JP2005129125A - Optical pickup and optical recording medium recording/reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the degree of flexibility in design, to provide a configuration for correcting spherical aberration, and to reduce the size/weight of the capacity of a movable section. <P>SOLUTION: A liquid crystal element 27 used as a diffraction means for obtaining a spherical aberration correction signal is made independent of an objective lens, and an objective lens actuator 26 for driving the objective lens and a liquid crystal element actuator 28 are provided. The liquid crystal actuator 28 has nearly the same structure as the objective lens actuator 26 and separately retains the liquid crystal element 27. The liquid crystal element actuator 28 is controlled by a servo control section 109 so that the center in the liquid crystal pattern of the liquid crystal element 27 coincides with an optical axis. The liquid crystal element actuator 28 is driven in synchronization with movement in the tracking direction of the objective lens actuator 26 by utilizing a tracking servo signal, thus separating the liquid crystal element 27 from the objective lens 25 for arranging at an arbitrary position in parallel light. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical pickup and an optical recording medium recording / reproducing apparatus to which a spherical aberration compensation method for correcting spherical aberration of an optical recording medium (DVD ± R / RW, CD-R / RW, etc.) spherical aberration is applied.

  The recording density of the optical disk is almost limited by the size of the light spot λ / NA (λ: light wavelength, NA: objective lens numerical aperture) to be recorded and reproduced. Therefore, in order to increase the capacity of the recording medium, it is necessary to shorten the wavelength of the recording / reproducing light or increase the numerical aperture. In recent years, a blue-violet semiconductor laser having a wavelength of 405 nm has been developed as a method for shortening the wavelength of recording / reproducing light. As an example of a technique for increasing the numerical aperture (NA) of an objective lens, there is a technique for increasing NA to 0.85 at maximum using two objective lenses in two groups. However, there is a problem that aberrations caused by an optical system shift or an error due to the thickness and tilt of the disk substrate increase as the NA increases.

  Further, as described above, in order to realize a high density of information signals to be written on the optical recording medium, when the NA is increased and the recording film is multilayered, for example, it corresponds to an interlayer distance of 20 μm to 30 μm. The thickness of the disk substrate from the surface of the disk substrate to the recording layer changes by the distance. When the thickness of the disk substrate changes, the amount of spherical aberration changes, and there are cases where information signals cannot be written and read on a high-density optical disk. In general, it is known that the following relational expression holds among the substrate thickness, the numerical aperture (NA) of the objective lens, the wavelength, and the spherical aberration.

Spherical aberration ∝ΔD × {(n ² −1) / n ³ } × (NA) ⁴ / λ

  In the above equation, D is the substrate thickness, ΔD is the difference in substrate thickness, and n is the refractive index of the substrate. According to the above equation, the amount of spherical aberration generated is proportional to the fourth power of the numerical aperture of the objective lens, and the amount of spherical aberration generated increases as the numerical aperture increases. For this reason, detection and compensation of slight variations in the substrate thickness of the disk surface becomes essential as the information signal density increases.

  For example, coma aberration caused by disc tilt is reduced by reducing the substrate thickness to 0.1 mm, and spherical aberration caused by substrate thickness error is the difference in defocus signal between the optical disc surface and the recording surface. Then, the thickness of the substrate is detected and compensated by changing the distance between the two lenses based on the detection signal. As one of the methods for compensating the spherical aberration, there is a method using a spherical aberration correcting liquid crystal having a function of correcting the aberration by changing the wavefront of the transmitted light in the liquid crystal layer. For example, the liquid crystal aberration correction element is mounted on the objective lens so that the optical axes thereof coincide with each other, so that the objective lens and the liquid crystal aberration correction element move together during tracking (see, for example, Patent Document 1).

  In the case of this method, it is necessary for the center of the liquid crystal pattern and the optical axis to coincide with each other in order to correct the aberration. It is mounted on a 2-axis actuator. In addition, the lens interval between the second lens mounted on the spherical aberration correcting actuator that is driven integrally with the objective lens that is the first lens is changed even if the objective lens is not fixed. Thus, a technique for correcting spherical aberration has also been disclosed (see, for example, Patent Document 2).

  However, in the above-described technology, mounting on a biaxial actuator increases the mass of the movable part, and decreases the response sensitivity of the actuator. In addition to the conventional focus / tracking driving, it is necessary to supply a driving signal for the liquid crystal element to the movable part, which complicates the structure of the movable part. For example, the movable part of the biaxial actuator is conventionally supported by four wires, but if a control line is included by mounting a liquid crystal element, it must be supported by six or eight wires. For this reason, there is a problem that the movable part capacity of the biaxial actuator is increased and cannot be applied to a reduction in thickness and weight.

JP 2002-319172 A JP 2001-307349 A

  The present invention has been made in view of the above-described conventional situation, and it is possible to improve the degree of design freedom, provide a configuration for correcting spherical aberration, and reduce the size and weight of the movable part. An object of the present invention is to provide an optical pickup and an optical recording medium recording / reproducing apparatus that can be used.

  The optical pickup according to the present invention includes a diffracting unit that drives the objective lens by the first driving unit and diffracts the light beam emitted from the light source or the reflected beam reflected by the optical recording medium after being emitted by the light source. Driven by the second driving means. Then, the second drive means is controlled in synchronization with the first drive means by the drive control means.

  In this optical pickup, a movable optical system including an objective lens and the first driving means, a diffractive means, a second driving means, a light receiving element, And a fixed optical system including drive control means. Further, it is assumed that the diffractive means is a liquid crystal element.

  The optical recording medium recording / reproducing apparatus according to the present invention further includes an optical pickup for recording / reproducing, which is driven to rotate by an optical recording medium and is moved in a radial direction of the optical recording medium by a feeding unit. Is a device that controls the rotation of the optical pickup and the movement of the optical pickup in accordance with the recording and / or reproducing operation. The optical pickup drives the objective lens by the first driving means and the light beam emitted from the light source or The second driving means drives the diffracting means for diffracting the reflected beam emitted from the light source and then reflected by the optical recording medium.

  In the optical pickup of the optical recording medium recording / reproducing apparatus, in order to increase the degree of freedom of arrangement of the liquid crystal elements and the degree of freedom of design, a movable optical system including the objective lens and the first driving unit, a diffractive unit, a second unit And a fixed optical system including a driving means, a light receiving element, and a driving control means. Further, it is assumed that the diffractive means is a liquid crystal element.

  An optical pickup and an optical recording medium recording / reproducing apparatus according to the present invention have a diffraction unit disposed at an arbitrary position in parallel light between a light source and an optical recording medium, the position being independent from the objective lens, The degree of freedom in designing the optical system is improved by driving the diffractive means with driving means independent from each other and performing drive control in synchronization with each other. In particular, when a separation optical system is adopted, the volume of the movable part can be reduced by making the diffractive means and the second drive means a fixed optical system. Will not be damaged.

  An optical pickup shown as a specific example of the present invention is an optical pickup capable of correcting spherical aberration, and is independent of the objective lens without mounting the liquid crystal element for spherical aberration correction on the actuator for driving the objective lens, Separately driven by an independent actuator. In order to correct spherical aberration, it is necessary that the center of the liquid crystal pattern of the liquid crystal element and the optical axis of the beam from the light source coincide with each other. In this specific example, the liquid crystal element for correcting spherical aberration is driven. The driving actuator has a structure substantially the same as that of the objective lens driving actuator, and the new actuator provided independently is driven by following the tracking direction of the objective lens. In this case, the operation of the independent actuator for driving the liquid crystal element for correcting the spherical aberration needs to be completely synchronized with the operation of the actuator for driving the objective lens, so that a new drive control signal is required. A conventional tracking servo signal can be used.

  According to the present invention, since a liquid crystal element for correcting spherical aberration and this drive mechanism need only be added to the conventional optical pickup, the mechanisms and elements arranged on the lower surface of the disk are the same as the conventional configuration. Therefore, the newly added spherical aberration correction function does not reduce the degree of freedom in reducing the size, thickness and weight of the drive.

  Hereinafter, specific examples of an optical pickup according to the present invention and an optical recording medium recording / reproducing apparatus using the optical pickup will be described in detail with reference to the drawings.

  The configuration of the optical recording medium recording / reproducing apparatus 101 shown in FIG. 1 will be described. This optical recording medium recording / reproducing apparatus 101 includes a spindle motor 103 as a driving means for rotationally driving an optical disk 102 which is a high-density recording medium such as a DVD-R / RW and a CD-R / RW, and an optical pickup 104 as an optical disk. And a feed motor 105 as a driving means for moving in the radial direction 102. Here, the spindle motor 103 and the feed motor 105 are driven and controlled at a predetermined rotational speed by a servo control unit 109 controlled based on a command from the system controller 107.

  A signal modulator / demodulator and error correction code block (hereinafter referred to as a signal modulation / demodulation & ECC block) 108 shown in FIG. 1 performs signal modulation / demodulation and ECC (error correction code) addition. The optical pickup 104 separates the light flux from the light source into one main spot for recording and reproduction and two side spots for tracking on the signal recording surface of the rotating optical disk 102 in accordance with a command from the signal modulation / demodulation & ECC block 108. It is comprised so that it may be irradiated.

  Furthermore, the optical pickup 104 receives various signals output from the light detection means of the optical pickup 104 according to the reflected light fluxes corresponding to the main spot and the side spot reflected from the signal recording surface of the optical disc 102 and the preamplifier 120 and the radial skew. The signal processing unit 116 is configured to be supplied.

  The preamplifier 120 is configured to generate a focus error signal, a tracking error signal, an RF signal, and the like based on various signals output from the light detection means of the optical pickup 104 corresponding to the main spot and the side spot. Yes. Also, predetermined processing such as demodulation and error correction processing based on these signals is performed by the servo control unit 109, the signal modulation / demodulation & ECC block 108, and the like according to the type of recording medium to be reproduced.

  Here, for example, if the recording signal demodulated by the signal modulation / demodulation & ECC block 108 is for computer data storage, it is sent to the external computer 130 via the interface 111. Thereby, the external computer 130 or the like can receive a signal recorded on the optical disc 102 as a reproduction signal.

  If the recording signal demodulated by the signal modulation / demodulation & ECC block 108 is for audio / visual use, it is digital / analog converted by the D / A conversion unit of the D / A / A / D converter 112, and the audio / visual processing unit 113. To be supplied. The audio / visual processing unit 113 performs audio / visual processing and transmits the audio / visual signal to an external imaging / projection device or the like via the audio / visual signal input / output unit 114.

  In the optical pickup 104, for example, control of the feed motor 105 for moving to a predetermined recording track on the optical disc 102, control of the focusing direction and tracking direction of the biaxial actuator that holds the objective lens of the optical pickup 104, and spherical surface Control of the actuator for the liquid crystal element that holds the aberration correcting liquid crystal element is performed by the servo control unit 109.

  The laser control unit 121 controls the laser light source 21 in the optical pickup 104, and is configured to control the output power of the laser light source 21 in the recording mode and the reproduction mode.

  The radial skew signal processing unit 116 receives a reflected light beam corresponding to the main spot when performing tracking servo along a signal output from the light detection means of the optical pickup 104, that is, a wobbled groove formed on the optical disk 102. Detects a phase error with the wobble signal output for each side spot from the light detection means, and generates a skew signal including the tilt direction and the tilt amount of the optical disk 102 from the difference between the two phase errors. .

  The skew signal output from the radial skew signal processing unit 116 is a skew driving means for swinging the optical pickup 104 so that its optical axis (optical axis of the objective lens) is orthogonal to the signal recording surface of the optical disk 102. The skew actuator 117 is configured to be supplied to the actuator 117, and the skew actuator 117 includes a skew servo signal processing unit 118 that is driven and controlled based on a skew signal from the radial skew signal processing unit 116. The skew servo signal processing unit 118 is configured to be controlled based on a control command from the system controller 107.

  Next, the configuration of the optical pickup 104 according to the present invention will be described with reference to FIG. As shown in FIG. 2, the optical pickup 104 is arranged as a recording / reproducing beam emitting system, a laser light source 21 that emits a light beam for recording / reproducing, and a light beam emitting direction of the laser light source 21. A collimator lens 22, a polarizing beam splitter 23 disposed on the light output side of the collimator lens, a rising mirror 24 that reflects the parallel light beam transmitted through the polarizing beam splitter 23 in the vertical direction, and a parallel light beam from the light source. The objective lens 25 which condenses on the optical disk 102, and the objective lens actuator 26 which drives this objective lens are provided.

  Further, as a detection system, a liquid crystal element 27 as a grating for correcting a spherical aberration error included in reflected light reflected by the optical disk 102 and guided by the rising mirror 24, and a liquid crystal element actuator 28 for driving the liquid crystal element, And a photodetector 30 that receives the light beam reflected by the optical disk 102 and transmitted through the liquid crystal element and converts it into an electrical signal. The aberration correction light beam reflected by the polarization beam splitter 23 is condensed on the photodetector 30 by the condenser lens 29.

  The objective lens actuator 26 is a biaxial actuator that holds the objective lens 25 and is movable in the focusing direction and the tracking direction, and is controlled by the servo control unit 109.

  The liquid crystal element 27 can be disposed in any parallel light between the laser light source 21 and the optical disk 102 when provided in the forward path, and is disposed in any parallel light from the optical disk 102 to the photodetector 30 when provided in the return path. However, the liquid crystal element 27 used in this specific example is composed of two liquid crystal elements for the forward path and the backward path, and a wave plate is bonded to separate the liquid crystal acting on the forward path and the liquid crystal acting on the backward path. The liquid crystal element is made into one unit by using this element. In this specific example, the liquid crystal element 27 is provided at the position illustrated in FIG. 2, but may be disposed at any position as long as it is in parallel light where the forward path and the backward path overlap.

  The liquid crystal element actuator 28 has substantially the same structure as the objective lens actuator 26 and holds the liquid crystal element 27 alone. The liquid crystal element actuator 28 is controlled by the servo control unit 109 so that the center of the liquid crystal pattern of the liquid crystal element 27 coincides with the optical axis. The objective lens actuator 26 is driven in synchronization with the movement in the tracking direction. Since the liquid crystal element actuator 28 may have the same configuration as the objective lens actuator 26, a tracking servo signal for the objective lens actuator can be used as the control signal.

  As described above, when the liquid crystal element 27 is separated from the objective lens 25 and driven in synchronization with the objective lens 27, the liquid crystal element 27 as a grating for correcting the spherical aberration error can be arranged at an arbitrary position in the parallel light. This is very useful for power supply to the liquid crystal element 27, heat dissipation measures, simplification and weight reduction of the movable part, and the like. In this specific example, as shown in FIG. 1, the rising mirror 24, the objective lens 25, and the objective lens actuator 26 are separated as a movable part optical system 31, and the remaining configuration is separated as a fixed part optical system 32.

  Here, an example of a spherical aberration correction method using a liquid crystal element will be described. The liquid crystal element diffracts the light beam emitted by the light source or the reflected beam reflected by the optical recording medium after being emitted by the light source, and determines the surface of the optical recording medium from the diffracted light intensities of the 0th order diffracted light and the ± 1st order diffracted light. A method for generating a thickness error is described.

  In this specific example, the laser light reflected on the optical disk board surface is diffracted by the liquid crystal element 27 and branched into a main light beam (0th order light) and a sub light beam (± first order light). The main light beam is a light beam that forms a spot on one photodetecting element of the light receiving surface of the photodetector 30, which will be described later, and the pair of sub-light beams have a certain aberration having opposite polarities and receive light. It is a light beam that forms a spot on another photodetecting element at a position separated from the main spot formed on one photodetecting element on the surface. The aberration of the pair of sub-beams is spherical aberration generated by the optical disk surface protective layer formed on the disk surface of the optical disk 102, and has opposite polarities and equal aberration amounts.

  The laser light source 21 is driven by a drive circuit (not shown) and emits laser light. The laser light emitted from the laser light source 21 becomes a parallel light beam by the collimator lens 22, passes through the polarization beam splitter 23, and reaches the objective lens 25. The objective lens 25 converges the laser beam on the recording surface of the optical disc 102.

  The light beam reflected by the recording surface of the optical disk 102 is converted into a parallel light beam by the objective lens 25 and then transmitted through the liquid crystal element 27. The liquid crystal element 27 generates 0th-order diffracted light and ± 1st-order diffracted light of the reflected laser light. The third diffracted light of the 0th order diffracted light and the ± 1st order diffracted light generated by the liquid crystal element 27 is reflected by the polarization beam splitter 23 and passes through the focusing lens 29 and then reaches the light receiving surface of the photodetector 30. The photodetector 30 sends a detection signal to the aberration signal processing unit 33.

  The aberration signal processing unit 33 generates an aberration signal from detection signals of the 0th-order diffracted light of the reflected laser light and the 3rd-diffracted light of ± 1st-order diffracted light on the disk surface diffracted by the liquid crystal element 27. The aberration signal output from the aberration signal processing unit 33 is sent to the aberration control unit 34.

  The aberration control unit 34 controls the liquid crystal element actuator 28 so that the optical axis of the liquid crystal element 27 coincides with the optical axis of the objective lens, and drives the liquid crystal element 27 based on the aberration signal from the aberration signal processing unit 33. Control. The aberration control unit 34 is controlled based on a control command from the servo control unit 109.

  As described above, the optical pickup 104 shown as a specific example of the present invention has a spherical aberration correction function and is downsized and thinned. In addition, since a liquid crystal element for correcting spherical aberration and this drive mechanism need only be added to the configuration of the conventional optical pickup, the mechanism and elements of the movable part can be made the same as the conventional configuration, and new The spherical aberration correction function added to the drive does not reduce the degree of freedom in making the drive smaller, thinner and lighter.

  The present invention is a disk substrate thickness change that cannot be ignored when a high-density recording medium such as a DVD-R / RW or a CD-R / RW is used with a high NA and a multilayered recording film. The present invention is applicable to any optical pickup having a configuration that compensates for spherical aberration caused by the liquid crystal element, and a liquid crystal element that diffracts reflected laser light and an actuator that drives the liquid crystal element are provided separately from the objective lens and the actuator of the lens. Just do it. Therefore, it can be realized by simply adding a liquid crystal element for correcting spherical aberration and this drive mechanism to a conventional pickup.

It is a block diagram explaining the optical recording medium recording / reproducing apparatus shown as a specific example of this invention. It is a block diagram explaining the optical pick-up shown as a specific example of this invention.

Explanation of symbols

21 laser light source, 22 collimator lens,
23 Polarizing beam splitter, 24 Rising mirror, 25 Objective lens,
26 Objective lens actuator, 28 Liquid crystal element actuator,
30 optical detectors, 31 fixed part optical system, 32 movable part optical system,
33 Aberration signal processing unit, 34 Aberration control unit,
101 optical recording medium recording / reproducing apparatus, 102 optical disc,
104 optical pickup, 116 radial skew signal processing unit

Claims (6)

A light source that emits a light beam to the optical recording medium;
An objective lens for condensing the light beam from the light source on the optical recording medium;
First driving means for driving the objective lens;
Diffraction means for diffracting the light beam emitted by the light source or the reflected beam reflected by the optical recording medium after being emitted by the light source;
Spherical aberration calculating means for calculating spherical aberration on the surface of the optical recording medium from the diffracted light generated by the diffracting means;
Spherical aberration compensation means for controlling the diffraction means based on the spherical aberration and compensating the reflected beam;
Second driving means for driving the diffraction means;
A light receiving element that receives the reflected beam reflected by the optical recording medium and compensated by the diffraction means and converts it into an electrical signal;
An optical pickup comprising: drive control means for controlling the second drive means in synchronization with the first drive means. A movable optical system including the objective lens and the first driving means;
2. The optical pickup according to claim 1, wherein the optical pickup is separated into a diffracting unit, a second driving unit, the light receiving element, and a fixed optical system including the driving control unit.   2. The optical pickup according to claim 1, wherein the diffracting means is a liquid crystal element. The optical recording medium has a recording / reproducing optical pickup that is rotationally driven and moved in the radial direction of the optical recording medium by feeding means, and recording and / or reproducing the rotation of the optical recording medium and the movement of the optical pickup is performed. In the optical recording medium recording / reproducing apparatus that controls the operation according to the operation,
The above optical pickup
A light source that emits a light beam to the optical recording medium;
An objective lens for condensing the light beam from the light source on the optical recording medium;
First driving means for driving the objective lens;
Diffraction means for diffracting the light beam emitted by the light source or the reflected beam reflected by the optical recording medium after being emitted by the light source;
Spherical aberration calculating means for calculating spherical aberration on the surface of the optical recording medium from the diffracted light generated by the diffracting means;
Spherical aberration compensation means for controlling the diffraction means based on the spherical aberration to compensate the reflected beam;
Second driving means for driving the diffraction means;
A light receiving element that receives the reflected beam reflected by the optical recording medium and compensated by the diffraction means and converts it into an electrical signal;
An optical recording medium recording / reproducing apparatus comprising: drive control means for controlling the second drive means in synchronization with the first drive means. The above optical pickup
A movable optical system including the objective lens and the first driving means;
5. The optical recording medium recording / reproducing apparatus according to claim 4, wherein the optical recording medium recording / reproducing apparatus is separated into a diffracting unit, a second driving unit, the light receiving element, and a fixed optical system including the driving control unit. 5. The optical recording medium recording / reproducing apparatus according to claim 4, wherein the diffraction means is a liquid crystal element.

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