JP2007052864A - Optical pickup apparatus and optical disk system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup apparatus and an optical disk system corresponding to a BD (Blu-ray disc)(R) having ≤0.1 mm disk substrate thickness and also to an optical disk whose disk substrate has thickness thicker than 0.1 mm. <P>SOLUTION: A laser beam emitted from a semiconductor laser 31 is transmitted through a polarization beam splitter 34, a diameter of the luminous flux thereof is compensated by a collimator lens 34 to be a parallel beam, then spherical aberration and the numerical aperture NA thereof are compensated by a compensation element 36 via a raising mirror 35 and a linearly polarized beam of the semiconductor laser 31 is changed into a circularly polarized beam by a 1/4 wavelength plate 37. Information tracks on the optical disk 2 is illuminated with the circularly polarized light via an objective lens 38. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical pickup device and an optical disc system for recording and reproducing an optical disc.

  BD (Blu-ray Disc) (trademark) is superior in that it does not require a mechanism to correct coma aberration in the recording / playback device unlike HD DVD (High-Density Digital Versatile Disc) because the disc substrate is thin and the tilt margin is large. It is an optical disk. Also, since BD has a higher recording density than HD DVD, for example, HDTV (High Definition Television) video can be recorded for a long time.

  By the way, conventionally, an optical pickup device for reproducing BD and HD DVD in a compatible manner has been proposed (see Non-Patent Document 1). However, since the disk substrate from the surface of the BD to the recording layer is 0.1 mm or less and the disk substrate of HD DVD is 0.6 mm, the spherical aberration correction amount due to the difference in thickness of this disk substrate is extremely large. Therefore, it has been difficult to perform compatible reproduction substantially by correction using a liquid crystal or the like. In addition, since the same wavelength is used, it is difficult to perform compatible reproduction in which aberration correction is performed using a diffraction element utilizing wavelength dependency.

Nikkei Electronics, 2004.9.27, p105-121

  As described above, since a BD recording / reproducing apparatus is difficult to be compatible with an optical disc such as an HD DVD, an optical disc compatible with the BD is desired, and an apparatus for recording / reproducing the optical disc is desired.

  The present invention has been made to solve the above-mentioned problems, and is an optical disc that can cope with a BD having a disc substrate thickness of 0.1 mm or less and an optical disc having a disc substrate thicker than 0.1 mm. An object is to provide a pickup device and an optical disc system.

  In order to solve the above-described problems, an optical pickup device according to the present invention uses an objective lens having a numerical aperture of 0.85 or more, and at least a disc substrate thickness from the surface to the recording surface is 0.1 mm or less. An optical pickup device for recording / reproducing, comprising an aberration correcting means for correcting aberration according to the disc substrate thickness, for recording / reproducing an optical disc having a disc substrate thickness greater than 0.1 mm and less than or equal to 0.5 mm It is characterized by that.

  The optical disk system according to the present invention is an optical disk system for recording / reproducing an optical disk having a thickness of 0.1 mm or less from at least the surface to the recording surface using an objective lens having a numerical aperture of 0.85 or more. A discriminating unit for discriminating the disc substrate thickness; and an aberration correcting unit for correcting aberration according to the disc substrate thickness discriminated by the discriminating unit, wherein the disc substrate thickness is 0.1 mm or more and 0.5 mm or less. It is characterized by recording and reproducing an optical disc.

  According to the present invention, by correcting the aberration according to the disc substrate thickness of the optical disc, the disc substrate thickness corresponds to a BD having a thickness of 0.1 mm or less and also supports an optical disc having a disc substrate thicker than 0.1 mm. Can do.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an appearance of an optical disc system according to an embodiment of the present invention. The optical disc system 1 includes an optical disc 2 in a housing 100, a disc table 101 that holds the optical disc 2, and an optical pickup device 3 that reads information on the recording surface of the optical disc 2 or writes information on the recording surface of the optical disc 2. The disk table 101 rotates the optical disk 2 and the optical pickup device 3 moves in the diameter direction of the optical disk 2 to read or write information from the inner circumference to the outer circumference or from the outer circumference to the inner circumference. Do.

  FIG. 2 is a block diagram showing a configuration of an optical disc system according to an embodiment of the present invention. The optical disc system 1 includes an optical pickup device 3 that reads information recorded on the optical disc 2 or writes information on the optical disc 2, a preamplifier 4 that amplifies the signal level of the information read by the optical pickup device 3, A servo control circuit 5 for controlling the accurate track position and focus position, a feed motor 6 for sending the optical pickup device 3 to the accurate track position and focus position, and a spindle motor 7 for rotating the optical disk 2 via the disk table 101. A signal modulator / demodulator 8 for modulating / demodulating the signal amplified by the preamplifier 4, a laser control unit 9 for controlling the output of the laser light source installed in the optical pickup device 3, and a disc type discriminating unit for discriminating the type of the optical disc 2. 10 and the servo control circuit 5 and the signal depending on the type of the optical disc 2. A system controller 11 for controlling the modem 8, a D / A / A / D converter 12 for D / A conversion or A / D conversion of the signal, and an audio / visual processing unit 13 for signal processing of the audio / visual signal , An audio / visual signal input / output unit 14 for inputting / outputting audio / visual signals, an interface 15 for transmitting / receiving signals, and an external computer 16 for transmitting / receiving information via the interface 15.

  Here, the servo control circuit 5 controls the aberration correction of the optical pickup device 3 according to the disk type from the system controller 11 and also controls the spindle motor 7 that rotates the optical disk 2. Further, based on the signal amplified by the preamplifier 4, the feed motor 6 is controlled so as to send the optical pickup device 3 to an accurate track position and focus position.

  The signal modulation / demodulation circuit 8 demodulates the analog signal amplified by the pudding amplifier 4 into a digital signal. The signal modulation / demodulation circuit 8 modulates the digital signal output from the interface 15 or the D / A / A / D converter 12 into an analog signal.

  The system controller 11 controls the servo control circuit 5 and the signal modulator / demodulator 8 in accordance with the disk type output from the disk type determination unit 10.

  Next, the optical pickup device 3 according to an embodiment of the present invention will be described in detail with reference to FIG.

  The optical pickup device 3 includes a semiconductor laser 31, a polarization beam splitter 32, a photodetector 33, a collimator lens 34, a rising mirror 35, a correction element 36, a quarter wavelength plate 37, and an objective lens 38. And is configured.

  Since the optical pickup device 3 records and reproduces the optical disc 2 having a thin disc substrate from the surface of the optical disc 2 to the recording surface like a BD (Blu-ray Disc), the tilt margin due to the tilt of the optical axis of the lens is reduced. Large, no coma correction mechanism is required.

  The semiconductor laser 31 is a blue-violet semiconductor laser element corresponding to BD, and emits laser light having a wavelength of 405 nm. It is also possible to use a three-wavelength laser containing elements of a blue-violet semiconductor laser for BD, a red semiconductor laser for DVD (Digital Versatile Disc), and an infrared semiconductor laser for CD (Compact Disc).

  The collimator lens 34 converts the light emitted from the semiconductor laser 31 into parallel light. Further, it moves in the direction of the optical axis between the polarizing beam splitter 32 and the rising mirror 35, and corrects the diameter and spherical aberration of the light beam. That is, the divergence / convergence angle of light incident on the objective lens 38 is adjusted.

The correction element 36 is a phase generation device such as liquid crystal or PLZT ((Pb, La) (Zr, Tr) O ₃ ), and corrects spherical aberration and NA. The correction element 36 generates a wavefront that is substantially equivalent to the correction amount of spherical aberration that occurs due to the difference in thickness of the disk substrate, for example, according to the voltage applied to each electrode. In addition, when using a wavelength different from BD, you may use a diffraction element for the correction | amendment element 36. FIG.

  Laser light emitted from the semiconductor laser 31 is guided to the polarization beam splitter 32. The light transmitted through the polarization beam splitter 32 is converted into parallel light by the collimator lens 34, and then the spherical aberration and the numerical aperture NA are corrected by the correction element 36 via the rising mirror 35. The linearly polarized light of the laser 31 is changed to circularly polarized light, and the information track on the optical disk 2 is illuminated via the objective lens 38.

  The reflected light from the optical disk 2 is reflected by the beam splitter 32 via the raising mirror 35 and then guided to the photodetector 33.

  Since this optical pickup device 3 is compatible with a BD having a disc substrate thickness of 0.1 mm, the aberration when the numerical aperture NA of the objective lens is 0.85 is removed to the limit.

When the disc substrate thickness is thicker than 0.1 mm, the spherical aberration to be corrected increases. The third-order spherical aberration coefficient W ₄₀ due to the disc substrate thickness difference dt is calculated by the equation (1).

  Further, since the NA corresponding to BD is as high as 0.85, the spherical aberration to be corrected further increases when the disk substrate becomes thicker than 0.1 mm.

FIG. 4 is a graph showing the value of the third-order spherical aberration coefficient W ₄₀ with respect to the disc substrate thickness difference dt at each NA value. As can be seen from FIG. 4, the third-order spherical aberration coefficient W ₄₀ with respect to the thickness difference dt increases as the value of NA increases. For this reason, the optical pickup device 3 performs aberration correction by driving the collimator lens 34 in the optical axis direction and adjusting the divergence / convergence angle of the light incident on the objective lens. Further, the light is partially blocked by the correction element 36 to reduce the NA. As described above, the optical pickup device 3 controls the aberration correction and the numerical aperture NA so that the third-order spherical aberration coefficient W ₄₀ does not increase.

Here, for example, if the numerical aperture is controlled to 0.7 or less and the value of the third-order spherical aberration coefficient W ₄₀ is within an allowable range of about 10λ or less, dt = 0.4 mm, that is, the disc substrate thickness. Can be applied to the optical disc 2 having a thickness of 0.5 mm or less. In other words, by switching the numerical aperture to 0.7 or less, the aberration of the optical disc having the disc substrate thickness greater than 0.1 mm and 0.5 mm or less becomes approximately 10λ or less, and the aberration can be corrected.

Further, the third-order coma aberration coefficient W ₃₁ due to the disc tilt is calculated by the equation (2).

The third-order coma aberration coefficient W31 also increases the disk substrate thickness t is increased, but by controlling to decrease the value of the numerical aperture NA as described above, an increase in third-order coma aberration coefficient W ₃₁ Suppress. As a result, the optical pickup device 3 does not need a coma aberration correction mechanism.

  As described above, the optical disk having a thicker disk substrate (0.1 mm to 0.5 mm) with reference to the numerical aperture NA of 0.85 corresponding to the BD having a disk substrate thickness of 0.1 mm is provided by the collimator lens 34 and the correction element 36. Aberration correction and numerical aperture NA can be controlled.

  FIG. 5 is a flowchart showing the operation of the optical disc system in one embodiment of the present invention.

  The disc type discrimination unit 10 detects a disc discrimination signal from the optical disc 2 and notifies the system controller 11 of the disc discrimination signal. The system controller 11 determines whether or not the optical disk 2 is a BD from the disk determination signal (step S1).

  If it is determined in step S1 that it is not a BD, that is, if the disc substrate thickness is an optical disc having a thickness of 0.1 mm to 0.5 mm, a laser beam corresponding to the optical disc is selected (step S2). Further, the aberration correction process as described above is performed according to the disc substrate thickness determined and the selected laser beam (step S2). In other words, the collimator lens 34 is driven in the optical axis direction, the numerical aperture NA is controlled by the correction element 36, and spherical aberration and coma are corrected. After aberration correction, the process proceeds to step S4.

  If it is determined in step S1 that the image is a BD, the process proceeds to step S4, and recording / reproduction processing is performed using the numerical aperture NA 0.85 set as a reference.

  In step S4, the recording / reproducing process is performed using the numerical aperture NA corresponding to the thickness of the disk substrate. When reproduction processing is performed, a signal read from the optical disk 2 by the optical pickup device 3 is amplified by a preamplifier, converted into a digital signal by the signal modulator / demodulator 8, and various signal processing is performed. 16 and the audio / visual signal input / output unit 14 to other external devices. When recording processing is performed, a signal input from the external computer 16 or another external device via the audio / visual signal input / output unit 14 is output by the laser control unit 9 according to the disk thickness. Is written on the optical disc 2.

  As described above, according to the present invention, not only corresponds to a BD having a disk substrate thickness of 0.1 mm or less, but also has a disk substrate thickness of less than 0.1 mm with a small aberration correction amount and 0.5 mm or less. Recording / reproduction processing can be performed in correspondence with an optical disc. That is, an optical disc having a recording density equivalent to or higher than that of HD DVD can be easily compatible at low cost.

  Further, since the corresponding optical disk has a small disk thickness, the disk tilt margin is wide, and a mechanism such as coma aberration correction is not required, and the number of parts can be reduced.

  An optical disc having a disc thickness of 0.1 mm or more can be easily injection-molded onto a polycarbonate substrate, and a conventional disc manufacturing apparatus can be used. Therefore, the manufacturing cost is advantageous.

  In this embodiment, the aberration correction and the numerical aperture NA are controlled by the collimator lens 34 and the correction element 36. However, the numerical aperture NA may be switched by a mechanism for exchanging the objective lens.

1 is an external view showing an optical disc system according to an embodiment of the present invention. It is a block diagram which shows the structure of the optical disk system in one Embodiment of this invention. It is a figure which shows the structure of the optical pick-up apparatus in one Embodiment of this invention. It is a figure for demonstrating the spherical aberration by the thickness error of a disc board | substrate. 5 is a flowchart showing the operation of the optical disc system in one embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk system 2 Optical disk 3 Optical pick-up apparatus 4 Preamplifier 5 Servo control circuit 6 Feed motor 7 Spindle motor 8 Signal modulator / demodulator 9 Laser control part 10 Disk type discrimination | determination part 11 System controller 12D / A / A / D converter, 13 audio / visual processing unit, 14 audio / visual signal input / output unit, 15 interface, 16 external computer, 31 semiconductor laser, 32 polarization beam splitter, 33 photodetector, 34 collimator lens, 35 Raising mirror, 36 Correction element, 37 1/4 wavelength plate, 38 Objective lens, 100 Case, 101 Disk table

Claims (6)

An optical pickup device that uses an objective lens having a numerical aperture of 0.85 or more and records and reproduces an optical disc having a disc substrate thickness of at least 0.1 mm from the surface to the recording surface,
Aberration correction means for correcting aberration according to the disk substrate thickness,
An optical pickup device for recording / reproducing an optical disc having a thickness of more than 0.1 mm and not more than 0.5 mm.   2. The aberration correction means corrects aberrations of an optical disc having a thickness of the disc substrate larger than 0.1 mm and 0.5 mm or less by switching the numerical aperture to 0.7 or less. The optical pickup device described.   The aberration correction means moves the lens in the optical axis direction and adjusts the divergence / convergence angle of light incident on the objective lens, whereby the disk substrate thickness is greater than 0.1 mm and less than or equal to 0.5 mm. 2. The optical pickup device according to claim 1, wherein aberrations of the optical disk are corrected.   The aberration correction means is characterized by correcting the aberration of an optical disc having a thickness of the disc substrate larger than 0.1 mm and less than or equal to 0.5 mm by partially controlling the phase of light by a phase generating element. The optical pickup device according to claim 1. An optical disc system for recording and reproducing an optical disc having a thickness of 0.1 mm or less from at least the surface to the recording surface using an objective lens having a numerical aperture of 0.85 or more,
A discriminating means for discriminating the disc substrate thickness;
Aberration correction means for correcting aberration according to the disc substrate thickness determined by the determination means,
An optical disc system for recording and reproducing an optical disc having a disc substrate thickness of 0.1 mm or more and 0.5 mm or less.   6. The aberration correcting means corrects an aberration of an optical disk having a disk substrate thickness greater than 0.1 mm and 0.5 mm or less by switching the numerical aperture to 0.7 or less. The optical disc system described.

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