JPH04328329A - Optical information recording/reproducing device - Google Patents

Abstract

PURPOSE:To reproduce a signal even if a recording pit is small and to set a reproduction error to be small even if the pit is sufficiently large by delaying the detection signal of reflected light in a preceding light spot between two optical spots. CONSTITUTION:Out of laser beams from a semiconductor laser 1, the light flux of P-polarized light which does not pass through a phase filter 8 converges a first light spot on an optical axis, and the light flux of S-polarized light which passes through the phase filter 8 converges second and third spots. Then, an information storage carrier 14 is irradiated with light flux. The reflected light of second and third light flux is detected in a photodetector 18 and a differential amplifier 20 detects differential output and reproduces the output signal. At that time, the detection signal of the photodetector 18 detecting the reflected light of the preceding optical spot is delayed for prescribed time by a delay circuit 19 and it is inputted to the differential amplifier 20. Thus, the width of a dark line existing between the two spots can be set to almost zero.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording/reproducing apparatus for recording or reproducing information using optical means.

0002

[Prior Art] Information storage carriers for recording or reproducing information using optical means include those for reproduction only, write-once types using thin metal films or dye-based recording materials, and magneto-optical recording media. There are also rewritable types that use a phase transition recording method. Furthermore, the forms of these information storage carriers include disk-like, card-like, and the like. Methods for recording information on these information storage carriers include pit position recording, which gives meaning to the position of the center of a pit, and pit edge recording, which gives meaning to the position of the edge of a pit.

FIG. 2 explains both of these methods, and FIG. 2(a) shows a pit row in pit position recording. The size of the pit is approximately constant among nearby pits. In addition, FIG. 5(b) is a detection signal obtained by optically reproducing the pit row of FIG. 2(a). On the other hand, FIG. 2(c) shows a pit string in pit edge recording, and FIG. 2(d) shows a detection signal obtained by optically reproducing the pit string. In order to know the edge position of the pit from this signal, for example, by setting an electrical slice level as shown in the figure (d) and finding the position where the detection signal crosses the slice level, as shown in the figure (e), An edge detection signal like this can be obtained.

[0004] When information is recorded using optical means, if the sensitivity of the pits of the information storage carrier to the heat generated by the light spot is gentle, the size of the pits will vary. However, the position of the center of the pit does not change. Conventionally, pit positions are often recorded on information storage carriers using optical means. On the other hand, if the sensitivity of writing the pits on the information storage carrier to the heat generated by the light spot is steep, the variation in pit size can be kept below a certain amount.
Pit edge recording becomes possible and storage density can be increased. Currently, information storage carriers are being developed, and there is a transition from pit position recording to pit edge recording. In the conventional example above, it was assumed that if the sensitivity of the information storage carrier was improved, it would be possible to shift to pit-edge recording, but the size of the minimum pit would be equal to or smaller than the size of the optical spot. As the transmission characteristics of the optical head etc. deteriorate, fluctuations occur in the DC component of the signal detected by optical means.
Detecting edges at a constant slice level has the disadvantage that edge shifts occur.

[0005] As mentioned above, in order to increase the density of information recording, it is necessary to miniaturize the size of the spot light and to devise a photodetection system, and many studies have been made in this regard. For example, for miniaturization of the spot light size, 1
As reported in ``High-density recording of magneto-optical disks using super-resolution'' on page 901 of Volume 3 of the 36th Spring 989 Japan Applied Physics Association Lecture Proceedings, A method has been described in which an optical filtering technique called super-resolution is used in an optical optical system to narrow the projected light spot in the information track direction, thereby improving the resolution of readout. Regarding the improvement of the photodetection system, Japanese Patent Application Laid-open No. 187442/1983 discloses a method in which a photoelectric conversion sensor is provided that is divided in the direction of the information track in the reflected light beam from the information pit, and edge detection is performed from the differential output. It has been stated.

However, even in the above-mentioned super-resolution technology, the light intensity distribution is improved from a Gaussian distribution to a special spot shape with a narrow distribution in one direction, but with this alone, the size of the single spot light still increases. There is a limit to the reproduction resolution. That is, to describe this point specifically, even if the above-mentioned super-resolution technique is used, the size of the spot light can only be reduced by about 20%. Also, the aforementioned Unexamined Patent Publication No. 63-1
Even if the technique described in 87442 was used, the problem of low edge detection ability was not solved.

[0007] Therefore, the inventor of the present application previously filed an application for an optical head that solved these problems as Japanese Patent Application No. 2-279711. The optical head records and/or reproduces information using optical means on an information storage carrier having a plurality of tracks. Make a spot and
Second and third optical spots are created on both sides of the spot in a direction parallel to the tracks of the information storage carrier, the first spot is used to record information and detect the control signal of the optical head, and the second and third optical spots are The light reflected from the information storage carrier with respect to the third light spot is detected by a photodetector, and the boundaries of pits written on the information storage carrier are detected by differential detection. According to this optical head, it is possible to optically detect the edge of a pit better, and the position of the edge can be detected accurately.

In the above optical head, the second and third light spots are formed by providing a filter in the parallel light flux such that the phase of half of the light flux is shifted from the phase of the other half of the light flux, and the second and third light spots are formed. The light spot is formed when the filter is not present. The situation is shown in Figure 3. First, when no filter is inserted, the amplitude and light intensity of the light spot are well known, as shown in the figure (
a) and (b). On the other hand, when a 0-π filter as shown in the same figure (e) is inserted into the parallel light beam, the amplitude and light intensity of the light spot at that time are as shown in the same figure (c) and (d).
become that way. (Refer to Wave Optics, 1st printing, p. 285, by Hiroshi Kubota, published by Iwanami Shoten, 1971) In other words, the light spot has two peaks, and there is a very sharp dark line between the two light spots. Here, it is assumed that the light beams in (a) and (b) in the same figure and the light beams in (c) and (d) in the same figure do not interfere,
If the light spots are formed using an objective lens after being superimposed by some means, it is possible to form a light spot having three peaks on the optical axis and on both sides thereof, as shown in FIG.

Next, detection of pit boundaries using the second and third light spots will be described with reference to FIG. 4. Now, the aforementioned second light spot is in a position preceding the third light spot, and the light reflected by the second light spot is detected by the photodetector 18-2, and the light reflected by the third light spot is detected by the photodetector 18-2. is detected by the photodetector 18-1. 4(a), (b), and (c) show the intensity distribution on the two-split photodetector 18 when the second and third light spots move from an area of high reflectance to an area of low reflectance. It is roughly shown. In the same figure (a), when both spots are in the area of high reflectance, the photodetector 18-1
, 18-2, there is a large intensity distribution symmetrical about the Y axis. On the other hand, in the same figure (c), both spots are in the low reflectance area, and the photodetectors 18-1 and 18-
2, there is a small intensity distribution symmetrical about the Y axis. In the case of both (a) and (c) in the same figure, the photodetector 18-1
, 18-2, the intensity detected individually is the same, so
When differentially detected by a differential amplifier (not shown), the reproduced signal is 0. However, as in the case of the same figure (b), the second
When the third spot enters the region of low reflectance and the third spot is still in the region of high reflectance, there will be a large intensity distribution on photodetector 18-1, and there will be a large intensity distribution on photodetector 18-2. This results in a small intensity distribution. If this is detected differentially, a positive value signal will be obtained. That is, when moving from a region of high reflectance to a region of low reflectance, a positive peak signal is obtained as a reproduced signal at the boundary.

[0010] Figures (d), (e), and (f) conversely show how both spots move from an area of low reflectance to an area of high reflectance. In the figure (d), both spots are in the low area, and in the figure (f), the spots are in the high area, and the reproduced signal is 0 as in the figures (c) and (a), respectively. However, when the second spot enters the region of high reflectance and the third spot remains in the region of low reflectance, as in the case of FIG. This results in a small intensity distribution, and a large intensity distribution appears on the photodetector 18-2. If this is detected differentially, a negative value signal will be obtained. That is, when moving from a region of low reflectance to a region of high reflectance, a negative peak signal is obtained as a reproduced signal at the boundary.

FIG. 5 shows the reproduced signal (edge detection signal) obtained as described above. FIG. 5A shows a pit row based on the pit edge recording method. If the black checked area is a region with low reflectance, the reproduced signal will be as shown in the same figure (b).
) edge detection signal is obtained. By detecting the positions of positive and negative peaks from this signal, the position of the edge can be known.

0012

However, in the conventional example described above, the intensity distribution of the second and third light spots is as shown in FIG. 3(d), with a sharp dark line between the two light spots. exist. The width of the dark line is about 1/2 of the diameter of the first light spot. Therefore, the distance between the peaks of the second and third light spots is approximately 1/1/2 of the first spot diameter.
2 or more, and it was difficult to reproduce pit edges that were less than that distance. Furthermore, even if the size of the pit is sufficiently large, there is a problem in that reproduction errors become large if the distance between the peaks of two light spots is large.

The present invention has been made to solve these problems, and its purpose is to enable reproduction of pits even if they are smaller than the distance between the peaks of two light spots, and to reproduce them sufficiently. It is an object of the present invention to provide an optical information recording/reproducing device that can reduce reproduction errors even for edges of large pits.

[0014]

[Means for Solving the Problems] Such an object of the present invention is to irradiate an information track of an optical information recording medium with a first light spot for information recording and servo control;
A second and third light spot for information reproduction is irradiated before and after the light spot, the reflected light of the second and third light spots is detected by a photodetector, and the output of each of the photodetectors is In an optical information recording and reproducing apparatus that detects edges of pits recorded on the recording medium by differentially detecting signals, the optical spot whichever precedes the second and third optical spots; This is achieved by an optical information recording/reproducing device characterized by delaying a detection signal of a photodetector for detecting reflected light by a predetermined period of time.

[0015]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an optical information recording/reproducing apparatus of the present invention.

In FIG. 1, reference numeral 1 denotes a semiconductor laser used as a light source for recording and reproduction. The diverging light emitted from this semiconductor laser 1 passes through a collimator lens 2 and a beam shaping prism 3, and becomes a parallel light beam having an approximately circular shape. This parallel light beam is linearly polarized light (P-polarized light) whose polarization direction is parallel to the plane of the paper. 4 is Faraday cell, 5
is an electromagnet for applying an external magnetic field to the Faraday cell. When an external magnetic field is applied to the Faraday cell 4, the polarization direction of the linearly polarized light is rotated, and a polarized light component (S-polarized light component) perpendicular to the plane of the paper is generated. By changing the external magnetic field, the ratio of the P-polarized light component and the S-polarized light component can be changed. When there is no external magnetic field, the P-polarized light is transmitted as it is. 6 is a polarizing beam splitter, which is approximately 1 for P polarized light.
00% transmission, 0% reflection, almost 1 for S polarized light
00% reflection, 0% transmission. That is, the P-polarized light component is transmitted as is, and the S-polarized light component is reflected and separated. The separated S-polarized light component first passes through the quarter-wave plate 7 and becomes circularly polarized light. Then, it passes through the phase filter 8, is reflected by the mirror 9, passes through the phase filter 8 again, and the quarter-wave plate 7, and then passes through the P
It becomes polarized light. Now, assuming that the track direction of the information storage carrier 14 is direction A in the figure, the phase filter 8 creates a phase difference of π when it reciprocates between the light beam above the optical axis (shaded area) and the light beam below. It is something. Note that the information storage carrier 14 is A
It is assumed that there are a plurality of tracks parallel to the direction.

The light beam that has traveled back and forth through the quarter-wave plate 7, phase filter 8, and mirror 9 in this manner becomes P-polarized light and enters the polarization beam splitter 6. The light then passes through this beam splitter 6, passes through a quarter-wave plate 10, and becomes circularly polarized light. Next, this luminous flux is reflected by the mirror 11 and is reduced to 1/4 again.
The light returns to S-polarized light through the wave plate 10, is reflected by the polarizing beam splitter 6, and is combined with the original light beam. The P and S polarized lights that have passed through the polarization beam splitter 6 pass through a half mirror 12 and an objective lens 13 to form a light spot on an information storage carrier 14 . At this time, since the P and S polarized lights are linearly polarized lights that are orthogonal to each other, they do not interfere.

Here, since the P-polarized light beam does not pass through the phase filter 8, it forms a first light spot on the optical axis, as explained with reference to FIGS. 3(a) and 3(b). On the other hand, since the S-polarized light beam passes through the phase filter 8,
) and (d), the second and third light spots are connected around the first light spot. A sharp dark line exists between the second and third light spots. Specifically, three spots are formed on the information storage carrier 14, the first spot is centered on the optical axis, and the second and third spots sandwich the first spot in a direction parallel to the track (
A direction). Information storage carrier 14
The reflected light is again passed through the objective lens 13 and the half mirror 1.
2 and is reflected, and reaches the polarizing beam splitter 15. At this time, the P-polarized light passes through the beam splitter 15 and becomes a light beam 16, which is used to detect control signals for autofocus and autotracking of the optical head by a conventionally well-known detection method.

On the other hand, the S-polarized light is transmitted through the polarization beam splitter 15.
, and passes through the condensing lens 17 to the two-split photodetector 18
incident on . The two-split photodetector 18 is arranged such that the dividing line is perpendicular to the track direction. Here, the second light spot is located at a position earlier than the third light spot on the information storage carrier 14, and the reflected light of the second light spot is detected by the photodetector 18-2. Each reflected light is detected by a photodetector 18-1. The detection signal of the photodetector 18-2, that is, the detection signal of the reflected light of the preceding second light spot is sent to the delay circuit 19, where it is delayed for a predetermined time and then output to the differential amplifier 20. . Furthermore, a detection signal from the photodetector 18 - 1 that detects the reflected light of the third light spot is directly output to the other terminal of the differential amplifier 20 . The delay time of the delay circuit 19 is as shown in FIG. 3(d).
The settings are set so that the dark lines explained in . In this case, the maximum delay time is such that the peaks of the light spots do not overlap.

Next, the operation of this embodiment will be explained. first,
This is a recording operation. When recording information, the external magnetic field is cut off by the Faraday cell drive circuit 22 so that only P-polarized light is produced. Therefore, only the first spot described above is formed on the information storage carrier 14. The laser drive circuit 24 modulates the power of the semiconductor laser 1 in accordance with the signal 23 to be recorded, thereby modulating the intensity of the first spot, forming and recording pits on the information storage carrier 14 due to differences in reflectance. A part of the reflected light from the information storage carrier 14 is a luminous flux 1
6, and is used for detecting control signals of the optical head. Further, when reproducing information, an external magnetic field is applied to the Faraday cell 4 by the Faraday cell drive circuit 22 to generate P polarized light and S polarized light as described above. The ratio of the P polarized light component and the S polarized light component at this time is determined by the Faraday cell drive circuit 22.
It can be set arbitrarily. The effect of applying a magnetic field to the Faraday cell 4 and the polarizing beam splitter 6
, quarter wavelength plate 7, phase filter 8, mirror 9, etc., the first, second and third light spots are imaged onto the information track of the information storage carrier 14 as described above. . In this case, the P-polarized light forms a first light spot, and its reflected light becomes a light beam 16 and is guided to a control optical system (not shown), from which control signals for tracking control and focusing control are generated. Ru. On the other hand, the S-polarized light forms the second and third light spots as described above, and the reflected light passes through the condenser lens 17 and enters the two-split photodetector 18, and is preceded by the photodetector 18-2. The reflected light from the second light spot is detected by the photodetector 18-1 at the third light spot.
The reflected light of each light spot is detected. The detection signal from the photodetector 18-2 is then delayed by a delay circuit 19 for a predetermined time and then output to the differential amplifier 20.
The −1 detection signal is directly output to the differential amplifier 20. The differential amplifier 20 performs differential detection of both detection signals and generates a reproduced signal 21. In this case, since the detection signal of the reflected light of the preceding second light spot is delayed, the distance between the peaks of the second and third light spots can be reduced in appearance, and the dark line existing between the two spots can be reduced. The width of can be reduced to almost 0. Therefore, it is possible to reproduce the edges of smaller pits than in the past, and it is also possible to reduce the reproduction error even for the edges of sufficiently large pits.

The amount of delay of the delay circuit 19 is determined based on the specifications of the optical system and the rotational speed of the disk, and the value may be fixed or may be adjusted while checking the quality of the reproduced signal. Furthermore, in a device that changes the rotational speed of the disk according to the position, it is preferable to configure the device to change the amount of delay accordingly.

[0022]

[Effects of the Invention] As explained above, according to the present invention, two
Since the detection signal of the reflected light from the preceding optical spot of the two optical spots is delayed, even pits smaller than the distance between the peaks of the two optical spots can be effectively reproduced, and pits that are sufficiently large can be reproduced effectively. This has the effect of reducing reproduction errors even at the edges of pits.

[Brief explanation of drawings]

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

FIG. 2 is an explanatory diagram showing pits and their detection signals in pit position recording and pit edge recording, respectively.

FIG. 3 is a diagram for explaining the operation of connecting an optical axis of an information track and three light spots on both sides thereof in a conventional device.

FIG. 4 shows the intensity distribution when the two light spots used for reproduction out of the three light spots in FIG. 3 move from a high reflectance area to a low reflectance area of the information storage carrier, and from a low reflectance area to a high reflectance area. FIG. 3 is an explanatory diagram showing an intensity distribution when moving to a region.

5 is an explanatory diagram showing pits recorded as pit edges and their edge detection signals when information is reproduced using the two reproduction light spots in FIG. 4; FIG.

[Explanation of symbols]

1 Semiconductor laser 4 Faraday cell 5 Electromagnet 6, 15 Polarizing beam splitter 7, 10
1/4 wavelength plate 8 Phase filters 9, 11 Mirror 12 Half mirror 13 Objective lens 14 Information storage carrier 18 2-split photodetector 19 Delay circuit 20 Differential amplifier 22 Faraday cell drive circuit 24 Laser drive circuit

Claims (2)

[Claims] Claim 1: A first light spot for information recording and servo control is irradiated onto an information track of an optical information recording medium, and second and third light spots for information reproduction are emitted before and after the first light spot. A light spot is irradiated, the reflected light of the second and third light spots is detected by a photodetector, and the output signals of the respective photodetectors are differentially detected. In an optical information recording and reproducing device that detects the edge of a pit, the detection signal of a photodetector that detects the reflected light of the preceding one of the second and third light spots is transmitted for a predetermined period of time. An optical information recording/reproducing device characterized by delaying the information. 2. The optical information recording device according to claim 1, wherein the delay time is set to such an extent that the width of a dark line existing between the second and third light spots becomes approximately 0. playback device.