JP2005222587A - Optical apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical apparatus in which it is prevented that light in which desired phase modulation is not performed is transmitted from a liquid crystal optical element for phase modulation while keeping miniaturization and which is compact and excellent in aberration compensation performance. <P>SOLUTION: This apparatus holds a liquid crystal layer between first and second transparent substrates, the apparatus is provided with the optical element for phase modulation having a first layer in which a plurality of electrode groups for phase modulation are formed with gap and a second layer in which an electrode for compensation for compensating the gap of the electrode for phase modulation is provided at at least one side of the first or the second transparent substrate, and a drive signal of the same potential is supplied to the electrode for compensation and one side of the electrode for phase modulation being overlapped with the electrode for compensation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical apparatus provided with a phase modulation optical element, and more particularly to a phase modulation optical that functions as an aberration correction optical element for correcting wavefront aberrations such as spherical aberration, coma aberration, and astigmatism of light. The present invention relates to an optical device including an element.

  In order to correct aberrations of light generated during writing and reading of information in an optical pickup device such as a CD or DVD, which is an optical device, a phase modulation optical element made of liquid crystal optical elements is used. It has been. Such a phase modulation optical element has a wavefront including coma aberration, spherical aberration, and astigmatism that occurs in a disk such as a DVD due to an inclination of the optical axis of laser light applied to a CD, DVD, or the like. Aberrations are optically corrected.

Here, a conventional phase modulation optical element will be described. FIG. 8A illustrates an electrode pattern of a liquid crystal optical element for correcting spherical aberration.
This optical element for phase modulation modulates the phase of transmitted light by applying different voltages to the electrodes Ea, Eb, Ec, Ed, and Ee shown by oblique lines, and the aberration of linearly polarized light incident on this element Can be corrected.
However, in the gap S between the electrodes Ea, Eb, Ec, Ed, and Ee, the light transmitted through the gap S is not phase-modulated, and this acts as noise particularly when light having a wavelength of 405 nm is used. As a result, a large aberration is caused.

  FIG. 8B is a diagram showing the situation at this time. The vertical axis of the graph indicates the phase or transmittance of light transmitted through the phase modulation liquid crystal optical element, and the horizontal axis indicates the corresponding liquid crystal optical element 10. Indicates the position.

  8B, the common electrode Ecom on the second transparent substrate 14 of the liquid crystal optical element 10 has, for example, a GND potential, and the E1 electrode on the first transparent substrate 12 has an AC of, for example, 2.01 [V]. Similarly, the potential is 2.02 [V] for E2, 2.03 [V] for E3, 2.04 [V] for E4, 2.05 [V] for E5, and 2.5 for E6. An AC potential of 2.07 [V] is applied to 06 [V], E7, 2.08 [V] to E8, 2.09 [V] to E9, and 2.10 [V] to E10. Yes.

  These voltages are given according to the magnitude of the aberration in order to correct the aberration of the light incident on the liquid crystal optical element 10, but as shown in the graph of FIG. The phases are greatly different, and this difference in phase causes a problem that correction with high accuracy cannot be performed as a whole.

  In order to solve such a problem, as shown in FIG. 9A, a liquid crystal layer 22 is sandwiched between the first transparent substrate 12 and the second transparent substrate 14 having electrodes inside, On the at least one first or second transparent substrate 12, 14, a plurality of phase modulation electrode groups 16 formed with a predetermined gap and a gap between the phase modulation electrode groups 16 are provided. A liquid crystal optical element 10 having a supplementary electrode group 18 for complementation and a second layer that is spaced apart from the first layer with an insulating film 24 interposed therebetween. The laser light emitted from the laser light source is used as a recording medium. A proposal has been made to correct the aberration of light by arranging it in the optical path between the irradiating optical member (see, for example, Patent Document 1).

The phase modulation electrode group 1 configured in this way and adjacent to each electrode of the complementary electrode group 18
When the voltage of 6 is applied, the problem of leakage of light that has not undergone the desired phase modulation from the gap S as shown in FIG. 8B is eliminated, and aberrations can be corrected smoothly.

JP 2001-176108 A (page 4-5, FIG. 3-5)

  However, the technique of Patent Document 1 still has problems to be improved. The first problem is that, as shown in FIG. 9B, the width of the complementary electrode group 18 is formed with a width substantially equal to the gap of the phase modulation electrode group 16, which is a manufacturing problem. Thus, the phase modulation electrode group 16 and the complementary electrode group 18 may be misaligned.

  Thus, when the phase modulation electrode group 16 and the complementary electrode group 18 are displaced, the region where the phase modulation electrode group 16 or the complementary electrode group 18 shown in FIG. In L, the incident light K transmits the phase-modulated light. However, since there is a region M in which neither the phase modulation electrode group 16 nor the complementary electrode group 18 exists due to this positional deviation, light that is not subjected to desired phase modulation is transmitted as it is.

  FIG. 10 shows this state in a diagram corresponding to FIG. 8B. From the region M in which neither the phase modulation electrode group 16 nor the complementary electrode group 18 exists, the phase shown in FIG. Although leakage of light that has not been modulated is reduced, light that is not subjected to desired phase modulation is transmitted, and there has been a problem that accurate correction cannot be performed as a whole.

  The second problem of the phase modulation optical element described in Patent Document 1 is that the total number of electrode groups increases because the complementary electrode group 18 is provided, and the drive circuit 40 and the phase modulation liquid crystal element 10 are connected. The number of conductive wires of the cable to be connected increases, and it is difficult to reduce the size of the liquid crystal optical element and the optical device on which the liquid crystal optical element is mounted.

  An object of the present invention is to solve the above-mentioned problems, prevent light that is not subjected to desired phase modulation from being transmitted from a liquid crystal optical element for phase modulation while maintaining miniaturization, and is small in size and aberration An optical device having excellent correction performance is provided.

In order to solve the above problems, the optical apparatus of the present invention basically employs the following configuration.
The optical device of the present invention is arranged in an optical path between a laser light source and an optical member that irradiates a recording medium with laser light emitted from the laser light source, and includes first and second electrodes having electrodes on the inside. A first layer in which a liquid crystal layer is sandwiched between transparent substrates, and a plurality of phase modulation electrode groups are formed on at least one of the first or second transparent substrates with a gap, and a phase modulation electrode A phase modulation optical element having a second layer in which a complementary electrode for complementing the gap of the first layer is provided apart from the first layer via an insulating film, and a drive circuit for supplying a drive signal In the provided optical device, a part of the complementary electrode is arranged so as to overlap the phase modulation electrode, and one of the complementary electrode and the phase modulation electrode overlapping the complementary electrode is set to the same potential by the drive circuit. The drive signal is configured to be supplied And wherein the Rukoto.

  The optical device according to the present invention is characterized in that the second layer and the first layer are sequentially laminated on at least one of the first or second transparent substrates.

  In the optical device of the present invention, the phase modulation electrode is an aberration correction electrode, and the phase modulation optical element is an aberration correction optical element.

  Further, the optical device of the present invention is configured such that the complementary electrode and one of the phase modulation electrodes overlapping with the complementary electrode are electrically short-circuited on the phase modulation optical element, thereby driving the same potential to both. It is characterized in that a signal can be supplied.

  According to the present invention, it is possible to prevent transmission of light that is not subjected to desired phase modulation while maintaining miniaturization. Therefore, it is possible to provide a small optical device that is effective for increasing the density of an information recording medium. it can.

  Since the optical element for phase modulation used in the optical apparatus of the present invention has basically the same configuration requirements as the configuration of the element shown in the background art, the same reference numerals are used for the same members in the following description. I will explain.

  The optical device of the present invention is arranged in an optical path between a laser light source and an optical member that irradiates a recording medium with laser light emitted from the laser light source, and includes first and second electrodes having electrodes on the inside. A first layer in which a liquid crystal layer is sandwiched between transparent substrates, and a plurality of phase modulation electrode groups are formed on at least one of the first or second transparent substrates with a gap, and a phase modulation electrode A phase modulation optical element having a second layer in which a complementary electrode for complementing the gap of the first layer is provided apart from the first layer via an insulating film, and a drive circuit for supplying a drive signal In the provided optical device, a part of the complementary electrode is arranged so as to overlap the phase modulation electrode, and one of the complementary electrode and the phase modulation electrode overlapping the complementary electrode is set to the same potential by the drive circuit. The drive signal is configured to be supplied. It is the location. This specific configuration example will be described in detail below.

FIG. 1A is a cross-sectional view showing the structure of a phase modulation optical element mounted on the optical device of the present invention, and FIG. 1B shows an overlapping portion of the phase modulation electrode 16 and the complementary electrode 30. Fig. 1 (c) shows a modification of Fig. 1 (a).
A phase modulation optical element 10 shown in FIG. 1A is a liquid crystal optical element that functions as an aberration correction optical element for correcting aberrations such as spherical aberration and coma generated in an optical pickup device that is a kind of optical device. Is shown.

The liquid crystal optical element is configured by sandwiching a liquid crystal layer 22 between a first transparent substrate 12 and a second transparent substrate 14 which are provided to face each other. Then, on both surfaces of the first transparent substrate 12 and the second transparent substrate 14 on the liquid crystal layer side, a complementary electrode group 30 which is a transparent conductor, and a phase modulation electrode which is also a transparent conductor. The groups 16 are stacked in order. Further, the complementary electrode group 30 and the phase modulation electrode group 16 are provided apart from each other with the insulating film 24 interposed therebetween. An alignment film 26 for aligning liquid crystal molecules is provided on the upper surface of the phase modulation electrode group 16 on the liquid crystal layer side.
Here, polyimide resin is used for the alignment film 26, and silicon dioxide is generally used for the insulating film 24. However, it is also possible to use polyimide resin for the insulating film 24 as well. The thickness of the insulating film was set to about 500 mm.

  Further, in the phase modulation optical element used in the optical device of the present invention, the complementary electrode group 30 for complementing the gap between the electrodes of the phase modulation electrode group 16 includes both of the adjacent phase modulation electrode groups 16. And the width of the overlapping portion is configured to be larger than the width of the gap between the phase modulation electrodes.

FIG. 1B is a drawing for explaining this relationship.
The complementary electrode group 30 is set so as to overlap the phase modulation electrode group 16 by a width D larger than (1/2) W with respect to the gap W between the electrodes of the phase modulation electrode group 16. . Accordingly, the total overlap width 2D is configured to be larger than the width W of the gap between the phase modulation electrodes, that is, 2D ≧ W.

  Since the width W of the gap between the phase modulation electrodes is preferably as small as possible, in this embodiment, the width W is suppressed to about 3 μm in consideration of manufacturing errors. Since the material of the transparent electrode used was indium tin oxide (ITO) and the thickness was 1000 mm or less, it was easy to realize a gap of 3 μm. Therefore, the overlap width D is set to 1.5 μm or more. On the other hand, since the positional deviation due to manufacturing variation is 1 μm or less, a region in which neither the phase modulation electrode group 16 nor the complementary electrode group 30 exists in the manufacturing process (a region corresponding to M in FIG. 9C) can appear. It turns out that sex is very few.

  Therefore, with the above configuration, it is possible to realize a phase modulation optical element that can almost completely prevent transmission of light that is not subjected to desired phase modulation, and that can realize highly accurate aberration correction as a whole. . In addition, by adopting this configuration, the yield is not greatly reduced due to manufacturing variations, and the phase modulation optical element can be manufactured at low cost.

Next, a modification of the phase modulation optical element mounted on the optical device of the present invention will be described.
FIG. 1C is a cross-sectional view showing a modification of the phase modulation optical element mounted on the optical device of the present invention. In this modification, the complementary electrode group 30 and the phase modulation electrode group 16 are sequentially stacked only on the first transparent substrate 12, and the entire surface is a common electrode on the second transparent substrate 14. 34 is provided. It goes without saying that this configuration can also function as a phase modulation optical element.

Next, a specific configuration example for causing the phase modulation optical element mounted on the optical device of the present invention to function as an aberration correction optical element will be described in more detail.
2A is a plan view of the phase modulation electrode group 16, and FIG. 2B is a plan view of the complementary electrode group 30. As shown in the figure, the complementary electrode group 30 is an electrode pattern having a width smaller than that of the phase modulation electrode group 16 so as to complement the inter-electrode gap of the phase modulation electrode group 16.

  In this specification, the electrode pattern of the liquid crystal optical element for correcting spherical aberration is described as an example. However, problems and solutions are also found in a phase modulation optical element for correcting coma aberration or correcting astigmatism. The law is common.

  FIG. 3 shows a first embodiment showing one of the phase modulation electrodes overlapping the complementary electrode group 30 and means for applying a drive signal of the same potential to the complementary electrode. The dotted line in the figure indicates the electrical connection state between the drive circuit 40 and each electrode. If the phase modulation optical element is configured as shown here, the drive circuit 40 applies the same drive voltage to the complementary electrode group 30 as applied to any one of the overlapping phase modulation electrode groups 16. Can be driven.

  In other words, in this configuration, each of the complementary electrode group 30 is not given an intermediate potential between the potentials applied to any one of the electrodes of the overlapping phase modulation electrode group 16, but is used for the overlapping phase modulation. Any one of the electrodes 16 is electrically short-circuited. With such a configuration, although the aberration correction is not smoother than when an intermediate potential is applied in terms of applied voltage, it is possible to perform correction at a level that causes no problem in practice. Further, according to this means, the number of connection cables between the drive circuit 40 and the phase modulation liquid crystal element 10 can be reduced, which brings about a remarkable effect on downsizing of the optical device.

  The electrical short circuit described above can be short-circuited in the drive circuit 40 or can be short-circuited in a cable connecting the drive circuit 40 and the liquid crystal optical element 10. Furthermore, a short circuit can be made at the stage of arrangement of the electrodes of the complementary electrode group 30 and the phase modulation electrode group 16 in the liquid crystal optical element 10, but in order to reduce the size of the optical apparatus, It is desirable to do.

FIG. 4 is a view showing an optical pickup device as an example of an optical device on which the phase modulation optical element according to the present invention is mounted.
FIG. 4 is a block diagram showing the overall configuration of an optical pickup device using the liquid crystal optical element 10 according to the present invention. The laser light source 50, the collimator lens 52, the polarization beam splitter 54, the liquid crystal optical element 10, and the liquid crystal optical element. The driving circuit 40 for supplying a voltage signal for phase modulation to the element 10, a ¼ phase difference plate 66, an objective lens 56, a condenser lens 60, and a light receiver 62 are included.

  In FIG. 4, laser light 64 emitted from the laser light source 50 is converted into P-polarized parallel light by the collimator lens 52 and passes through the beam splitter 54 and the liquid crystal optical element 10. The laser light 64 is corrected by the liquid crystal optical element 10 for wavefront aberration including coma aberration or spherical aberration of incident parallel light, and then converted into circularly polarized light by the ¼ phase plate 66, and the disc 58 by the objective lens 56. Irradiate the beam.

  Further, the laser beam reflected from the disk 58 passes through the objective lens 56, is converted into S-polarized light by the phase difference plate 66, passes through the liquid crystal optical element 10, and changes the optical path by the beam splitter 54. Then, the laser beam that has passed through the condenser lens 60 and reflected from the disk 58 is collected on the light receiver 62. Based on the data, information recorded on the disk 56 can be read or written on the disk surface.

  This optical pickup device uses the optical element for phase modulation according to the present invention capable of correcting aberrations with high accuracy, so that information can be written and read with high accuracy, and the information recording medium can also be increased in density. Can do.

  If this optical pickup device is applied to an information recording device such as magnetic recording, the same effect can be expected.

  FIG. 5 is a diagram showing a second embodiment of the optical element for phase modulation mounted on the optical apparatus of the present invention. This phase modulation optical element is electrically connected to any one of the electrodes of the phase modulation electrode group 16 that overlaps each electrode of the complementary electrode group 30 in the connection region 44 with the drive circuit 40 in the liquid crystal element 10. The example of a structure which makes a short circuit state is shown. FIG. 5A shows a sectional view thereof, and FIG. 5B shows a plan view thereof.

  In FIG. 5A, the insulating film 24 is not provided in the connection region 44. Therefore, if the electrodes of the complementary electrode group 30 and the electrodes of the phase modulation electrode group 16 are formed so as to overlap in the connection region 44, both electrodes are electrically short-circuited.

  In FIG. 5B, in the connection region 44, the electrodes of the complementary electrode group 30 are bent, and an electrode pattern is formed so as to largely overlap the electrodes of the adjacent phase modulation electrode group 16. Therefore, the electrode of the complementary electrode group 30 and the electrode of the phase modulation electrode group 16 can be electrically short-circuited in the connection region 44.

Thus, if both electrodes can be short-circuited in the liquid crystal optical element 10, the number of wires from the drive circuit 40 to the liquid crystal optical element 10 can be reduced, thereby enabling a reduction in the size of the optical device. There is a structural effect.

Here, the wavefront aberration characteristics of the optical element for phase modulation shown in Example 2 are shown.
FIG. 6 is a diagram showing the measurement result of the transmitted light phase characteristic of the optical element for phase modulation used in the optical pickup device of the present invention, and is shown for comparison with FIG. 8B and FIG. It was.

  As apparent from FIG. 6, although a slight phase shift is recognized in the gap portion of the phase modulation electrode group 16, the gap of the phase modulation electrode group 16 is completely complemented by the complementary electrode group 30. It can be seen that this phase shift can be suppressed to be extremely small as compared with the conventional example. For this reason, it is apparent from this figure that the phase modulation optical element having this structure can perform accurate correction as a whole.

  By mounting the phase modulation optical element shown in the second embodiment on the optical pickup device that is the optical device shown in the first embodiment, it is possible to write and read information with high accuracy, and to record information. It becomes the structure which can respond also to the high density of a medium.

  In this embodiment, an example in which the electrode groups 30 and the phase modulation electrode group 16 are stacked in this order on the transparent substrate is shown. However, although not shown, the positional relationship between the two is reversed. Even if it is arranged, an effect similar to the characteristic diagram shown in FIG. 5 can be obtained.

  FIG. 7 is a diagram showing a third embodiment of the phase modulation optical element mounted on the optical apparatus of the present invention. In the phase modulation region in the liquid crystal optical element 10 in the drawing, that is, in the spherical aberration correction element, the phase modulation electrode group 16 is a region having a substantially circular shape, and the phases of the electrodes of the complementary electrode group 30 overlapping each other. A configuration example in which one of the electrodes of the modulation electrode group 16 is electrically short-circuited is employed.

  In FIG. 7, each electrode of the complementary electrode group 30 and each electrode of the phase modulation electrode group 16 are overlapped on both sides of the electrode in the phase modulation region, but the insulating film 24 is removed only on one side thereof. ing. Then, each electrode of the complementary electrode group 30 and each electrode of the phase modulation electrode group 16 are electrically short-circuited at a portion where the insulating film 24 is removed.

  According to this short-circuiting method, it is necessary to precisely remove the insulating film, which is costly. However, the electrical short-circuit between each electrode of the complementary electrode group 30 and each electrode of the phase modulation electrode group 16 is more phase-controlled. Since it can be performed in the vicinity of the electrode to be modulated, it is possible to reduce the possibility that the voltage applied to the complementary electrode group 30 will deviate from a desired value due to the influence of a voltage drop due to the resistance of the transparent electrode. More accurate correction with the optical element 10 is possible.

  And by mounting the optical element for phase modulation shown in the third embodiment on the optical pickup device which is the optical device shown in the first and second embodiments, it is possible to write and read information with high accuracy, It becomes a structure which can respond also to the high density of an information recording medium.

It is sectional drawing which shows the structure of the optical element for phase modulation mounted in the optical apparatus of this invention. (Example 1) It is drawing for demonstrating the relationship between the electrode group for phase modulation and the electrode group for complementation which comprises the optical element for phase modulation mounted in the optical apparatus of this invention. (Example 1) It is drawing which shows one structural example of the optical element for phase modulation mounted in the optical apparatus of this invention. (Example 1) It is the schematic which shows the structural example of the optical apparatus of this invention. (Example 1) It is drawing which shows the other structural example of the optical element for phase modulation mounted in the optical apparatus of this invention. (Example 2) It is a transmitted light phase characteristic measurement figure in the optical element for phase modulation mounted in the optical apparatus of this invention. (Example 2) It is drawing which shows the further another structural example of the optical element for phase modulation mounted in the optical apparatus of this invention. Example 3 It is drawing which shows the transmitted light phase characteristic of the electrode pattern of the conventional phase modulation optical element, and its phase modulation optical element. 1 is a diagram illustrating a conventional phase modulation optical element. It is a transmitted light phase characteristic drawing of the conventional optical element for phase modulation.

Explanation of symbols

16 Phase modulation electrode group 30 Complementary electrode group 12 First transparent substrate 14 Second transparent substrate 10 Phase modulation optical element 22 Liquid crystal layer 50 Laser light source 58 Recording medium

Claims (4)

A liquid crystal layer is disposed between the first and second transparent substrates disposed in the optical path between the laser light source and an optical member that irradiates the recording medium with laser light emitted from the laser light source. A first layer in which a plurality of phase modulation electrode groups are formed on the at least one first or second transparent substrate with gaps therebetween, and the gap between the phase modulation electrodes is complemented. Optical modulator including a phase modulation optical element having a second electrode provided with a supplementary electrode spaced apart from the first layer via an insulating film, and a drive circuit for supplying a drive signal In the device
A portion of the complementary electrode is arranged to overlap the phase modulation electrode;
An optical apparatus, wherein the complementary electrode and one of the phase modulation electrodes overlapping with the complementary electrode are configured to be supplied with a drive signal having the same potential by the drive circuit.   2. The optical device according to claim 1, wherein the second layer and the first layer are sequentially stacked on at least one of the first and second transparent substrates.   The optical apparatus according to claim 1, wherein the phase modulation electrode is an aberration correction electrode, and the phase modulation optical element is an aberration correction optical element.   By electrically short-circuiting the complementary electrode and one of the complementary electrodes for the phase modulation on the optical element for phase modulation, a drive signal having the same potential can be supplied to both. The optical apparatus according to claim 1, wherein the optical apparatus is configured as described above.

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