JPH09282733A - Recording and reproducing device for optical information - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce cross talk and to stably reproduce a recorded signal by providing an exclusive optical information-detecting optical system having phase compensating means in a land part and a groove part, respectively. SOLUTION: A laser beam emitted from semiconductor lasers 1, 14 to irradiate a magneto-optical recording medium 13 through collimator lenses 2, 15, polarization beam splitters 3, 16, rising mirrors 4, 17, and object lenses 5, 18 is used for reproducing a magneto-optical signal recorded in a land 27 and a groove 28, respectively. Respective luminous fluxes reflected by the recording medium 13 are passed through a 1/2 wavelength plate 7, 21 tilted to luminous flux for phase compensation by passing through again object lenses 5, 18, polarization beam splitters 3, 16. Therefore, optimum phase compensation for the land 27 and the groove 28 can be realized, and a recorded signal can be stably reproduced without loading a special burden to the magneto-optical recording medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus for recording and reproducing a magneto-optical signal on both a land portion and a groove portion on a magneto-optical recording medium.

[0002]

2. Description of the Related Art At present, optical recording media are widely used as recording media capable of reproducing audio signals and image signals. In particular, magneto-optical recording media and phase-change recording media have been researched and developed in various places as rewritable high-density recording media.

In order to improve the recording density of an optical recording medium for recording information spirally or concentrically, there are two methods of shortening the track pitch and improving the linear recording density. In either case, this can be achieved by shortening the wavelength of the semiconductor laser used for recording and reproduction.However, it has been a while before a semiconductor laser with a short wavelength, such as green or blue, stably continually oscillates at room temperature for a long time. It will take time. In such a situation, a method for greatly improving the recording density while using a laser of the current wavelength, such as MSR (magnetic super-resolution) in a magneto-optical recording medium, is being sought.

In a RAM medium such as a magneto-optical recording medium, light having the same wavelength is used for writing and reading information. On the other hand, in a ROM medium in which information is recorded in advance,
Phase pits are formed using a short wavelength gas laser or the like. From the viewpoint of the RAM medium, although the ROM medium has the same reproduction conditions, it is as if it were recorded using a light source that can be used in the future. Disadvantageous. For this reason,
D attracts attention as a next-generation home video recording medium
In the VD standard, no proposal has yet been made to support the recording capacity of a ROM medium with a RAM medium of the same medium size.

[0005] The land and groove recording is a very important method for developing a high-density recording medium because the recording density can be simply doubled with the same linear recording density and the same track pitch. It has been reported that in the magneto-optical recording medium, the above-mentioned MSR can reduce not only the linear recording density but also the crosstalk between tracks, and its application to land and groove recording has been studied in various places.
However, the conditions for developing magnetic super-resolution, such as the case where the reproducing laser power depends on the linear velocity, the case where a reproducing magnetic field is required, and the case where at least about three magnetic layers are required, are extremely complicated, and the stability is low. Is also anxious and prone to high costs.

[0006]

By narrowing the track pitch, there arises a problem of crosstalk in which data signals of adjacent areas are mixed in the output signal during reproduction. In conventional land recording or groove recording,
Crosstalk is suppressed because grooves or lands exist between lands or grooves, and there is a gap between regions where information is written. But,
In land and groove recording, since information recording areas are adjacent to each other, crosstalk greatly affects reproduction characteristics. Japanese Patent Laid-Open No. 8-7357 discloses that crosstalk from a land or a groove can be reduced by selecting the depth of the groove. However, in a normal medium, crosstalk becomes free when the groove depth is about 1/6 wavelength. Therefore, in a magneto-optical recording medium, the signal carrier level is lower than that in a case where the groove depth is 1/8 wavelength. Decrease. In addition, the push-pull signal serving as a track error signal also decreases. In addition, it has already been reported that the above-mentioned crosstalk-free condition is easily changed by Kerr ellipticity, a focus error of an objective lens, spherical aberration, and the like.

In order to solve the above problems, the present invention improves the optical information recording / reproducing apparatus to stabilize the signals recorded in the land portion and the groove portion without imposing a special burden on the magneto-optical recording medium. It is a main object of the present invention to provide an optical information recording / reproducing apparatus capable of reproducing.

[0008]

According to the present invention, in reproducing a magneto-optical signal recorded in a land portion and in reproducing a magneto-optical signal recorded in a groove portion, when reproducing a land portion, The electric vector of the laser light is orthogonal to the flowing direction of the recorded signal, and when reproducing the groove part, the electric vector of the laser light is parallel to the flowing direction of the recorded signal. It has a magnetic Kerr effect detection optical system which is a magnetic signal, and uses means having different phase compensation amounts in each, and one of them detects a signal from a land or a groove. In particular, it is important that the polarization of the laser light emitted during reproduction can be easily controlled. Therefore, in the present invention,
The problem is solved by using two optical information detection optical systems for reproducing the land portion and for reproducing the groove portion.

According to the first aspect of the present invention, when reproducing the land portion or the groove portion, a dedicated optical information detecting optical system is assigned to each of them, and a phase compensating means is provided in each magneto-optical signal detecting optical system. The amount of phase compensation is different for land reproduction and groove reproduction.
Further, according to the invention of claim 2, in the optical information detecting optical system for reproducing the land portion, the electric vector of the luminous flux irradiating the magneto-optical recording medium is orthogonal to the direction in which the recorded signal flows, and the reproducing portion for the groove portion is reproduced. In the optical information detection optical system of, since the electric vector of the light beam irradiating the magneto-optical recording medium is parallel to the direction in which the recorded signal flows,
Stable reproduction is possible regardless of the substrate material of the recording medium. According to the third aspect of the invention, one of the optical information detection optical systems has a high output that can be used for recording, and the other has a low output, so that cost increase can be minimized. Further, according to the invention of claim 4, if the low-output light source has a shorter wavelength, it is advantageous when reproducing a high-density optical recording medium for reproduction only having a spiral single track. However, since the optical recording media have different plate thicknesses, the optical information detecting optical system having a light source of low output or short wavelength according to the invention of claim 5 has a thin plate thickness of, for example, 0.6 m.
Objective lens selection such that an objective lens with a numerical aperture of 0.6 is used when reproducing an optical recording medium of m, and a numerical aperture of 0.55 is used when reproducing an optical recording medium with a plate thickness of 1.2 mm. Provide a mechanism.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An optical information recording / reproducing apparatus of the present invention will be described below in detail with reference to the drawings according to the embodiments.

FIG. 1 is a diagram showing a positional relationship between an optical system configuration of an optical information recording / reproducing apparatus of the present invention and a disc-shaped optical recording medium. Laser light emitted from the high-power semiconductor laser 1 having a wavelength of 680 nm is converted into parallel light by the collimator lens 2, and Tp: Rp = 80: 20, Ts: Rs =
After passing through a polarization beam splitter 3 of 2:98, a rising mirror 4 guides it to an objective lens 5 with a numerical aperture of 0.55 and a plate thickness of 1.2 mm, and the light flux narrowed down to the diffraction limit by the objective lens 5 is magneto-optical. The recording medium 13 is irradiated. Here, the electric vector of the laser beam applied to the magneto-optical recording medium 13 is orthogonal to the flowing direction of the recorded signal, and is used when reading the magneto-optical signal recorded on the land 27. The light beam reflected from the magneto-optical recording medium 13 again passes through the objective lens 5 and is amplitude-divided by the polarization beam splitter 3 into a transmission component and a reflection component. The reflected component gives a certain phase difference, passes through the half-wave plate 7 inclined with respect to the light beam for phase compensation, and is divided into a P component transmitted by the polarization beam splitter 8 and an S component reflected. Will be divided. The P component and the S component are converged on the photodetectors 10 and 12 by the converging lenses 9 and 11, respectively, and photoelectrically converted. The photoelectrically converted signal is detected as a magneto-optical signal from the land by the differential amplifier. The entire optical system configured as described above moves in the direction indicated by the moving direction 29. Further, the laser light emitted from the low-power semiconductor laser 14 of 635 nm is converted into parallel light by the collimator lens 15, and Tp: Rp
= 80: 20, Ts: Rs = 2: 98, and then the rising mirror 17 guides it to the objective lens 18 with a numerical aperture of 0.55 and a plate thickness of 1.2 mm. The objective lens 18 diffracts the light. The light flux narrowed to the limit is applied to the magneto-optical recording medium 13. Here, the electric vector 20 of the laser light with which the magneto-optical recording medium 13 is irradiated
Is parallel to the flowing direction of the recorded signal and is used when reproducing the magneto-optical signal recorded in the groove 28. The light beam reflected from the magneto-optical recording medium 13 passes through the objective lens 18 again, and is amplitude-divided by the polarization beam splitter 16 into a transmission component and a reflection component. The reflected component gives a certain phase difference, passes through the half-wave plate 21 inclined with respect to the light beam for phase compensation, and is divided into a P component transmitted by the polarization beam splitter 22 and an S component reflected. Will be divided. The P component and the S component are focused on the photo detectors 26 and 24 by the converging lenses 25 and 23, respectively, and are photoelectrically converted. The photoelectrically converted signal is detected as a magneto-optical signal from the groove by the differential amplifier. The entire optical system configured as described above moves in the direction indicated by the moving direction 30. Further, a rotary-sliding type two-dimensional actuator for focusing and tracking control of the objective lens 18 is further provided with an objective lens 19 having a numerical aperture of 0.6 and a plate thickness of 0.6 mm. Therefore, when reproducing a DVD having a plate thickness of 0.6 mm, the problem of wavefront aberration due to the difference in plate thickness can be solved by switching the objective lens 19 to the position of the objective lens 18. As described above, according to the optical information recording / reproducing apparatus configured as described above, it is possible to easily reproduce the magneto-optical recording medium or the CD or the DVD recorded on both the land and the groove. Next, the specifications of the magneto-optical recording medium used for recording / reproducing the land portion and the groove portion using the optical information recording / reproducing apparatus of the present invention will be described. When the land width and the groove width are approximately 0.7 μm, the optical phase difference between the land surface and the groove surface is about ⅛ wavelength (laser wavelength 680
90 nm thick S on a polycarbonate substrate
iN was formed into a film by the sputtering method. Hereinafter, the formation of the film is all by the sputtering method. Next, TbFeCo having a thickness of 20 nm was formed, SiN having a thickness of 22 nm was further formed, and Al serving as a reflective film was formed to have a thickness of 65 nm. Further, a UV resin was spin-coated about 10 μm as a protective coat. A method of recording a magneto-optical signal on the land and groove of the above-described magneto-optical recording medium will be described. In the embodiment of the present invention, an optical pulse synchronized with a clock is emitted, and R
A pulse-assisted magnetic field modulation method for applying an alternating magnetic field modulated to the LL1-7 code was used. The result of the reproduction characteristic by the optical information recording / reproducing apparatus of the present invention will be described. FIG. 2 shows the dependence of crosstalk between the land and the groove on the peak power of the recording laser pulse. A magnetic domain of 2 μm is recorded in the land portion or groove portion, and is a value obtained by subtracting the carrier level when the signal recorded in the land portion or groove portion is directly reproduced from the carrier level in the unrecorded land portion or groove portion. is there. In any case, the crosstalk due to the signal recorded on the land portion or the groove portion is -25 dB or less at a wide recording laser power.
Further, the results shown in FIG. 3 show that the shortest mark length 2T in the RLL1-7 code is 0.48 μm and the linear velocity is 4.
It is a jitter characteristic when recording / reproducing at 5 m / s. Recording on both land and groove (groove was recorded first), and when the recorded signals were reproduced, the jitter percentage was 9% over a wide laser power.
It can be seen that the following large margin can be secured. Here, the jitter percentage is 100 as the ratio of the standard deviation σ2T of the 2T signal to the window width (time).
It is a value obtained by multiplying by, and it is generally judged that if the jitter percentage is 10% or less, the level can be sufficiently used for data. Further, when a conventional optical information recording / reproducing apparatus is used, that is, when phase compensation is not performed for each of the signal reproduction at the land portion or the groove portion, it is 1 at any laser power.
It was impossible to achieve below 0%. Further, if the azimuth angle of the half-wave plate is not optimally adjusted for each of the land portion and the groove portion, it becomes difficult to reduce crosstalk and improve the reproduction signal strength.
Achieving a jitter of 10% is likewise impossible.

[0012]

As described in detail above, by using the optical information recording / reproducing apparatus of the present invention, optimum phase compensation can be realized for each of the land portion and the groove portion. By using two independent optical information detection optical systems with optimized phase compensation conditions for the land part or the groove part,
The crosstalk due to the signal of the adjacent groove portion or the signal of the land portion deviates from the phase compensation condition, and thereby the signal amplitude decreases. Due to this action, if the optical information recording / reproducing apparatus of the present invention is used, a great effect of reducing crosstalk can be obtained. Also, in one optical information detection optical system,
2 for focusing and tracking control of an objective lens that is compatible with optical recording media having other plate thicknesses
It is also possible to reproduce a DVD by arranging it on a three-dimensional actuator and switching the objective lens.

[Brief description of drawings]

FIG. 1 is a diagram showing an optical system configuration of an optical information recording / reproducing apparatus and an arrangement of a disc-shaped recording medium in an embodiment of the present invention.

FIG. 2 is a diagram showing the dependence of crosstalk from a land or a groove on a writing laser power.

FIG. 3 is a diagram showing the dependence of jitter on writing laser power when RLL1-7 code is recorded on both lands and grooves.

[Explanation of symbols]

 1 semiconductor laser 2 collimator lens 3 polarizing beam splitter 4 rising mirror 5 objective lens 6 electric vector 7 half-wave plate 8 polarizing beam splitter 9 converging lens 10 photodetector 11 converging lens 12 photodetector 13 magneto-optical recording medium 14 Semiconductor laser 15 Collimator lens 16 Polarizing beam splitter 17 Erecting mirror 18 Objective lens 19 Objective lens 20 Electric vector 21 Half-wave plate 22 Polarizing beam splitter 23 Converging lens 24 Photodetector 25 Converging lens 26 Photodetector 27 Land 28 Groove 29 Moving direction 30 Moving direction

Claims (5)

[Claims] 1. An optical information recording / reproducing apparatus for recording and reproducing information on both the land and the groove of a magneto-optical recording medium in which the widths of the land and the groove are substantially equal, the optical information detecting optical system for reproducing the land portion. And a groove portion reproducing optical information detecting optical system, each of which has a unique light source and an objective lens, the magneto-optical signal detecting optical system has a phase compensating means, and the phase compensating amount of the phase compensating means is An optical information recording / reproducing device, wherein the land portion reproduction and the groove portion reproduction are different from each other. 2. An electric vector of a light flux irradiating the magneto-optical recording medium in the land reproduction optical information detection optical system is orthogonal to a flowing direction of a signal recorded in the magneto-optical recording medium, and the groove portion is formed. 2. The reproducing optical information detecting optical system according to claim 1, wherein an electric vector of a light beam applied to the magneto-optical recording medium is parallel to a flowing direction of a signal recorded on the magneto-optical recording medium. Optical information recording / reproducing device. 3. The optical information recording / reproducing apparatus according to claim 1, wherein at least one of the light sources has an optical output capable of recording magneto-optical information on the magneto-optical recording medium. 4. The optical information recording / reproducing apparatus according to claim 3, wherein the wavelengths of the light sources are different. 5. An optical information detection optical system comprising at least one short wavelength light source or at least one low output light source of the optical information detection optical system, wherein two types of objective lenses are provided, and The optical information recording / reproducing apparatus according to any one of claims 1, 2, 3 and 4, further comprising an objective lens switching mechanism.