JPH07141682A - Device for detecting optical information - Google Patents

Abstract

PURPOSE:To attain high resolution at the time of reproducing in high density recording by providing a belt shape shielding plate in a position orthogonally intersecting with the direction where recording information on an optical information recording medium is moved and in a quadrature position passing through a center of a luminous flux. CONSTITUTION:A light beam irradiating a recording surface 6 is received by a magneto-optical effect to be reflected. The reflected luminous flux passes through an objective lens 4, and is led to a magneto-optical signal detection optical system by a polarizing beam splitter 3. A part of the luminous flux incident on the magneto-optical signal detection optical system incorporates the central part of the luminous flux, and is shielded by the belt shape shielding plate 7 arranged on the position orthogonally intersecting with the direction where the recording information is moved. The luminous flux not shielded is made incident on the polarizing beam splitter 9 through a 1/2 wavelength plate 8 to be polarization detected, and the luminous fluxes separated to two linear polarization whose polarization surfaces are orthogonally intersected with each other are photoelectric converted by photodetectors 12, 13 respectively, and magneto-optical signals are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for recording and reproducing information on an optical information recording medium, and more particularly to an apparatus capable of detecting information recorded at high density with high quality.

[0002]

2. Description of the Related Art In order to detect information recorded at high density on an optical information recording medium, it is most common to use laser light of short wavelength. In addition, a confocal optical system or a high-resolution detection system combining an apodization and a confocal optical system has been devised.

FIG. 3 shows an optical system configuration that realizes high resolution detection by combining a prior art apodization and a confocal optical system. The divergent light emitted from the semiconductor laser 14 is converted into parallel light by the collimator lens 15 and is incident on the double-Rohm prism 16, and the wavefront is divided into two beams maintained at a certain interval. Then, the light passes through the polarization beam splitter 17, and is irradiated onto the magneto-optical disk 19 by the objective lens 18. In the beam profile of the beam spot narrowed to the diffraction limit on the recording surface, the intensity of the side lobe increases in spite of the sharp main lobe.
The light flux reflected from the recording surface passes through the objective lens 18 again and is guided to the servo signal detection system and the magneto-optical signal detection system by the polarization beam splitters 17 and 20. The servo signal system includes a converging lens 21 and a cylindrical lens 22.
The focus error signal and the track error signal are obtained by the four-division photo detector 23 via. Further, the light flux that has passed through the polarization beam splitter 20 is narrowed to a diffraction limit by the converging lens 24, and the beam waist thereof is located in the slit 25. Here, the slit 25 is an optical element for eliminating the side lobes with increased intensity in order to realize high resolution, and the converging lens 2
Polarization detection is performed by the Wollanston prism 28 via the 6 and 1/2 wavelength plates 27, photoelectrically converted by the two-division photodiode 30 via the converging lens 29, and differential detection of the magneto-optical signal is performed by the differential amplifier. .

[0004]

The prior art method of combining apodization and confocal optics requires an expensive double-Rohm prism, and
A very narrow slit is required to suppress the influence of side lobes, and its position adjustment is difficult.
Moreover, since the side lobes of the beam spot are emphasized even during recording, there is a problem that the laser power required during recording increases. Further, there is a problem that the shape of the recorded magnetic domain is likely to be distorted, which leads to an increase in jitter.

The problem to be solved by the present invention is that it does not require an expensive double Rome prism or a very narrow slit whose position is difficult to adjust, does not increase the laser power during recording, and reproduces in high density recording. An object of the present invention is to provide an optical information detection device capable of achieving high resolution in time.

[0006]

In order to solve the above-mentioned problems, the present invention has a shortest pit length of 0.5 μm or less for information recorded on an optical information recording medium and a pit length next to the shortest pit length. In an optical information detecting device for reading out information recorded by a recording modulation method having a length twice the shortest pit length, a light beam emitted from a light source is passed through a first means for narrowing it down to a diffraction limit on the optical information recording medium, Further, the light flux reflected from the optical information recording medium is guided to the photoelectric conversion element.
Optical information, characterized in that a band-shaped shielding plate is provided at a position perpendicular to the direction in which the recorded information on the optical information recording medium moves after passing through the means It is to provide a detection device.

In the optical information detecting device of the present invention, the double-Rohm prism does not exist in the irradiation optical system for irradiating the optical information recording medium. That is, the effect of apodization is not used. However, a band-shaped shield plate is arranged so that the light beam reflected from the optical information recording medium is included in the optical path guided to the photoelectric conversion element and includes the central portion of the light beam and is orthogonal to the direction in which the recorded information moves. Here, the light flux may be either divergent light or convergent light, but especially in the case of convergent light, it is important that the shielding plate does not coincide with the focal plane.

[0008]

In the optical system constructed as described above, when a beam spot narrowed to the diffraction limit is applied to the recording surface of the optical information recording medium, the element at the beam center and the element around the beam are reflected from the recording surface. After passing through the objective lens, it is converted into a new diffraction distribution. In this newly converted diffraction distribution, there is a region where the central element on the recording surface is dominant, a region where the peripheral element is dominant, and a region where both elements are dominant. Therefore, high resolution can be realized by blocking the area where the peripheral elements on the recording surface are dominant. The area is
These are two strip-shaped areas slightly apart from the center in the moving direction of the recorded information. However, an area in which both the central element and the peripheral element on the recording surface are dominant exists in the area sandwiched between the above two band-shaped areas. Since the total amount of light in this area is large, if this area is not shielded, the resolution of this area becomes dominant and high resolution cannot be achieved. Therefore, high resolution can be achieved by shielding the two band-shaped regions in which the peripheral elements on the recording surface are dominant and the region sandwiched between the two band-shaped regions.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments using the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. The light beam emitted from the semiconductor laser 1 is once converted into parallel light by the collimator lens 2, passes through the polarization beam splitter 3, and then the objective lens 4
Incident on. The beam spot narrowed to the diffraction limit by the objective lens 4 is applied to the recording surface 6 of the optical information recording medium 5. In this example, a magneto-optical recording medium was used. The beam applied to the recording surface 6 receives the magneto-optical effect and is reflected. The reflected light flux passes through the objective lens 4 again and is guided to the magneto-optical signal detection optical system by the polarization beam splitter 3. A part of the light beam incident on the magneto-optical signal detection optical system is shielded by a band-shaped shield plate 7 including the central portion of the light beam and arranged at a position orthogonal to the direction in which the recorded information moves. The light flux not blocked is 1 /
The light beams that enter the polarization beam splitter 9 through the two-wave plate 8 and are polarization-detected and separated into two linearly polarized lights whose polarization planes are orthogonal to each other are convergent lenses 10 and 1, respectively.
Photoelectric conversion is performed by the photodetectors 12 and 13 via 1, and amplified by the preamplifier. Next, differential detection is performed by a differential amplifier, and a final magneto-optical signal is obtained.

FIG. 2 shows the relationship between the luminous flux and the shield plate 7 at the insertion positions of the optical information recording medium 5 and the shield plate 7.

FIG. 4 shows a magneto-optical recording medium with a duty 50.
%, A magnetic domain having a pit length of 0.46 μm is recorded, and a change in the signal amplitude S (r) when the light flux incident on the magneto-optical signal detection system is gradually shielded in the moving direction of the recorded information by the knife edge method. The differential value-dS (r) / dr was shown. The wavelength of the irradiation light is 780 nm, the numerical aperture of the objective lens is 0.55, and the focal length is 3.9 mm. The amount of light decreases monotonically when the light flux is blocked by the knife edge,
The signal amplitude generated by a magnetic domain as short as 0.46 μm does not monotonically decrease, but the knife edge starts to increase from about −1.0 mm before the diameter position of the light beam and increases to about 1.0 mm past the diameter position. On the way, there is almost no change in signal amplitude from -0.5 mm to 0.5 mm. Furthermore, 1.
If you shield more than 0 mm, it will start to decrease. This will be described using the differential value −dS (r) / dr. In the positive area, the central element in the irradiation beam on the recording surface is dominant, and in the negative area, the peripheral area on the recording surface is dominant. A region having a value close to zero sandwiched between the negative regions is a region where elements in the central portion and the peripheral portion on the recording surface are equally present. By shielding the negative region of −dS (r) / dr, which is dominated by the peripheral portion of the recording surface, the signal amplitude generated by the 0.46 μm magnetic domain increases and the carrier level rises. Next, by blocking the area where the central portion and the peripheral portion of the recording surface are the same, the amount of light incident on the photodetector is reduced, and thus shot noise is reduced. Therefore, if the two areas described above, that is, the area where the peripheral elements on the recording surface are dominant and the central area and the peripheral elements are equally present, and the diffraction distribution after passing through the objective lens, respectively, Range from 0.0mm to -0.5mm, 0.5
The range is from mm to 1.0 mm and the range from -0.5 mm to 0.5 mm. In the optical system shown in the embodiment of the present invention, the light flux after passing through the objective lens is shielded so as to be orthogonal to the moving direction of the recorded information in the range of about -1.0 mm to 1.0 mm. If so, high resolution can be obtained and the improvement of the signal-to-noise ratio can be easily achieved.

Actually, an optical system in which a shield plate having a width of 1.5 mm is inserted using a magneto-optical recording medium in which a magnetic domain having a duty of 50% and a pit length of 0.46 μm is recorded at a linear velocity of 5.68 m / sec. When the signal-to-noise ratio was measured with a read power of 1.0 mW, the normal optical information detecting device could obtain only 32.4 dB. However, in the optical information detecting device shown in the embodiment of the present invention, the carrier level was Is about 1.6d
Bm was improved, and the noise level was improved by -4.2 dBm, and a signal-to-noise ratio of 38.2 dB was obtained. Moreover, it was 39.5 dB at a reproducing power of 1.5 mW.

FIGS. 5 and 6 show the jitter distribution when GCR8-9 modulation consisting of a combination of mark lengths of 1T to 4T is recorded and reproduced. FIG. 5 is a jitter distribution of 1T to 4T when reproduced by a conventional optical information detection device without a shield plate inserted. 2T to 4
Although the mark length of T is within the detection window width, 1T, which is easily affected by the interference between the pits, shows a jitter distribution larger than the detection window width and is not practical. However, as shown in FIG. 6, when reproduced by the optical information detecting device according to the present invention, 1T
The entire mark length from 4 to 4T is within the detection window width,
Clearly, the effect of super-resolution appears.

[0015]

The optical information detecting device of the present invention is not a super-resolution utilizing the apodization effect in which a double-rhomb prism or a shielding plate is arranged in the optical system for irradiating the optical information recording medium, and therefore, it is completely normal. The irradiation optical system of is used. Therefore, in the beam spot narrowed to the diffraction limit and irradiated on the recording surface, side lobes are not emphasized, and stable focus servo signals and track servo signals can be obtained. Further, since there is no thermal interference from the side lobes during writing, the margin for the recording laser power is wide.

Further, the optical information detecting device of the present invention is basically applicable to any of parallel light flux, convergent light and divergent light after the light flux reflected from the optical information recording medium has passed through the objective lens. That is, as described in the embodiment, a high resolution is achieved by a very simple method of arranging the band-shaped shield plate around the diameter position so as to be orthogonal to the direction in which the recording information moves for the light flux after passing through the objective lens. The image can be realized.

Further, also in the assembling adjustment, in the system utilizing the apodization and the confocal optical system, a shielding plate having a slit width of 10 μm or a pinhole of 10 μm is required, and if the confocal optical system is not used. Therefore, it is necessary to adjust the slits or pinholes on the focal plane two-dimensionally or three-dimensionally in the order of micron, and the adjustment is extremely difficult. However, in the optical information detecting device of the present invention, a sufficiently wide light beam, for example, a parallel light beam having a width of about 4 mm after being reflected from the optical information recording medium and passing through the objective lens, has a width of about 1.5 mm. Since a shielding plate is inserted and the accuracy is only a few tens of μm, the assembly and adjustment are extremely easy.

Furthermore, in the optical information detecting device of the present invention,
As shown in the embodiment, a light source with a wavelength of 780 nm and NA0.
Even if the reading beam spot by the 55 objective lens is used, if the GCR8-9 modulation is used to record the mark length, the recording capacity of 512 MB or more is realized even with a 3.5-inch magneto-optical disk when the length of 1T is 0.46 μm. it can.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical information detection device of the present invention.

FIG. 2 is a schematic diagram showing a relationship between a shielding plate, an optical information recording medium, and a light beam at a shielding position.

FIG. 3 is a block diagram showing a conventional optical information detection device.

FIG. 4 is a chart showing a change in signal amplitude using a knife edge method when recording and reproducing a 0.46 μm magnetic domain at a duty of 50%.

FIG. 5 G that combines mark lengths from 1T to 4T
In CR8-9 modulation, 1T which is the shortest pit length is 0.
6 is a chart showing a jitter distribution when recording is performed so as to have a size of 46 μm and reproduction is performed by a conventional optical information detection device.

FIG. 6 is a G that combines mark lengths from 1T to 4T.
In CR8-9 modulation, 1T which is the shortest pit length is 0.
9 is a chart showing a jitter distribution when recording is performed so as to have a size of 46 μm and reproduction is performed by the optical information detection device of the present invention.

[Explanation of symbols]

 1 Semiconductor Laser 2 Collimator Lens 3 Polarizing Beam Splitter 4 Objective Lens 5 Optical Information Recording Medium 6 Recording Surface 7 Shielding Plate 8 1/2 Wavelength Plate 9 Polarizing Beam Splitter 10 Converging Lens 11 Converging Lens 12 Photo Detector 13 Photo Detector 14 Semiconductor Laser 15 Collimator Lens 16 Double-Roam Prism 17 Polarizing Beam Splitter 18 Objective Lens 19 Magneto-Optical Recording Medium 20 Polarizing Beam Splitter 21 Converging Lens 22 Cylindrical Lens 23 4-Division Photo Detector 24 Converging Lens 25 Slit 26 Converging Lens 27 1/2 Wave Plate 28 Wollaston prism 29 Converging lens 30 Two-division photo detector

Claims (1)

[Claims] 1. The information recorded on the optical information recording medium is recorded by a recording modulation method in which the shortest pit length is 0.5 μm or less and the second longest pit length is twice the shortest pit length. In the optical information detection device for reading information, the light flux emitted from the light source is passed through the first means for narrowing the light information on the optical information recording medium to the diffraction limit, and the light flux reflected from the optical information recording medium is further photoelectrically converted. After passing through the second means which is guided to, the strip-shaped shielding plate is provided at a position orthogonal to the moving direction of the recorded information on the optical information recording medium and at a diameter position passing through the center of the light beam. A characteristic optical information detection device.