JPH0474783B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical reproducing device that irradiates a light beam onto an optical disk and reproduces information from changes in the reflected light.

[Technical background of the invention and its problems]

A conventional reproducing apparatus of this type is configured to reproduce recorded information by the sum of output signals of a detector that receives reflected light.

However, this device has a problem in that it is not suitable for reproducing optical discs with high-density recording because the reproduction output level in the high frequency range drops rapidly when reproducing optical discs with high-density recording.

[Purpose of the invention]

The purpose of the present invention is to reproduce information from changes in the reflected light of a light beam, and to obtain a reproduction signal from the diagonal differential output of a 4-split detector, thereby eliminating the drop in output in the short wavelength region, that is, the high frequency region. An object of the present invention is to provide an optical reproducing device suitable for reproducing an optical disc on which high-density recording has been performed.

[Summary of the invention]

In order to achieve the above object, the present invention is characterized by the following configuration. That is, in the present invention, a four-part detector in which the area for receiving the reflected light beam is divided into four parts in a cross shape is installed in the far field with the direction of the dividing line tilted at 45 degrees with respect to the direction of relative movement between the optical disk and the light beam. , after obtaining the sum of the output signals of the detection elements located at diagonal positions of this 4-split detector, the difference between these sum signals is obtained by a differential amplifier, and the change in the difference signal output from the differential amplifier is obtained. It is characterized in that the recorded information is reproduced by

[Embodiments of the invention]

FIG. 1 is a diagram showing an embodiment of the present invention. In Fig. 1, numeral 1 is a four-part detector, and the dividing line is the optical disc (not shown) and the light beam (not shown).
It is installed in the far field at an angle of 45 degrees with respect to the direction of relative movement with respect to the track direction indicated by the arrow. The respective sum signals of the detection elements 1a, 1c and 1b, 1d located at diagonal positions of the four-division detector 1 are supplied to a differential amplifier 2. Thus, the difference between the two sum signals is obtained from the differential amplifier 2,
This is sent out from the output terminal 3 as a reproduction information signal.

This device configured as described above has the following effects. Pit 1 is shown in Figure 2 a-d.
1 shows the state in which the beam spot 12 scans the beam spot 12.
Figure 2a shows a state where the beam spot 12 is on the left end of the pit 11, b shows a state where the beam spot 12 is in the center of the pit 11, c shows a state where the beam spot 12 is on the right end of the pit 11, and d indicates a state in which the beam spot 12 is not placed on the pit. When the beam spot 12 hits the pit 11, the light intensity distribution on the detector 1 is affected by diffraction due to the edge of the pit 11.

FIGS. 3a to 3d show the light amount distribution on the detector 1 corresponding to FIGS. 2a to d. Figure 3 a, b, c,
When a light amount distribution as shown in d occurs, an output signal having a waveform as shown in S2 is obtained from the differential amplifier 2 shown in FIG. , , is shown in Figure 3a
The area corresponding to ~d is shown. In addition, Figure 4 S
1 is an information signal based on the sum output obtained by conventional means regarding the light intensity distribution on the detector 1.

Figure 5 shows pit 2 when the pit density increases.
1 and beam spot 22 are shown. Figure 5A
5B shows a state in which the beam spot 22 completely includes the pit 21, and FIG. 5B shows a state in which the beam spot 22 is located between two adjacent pits 21.

6A and 6B show the light amount distribution states on the detector 1 corresponding to FIGS. 5A and 5B, respectively.

FIG. 7 X to Z are waveform diagrams showing changes in the output signal when the density of the pits gradually increases,
Sx1, Sy1, and Sz1 show changes in the sum output signal by conventional means, and Sx2, Sy2, and Sz2 show changes in the differential output signal in the present device. As is clear from FIG. 7A, B, and C, the signal level of the sum output decreases rapidly as the recording pit density increases, but the signal level of the differential output that detects changes in the diffraction pattern decreases. It doesn't drop that much.

FIG. 8 shows changes in the sum output signal M and the differential output signal N with respect to pit spacing (density). However, the amplification degree of each output is not the same. As is clear from Fig. 8, even at pit spacings of 1 μm or less, where the signal level of the sum output drops rapidly, there is almost no drop in the signal level of the differential output, and the cutoff frequency extends to short pit spacings. . That is, the means for obtaining diagonal differential output signals according to the present invention makes it possible to reproduce high-density recorded optical discs, which was impossible with the conventional means using sum output signals.

〔Effect of the invention〕

According to the present invention, a four-segment detector whose area for receiving reflected light beams is divided into four parts in a cross shape is installed in the far field with the direction of the dividing line inclined at 45 degrees with respect to the direction of relative movement between the optical disk and the light beam. , after obtaining the sum of the output signals of the detection elements located at diagonal positions of this 4-split detector, the difference between these sum signals is obtained by a differential amplifier, and the change in the difference signal output from this differential amplifier is Since the information is reproduced by the above-mentioned method, there is little drop in the level of the reproduced output signal in the high frequency range, and it is possible to provide an optical reproducing apparatus suitable for reproducing optical discs recorded at high density.

[Brief explanation of the drawing]

1 to 8 are diagrams showing one embodiment of the present invention, FIG. 1 is a block diagram showing the configuration, and FIGS.
d~Figure 4 is a diagram for explaining the basic operation,
FIGS. 5 to 8 are diagrams for explaining the reproducing operation when high-density recording is performed. 1... 4-division detector, 2... Differential amplifier,
3... Output terminal, 11, 21... Pitt, 12,
22...Beam spot.

Claims (1)

[Claims] 1. In an optical reproducing device that irradiates a light beam onto an optical disk and reproduces information from changes in the reflected light, the area that receives the reflected light beam is divided into four sections in a cross shape, and the direction of the dividing line is aligned with the optical disk. A four-part detector is arranged in the far field at an angle of 45 degrees with respect to the direction of relative movement with the light beam, and
It comprises means for obtaining the sum of the output signals of the detection elements located at diagonal positions of the divided detector, and a differential amplifier for obtaining the difference between the respective sum signals obtained by this means, and the output signal is output from the differential amplifier. An optical reproducing device characterized in that information recorded on an optical disc is reproduced by changing a difference signal.