

  The birefringent diffractive lens 23 fills and flattens the Fresnel lens-shaped second birefringent material 203b provided on the surface side of the transparent substrate 201c different from the transparent electrode 202d with the isotropic material 206, and transparent substrates 201c and 201d. And is sealed with a sealing material 205.

  Settings relating to each material and Fresnel lens shape in the second embodiment are the same as the conditions of the first embodiment. The external signal source 27 may supply a voltage to the liquid crystal diffractive lens 21 and the liquid crystal phase modulation element 22 in common, or may be supplied by separate signal sources.

  Hereinafter, an operation when linearly polarized light enters the liquid crystal diffractive lens element 20 in the traveling direction of 200 in the X-axis direction or the Y-axis direction will be described with reference to FIG.

(No voltage applied, linearly polarized light incident in the X-axis direction)
At this time, the first liquid crystal material 204a is oriented along the X axis on the Fresnel lens surface as indicated by 25b, and is similarly oriented along the X axis on the opposing transparent electrode 202b. The second liquid crystal material 204b is oriented at 45 ° with respect to the X-axis direction as indicated by 25c. The birefringent materials 203a and 203b are oriented along the X axis and the Y axis, respectively. When X-axis linearly polarized light travels in the Z-axis direction and enters the liquid crystal diffractive lens 21 as in 200, both the first liquid crystal material 204a and the birefringent material 203a are aligned in the X-axis direction. It is the direction of the optical refractive index, and light that has entered straight along the optical axis parallel to the Z axis due to the action of the Fresnel lens from the relationship of _{ne_LC} > _{ne_B travels in} the same polarization state as condensed light.

  The light emitted from the liquid crystal diffractive lens 21 enters the liquid crystal phase modulation element 22, and the slow axis direction of the second liquid crystal material 204b is at an angle of 45 ° with respect to the X axis direction of the incident light, and λ / Acts as two plates. For this reason, the light passing through the liquid crystal phase modulation element 22 is modulated and emitted as linearly polarized light in the Y-axis direction.

When the light in the Y-axis direction of the linearly polarized light is incident on the birefringent diffraction lens 23, birefringent material 203b is the direction of extraordinary refractive index because it is oriented to the Y-axis, Fresnel the relationship of _{n e_B>} n _s Light that is condensed and incident by the action of the lens travels as diverging light.

  Here, from the equations (1) and (2), the condensing action of the liquid crystal diffractive lens 21 and the diverging action of the birefringent lens 23 cancel each other, and as a result, linearly polarized light in the X direction when no voltage is applied. When the light enters the liquid crystal diffractive lens element 20, it passes through straight.

(Voltage applied, linearly polarized light incident in the X-axis direction)
When a voltage is applied to the first liquid crystal material 204a and the second liquid crystal material 204b, the liquid crystal materials in the alignment directions 25b and 25c are aligned substantially parallel to the Z-axis that is the electric field direction. When X-axis linearly polarized light travels in the Z-axis direction and enters the liquid crystal diffraction lens 21 as indicated by 200, the birefringent material 203a is aligned with the extraordinary refractive index in the X-axis direction, and the liquid crystal material 204a is aligned in the Z-axis direction. Therefore, it is an ordinary refractive index, and light that has entered straight from the action of the Fresnel lens from the relationship of _{ne_B} > _{no_LC} proceeds as divergent X-axis linearly polarized light.

The light emitted from the liquid crystal diffractive lens 21 passes through the liquid crystal phase diffractive element 22 of the second liquid crystal material 204b oriented in the Z axis as it is, and enters the birefringent diffractive lens 23 as X-axis linearly polarized light. In this case, the birefringent material 203b is the direction of the ordinary refractive index, is transmitted as the relationship _n o_B ₌ n _s of light scattered without the action of the Fresnel lens.

(No voltage applied, linearly polarized light incident in the Y-axis direction)
At this time, since the birefringent material 203a and the first liquid crystal material 204a are oriented along the X axis as shown by 25b, they have ordinary refractive indices even when light in the Y axis direction is incident. From the relationship of n _{o_B} = _{no_LC,} the liquid crystal diffractive lens 21 passes straight without acting as a Fresnel lens.

  The light emitted from the liquid crystal diffractive lens 21 enters the liquid crystal phase modulation element 22, and the slow axis direction of the second liquid crystal material 204b is at an angle of 45 ° with respect to the Y axis direction of the incident light, and λ / Acts as two plates. For this reason, the light passing through the liquid crystal phase modulation element 22 is modulated and emitted as linearly polarized light in the X-axis direction.

When linearly polarized light in the X-axis direction is incident on the birefringent diffractive lens 23, the birefringent material 203b is oriented in the Y-axis and thus is in the direction of ordinary light refractive index, and the isotropic material 206 also has _{no_B} = n. _The incident light is transmitted and transmitted as it is because of the relationship _s . Therefore, although the light incident on the liquid crystal diffractive lens element 20 changes its polarization state, it is transmitted without any action of the Fresnel lens.

(Voltage applied, linearly polarized light incident in the Y-axis direction)
When a voltage is applied to the first liquid crystal material 204a and the second liquid crystal material 204b, the liquid crystal materials in the alignment directions 25b and 25c are aligned substantially parallel to the Z-axis that is the electric field direction. When Y-axis linearly polarized light travels in the Z-axis direction and enters the liquid crystal diffractive lens 21 as indicated by 200, the birefringent material 203a is aligned with the ordinary refractive index in the Y-axis direction, and the first liquid crystal material 204a is aligned in the Z-axis direction. Accordingly, the refractive index is ordinary light, and the liquid crystal diffractive lens 21 passes straight without acting as a Fresnel lens _because of the relationship of _{no_B} = _{no_LC} . Further, the polarization state of the light emitted from the liquid crystal diffraction lens 21 remains in the Y-axis direction.

The light emitted from the liquid crystal diffractive lens 21 passes through the liquid crystal phase diffractive element 22 of the second liquid crystal material 204b oriented in the Z axis as it is, and enters the birefringent diffractive lens 23 as Y-axis linearly polarized light. In this case, the birefringent material 203b is the direction of extraordinary refractive index, light entering from the relation _{n e_B>} n _s by the action of the Fresnel lens and emits the divergent.

  As described above, in the second embodiment, the liquid crystal diffractive lens element 20 is in a polarization state if the optical axis is Z-axis light when no voltage is applied to the first liquid crystal material 204a and the second liquid crystal material 204b. Regardless, the liquid crystal diffractive lens element 10 goes straight. On the other hand, when a voltage is applied, Fresnel lens action is generated by the Fresnel lens-shaped birefringent materials 103a and 103b, and the light is emitted as divergent light.

(Third embodiment)
FIG. 4 shows a cross-sectional view of a liquid crystal diffractive lens element 30 according to a third embodiment of the present invention. In order to simplify the description, the portion sandwiched between the transparent substrate 301a and the transparent substrate 301b is the liquid crystal diffraction lens 31, and the portion sandwiched between the transparent substrate 301b and the transparent substrate 301c is the birefringence diffraction lens 32. And

  The liquid crystal diffractive lens 31 is provided on the first liquid crystal material 304 sandwiched between the transparent substrates 301a and 301b, the transparent electrodes 302a and 302b for applying a voltage to the first liquid crystal material 304, and the transparent substrate 301a side. It is made of a first birefringent material 303 a having a Fresnel lens shape, and is sealed by a sealing material 305. The transparent electrode only needs to be able to apply a voltage to the liquid crystal in the Z-axis direction, and may be provided on the Fresnel lens-shaped surface of the birefringent material 303a. To the transparent substrate 301a.

  The first liquid crystal material 304 and the birefringent material 303a having refractive index anisotropy each have an alignment direction. In particular, the liquid crystal material 304 is aligned by an alignment film (not shown). In the layer of the birefringent material 303a and the first liquid crystal material 304, the alignment direction of the first liquid crystal material 304 in contact with the Fresnel lens surface is the X-axis direction, and the alignment direction of the first liquid crystal material 304 in contact with the opposing transparent electrode 302b is This is the direction of the Y axis. That is, as in 35b, the first liquid crystal material 304 has a twist angle of 90 ° in the thickness direction (Z axis).

  The birefringent diffractive lens 32 is filled with an isotropic material 306 to flatten a Fresnel lens-shaped birefringent material 303b provided on the surface of the transparent substrate 301c opposite to the surface of the transparent substrate 301b, which is different from the transparent electrode 302b. It is sandwiched between 301b and 301c and sealed with a sealing material 305. Settings relating to each material and Fresnel lens shape in the third embodiment are the same as the conditions in the first embodiment.

  Hereinafter, an operation when linearly polarized light enters the liquid crystal diffractive lens element 30 in the traveling direction of 200 in the X-axis direction or the Y-axis direction will be described with reference to FIG.

(No voltage applied, linearly polarized light incident in the X-axis direction)
At this time, as shown in 35b, the first liquid crystal material 304 is oriented along the X axis on the Fresnel lens surface, while being oriented along the Y axis on the opposing transparent electrode 302b and twisted by 90 ° in the liquid crystal material layer. . In addition, the orientation direction of the birefringent material is the direction of 35a and 35c. When X-axis linearly polarized light travels in the Z-axis direction and enters the liquid crystal diffractive lens 31 as indicated by 300, both the first liquid crystal material 304 and the birefringent material 303a are aligned in the X-axis direction. It is the direction of the optical refractive index, and the light that has entered straight on the optical axis parallel to the Z axis by the action of the Fresnel lens from the relationship of _{ne_LC} > _{ne_B} travels as condensed light.

Since the first liquid crystal material 304 is twisted by 90 ° in the liquid crystal layer, the polarization state of the incident light is rotated by 90 °, and the condensed light becomes linearly polarized light in the Y direction. The light emitted from the liquid crystal diffraction lens 31 enters the birefringence lens 32. Unlike the first embodiment, the light traveling direction 300 passes through the isotropic material 306 and then passes through the second birefringent material 303b having a Fresnel lens shape. Birefringent material 303b is the direction of extraordinary refractive index because it is oriented to the Y-axis, the light incident to the condenser from the action of the Fresnel lens from the relation of _{n e_B>} n _s is advanced as a divergent light To do.

  Here, from the equations (1) and (2), the condensing action of the liquid crystal diffractive lens 31 and the diverging action of the birefringent lens 32 cancel each other, and as a result, linearly polarized light in the X direction when no voltage is applied. When the light enters the liquid crystal diffractive lens element 30, it passes straight through.

(Voltage applied, linearly polarized light incident in the X-axis direction)
When a voltage is applied to the first liquid crystal material, the first liquid crystal material 304 twisted in the alignment direction 35b is aligned substantially parallel to the Z-axis that is the electric field direction. When X-axis linearly polarized light travels in the Z-axis direction and enters the liquid crystal diffraction lens 31 as indicated by 300, the birefringent material 303a is aligned with the extraordinary light refractive index in the X-axis direction, and the liquid crystal material 304 is aligned in the Z-axis direction. Therefore, it is an ordinary refractive index, and light that has entered straight from the action of the Fresnel lens from the relationship of _{ne_B} > _{no_LC} proceeds as divergent X-axis linearly polarized light.

Light emitted from the liquid crystal diffraction lens 31, is incident with linearly polarized light of the X axis to the birefringent diffraction lens 32, birefringent material 303b is the direction of the ordinary light refractive index, Fresnel from the relationship _n o_B ₌ n _s The light is transmitted without diverging the light.

(No voltage applied, linearly polarized light incident in the Y-axis direction)
At this time, since the first liquid crystal material 304 in contact with the Fresnel lens shape made of the birefringent material 303a and the birefringent material 303a is oriented along the X axis as shown in 35b, even if light in the Y axis direction is incident thereon. It becomes an ordinary light refractive index mutually. _{Due to} the relationship of _{no_B} = _{no_LC,} the liquid crystal diffractive lens 31 passes straight without acting as a Fresnel lens, and the alignment direction of the first liquid crystal material 304 is twisted by 90 ° in the thickness direction as in 35b. Therefore, the polarization state is emitted as linearly polarized light in the X-axis direction.

The light incident on the birefringent lens 32 in the polarization state of the X axis becomes the ordinary refractive index in the birefringent material 303b of the Fresnel lens shape, isotropic material 306 also causes the Fresnel lens functions from the relationship _n o_B ₌ n _s Without going straight.

(Voltage applied, linearly polarized light incident in the Y-axis direction)
When a voltage is applied to the first liquid crystal material 304, the first liquid crystal material 304 twisted in the alignment direction 35b is aligned substantially parallel to the Z-axis that is the electric field direction. When Y-axis linearly polarized light travels in the Z-axis direction and enters the liquid crystal diffractive lens 31 as indicated by 300, the first birefringent material 303a is the ordinary refractive index in the Y-axis direction, and the first liquid crystal material 304 is the Z-axis. Since it is oriented in the direction, it is an ordinary refractive index, and the liquid crystal diffractive lens 31 passes straight without acting as a Fresnel lens _because of the relationship of _{no_B} = _{no_LC} . Further, the polarization state of the light emitted from the liquid crystal diffractive lens 31 remains in the Y-axis direction.

Unlike the first embodiment, the light emitted from the liquid crystal diffraction lens 31 passes through the isotropic material 306 in the light traveling direction 300 and then passes through the second birefringent material 303b having a Fresnel lens shape. Birefringent material 303b is the direction of extraordinary refractive index because it is oriented to the Y-axis, the light incident to the condenser from the action of the Fresnel lens from the relation of _{n e_B>} n _s is advanced as a divergent light To do.

  As described above, in the third embodiment, the liquid crystal diffractive lens element 30 is not limited to the liquid crystal diffractive lens element 10 as long as the optical axis is Z-axis light when no voltage is applied to the first liquid crystal material 304. Go straight on. On the other hand, when a voltage is applied, Fresnel lens action occurs in the Fresnel lens-shaped birefringent materials 303a and 303b, and thus the light is emitted as divergent light.

Further, in the schematic cross-sectional view of FIG. 4 according to the third embodiment, the refractive index of the isotropic material 306 is n _s = _{ne_B2} , and the orientation direction 35c of the birefringent material 303b is the Y-axis direction. A case where the conditions are the same will be described. At this time, when no voltage is applied, linearly polarized light in the X-axis direction and Y-axis direction is collected, while when applied with voltage, both linearly-polarized light in the X-axis direction and Y-axis direction pass straight through. Therefore, not only switching between transmitted light and diverging light, but also switching between transmitted light and condensed light can be freely designed depending on the positions where these materials and Fresnel lenses are formed.

  Further features of the liquid crystal diffractive lens element and the optical head device of the present invention will be specifically described with reference to the following examples.

Example 1
A method for producing the liquid crystal diffractive lens element 10 of FIG. 1 according to Example 1 of the present invention will be described. First, quartz substrates are used as the transparent substrates 101a and 101b. ITO is used as a material for the transparent electrodes 102a and 102b. The transparent electrode is formed by depositing ITO to a film thickness with a sheet resistance value of about 300Ω / □ by sputtering, and patterning the ITO film using a photolithography technique and a wet etching technique. As the birefringent materials 103a and 103b, polymer liquid crystals having an ordinary light refractive index of 1.55 and an extraordinary light refractive index of 1.72 were used. The Fresnel lens is formed by forming a polymer liquid crystal layer having a film thickness of 1.7 μm on the transparent electrode 102a and aligning it in the X direction in FIG. Similarly, a polymer liquid crystal layer having a film thickness of 1.7 μm is formed on the transparent substrate 103b and is oriented in the Y direction in FIG. The polymer liquid crystal is produced by applying light to the photopolymerizable liquid crystal on the alignment-treated surface to form a polymer, and releasing the polymer.

  As for the formation of the Fresnel lens structure, the polymer liquid crystal is patterned using a photolithography technique and a reactive ion etching technique to form each blaze zone. Here, the wavelength of the light source is set to 405 nm, and the thickness in the optical axis direction of each blaze ring zone is set so as to obtain the phase distribution indicated by F2 in FIG. Next, a polyimide film is formed as an alignment film on the surface of the birefringent material 103a and the surface of the transparent electrode 102b (not shown), and alignment processing is performed in the X-axis direction and the Y-axis direction by a rubbing method, respectively.

  As a material for the sealing material 105, a glass fiber having a diameter of 11 μm is mixed as a spacer in an epoxy resin adhesive, printed on the outer periphery of the optically effective area, and then thermocompression bonded to form a liquid crystal cell having a gap with a substrate gap of 11 μm. Was made. A nematic liquid crystal having an ordinary light refractive index of 1.55, an extraordinary light refractive index of 1.89, and a dielectric anisotropy Δε of 9 was injected into the liquid crystal cell as a first liquid crystal material 104a by vacuum injection. The nematic liquid crystal was added with a chiral material in an amount of 0.1 wt% with respect to the liquid crystal.

  After the first liquid crystal material 104a is injected into the above liquid crystal cell, the liquid crystal diffractive lens element 10 is manufactured by sealing the injection port with an acrylic resin adhesive. Terminal extraction portions 110a and 110b are provided when the transparent electrodes 102a and 102b are formed, and a flexible circuit board is connected to the terminal portions, and an external signal source 17 that generates a rectangular AC wave signal having a frequency of 1 kHz is attached.

Next, the birefringent lens 12 is produced by producing the Fresnel lens-shaped birefringent material 103b in the same manner as described above, and using an isotropic material having a refractive index of 1.55 as a filling material in the same gap as described above. Fill. As the filling material, a UV curable acrylic resin is used, but an organic material such as an epoxy resin or a polyimide resin, an inorganic material film such as SiO ₂ , SiON, TiO ₂ , or Ta ₂ O ₅ , and formed from these materials. You may comprise by the multilayer film etc. which are made.

  Light of the optical axis in the Z-axis direction in FIG. 1 was incident on the liquid crystal diffractive lens element 10 thus manufactured, and the light utilization efficiency in the forward path was investigated. When no voltage is applied, the voltage of the external signal source 17 is 0 Vrms, and the voltage when the voltage is applied is 20 Vrms. About 95% when linearly polarized light in the X-axis direction is incident when no voltage is applied, and about 85% when linearly polarized light in the Y-axis direction is incident. In addition, it becomes about 95% when linearly polarized light in the X-axis direction is incident upon voltage application, and about 85% when linearly polarized light in the Y-axis direction is incident.

(Example 2)
A method of manufacturing the liquid crystal diffractive lens element 20 of FIG. 3 according to Example 2 of the present invention will be described. The liquid crystal diffractive lens 21 and the birefringent lens 23 use the same materials and manufacturing method as in Example 1, but the rubbing direction on the transparent electrode 202b of the liquid crystal diffractive lens 21 is the X-axis orientation. Next, the liquid crystal phase modulation element 22 is similarly manufactured by forming ITO transparent electrodes on the opposing surfaces of the quartz substrates 201b and 201c, which are transparent substrates, and forming a polyimide film (not shown) from the X axis (or Y axis). Alignment treatment is performed by rubbing in a direction forming an angle of 45 °.

  As the sealing material 205 of the liquid crystal phase modulation element 22, a glass fiber having a diameter of 2.2 μm is mixed as a spacer in an epoxy resin adhesive, printed on the outer periphery of the optically effective area, and then subjected to thermocompression bonding to provide a gap 2 between the substrates. A liquid crystal cell of 2 μm is produced. A nematic liquid crystal having an ordinary light refractive index of 1.51, an extraordinary light refractive index of 1.60, and a dielectric anisotropy Δε of 3.8 is injected into the liquid crystal cell as a second liquid crystal material 204b by vacuum injection.

  As in the first embodiment, an external signal source 27 is provided which is provided with a terminal lead-out portion when the transparent electrodes 202a, 202b, 202c and 202d are formed, and a flexible circuit board is connected to the terminal portion to generate a rectangular AC wave signal having a frequency of 1 kHz. Install.

  The light utilization efficiency is investigated by making the light of the optical axis in the Z-axis direction of FIG. 2 incident on the liquid crystal diffractive lens element 20 thus manufactured. When no voltage is applied, the voltage of the external signal source 17 is 0 Vrms, and the voltage when the voltage is applied is 20 Vrms. About 95% when linearly polarized light in the X-axis direction is incident when no voltage is applied, and about 90% when linearly polarized light in the Y-axis direction is incident. In addition, it becomes about 90% when linearly polarized light in the X-axis direction is incident upon application of a voltage, and about 90% when linearly polarized light in the Y-axis direction is incident.

  An example in which these liquid crystal diffractive lens elements are assembled in the optical head device shown in FIG. 5 will be described. The optical head device 40 includes a semiconductor laser 41 that emits a light beam having a wavelength of 405 nm, a polarization beam splitter 42 that transmits or reflects light according to the polarization direction, a collimator lens 43 that converts the incident light beam into substantially parallel light, The liquid crystal diffractive lens element 44, the quarter wave plate 45, the objective lens 46 for condensing the light transmitted through the quarter wave plate on the optical disk 47, and the return light from the optical disk reflected by the polarization beam splitter A cylindrical lens 48 for causing point aberration and a photodetector 49 for detecting return light are provided. The liquid crystal diffractive lens element 44 corresponds to the liquid crystal diffractive lens element 10, 20 or 30.

  The optical disc 47 has a two-layer information recording surface and has 47a and 47b surfaces. Here, the objective lens is set so that the incident light is condensed on the first information recording surface when the incident light passes through the liquid crystal diffraction lens element 44 without acting as a lens. When no voltage is applied to the liquid crystal diffractive lens element 44 (applied voltage is 0 Vrms), the optical head device operates substantially in the same manner as when the liquid crystal diffractive lens element 44 is removed, and incident light is incident on the first information recording surface. Condensed to

  On the other hand, when a voltage of 20 Vrms is applied to the liquid crystal diffractive lens element 44, the light incident on the liquid crystal diffractive lens element 44 is switched in focal length by the liquid crystal diffractive lens element 44 to become divergent light. The liquid crystal diffraction lens element 44, the quarter wavelength plate 45, and the objective lens 46 were set so as to be condensed on the second information recording surface of the optical disk. The return light from the optical disk passes through the objective lens, is converted into linearly polarized light whose polarization direction is 90 degrees different from the incident light by the quarter wavelength plate 45, and the focal length is switched by the liquid crystal diffractive lens element 44 to be transmitted. To do. The light that has passed through the liquid crystal diffractive lens element passes through the collimator lens 33, is reflected by the polarization beam splitter 42, and enters the photodetector 49. Thus, good information recording / reproducing can be efficiently performed on the two information recording layers by switching the voltage to the liquid crystal diffractive lens element.

  The above optical head device has a configuration in which divergent light is applied to the liquid crystal diffractive lens element 44 when a voltage is applied, and linearly transmitted light is applied when no voltage is applied. There is also a configuration of the liquid crystal diffractive lens element 44 that becomes light light, and the like, and it may be designed to focus on the first information recording surface or the second information recording surface according to the respective voltage switching characteristics.

1 is a cross-sectional view showing a conceptual configuration of a liquid crystal diffractive lens element according to a first embodiment of the present invention. Sectional drawing of the Fresnel lens shape part of the liquid-crystal diffractive lens element of this invention. The top view which shows the notional structure of the liquid-crystal diffractive lens element concerning the 2nd Embodiment of this invention. The top view which shows the notional structure of the liquid-crystal diffractive lens element concerning the 3rd Embodiment of this invention. 1 is a diagram showing a conceptual configuration of an optical head device according to an embodiment of the present invention. Explanatory drawing for demonstrating the shape of the birefringent Fresnel lens member which comprises the liquid-crystal diffractive lens element concerning embodiment of this invention. Sectional drawing which shows the notional structure of the conventional liquid-crystal diffractive lens element.

Explanation of symbols

10, 20, 30, 44, 50: liquid crystal diffractive lens elements 11, 21, 31: liquid crystal diffractive lenses 12, 23, 32: birefringent lenses 15a, 25a, 35a: orientation directions 15b, 25b of the first birefringent material 35b: first liquid crystal material alignment direction 25c: second liquid crystal material alignment direction 15c, 25d, 35c: second birefringent material alignment directions 17, 27, 37, 57: external signal source 22: liquid crystal Phase modulation element 40: optical head device 41: semiconductor laser 42: polarization beam splitter 43: collimator lens 45: 1/4 wavelength plate 46: objective lens 47: optical disc 47a: first recording layer 47b: second recording layer 48: cylindrical Lens 49: photodetector 55a, 55c: orientation direction of birefringent material 55b: orientation direction of liquid crystal material 100, 200, 300, 500: incident light (outward path) Traveling direction 101a, 101b, 101c, 201a, 201b, 201c, 201d, 301a, 301b, 301c, 501a, 501b: transparent substrate 102a, 102b, 202a, 302a, 302b, 202b, 202c, 202d, 502a, 502b: transparent electrode 103a, 203a, 303a: first birefringent materials 103b, 203b, 303b: second birefringent materials 104, 204a, 304: first liquid crystal materials 105, 205, 305, 505: sealants 106, 206, 306 : Filling material (isotropic material)
110a, 110b: terminal extraction portion 204b: second liquid crystal material 503a, 503b: birefringent material 504: liquid crystal material

Claims (9)

Three or more transparent substrates arranged in parallel;
A first birefringent material in which a cross-sectional shape provided on any one of the opposing surfaces of the pair of transparent substrates among the transparent substrates is a Fresnel lens shape;
A first liquid crystal material that fills a space between the surface of the first birefringent material and the transparent substrate surface facing the first birefringent material;
An electrode for applying a voltage to the first liquid crystal material;
A cross-sectional shape provided on one of the opposing surfaces of the pair of transparent substrates, which is different from the opposing surfaces of the pair of transparent substrates having the first birefringent material, is a Fresnel lens shape. A birefringent material;
A filling material that fills a space between the surface of the second birefringent material and the transparent substrate surface facing the second birefringent material,
The extraordinary refractive index direction of the first birefringent material and the extraordinary refractive index direction of the second birefringent material are parallel or orthogonal,
When the ordinary refractive index of the first birefringent material is _{no_B1} , the extraordinary refractive index is _{ne_B1} , the ordinary refractive index of the first liquid crystal material is _{no_LC} , and the extraordinary refractive index is _{ne_LC} .
_{n e_LC -n e_B1 = n e_B1 -n} o_LC> 0
_{no_B1} = _{no_LC}
A liquid crystal diffractive lens element composed of a material that substantially satisfies the equation Said filler material is isotropic material, the refractive index n _s of the isotropic _material, the second the ordinary refractive index of the birefringent material n _{O_B2,} the extraordinary refractive index when the n _{E_B2,
n} o_B2 = n _s
Or
_n e_B2 = n _s
The liquid crystal diffractive lens element according to claim 1, wherein the liquid crystal diffractive lens element is made of a material that substantially satisfies any of the equations.   The first birefringent material and the second birefringent material are the same material, and the Fresnel lens shape made of the first birefringent material and the Fresnel lens shape made of the second birefringent material are the same. The liquid crystal diffractive lens element according to claim 1, wherein: The refractive index of the isotropic material and the ordinary light refractive index of the first liquid crystal material are:
n _s = _{no_LC}
4. The liquid crystal diffractive lens element according to claim 2, wherein the liquid crystal diffractive lens element is made of a material that substantially satisfies the following equation.   The first liquid crystal material on the surface of the first birefringent material and the alignment direction of the first liquid crystal material on the surface of the transparent substrate facing the first birefringent material are orthogonal to each other. The liquid crystal diffractive lens element according to claim 1. The first birefringent material and the second birefringent material, and different from the opposing surfaces of the pair of transparent substrates having the first birefringent material;
A second liquid crystal material that fills the space between the opposing surfaces of the pair of transparent substrates, which is different from the opposing surfaces of the pair of transparent substrates having the second birefringent material,
The liquid crystal diffractive lens element according to claim 1, further comprising an electrode that applies a voltage to the second liquid crystal material.   The optical thickness of the space in which the second liquid crystal material is uniformly aligned and filled with the second liquid crystal material is (2n + 1) · (λ / 2) with respect to the incident light of wavelength λ. The liquid crystal diffractive lens element according to claim 6, wherein n is an integer. The alignment directions of the first liquid crystal material on the surface of the first birefringent material and the first liquid crystal material on the surface of the transparent substrate facing the first birefringent material are parallel,
The liquid crystal diffractive lens element according to claim 7, wherein an angle formed by an alignment direction of the first liquid crystal material and an alignment direction of the second liquid crystal material on the surface of the first birefringent material is approximately 45 °.   Optical recording comprising a light source that emits linearly polarized light of a specific wavelength, an objective lens that condenses the light that emits linearly polarized light on the optical recording medium, and a photodetector that detects the reflected light from the optical recording medium An optical head device for recording / reproducing information on a medium, wherein the liquid crystal diffractive lens element according to any one of claims 1 to 8 is provided in an optical path between the objective lens and the photodetector. Installed optical head device.

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