JPH1064135A - Optical information recording and detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease crosstalks and to execute simultaneously reproduction of lands and grooves by using a magneto-optical detecting optical system optimized in phase compensation conditions for the land parts and the groove parts. SOLUTION: The luminous flux radiated from a laser diode 16 is made into parallel luminous fluxes by a lens 17. These luminous fluxes are separated by zero order lght and ±1st order light by a diffraction grating 18. The luminous fluxes are subjected to amplitude sepn. by a mean splitter. The luminous flux transmitted through this splitter is converged into the diffraction threshold by a lens 20 and is cast on a magneto-optical recording medium 21. The zero order lght and ±1st order light reflected by the medium 21 are subjected to amplitude sepn. by the splitter 19. The reflected component is separated to a transmitted component and a reflected component by a half mirror 22. The reflected component is used for reproducing the information recorded in the grooves and the transmitted component is used for reproducing the information recorded in the lands. The luminous fluxes reflected and transmitted by and through the mirror 22 are independently subjected to phase compensation by half-wave plates 23, 30, thereby, the crosstalks are removed. The luminous fluxes are then separted to the P component and the S component by polarization beam splitters 24, 31 and are condensed to photodiodes 26, 28, 33, 35.

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 / detecting apparatus for recording and reproducing a magneto-optical signal on both a groove and a land 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, a semiconductor laser with a short wavelength such as green or blue stably oscillates for a long time at room temperature, and is inexpensive. It will take some 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,
The 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] Land and groove recording can be simply doubled if they have the same linear recording density and the same track pitch, and are extremely important in developing a high-density recording medium. For magneto-optical recording media, the above-described MSR
Is reported to be able to reduce not only the linear recording density but also the crosstalk between tracks, and the possibility of application to land and groove recording has been studied in various places. However, the conditions for developing magnetic super-resolution are extremely complicated, for example, when the reproducing laser power depends on the linear velocity, when a reproducing magnetic field or an initialization magnet is required, or when at least about three magnetic layers are required. Also, there are concerns about stability and the cost is likely to be high.

[0006]

As the track pitch is narrowed, a problem of crosstalk in which data signals in adjacent areas are mixed in an output signal during reproduction is a problem. 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 Application Laid-Open No. 8-7357 states 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. Further, if the land and the groove can be reproduced simultaneously, the transfer speed can be doubled at a stretch.

[0007]

The above object is achieved by improving an optical information recording / detection device without imposing a special burden on a magneto-optical recording medium.

The first invention proposes providing means for irradiating the reproduction laser spot so that the adjacent land and groove are substantially semicircular.

The second invention provides a means for irradiating at least two or more laser spots in addition to the first laser spot, and a laser spot disposed on both sides of the first laser spot and a first laser spot. It is proposed that the spots be arranged at an odd multiple of a quarter of the period of the groove or land in the radial direction of the magneto-optical recording medium.

A third invention proposes that the first laser spot and at least two more laser spots are generated by a diffraction grating.

According to a fourth aspect of the present invention, the first laser spot is used when recording information on the groove and the land, and the polarity of the push-pull signal, which is a tracking signal generated by the first laser spot, is set to 1 for the magneto-optical recording medium. It is proposed to provide a means for alternately recording information on the groove and the land by inverting each time it rotates.

According to a fifth aspect of the present invention, when recording information on a groove or a land, either the groove or the land is recorded first, and after all the recording tracks have been used,
It is proposed to provide means for inverting the polarity of the push-pull signal generated by the first laser spot and recording the remaining groove or land.

According to a sixth aspect of the present invention, there is provided means for providing two different magneto-optical signal detection optical systems, one for groove reproduction and the other for land reproduction, wherein the two magneto-optical signal detection optical systems provide different phase compensation amounts. It is proposed to have

The seventh invention proposes that the means for providing different amounts of phase compensation is a crystalline wave plate having a refractive index anisotropy.

According to an eighth aspect of the present invention, the crystalline wave plate is a half-wave plate, and the half-wave plate disposed in the two magneto-optical signal detection optical systems is arranged so that the half-wave plate is arranged in the traveling direction of the laser light. Different slopes, and each half
It is proposed that the azimuthal angle of the crystal optical axis with respect to the direction of the electric vector of the laser beam incident on the wave plate is different.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical information recording / detection apparatus according to an embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1A is a schematic plan view showing a positional relationship of a laser spot on a magneto-optical recording medium in the optical information recording / detecting device of the present invention. A laser spot 4 is applied to a groove 1 and a land 2 which have substantially the same width and are adjacent to each other, in a substantially semicircular shape. By irradiating in this manner, the magnetic domains 3 recorded in the groove and the land are reproduced at the same time. FIG. 1B is a schematic cross-sectional view of FIG. 1A. The laser light narrowed down to the diffraction limit by the objective lens 6 is applied to the groove 1 and the land 2 via the substrate 5.

Next, a method of scanning the reproduction laser spot as shown in FIG. 1 will be described. FIG. 2A is a schematic plan view showing the positional relationship of the + 1st-order light 7, the 0th-order light 8 and the -1st-order light 9 generated by the diffraction grating on the magneto-optical recording medium. The + 1st-order light 7, the 0th-order light 8 and the -1st-order light 9 are arranged in the radial direction of the magneto-optical recording medium at intervals of a quarter of a groove or land period. FIG.
(B) shows the + 1st-order light 1 reflected from the magneto-optical recording medium.
The 3, 0-order light 14 and the -1st-order light 15 reach the two-division photodiodes 10, 11, and 12, respectively, and generate a push-pull signal by differentially detecting each.

FIG. 3 shows the waveform of the push-pull signal generated by the photodiodes 10, 11 and 12. FIG. 3A shows a push-pull signal generated by the + 1st order light 13,
(B) is a push-pull signal by the -1st order light 14, (c)
Represents a push-pull signal by the zero-order light 15.
(A) and (b) are 180 degrees out of phase with each other,
The polarity is reversed. That is, by taking the difference between the push-pull signals of the +1 order light and the -1 order light, a stable tracking signal having no DC component can be obtained. (C) is 90 degrees or-with respect to (a) and (b).
There is a 90 degree phase difference. That is, when the track servo operates, the zero-order light 8 scans on the boundary between the adjacent groove and land. Therefore, the zero-order light 8
Will convey information recorded on the groove and the land at the same time. At the time of recording, it is possible to perform recording by using the zero-order light on lands and grooves by a push-pull signal from the zero-order light. However, in reproduction, information from the groove and information from the land are mixed and not separated.

Next, in order to explain a method of separating the information from the groove and the information from the land, FIG. 4 is a schematic diagram showing the configuration of the optical information recording / detecting apparatus of the present invention. The light beam emitted from the laser diode 16 is converted into parallel light by a collimator lens 17 and separated into zero-order light and ± first-order light by a diffraction grating 18. The separated light beam is amplitude-separated by the beam splitter 19 and the transmitted light beam is passed through the objective lens 2.
The beam is narrowed down to the diffraction limit by 0, and is irradiated on the magneto-optical recording medium 21.

The illuminated zero-order light and ± first-order light are arranged as shown in FIG. Each of the 0th-order light and ± 1st-order light reflected by the magneto-optical recording medium 21 passes through the objective lens 20 again, and is subjected to amplitude separation by the beam splitter 19 and reflected by the half mirror 22 into a transmission component and a reflection component. Separated. Here, the reflection component is used for reproducing information recorded on the groove, while the transmission component is used for reproducing information recorded on the land. The reflected component passes through the half-wave plate 23.

The half-wave plate 23 has a certain inclination with respect to the traveling direction of the light beam and a crystal optic axis having a certain azimuth with respect to the electric vector of the passing light beam in order to remove a crosstalk signal from the land. Are located. The light beam that has passed through the half-wave plate 23 is separated into a P component and an S component by a polarization beam splitter 24, and the P component is condensed on a photodiode 26 by a converging lens 25. Here, the 0th-order light and the ± 1st-order light are respectively subjected to signal detection by the respective elements of the photodiode 26 divided for exclusive use. Here, as described with reference to FIGS. 2 and 3, each element is divided into two to obtain a push-pull signal. On the other hand, the S component reflected by the polarization beam splitter 24 is similarly condensed on a photodiode 28 by a converging lens 27, and a signal of zero-order light is detected. The signal of the zero-order light focused on the photodiodes 26 and 28 is detected by the differential amplifier 29 as a signal from the groove.

Next, the component transmitted through the half mirror 22 is transmitted through the half-wave plate 30 for detecting information from the land. The half-wave plate 30 is arranged with a certain inclination with respect to the traveling direction of the light beam and its crystal optical axis at a certain azimuth angle with respect to the electric vector of the passing light beam in order to remove a crosstalk signal from the groove. ing. here,
The tilt and azimuth of the half-wave plate 30 are different from those of the half-wave plate 23.

The light beam transmitted through the half-wave plate 30 is split into a P component and an S component by a polarizing beam splitter 31, and the P component is separated by a converging lens 34 into a photodiode 3.
The light is condensed at 5, and the signal of the zero-order light is detected. The S component is condensed on the photodiode 33 by the converging lens 32, and the signal of the zero-order light is detected. The signal of the zero-order light collected on the photodiodes 32 and 35 is detected by the differential amplifier 36 as a signal from the land. As described above, the 0th-order light has both signals of adjacent grooves and lands in a mixed form. However, by performing phase compensation independently for each of them by a half-wave plate, crosstalk between each other is obtained. Can be removed, and reproduction can be performed at the same time.

FIG. 5 shows the dependence of the crosstalk between the land and the groove on the peak power of the recording laser pulse when the phase compensation is optimized for the groove and the land. 2 μm on land or groove
Is a value obtained by subtracting the carrier level when a signal recorded in the land or groove is directly reproduced from the carrier level in the land or groove where no magnetic domain is recorded. The magneto-optical recording medium used had a groove depth of about 1/8 wavelength, a groove (or land) pitch of 1.4 μm, and a recording layer of SiN / T.
It has a four-layer structure of bFeCo / SiN / Al. Note that the depth of the groove of the magneto-optical recording medium is approximately (１ ／ + (１ ／) n) λ, where n is 0 or a positive integer, and λ is selected to be the wavelength of the laser. it can.

The optical information recording and detecting apparatus of the present invention used for reproduction is equipped with a semiconductor laser having a wavelength of 680 nm and an objective lens having a numerical aperture of 0.55. The recording method is a pulse assist magnetic field modulation method, and the recording mark length is 2.0 μm.
In any case, the crosstalk due to the signal recorded in the land portion or the groove portion is -25 dB or less at a wide recording laser power.

[0027]

As described above in detail, the provision of the magneto-optical detecting optical system in which the phase compensation condition is optimized for the land and the groove allows the signal of the adjacent groove or the signal of the land to be obtained. Crosstalk deviates from optimal phase compensation conditions, thereby reducing signal amplitude. By this action, the use of the optical information detection device of the present invention can reduce crosstalk from a land or a groove. By reproducing a read laser spot almost equally over the land and the groove, the land and the groove can be reproduced simultaneously. This is a very important technology in high-density recording and reproduction.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a positional relationship between a reading laser spot, a land, and a groove of the optical information recording / detecting device of the present invention.

FIG. 2 is a schematic diagram showing a positional relationship between a laser spot on a magneto-optical recording medium and a laser spot on a photodetector.

FIG. 3 is a diagram illustrating a phase relationship between push-pull signals generated by + 1st-order light, 0th-order light, and −1st-order light.

FIG. 4 is a schematic plan view of the optical information recording / detecting device of the present invention.

FIG. 5 is a diagram showing recording laser power dependence of crosstalk when the optical information recording / detection device of the present invention is used.

[Explanation of symbols]

 Reference Signs List 1 groove 2 land 3 magnetic domain 4 laser spot 5 substrate 6 objective lens 7 +1 order light 8 0 order light 9 -1 order light 10, 11, 12 photodiode 13 +1 order light 14 0 order light 15 -1 order light 16 laser Diode 17 Collimator lens 18 Diffraction grating 19 Beam splitter 20 Objective lens 21 Magneto-optical recording medium 22 Half mirror 23 Half-wave plate 24 Polarizing beam splitter 25 Convergent lens 26 Photodiode 27 Convergent lens 28 Photodiode 29 Differential amplifier 30 Half-wave plate 31 Polarizing beam splitter 32 Converging lens 33 Photodiode 34 Converging lens 35 Photodiode 36 Differential amplifier

Claims (8)

[Claims] 1. An optically transparent substrate having a concentric or spiral optical groove depth of approximately (1/8 + (1/2) n) λ, where n is 0 or a positive integer, and λ is a laser. In a device for reading information recorded on a magneto-optical recording medium in which a groove having a wavelength of and a land is formed and the widths of the groove and the land are substantially equal, a first laser spot applied to the magneto-optical recording medium is An optical information recording / detecting device, comprising: means for irradiating each of the adjacent grooves and lands approximately semicircularly. 2. The apparatus according to claim 1, further comprising: means for irradiating at least two or more laser spots in addition to the first laser spot. 2. The optical information recording detection according to claim 1, wherein one laser spot is arranged at an interval of an odd multiple of a quarter of a period of a groove or a land in a radial direction of the magneto-optical recording medium. apparatus. 3. The optical information recording and detecting device according to claim 2, wherein the first laser spot and the at least two or more laser spots are generated by a diffraction grating. 4. The method according to claim 1, wherein the first laser spot is used for recording information on the groove and the land, and the polarity of a push-pull signal, which is a tracking signal generated by the first laser spot, is changed by the magneto-optical recording medium. 2. The optical information recording / detecting apparatus according to claim 1, further comprising means for alternately recording information on the groove and the land by inverting the rotation every one rotation. 5. A push-pull system in which, when recording information on the groove and the land, one of the groove and the land is recorded first, and after all the recording tracks have been used up, the first laser spot is generated. 5. The optical information recording / detecting apparatus according to claim 4, further comprising means for inverting the polarity of the signal and recording the remaining groove or land. 6. A means for providing two different magneto-optical signal detecting optical systems, one for reproducing a groove and the other for reproducing a land, wherein said two magneto-optical signal detecting optical systems provide means for respectively providing different amounts of phase compensation. The optical information recording / detecting device according to claim 1, further comprising: 7. An optical information recording / detecting apparatus according to claim 6, wherein said means for providing different amounts of phase compensation is a crystalline wave plate having refractive index anisotropy. 8. The half-wave plate according to claim 1, wherein said crystalline wave plate is a half-wave plate, and said half-wave plate disposed in said two magneto-optical signal detecting optical systems is arranged in a traveling direction of a laser beam. 8. The azimuthal angle of the crystal optical axis with respect to the direction of the electric vector of the laser beam incident on each half-wave plate is different from each other.
The optical information recording and detecting device according to the above.