JP4581969B2 - Liquid crystal device and optical pickup - Google Patents

Description

  The present invention relates to a liquid crystal device that corrects aberrations occurring in an optical system by applying a voltage to a liquid crystal layer between a first transparent substrate and a second transparent substrate to change the phase of transmitted light, and And an optical pickup including the liquid crystal device.

  A liquid crystal having dielectric anisotropy is very suitable for an optical element because its optical characteristics can be controlled by changing its direction depending on the direction of the electric field. An optical element using such a liquid crystal is disclosed in Patent Document 1 or 2, for example. In Patent Document 1, one of the electrodes provided on both sides of the liquid crystal layer is divided into a plurality of parts, and the voltage applied to each of the divided electrodes is changed, whereby the refractive index of the liquid crystal layer is changed for each divided region, and wavefront aberration is obtained. (Mainly spherical aberration and coma aberration) are corrected.

Also, in Patent Document 2, an optical system in which a transmissive liquid crystal panel and an optical lens are combined by generating a Fresnel zone plate pattern on the transmissive liquid crystal panel and electrically controlling the spatial frequency of the Fresnel zone plate. The composite focal length is made variable.
Japanese Patent No. 3443226 JP-A-63-249125

  In general, the spherical aberration includes an aberration generated by the central portion (portion near the optical axis) of the lens constituting the optical system and an aberration generated by the peripheral portion of the lens. The former aberration corresponds to, for example, a third-order component of spherical aberration, and the latter aberration corresponds to, for example, a fifth-order component (high-order component) of spherical aberration.

  When trying to correct higher-order components of spherical aberration with a liquid crystal device, the technique of changing the number of electrode divisions as in Patent Document 1, for example, is not desirable because the configuration of the liquid crystal device becomes complicated.

  In an optical pickup, divergent light from a light source is collimated by a collimator lens and condensed on an optical disc by a condenser lens (objective lens). The type of optical disc (CD, DVD, next generation DVD (Blu) -ray Disc, HD (High Definition (DVD))), a method to change the condensing position on the optical disc by driving a collimator lens or zooming by adding another zoom lens has been developed. ing. In a liquid crystal device, by applying a voltage to the electrodes on both sides of the liquid crystal layer and changing the refractive index of the liquid crystal layer, the liquid crystal layer has not only an aberration correction function but also a lens function (function to change the focal length). However, when a liquid crystal device is applied to the above optical pickup, the function of changing the focal length is exclusively used from the viewpoint of being able to control the aberration correction and the focal position separately. It is desirable to allow the liquid crystal device to have only an aberration correction function.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to correct a high-order component of spherical aberration with a simple configuration and to include a focal position control mechanism. An object of the present invention is to provide a liquid crystal device that can be easily applied to an optical pickup and an optical pickup including the liquid crystal device.

The liquid crystal device of the present invention changes the refractive index of the liquid crystal layer by applying a voltage to the liquid crystal layer between the first transparent substrate and the second transparent substrate, and changes the phase of light transmitted through the liquid crystal layer. Accordingly, in the liquid crystal device for correcting aberration generated in the optical system, the first transparent electrode is formed on the liquid crystal layer side of the first transparent substrate so as to include the entire incident range of the light beam. On the other hand, an opening electrode having an opening in the center is formed on the opposite side of the liquid crystal layer of the second transparent substrate, the opening diameter of the opening electrode is D, and the thickness of the second transparent substrate is t1. Then
7 <D / t1 <40
It is characterized by satisfying.

  According to the above configuration, the first transparent electrode is formed on the liquid crystal layer side of the first transparent substrate so as to include the entire incident range of the light beam, and is opposite to the liquid crystal layer of the second transparent substrate. On the side, an opening electrode is formed. Therefore, when this liquid crystal device is applied to, for example, an optical pickup and a light beam from a light source is configured to enter the liquid crystal device, a voltage is applied to the liquid crystal layer by applying a voltage to the first transparent electrode and the aperture electrode. Then, the refractive index of the liquid crystal layer changes according to its radial position (distance from the optical axis), so that the phase of the light transmitted through the liquid crystal layer can be changed according to the radial position. This makes it possible to correct aberrations that occur in an optical system (optical pickup) using a liquid crystal device.

  At this time, the ratio (D / t1) between the opening diameter D of the opening electrode and the thickness t1 of the second transparent substrate is set so as to satisfy the above conditional expression. If the value of D / t1 is equal to or greater than the upper limit value, it is difficult to correct spherical aberration having a high degree of coincidence with the theoretical expression of the higher-order component (for example, fifth order) of spherical aberration. On the other hand, when the value of D / t1 is equal to or lower than the lower limit value, not only the aberration correction function but also the lens function is generated in the liquid crystal layer. In this case, with the two types of electrodes, the first transparent electrode and the aperture electrode, the aberration correction and the focal position cannot be controlled separately by applying a voltage.

  Therefore, by satisfying the above conditional expression, it is possible to correct spherical aberration having a high degree of coincidence with the theoretical expression of the higher order component of spherical aberration. In addition, since it is not necessary to divide the first transparent electrode and the aperture electrode when correcting the higher order component of the spherical aberration, the higher order component of the spherical aberration can be corrected with a simple configuration. Further, by satisfying the above conditional expression, the liquid crystal layer can have only an aberration correction function. For example, the aberration correction is controlled by a liquid crystal device, and the focal position is controlled by another mechanism (for example, a collimator lens). The aberration correction and the focal position can be controlled separately, as in the case of using a driving mechanism or the like. As a result, the liquid crystal device of the present invention can be easily applied to an optical pickup having a focal position control mechanism.

  In particular, it is desirable that the conditional expression 10 <D / t1 <20 is further satisfied. In this case, it is possible to correct spherical aberration having a higher degree of coincidence with the theoretical expression of the higher-order component of spherical aberration, and it is possible to reliably provide only the aberration correction function to the liquid crystal layer.

  A second transparent electrode is formed on the opposite side of the aperture electrode from the liquid crystal layer so as to include the entire incident range of the light beam. The second transparent electrode includes the aperture electrode and the insulating layer. The structure currently formed may be sufficient.

  In this configuration, by adjusting the voltage applied to the first transparent electrode, the aperture electrode, and the second transparent electrode, the light transmitted through the peripheral portion of the liquid crystal layer (the portion away from the optical axis) It is possible to advance or delay the phase of light transmitted through the central portion (portion close to the optical axis). Therefore, the control range of the phase difference of light transmitted through the liquid crystal layer can be expanded, and the control range of aberration correction can be expanded.

  When the opening electrode is a first opening electrode, a second opening electrode having an opening in the center is formed on the opposite side of the liquid crystal layer of the first opening electrode. The opening electrode may be configured to be formed via the first opening electrode and an insulating layer.

  In this configuration, by applying a potential difference between the first transparent electrode and the first aperture electrode, higher-order components of spherical aberration can be corrected, and the first transparent electrode, the second aperture electrode, The focal length can be changed by applying a potential difference between the two. That is, in this configuration, the aberration correction and the focal length can be controlled separately by adjusting the voltage applied to the first transparent electrode, the first opening electrode, and the second opening electrode. In this way, both aberration correction and focal length can be individually controlled by one element, so that an optical pickup having a focal length control mechanism such as a collimator lens driving mechanism, and light without the above control mechanism. It can correspond to both pickups.

In the liquid crystal device of the present invention, a voltage is applied to the liquid crystal layer between the first transparent substrate and the second transparent substrate to change the refractive index of the liquid crystal layer, and the phase of light transmitted through the liquid crystal layer is changed. In this liquid crystal device, the first transparent electrode is formed on the liquid crystal layer side of the first transparent substrate so as to include the entire incident range of the light beam. On the other hand, an opening electrode having an opening in the center is formed on the liquid crystal layer side of the second transparent substrate, and the opening electrode is formed through a liquid crystal layer and an insulator. Is D, and the thickness of the insulator is t2.
7 <D / t2 <40
It is characterized by satisfying.

  According to the above configuration, the first transparent electrode is formed on the liquid crystal layer side of the first transparent substrate so as to include the entire incident range of the light flux, and on the liquid crystal layer side of the second transparent substrate. An opening electrode is formed. The opening electrode is formed through a liquid crystal layer and an insulator. Therefore, when this liquid crystal device is applied to, for example, an optical pickup and a light beam from a light source is configured to enter the liquid crystal device, a voltage is applied to the liquid crystal layer by applying a voltage to the first transparent electrode and the aperture electrode. Then, the refractive index of the liquid crystal layer changes according to its radial position (distance from the optical axis), so that the phase of the light transmitted through the liquid crystal layer can be changed according to the radial position. This makes it possible to correct aberrations that occur in an optical system (optical pickup) using a liquid crystal device.

  At this time, the ratio (D / t2) between the opening diameter D of the opening electrode and the thickness t2 of the insulator is set so as to satisfy the above conditional expression. If the value of D / t2 is equal to or greater than the upper limit value, it is difficult to correct spherical aberration having a high degree of coincidence with the theoretical expression of the higher-order component (for example, fifth order) of spherical aberration. On the other hand, when the value of D / t2 is less than or equal to the lower limit value, not only the aberration correction function but also the lens function occurs in the liquid crystal layer. In this case, with the two types of electrodes, the first transparent electrode and the aperture electrode, the aberration correction and the focal position cannot be controlled separately by applying a voltage.

  Therefore, by satisfying the above conditional expression, it is possible to correct spherical aberration having a high degree of coincidence with the theoretical expression of the higher order component of spherical aberration. In addition, since it is not necessary to divide the first transparent electrode and the aperture electrode when correcting the higher order component of the spherical aberration, the higher order component of the spherical aberration can be corrected with a simple configuration. Further, by satisfying the above conditional expression, the liquid crystal layer can have only an aberration correction function. For example, the aberration correction is controlled by a liquid crystal device, and the focal position is controlled by another mechanism (for example, a collimator lens). The aberration correction and the focal position can be controlled separately, as in the case of using a driving mechanism or the like. As a result, the liquid crystal device of the present invention can be easily applied to an optical pickup having a focal position control mechanism.

  In particular, it is desirable that the conditional expression; 10 <D / t2 <20 is further satisfied. In this case, it is possible to correct spherical aberration having a higher degree of coincidence with the theoretical expression of the higher-order component of spherical aberration, and it is possible to reliably provide only the aberration correction function to the liquid crystal layer.

  Alternatively, the second transparent electrode may be formed on the opposite side of the second transparent substrate from the liquid crystal layer so as to include the entire incident range of the light flux. Further, a second transparent electrode is formed on the liquid crystal layer side of the second transparent substrate so as to include the entire incident range of the light beam, and the second transparent electrode is interposed through the opening electrode and the insulating layer. The structure currently formed may be sufficient.

  In these configurations, by adjusting the voltage applied to the first transparent electrode, the opening electrode, and the second transparent electrode, the light transmitted through the peripheral portion of the liquid crystal layer (part away from the optical axis) It becomes possible to advance or delay the phase of light transmitted through the central portion (portion close to the optical axis). Therefore, the control range of the phase difference of light transmitted through the liquid crystal layer can be expanded, and the control range of aberration correction can be expanded.

  Further, when the opening electrode is a first opening electrode, a second opening electrode having an opening in the center may be formed on the opposite side of the liquid crystal layer of the second transparent substrate.

  In this configuration, by applying a potential difference between the first transparent electrode and the first aperture electrode, higher-order components of spherical aberration can be corrected, and the first transparent electrode, the second aperture electrode, The focal length can be changed by applying a potential difference between the two. That is, in this configuration, the aberration correction and the focal length can be controlled separately by adjusting the voltage applied to the first transparent electrode, the first opening electrode, and the second opening electrode. In this way, both aberration correction and focal length can be individually controlled by one element, so that an optical pickup having a focal length control mechanism such as a collimator lens driving mechanism, and light without the above control mechanism. It can correspond to both pickups.

  The insulator described above is preferably made of glass. In this case, the device can be easily manufactured.

  The insulating layer described above is preferably made of silicon nitride, silicon dioxide, or polyimide. In this case, the thickness of the device can be easily reduced as compared with the case where the insulating layer is made of, for example, glass.

  The optical pickup of the present invention is characterized by including the above-described liquid crystal device of the present invention. As a result, the aberration correction and the focal position can be controlled separately, such that the aberration correction is controlled by a liquid crystal device and the focal position is controlled by another mechanism (for example, a collimator lens driving mechanism). it can.

  According to the present invention, it is possible to correct spherical aberration having a high degree of coincidence with the theoretical formula of the higher-order component of spherical aberration. In addition, since it is not necessary to divide the first transparent electrode and the aperture electrode when correcting the higher order component of the spherical aberration, the higher order component of the spherical aberration can be corrected with a simple configuration. In addition, the liquid crystal layer can have only an aberration correction function, and the aberration correction and the focal position can be controlled separately. As a result, the liquid crystal device of the present invention can be easily applied to an optical pickup having a focal position control mechanism.

[Embodiment 1]
An embodiment of the present invention will be described below with reference to the drawings.

(1. Configuration of optical pickup)
FIG. 2 is an explanatory diagram showing a schematic configuration of the optical pickup according to the present embodiment. This optical pickup includes light sources 1, 2, 3, beam splitters 4, 5, 6, collimator lens 7, adjustment lens 8, collimator lens 9, half mirror 10, liquid crystal device 11, 1 / 4 wavelength plate 12, condenser lens (objective lens) 13, and light receiving elements 14 and 15.

  The light sources 1, 2, and 3 are configured by, for example, laser diodes, and emit light toward the optical disc D. In this embodiment, the light source 1 emits light having a wavelength corresponding to CD (for example, 785 nm), the light source 2 emits light having a wavelength corresponding to DVD (for example, 660 nm), and the light source 3 is a next-generation DVD. Light of a wavelength (for example, 405 nm) corresponding to (Blu-ray Disc, HD (High Definition) DVD) is emitted. As a result, any one of CD, DVD, and next-generation DVD can be used as the optical disc D.

  The light source that emits a wavelength corresponding to CD, DVD, or next-generation DVD may be any one of light sources 1, 2, and 3. For example, the light source that emits a wavelength corresponding to CD is limited to light source 1. It is not done.

  The beam splitters 4 and 5 reflect the light from the light sources 1 and 2 in the direction of the optical disk D, respectively, while transmitting the return light from the optical disk D. The beam splitter 6 transmits light from the light source 3 and reflects return light from the optical disc D. The collimator lens 7 collects the light (diverged light) from the light sources 1 and 2 to make it substantially parallel light. The adjustment lens 8 condenses the light from the light source 2 together with the collimator lens 7 to make it substantially parallel light. The collimator lens 9 condenses light (diverged light) from the light source 3 to make it substantially parallel light. The collimator lenses 7 and 9 and the adjustment lens 8 are driven and controlled by a drive mechanism (not shown) in order to change the condensing position of the light applied to the optical disc D according to the optical disc D to be used. The half mirror 10 transmits the light from the light sources 1 and 2 to the optical disc D, reflects the light from the light source 3 and guides it to the optical disc D.

  The liquid crystal device 11 is an aberration correction element having an aberration correction function, and details thereof will be described later. The quarter-wave plate 12 converts light (linearly polarized light) emitted from the light sources 1, 2, and 3 into circularly polarized light, while returning light (circularly polarized light) from the optical disk D is polarized light that is orthogonal to the incident time. Convert to linearly polarized light in the direction. The condensing lens 13 condenses incident light on the information recording surface of the optical disc D. The light receiving elements 14 and 15 receive return light from the optical disc D, and detect a servo signal (focus error signal, tracking error signal), an information signal, an aberration signal, and the like during recording and reproduction of the optical disc D.

  In the above configuration, the linearly polarized light emitted from the light source 1 is reflected by the beam splitter 4, passes through the beam splitter 5, enters the collimator lens 7, where it is converted into substantially parallel light, and the half mirror 10 is The light passes through and enters the liquid crystal device 11. The linearly polarized light emitted from the light source 2 passes through the adjustment lens 8, is reflected by the beam splitter 5, and enters the collimator lens 7. The light from the light source 2 is converted into substantially parallel light by the adjustment lens 8 and the collimator lens 7, then passes through the half mirror 10 and enters the liquid crystal device 11. The linearly polarized light emitted from the light source 3 passes through the beam splitter 6, is converted into substantially parallel light by the collimator lens 9, is reflected by the half mirror 10, and enters the liquid crystal device 11. The light incident on the liquid crystal device 11 is emitted after correcting higher-order components of spherical aberration, which will be described later, and converted into circularly polarized light by the quarter-wave plate 12, and then the information on the optical disk D by the condenser lens 13. Condensed on the recording surface.

  The return light from the optical disk D is incident again on the quarter-wave plate 12 via the condenser lens 13, where it is converted into linearly polarized light having a polarization direction orthogonal to that at the time of incidence, and the half mirror is obtained via the liquid crystal device 11. 10 is incident. Here, if the return light from the optical disk D is light having a wavelength corresponding to CD or DVD (785 nm, 660 nm), the return light passes through the half mirror 10 as it is, and the collimator lens 7, the beam splitter 5. 4 is sequentially transmitted and received by the light receiving element 14, and is converted into an electric signal there. If the return light from the optical disk D is light having a wavelength (405 nm) corresponding to the next-generation DVD, the return light is reflected by the half mirror 10, passes through the collimator lens 9, and enters the beam splitter 6. The light is reflected by the light receiving element 15 and converted into an electric signal there.

(2. Configuration of liquid crystal device)
Next, details of the liquid crystal device 11 will be described.
1A, 1B, and 1C are a plan view, a cross-sectional view, and a graph showing the relationship between the radial position (distance from the optical axis) and the phase of transmitted light, respectively, of the liquid crystal device 11. FIG. In this liquid crystal device 11, a voltage is applied to the liquid crystal layer 23 between the first transparent substrate 21 and the second transparent substrate 22 to change the refractive index of the liquid crystal layer 23, and the light transmitted through the liquid crystal layer 23 is transmitted. It is an aberration correction device that corrects aberrations that occur in an optical system by changing the phase. Hereinafter, a specific configuration of the liquid crystal device 11 will be described.

  In the liquid crystal device 11, the first transparent substrate 21 and the second transparent substrate 22 are made of glass, for example. A transparent first transparent electrode 24 is formed on the liquid crystal layer 23 side of the first transparent substrate 21. In the present embodiment, the first transparent electrode 24 is formed on the entire surface of the first transparent substrate 21 on the liquid crystal layer 23 side. Thereby, the first transparent electrode 24 is formed so as to include the entire incident range of the light flux, and the light flux incident on the liquid crystal device 11 is transmitted through the first transparent electrode 24 in its entirety. Become.

  On the other hand, on the opposite side of the second transparent substrate 22 from the liquid crystal layer 23, a transparent opening electrode 25 (first opening electrode) having an opening in the center is formed. In the present embodiment, the aperture electrode 25 is formed so that the aperture diameter is larger than the beam diameter of the incident light beam, and is not positioned on the optical path of the incident light beam.

  A voltage applying means 20 is connected to the first transparent electrode 24 and the opening electrode 25. Since the liquid crystal molecules of the liquid crystal layer 23 are fixed when a constant voltage is applied, an AC voltage is applied to the first transparent electrode 24 and the opening electrode 25 by the voltage applying means 20 in order to avoid this. The

  The liquid crystal layer 23 is sealed between the first transparent substrate 21 and the second transparent substrate 22 by a sealing material 26. An alignment film (not shown) is formed on the liquid crystal layer 23 side of the first transparent electrode 24 and the liquid crystal layer 23 side of the second transparent substrate 22.

  In this configuration, when a voltage is applied to the first transparent electrode 24 and the opening electrode 25 by the voltage application unit 20 and a voltage is applied to the liquid crystal layer 23, the refractive index of the liquid crystal layer 23 depends on the radial position. Change. That is, since the opening electrode 25 is formed with an opening in the center, a strong electric field is applied to the peripheral part (part away from the optical axis) of the liquid crystal layer 23 when a voltage is applied, and the central part (on the optical axis). A weak electric field is applied to the nearby part. Thereby, the refractive index of the liquid crystal layer 23 changes smoothly from the peripheral part to the central part, and the phase of light transmitted through the liquid crystal layer 23 changes according to the radial position. Therefore, by controlling the voltage applied to the first transparent electrode 24 and the aperture electrode 25, it becomes possible to correct spherical aberration caused by other optical elements constituting the optical pickup.

  In the present embodiment, since the aperture electrode 25 is not located in the optical path, it is possible to avoid a decrease in the transmittance of light transmitted through the liquid crystal device 11.

(3. Restriction on D / t1)
In the present embodiment, the liquid crystal device 11 is configured to satisfy the following conditional expression (1) when the opening diameter of the opening electrode 25 is D and the thickness of the second transparent substrate 22 is t1. Yes.
7 <D / t1 <40 (1)

Considering fifth-order spherical aberration as a higher-order component of spherical aberration, a theoretical expression of fifth-order spherical aberration can be expressed as follows using a Zernike polynomial.
Spherical aberration y = 20 · r ⁶ −30 · r ⁴ + 12 · r ² −1
Where r: radius of circular pupil (mm)
If the value of D / t1 is greater than or equal to the upper limit value, it will be difficult to correct spherical aberration having a high degree of coincidence with the above theoretical formula.

  On the other hand, when the value of D / t1 is less than or equal to the lower limit, when the voltage is applied to the liquid crystal layer 23 to change the refractive index of the liquid crystal layer 23, the liquid crystal layer 23 has not only an aberration correction function but also a focal length. The lens function that changes As in this embodiment, in an optical pickup having a driving mechanism for the adjustment lens 8 and the collimator lenses 7 and 9 in order to adjust the focal position, if the light condensing state is best for a certain medium, Since the generation state of spherical aberration changes and the light condensing state may be deteriorated, a configuration in which the aberration correction and the focal position can be controlled separately is desirable. In other words, it is desirable that the drive mechanism is exclusively provided with the function of changing the focal length, and only the aberration correction function is provided in the liquid crystal device 11 so that the aberration correction and the focal position can be controlled separately.

  Note that the liquid crystal device 11 of the present embodiment has only two types of electrodes, that is, the first transparent electrode 24 and the opening electrode 25 as electrodes. Therefore, the liquid crystal device 11 alone has an aberration caused by voltage control. Correction and focus position cannot be controlled separately.

  Therefore, by configuring the liquid crystal device 11 so as to satisfy the above-described conditional expression (1), it is possible to correct spherical aberration having a high degree of coincidence with the theoretical expression of the higher order component of spherical aberration. In addition, since it is not necessary to divide the first transparent electrode 24 and the aperture electrode 25 in correcting the higher order component of spherical aberration, the higher order component of spherical aberration can be corrected with a simple configuration.

  Further, by satisfying the conditional expression (1), the liquid crystal layer 23 can have only an aberration correction function. Accordingly, the aberration correction can be controlled by the liquid crystal device 11, and the focal position can be controlled by another mechanism (the driving mechanism of the adjustment lens 8 and the collimator lenses 7 and 9). Can be controlled separately. As a result, the liquid crystal device 11 of the present invention can be easily applied to an optical pickup having a focal position control mechanism.

In particular, in order to correct spherical aberration having a higher degree of coincidence with the theoretical expression of the higher-order component of spherical aberration, and to ensure that the liquid crystal layer 23 only has an aberration correction function, the following conditional expression (2) is satisfied. It is desirable to configure the liquid crystal device 11 as described above.
10 <D / t1 <20 (2)

As can be seen from the above description, the value of D / t1 may be less than 40, and is preferably less than 20. Further, the value of D / t1 may be larger than 7, and is desirably larger than 10. Therefore, the conditional expression for obtaining the effect of the present invention can be set by a combination of the above upper limit value and lower limit value. In other words, the conditional expression for obtaining the effect of the present invention may be any of the following conditional expressions.
7 <D / t1 <20
10 <D / t1 <40

[Embodiment 2]
The following will describe another embodiment of the present invention with reference to the drawings. For convenience of explanation, the same components as those in the first embodiment are denoted by the same member numbers, and the description thereof is omitted.

  3A and 3B are a plan view and a cross-sectional view of the liquid crystal device 11 of the present embodiment, respectively. The liquid crystal device 11 of the present embodiment is different from the liquid crystal device 11 of the first embodiment in the layer configuration on the side opposite to the first transparent substrate 21 with respect to the liquid crystal layer 23, and other configurations are implemented. This is the same as the liquid crystal device 11 of the first embodiment.

  More specifically, in this embodiment, the opening electrode 25 is formed on the liquid crystal layer 23 side of the second transparent substrate 22. The opening electrode 25 is formed through the liquid crystal layer 23 and the insulator 27. The insulator 27 is made of thin glass, for example. An insulating layer 28 is formed between the insulator 27 and the second transparent substrate 22 and in the opening region of the opening electrode 25. The insulating layer 28 functions as an adhesive layer that bonds the insulator 27 and the second transparent substrate 22 together.

In the present embodiment, when the opening diameter of the opening electrode 25 is D and the thickness of the insulator 27 is t2, the liquid crystal device 11 is configured to satisfy the following conditional expression (3).
7 <D / t2 <40 (3)

  If the value of D / t2 is equal to or greater than the upper limit value, it is difficult to correct spherical aberration having a high degree of coincidence with the theoretical expression of the higher-order component of spherical aberration shown in the first embodiment. On the other hand, when the value of D / t2 is less than or equal to the lower limit value, when the voltage is applied to the liquid crystal layer 23 to change the refractive index of the liquid crystal layer 23, the liquid crystal layer 23 has not only an aberration correction function but also a focal length. The lens function that changes In the liquid crystal device 11 of the present embodiment, as in the first embodiment, since there are two types of electrodes, that is, the first transparent electrode 24 and the opening electrode 25, in the liquid crystal device 11, aberration is caused by voltage control. Correction and focus position cannot be controlled separately.

  Therefore, by configuring the liquid crystal device 11 so as to satisfy the above-described conditional expression (3), the same effect as in the first embodiment can be obtained. That is, it is possible to correct spherical aberration having a high degree of coincidence with the theoretical formula of the higher order component of spherical aberration with a simple configuration. Further, only the aberration correction function can be provided in the liquid crystal layer 23, and the aberration correction and the focal position can be controlled separately. As a result, the liquid crystal device 11 of the present invention can be easily applied to an optical pickup having a focal position control mechanism.

In particular, in order to correct spherical aberration having a higher degree of coincidence with the theoretical expression of the higher-order component of spherical aberration and to ensure that the liquid crystal layer 23 only has an aberration correction function, the following conditional expression (4) is satisfied. It is desirable to configure the liquid crystal device 11 as described above.
10 <D / t2 <20 (4)

In addition, from the above, in this embodiment, the value of D / t2 should just be less than 40, and it is desirable that it is less than 20. Further, the value of D / t2 only needs to be larger than 7, and is desirably larger than 10. Therefore, the conditional expression for obtaining the effect of the present invention can be set by a combination of the above upper limit value and lower limit value, and can be said to be any of the following conditional expressions.
7 <D / t2 <20
10 <D / t2 <40

  Moreover, in this embodiment, since the insulator 27 is formed with glass, the liquid crystal device 11 can be easily manufactured compared with the case where it forms with another material.

[Embodiment 3]
The following will describe still another embodiment of the present invention with reference to the drawings. For convenience of explanation, the same components as those in the first and second embodiments are denoted by the same member numbers, and description thereof is omitted.

  4A, 4B, and 4C are a plan view, a cross-sectional view, and a graph showing the relationship between the radial position and the phase of transmitted light, respectively, of the liquid crystal device 11 of the present embodiment. In the liquid crystal device 11 of the present embodiment, the second transparent electrode 29 is formed on the opposite side of the second transparent substrate 22 from the liquid crystal layer 23, and the opening electrode 25 is formed so as to protrude into the incident range of the light flux. These are the same structures as the liquid crystal device 11 of Embodiment 2. FIG.

  The second transparent electrode 29 is formed on the entire surface of the second transparent substrate 22 opposite to the liquid crystal layer 23. As a result, the second transparent electrode 29 is formed so as to include the entire incident range of the light beam, and the light beam incident on the liquid crystal device 11 is transmitted through the second transparent electrode 29 in its entirety. Become. The first transparent electrode 24, the opening electrode 25, and the second transparent electrode 29 are connected to the voltage application unit 20.

  In this embodiment, when the potential difference between the first transparent electrode 24 and the opening electrode 25 is V1, and the potential difference between the first transparent electrode 24 and the second transparent electrode 29 is V2, V1> V2. In addition, if a voltage is applied to the first transparent electrode 24, the opening electrode 25, and the second transparent electrode 29, the transmitted light near the optical axis of the liquid crystal layer 23 and the peripheral portion thereof are transmitted to the same level as in FIG. A phase difference occurs. On the other hand, if a voltage is applied to the first transparent electrode 24, the opening electrode 25, and the second transparent electrode 29 so that V1 ≦ V2, the transmitted light is transmitted near the optical axis of the liquid crystal layer 23 and in the periphery. A phase difference as shown in 4 (c) occurs. That is, when V1 ≦ V2, a phase pattern opposite to the phase pattern when V1> V2 is obtained.

  Thus, by further providing the second transparent electrode 29, it is possible to advance or delay the phase of the light transmitted through the central portion with respect to the light transmitted through the peripheral portion of the liquid crystal layer 23. Become. Therefore, according to the configuration of the present embodiment, the control range of the phase difference of light transmitted through the liquid crystal layer 23 can be expanded, and the control range of aberration correction can be expanded. That is, in the present embodiment, the second transparent electrode 29 is required in the optical path, but aberration correction can be performed in a wider range than the configuration of the first or second embodiment.

  In the present embodiment, the reason why the aperture electrode 25 is formed so as to protrude into the incident range of the light beam is reduced by forming the second transparent electrode 29, and the light transmitted through the peripheral portion of the liquid crystal layer 23 is reduced. This is because the difference between the phase and the phase of the light transmitted through the central portion is increased as shown in FIG.

[Embodiment 4]
The following will describe still another embodiment of the present invention with reference to the drawings. For convenience of explanation, the same components as those in the first to third embodiments are denoted by the same member numbers, and description thereof is omitted.

  5A and 5B are a plan view and a cross-sectional view of the liquid crystal device 11 of the present embodiment, respectively. In the liquid crystal device 11 of the present embodiment, the second transparent electrode 29 is formed on the liquid crystal layer 23 side of the second transparent substrate 22, and the second transparent electrode 29 is formed with the opening electrode 25 and the insulator 27 and the insulating layer. The configuration is the same as that of the liquid crystal device 11 of the third embodiment except that it is formed on the opposite side of the liquid crystal layer 23 via 28.

  In the present embodiment, the thickness of the insulating layer 28 is different from that of the third embodiment, but the potential difference V1 between the first transparent electrode 24 and the opening electrode 25, and the first transparent electrode 24 and the second transparent electrode 29. The embodiment can control the phase difference of the light transmitted through the central portion with respect to the light transmitted through the peripheral portion of the liquid crystal layer 23 by controlling the potential difference V2 between the first and second embodiments. It is exactly the same as 3. Therefore, also with the configuration of the present embodiment, the control range of the phase difference of the light transmitted through the liquid crystal layer 23 can be expanded and the control range of the aberration correction can be expanded as in the case of the third embodiment.

The insulating layer 28 can be composed of, for example, any one of silicon nitride (Si ₃ N ₄ ), silicon dioxide (SiO ₂ ), and polyimide. If the insulating layer 28 is formed of such a material, the opening electrode 25 and the second transparent electrode 29 are compared to the case where the insulating layer 28 between the opening electrode 25 and the second transparent electrode 29 is formed of glass. And the entire device can be easily reduced in thickness.

[Embodiment 5]
The following will describe still another embodiment of the present invention with reference to the drawings. For convenience of explanation, the same components as those in the first to fourth embodiments are denoted by the same member numbers, and the description thereof is omitted.

  6A and 6B are a plan view and a cross-sectional view of the liquid crystal device 11 of this embodiment, respectively. The liquid crystal device 11 according to the present embodiment has the second transparent electrode 29 formed on the opposite side of the opening electrode 25 from the liquid crystal layer 23 in the configuration of the first embodiment, and the second transparent electrode 29 is opened. It is formed on the opposite side of the liquid crystal layer 23 with the electrode 25 and the second transparent substrate 22 and the insulating layer 28 interposed therebetween.

  The second transparent electrode 29 is formed on the insulating layer 28 so as to include the entire incident range of the light flux. As a result, the entire light beam incident on the liquid crystal device 11 passes through the second transparent electrode 29. The first transparent electrode 24, the opening electrode 25, and the second transparent electrode 29 are connected to the voltage application unit 20.

  Also in the present embodiment, as in the third or fourth embodiment, the potential difference V1 between the first transparent electrode 24 and the opening electrode 25 and the potential difference V2 between the first transparent electrode 24 and the second transparent electrode 29 are set. By controlling, the phase of the light transmitted through the central portion can be advanced or delayed with respect to the light transmitted through the peripheral portion of the liquid crystal layer 23. Therefore, also with the configuration of the present embodiment, the control range of the phase difference of the light transmitted through the liquid crystal layer 23 can be expanded and the control range of the aberration correction can be expanded, as in the case of the third or fourth embodiment.

  In the present embodiment, the aperture electrode 25 is formed so as to protrude into the incident range of the light beam, for the same reason as described in the third embodiment. That is, this is to increase the difference between the phase of light transmitted through the peripheral portion of the liquid crystal layer 23 and the phase of light transmitted through the central portion, which is reduced by forming the second transparent electrode 29.

[Embodiment 6]
The following will describe still another embodiment of the present invention with reference to the drawings. For convenience of explanation, the same components as those in the first to fifth embodiments are denoted by the same member numbers, and the description thereof is omitted.

  7A and 7B are a plan view and a cross-sectional view of the liquid crystal device 11 of the present embodiment, respectively. In the liquid crystal device 11 of the present embodiment, in the configuration of the second embodiment, an opening electrode 30 (second opening electrode) having an opening in the center is formed on the opposite side of the second transparent substrate 22 from the liquid crystal layer 23. It is a thing. The first transparent electrode 24, the opening electrode 25 and the opening electrode 30 are connected to the voltage application unit 20.

  In this configuration, a high-order component of spherical aberration can be corrected by applying a potential difference between the first transparent electrode 24 and the opening electrode 25. Further, the focal distance can be changed by applying a potential difference between the first transparent electrode 24 and the opening electrode 30. That is, in this configuration, the aberration correction and the focal length can be controlled separately by adjusting the voltage applied to the first transparent electrode 24 and the opening electrodes 25 and 30. In this way, both the aberration correction and the focal length can be individually controlled by one element, so that an optical pickup having a focal length control mechanism such as a drive mechanism for the collimator lenses 7 and 9 and the adjusting lens 8 can be used. It is possible to cope with both the optical pickup without the control mechanism.

[Embodiment 7]
The following will describe still another embodiment of the present invention with reference to the drawings. For convenience of explanation, the same components as those in the first to sixth embodiments are denoted by the same member numbers, and description thereof is omitted.

  8A and 8B are a plan view and a cross-sectional view of the liquid crystal device 11 of the present embodiment, respectively. In the liquid crystal device 11 of the present embodiment, in the configuration of the first embodiment, an opening electrode 30 having an opening in the center is formed on the opposite side of the opening electrode 25 from the liquid crystal layer 23, and the opening electrode 30 is formed as an opening electrode. 25 and the second transparent substrate 22 and the insulating layer 28. The first transparent electrode 24, the opening electrode 25 and the opening electrode 30 are connected to the voltage application unit 20.

  Also in the configuration of the present embodiment, as in the sixth embodiment, by applying a potential difference between the first transparent electrode 24 and the opening electrode 25, higher-order components of spherical aberration can be corrected. By providing a potential difference between one transparent electrode 24 and the opening electrode 30, the focal length can be changed. Therefore, the configuration of the present embodiment can cope with both the optical pickup having the drive mechanism for the collimator lenses 7 and 9 and the adjusting lens 8 and the optical pickup without the control mechanism.

  Of course, the liquid crystal device 11 can be configured by appropriately combining the configurations described in the above embodiments. For example, the liquid crystal device 11 can be configured by combining the configuration of the third to fifth embodiments where the second transparent electrode 29 is provided with the configuration of the sixth or seventh embodiment where the opening electrode 30 is provided. In this case, an insulating layer may be provided between the opening electrode 30 and the second transparent electrode 29 as necessary.

(A) is a top view of the liquid crystal device used for the optical pick-up which concerns on one Embodiment of this invention, (b) is sectional drawing of the said liquid crystal device, (c) is in the said liquid crystal device. It is a graph which shows the relationship between a radial position and the phase of transmitted light. It is explanatory drawing which shows the schematic structure of the said optical pick-up. (A) is a top view of the liquid crystal device which concerns on other embodiment of this invention, (b) is sectional drawing of the said liquid crystal device. (A) is a top view of the liquid crystal device which concerns on other embodiment of this invention, (b) is sectional drawing of the said liquid crystal device, (c) is a radial position in the said liquid crystal device, and It is a graph which shows the relationship with the phase of transmitted light. (A) is a top view of the liquid crystal device which concerns on other embodiment of this invention, (b) is sectional drawing of the said liquid crystal device. (A) is a top view of the liquid crystal device which concerns on other embodiment of this invention, (b) is sectional drawing of the said liquid crystal device. (A) is a top view of the liquid crystal device which concerns on other embodiment of this invention, (b) is sectional drawing of the said liquid crystal device. (A) is a top view of the liquid crystal device which concerns on other embodiment of this invention, (b) is sectional drawing of the said liquid crystal device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Liquid crystal device 21 1st transparent substrate 22 2nd transparent substrate 23 Liquid crystal layer 24 1st transparent electrode 25 Opening electrode (1st opening electrode)
27 Insulator 28 Insulating Layer 29 Second Transparent Electrode 30 Open Electrode (Second Open Electrode)

Claims (10)

By applying a voltage to the liquid crystal layer between the first transparent substrate and the second transparent substrate to change the refractive index of the liquid crystal layer and to change the phase of light transmitted through the liquid crystal layer, the optical system A liquid crystal device for correcting the generated aberration,
On the liquid crystal layer side of the first transparent substrate, a first transparent electrode is formed so as to include the entire incident range of the light beam, while on the opposite side of the liquid crystal layer of the second transparent substrate, in the center. An opening electrode having an opening is formed;
When the opening diameter of the opening electrode is D and the thickness of the second transparent substrate is t1,
7 <D / t1 <40
A liquid crystal device characterized by satisfying 10 <D / t1 <20
The liquid crystal device according to claim 1, further satisfying: On the side opposite to the liquid crystal layer of the aperture electrode, a second transparent electrode is formed so as to include the entire incident range of the light beam,
The liquid crystal device according to claim 1, wherein the second transparent electrode is formed through the opening electrode and an insulating layer. By applying a voltage to the liquid crystal layer between the first transparent substrate and the second transparent substrate to change the refractive index of the liquid crystal layer and to change the phase of light transmitted through the liquid crystal layer, the optical system A liquid crystal device for correcting the generated aberration,
The first transparent electrode is formed on the liquid crystal layer side of the first transparent substrate so as to include the entire incident range of the light flux, while the liquid crystal layer side of the second transparent substrate has an opening in the center. An opening electrode is formed,
The opening electrode is formed through a liquid crystal layer and an insulator,
When the opening diameter of the opening electrode is D and the thickness of the insulator is t2,
7 <D / t2 <40
A liquid crystal device characterized by satisfying 10 <D / t2 <20
The liquid crystal device according to claim 4, further satisfying: 6. The liquid crystal device according to claim 4, wherein a second transparent electrode is formed on the side opposite to the liquid crystal layer of the second transparent substrate so as to include the entire incident range of the light flux. A second transparent electrode is formed on the liquid crystal layer side of the second transparent substrate so as to include the entire incident range of the luminous flux,
The liquid crystal device according to claim 4, wherein the second transparent electrode is formed through the opening electrode and an insulating layer. The liquid crystal device according to claim 4, wherein the insulator is made of glass. 8. The liquid crystal device according to claim 3, wherein the insulating layer is made of any one of silicon nitride, silicon dioxide, and polyimide. An optical pickup comprising the liquid crystal device according to claim 1.

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