CN100492505C - Liquid crystal lens element and optical head device - Google Patents

Abstract

The present invention provides liquid crystal lens element comprising no movable part, having a small size, having a lens function capable of being subjected to stable spherical aberration correction including the power component corresponding to the focus variation of the incident light. The liquid crystal lens element has a variable focal length to the light transmitted through a liquid crystal(16) interposed between a pair of transparent substrates(11, 12). The variable focal length can be varied with the voltage applied to the liquid crystal(16). The liquid crystal lens comprises transparent electrodes(13, 14) provided to the respective transparent substrates(11, 12) and used to apply a voltage to the liquid crystal(16) and an irregular part(17) which has a serrated cross section and a rotational symmetry with respect to the optical axis and is formed of a transparent material on one side of the transparent electrode(13). The liquid crystal(16) is placed at least in the recesses of the irregular part(17) so as to vary the substantial index of refraction of the liquid crystal(16) depending on the applied voltage.

Description

Liquid crystal lens element and optical head device

technical field

The present invention relates to a liquid crystal lens element and an optical head device, in particular to a liquid crystal lens that can be switched to a plurality of different focal lengths according to the magnitude of the applied voltage, and a device equipped with the liquid crystal lens for recording information on an optical recording medium and/or Replay optical head device.

Background technique

An optical recording medium (hereinafter referred to as an "optical disc") has an information recording layer formed on the light-incident side surface, and a cover layer formed of a transparent resin covering the information recording layer. As such an optical recording medium, the CD CDs and DVDs, etc. In addition, in the optical head device for recording and/or reproducing information on the DVD disc, a semiconductor laser with a wavelength of 660 nm is used as a light source, and an objective lens with an NA (numerical aperture) of 0.6 to 0.65, etc. .

Conventionally, generally used DVD discs (hereinafter referred to as "single-layer discs") have an information recording layer of a single layer and a cover layer thickness of 0.6 mm. However, in recent years, in order to increase the amount of information per optical disc, an optical disc (hereinafter referred to as a "dual-layer optical disc") in which the information recording layer is formed into two layers (reproducible or capable of reproducing and recording) has also been developed. , in the dual-layer optical disc, information recording layers were formed at positions where the thickness of the cover layer on the light incident side was 0.57 mm and 0.63 mm.

In this way, in the case of recording and/or reproducing a double-layer optical disc using an optical head device with an objective lens that is optimally designed for a single-layer optical disc so that the aberration is zero, if the thickness of the cover layer is different, the The difference in thickness results in poor focusing of incident light on the information recording layer by spherical aberration. In particular, in recording-type dual-layer optical disks, the poor focus will reduce the focus power density during recording accordingly, causing a problem of writing errors.

In recent years, in order to further increase the recording density of optical discs, optical discs with a cover layer thickness of 0.1 mm (hereinafter referred to as "optical discs for BD") have also been proposed. In addition, an optical head device for recording information on such an optical disc uses a semiconductor laser emitting laser light having a wavelength of 405 nm as a light source and an objective lens with an NA of 0.85. However, in this case, also in a recording-type dual-layer optical disk, spherical aberration occurs due to a difference in the thickness of the cover layer, and this spherical aberration causes a problem of writing errors.

Conventionally, as a method for correcting the spherical aberration caused by the difference in the thickness of the cover layer of the above-mentioned double-layer optical disc, there is known a method of using a movable lens to form a liquid crystal lens.

(I) For example, in order to correct spherical aberration using a movable lens group, an optical head device 100 for recording and reproducing an optical disc D shown in FIG. 16 has been proposed (for example, refer to Patent Document 1).

Such an optical head device 100 includes first and second movable lens groups 160 and 170 in addition to a light source 110 , various optical systems 120 , a light receiving element 130 , a control circuit 140 , and a modulation/demodulation circuit 150 . In addition, the first movable lens group 160 has a concave lens 161, a convex lens 162, and a driver 163, and the convex lens 162 fixed on the driver 163 is moved along the optical axis direction, so that the magnification of the movable lens group 160 is changed from positive (convex lens) Zoom lens function to change continuously to negative (concave lens).

By arranging such a movable lens group 160 on the optical path of the optical disc D, it is possible to focus incident light incident on an information recording layer (not shown) having a different cover layer thickness of the optical disc D, and to correct spherical aberration including a magnification component.

However, when such a movable lens group 160 is used, a pair of lenses 161 and 162 and an actuator 163 are required, so that the size of the optical head device 100 is increased, and the mechanism design is complicated due to the movement.

(II) In order to correct the spherical aberration caused by the difference in the thickness of the cover layer of the optical disc, an optical head device using the liquid crystal lens 200 shown in FIG. 17 has also been proposed (for example, refer to Patent Document 2).

This liquid crystal lens 200 is the sum of the exponentiation of the substrate 230 on which the transparent electrode 210 and the alignment film 220 are formed on the flat surface and the axis-symmetrical radius r, that is, the following formula

[mathematical formula 1]

S(r)＝α ₁ r ² +α ₂ r ⁴ +α ₃ r ⁶ …(1)

where r ² =x ² +y ²

α ₁ , α ₂ , α ₃ : constants

The transparent electrode 240 and the alignment film 250 are formed on the curved surface of the described surface shape S(r), and the nematic liquid crystal 270 sandwiched between the substrates 260 is formed.

When a voltage is applied between the transparent electrodes 210 and 240, the molecular orientation of the liquid crystal 270 of the liquid crystal lens 200 changes, and the refractive index changes. As a result, the wavefront of the transmitted light changes according to the difference in refractive index between the substrate 260 and the liquid crystal 270 .

Here, the refractive index of the substrate 260 is equal to that of the liquid crystal 270 when no voltage is applied. Therefore, when no voltage is applied, the transmitted wavefront of the incident light does not change.

In addition, if a voltage is applied between the transparent electrodes 210 and 240, a difference Δn in refractive index occurs between the substrate 260 and the liquid crystal 270, and the transmitted light produces a value corresponding to Δn×S(r) (wherein, S(r) refers to the formula (1)) distribution of the difference in optical path length.

Therefore, by processing the surface shape S(r) of the substrate 260 and adjusting the refractive index difference Δn according to the applied voltage, the spherical aberration caused by the difference in cover layer thickness of the optical disc D can be corrected, thereby correcting the aberration.

However, in the case of the liquid crystal lens shown in FIG. 17, since the change in the refractive index of the liquid crystal 270 with respect to the applied voltage is at most about 0.3, in order to generate a large difference in optical path length corresponding to the magnification component that changes the focus of the incident light The distribution of Δn×S(r) must increase the unevenness of S(r). As a result, the layer of the liquid crystal 270 becomes thicker, causing problems of an increase in driving voltage and a slow response.

Therefore, in order to thin the liquid crystal layer, it is more effective to correct only the spherical aberration with the smallest aberration correction amount by removing the magnification component. However, when the surface shape S(r) of the substrate 260 is processed so that only the spherical aberration is corrected, when the optical axis of the objective lens focusing the incident light on the information recording layer of the optical disc is decentered from the optical axis of the liquid crystal lens, a Comatic aberration causes problems such as poor focus on the information recording layer, making recording or reproduction impossible.

(III) Due to finding the substantially lens function that the magnification component corresponding to the change of the focal point of the incident light is also variable without thickening the liquid crystal layer, a liquid crystal diffractive lens 300 shown in FIG. 3).

In this liquid crystal diffractive lens 300 , a transparent electrode 320 is formed on one side of a substrate 310 formed with predetermined zigzag undulations, and a liquid crystal layer 340 is sandwiched between the transparent electrode 320 and the counter electrode 330 . If a voltage is applied between the electrodes 320 and 330, the actual refractive index of the liquid crystal layer 340 changes from the extraordinary refractive index _ne to the ordinary refractive index _no for extraordinary polarized light. Here, the "actual refractive index" means the average refractive index in the thickness direction of the liquid crystal layer.

When the refractive index of the substrate 310 having the sawtooth undulation structure is _n1 , and the wavelength of the incident light is λ, the groove depth d of the sawtooth undulation is formed to satisfy the following relationship:

d=λ/(n _e -n ₁ )

By thus obtaining the maximum diffraction efficiency from the wavelength λ when no voltage is applied, a diffractive lens is formed. In addition, even if the wavelength λ of the incident light changes, the applied voltage can be adjusted so that the maximum diffraction occurs at the wavelength λ.

In the liquid crystal diffractive lens 300 constructed in this way, since it is only required to fill the liquid crystal layer 340 so as to bury the jagged undulating grooves, it is different from using the liquid crystal lens 200 shown in FIG. 17 to correct the spherical aberration including the magnification component. Compared with this type of liquid crystal 270, the liquid crystal layer 340 can be thinned.

However, in this liquid crystal diffractive lens 300, since the transparent electrode 32 is formed on the saw-toothed undulating surface, the transparent electrode 320 is easily disconnected at the edge. In addition, if the liquid crystal layer 340 is thinned, the transparent electrode 320 and the opposite electrode 330 are likely to be short-circuited.

Patent Document 1: JP-A-2003-115127

Patent Document 2: JP-A-5-205282

Patent Document 3: Japanese Unexamined Patent Publication No. 9-189892

The present invention is made in view of the above circumstances, and its object is to provide a liquid crystal lens element that can realize a small-sized element without movable parts, and is a liquid crystal element with a relatively thin liquid crystal layer, and has a liquid crystal element that can respond to an applied voltage. A lens function that corrects spherical aberration including a magnification component corresponding to a stable incident light focus change. In addition, an object of the present invention is to provide an optical pickup device capable of correcting spherical aberration caused by a difference in cover layer thickness in single-layer and double-layer optical discs by using the liquid crystal lens element, and stabilizing recording and/or playback.

Contents of the invention

The present invention is constituted by the following points.

1. A liquid crystal lens element is a variable focal length liquid crystal lens element, wherein it has

a pair of transparent substrates respectively having transparent electrodes;

A voltage applying device for applying a voltage between the respective transparent electrodes of the pair of substrates;

formed of a transparent material and having a saw-toothed cross-sectional shape with rotational symmetry with respect to the optical axis of the liquid crystal lens element or a saw-toothed cross-sectional shape that is approximately stepped, and formed on at least one of the transparent electrodes at the same time bumps; and

the liquid crystal filling at least the concave-convex portion of the concavo-convex portion,

According to the magnitude of the voltage applied between the transparent electrodes by the voltage applying device, the actual refractive index of the liquid crystal changes correspondingly.

According to this structure, the transparent electrode is formed on the flat surface of the transparent substrate, and the concavo-convex portion for correcting the wavefront aberration is formed thereon. As a result, the uniformity of the electric field applied to the liquid crystal layer filled with liquid crystal is good, and stable operation can be obtained in the plane of the liquid crystal lens element. In addition, since the gap between the transparent electrodes can be kept constant, it has a structure in which a short circuit between the electrodes is less likely to occur. In addition, since the liquid crystal is filled in the concave portion of the transparent material having a zigzag cross section or a zigzag cross section approximately in a stair shape, the thickness of the liquid crystal layer can be reduced. As a result, low-voltage drive and high-speed response can be realized. In addition, it is preferable that the above-mentioned concave-convex part is consistent with the height of each convex part and each concave part of the transparent substrate surface, that is, in a saw-toothed cross-sectional shape or a saw-toothed cross-sectional shape approximately stepped, the concave part is relatively The depth of the raised portion is uniform, that is, it is preferably in the shape of a so-called Fresnel lens.

2. The above-mentioned 1. described liquid crystal lens element, described liquid crystal adopts and has ordinary light refractive index n _o and extraordinary light refractive index _ne (here n _o ≠ n _e ), and the actual refractive index of liquid crystal layer is applied according to described A liquid crystal material in which the magnitude of the voltage varies between the values in the range from no to ne, and has the characteristic that the orientation direction of the liquid crystal molecules is aligned along a specific direction in the liquid crystal layer when no voltage is applied, and at the same time, the transparency of the concave-convex part The material is a transparent material having a refractive index n _s at least for incident light of extraordinary optical polarization, and the refractive index n _s is between n _o and _ne (including cases where the value of the refractive index n _s is equal to n _o and ne _e ).

In addition, as long as the transparent material of the concavo-convex portion has a refractive index of ns for the incident light of extraordinary optical polarized light, a birefringent material may be used in addition to a uniform refractive index transparent material.

According to this structure, it was found that the refractive index of the liquid crystal and the transparent material of the concavo-convex portion has a different state and a consistent state according to the magnitude of the applied voltage. This provides a liquid crystal lens element capable of switching between a lens function that changes the transmitted wavefront of incident light to correct spherical aberration including a magnification component, and a function that does not change the transmitted wavefront of incident light. In particular, when the refractive index ns and ne of the concave-convex portion are made to match, the function of the transmission wavefront of the incident light not changing due to no difference in refractive index between the concave-convex portion and the liquid crystal layer when no voltage is applied to the extraordinary optically polarized incident light was found. . In addition, when the refractive index ns and no of the concave-convex part are made to be the same, for ordinary light polarized incident light, it is found that the transmitted wavefront of the incident light does not change due to no difference in refractive index between the concave-convex part and the liquid crystal layer when no voltage is applied. Function. Since the change of the transmission wavefront is substantially independent of the wavelength, a function has been found that the transmission wavefront does not change even when light of multiple wavelength bands such as BD for DVD or CD enters the liquid crystal lens element.

3. above-mentioned 2. described liquid crystal lens element, the refractive index n _s of the transparent material of described concavo-convex part satisfies the relation of following formula 2:

[mathematical formula 2]

|n _e -n _s |≦|n _e -n _o |/2

Simultaneously, the depth d of the concave-convex portion of the concave-convex portion is within the range of the following formula 3 for the wave-in lambda of the light passing through the liquid crystal:

[mathematical formula 3]

(m-0.25)·λ/|n _e -n _s |≦d

≦(m+0.25)·λ/|n _e -n _s | …(2)

In the formula, m=1, 2 or 3.

In addition, as long as the transparent material of the concave-convex portion has a refractive index n _s for the extraordinary light polarized incident light, in addition to a uniform refractive index transparent material, a birefringent material may also be used. That is, the liquid crystal lens element is provided, and the refractive index of the transparent material of the concave-convex part of the liquid crystal lens element satisfies the relationship of the following formula 4:

[mathematical formula 4]

|n _e -n _s |≦|n _e -n _o |/2

At the same time, the depth d of the concave-convex part of the concave-convex part is within the range of the formula (2) with respect to the wavelength λ of the light.

According to this structure, for the diameter polarized incident light having a polarization plane in the molecular orientation direction of the liquid crystal, if the actual refractive index n(V) of the liquid crystal layer and the refraction of the transparent material of the concave-convex part correspondingly changed according to the magnitude of the applied voltage V are set The difference of rate ns is Δn(V)=n(V)-n _s , then the difference Δn(V)·d of the maximum optical path length of the transparent material in the convex part and the liquid crystal in the concave part is substantially in the Varies from +mλ to -mλ. In addition, when Δn(V _o ) = 0, that is, when the refractive index _of the liquid crystal layer is equal to the refractive index n _s of the transparent material of the concave-convex portion, the function of transmitting the incident light does not change.

In addition, a function of switching the magnification component of the transmitted wavefront by the applied voltage before and after it to be positive (convex lens) and negative (concave lens) was also found. By doing so, it is possible to obtain a liquid crystal lens element capable of switching spherical aberration including a focal length, that is, a magnification component, by applying a voltage.

In the case of m=1, when voltages V ₊₁ and V _-1 are applied (V ₊₁ <V ₀ <V _-1 ), Δn(V)·d=+λ and -λ,

In the case of m=2, plus the case of m=1, when applying voltage V ₊₂ , V _-2 (V ₊₂ <V ₊₁ <V ₀ <V _-1 <V _-2 ), Δn( V) d=+2λ and -2λ,

In the case of m=3, plus the case of m=2, when the applied voltage V ₊₃ , V _-3 (V ₊₃ <V ₊₂ <V ₊₁ <V ₀ <V _-1 <V _-2 < V _-3 ), Δn(V)·d=+3λ and -3λ,

That is, a liquid crystal lens element is formed that switches the spherical aberration including the transmitted wavefront, that is, the magnification component, by (2m+1) applied voltage values according to the value of m. In addition, it was also found that there is an amplification factor generation effect at intermediate voltage values.

When the depth d of the concave-convex portion of the concave-convex portion satisfies the formula (2), in order to effectively discover such a function, it is preferable that the resistivity ρ _F of the material of the concave-convex portion is much lower than the resistivity ρ _LC of the liquid crystal layer. Specifically, ρ _F /ρ _LC is preferably equal to or less than 10 ^-5 . As a result, in the voltage applied between the transparent electrodes, the voltage drop in the uneven portion is reduced, and the voltage is efficiently applied to the liquid crystal layer.

In addition, when the resistivity ρ _F of the material of the concave-convex part is not much lower than the resistivity ρ _LC of the liquid crystal layer, for the applied voltage V between the transparent electrodes, a voltage drop in the concave-convex part will occur, effectively applying the voltage on the liquid crystal layer V _LC will decrease.

In the case where the material of the concave-convex part and the liquid crystal layer are regarded as an electrical insulator with high resistivity, the applied voltage V is distributed according to the capacitance C _F of the concave-convex part and the capacitance C _LC of the liquid crystal layer to determine the voltage applied to the liquid crystal layer V _LC . That is, by adjusting the capacitance C _F and C _LC that vary according to the ratio of the thickness of the liquid crystal layer to the thickness of the liquid crystal layer in the zigzag cross-section or the zig-zag cross-section approximately in the shape of a step, it is possible to Correspondingly adjust the average refractive index between the electrodes, that is, the optical path length. As a result, there is an applied voltage V ₀ in which the transmitted wavefront of incident light does not change, or an applied voltage V ₊₁ in which the magnification component of the transmitted wavefront is positive (convex lens), or an applied voltage V +1 is applied where the magnification component of the transmitted wavefront is negative (concave lens). voltage V _-1 . By doing so, it is possible to obtain a liquid crystal lens element capable of switching spherical aberration including a focal length, that is, a magnification component, by applying a voltage.

4. The liquid crystal lens element according to any one of 1. to 3. above, wherein a phase plate whose phase difference between the wavelength λ and the light is an odd multiple of π/2 is integrated.

5. A liquid crystal lens element in which a phase plate is laminated on the liquid crystal lens element described in 1. above.

According to this configuration, the polarization state can also be changed together with the wavefront of transmitted light by using a single liquid crystal lens element that can be miniaturized.

6. To provide a liquid crystal lens element in which two liquid crystal lens elements described in 1. above are stacked and laminated.

According to this configuration, the effect of the liquid crystal lens element is the result of adding the effects of the two liquid crystal lenses to each other. In addition, when the alignment directions of the liquid crystal molecules constituting the respective liquid crystal lens elements are perpendicular to each other, no matter what the polarization state is, there is a lens effect. At the same time, it functions as a liquid crystal lens having different magnifications.

7. A liquid crystal lens element in which a polarizing diffraction grating and a phase plate are stacked in this order on the liquid crystal lens element described in 1. above.

According to this configuration, by using a single liquid crystal lens element that can be miniaturized, the polarization state can also be changed along with the wavefront of the transmitted light, and diffracted light depending on the polarized light can also be generated.

8. Provide an optical head device, having a light source emitting light of wavelength λ, an objective lens for focusing light from the light source onto an optical recording medium, and a spectroscopic mirror for splitting light focused by the objective lens and reflected by the optical recording medium , and a photodetector for detecting said split light, wherein,

In the optical path between the light source and the objective lens, the liquid crystal lens element described in any one of 1. to 4. is provided.

In addition, by using an optical head device having any of the above-mentioned liquid crystal lens elements, since it is possible to correct spherical aberration including a magnification component caused by a difference in cover layer thickness in a single-layer and a double-layer optical disk, even in a liquid crystal lens element A stable aberration correction effect can be obtained even in an eccentric positional relationship with the objective lens, so that an optical head device capable of improving focus on an information recording surface and performing stable recording and/or reproduction can be realized.

9. An optical head device, having a light source of light of emission wavelength λ ₁ and wavelength λ ₂ (where λ ₁ ≠ λ ₂ ), an objective lens focusing the outgoing light from the light source on an optical recording medium, and detecting A photodetector that focuses and utilizes the emitted light reflected by the optical recording medium, wherein, in the optical path between the light source and the objective lens, the liquid crystal lens element described in any one of the above 1. to 4. ,

At the same time, as the light of the wavelength _λ1 and the wavelength _λ2 incident on the liquid crystal lens element, linearly polarized light whose polarization planes are perpendicular to each other is used.

10. The optical head device according to 8. or 9. above, wherein the optical recording medium has a cover layer covering the information layer, and recording and/or reproduction are performed on optical recording media having different thicknesses of the cover layer.

By employing an optical head device having any of the above-mentioned liquid crystal lens elements, it is possible to correct spherical aberration caused by a difference in the thickness of the cover layer of the optical disc for incident light of wavelength _λ1 according to the magnitude of the applied voltage. In addition, it is possible to have a function that does not change the transmission wavefront of the incident light regardless of the magnitude of the applied voltage to the incident light of the wavelength _λ2 . As a result, even when the light of the wavelength _λ1 and the wavelength _λ2 is incident on the liquid crystal lens element, no adverse effect will be produced when recording and/or reproducing the optical disc using the light of the wavelength _λ2 .

According to the present invention, since the uniformity of the electric field applied to the liquid crystal layer is good, stable operation can be obtained in the plane of the liquid crystal lens element, and at the same time, the interval between the transparent electrodes can be kept constant, thus forming a structure that is less likely to cause a short circuit between electrodes. Moreover, since the liquid crystal is filled into the concave portion of the transparent material having a zigzag or approximately stepped zigzag cross-sectional shape, the thickness of the liquid crystal layer can be reduced, thereby realizing low-voltage driving and high-speed response. In other words, it is possible to provide a liquid crystal lens element that has no movable parts and can be miniaturized, and has a lens function capable of stably correcting spherical aberration including magnification according to an applied voltage.

In addition, it is possible to provide an optical head device that can correct the spherical aberration caused by the difference in the thickness of the cover layer in the single-layer and double-layer optical discs by adding the liquid crystal lens element, even in the liquid crystal lens element and the objective lens. Even in the case of eccentricity, stable recording and/or playback can be performed.

Description of drawings

Fig. 1 is a side sectional view showing the configuration of a liquid crystal lens element according to a first embodiment of the present invention.

FIG. 2 is a plan view showing the configuration of the liquid crystal lens element shown in FIG. 1 .

Fig. 3 is a graph showing the difference in the optical path length of the transmitted wavefront generated by the liquid crystal lens. α is a curve representing the difference in optical path length in units of wavelength λ, with the abscissa being the radius r, and β is the difference in wavelength λ subtracted from α. Integer multiples of , as the curve of the difference in optical path length between zero and λ, γ is a curve representing the difference in optical path length symmetrical to the plane with which the difference in optical path length is zero and β.

Fig. 4 is a side view showing the effect of switching the applied voltage to the liquid crystal lens element of the present invention, (A) shows the converged transmission wavefront when the voltage V+1 is applied, and (B) shows the transmission without wavefront change when the voltage Vo is applied The wavefront, (C) represents the divergent transmitted wavefront when the voltage V-1 is applied.

5 is an enlarged cross-sectional view between transparent electrodes in a side view of the liquid crystal lens element of the present invention.

Fig. 6 is a side cross-sectional view showing the configuration of a liquid crystal lens element according to a second embodiment of the present invention in which a phase plate is integrated.

Fig. 7 is a side cross-sectional view showing the configuration of a liquid crystal lens element according to a third embodiment of the present invention in which liquid crystal lens elements are stacked so that the alignment directions of liquid crystal molecules are perpendicular to each other.

Fig. 8 is a side cross-sectional view showing the structure of a liquid crystal lens element according to a fourth embodiment of the present invention in which liquid crystal lens elements having different transmitted wavefronts to be switched are stacked.

Fig. 9 is a side cross-sectional view showing the structure of a liquid crystal lens element according to a fifth embodiment of the present invention in which a phase plate, a polarizing diffraction grating and diffracted light are integrated.

Fig. 10 is a side view showing a configuration example of an optical unit according to the present invention in which a light source and a photodetector are housed in a single unit and a liquid crystal lens element is integrated.

Fig. 11 is a diagram showing the configuration of an optical head device according to a sixth embodiment incorporating the liquid crystal lens element according to the second embodiment of the present invention.

Fig. 12 is a block diagram showing a modified example of the optical head device according to the sixth embodiment incorporating the liquid crystal lens element according to the second embodiment of the present invention.

Fig. 13 is a diagram showing the configuration of an optical head device according to a seventh embodiment incorporating an optical unit integrating a liquid crystal lens element according to a fifth embodiment of the present invention.

Fig. 14 is a graph showing a measurement example in which the focus of the liquid crystal lens element of the present invention is switched by voltage.

Fig. 15 is a graph showing calculated values of wavefront aberrations for DVD discs with different cover layer thicknesses using an optical head device equipped with a liquid crystal lens element of the present invention.

Fig. 16 is a diagram showing the configuration of a conventional optical head device equipped with a movable lens group as a spherical aberration correcting element.

FIG. 17 is a side sectional view showing a conventional liquid crystal lens configuration example.

Fig. 18 is a side view showing an example of the configuration of a conventional liquid crystal diffractive lens.

Label description

1A, 1B, 61 semiconductor laser (light source)

1C Dual wavelength light source

2A, 2B, 2C, 53 Diffraction grating

2C Diffraction grating with wavelength selectivity

3 dichroic prism

4 Beamsplitter

4B Holographic Beamsplitter

5 Collimating lens

6 objective lens

7 Cylindrical lens

8, 8A, 8B, 62 photodetectors

10, 10A, 10B, 10C, 20, 30, 40, 50 LCD lens elements

11, 12, 12A, 12B, 21 transparent substrate

13, 13A, 13B, 14, 14A, 14B transparent electrodes

15, 15A, 15B Sealed

16, 16A, 16B, 16C LCD

17, 17A, 17B, 17C concave and convex part

18, 18A, 18B AC power supply

22 phase plate

51 birefringent diffraction grating

52 Adhesive material layer

60 optical units

63 metal blocks

64 components

70, 80, 90 optical head device

D disc

Detailed ways

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

[First Embodiment]

Next, a configuration example of the liquid crystal lens element 10 according to the first embodiment of the present invention will be described in detail with reference to the sectional view shown in FIG. 1 and the plan view shown in FIG. 2 .

The liquid crystal lens element 10 according to this embodiment has transparent substrates 11 and 12 , transparent electrodes 13 and 14 , a seal 15 , liquid crystal (liquid crystal layer) 16 , concave and convex portions 17 , and an AC power source 18 .

Wherein, the concavo-convex portion 17 is formed with a transparent material, for example, in this embodiment, a uniform refractive index transparent material with a refractive index n _s is formed, and the cross section has a saw-tooth shape or a step-like substantially saw-tooth shape, and in the region of the effective diameter φ has rotational symmetry with respect to the optical axis (Z axis) of the incident light. Here, it is preferable to adopt a Fresnel lens shape in which the depth of the concave-convex portion of the concavo-convex portion is uniform with respect to the depth of the convex portion thereof.

An example of the manufacturing steps of the liquid crystal lens element 10 will be described below.

First, the transparent electrode 13 is formed on one flat surface of the transparent substrate 11 . Then on a flat surface of the transparent electrode 13 (up to the surface in FIG. 1 ), a uniform refractive index transparent material with a refractive index n _s is used to form a concave-convex portion 17 whose cross section is sawtooth-like or substantially sawtooth-like in a stepped shape. .

Next, a transparent electrode 14 is formed, and an adhesive material other than that shown in the figure mixed with the gap control material is printed on the transparent substrate 12 to make a pattern, thereby forming a seal 15, and is overlapped with the aforementioned transparent substrate 11 and bonded by pressure. Make empty cells. Liquid crystal 16 having an ordinary refractive index n _o and an extraordinary refractive index _ne (here n _o ≠ n _e ) is injected from an injection port (not shown) provided in a part of the seal 15, the injection port is sealed, and the liquid crystal 16 is sealed. The liquid crystal 16 is sealed in the cell and is used as the liquid crystal lens element 10 of this embodiment.

In this way, the liquid crystal 16 is filled in at least the concave portion of the concave-convex portion 17, and the transparent electrodes 13 and 14 are applied with a rectangular wave AC voltage using the AC power supply 18. By this, the molecular orientation of the liquid crystal 16 changes, and the actual liquid crystal (layer) 16 The refractive index changes from ne _{to no} . As a result, the difference Δn(V) in the refractive index between the liquid crystal 16 and the concave-convex portion 17 changes according to the magnitude of the applied voltage, and the wavefront of the transmitted light with respect to the incident light changes.

Here, the concavo-convex portion 17 formed by a uniform refractive index transparent material can be organic materials such as ultraviolet curable resin, thermal effect resin, and photosensitive resin, and can also be SiO ₂ or Al ₂ O ₃ or SiOxNy (here, xy represents O and N The proportion of elements) and other inorganic materials. That is, the refractive index n _s of the homogeneous refractive _index transparent material may be any transparent material having an intermediate refractive index value between no and _ne including no _{or ne} .

After the concave-convex part 17 forms a uniform refractive index transparent material layer with a predetermined film thickness on the surface of the transparent electrode 13, it can be processed into a concave-convex shape by photolithography or reactive ion etching, or it can be transformed into a uniform refractive index transparent material layer by using a metal mold. The embossed part is formed.

In addition, in order to obtain a large change in the refractive index difference Δn(V) with respect to the applied voltage, it is preferable that the orientation direction of the liquid crystal molecules of the liquid crystal 16 filled in the concave portion coincides with the direction of the polarization plane of light incident on the liquid crystal lens element 10 . For example, in FIG. 2 , the alignment direction of the liquid crystal molecules (that is, the direction of the extraordinary refractive index ne) is aligned with the X-axis direction, and linearly polarized light having a polarization plane in the X-axis direction is incident.

In order to make the alignment direction of the liquid crystal molecules consistent with the X-axis direction, it is only necessary to apply an alignment material (not shown) such as polyimide on the surface of the transparent electrode 14 and the concave-convex portion 17, and perform rubbing treatment along the X-axis direction after curing. . It is also possible to use polyimide as the material of the concavo-convex part 17, and rub the surface thereof. In addition to the rubbing treatment of polyimide, it is also possible to use a SiO oblique vapor deposition film or a photo-focusing film to align the orientation of the liquid crystal molecules.

In addition, in order to apply a voltage to the transparent electrode 14 through the electrode 141 formed on the transparent substrate 11 side, the conductive metal particles are mixed in the seal 15 in advance, and the sealing pressure is carried out, so that conductivity is found in the thickness direction of the seal. Conducted with electrode 11. The AC power supply 18 is connected to the electrode 131 connected to the electrode 13 and the electrode 141 connected to the transparent electrode 14 , so that a voltage can be applied to the liquid crystal 12 .

Next, the cross-sectional shape of the sawtooth-shaped or stepped substantially saw-tooth-shaped concave-convex portion 17 will be described below. In order to use the liquid crystal lens 10 of the present invention, generate a transmitted wave surface that corrects the spherical aberration caused by the difference in the cover layer thickness of the optical disc, and generate a transmitted wave surface that imparts a positive or negative magnification component at the same time, when the plane wave incident on the liquid crystal lens 10 In the transmitted wavefront of , for the light at the center of the optical axis (coordinate origin: x=y=0), the difference OPD of the optical path length of the light passing through the position of the radius r is described by the power series of the following formula:

[mathematical formula 5]

OPD(r)＝a ₁ r ² +a ₂ r ⁴ +a ₃ r ⁶ +a ₄ r ⁸ + …(3)

In the formula, r ² =x ² +y ²

α ₁ , α ₂ , ...: constants (see [Table 1] described later)

Here, a specific example of a curve in which the abscissa is the radius r and the optical path length difference OPD is expressed in units of incident light wavelength λ is indicated by a symbol α in FIG. 3 .

In the case of coherent incident light of wavelength λ having the same phase, the transmitted wavefronts having a difference in optical path length that is an integer multiple of λ can be regarded as identical. Therefore, the curve β (difference in optical path length) shown by α in FIG. 3 is divided at intervals of wavelength λ, and the curve β representing the difference in optical path length projected on the surface where the difference in optical path length is zero is substantially the same as the curve α. . All the differences in the optical path length shown by the curve β are within λ, and the cross-section becomes sawtooth.

Here, the voltage applied between the transparent electrodes 13 and 14 is effectively applied to the liquid crystal 16 when the volume resistivity ρF/ρLC of the transparent material of the concavo-convex portion 17 is 10 −5 or less.

Hereinafter, the cross-sectional shape of the concavo-convex portion 17 and the operation of the liquid crystal lens element 10 under such a condition that the applied voltage between the transparent electrodes is substantially equal to the applied voltage of the liquid crystal 16 (this is referred to as "Case 1") will be described.

When the voltage V is applied to the transparent electrodes 13 and 14, if the actual refractive index of the liquid crystal (layer) 16 relative to the light of the extraordinary light polarized light is n (V), the concave-convex portion 17 made of a uniform refractive index transparent material The difference with the refractive index of the liquid crystal 16 is Δn(V)=n(V)-n _s .

For example, under the applied voltage V ₊₁ , in order to generate the difference in the optical path length of the transmitted wavefront corresponding to the curve β in FIG.

[mathematical formula 6]

d=λ/Δn(V ₊₁ ) …(4)

In the formula, λ: the wavelength of the incident light

Δn(V ₊₁ ): difference in refractive index (of the concave-convex portion 17 and the liquid crystal 16 ) of the applied voltage V +1 In the formula, the applied voltage V ₊₁ satisfying Δn ₍ V ₊₁ )>0 is assumed.

Here, by changing the applied voltage, the difference Δn in the refractive index is changed. For example:

i At the applied voltage V0 where Δ(V0)=0, the transmission wavefront of the liquid crystal lens element 10 does not change.

Also, ii) at the applied voltage V-1 of Δn(V-1)=-Δn(V+1), a transmitted wavefront with a difference in optical path length shown by the curve r in FIG. 3 occurs. This corresponds to the transmitted wavefront for the difference in optical path length between the plane for which the difference in optical path length is zero and the plane symmetric to the curve β of FIG. 3 .

However, since the refractive index n _s of the uniform refractive index transparent material forming the concave-convex portion 17 is between n 0 and _{n e} including the refractive index value n ₀ or n ₂ (including the value of the refractive index n _s and n ₀ and n _s are equal), so there are voltage values V ₀ and V ₊₁ or V ₋₁ . Therefore, when the refractive index of the liquid crystal 16 is n(V ₊₁ ) and n(V _-1 ), the concavo-convex portion 17 formed of a uniform refractive index transparent material is processed into a zigzag or stepped substantially zigzag cross-sectional shape, The spatial distribution corresponds to the difference in optical path length of the curve β and the curve γ in FIG. 3 .

In the liquid crystal lens element 10 of the present embodiment, if the refractive index n _s of the uniform refractive index transparent material forming the concave-convex portion 17 satisfies the relationship of the following formula:

[mathematical formula 7]

|n _e -n _s |≦|n _e -n _o |/2

Then there must exist a voltage value V ₊₁ <V ₀ <V _-1 that forms the following formula, namely

Δn(V ₀ )=0

Δn(V ₊₁ )=-Δn(V _-1 )>0

Therefore, by switching the applied voltages V ₊₁ , V ₀ , and V _-1 to the AC power source 18 , it is possible to selectively switch between the three types of transmission wavefronts. In addition, if the range of the following formula:

[mathematical formula 8]

|n _s -[(n _o +n _e )/2]|≦(n _e -n _o )/4

Then it can be said that the refractive index n _s of the homogeneous refractive index transparent material is substantially equal to (n _o + _ne )/2.

In addition, when the refractive index _ne of the liquid crystal 16 is not applied, when V ₊₁ and V _-1 are applied, in order to generate a difference in optical path length corresponding to the curve β and the curve γ in FIG. The depth d of is set to the range of the following formula:

[mathematical formula 9]

0.75·[λ/|n _e -n _s |]≦d

≦1.25·[λ/|n _e -n _s |]

This corresponds to the case of m=1 in the formula (2).

Here, under the applied voltages V ₊₁ , V ₀ , V _-1 (here, V ₊₁ <V ₀ <V _-1 ), the plane waves incident on the liquid crystal lens 10 respectively form the The transmitted wavefront shown in (C) exits. That is, depending on the voltage applied to the transparent electrodes 13 and 14 , lens functions corresponding to positive magnification, no magnification, and negative magnification can be obtained.

In addition, at an applied voltage V between the voltage values V _{+ 1} and V ₀ or between the voltage values V ₀ and V _-1 , two types of transmitted wavefronts are generated mainly according to the ratio corresponding to the voltage value V (Fig. 4( The wavefronts shown in A) and (B), or the wavefronts shown in Fig. 4(B) and (C)).

In the above, in the present embodiment under the condition of Case 1, it has been described that the liquid crystal lens element that divides the optical path length difference OPD represented by α in FIG. ) corresponds to the form of m=1), but may also be a form corresponding to the liquid crystal lens element of m=2 or 3 in the formula (2). In this case, it becomes a transmitted wavefront corresponding to the difference OPD in the optical path length divided by the wavelength m·λ (here, m=2 or 3) of α in FIG. 3 .

When the volume resistivity ρ _F of the transparent material of the concave-convex portion 17 is not much lower than the volume resistivity ρ _LC of the liquid crystal 16, according to the relative permittivity ε _F of the transparent material of the concave-convex portion 17 and its film thickness d _F The capacitance C _F of the liquid crystal 16 and the capacitance C _LC depending on the relative permittivity ε _LC of the liquid crystal 16 and its film thickness d _LC distribute the voltage applied between the transparent electrodes 13 and 14 to the concavo-convex portion 17 and the liquid crystal. (Layer) 16.

That is, in an equivalent circuit in which resistors R _F , R _LC and capacitances C _F and C _LC are respectively used for the concavo-convex portion 17 and the liquid crystal (layer) 16 , it is possible to apply a voltage V to the alternating current of the alternating frequency f between the transparent electrodes, The applied voltage V _LC to the liquid crystal (layer) 16 is calculated.

In addition, the volume resistivity ρ _F and ρ _LC of concave-convex portion 17 and liquid crystal 16 are sufficiently large in the following description, and in the equivalent circuit, according to the capacitance _CF and C _LC of concave-convex portion 17 and liquid crystal (layer) 16, the determination of the resistance to concave-convex portion 17 is determined. The voltage distribution between the part 17 and the liquid crystal (layer) 16 is, that is, under the condition that fx R _F ×C _F and f×R _LC ×C _LC are sufficiently smaller than 1 (set it as "Case2"), the concave-convex part 17 The cross-sectional shape and the role of the liquid crystal lens element 10.

FIG. 5 is an enlarged view showing the cross-sectional view of the liquid crystal lens element 10 in which the concave-convex portion 17 between the transparent electrodes 13 and 14 and the liquid crystal 16 are enlarged. In this FIG. 5 , the interval between the transparent electrodes 13 and 14 is assumed to be a constant value G. In FIG. In addition, the film thickness d _F of the concavo-convex portion 17 is distributed from zero to d, and the layer thickness d _LC of the liquid crystal 16 is distributed from G to Gd. Here, d _F +d _LC (=G) is a constant value.

In Case2, with respect to the AC applied voltage V between the transparent electrodes 13 and 14, the ratio V _LC /V of the applied voltage V _LC distributed to the liquid crystal (layer) 16 is represented by the following formula:

[mathematical formula 10]

V _LC /V＝C _F /(C _F +C _LC )

＝L/(L+(ε _LC /ε _F )×(d _F /d _LC )} …(5)

In the formula, ε _LC : relative permittivity of liquid crystal 16

ε _F : Relative permittivity of the concave-convex portion 17

Here, since the film thickness d _F of the concavo-convex portion 17 is distributed from zero to d corresponding to the saw-toothed or approximately stepped saw-toothed cross-sectional shape forming the Fresnel lens, d _F /d _LC is distributed from zero to d to d/(Gd) for distribution. As a result, the applied voltage V _LC to the liquid crystal (layer) 16 is spatially distributed in accordance with the shape of the concavo-convex portion 17 .

In order to effectively apply a voltage to the liquid crystal (layer) 16, it is preferable to use a material for the concavo-convex portion 17 with a large relative permittivity εF, so that the ratio V _LC /V in the formula (5) increases. Since the relative permittivity ε _LC of the liquid crystal (layer) 16 is about 4 or more, it is preferable to use a relative permittivity ε _F of 4 or more.

In addition, since general liquid crystals have anisotropic permittivity, the relative permittivity ε ₁₁ in the direction of the long axis of liquid crystal molecules is different from the relative permittivity ε _L in the direction of the short axis of liquid crystal molecules, so as the voltage is applied, the orientation of the liquid crystal molecules The relative permittivity ε _LC of the liquid crystal (layer) 16 also changes due to the change in the orientation of the liquid crystal molecules. Therefore, in Equation (5), the spatial distribution of the applied voltage V _LC of the liquid crystal (layer) 16 corresponding to the shape of the concavo-convex portion 17 is determined by reflecting the variation of the relative permittivity ε _LC corresponding to V _LC . Since V _LC changes according to d _F , it is expressed as V _LC [d _F ] after that. In addition, V _LC (0) is equal to the applied voltage V between electrodes.

The situation of Case2 is different from Case1, because the voltage V _LC applied to liquid crystal (layer) 16 is different corresponding to the shape of concavo-convex part 17, so the actual refractive index n ( V _LC [d _F ]) will produce a spatial distribution. In Fig. 5, the optical path length between the transparent electrodes 13 and 14 at the film thickness d _F of the concave-convex portion 17 is n _s ×d _F +n _c V _LC [d _F ])×d _LC , compared to no The difference OPD of the optical path length n (V) * G of the Fresnel lens central position (d _F =0) of the concavo-convex portion 17 forms the following formula:

[mathematical formula 11]

OPD＝{n _s ×d _F +n(V _LC [d _F ])×(Gd _F )}

-n(V)×G ...(6)

The film thickness dF is distributed from zero to d, and the difference OPD of the optical path length is distributed according to OPDd from zero to the next work:

[mathematical formula 12]

OPD _d ＝{n _s ×d+n(V _LC [d])×(Gd)}-n(V)×G

＝{n(V _LC [d])-n(V)}×G

-{n(V _LC [d])-n _s }×d

For example, in order to generate the difference in optical path length of the transmitted wavefront corresponding to the curve _β in _FIG . The film thickness d of the portion 17 and the distance G between the transparent electrodes 13 and 14 can be the cross-sectional shape of the concave-convex portion 17 whose film thickness ranges from zero to d.

Here, by changing the applied voltage V, the difference OPD of the optical path length in the formula (6) changes. For example,

i) When the film thickness d _F of the concave-convex portion 17 is distributed from zero to d, there is an applied voltage V ₀ at which the difference OPD of the optical path length in the formula (6) becomes a sufficiently small value with respect to the wavelength λ of incident light. At this time, the transmission wavefront of the liquid crystal lens element 10 does not change. Here, the sufficiently small difference in optical path length OPD is specifically less than or equal to λ/5, preferably less than or equal to λ/10.

In addition, ii) at a voltage V at which the difference in optical path length OPD _d is substantially -λ (that is, from -0.75λ to -1/25λ), the transmitted wavefront of the difference in optical path length shown by the curve γ in FIG. 3 can be generated . This corresponds to the transmitted wavefront for the plane for which the difference in optical path length is zero and the curve β of FIG. 3 for the plane-symmetrical optical path length difference.

Therefore, by switching the applied voltages V ₊₁ , V ₀ , and V _-1 to the AC power source 18 , it is possible to selectively switch between the three types of transmission wavefronts.

Here, under the applied voltages V ₊₁ , V ₀ , and V _-1 , the plane waves incident on the liquid crystal lens 10 form the transmitted wavefronts shown in FIG. 4(A), (B), and (C), respectively. That is, depending on the voltage applied to the transparent electrodes 13 and 14 , lens functions corresponding to positive magnification, no magnification, and negative magnification can be obtained. As in the case of Case 1 condition, except that the liquid crystal lens element that divides the optical path length difference OPD represented by α in FIG _. It is a form of a substantially mλ (m=2 or 3) liquid crystal lens element. In this case, the transmitted wavefront corresponding to the difference OPD of the optical path length divided by the wavelength m·λ (here m=2 or 3) of the curve α in FIG. 3 is formed.

In addition, unlike the case of Case 1, when three types of transmitted wavefronts are generated, the refractive index n _s of the uniform refractive index transparent material of the concave-convex portion 17 may also be substantially equal to the ordinary refractive index n _o or the extraordinary refractive index n of the liquid crystal 16. _e .

For example, when n _s =n ₀ and liquid crystals with a positive anisotropic dielectric constant (Δε=ε _// —ε⊥) are uniformly aligned, if the concave-convex portion 17 is formed so that when no voltage is applied (V ₊₁ =0) the difference in optical path length OPD _d =-(n _e -n _o )×d becomes λ, then in any case of Case1 to Case2, the plane wave of the extraordinary light polarized light incident on the liquid crystal lens 10 is formed as shown in Fig. 4 ( The transmitted wavefront corresponding to the positive magnification shown in A) is emitted. If the applied voltage between the transparent electrodes 13 and 14 is increased, then in the case of Case 1, with a high applied voltage greater than or equal to 10V, the refractive index of the liquid crystal (layer) 16 is close to n _s , and the liquid crystal (layer) 16 can be obtained as shown in FIG. A transmitted wavefront with no magnification is shown, but does not produce a transmitted wavefront equivalent to the negative magnification shown in FIG. 4(C). However, in the case of Case 2, at an applied voltage of 5 V or less, it is possible to generate a transmitted wavefront corresponding to no amplification shown in FIG. 4(B) and a transmitted wavefront corresponding to negative amplification shown in FIG. 4(C). Wave surface.

That is, in Case2, compared with Case1, by selecting the refractive index and relative permittivity of the liquid crystal 16 and the concave-convex portion 17, the film thickness d of the concave-convex portion 17, and the distance G between the transparent electrodes 13 and 14, etc., the photoelectricity of the liquid crystal lens element 10 is improved. The degree of freedom in designing the chemical properties is high, so it is possible to generate low-voltage driving or various transmission wavefronts. In addition, in Case 2, compared with Case 1, since the film thickness d of the concave-convex portion 17 can be reduced, the manufacturing process of film formation and concave-convex processing can be shortened.

In addition, it is preferable to make the refractive index n _s of the concavo-convex portion 17 substantially equal to the ordinary light refractive index n0 of the liquid crystal (layer) 16. In this case, there is an advantage that, regardless of the value of the applied voltage V between the electrodes, for For ordinary polarized light, there is no difference in refractive index between the concavo-convex portion 17 and the liquid crystal (layer) 16, so the transmission wavefront of ordinary polarized light incident on the liquid crystal lens element 10 does not change, and high transmittance can be obtained. That is, when a plurality of light beams are incident on the liquid crystal lens element 10 and it is desired to transmit a specific light beam without causing a change in the wavefront, it only needs to be incident on the liquid crystal lens element 10 as ordinary light polarized light. For example, different wavelengths for DVD and CD are incident, since the magnification switching effect of the liquid crystal lens element 10 is found only for the wavelength for DVD, so as long as it is incident on the liquid crystal lens element 10 as extraordinary light polarized light for DVD, and it is used for CD as Ordinary light polarized light may be incident on the liquid crystal lens element 10 .

In addition, in the present embodiment, for the case of generating the axisymmetric optical path length difference OPD described by the formula (3), its element structure and operation principle are described, but other than the formula (3) The liquid crystal lens element of OPD, which is equivalent to the difference in optical path length, such as coma or astigmatism, which is corrected for axial asymmetry, can also be manufactured by processing concave-convex shapes of transparent materials with uniform refractive index and filling liquid crystals in concave parts according to the same principle. become.

In addition, in this embodiment, the depth d of the concavo-convex portion 17 is set so that the absolute value of the difference OPD of the optical path length generated by the liquid crystal lens element 10 is equal to or less than the wavelength λ of the incident light, and the cross-sectional shape is zigzag. However, when high-speed responsiveness is not required, the concave-convex portion 17 may be processed so that the absolute value of the difference in optical path length OPD becomes equal to or greater than the wavelength λ of the incident light.

In this case, compared with the liquid crystal lens described in Patent Document 2 in the [Background Art] column, since the electrode spacing is constant, the uniformity of the electric field applied to the liquid crystal is good, and the in-plane driving voltage and response speed High uniformity. Similarly, unlike the liquid crystal diffractive lens described in Patent Document 3 in the [Background Art] column, the difference in optical path length changes continuously according to the magnitude of the applied voltage.

In addition, when the absolute value of the optical path length difference OPD to be corrected is equal to or less than the incident light wavelength λ, it is not necessary to form the cross-sectional shape of the concave-convex portion 17 made of a uniform refractive index transparent material in the liquid crystal lens element 10 into a sawtooth shape, and the light The difference in path length changes continuously according to the magnitude of the applied voltage.

In addition, in this embodiment, it is shown that the liquid crystal 16 having a positive anisotropic dielectric constant is used, and the liquid crystal molecules of the liquid crystal 16 are aligned parallel to the surfaces of the substrates 11 and 12 when no voltage is applied, and the The liquid crystal molecules are arranged along the vertical direction of the surfaces of the substrates 11 and 12, but other liquid crystal alignments or liquid crystal materials may also be used. For example, a liquid crystal having a negative anisotropic dielectric constant whose liquid crystal molecules are aligned perpendicular to the substrate surface when no voltage is applied and aligned parallel to the substrate surface according to the applied voltage V can also be used.

In addition, in this embodiment, the material for forming the concavo-convex portion 17 is a uniform refractive index transparent material with a refractive index of _ns , but it is also possible to use a bidirectional polymer liquid crystal such as a polymer liquid crystal whose molecular orientation direction is consistent along a single direction in the substrate plane. Refractive material. In this case, it is best to set the extraordinary refractive index n _s of the birefringent material so that the ordinary refractive index is equal to the ordinary refractive index no of the liquid crystal, and at the same time make the molecular orientation direction of the birefringent material (the extraordinary refractive index direction) is consistent with the alignment direction of the liquid crystal molecules. By employing such a structure, since the liquid crystal and the birefringent material have the same ordinary refractive index for incident light of ordinary polarized light regardless of the magnitude of the applied voltage, the wavefront of transmitted light does not change.

In addition, in the present embodiment, the structure shown is one in which AC voltage is applied to liquid crystal 16 through transparent electrode 13 and transparent electrode 14 which are all electrodes provided on each of the surfaces of transparent substrates 11 and 12 . However, in the present invention, in addition to this, at least one electrode such as the transparent electrode 13 and the transparent electrode 14 may be spatially divided so that different AC voltages can be applied independently. In this way, more diverse spatial distributions of the difference in optical path length OPD can be generated.

Alternatively, the space-divided transparent electrode may be used as a resistive film having a desired resistance, the applied voltage may be distributed in the radial direction, and the voltage applied to the liquid crystal may be distributed obliquely in the radial direction.

[Second Embodiment]

Next, a liquid crystal lens element 20 according to a second embodiment of the present invention will be described with reference to FIG. 6 . In addition, in this embodiment, the same reference numerals are assigned to the same parts as those in the first embodiment, and repeated descriptions are avoided.

The liquid crystal lens element 20 of this embodiment is formed by adding a phase plate 22 and a transparent substrate 21 to the liquid crystal lens element 10 of the first embodiment described above. That is, in this liquid crystal lens element 20 , the phase plate 22 made of a birefringent material is sandwiched between the transparent substrate 12 and the transparent substrate 21 on the surface opposite to the surface on which the transparent electrode 14 is mounted, and is integrally formed.

As the phase plate 22, a birefringent film obtained by stretching an organic film such as polycarbonate and having a slow axis along the stretching direction is used, and is bonded between the transparent substrates 12 and 21 with an adhesive material. Alternatively, a polymer liquid crystal film may be used, which is formed by coating a liquid crystal monomer on the transparent substrate 21 after orientation treatment, forming a predetermined film thickness, and then polymerizing and curing it. Alternatively, birefringent crystals such as crystals may also be used as the phase plate 22 instead of the transparent substrate 21 and bonded and fixed to the transparent substrate 12 .

In any case, the direction of the optical axis of the phase plate 22 forms an angle of 45° in the XY plane with respect to the direction of the incident light polarization plane, ie, the X axis. For example, with respect to the incident light waved into λ, the retardation value of the phase plate 22 is made to be an odd multiple of 1/4 of the wavelength λ, that is, the phase difference is an odd multiple of π/2, and the light passing through the liquid crystal lens element 20 in this way becomes a circle Polarized light is emitted.

Therefore, by attaching and using the liquid crystal lens element 20 of this embodiment to the optical head device, it is possible to change the wavefront and polarization state of transmitted light with a single element.

[third embodiment]

Next, a liquid crystal lens element 30 according to a third embodiment 3 of the present invention will be described with reference to FIG. 7 . In addition, in this embodiment, the same code|symbol is attached|subjected to the same part as 1st Embodiment, and repeated description is avoided.

The liquid crystal lens element 30 of the present embodiment is a structure in which the liquid crystal lens element 10 related to the first embodiment is stacked up and down in such a state that the two concavo-convex portions 17 face each other (however, the transparent substrate 11 is shared). ) has, as a rough structure, a first liquid crystal lens element 10A, a second lens element 10B, and an AC power supply 18 for applying an AC voltage to them.

That is, the first liquid crystal lens element 10A of the liquid crystal lens element 30 has two transparent substrates 11 and 12A, transparent electrodes 13A and 14A formed on these transparent substrates, a concave-convex portion 17A formed on the transparent electrode 14A, and The liquid crystal 16A is sealed in the space between the transparent electrode 13A and the transparent electrode 14A provided with the concavo-convex portion 17A. In addition, the second liquid crystal lens element 10B also has the same configuration as the first liquid crystal lens element 10A, but uses a common transparent substrate.

Next, the manufacturing method of this embodiment will be described

First, transparent electrodes 14A and 14B are formed on one surface of each transparent substrate 12A and 12B, respectively. Then, on the flat surfaces of these transparent electrodes 14A and 14B, use a uniform refractive index transparent material with a refractive index of n _s to form concave and convex portions 17A and 17B with a sawtooth-like cross section or a substantially sawtooth-like stepped shape. Each surface of these concave-convex portions 17A and 17B is processed into the same concave-convex shape having rotational symmetry with respect to the optical axis (Z axis) of incident light. In addition, transparent electrodes 13A and 13B are formed on both surfaces of transparent substrate 11 .

Then, on each of the transparent substrates 12A and 12B, seals 15A and 15B in which an adhesive material mixed with a gap control material is printed and patterned are formed, respectively. Then, the respective transparent substrates 12A and 12B are overlapped with the transparent substrate 11 so that the rotational symmetry axes of the concave-convex portion 17A and the concave-convex portion 17B coincide, and then pressure-bonded to form an empty cell. Then, liquid crystal is injected from an injection port (not shown) provided in a part of the seal, and the injection port is sealed to seal the liquid crystals 16A and 16B in the cell, whereby the liquid crystal lens element 30 is produced. In addition, the transparent electrodes 13A and 13B are electrically connected to form a common electrode, and the transparent electrodes 14A and 14B are electrically connected to be used as a common electrode.

In the liquid crystal lens element 10A thus formed, an AC voltage of a rectangular wave is applied between the common electrodes by the AC power source 18 . Then, the molecular orientations of the liquid crystals 16A and 16B change according to the applied voltage, and the actual refractive index of the liquid crystal layer changes from ne _{to no} . As a result, the difference Δm in refractive index between the liquid crystals 16A and 16B and the concave-convex portions 17A and 17B changes, and the wavefront of the transmitted light with respect to the incident light changes.

Although the configuration and function of the first and second liquid crystal lens elements 10A and 10B shown in FIG. 7 are the same as those of the liquid crystal lens 10 shown in FIG. 1 , they are different in that the orientation directions of the liquid crystal molecules of the liquid crystals 16A and 16B are perpendicular to each other. That is, in the first and second liquid crystal lens elements 10A and 10B, the orientation treatment directions of the liquid crystal layer interfaces are perpendicular to each other. As a result, according to the present embodiment, irrespective of the polarization state of the incident light, according to the applied voltage, it is possible to obtain, for example, positive and non-magnifying power as shown in FIGS. 4(A), (B) and (C). , The lens function of negative magnification.

In addition, at the applied voltage V ₀ where Δn(V ₀ )=0, when there is incident light corresponding to extraordinary light polarized light on the liquid crystal layer, the transmission wavefronts of the first and second liquid crystal lens elements 10A and 10B do not generate However, when there is incident light equivalent to ordinary light polarized light on the liquid crystal layer, regardless of the magnitude of the applied voltage, the transmitted wavefronts of the first and second liquid crystal lens elements 10A and 10B have a difference between the refractive index n _o —n _s corresponding to certain variants.

Since the alignment directions of the liquid crystals 16A and 16B of the first and second liquid crystal lens elements 10A and 10B are perpendicular to each other, this constant transmission wavefront variation occurs regardless of the incident polarization state. In order to offset the constant change in the transmission wavefront at such an applied voltage V _o , it is preferable to form a correction surface on the surface of the transparent substrate 10A or 12B.

Alternatively, the concavo-convex portions 17A and 17B are formed by using a birefringent index material such as a polymer liquid crystal whose ordinary birefringence index is equal to that of the liquid crystals 16A and 16B in the same orientation direction as that of the liquid crystals 16A and _16B , respectively. The transmission wavefront of the liquid crystal lens element 30 can be kept unchanged.

[Fourth Embodiment]

Next, a liquid crystal lens element 40 according to a fourth embodiment of the present invention will be described with reference to FIG. 6 . In addition, in this embodiment, the same code|symbol is attached|subjected to the same part as 1st and 2nd embodiment, and duplication description is avoided.

The liquid crystal lens element 40 of this embodiment differs from the liquid crystal lens element 30 shown in FIG. 7 in the configurations of the first and second liquid crystal lens elements 10A and 10C in the following points.

The liquid crystal alignment direction of the second liquid crystal lens element 10C is different from the second liquid crystal lens element 10B of the third embodiment, and is the same alignment direction as the liquid crystal 16A of the first liquid crystal lens element 10A. In addition, the outline shape of the concave-convex portion 17C of the second liquid crystal lens 10C is different from that of the concave-convex portion 17A, and the optical path length difference OPD shown by the curve α in FIG. 3 described by the formula (3) is different from each other. In addition, AC voltages of rectangular waves are applied to liquid crystals 16A and 16C by using AC power sources 18A and 18C independently, respectively.

In this way, when extraordinary light polarized light having a polarization plane corresponding to the alignment direction of the liquid crystals 16A and 16C enters, the first and second liquid crystal lens elements 10A and 10C function as liquid crystal lenses that independently produce different magnifications. effect.

For example, under the applied voltage V ₊₁ , V ₀ and V _-1 , if the magnification of the first liquid crystal lens element 10A is set to PA ₊₁ , PA ₀ (+0), and PA _-1 , and the second liquid crystal lens is set at the same time The magnification factors of the element 10C are PC ₊₁ , PC ₀ (=0), and PC _-1 , and their size relationship is PA ₊₁ <PC ₊₁ <0<PC _-1 <PA _-1 .

At this time, by using the AC power sources 18A and 18C without adjusting the applied voltage, the liquid crystal lens element 40 can generate seven types (PA ₊₁ <PC ₊₁ )<PA ₊₁ <PC ₊₁ 0<PC _-1 <PA _-1 < (PA ₊₁ <PC ₊₁ ) different magnifications.

As a result, by attaching and using the liquid crystal lens element 40 of this embodiment to the optical head device, it is possible to correct the amount of spherical aberration including seven types of magnification components generated due to the difference in the thickness of the cover layer.

[Fifth Embodiment]

Next, a liquid crystal lens element 50 according to a fifth embodiment of the present invention will be described with reference to FIG. 9 . In addition, in this embodiment, the same code|symbol is attached|subjected to the same part as 1st and 2nd embodiment, and duplication description is avoided.

The liquid crystal lens element 50 of this embodiment is the phase difference between one side of the transparent substrate 12 (the side without the transparent electrode) and the side mounted on the transparent substrate 21 in the liquid crystal lens 10 shown in the first or second embodiment. A birefringent diffraction grating 51 and an adhesive material layer 52 are interposed between the plates 22 .

The birefringent diffraction grating 51 is to form a birefringent material layer made of polymer liquid crystal on one side of the transparent substrate 12 (the side without the transparent electrode), and process it into the cross-sectional shape of the concave-convex grating, thereby forming the birefringent diffraction grating 51. Furthermore, an adhesive material made of uniform refractive index transparent material is used to fill at least the concave portion of the birefringent diffraction grating 51 as an adhesive material layer 52 and bonded to the transparent substrate on which the phase plate 22 is formed.

The birefringence grating 51 formed by the polymer liquid crystal is subjected to orientation treatment so that the molecular directions of the liquid crystal 16 and the polymer liquid crystal are perpendicular to each other. That is, on the transparent substrate 12, an alignment film (not shown) for alignment treatment along the Y-axis direction is formed, and the liquid crystal monomer is coated and polymerized and solidified, thereby forming alignment along the Y-axis direction (the direction of the extraordinary refractive index). ) consistent polymer liquid crystal. Then, etching and reactive ion etching are used to form a birefringent diffraction grating 51 with a concave-convex cross section.

For the concave part of the birefringence diffracted light 51, fill the adhesive agent whose refractive index is equal to the ordinary light refractive index of polymer liquid crystal substantially, form the adhesive material layer 52, by making the ordinary light polarized light transmission in the incident light like this, Polarizing Diffraction Grating for Extraordinary Polarized Light Diffraction.

The cross-sectional shape of the birefringent diffraction grating 51 may be a rectangular shape as shown in FIG. 9 , or a zigzag shape in order to obtain high diffraction efficiency for a specific number of diffraction poles. The birefringent diffraction grating 51 is configured by appropriately setting the difference (ΔN) between the extraordinary optical refractive index of the polymer liquid crystal forming the birefringent diffraction grating and the refractive index of the adhesive material layer 52 (ΔN), and the concave-convex depth of the polymer liquid crystal ( The product of D) (ΔN×D) can obtain a diffraction efficiency of a desired order of diffraction for incident light of extraordinary optical polarization of wavelength λ. In addition, by configuring the grating pitch and the angle in the longitudinal direction of the grating to form a hologram pattern with a predetermined distribution within the grating plane, it is possible to spatially control the diffraction direction of the incident light.

The phase plate 22 is the same phase plate as the phase inversion 22 described in the second embodiment (refer to FIG. 6 ), and the optical axis direction of the phase plate 22 is formed in the XY plane with respect to the direction required for the polarization of incident light, that is, the X axis. For the direction of the included angle of 45°, the hysteresis value is set to be 1/4 of the wavelength λ of the emitted light.

In addition, in the liquid crystal lens element 50 of this embodiment, as shown in FIG. diffracted light. The diffraction grating 53 is used as three beams for tracking an optical disc in, for example, an optical pickup device.

Next, the operation of this embodiment will be described.

If linearly polarized light having a polarization plane in the X-axis direction is incident on the liquid crystal lens element 50 of this embodiment from the side of the transparent substrate 11, the transmitted wavefront is transmitted according to the magnitude of the voltage applied to the liquid crystal lens element 10 by the AC power supply 18. According to the change, the polarized light as ordinary light enters the polarization diffraction grating composed of the birefringent grating 51 and the adhesive material layer 52 . The transmitted light that is not diffracted by the polarizing diffraction grating becomes circularly polarized light by the phase plate 22 and passes through the liquid crystal lens element 50 .

In addition, when the light reflected by a reflective surface such as an optical disk not shown in the figure enters again from the transparent substrate 21 side of the liquid crystal lens element 50, it becomes linearly polarized light having a polarization plane in the Y-axis direction by the phase plate 22 as extraordinary light. The polarized light is diffracted when it enters the polarizing diffraction grating, and is emitted from the liquid crystal lens element 50 .

In this way, by integrating the polarizing diffraction grating 51, the phase plate 22, and the diffraction grating 53 with the liquid crystal lens element 10, compared with the case where the elements are mounted one by one in the device, since the positional accuracy is improved, stable performance can be obtained. .

Next, a unit unit (hereinafter referred to as "optical unit 60") in which such a liquid crystal lens element 50 is integrated with a semiconductor laser and a photodetector in the same unit will be described with reference to FIG. 10 .

In this optical unit 60 , a semiconductor laser body 60 emitting linearly polarized light having a wavelength λ having a polarization plane in the X-axis direction and a photodetector 62 are fixed to a metal block 63 and housed in a package 64 . The photodetector 62 integrates circuits for converting an optical signal into an electrical signal, and performing signal amplification and signal processing on the signal. Openings are provided on the light emitting and light incident sides of the module 64, and the liquid crystal lens element 50 is bonded and fixed to the opening to form a unitized structure.

If such an optical unit 60 is installed in the optical head device, it will simultaneously have the function of a diffraction grating for generating three light beams for tracking, the function of aberration correction corresponding to the applied voltage, and the function of straight forward transmission and return on the way forward. The liquid crystal lens element that efficiently splits the polarized light toward the photodetector is a function of a beam splitter, making the optical head device miniaturized.

[Sixth Embodiment]

Next, an optical head device 70 for recording and reproducing optical discs for DVD and CD incorporating the liquid crystal lens element 20 according to the second embodiment of the present invention will be described with reference to FIG. 11 . In addition, in this embodiment, the same reference numerals are assigned to the same parts as those in the second embodiment, and repeated descriptions are avoided.

The optical head device 70 of the present embodiment has light sources that are first and second semiconductor lasers 1A and 1B, first and second diffraction gratings 2A and 2B, a dichroic prism 3, a beam splitter 4, a collimator lens 5, and an objective lens 6. , a cylindrical lens 7, a photodetector 8, and in addition, a liquid crystal lens element 20 is provided on the optical path between the beam splitter 4 and the collimator lens 5.

Next, the operation of this embodiment will be described.

(i) In the case of DVD discs:

The output light of wavelength λ ₁ (=660nm) emitted from DVD semiconductor laser 1A and having a polarization plane within the plane of FIG. 11 generates three beams for tracking by diffraction grating 2A. Then, it passes through the dichroic prism 3 , is reflected by the dichroic mirror 4 , and enters the liquid crystal lens element 20 . The light transmitted through the liquid crystal lens element 20 becomes circularly polarized light, is formed into parallel light by the collimator lens 5 , and is focused on the information recording layer of the optical disk D for DVD by the objective lens 6 .

In addition, the objective lens 6 is movable by a driver (not shown) for focus servo and tracking servo. The light reflected by the reflective surface of the optical disk D passes through the objective lens 6 and the collimator lens 5 again, and then passes through the liquid crystal lens element 20 to become linearly polarized light having a polarization plane perpendicular to the plane of the paper, and part of the light passes through the beam splitter 4 . Then, it passes through the cylindrical lens 7 provided for focus servo using the astigmatic method, and focuses on the photodetector 8 . In addition, although the light reflected by the beam splitter 4 is focused on the light-emitting point of the semiconductor laser 1A through the original optical path, because it is a linearly polarized light whose polarization plane is perpendicular to the laser sending light, it has no influence on the laser sending, and the laser sending intensity is stable. .

(ii) In the case of CD discs:

In addition, the emitted light having a wavelength λ ₂ (=790nm) emitted from the CD semiconductor laser 1B and having a polarization plane perpendicular to the plane of the paper generates three beams for tracking by the diffraction grating 2B, and is reflected by the dichroic prism 3. The light of wavelength λ1 for DVD advances along its optical axis and is reflected by the dichroic mirror 4 . Then, the reflection mirror is the same as the light of the wavelength _λ1 for DVD, and focuses it on the information recording layer of the optical disk D for CD by the collimator lens 5 and the objective lens 6. In addition, the optical path reflected by the reflective surface of the optical disc is the same as the optical path of the wavelength _λ1 for DVD.

In the optical head device 70 of the present embodiment, when the semiconductor lasers 1A and 1B adopt semiconductor lasers with high transmission output power, in order to make the polarization plane of the return light returning to the light emitting point of the laser perpendicular to the polarization plane of the laser transmission light, it is preferable to The phase plate 22 (see FIG. 6 ) in the liquid crystal lens element 20 is made to be a 1/4 wavelength plate with respect to the incoming _λ1 and the wavelength _λ2 .

Specifically, for the intermediate wavelength between wavelength _λ1 and wavelength _λ2 , polymer liquid crystal layers with retardation values at 1/4 wavelength and 1/2 wavelength are laminated so that the optical axis angle becomes a desired angle .

Next, using the optical head device 70 equipped with the liquid crystal lens element 20 (see FIG. 6 ) of the present invention, the recording and reproducing operations for single-layer and dual-layer DVD recording and reproducing optical discs with different cover layer thicknesses will be described below.

(i) In the case of a single-layer disc (cover layer thickness 0.60 mm):

Due to the design of the objective lens 6, the aberration for the single-layer optical disc D with a cover layer thickness of 0.60 mm is minimal, so when the single-layer optical disc D is recorded and/or reproduced, an AC voltage is applied between the electrodes of the liquid crystal lens element 20 V ₀ . This is because the liquid crystal 16 has the same refractive index as the concavo-convex portion 17, so the transmitted wavefront does not change as shown in FIG. 4(B).

(ii) In the case of a double-layer optical disc (thickness of the cover layer is 0.57mm):

When recording and/or reproducing the information recording layer with a cover layer thickness of 0.57 mm in a dual-layer optical disk, an AC voltage V ₊₁ is applied between the electrodes, so that the transmitted wave surface of the liquid crystal lens element 20 becomes a slightly focused spherical wave .

At this time, since the refractive index of the liquid crystal 16 is larger than that of the concave-convex portion 17, as shown in FIG. That is, the objective lens 6 can effectively focus on the information recording layer having a cover layer thickness of 0.57 mm.

(iii) In the case of a single-layer disc (cover layer thickness 0.63 mm):

In addition, when recording and/or reproducing the information recording layer not shown in the figure with a cover layer thickness of 0.63 mm, an AC voltage V _-1 is applied between the electrodes so that the transmitted wavefront of the liquid crystal lens element 20 becomes a slightly divergent spherical surface. Wave. At this time, since the refractive index of the liquid crystal 16 is smaller than that of the concave-convex portion 17, as shown in FIG. That is, the objective lens 6 can effectively focus on the information recording layer having a cover layer thickness of 0.63 mm.

Therefore, by switching the voltage applied to the liquid crystal lens element 20 between V ₀ , V ₊₁ , and V _-1 , stable recording and reproduction can be realized for DVD single-layer discs and dual-layer discs with different cover layer thicknesses.

Thus, according to the optical head device 70 of this embodiment, the liquid crystal lens element 20 not only corrects the spherical aberration caused by the difference in the thickness of the cover layer of the optical disk D, but also can add the function of switching the magnification component corresponding to the change of the focus position. Therefore, for example, when the objective lens 6 is used separately from the objective lens 6, and the objective lens 6 moves in the radial direction of the optical disc D during tracking, and is decentered from the liquid crystal lens element 20, the aberration hardly deteriorates even in this case. As a result, stable recording and/or reproduction can be realized compared to a liquid crystal element in which only spherical aberration is corrected.

In addition, in the liquid crystal lens element 20, by adopting the shape of the concavo-convex portion 17 corresponding to m=2 or 3 in the formula (2), since five or seven kinds of transmission wavefronts can be switched respectively, for optical disks with different cover layer thicknesses, , enabling more precise aberration correction.

In addition, if the liquid crystal lens element 30 according to the third embodiment shown in FIG. Focusing on the photodetector is also improved.

In addition, if the liquid crystal lens element 40 of the fourth embodiment shown in FIG. 8 is used instead of the liquid crystal lens element 20, not only the aberrations of three kinds of optical discs with different cover layer thicknesses can be corrected, but also other cover layers can be corrected. Aberrations in layer thickness. Therefore, more accurate pixel correction can be performed even when spherical aberration remains in an optical disc having a difference in cover layer thickness or in the optical system of the entire optical pickup device.

In addition, in the liquid crystal lens 20, since the outgoing linearly polarized light _{perpendicular} to the plane of polarization is incident on the liquid crystal of the liquid _crystal lens element 20 as ordinary light polarized light, there occurs Certain transmitted wavefront changes. In order to cancel this, it is only necessary to form a correction element that fills the concave and convex portions of the correction surface corresponding to the uneven shape of the liquid crystal 16 with a filling material having a uniform refractive index. Here, the refractive index of the birefringent material and the filling material is adjusted so that there is a difference in optical path length for ordinary light polarized light of the liquid crystal, and no difference in optical path length for extraordinary light polarized light.

At this time, since the polarized light of wavelength _λ2 for CD becomes ordinary light polarized light and enters the liquid crystal of the liquid crystal lens element 20, the transmission wavefront does not change regardless of the voltage applied to the liquid crystal lens element 20.

That is, it is possible to perform stable recording and reproduction on the optical disk for CD without deteriorating aberration.

Here, for example, as shown in the schematic diagram of the optical head device 80 shown in FIG. 12, when a two-wavelength light source 1C is used in which the light-emitting points of the semiconductor lasers for DVD and the semiconductor lasers for CD are arranged at intervals of about 100 μm in a single package, a simple structure can be formed. .

In this optical head device 80, a wavelength-selective diffraction grating 2C is used as a three-beam generating element for tracking instead of the diffraction gratings 2A and 2B in FIG. 11 .

This wavelength-selective diffraction grating 2C is a diffraction grating that does not diffract the light of wavelength _λ1 for DVD and transmits it, and diffracts light of wavelength _λ2 for CD, or does not diffract light of wavelength _λ2 for CD. The diffraction grating that diffracts the light that is transmitted and diffracts the light of the wavelength λ ₁ used by DVD, or the element that laminates them, can suppress the generation of unnecessary scattered light and obtain high light utilization efficiency.

In addition, in this optical head device 80 , by arranging the liquid crystal lens element 20 in the optical path between the two-wavelength light source 1C and the beam splitter 4 , it is possible to achieve miniaturization of the device. In addition, by integrating the liquid crystal lens element 20 with the wavelength-selective diffraction grating 2C, the size of the device can be further reduced.

In addition, in this embodiment, an optical head device 80 equipped with a liquid crystal lens element 20 that operates a single-layer or double-layer optical disk D for DVD using a semiconductor laser having a wavelength of 660 nm as a light source has been described. However, the same function and effect can be obtained for an optical head device equipped with a liquid crystal lens element that operates a single-layer or double-layer optical disc D for BD using a semiconductor laser with a wavelength of 405 nm as a light source.

[Seventh Embodiment]

Next, an optical head device 90 according to a seventh embodiment of the present invention will be described with reference to FIG. 13 . In addition, in this embodiment, the same reference numerals are attached to the same parts as those in the sixth embodiment, and repeated descriptions are avoided.

The optical head device 90 of this embodiment has a unit 90A for DVD, a unit 90B for CD, a dichroic prism 3 , a collimator lens 5 , and an objective lens 6 .

Unit 90A for DVD is optical unit 60 shown in FIG. The knot is fixed to form a whole and constitute a unit. In addition, in the unit for CD, the semiconductor laser 1B for CD, the photodetector 8B, and the holographic beam splitter 4B are integrated as a unit.

Next, the effect of this embodiment will be described

(i) Regarding the recording and/or playback of DVD discs:

For recording and/or reproducing the optical disc for DVD, unit 90A for DVD, ie, optical unit 60 shown, is used.

Outgoing from the semiconductor laser 1A for DVD in the optical unit 60, the outgoing light having a wavelength λ ₁ (=66 nm) having a polarization plane in the paper plane of FIG. , through the dichroic prism 3. Then, the transmitted light is collimated by the collimator lens 5 and focused on the information recording layer of the optical disc D for DVD by the objective lens.

In addition, the light reflected by the reflective surface of the optical disk D advances in the reverse direction, passes through the objective lens 6, the collimating lens 5 and the dichroic prism 3 again, and then passes through the 1/4 wavelength plate in the liquid crystal lens element 50, that is, the phase plate 22 (Refer to Figure 9). Then, the transmitted light becomes linearly polarized light having a plane of polarization perpendicular to the plane of paper in FIG. The grating (see FIG. 9 ) diffracts and effectively focuses on the light receiving surface of the photodetector 8A.

(ii) Regarding the recording and playback of CDs:

In addition, the recording and reproducing of the optical disc for CD uses the unit 90B for CD in which the semiconductor laser 1B for CD, the photodetector 8B, and the holographic beam splitter 4B are integrally assembled.

Light of wavelength λ ₂ (=790 nm) emitted from semiconductor laser 1B passes through holographic beam splitter 4B integrating diffraction gratings for generating three beams for tracking.

Then, the transmitted light is reflected by the dichroic prism 3 and travels so that the optical axis coincides with the light of the wavelength _λ1 for DVD, and is focused on the information recording layer of the optical disc D for CD by the collimator lens 5 and the objective lens 6.

In addition, the light reflected by the reflective surface of the optical disc D goes backwards, passes through the objective lens 6 and the collimator lens 5 again, is reflected by the dichroic prism 3, and then diffracts a part of the light by the holographic beam splitter 4B, focusing on the photodetector The light-receiving surface of 8B.

Thus, in this embodiment, the operation for stable recording and/or reproducing with respect to single-layer and dual-layer optical disks D for DVD with different cover layer thicknesses is the same as that in the sixth embodiment. Therefore, according to the optical head device 10 of this embodiment, the assembly and adjustment of the optical head device 90 can be simplified, and the entire device can be downsized and reduced in weight.

Example

[example 1]

Next, a specific example of the liquid crystal lens element 20 of the present invention shown in the second embodiment will be described with reference to FIG. 6 .

First, a method of manufacturing the liquid crystal lens element 20 will be described.

A transparent conductive film (ITO film) is formed on a glass substrate of the transparent substrate 11 as the transparent electrode 13 . Further, photosensitive polyimide, which is a uniform refractive index material having a refractive index n _s (=1.66), is coated on the transparent electrode 13 to form a film thickness d (=5.5 μmm).

Next, the photosensitive polyimide is irradiated with ultraviolet rays using a step mask having a radially distributed ultraviolet transmittance corresponding to the shape of the curve β in FIG. 3 , and developed after the step mask pattern is sintered. As a result, the concave-convex portion 17 having a zigzag cross-sectional shape and rotational symmetry with respect to the optical axis (Z axis) of the incident light as shown in FIG. 6 is processed in the region of the effective diameter φ (=4.9 mm). The surface of the uneven portion 17 formed of polyimide is then subjected to rubbing alignment treatment in the X-axis direction. As a transparent material for the concave-convex portion 17 formed of polyimide thus obtained, a low-resistance material whose volume resistivity ρ _F is 106 or more lower than the volume resistivity ρ _LC of the liquid crystal 16 is used.

In addition, after forming a transparent conductive film (ITO film) on the glass substrate of the transparent substrate 12 as the transparent electrode 14, apply a polyimide film with a film thickness of about 50 nm, and then sinter, and the surface of the polyimide film along the X axis direction for rubbing orientation. On it, the adhesive material mixed with the spacing control material with a diameter of 7 μm is printed into a pattern to form a seal 15, which is overlapped with the transparent substrate 11 and crimped to form an empty cell with a transparent electrode spacing of 7 μm.

Then, liquid crystal 16 is injected from the injection port (not shown) of the empty cell, and the injection port is sealed to form the liquid crystal lens element 10 shown in FIG. 6 .

The liquid crystal 16 is a nematic liquid crystal having a positive anisotropic dielectric constant with an ordinary refractive index n _o (=1.50) and an extraordinary refractive index _ne (=1.78). In addition, the liquid crystal 16 whose orientation of the liquid crystal molecules is parallel to the planes of the transparent electrodes 13 and 14 and aligned along the X-axis direction is filled in the concave and convex portions 17 . In addition, since the slope of the sawtooth-shaped concave-convex portion 17 is inclined at a maximum of about 3°, the orientation of the liquid crystal molecules can be considered to be parallel to the surface of the transparent electrode.

Then, after coating a polyimide film with a film thickness of about 50 nm on the glass substrate of the transparent substrate 21, it is sintered, and the surface of the polyimide film is subjected to rubbing alignment treatment along a direction forming a 45° sandwich with the X axis.

The liquid crystal monomer is coated on it to make a film thickness of 6.6 μm, and then polymerized and cured to make the slow axis along the 45° clamping direction with the X axis, and the difference between the ordinary light refractive index and the extraordinary light refractive index The phase plate 22 is formed by a polymer liquid crystal film with a difference of 0.2. Then, the phase plate 22 and the transparent substrate 12 are bonded and fixed with an adhesive material, and the transparent substrate 21 and the like are bonded to the liquid crystal lens element 10 to form the liquid crystal lens element 20 .

The hysteresis value (Rd) of the phase plate 22 is

R _d =0.20×6.6

＝1.32μm

Equivalent to 5/4 times the wavelength λ (=666nm) for DVD, it has the function of a 114 wavelength plate.

The AC power supply 18 is connected to the transparent electrodes 13 and 14 of the liquid crystal lens element 20 obtained in this way, and the voltage is effectively applied to the liquid crystal under the conditions corresponding to Case 1 shown in the first embodiment in which the voltage drop at the concave-convex portion 17 is small. 16 on. When the applied voltage is increased from 0 V, the actual refractive index of the liquid crystal (layer) 16 along the X-axis direction changes from _ne (=1.78) to n _o (=1.50). As a result, for linearly polarized incident light having a polarization plane of the X axis, the difference (Δn) in the refractive index between the liquid crystal 16 and the concave-convex member 17 changes from

Δn _max (=n _e -n _s )=0.12

(where n _s =1.66)

becomes

Δn _min (=n _o -n _s )=-0.16

According to the thickness distribution of the liquid crystal 16 filled in the concave and convex portions 17, the transmission wavefront changes accordingly.

Here, for example, an objective lens with a numerical aperture (NA) of 0.65 and a focal length of 3.05 mm is designed so that the aberration is zero for a single-layer optical disc for DVD using a wavelength λ (=660 nm) and a cover layer thickness of 0.60 mm. For covering layer thickness of 0.57mm and. 063mm DVD double-layer optical disc, the difference in maximum optical path length is about 0.15λ, resulting in spherical aberration equivalent to the square mean wavefront aberration of about 43mλ, [rms].

Therefore, in order to correct this spherical aberration using the liquid crystal lens element 20, the concave-convex portion 17 is processed so that the transmitted wavefront when no voltage is applied corresponds to the _{equation (} 3) represents the difference in optical path length OPD. Here, the optical path length difference OPD in the formula (3) is in units of [μm], and r is in units of [mm].

[Table 1]

coefficient value a₁ -0.744431 a₂ 0.004292 a₃ 0.004880

a₄ 0.001341 a₅ 0.000112

In this way, using the coefficient values a ₁ to a ₅ in [Table 1], a value obtained by subtracting an integer multiple of the wavelength λ from the difference in the optical path length corresponding to the curve α in FIG. equal to zero, less than or equal to the difference of the optical path length of λ), and the transmitted wavefront of the difference of the optical path length represented by the curve β of Fig. 3 .

Here, since the difference (Δn) in the refractive index between the liquid crystal 16 and the concavo-convex portion 17 when no voltage is applied is as described above, is

Δn(=n _e -n _s )=0.12

Therefore, in order to generate the above-mentioned transmitted wavefront by utilizing the concave-convex portion 17 and the liquid crystal 16 filled in the concave-convex portion, it is only necessary to satisfy the aforementioned formula (4). That is, in formula (2), when m=1,

Δn×d=0.66μm

According to this formula, the depth d (μm) of the concavo-convex portion 17 is determined such that the difference in maximum optical path length corresponds to the wavelength λ=660 nm (=0.66 μm).

In this way, the depth (d) of the concave-convex portion 17 was set to d=5.5 μm, and the cross-sectional shape shown in FIG. 1 was processed. In addition, a sawtooth-shaped concavo-convex portion 17 having a substantially stepped shape may also be used. In order to generate a smooth transmitted wave surface corresponding to the curve α in FIG. 3, it is preferable to set the depth (d) of the concave and convex portion 17

(0.75×λ/Δn)≤d≤(1.25×λ/Δn)

In addition, since the effective diameter of the concavo-convex portion 17 is 4.9 mm, the maximum radius is 2.45 mm.

_The transmitted wavefront of DVD wavelength λ (=660nm) incident on the liquid crystal lens element 20 becomes the focused light shown in FIG. It is the convex lens effect of f=675mm. Next, when the applied voltage is increased, Δn(V ₀ )=0 at about V ₀ =2.5V, and the transmitted wavefront remains unchanged as shown in FIG. 4(B) (no amplification factor ) for transmission. If the applied voltage is further increased, when V _{= 1} = about 6V, it becomes Δn(V _-1 )=-Δn(V ₊₁ ), and the transmitted wavefront becomes divergent light as shown in Fig. 4(C), indicating that the focal length is equivalent to (f) is the concave lens effect of f=-675mm.

[Example 2]

Next, a specific example in which the liquid crystal lens element 20 of the aforementioned [Example 1] is mounted on the optical head device 70 of the sixth embodiment shown in FIG. 11 will be described. In addition, since the structure of this optical head apparatus 70 was already demonstrated in 6th Embodiment, it is abbreviate|omitted here.

When recording and reproducing on a DVD single-layer disc D with a cover layer thickness of 0.60mm, if the applied voltage to the liquid crystal lens element 20 is about V ₀ =2.5V, the incident light is focused on the information recording layer by the objective lens 6 .

For the double-layer disc D used for DVD, if the applied voltage of the liquid crystal lens element 20 is about V ₊₁ (=0V), then the incident light is focused on the information recording layer with a cover layer thickness of 0.57mm. 1 (=6V), the incident light is focused on the information recording layer with a cover layer thickness of 0.63mm. No matter what the situation is, the calculation value of the remaining square mean wavefront aberration becomes less than or equal to 3mλ[rms].

In addition, if the applied voltage is set to V ₊₁ in the range of coating thickness from 0.555mm to 0.585mm, or if the applied voltage is set to V0 in the range of coating thickness from 0.585mm to 0.615mm, or The overlay thickness is . In the range of 615 mm to 0.645 mm, if the applied voltage is V ₋₁ , the calculated values of the remaining square mean wavefront aberrations are all reduced to about 20 mλ [rms] or less.

In addition, when the objective lens 6 moves about ±0.3 mm in the radial direction of the half disk D for tracking, although the liquid crystal lens element 20 is decentered, there is no aberration corresponding to this, so the focus point does not deteriorate.

Therefore, by switching the voltage applied to the liquid crystal lens element 20 to V ₀ , V ₊₁ , and V _-1 , an optical head device capable of stably recording and reproducing each of single-layer and double-layer optical disks D for DVD is realized. .

[Example 3]

Next, in the liquid crystal lens element 20 of the present invention shown in the embodiment of Example 1, an embodiment in which a material whose volume resistivity _pF is greater than or equal to the volume resistivity _pLC of the liquid crystal 16 is used as the transparent material of the concave-convex portion 17, This will be described below with reference to FIG. 6 .

First, a method of manufacturing the concave-convex portion 17 in the liquid crystal lens element 20 will be described.

On the transparent electrode 13 formed on the glass substrate of the transparent substrate 11, a uniform refractive index material SiOxNy having a refractive index _ns (=1.507) substantially equal to the ordinary light refractive index n _o of the liquid crystal 16 is formed by sputtering. (Here, x and y represent the element ratios of O and N) thin film. Here, a SiOxNy film having a transparent uniform refractive index of _ns and a film thickness of d (= 2.94 μm) was formed by using a Si sputtering target and a discharge gas in which oxygen and nitrogen were mixed in Ar gas. The relative permittivity ε _F of SiOxNy is 4.0, and the volume resistivity ρ _F is greater than or equal to 10 ¹⁰ Ω·cm.

Furthermore, after patterning the resist by photolithography using a photomask, the SiOxNy film is processed by reactive ion etching to a shape corresponding to the curve γ in FIG. 3 . As a result, in the region of the effective diameter φ (=4.9 mm), the convex portion and the concave portion of the concave-convex portion 17 shown in FIG. Partially reversed convex Fresnel lens shape.

That is, in FIG. 6, the center portion of the Fresnel lens shape constituted by the concavo-convex portion 17 is a concave portion, but in this embodiment, a Fresnel lens shape with a convex center portion is formed. Compared with the central part and the concave, the average thickness of the liquid crystal layer can be thinned by using the convex, so the speed of the voltage response can be increased when the focus is switched.

Then, a transparent conductive film (ITO film) is formed on the surface of the concave-convex portion 17 to serve as the first transparent electrode 13 . Coat polyimide film (not shown) on the first transparent electrode 13 again, make its film thickness about 50nm, carry out sintering then, carry out rubbing alignment treatment with the surface of polyimide film along X-axis direction, as Alignment film.

In addition, after forming a transparent conductive film (ITO film) on the glass substrate of the transparent substrate 12 as the transparent electrode 14, apply a polyimide film with a film thickness of about 50 nm, and then sinter, and the surface of the polyimide film along the X axis direction for rubbing orientation. On it, the adhesive material mixed with a gap control material with a diameter of 15 μm is printed to form a pattern to form a seal 15, which is overlapped with the transparent substrate 11 and crimped to form an empty cell with a transparent electrode gap G of 15 μm.

Then, liquid crystal 16 is injected from the injection port (not shown) of the empty cell, and the injection port is sealed to be used as a liquid crystal lens element shown in FIG. 6 .

The liquid crystal 16 is a nematic liquid crystal having a positive anisotropic dielectric constant with an ordinary refractive index n ₀ (=1.507) and an extraordinary refractive index _ne (=1.705). In addition, the liquid crystal 16 with uniform orientation parallel to the planes of the transparent electrodes 13 and 14 and aligned along the X-axis direction is filled in the concave and convex portions 17 . The relative permittivity ε of the liquid crystal 16 . The relative permittivity ε _// of the long axis direction of the liquid crystal molecules of _{the LC} is 15.2, and the relative permittivity ε⊥ of the short axis direction of the liquid crystal molecules is 4.3, which has a positive anisotropic permittivity. In addition, the volume resistivity ρ _LC of the liquid crystal 16 is equal to or greater than 10 ¹⁰ Ω·cm. In addition, the phase plate 22 was fabricated in the same manner as in Example 1.

The AC power source 18 was connected to the transparent electrodes 13 and 14 of the liquid crystal lens element 20 obtained in this way, and a distance AC voltage of frequency f = 1 kHz was applied. Since it corresponds to the condition of Case 2 shown in the first embodiment, the ratio V _LC /V of the applied voltage V _LC distributed to the liquid crystal (layer) 16 to the applied voltage V of the transparent electrodes 13 and 14 is determined according to the formula shown in FIG. 5 . The film thickness d _F of the concavo-convex part 17 and the layer thickness d _LC of the liquid crystal (layer) have the relationship of formula (5), and a voltage distribution V _LC corresponding to the shape of the Fresnel lens formed by the concavo-convex part 17 is generated. As a result, since linearly polarized light having an X-axis polarization plane enters light, the film thickness _dF of the concave-convex portion 17 is distributed, and the difference in optical path length OPD between the transparent electrodes is distributed as shown in the following equation. Since the central part of the shape of the Fresnel lens is convex, it becomes a different description form from the expression (6) which shows the concave.

[mathematical formula 13]

OPD＝n(V _LC [d _F ])×(Gd _F )

-n(V _LC [d])×(Gd)-n _s ×(dd _F )

The film thickness d _F of the concavo-convex portion 17 formed by the SiOxNy film is distributed from d to zero, and the difference OPD of the optical path length for the central portion of the Fresnel lens shape is distributed from zero to OPD _d of the following formula:

[mathematical formula 14]

OPD _d ＝{n(V _LC [d])-n _s }×d

-{n(V _LC [d])-n(V)}×G

When no voltage is applied between the transparent electrodes, since V=V _LC [d]=0, n(0)= _ne , the difference in optical path length OPD _d takes the value of the following formula.

OPD _d ＝(n _e -n _s )×d

＝0.238×2.94

＝0.70μm

If the applied voltage V between the transparent electrodes is increased _, the OPD _d decreases, and for the wavelength λ=66nm for DVD, there are applied voltages V _-1 , V ₀ , V ₊₁ (V _-1 < V ₀ < V ₊₁ ). Therefore, when the applied voltages V ₋₁ , V ₀ , and V ₊₁ are switched, the plane waves of wavelength λ=660 nm incident on the liquid crystal lens element 20 become transmitted wavefronts corresponding to γ, OPD zero, and β in FIG. 3 , respectively. That is, the applied voltage V ₋₁ generates a lens wavefront corresponding to negative magnification shown in FIG. 4(C), and the applied voltage V ₀ generates a transmitted wavefront corresponding to no magnification shown in FIG. The applied voltage V ₊₁ generates a transmitted wavefront corresponding to the positive magnification shown in FIG. 4(A).

The focus lens is arranged on the light emitting side of the liquid crystal lens element 20, and the focus point position is switched correspondingly according to the applied voltage V _-1 , V ₀ , V ₊₁ , and the operation of the zoom liquid crystal lens element with three numerical values is confirmed. The aperture stop and photodetector are arranged at the dot position. When the applied voltage V between the transparent electrodes of the liquid crystal lens element 20 is changed, FIG. Example of measurement of focusing efficiency of incident light.

In the range of applied voltage V _-1 from 0 to 1.2V, it becomes negative magnification (concave lens), in the range of applied voltage V ₀ of 1.6V, it becomes no magnification (no lens effect), and in the range of applied voltage V ₊₁ from In the range of 2.5 to 3V, it becomes a positive magnification (convex lens). In addition, the reason why the focusing efficiency is less than 100% is the deviation from the optimum value of the processed shape of the concave-convex part and the reflection loss at multiple interfaces with different refractive indices, which can be improved.

In addition, since the refractive index n _s of the concavo-convex part 17 formed by the SiOxNy film of uniform refractive index material is substantially equal to the ordinary light refractive index n _o of the liquid crystal 16, when the ordinary light polarized light is incident on the liquid crystal lens element 20, it is transmitted. The wave front does not change. For incident light of ordinary light polarized light, a high transmittance of 98% can be obtained without changing the transmitted wavefront (no magnification) regardless of the voltage applied between the transparent electrodes of the liquid crystal lens element 20 and the wavelength of the incident light.

Similar to [Example 2], this liquid crystal lens element 20 was mounted on the optical head device 70 of the sixth embodiment shown in FIG.

When using this optical head device 70 to record and reproduce a single-layer DVD disc with a cover layer thickness of 0.60mm, if the applied voltage of the liquid crystal lens element is about V ₀ =1.6V, then the incident light is effectively focused on by the objective lens 5 Information recording layer.

In addition, for a double-layer DVD disc, if the applied voltage of the liquid crystal lens element 20 is about V _-1 (1V), then the incident light is focused on the information recording layer with a cover layer thickness of _0.63mm . =3V), the incident light is focused on the information recording layer with a cover layer thickness of 0.57mm. In either case, the calculated value of the remaining RMS wavefront aberration becomes 3 mλ [rms] or less.

Next, when the transmitted wavefronts generated corresponding to the applied voltages V ₀ , V _-1 , and V ₊₁ of the liquid crystal lens element 10 are used for an optical disc with a cover layer thickness ranging from 0.56 mm to 0.64 mm, the remaining RMS Calculation results of the wavefront aberration.

Therefore, in the range of coating thickness from 0.56mm to 0.585mm, by setting the applied voltage V ₊₁ , in the range of coating thickness from 0.585mm to 0.615mm, by setting the applied voltage V ₀ , and then covering When the layer thickness is in the range of 0.615 mm to 0.64 mm, by setting the applied voltage V _-1 , the remaining RMS wavefront aberrations are reduced to approximately 20 mλ [rms] or less.

In addition, when the objective lens 5 moves about ±0.3 mm in the radial direction of the optical disk D for tracking, although the liquid crystal lens element 20 is decentered, there is no aberration corresponding to this, so the focus point does not deteriorate.

Therefore, by switching the voltage applied to the liquid crystal lens element 20 to V ₀ , V _-1 , and V ₊₁ , an optical head device capable of stably recording and reproducing single-layer and double-layer DVD discs D is realized.

In addition, when the liquid crystal lens element 20 is incident on light of other wavelengths, such as the 790 nm wavelength band for CD, the liquid crystal 16 in the liquid crystal lens element 20 adopts linearly polarized light that becomes ordinary light polarized light, so that no voltage is applied. The transmission wavefront does not change and high transmittance can be obtained, which is preferable.

Industrial Applicability

The liquid crystal lens element of the present invention can be used as a focal length switching lens that switches a plurality of focal lengths correspondingly according to the applied voltage, especially when recording and/or In playback, since it can be used as a liquid crystal lens element that corrects the spherical aberration including the magnification component generated, there will be no aberration when the liquid crystal lens element and the objective lens are decentered, so it can be used to reduce the restrictions on the arrangement, and to combine the light source and light detection. An optical head device that integrates a device, a beam splitter, etc. as a small unit.

In addition, Japanese Patent Application No. 2004-026685 (applied to the Japan License Office on February 3, 2004) and Japanese Patent Application No. 2004-230606 (applied to the Japan License Office on August 6, 2004) which are the basis of the priority claim of the present application are cited here. The contents of all the specifications filed in the Japan Patent Office) shall adopt the contents disclosed as the specification of the present invention.

Claims (9)

1. a liquid crystal lens element has variable focal length, it is characterized in that having:

The a pair of transparency carrier that has transparency electrode respectively;

Between the transparency electrode separately that this a pair of transparency carrier has, apply the voltage bringing device of voltage;

Jog, it forms with transparent material and the optical axis that has for liquid crystal lens element has the serrated crosssection shape of rotational symmetry or the jagged cross sectional shape of approximate stairstepping, forms on the transparency electrode of this jog in described each transparency electrode simultaneously; And

At least the liquid crystal of the recessed part of the described jog of filling,

Wherein, according to utilizing described voltage bringing device to be applied to the size of the voltage between described transparency electrode, make the actual refractive index respective change of described liquid crystal, described liquid crystal adopts has ordinary refraction index n _oReach very optical index n _e, simultaneously the actual refractive index of liquid crystal layer according to the size of the described voltage that applies at n _oTo n _eThe numerical value of scope between the liquid crystal material that changes, and the direction of orientation with the liquid crystal molecule when not applying voltage in liquid crystal layer all along the characteristic of specific direction orientation, simultaneously

The transparent material of described jog is for unusual light polarization light incident light refractive index n to be arranged at least _sTransparent material, refractive index n _sValue at n _oWith n _eBetween, and the refractive index n of described transparent material _sSatisfy the relation of following formula:

|n _e—n _s|≦|n _e—n _o|/2

Simultaneously, the depth d of the recessed part of described jog is in the scope of following formula for the light wavelength λ that sees through described liquid crystal:

(m—0.25)·λ/|n _e—n _s|≦d

≦(m+0.25)·λ/|n _e—n _s｜

In the formula, m=1,2 or 3, and m determines the number of the changeable focal length of described liquid crystal lens element, wherein, and n _o≠ n _e, n _s≠ n _o, n _s≠ n _e

2. liquid crystal lens element comprises:

Liquid crystal lens element as claimed in claim 1; With

Form incorporate phase-plate with liquid crystal lens element as claimed in claim 1, this phase-plate is the odd-multiple of pi/2 for the phase differential of the described light of wavelength X.

3. liquid crystal lens element comprises:

Liquid crystal lens element as claimed in claim 1; And

Be stacked in the phase-plate on the liquid crystal lens element as claimed in claim 1.

4. a liquid crystal lens element is characterized in that,

Comprise two liquid crystal lens elements as claimed in claim 1 that are stacked in together.

5. a liquid crystal lens element is characterized in that, comprising:

Be stacked in together liquid crystal lens element as claimed in claim 1, polarizability diffraction element and phase-plate successively.

6. optic probe device, have the light source of the light that penetrates wavelength X, the photodetector that will focus on object lens on the optical recording media from the emergent light of this light source, will utilize this object lens focusing and utilize the light of described optical recording media reflection to carry out the spectroscope of beam split and detect the light of described beam split, it is characterized in that

In the light path between described light source and described object lens liquid crystal lens element as claimed in claim 1 is set.

7. an optic probe device has the ejaculation wavelength X ₁And wavelength X ₂Light light source, will focus on the object lens on the optical recording media from the emergent light of this light source and detect the photodetector utilize this object lens focusing and to utilize the light of described optical recording media reflection, it is characterized in that,

In the light path between described light source and described object lens liquid crystal lens element as claimed in claim 1 is set, and as the described wavelength X that is incident to described liquid crystal lens element ₁And wavelength X ₂Light, described liquid crystal lens element adopts the mutually perpendicular rectilinearly polarized light bundle of plane of polarization, wherein, λ ₁≠ λ ₂

8. optic probe device as claimed in claim 6 is characterized in that,

Described optical recording media has the overlayer of coverage information recording layer, and described optic probe device writes and/or reads the optical recording media that this tectal thickness differs from one another.

9. optic probe device as claimed in claim 7 is characterized in that described optical recording media has the overlayer of coverage information recording layer, and described optic probe device writes and/or reads the optical recording media that this tectal thickness differs from one another.

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