JP3022660B2 - Optical recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus for reproducing information recorded on an optical recording medium such as an optical disk, an optical card, etc., and more particularly to a multi-valued apparatus for improving recording density and data transfer speed. Regarding records.

[0002]

2. Description of the Related Art Conventionally, on an optical disk, one-bit information is represented by the presence or absence of one recording pit. On the other hand, multi-level recording in which multi-level information is added to one recording area has been proposed. ing. The following apparatus is an example using such multi-value recording.

[0003] First, a device for multi-valued information by changing the reflectance stepwise in a phase-change optical recording medium or the like, and secondly, multi-valued by changing the depth or width of a pit. Thirdly, there is a device which uses a multilayer film to record information in each layer and multi-values it. These are all devices that record multi-value information by changing the state of one pit in various ways.

As another example, a fourth set of information is converted into a pattern (optical interference or diffraction pattern) of a certain area having a different surface shape and recorded, and upon reproduction, light is irradiated. There is a device for obtaining a set of information by optical interference from a pattern and a diffraction pattern.

Further, as a device similar to the above-mentioned fourth device, as shown in FIG. 8, information of a fixed length (several bits) is coded and converted into intervals of two or three pits. Japanese Patent Application No. 3-141333 discloses an apparatus for recording a mark set composed of a set in the track width direction and reproducing information by optical interference and diffraction patterns obtained by irradiating a set of mark sets with laser light during reproduction. Has been proposed. Each of the above-described apparatuses is characterized in that information is recorded and reproduced by compounding information also in the track traveling direction.

[0006]

However, in the first to third apparatuses for performing multi-level recording by changing the reflectivity, depth and width of one pit, and the state of the multilayer film in the thickness direction in a stepwise manner, It is difficult to perform stepwise control to such an extent that the state can be determined, and multi-leveling of 2 to 4 values is the limit.

The fourth apparatus for recording a set of information as a pattern in a fixed area as described above can be used in a simple system that does not require a tracking servo or a focusing servo. Cannot be used in the system.

An apparatus for recording information by using a mark set in the track width direction is capable of multi-level recording at high density and capable of high-density recording. In order to do so by determining position or intensity, the pattern projected on the detector must always have a constant envelope.

Further, for that purpose, it is necessary to increase the focusing servo and the tracking servo, or to perform correction so that the detected value is changed to a true value when the envelope changes.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to stably perform multi-level recording in the track width direction, and to perform correction data from a zero-order light component of a signal light during reproduction. It is an object of the present invention to provide an optical recording / reproducing apparatus that reproduces high-density information with high accuracy by detecting the error and correcting the detected value.

[0011]

According to a first aspect of the present invention, there is provided an optical recording / reproducing apparatus comprising: a plurality of pits arranged in a width direction of a track on an optical recording medium; By changing the interval, multi-valued information is recorded, and at the time of reproducing the recorded information, the entire mark set including the pit pairs is irradiated with light to obtain reproduction information based on interference generated from the mark set and diffracted light. In the optical recording / reproducing apparatus, a detecting unit for detecting a defocus amount of the diffracted light, and the defocus amount detected by the detecting unit are compared with a predetermined reference value set in advance to obtain the reproduction information. And correction means for correcting the Further, the optical recording / reproducing apparatus according to the second aspect is characterized in that the detection of the defocus amount by the detection means is performed by detecting the beam diameter of the zero-order light of the diffracted light.

[0012]

That is, in the optical recording / reproducing apparatus according to the first aspect of the present invention, when the defocus amount of the diffracted light is detected by the detection unit, the correction unit sets the defocus amount to a predetermined value. The reproduction information is corrected by comparing it with a reference value. Further, in the optical recording / reproducing apparatus according to the second aspect, the detection of the defocus amount by the detection means is performed by detecting the beam diameter of the zero-order light of the diffracted light.

[0013]

FIG. 1 is a diagram showing a configuration of an optical recording / reproducing apparatus according to one embodiment of the present invention. As shown in FIG. 1, the light emitted from the reproducing light source 1 passes through the collimator lens 2 and the shaping prism 3, and becomes a circular or elliptical light beam having a predetermined axial ratio. Then, this light beam passes through a polarizing beam splitter (PBS) 4 and a 波長 wavelength plate 5 and is condensed by an objective lens 6 to irradiate a pit pair on an optical recording medium 12.

On the other hand, the light reflected by the optical recording medium 12 is reflected by the PBS 4 and input to the servo detector 9. Then, the actuator 13 is driven based on the servo signal from the servo detector 9, and tracking and focusing servo are performed.

A diffracted light is generated from the pit pair irradiated with light on the optical recording medium 12 according to a pit interval d shown in FIG. The diffracted light is converted into substantially parallel light by the condenser lens 7 and projected onto the detector 10. The detector 10 detects the position or intensity of the ± 1st-order light of the diffracted light and reproduces the pit interval information.

On the other hand, the diffracted light transmitted through the medium 12 is reflected by the half mirror 8 and then projected on the correction detector 11. Then, for example, a knife-edge method in which a part of the reflected light returned from the optical recording medium is blocked by placing a knife-edge light blocking plate in front of the correction detector 11, or a knife-edge method in front of the correction detector 11 The defocus amount is detected by a critical angle method or the like that changes the amount of light detected by the correction detector 11 by utilizing the fact that the incident angle varies depending on the focus state by placing the prism at an appropriate angle.

In detecting the amount of defocus, the correlation between the amount of defocus and the optical axis diameter of the diffracted light in the detector 10, and the correlation between the optical axis diameter and the detection value detected by the detector 10 The pit interval information reproduced by the detector 10 is obtained by checking the correlation of the pits beforehand and switching the table to be used in accordance with the defocus amount detected by the correction detector 11 by the correction unit 14. To make corrections. The timing of taking in the information is determined by detecting the zero-order light and detecting the peak position of the intensity of the light amount of the zero-order light. Hereinafter, the detector 1 will be described with reference to FIGS.
Signal detection from a pattern based on 0 will be described.

First, as shown in FIG.
Is a two-division photodiode (2D-P
D) 31a and 31b are adopted. The inner ends of the two-divided photodiodes 31a and 31b correspond to the first darkening portions 32a and 32b having a pit interval of 1.5 μm, and the outer ends have the second dark spots 33a and 33b in the pattern having the pit interval of 3.0 μm when focused. To be located at

Then, as shown in FIG.
Then, a, a ', b, b in the 2D-PDs 41a, 41b are synchronized with the synchronization signal from the zero-order photodetector 40.
And a current-voltage converter (hereinafter abbreviated as an IV converter) 42a, 42b converts the current into a voltage. Then, the adder 43 calculates (A + B) from the output A from the IV converter 41a and the output B from the IV converter 41b, and the subtractor 44 calculates (AB). The divider 45 obtains (AB) / (A + B) and outputs it as a detection value. The detector 10 detects a signal from a pattern through such a process.

FIG. 5 shows the correlation between the size of the light beam including the pattern projected on the detector 10 and the defocus amount. In the figure, the vertical axis indicates the major axis of the zero-order light on the element, and the horizontal axis indicates the defocus amount. Then, it indicates that the medium approaches the medium as it goes in the negative direction from the focus point (point F) on the horizontal axis, and that it moves away from the medium as it goes in the positive direction.

FIG. 6 shows that the defocus amount is constant (+5
2 shows the correlation between each pit pattern and the value detected by the detector 10 in the case of .mu.m. In the figure, the vertical axis indicates the detection value (AB) / (A + B), and the horizontal axis indicates the pit interval. In this embodiment, the results shown in the figure are tabulated. Next, FIG. 7 is a diagram illustrating a configuration of the correction unit 14 in the present embodiment. As shown in the figure, the correction unit 14 includes a defocus amount input unit 141 and (A
−B) / (A + B) input section 142, correction table section 1
43.

In such a configuration, upon receiving the defocus amount detected by the correction detector 11, the defocus amount input section 141 selects a row and inputs it to the correction table section 143. And (AB) / (A +
B) Upon receiving the detection value (A−B) / (A + B) detected by the detector 10, the input unit 142 selects a column and inputs the column to the correction table unit 143. Thus, the detected value is demodulated in the correction table section 143.
In this embodiment, when the above detection value was demodulated, it was possible to reproduce the pattern signal satisfactorily without applying servo to the condenser lens 7. The embodiment of the present invention has been described above. An improved example of the recording optical system of the embodiment will be described with reference to FIG.

As shown in the figure, the recording optical system of the present modified example has basically the same configuration as the conventional one, but has an acousto-optic system for forming a pit mark set by changing the interval in the track width direction. (AO) The configuration is such that a deflection element 20 is added. The optical recording medium 12 used in this embodiment is a Te substrate formed on a glass substrate by vacuum evaporation.
It is a thin film (2000 angstroms) medium. A pit pair having a pit diameter of 1 μm and a pit interval of 1.5 to 3.0 μm is formed on this medium by the above-described optical system.

As described in detail above, according to the optical recording / reproducing apparatus of the present invention, an interference pattern obtained by illuminating a mark set including a plurality of pits is reproduced by a table corresponding to the defocus amount. Thus, the detection accuracy can be improved with a simple optical system.

Although the embodiment of the present invention has been described above, it is needless to say that the present invention is not limited to this, but can be changed and improved. For example, in this embodiment, only the transmission type optical recording / reproducing apparatus has been described. However, if the present invention is applied to the reflection type, it is possible to reproduce the recorded information with high precision even in a situation where focusing accuracy is poor. Becomes possible.

[0026]

According to the present invention, for multi-valued information recorded as a change in the pit interval in the track width direction, the beam diameter of the diffracted light is used as correction data.
It is possible to provide an optical recording / reproducing apparatus capable of reproducing information as simple and highly accurate information.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a recording optical system of the optical recording / reproducing apparatus according to the embodiment.

FIG. 3 is a diagram for explaining an arrangement of a two-divided PD of the detector 10 in the embodiment.

FIG. 4 is a diagram illustrating a configuration of a detector 10 according to the embodiment.

FIG. 5 is a diagram showing a correlation between the amount of defocus and the size of a light beam including a pattern projected on a detector 10.

FIG. 6 is a detection value 10 when the defocus amount is fixed.
FIG. 7 is a diagram showing changes in each pit pattern in FIG.

FIG. 7 shows a correction unit 1 in the optical recording / reproducing apparatus of the present invention.
4 is a diagram showing a detailed configuration of FIG.

FIG. 8 is a diagram showing a mark set in which information of an optical recording medium is recorded.

[Explanation of Signs] 1 ... reproduction light source, 2 ... collimator lens, 3 ... shaping prism, 4 ... polarization beam splitter, 5 ... 1/4 wavelength plate, 6 ...
… Objective lens, 7… condenser lens, 8… half mirror, 9
Detector for servo, 10 Detector, 11 Detector for correction, 12 Medium, 13 Actuator, 14 Correction unit, 20 A / D polarizing element.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G11B ^7/ 00-7/013 G11B 7/09-7/10

Claims (2)

(57) [Claims] 1. A multi-valued information is recorded by changing a pit interval of a plurality of pits arranged in a track width direction on an optical recording medium, and when the recorded information is reproduced, the multi-valued information is composed of the pit pairs. In an optical recording / reproducing apparatus that irradiates the entire mark set with light and obtains reproduction information based on interference generated from the mark set and diffracted light, a detecting unit that detects a defocus amount of the diffracted light, An optical recording / reproducing apparatus, comprising: a correction unit that compares the detected defocus amount with a predetermined reference value set in advance and corrects the reproduction information. 2. The optical recording / reproducing apparatus according to claim 1, wherein the detection of the defocus amount by the detection means is performed by detecting a beam diameter of the zero-order light of the diffracted light.