JP2006344332A - Polarizing optical element, control board, and method of control - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing optical element, a control board and a method of control by which an optional phase difference can be set to an arbitrary area by simple wiring and simple control. <P>SOLUTION: A liquid crystal technique is used for the polarizing optical element. Voltage is applied to liquid crystal by transparent electrodes 14 arranged in the state of a matrix. Voltage is applied to "the arbitrary area" and "the other area" at a ratio of 3:1. In this case, the voltage applied to "the other area" is made to be not higher than a voltage threshold. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polarizing optical element, a control board, and a control method, and more particularly, to a polarizing optical element, a control board, and a control method that form regions to which different phase differences are added.

  In recent years, in order to achieve high-density and large-capacity data storage, optical memory technology using an optical disk as a storage medium has been widely used.

  An optical disk has a larger storage capacity than a recording medium such as a floppy (registered trademark) disk and is more portable than a hard disk. Therefore, multimedia data such as video and music, data files, programs such as software, etc. It is used as a data retention disk.

  In recent years, optical discs having a plurality of recording layers have been proposed, and optical pickup devices and recording / reproducing devices for recording / reproducing the optical discs have been proposed. In these apparatuses, the problem is how to focus the laser beam on a recording surface having a plurality of layers.

  As a technique related to such a recording / reproducing apparatus compatible with a multi-layer optical disc, the following has been proposed.

Patent Document 1 proposes an optical recording / reproducing apparatus having a guest-host type liquid crystal that selectively blocks a peripheral light beam out of a divergent light beam from a semiconductor laser. With this configuration, it is possible to selectively apply a voltage to the guest-host type liquid crystal according to the substrate thickness of the optical recording medium, and to selectively block the peripheral rays of the divergent light beam from the semiconductor laser. Therefore, the numerical aperture of the objective lens can be controlled.
JP 9-326127 A

  When recording / reproducing a multi-layer optical disc, reflected light from a layer other than the recording / reproducing target layer is projected onto the light receiving element, and flare light that causes reading deterioration of the light receiving element may occur. Since the influence of flare light increases as the layer spacing becomes narrower, the adverse effects of such flare light cannot be ignored with the recent increase in the density of optical disks and the increase in the number of layers. For this reason, removing flare light is an important issue, but the above technique does not consider this point at all.

  As a technique for removing flare light, there is a technique for removing flare light by providing a fine opening such as a pinhole. However, in such a form, adjustment and alignment of the opening position are very difficult because of a mechanical fixed opening. It was.

  In this regard, as a method for forming a fine aperture without using a fixed aperture, a method using liquid crystal technology for an optical element is conceivable. The liquid crystal has a characteristic that its phase difference changes according to the applied voltage. Moreover, since a liquid crystal can apply a voltage only to arbitrary places, it can add a phase difference to arbitrary places. Therefore, for example, if an optical element and a polarizing plate using liquid crystal technology are used, unnecessary light can be eliminated, and as a result, flare light can be suppressed.

  Moreover, if an arbitrary phase difference can be set in an arbitrary region, the present invention is not limited to the purpose of removing flare light, and can be used for various purposes. For example, use as an optical element for forming an arbitrary wave plate only in an arbitrary region, use as an attenuator, and the like. Therefore, it can be said that such a polarizing optical element is very useful.

  As an optical element for setting an arbitrary phase difference in an arbitrary region, for example, an optical element using a TFT liquid crystal (Thin Film Transistor Liquid Crystal) can be proposed. However, since TFT liquid crystal needs to incorporate wiring and transistors, it is inevitable that the transmittance is reduced, and is not practical as an optical element. Further, since the functions required as an element are an aperture limit and a wave plate function, the required functions are over-spec and are not cost effective.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a polarizing optical element, a control board, and a control method that can set an arbitrary phase difference in an arbitrary region by simple wiring and simple control. To do.

  The invention according to claim 1 is a polarizing optical element in which a transparent substrate in which a transparent electrode, an insulating layer, and an alignment film are laminated is opposed to the liquid crystal layer, and one of the transparent electrodes facing the liquid crystal layer. Are arranged side by side in the vertical direction, and the other is arranged side by side in the horizontal direction, and a first voltage is applied to an arbitrary lattice point among lattice points where the transparent electrode intersects, and other than the arbitrary lattice points. By applying a second voltage to the lattice point, two regions having different phase differences to be added are formed.

  The invention according to claim 2 is a control board for driving and controlling the polarizing optical element according to claim 1, wherein the first voltage and the second voltage are applied at a voltage ratio of 3: 1. It is characterized by.

  According to a third aspect of the present invention, in the control substrate according to the second aspect, the transparent electrode that forms the arbitrary lattice point and the transparent electrode that forms a lattice point other than the arbitrary lattice point are 3: 1. By applying a voltage in the opposite phase, the relationship of “first voltage: second voltage = 3: 1” is obtained.

  According to a fourth aspect of the present invention, in the control substrate according to the second or third aspect, the second voltage is not more than a threshold voltage that causes a phase difference change in the liquid crystal alignment of the liquid crystal molecules in the liquid crystal layer. It is characterized by.

  Invention of Claim 5 has a temperature detection means to detect the element temperature of the said polarization optical element in the control board of any one of Claim 2 to 4, It applies according to the said element temperature It is characterized in that the voltage to be changed is adjusted.

  According to a sixth aspect of the present invention, in the control board according to any one of the second to fifth aspects, the region to which the first voltage is applied has a wavelength of transmitted light transmitted through the polarizing optical element ( 2n-1) / 4 (n is an integer equal to or greater than 1), and the region to which the second voltage is applied is (2n + 1) / 4 of the wavelength of transmitted light transmitted through the polarizing optical element. The first voltage and the second voltage are applied so as to add a phase difference of.

  According to a seventh aspect of the present invention, in the control substrate according to any one of the second to fifth aspects, the region to which the first voltage is applied has a wavelength of transmitted light that passes through the polarizing optical element ( 2n-1) / 4 (n is an integer greater than or equal to 1), and the region to which the second voltage is applied has a phase difference of n times the wavelength of the transmitted light transmitted through the polarizing optical element. The first voltage and the second voltage are applied so as to add.

  According to an eighth aspect of the present invention, in the control board according to any one of the second to fifth aspects, the region to which the first voltage is applied has a wavelength of transmitted light transmitted through the polarizing optical element ( 2n-1) / 2 (n is an integer equal to or greater than 1), and the region to which the second voltage is applied has a phase difference of n times the wavelength of the transmitted light transmitted through the polarizing optical element. The first voltage and the second voltage are applied so as to add.

  According to a ninth aspect of the present invention, in the control board according to any one of the second to fifth aspects, the polarizing optical element has an analyzer having an optical axis in a predetermined direction in the subsequent stage, and The transmitted light passing through the region to which the voltage is applied is shielded, and the transmitted light passing through the region to which the first voltage is applied is transmitted with a desired amount of transmitted light. And adjusting the voltage.

  A tenth aspect of the present invention is a control method for driving and controlling the polarizing optical element according to the first aspect, wherein the applied voltage is set so that a ratio of the first voltage to the second voltage is 3: 1. It is characterized by setting.

  According to an eleventh aspect of the present invention, in the control method according to the tenth aspect, the second voltage is set to a voltage equal to or lower than a threshold voltage that causes a phase difference change in the liquid crystal alignment of the liquid crystal molecules in the liquid crystal layer. It is characterized by that.

  According to a twelfth aspect of the present invention, in the control method according to the tenth or eleventh aspect, the temperature detection step of detecting the element temperature of the polarizing optical element, and the application according to the element temperature detected by the temperature detection step And a voltage adjustment step of changing / adjusting the voltage to be performed.

  A thirteenth aspect of the present invention is the control method according to any one of the tenth to twelfth aspects, wherein the region to which the first voltage is applied has a wavelength of transmitted light transmitted through the polarizing optical element ( 2n-1) / 4 (n is an integer equal to or greater than 1), and the region to which the second voltage is applied is (2n + 1) / 4 of the wavelength of transmitted light transmitted through the polarizing optical element. The first voltage and the second voltage are set so as to add a phase difference of.

  A fourteenth aspect of the present invention is the control method according to any one of the tenth to twelfth aspects, wherein a region to which the first voltage is applied has a wavelength of transmitted light transmitted through the polarizing optical element ( 2n-1) / 4 (n is an integer greater than or equal to 1), and the region to which the second voltage is applied has a phase difference of n times the wavelength of the transmitted light transmitted through the polarizing optical element. The first voltage and the second voltage are set so as to add.

  A fifteenth aspect of the present invention is the control method according to any one of the tenth to twelfth aspects, wherein the region to which the first voltage is applied has a wavelength of transmitted light transmitted through the polarizing optical element ( 2n-1) / 2 (n is an integer equal to or greater than 1), and the region to which the second voltage is applied has a phase difference of n times the wavelength of the transmitted light transmitted through the polarizing optical element. The first voltage and the second voltage are set so as to add.

  The invention according to claim 16 is the control method according to any one of claims 10 to 12, wherein the polarizing optical element has an analyzer having an optical axis in a predetermined direction in the subsequent stage, and The transmitted light passing through the region to which the voltage is applied is shielded, and the transmitted light passing through the region to which the first voltage is applied is transmitted with a desired amount of transmitted light. The voltage is set.

  According to the present invention, the phase difference added by the polarizing optical element can be set to a desired value, and the region to which the phase difference is added can also be set to a desired position, thereby realizing a flexible polarizing optical element. Is possible.

<Polarized optical element>
The polarizing optical element according to the present invention will be described. The configuration of the polarizing optical element is shown in FIG.

  The polarizing optical element 10 is configured by sequentially laminating an alignment film 12, an insulating layer 13, a transparent electrode 14, and a glass substrate 15 with a liquid crystal layer 11 interposed therebetween.

  The liquid crystal layer 11 is a layer containing liquid crystal molecules. Liquid crystal molecules have a birefringence effect, and the refractive index is different between the optical axis direction of the liquid crystal molecules and the direction perpendicular to the optical axis direction. The direction of the liquid crystal molecules changes from the horizontal direction to the vertical direction according to the voltage applied to the transparent electrode 14, and the phase of the transmitted light also changes accordingly.

  The alignment film 12 is a film that gives a predetermined molecular orientation to the liquid crystal molecules of the liquid crystal layer 11. The transparent electrode 14 is made of ITO (Indium Tin Oxide / Indium Tin Oxide) or the like, and is deposited on the outer side of the alignment film 12 via the insulating layer 13. The glass substrate 15 as a transparent substrate is made of a glass material having translucency, and is provided as a protective layer on the outermost part (uppermost layer) of the polarizing optical element 10.

  The phase difference added to the transmitted light by the polarizing optical element 10 is Δn which is the value of the change in the refractive index of the liquid crystal molecules and the thickness d between the alignment films 12 in a potentialless state where no voltage is applied. , (Δn × d). In a state in which a voltage is applied, the voltage is determined according to the applied voltage and the application characteristics (relationship between phase difference and voltage) of the polarizing optical element 10.

  The phase control of each area on the polarizing optical element 10 is performed by controlling the voltage applied to the area. In order to enable such phase control for each region, the transparent electrodes 14 of the polarizing optical element 10 are arranged in a matrix (lattice).

  FIG. 2 shows an electrode pattern of the transparent electrode 14 when the polarizing optical element 10 is viewed from above. As shown in FIG. 2, the transparent electrodes 14 are arranged in a matrix. Specifically, a plurality of fine strip-shaped transparent electrodes 14 are arranged side by side (X1 to X5 / X address), and the same transparent electrode 14 is rotated 90 degrees on the opposite side across the liquid crystal layer 11. (Y1-Y5 / Y address). Each transparent electrode 14 is provided independently, and a different voltage can be applied to each transparent electrode 14.

  Control of voltage application to the transparent electrode 14 is performed by a control board provided outside the polarizing optical element 10. The control board controls the voltage to be applied based on the corresponding laser wavelength or feedback signal.

  The place where the transparent electrode 14 overlaps (the layers that exist are not directly overlapped) is a point (point) where voltage is actually applied to the liquid crystal molecules as a lattice point. The voltage applied to the liquid crystal molecules is represented by the absolute value of the difference between the X address voltage and the Y address voltage at that point.

  Next, voltage application control of the polarizing optical element 10 will be described. The control substrate forms a region having a certain phase difference at an arbitrary position on the polarizing optical element 10 (hereinafter referred to as “arbitrary region”), and sets a region other than the “arbitrary region” as a phase difference of the arbitrary region. Are formed as regions having different phase differences (hereinafter “other regions”).

  In order to form each region as described above, it is necessary to apply a voltage so that the phase difference of “arbitrary region” differs from the phase difference of “other regions (regions other than the arbitrary region)”. That is, the voltage applied to the “arbitrary region” and the voltage applied to the “other region” must be different, and the voltage applied to the “other region” must be uniform.

  Therefore, as shown in FIGS. 3 and 4, a voltage is applied to the “arbitrary region” and the “other region” at a ratio of 3: 1. Specifically, in the X address (Y address) direction, the voltage ratio between the transparent electrode 14 forming the “arbitrary region” and the transparent electrode forming the “other region” is set to 3: 1 and in reverse phase ( -1.5 and 0.5), and the voltage ratio between the transparent electrode 14 forming the “arbitrary region” and the transparent electrode 14 forming the “other region” in the Y address (X address) direction is 3: 1. To set in reverse phase (1.5 and -0.5).

  The potential difference (voltage) in each region is represented by the difference between the X address voltage and the Y address voltage. Looking at FIGS. 3 and 4, the potential difference between “arbitrary region” and “other regions”. The absolute value of the ratio is 3: 1. The potential difference between the “arbitrary region” and the potential difference between the “other regions” is different, and the “other region” is a uniform potential difference. I understand that.

  In general, in liquid crystal technology, AC driving is performed in order to prevent electrolysis of liquid crystal molecules. Therefore, the voltage applied in FIG. 3 (FIG. 4) and the sign of FIG. 3 (FIG. 4) are reversed. However, since the phase difference is determined only by the absolute value of the potential difference (voltage) applied to the liquid crystal element, the phase difference is not affected even if the positive / negative (polarity) of the potential difference is reversed. does not change. Therefore, the phase difference added by each region does not change as long as the applied voltage is constant.

  As a basic characteristic, liquid crystal molecules have a voltage value (hereinafter referred to as “voltage threshold value”) that has a small phase difference change with respect to a potential difference change. Even if a voltage not exceeding this voltage threshold value is applied, the orientation of the liquid crystal molecules Hardly changes and does not cause a phase difference of transmitted light. In the polarizing optical element 10 of the present embodiment, the voltage ratio applied to the “arbitrary region” and the “other region” is set to 3: 1, but the “arbitrary region” on the high potential side (ratio 3 side). Is set to a voltage at which a desired phase difference can be obtained, and the “other region” on the low potential side (the ratio 1 side) is set to a voltage equal to or lower than the voltage threshold. This point will be specifically described in each embodiment.

  As described above, the polarizing optical element 10 and its control board of the present embodiment set the phase difference added by the polarizing optical element to a desired value, and the region to which the phase difference is added is also set to a desired location. Since it can be set, a flexible optical element can be realized.

  Hereinafter, driving modes of the polarizing optical element 10 and the control board will be described according to the embodiments.

<First Embodiment>
First, a first embodiment of the present invention will be described. In the present embodiment, the polarizing optical element 10 is configured such that a phase difference of λ / 4 is added to the transmitted light in “any region” and a phase difference of 3 / 4λ is added to the transmitted light in “other region”. Apply voltage to

  The voltage to be actually applied is set as follows. For example, in the case of using it corresponding to a laser beam of 780 nm, Δn and d of the polarizing optical element 10 are determined so that the phase difference represented by Δn × d is near 585 nm (3/4 of 780 nm).

  A voltage determined from the phase characteristics is applied to the determined polarizing optical element 10. FIG. 5 is a graph showing phase characteristics. Based on this graph, first, a voltage to be applied to “another region” to which a phase difference of 3 / 4λ is added is determined. About this, since the graph of wavelength 780nm is a voltage which takes a phase difference of 585nm, it will be 0.93V. Further, as described above, the voltage ratio applied to the “arbitrary region” and the “other region” is set to 3: 1, so the voltage of the “arbitrary region” to which the phase difference of λ / 4 is added is 0. The voltage is 2.8V, three times 93V. When a voltage of 2.8 V is applied to the “arbitrary region” and a voltage of 0.93 V is applied to the “other region”, the polarizing optical element 10 capable of adding the above phase difference can be realized.

  A polarizing optical element 10 that can add a phase difference of λ / 4 to transmitted light in such “arbitrary region” and add a phase difference of 3 / 4λ to transmitted light in “other region” is, for example, It can be used as an optical isolator of an optical pickup device.

  An optical pickup device to which the polarizing optical element 10 of this embodiment is applied as an optical isolator will be described with reference to FIG. FIG. 6 shows a configuration of an optical pickup device of a recording / reproducing apparatus compatible with a multilayer structure optical disk.

  The optical pickup device 20 includes a laser diode 21, a collimator lens 22, a beam splitter 23, expander lenses 24a and 24b, a polarizing optical element 10, a reflecting prism 25, an objective lens 26, a detection lens 27, And a light receiving element 28.

  The laser diode 21 is a laser light source that emits laser light (light beam), and emits laser light having a wavelength of 780 nm, for example. The collimator lens 22 converts the laser light emitted from the laser diode 21 into a parallel light beam.

  The parallel light beam passes through the beam splitter 23, the expander lens 24a, and the polarizing optical element 10. At this time, the light beam focused by the expander lens 24a passes through the “arbitrary region” of the polarizing optical element 10 and is added with a phase of λ / 4.

  Then, the light beam passes through the expander lens 24 b and the reflecting prism 25, is condensed by the objective lens 26, and is irradiated onto the recording / reproducing target layer of the optical disc 30. The irradiated light beam is reflected by the optical disc 30, passes through the objective lens 26, the reflecting prism 25, and the expander lens 24b, and reaches the polarizing optical element 10 again.

  The light beam reflected by the optical disc 30 includes a light beam reflected by a recording / reproduction target layer and a light beam reflected by a layer other than the recording / reproduction target layer. Along with the forward path, the light passes through an “arbitrary region” of the polarizing optical element 10 and is added with a phase of λ / 4. As a result, a total phase of λ / 2 is added, so that the polarization plane rotates by 90 degrees, resulting in a light beam whose forward path and polarization plane differ by 90 degrees. Therefore, the light beam is reflected by the beam splitter 23 and guided to the detection lens 27 and the light receiving element 28 to be detected.

  On the other hand, the light beam reflected by the layer not to be recorded / reproduced is transmitted through the “other region” of the polarizing optical element 10 and is added with a phase of 3 / 4λ. As a result, a total of λ phases are added, so the polarization plane does not change, and the light beam has the same polarization plane as the forward path. Therefore, since this light beam passes through the beam splitter 23, the reflected light of the layer not to be recorded / reproduced is not guided to the light receiving element 28.

  Therefore, the reflected light of the layer not to be recorded / reproduced is not flare light and projected onto the light receiving element 28, so that it is possible to suppress the occurrence of servo signal error and the degradation of the reproduced signal. Further, since the polarizing optical element 10 of the present embodiment can freely form an “arbitrary area” in the area on the polarizing optical element 10, it is possible to perform fine adjustments that could not be made with a mechanical fixed aperture. It becomes possible.

  Such region formation control is realized by the control board performing feedback control and closed loop control for performing control adjustment based on the detection signal of the light receiving element 28 of the optical pickup device 20.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. In the present embodiment, a voltage is applied to the polarizing optical element 10 so that a phase difference of λ / 4 is added to the transmitted light in “any region” and a phase difference of λ is added to the transmitted light in “other region”. Apply.

  The voltage to be actually applied is set as follows. For example, in the case of using it corresponding to a laser beam of 780 nm, Δn and d of the polarizing optical element 10 are determined so that the phase difference represented by Δn × d is in the vicinity of 780 nm.

  A voltage determined from the phase characteristics is applied to the determined polarizing optical element 10. FIG. 7 is a graph showing phase characteristics. Based on this graph, first, the voltage to be applied to the “other region” to which the phase difference of λ is added is determined. About this, since the graph of wavelength 780nm is a voltage which takes a phase difference of 780nm, it will be 1.1V. As described above, the voltage ratio applied to the “arbitrary region” and the “other region” is set to 3: 1. Therefore, the voltage of the “arbitrary region” to which the phase difference of λ / 4 is added is 1. It becomes 3.3V, which is three times 1V. When a voltage of 3.3 V is applied to the “arbitrary region” and a voltage of 1.1 V is applied to the “other region”, the polarizing optical element 10 capable of adding the above phase difference can be realized.

  According to the present embodiment, an “arbitrary region” that freely adds a phase difference of λ / 4 can be formed in the region on the polarizing optical element 10. That is, a λ / 4 wavelength plate can be freely formed in the region on the polarizing optical element 10.

<Third Embodiment>
Next, a third embodiment of the present invention will be described. In the present embodiment, a voltage is applied to the polarizing optical element 10 so that a phase difference of λ / 2 is added to the transmitted light in “any region” and a phase difference of λ is added to the transmitted light in “other region”. Apply.

  The voltage to be actually applied is set as follows. For example, in the case of using it corresponding to a laser beam of 780 nm, Δn and d of the polarizing optical element 10 are determined so that the phase difference represented by Δn × d is in the vicinity of 780 nm.

  A voltage determined from the phase characteristics is applied to the determined polarizing optical element 10. FIG. 8 is a graph showing phase characteristics. Based on this graph, first, the voltage to be applied to the “other region” to which the phase difference of λ is added is determined. About this, since the graph of wavelength 780nm is a voltage which takes a phase difference of 780nm, it will be 0.7V. Further, as described above, the voltage ratio applied to the “arbitrary region” and the “other region” is set to 3: 1, so the voltage of the “arbitrary region” to which the phase difference of λ / 2 is added is 0. It becomes 2.1V which is 3 times 7V. When a voltage of 2.1 V is applied to the “arbitrary region” and a voltage of 0.7 V is applied to the “other region”, the polarizing optical element 10 capable of adding the above phase difference can be realized.

  According to the present embodiment, an “arbitrary region” that freely adds a phase difference of λ / 2 can be formed in the region on the polarizing optical element 10. That is, a λ / 2 wavelength plate can be freely formed in the region on the polarizing optical element 10.

<Fourth Embodiment>
Next, a fourth embodiment of the present invention will be described. In the present embodiment, in order to use the polarizing optical element 10 as an attenuator, an analyzer 40 is provided at the subsequent stage of the polarizing optical element 10 as shown in FIG. An attenuator is a device that performs light transmission / shielding switching and light amount adjustment.

  The polarization optical element 10 and the analyzer 40 are in a positional relationship as shown in FIG. 9, the optical axis of the analyzer 40 is in the horizontal direction, and the “arbitrary region” of the polarization optical element 10 transfers λ to the transmitted light. And an “attenuator” in which the “other region” adds a phase of λ / 2 to the transmitted light is assumed. If a light beam polarized in the horizontal direction is incident on the attenuator and this light beam passes through “another region” of the polarizing optical element 10, the light beam is blocked by the analyzer 40. become. This is because when the light beam passes through the “other area”, a phase of λ / 2 is added, the polarization plane of the light beam is rotated by 90 degrees, and the polarization direction changes from the horizontal direction to the vertical direction. This is because the analyzer cannot transmit the analyzer 40 having the horizontal optical axis in the polarization direction.

  On the other hand, the phase of λ is added to the light beam that passes through the “arbitrary region”, but this does not change the polarization direction itself, so that the polarization direction reaches the analyzer 40 while maintaining the horizontal direction. Since the polarization direction of the polarizing optical element 10 and the optical axis of the analyzer 40 are in the horizontal direction, this light beam is transmitted through the analyzer 40.

  Here, considering the concept of light quantity, the light quantity that passes through the attenuator varies according to the phase difference added by the “arbitrary region”. For example, the maximum value of the light beam transmitted through the attenuator is when the phase difference added by “arbitrary region” is λ and the analyzer 40 is completely transmitted. This is because the amount of light is the same as the original incident light if it is completely transmitted. Further, the light quantity of the light beam transmitted through the attenuator is the minimum value when the phase difference added by the “arbitrary region” is λ / 2 and is completely shielded by the analyzer 40. This is because the amount of light is naturally zero when completely shielded.

  Therefore, in the present embodiment, a phase difference of λ to λ / 2 is added to the transmitted light in “any region”, and a phase difference of λ / 2 is added to the transmitted light in “other region”. Then, a voltage is applied to the polarizing optical element 10.

  The voltage to be actually applied is set as follows. For example, when used in correspondence with a laser beam of 400 nm, Δn and d of the polarizing optical element 10 are determined so that the phase difference represented by Δn × d is in the vicinity of 600 nm (400 + 400/2 nm).

  A voltage determined from the phase characteristics is applied to the determined polarizing optical element 10. FIG. 10 is a graph showing phase characteristics. Based on this graph, first, a voltage to be applied to an “arbitrary region” to which a phase difference of λ is added is determined. About this, since the graph of wavelength 400nm is a voltage which takes a phase difference of 400 nm, it becomes 1.8V. The voltage applied to the “arbitrary region” to which the phase difference of λ / 2 is added is 2.8 V because the graph with the wavelength of 400 nm takes the value of the phase difference of 200 nm.

  Further, as described above, the voltage ratio applied to the “arbitrary region” and the “other region” is set to 3: 1, so that the voltage value applied to the “other region” is 0.6 V to 0. It is between 93V. In this voltage value range, a phase difference of 600 nm, that is, λ / 2 (exactly 3 / 2λ) is given to the “other regions”.

  Therefore, by applying a voltage of “arbitrary region” between 1.8 and 2.8 V, it is possible to realize an attenuator that performs light transmission / shading switching and light amount adjustment.

<Additional notes>
In addition, the phase difference added to the polarizing optical element 10 described above changes due to a temperature change of the element itself. Therefore, by changing the voltage to be applied according to the temperature change of the element, it is possible to control so that the phase difference added in the “arbitrary region” and the phase difference added in the “other region” do not change. desirable.

  FIG. 11 shows a graph of the phase difference added by the polarizing optical element 10 when the element temperatures are 0 ° C., 30 ° C., and 60 ° C. From the graph, it can be seen that the phase change on the low potential side is steep and the phase change on the high potential side is gentle. Here, using this characteristic, the applied voltage at each element temperature is set so that the phase difference at a low potential does not change, and the potential difference ratio is set at 3: 1 at a high potential.

  For example, in the polarizing optical element 10 having the characteristics shown in FIG. 11, it is assumed that a λ / 4 phase difference is added to transmitted light in “any region” and a λ phase difference is added to transmitted light in “other regions”. (Second Embodiment) In order to make this correspond to a laser beam having a wavelength of 650 nm, an applied voltage that takes 650 nm on the low potential side is first determined. From the graph, it can be seen that the applied voltage at 0 ° C. is 1.6 V, the applied voltage at 30 ° C. is 1.4 V, and the applied voltage at 60 ° C. is 1.1 V. On the high potential side, 4.9 V, 4.2 V, and 3.8 V, which are three times the respective low potential side applied voltages, are applied.

  As described above, by changing the applied voltage according to the element temperature, it becomes possible to eliminate the change in the phase difference due to the temperature change, so that the polarization optics that can give the desired phase difference without being influenced by the element temperature The element 10 can be realized.

  In order to change the applied voltage in response to such a temperature change, a thermometer for measuring the temperature is provided in the vicinity of the polarizing optical element 10, and the control board applies the applied voltage according to the temperature of the polarizing optical element 10 obtained from the thermometer. This is realized by performing feedback control / closed loop control for changing.

  In the first embodiment, a region for adding a phase difference of λ / 4 and a region for adding a phase difference of 3 / 4λ are formed. When this phase difference is expressed by a general formula, (2n− 1) λ / 4 and (2n + 1) λ / 4 (where n is an integer of 1 or more). Therefore, the phase difference added in the first embodiment is not limited to the values of λ / 4 and 3 / 4λ, and may be a value represented by this general formula. Similarly, the phase difference added in the second embodiment is (2n−1) λ / 4 and nλ, and the phase difference added in the third embodiment is (2n−1) λ / 2 and nλ. Any value can be used as long as it is expressed by an expression.

  The above-described embodiment is merely an example of a preferred embodiment of the present invention, and is not intended to limit the embodiment of the present invention. Therefore, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

It is a figure which shows the structure of a polarizing optical element. It is a figure which shows arrangement | positioning of a transparent electrode. It is a figure for demonstrating the ratio of the voltage applied to a transparent electrode. It is a figure for demonstrating the ratio of the voltage applied to a transparent electrode. It is a graph which shows an application characteristic. It is a figure which shows the structure of an optical pick-up apparatus. It is a graph which shows an application characteristic. It is a graph which shows an application characteristic. It is a figure for demonstrating the structure of an attenuator. It is a graph which shows an application characteristic. It is a graph which shows the relationship between element temperature and an application characteristic.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Polarization optical element 11 Liquid crystal layer 14 Transparent electrode 20 Optical pick-up apparatus 40 Analyzer

Claims (16)

A polarizing optical element in which a transparent substrate in which a transparent electrode, an insulating layer, and an alignment film are stacked is opposed to each other with a liquid crystal layer interposed therebetween,
One of the transparent electrodes facing each other across the liquid crystal layer is arranged in a row in the vertical direction, the other is arranged in a row in the horizontal direction,
The first voltage is applied to an arbitrary lattice point among the lattice points where the transparent electrode intersects, and the second voltage is applied to a lattice point other than the arbitrary lattice point, thereby adding the phase difference to be added. A polarizing optical element characterized by forming two different regions. A control board for driving and controlling the polarizing optical element according to claim 1,
The control board, wherein the first voltage and the second voltage are applied at a voltage ratio of 3: 1.   By applying a voltage with a reverse phase of 3: 1 to the transparent electrode that forms the arbitrary lattice point and the transparent electrode that forms a lattice point other than the arbitrary lattice point, “first voltage: first The control board according to claim 2, wherein a relationship of “voltage of 2 = 3: 1” is obtained.   4. The control substrate according to claim 2, wherein the second voltage is equal to or lower than a threshold voltage that causes a phase difference change in liquid crystal alignment of liquid crystal molecules in the liquid crystal layer. 5. Having temperature detecting means for detecting the element temperature of the polarizing optical element;
5. The control board according to claim 2, wherein a voltage to be applied is changed / adjusted according to the element temperature. 6. The region to which the first voltage is applied adds a phase difference of (2n-1) / 4 (n is an integer of 1 or more) of the wavelength of transmitted light that passes through the polarizing optical element,
The first voltage and the second voltage are set such that the region to which the second voltage is applied adds a phase difference of (2n + 1) / 4 of the wavelength of transmitted light that passes through the polarizing optical element. The control board according to claim 2, wherein the control board is applied. The region to which the first voltage is applied adds a phase difference of (2n-1) / 4 (n is an integer of 1 or more) of the wavelength of transmitted light that passes through the polarizing optical element,
Applying the first voltage and the second voltage so that a region to which the second voltage is applied adds a phase difference of n times the wavelength of transmitted light that passes through the polarizing optical element; The control board according to claim 2, wherein: The region to which the first voltage is applied adds a phase difference of (2n-1) / 2 (n is an integer of 1 or more) of the wavelength of transmitted light that passes through the polarizing optical element,
Applying the first voltage and the second voltage so that a region to which the second voltage is applied adds a phase difference of n times the wavelength of transmitted light that passes through the polarizing optical element; The control board according to claim 2, wherein: The polarizing optical element has an analyzer having an optical axis in a predetermined direction in the subsequent stage,
Transmitted light that passes through the region to which the second voltage is applied is shielded;
3. The first voltage and the second voltage are adjusted so that transmitted light transmitted through the region to which the first voltage is applied is transmitted with a desired transmitted light amount. The control board according to any one of 5. A control method for driving and controlling the polarizing optical element according to claim 1,
A control method, wherein an applied voltage is set so that a ratio of the first voltage to the second voltage is 3: 1.   The control method according to claim 10, wherein the second voltage is set to a voltage equal to or lower than a threshold voltage that causes a phase difference change in the liquid crystal alignment of the liquid crystal molecules in the liquid crystal layer. A temperature detection step of detecting an element temperature of the polarizing optical element;
The control method according to claim 10, further comprising: a voltage adjustment step of changing / adjusting a voltage to be applied according to the element temperature detected by the temperature detection step. The region to which the first voltage is applied adds a phase difference of (2n-1) / 4 (n is an integer of 1 or more) of the wavelength of transmitted light that passes through the polarizing optical element,
The first voltage and the second voltage are set such that the region to which the second voltage is applied adds a phase difference of (2n + 1) / 4 of the wavelength of transmitted light that passes through the polarizing optical element. The control method according to claim 10, wherein the control method is set. The region to which the first voltage is applied adds a phase difference of (2n-1) / 4 (n is an integer of 1 or more) of the wavelength of transmitted light that passes through the polarizing optical element,
Setting the first voltage and the second voltage so that a region to which the second voltage is applied adds a phase difference of n times the wavelength of transmitted light that passes through the polarizing optical element; The control method according to any one of claims 10 to 12, wherein: The region to which the first voltage is applied adds a phase difference of (2n-1) / 2 (n is an integer of 1 or more) of the wavelength of transmitted light that passes through the polarizing optical element,
Setting the first voltage and the second voltage so that a region to which the second voltage is applied adds a phase difference of n times the wavelength of transmitted light that passes through the polarizing optical element; The control method according to any one of claims 10 to 12, wherein: The polarizing optical element has an analyzer having an optical axis in a predetermined direction in the subsequent stage,
Transmitted light that passes through the region to which the second voltage is applied is shielded;
11. The first voltage and the second voltage are set so that transmitted light transmitted through a region to which the first voltage is applied is transmitted with a desired transmitted light amount. 13. The control method according to any one of items 12.

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