JP2005339621A - Aberration compensation element, optical pickup, and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aberration compensation element which is thin in thickness and small in size and can easily be incorporated in a pickup. <P>SOLUTION: A quartz plate 21, a liquid crystal layer 22, a glass plate 23, a liquid crystal layer 24, and a glass plate 25 are laminated in this order to constitute the aberration compensation element, and light is polarized by the quartz plate 21, and spherical aberrations of going and returning laser light are compensated by the liquid crystal layers 22 and 24, and the number of glass plates can be made one smaller than a conventional element because the quartz plate 21 has a function of holding the liquid crystal layer 22, and thus the aberration compensation element can be made thin. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an aberration correction element that corrects spherical aberration generated by a cover glass of an optical disk when the optical disk is recorded and reproduced, an optical pickup equipped with the aberration correction element, and an optical disk apparatus using the optical pickup.

  In recent years, CDs and DVD discs for recording and reproducing video information and music information have become widespread, but in order to meet the demand for further improvement in recording density and capacity, Blu-ray discs that use laser light with a wavelength of 407 nm in the blue wavelength region Has appeared.

  FIG. 4 is a schematic view showing a part of an optical pickup that collects laser light on the above-described various disk-type recording media (hereinafter referred to as optical recording media) and receives reflected light. Laser light emitted from a laser light source (not shown) is converted into parallel light by the collimator lens 1, which is circularly polarized through the quarter-wave plate 2 and incident on the objective lens 3, and is incident on the optical recording medium 4 by the objective lens 3. Focused. At that time, spherical aberration is generated in the laser beam condensed by the thickness of the cover glass 41 of the optical recording medium 4. In particular, when the optical recording medium 4 is a Blu-ray disc, the NA of the objective lens 2 is large and the wavelength of the laser light is short, so that the spherical aberration described above becomes large and must be corrected (for example, Patent Document 1). . For example, as shown in FIG. 5, the parallel light before entering the objective lens 3 can be passed through the optical element 5 for correcting spherical aberration. 3 and move together.

  FIG. 6 is a cross-sectional view showing a configuration of an aberration correction element 50 in which a conventional spherical aberration correction optical element 4 and a quarter-wave plate are integrated. The glass plate 6, the organic film 7, the glass plate 8, the liquid crystal layer 9, the glass plate 10, the liquid crystal layer 11, and the glass plate 12 are stacked in a sandwich shape. The organic film 7 held by the glass plate 6 and the glass plate 8 functions as a quarter-wave plate, and the liquid crystal layer 9 held by the glass plate 8 and the glass plate 10 irradiates the optical recording medium with a spherical surface of laser light. The liquid crystal layer 11 held by the glass plate 10 and the glass plate 12 has a function of correcting spherical aberration of laser light (reflected light) reflected from the optical recording medium.

Therefore, the spherical aberration correction amount is obtained by inserting the aberration correction element 50 shown in FIG. 6 in front of the objective lens 3 and changing the voltage applied to the liquid crystal layers 9 and 11 according to the thickness of the cover glass of the optical recording medium 4. Thus, the spherical aberration caused by the cover glass of the optical recording medium 4 of laser light can be made almost zero, and a spot having a good shape can be formed on the information recording layer of the optical recording medium 4.
JP 2003-323735 A (Page 9, FIG. 1)

  However, since the conventional aberration correction element 50 has a laminated structure having four glass plates, the element is thick and takes up a vertical space. In particular, when it is incorporated in the pickup together with the objective lens 3 and other optical elements, the space restriction in the vertical direction is severe, and the thickness of the aberration correction element 50 is too large as it is, so the aberration correction element 50 is inserted at a position as shown in FIG. In this case, there is a problem that the optical system does not fit in the standard space in the vertical direction of the pickup. Although it is conceivable to reduce the thickness of the glass plate constituting the aberration correction element 50, since the wavefront of the light becomes rough if the glass plate is made thin, the control of spherical aberration becomes strict and the glass plate can be easily made thin. The thickness of the aberration correction element 50 cannot be reduced.

  The present invention has been devised in view of the above circumstances, and an object of the present invention is to provide an aberration correction element that is thin and small and can be easily incorporated into a pickup, an optical pickup incorporating the aberration correction element, and An object of the present invention is to provide an optical disc apparatus equipped with this optical pickup.

  In order to achieve the above object, the present invention is characterized in that a first layer having a wavelength plate function, a second layer having a spherical aberration correction function, and a glass plate are sequentially laminated.

  The present invention also provides a first layer having a wavelength plate function, a second layer having a spherical aberration correction function, a first glass plate, a third layer having a spherical aberration correction function, and a second glass plate. And are laminated in order.

  The present invention also provides an optical pickup for condensing laser light on an optical recording medium by an objective lens and receiving reflected light from the optical recording medium through the objective lens, wherein the laser light of the objective lens An aberration correction element that polarizes the laser light and the reflected light at the same time as correcting the spherical aberration of the laser light and the reflected light caused by the cover glass of the optical recording medium in the vicinity of the light source side is disposed. A quartz plate having a wavelength plate function, a first liquid crystal layer having a function of correcting spherical aberration of laser light for irradiating the optical recording medium, a first glass plate, and correcting spherical aberration of reflected light from the optical recording medium A second liquid crystal layer having a function and a second glass plate are sequentially laminated.

  The present invention also provides an optical disc apparatus that records and reproduces data by condensing laser light from an optical pickup onto an optical recording medium and receiving reflected light from the optical recording medium by the optical pickup. The pickup corrects the spherical aberration of the laser light and reflected light caused by the cover glass of the optical recording medium, and has an aberration correction element for polarizing the laser light and reflected light in the optical system, and the aberration correction. The element includes a quartz plate having a wavelength plate function, a first liquid crystal layer having a spherical aberration correction function, a first glass plate, a second liquid crystal layer having a spherical aberration correction function, and a second glass plate. And are laminated in order.

  As described above, in the present invention, in configuring an aberration correction element having a wave plate function and an aberration correction function, it is conventionally necessary to use a quartz plate that combines the wave plate function and the liquid crystal layer holding function. Since one existing glass plate can be omitted, the thickness of the aberration correction element can be made thinner and lighter accordingly. Therefore, the above-described aberration correction element can be easily incorporated into an optical system of a pickup mounted on an optical disc apparatus with severe height restrictions, and the optical disc apparatus using this pickup impedes smooth access to an optical recording medium. In addition, the spherical aberration caused by the cover glass of the optical recording medium can be corrected to form a well-shaped spot on the information recording layer, and therefore data can be recorded and reproduced with high quality.

  According to the present invention, since the aberration correction element is a quartz plate that has both the wavelength plate function and the liquid crystal layer holding function, it is possible to omit one conventionally required glass plate. The thickness can be reduced, and it can be easily incorporated into a pickup with severe height constraints.

  For the purpose of manufacturing an aberration correction element that is thin and small and can be easily incorporated into a pickup, the aberration correction element is conventionally used by laminating a crystal plate that has both a wavelength plate function and a liquid crystal layer holding function. This was realized by omitting one glass plate which was necessary.

  FIG. 1 is a cross-sectional view showing the configuration of an aberration correction element according to the first embodiment of the present invention. The aberration correction element 60 of the present embodiment is configured by laminating a crystal plate 21, a liquid crystal layer 22, a glass plate 23, a liquid crystal layer 24, and a glass plate 25.

  The crystal plate 21 of the aberration correction element 60 functions as a quarter-wave plate, the liquid crystal layer 22 has a spherical aberration correction function (for laser light that irradiates an optical recording medium), and the liquid crystal layer 24 has a spherical aberration correction function ( For reflected light from an optical recording medium).

  According to the present embodiment, the quartz plate 21 is used as a ¼ wavelength plate and also functions as a holding material for the liquid crystal layer 22, so that one glass plate is omitted compared to the conventional case. Accordingly, the thickness of the aberration correction element 60 can be reduced and the size and weight can be reduced accordingly. Incidentally, since the thickness of the aberration correction element 60 is substantially determined by the thickness of the glass plate, the thickness is about 3/4 of that of the conventional one. As a result, the aberration correction element 60 can be easily incorporated into an optical system of a pickup having severe height restrictions.

  FIG. 2 is a block diagram showing the configuration of the optical pickup according to the second embodiment of the present invention. The optical pickup is used in an optical disk device (see FIG. 3), and includes the semiconductor laser 101, which is a light source in the blue wavelength region, the collimator lens 102, the polarization beam splitter 103, the deflecting prism 104, and the aberrations shown in the first embodiment. The correction element 60 includes an objective lens 106, a detection lens 1008, a light beam splitting unit 109, and a light receiving element 110.

  Next, the operation of the present embodiment will be described. The linearly polarized divergent light emitted from the semiconductor laser 10l having a wavelength of 407 nm is converted into substantially parallel light by the collimator lens 102, passes through the polarization beam splitter 103, and is deflected by 90 degrees in the optical path by the deflecting prism 104. By passing through, it becomes circularly polarized light, and the spherical aberration generated by the cover glass of the disk-type optical recording medium 1007 is corrected, enters the objective lens 106, and is condensed as a minute spot on the optical recording medium 1007. Information is reproduced, recorded or erased by this spot. At this time, since the spherical aberration generated by the cover glass of the optical recording medium 1007 is corrected by the aberration correction element 60, the spot is formed with a good shape.

  The light reflected from the optical recording medium 107 becomes circularly polarized light in the opposite direction to the outward path, and is converted into substantially parallel light again by the objective lens 106 and passes through the aberration correction element 60, thereby becoming linearly polarized light orthogonal to the forward path. The spherical aberration generated by the cover glass of the disk-type optical recording medium 1007 is corrected and is incident on the polarization beam splitter 103, but is reflected here, and is converged by the converging lens 1008, and a plurality of light beams are split by the light beam splitting means 109. The light is deflected and divided to the light receiving element 110. An aberration signal, an information signal, and a servo signal are detected from the light receiving element ll0.

  According to the present embodiment, there is a dimensional restriction in the vertical direction of the pickup (corresponding to the vertical direction in FIG. 2) by using the small-sized thin aberration correction element 60 described in the first embodiment. In addition, the aberration correction element 2 can be easily and optimally incorporated in the pickup. Since the aberration correction element 2 is small and lightweight, the pickup does not become heavy and can smoothly move following the recording / reproducing position on the optical recording medium 107.

  FIG. 3 is a block diagram showing a configuration of a main part of an optical disc apparatus according to the third embodiment of the present invention. The optical disc apparatus accesses a disc type optical recording medium 202 such as DVD ± R / RW, CD-R / RW, or Blu-ray disc by an optical pickup 204, and records and reproduces data. A spindle motor 203 as a driving means for rotationally driving the medium 202, an optical pickup 204 for reading / writing data from / to the optical recording medium 202, and a driving means for moving the optical pickup 204 in the radial direction of the optical recording medium 202 Feed motor 205, system controller 207 that controls the entire apparatus, signal processing unit 208 that performs predetermined processing such as demodulation and error correction processing based on an output signal from the preamplifier 220, spindle motor 203, and feed motor 205. Servo control unit 209 for controlling the optical pickup and optical pickup A preamplifier 220 that generates a focus error signal, a tracking error signal, an RF signal, and the like based on various signals output from 204, an interface 211 that connects the signal processing unit 208 and the external computer 230, and a laser in the optical pickup 204 A laser control unit 221 that drives a light source (corresponding to the semiconductor laser 101 in FIG. 2) and a signal recorded on the optical recording medium 202 are received as a reproduction signal, and data is modulated by a signal processing unit 208 to be laser control unit 221. D / A converts the signal from the external computer 230 that drives the laser light source in the optical pickup 204 and the signal processing unit 208 or A / D converts the signal from the audio / visual processing unit 213. / A, A / D converter 212 and recording or playback audio An audio / visual processing unit 213 for processing a video signal is configured. Here, the optical pickup 204 has the same configuration as that of the second embodiment shown in FIG.

  For example, a feed motor 205 for moving to a predetermined recording track on the optical recording medium 202 is connected to the optical pickup 204. Control of the spindle motor 203, control of the feed motor 205, and control of the focusing direction and tracking direction of the biaxial actuator that holds the objective lens of the optical pickup 204 are the focus error signal input from the preamplifier 220 by the servo control unit 209, respectively. This is performed based on the tracking error signal. The laser control unit 221 controls the laser light source 101 in the optical pickup 204, and variably controls the output power of the laser light source 101 in the recording mode and the reproduction mode.

  According to the present embodiment, since the aberration correction element 60 is mounted on the optical pickup 204, the spherical aberration is corrected according to the thickness of the cover glass of the optical recording medium 202, so that the optical recording medium 202 Regardless of the type, an always good spot can be formed on the information recording layer of the optical recording medium 202. Therefore, high-accuracy servo can be performed, and high-quality data can be recorded and reproduced. At this time, since the aberration correction element 60 is lightweight, even if it is mounted, it does not hinder the movement of the optical pickup 204 and can smoothly access the target address portion of the optical recording medium 202. .

  In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the summary, it can implement also with another various form in a concrete structure, a function, an effect | action, and an effect. For example, in the first embodiment described above, a configuration in which two liquid crystal layers are provided to correct spherical aberration for each of the outgoing laser beam and the returning laser beam (reflected light) has been shown. If it is sufficient to correct polarization and spherical aberration with respect to laser light in only one direction, the aberration correction element may be formed by laminating the crystal plate 21, the liquid crystal layer 22, and the glass plate 23. As compared with the above, one glass plate is omitted, and the thickness can be reduced.

  In the above embodiment, a quartz plate is used as a member having a wave plate function, but other members may be used as long as they have a wave plate function. Similarly, liquid crystal is used as a member having an aberration correction function, but other members may be used as long as they have an aberration correction function. Further, the glass plate holding the liquid crystal may be another member as long as it is transparent and can hold the liquid crystal.

It is sectional drawing which showed the structure of the aberration correction element which concerns on the 1st Embodiment of this invention. It is the block diagram which showed the structure of the optical pick-up based on the 2nd Embodiment of this invention. It is the block diagram which showed the structure of the principal part of the optical disk apparatus based on the 3rd Embodiment of this invention. It is the schematic which showed a part of optical system incorporated in the conventional optical pick-up which writes data in an optical recording medium, or reads recording data. FIG. 5 is a schematic view when a spherical aberration element is inserted into the optical system of the pickup shown in FIG. 4. It is sectional drawing which showed the structure of the aberration correction element which united the conventional optical element for spherical aberration correction, and the quarter wavelength plate.

Explanation of symbols

  21 ... Quartz plate, 22, 24 ... Liquid crystal layer, 23, 25 ... Glass plate, 60 ... Aberration correction element 60, 101 ... Semiconductor laser, 102 ... Collimate lens, 103 ... Polarized beam splitter, 104 ... Deflection prism, l06 ... objective lens, l08 ... detection lens, l09 ... beam splitting means, 110 ... light receiving element, 202 ... optical disc, 203 ... spindle motor, 204 ... optical pickup, 205 ... feed Motor 207... System controller 208. Signal processor 209. Servo controller 211 211 Interface 220 Preamplifier 221 Laser controller 230 External computer

Claims (7)

A first layer having a wave plate function;
A second layer having a spherical aberration correction function;
A light transmissive holding member;
Aberration correction element characterized by being stacked in order. A first layer having a wave plate function;
A second layer having a spherical aberration correction function;
A light transmissive first holding member;
A third layer having a spherical aberration correction function;
A light transmissive second holding member;
Aberration correction element characterized by being stacked in order.   The first layer is a crystal plate, the second layer, or the second and third layers are liquid crystals, the holding member, or the first holding member and the second holding member are glass plates, 3. The aberration correction element according to claim 1, wherein the function of a light transmissive holding member is imparted to one layer. An optical pickup that focuses laser light on an optical recording medium with an objective lens and receives reflected light from the optical recording medium through the objective lens,
An aberration correction element that corrects spherical aberration of the laser light and reflected light caused by the cover glass of the optical recording medium close to the light source side of the laser light of the objective lens and simultaneously polarizes the laser light and reflected light. Place and
The aberration correction element includes a quartz plate having a wavelength plate function, a first liquid crystal layer having a spherical aberration correction function, a first glass plate, a second liquid crystal layer having a spherical aberration correction function, and a second liquid crystal layer. An optical pickup comprising a plurality of glass plates laminated in order.   5. The optical pickup according to claim 4, wherein the optical recording medium is a Blu-ray disc. An optical disc apparatus for condensing laser light on an optical recording medium from an optical pickup, receiving reflected light from the optical recording medium by the optical pickup, and recording and reproducing data,
The optical pickup has, in its optical system, an aberration correction element that polarizes the laser light and reflected light simultaneously with correcting the spherical aberration of the laser light and reflected light caused by the cover glass of the optical recording medium,
The aberration correction element includes a quartz plate having a wavelength plate function, a first liquid crystal layer having a spherical aberration correction function, a first glass plate, and a second liquid crystal layer having a spherical aberration correction function, An optical disc apparatus comprising: a second glass plate laminated in order.   7. The optical disc apparatus according to claim 6, wherein the optical recording medium is a Blu-ray disc.

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