JPS60234235A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To attain the reproduction of a photomagnetic disk or a disk where the information is recorded with recesses/projections or variation of reflection factors, by rotating the polarizing direction of the reflected light separated by a half mirror by 45 deg. to obtain the separated polarization components orthogonal to each other. CONSTITUTION:When a photomagnetic disk is used to an information recording medium 5, an equal amplitude is obtained between the transmitted light and the reflected light of a polarized beam splitter 14. Thus the signal beams containing information phases are opposite to each other. Then said transmitted light and reflected light are converted into electric signals to obtain a difference between them. Thus the in-phase components are offset to each other, and the information components of phases opposite to each other are magnified double to obtain a reproduction signal having a high S/N. In the case of a disk where the information is recorded with recesses/projections or variation of reflection factors, the reflected light undergoes modulation of intensity and the information signal light made incident on the two-split and four-split detectors 15 and 18 have the same phase and an equal amplitude. Thus the highly efficient reproduction is possible by adding the output of an adder 22 of electric signals detected by the detector 15 and that of the electric signals detected by the detector 18 by an adder 24.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to read-only optical disks such as compact disks that have already been commercialized, recording/reproducing optical disks whose reflectance changes when recording is performed, and recording devices whose recording portions are evaporated. This relates to an optical recording and reproducing device that can be used for both reproducing optical discs and magneto-optical discs that allow recording, reproducing and erasing, and is suitable for both consumer and professional audio equipment, video equipment, computer memory, etc. It is applicable.

37\-1 Structure of Conventional Example and Its Problems FIG. 1 is a schematic diagram of an optical head for a magneto-optical disk that has been widely used in the past. In Fig. 1, 1 is a semiconductor laser, 2 is a collimating lens, and 3 is a half mirror 14.
is an objective lens, 6 is an information recording medium, 6 is a half mirror 1
7 is a convex lens, 8 is an analyzer, 9 is a photodetector, and 1o is a focus error.

An optical device for error signal detection detects a signal such as a tracking error, and reference numeral 11 is a split-type photodetector that detects the error signal.

The operation of this conventional example will be explained below. First, the diverging light emitted from the semiconductor laser 1 is transmitted through the collimating lens 2.
The light is converted into parallel light, passes through a half mirror 3, and is focused onto an information recording medium 5 by an objective lens 4. The reflected light from the information recording medium 5 is reflected by the half mirror 3 in the opposite path, and is further separated into two beams by the half mirror 6. One of the beams passes through the error signal detection optical device 1o, and is then used for focusing and tracking. The light enters a split-type photodetector for detecting the error signal. The other light passes through a convex lens 7 and an analyzer 8 and enters a photodetector 9, thereby making it possible to reproduce the information signal of the information recording medium 5 on which magneto-optical recording has been performed.

When a magneto-optical disk is used as an information recording medium, the reflected light is not modulated in optical intensity, but is modulated in the form of a minute rotation of the plane of polarization.

When reproducing information, the Kerr rotation angle of the magneto-optical disk is 0.
．． It is difficult to detect because it is extremely small at 4 degrees and 8 degrees.

Therefore, in the conventional method, in order to obtain a high-quality signal, the analyzer 8 is normally used in a state close to the extinction position with respect to the incident light. By doing so, although the amount of light reaching the photodetector 9 is extremely small, it is possible to reproduce a signal with good contrast.

Let us now consider the case of using a disc, such as a compact disc, in which information is recorded in a concave and convex manner, or a disc in which information is recorded in shading.

When these disks are used as the information recording medium 5 and the information is reproduced, the reflected light from the information recording medium 5 returns as reflected light that is itself modulated in light intensity. Unlike when a magneto-optical disk is used, this reflected light is hardly modulated by rotation of the plane of polarization, so most of it is absorbed by the analyzer 8 and is detected by the photodetector 9.
It becomes difficult for information light to reach.

Therefore, in the optical head shown in FIG. 1, when playing a disk other than a magneto-optical disk, the analyzer 8
This method has the drawback that it is inconvenient that it has to be removed.

OBJECTS OF THE INVENTION The present invention is intended to eliminate the drawbacks mentioned in the prior art, and it is an object of the present invention to provide an optical recording/reproducing apparatus that is compatible not only with magneto-optical disks but also with disks of other types.

Structure of the Invention The present invention comprises a semiconductor laser, a collimating lens that converts the diverging light of the semiconductor laser into parallel light, an objective lens that focuses the parallel light on an information recording medium as a minute light spot, and the objective lens. 67,-2 A half mirror located between the collimating lenses and separating the reflected light from the information recording medium, and a difference wavelength plate installed so as to rotate the polarization direction of the separated reflected light by approximately 46 degrees. a polarizing beam splitter that separates the light transmitted through the wavelength plate into two mutually orthogonal polarized components, and detects a focus error signal between the objective lens and the information recording medium in one of the two polarized components. a first split-type photodetector that receives light that has passed through the optical means that detects the focus error signal; the other of the two polarization components; an information track on the information recording medium; a second split-type photodetector arranged to detect a tracking error with the light spot; and a first addition that takes the sum of electrical signals emitted and lost in each light-receiving area of the first split-type photodetector. a second adder that sums the electrical signals generated in each light-receiving area of the second split-type photodetector; an output of the first adder; and an output of the second adder. A subtracter that takes the difference, and a third adder that takes the sum of the output of the first adder and the output of the second adder. It can also have playable functions.

DESCRIPTION OF THE EMBODIMENTS FIG. 2 is a schematic diagram of an optical recording/reproducing apparatus according to an embodiment of the present invention, and the same members as in FIG. 1 are given the same numbers. In FIG. 2, 12 is an objective lens actuator, 13 is a difference wavelength plate, 14 is a polarizing beam splinter, 16 is a two-split photodetector, 16.17 is a convex cylindrical lens, 18 is a four-split photodetector, 19, 20 .23 is a subtracter, and 21.22.24 is an adder.

The operation of one embodiment of the present invention will be described below.

First, the light emitted from the semiconductor laser 1 is converted into parallel light by the collimating lens 2, and after passing through 3, the objective lens 4 incorporated in the objective lens actuator 12 produces a parallel beam onto the information recording medium 5. The light is focused as a light spot of about 1 μm. The reflected light from the information recording medium 5 follows the opposite path, is reflected and separated by the mirror 3, and enters the difference wavelength plate 13. Semiconductor laser 1
is installed so that the polarization direction is parallel to the plane of the paper,
The difference wavelength plate 13 is set to rotate the polarization direction of the reflected light by approximately 46 degrees. The reflected light that has passed through the wavelength plate 13 is separated into two mutually orthogonal polarized components by the polarization beam splitter 14, one of which is transmitted and enters the two-split photodetector 16, and the other is reflected and passes through the convex cylindrical lens. 16 and 17, and enters the four-split photodetector 18. The two-split photodetector 15 has a dividing line 15 at its center.
2L, and the reflected light from the information recording medium 6 is irradiated onto a portion of the two-split photodetector 16 indicated by a hatched portion 15b. A tracking error signal is detected by subtracting each electrical signal generated in each divided area of the two-divided photodetector 15 from each other using a subtracter 20. This tracking error detection method is a method called a far field method or a push-pull method.

On the other hand, the light reflected by the polarizing beam splitter 14 passes through convex cylindrical lenses 16 and 17, which are optical means for detecting focus errors, and enters the 4-split light 9Peno detector 18. The 4-split photodetector 18 has dividing lines 18a, 18b as shown in FIG. . Of the four electric signals generated in each divided area of the four-divided photodetector 18, the sum of the two electric signals generated in the opposing divided areas is calculated as, respectively, and the subtracter 1
9, the focus error signal is detected by taking the difference between the electrical signals obtained by taking the above-mentioned sums.

This method is a focus error detection method called the astigmatism method, but it goes without saying that other detection methods may be used.

Next, a case will be described in which a magneto-optical disk is used as the information recording medium 5 and information recorded on the disk is reproduced. As mentioned above, in FIG. 2, the wave plate 13 is used to adjust the amount of light transmitted through the polarizing beam splitter 14 and the amount of reflected light to be approximately equal. When reproducing information recorded on a magneto-optical disk, the transmitted light and the reflected light of the polarizing beam splitter 14 have approximately the same amplitude;
The signal light contains information with phases opposite to each other by 10·-7. Therefore, by converting the transmitted light and reflected light into electrical signals and taking the difference between them, the in-phase components are canceled out, and the information components in the opposite phase are doubled, making it possible to obtain a reproduced signal with a good S/N ratio. It is possible. This method is often used as a reproduction method for magneto-optical disks, and is called a differential detection method. In FIG. 2, the two-split photodetector 15
The electrical signals detected by the four-part photodetector 18 are added by the adder 22, the electrical signals detected by the 4-split photodetector 18 are added by the force calculator 21, and the difference between each is calculated by using the subtracter 23. By implementing the above-mentioned differential detection method, it is possible to obtain reproduction signals from the magneto-optical disk.

Next, a case will be described in which a disc such as a compact disc on which information is recorded on uneven surfaces or a disc on which information is recorded as a change in reflectance is used as the information recording medium 6 and the information is reproduced. When reproducing information, the light emitted by the semiconductor laser 1 is kept substantially uniform, and the reflected light is modulated in light intensity by the signal recorded on the information recording medium 6. Therefore, 2
The information signal lights incident on the split photodetector 15 and the 4-split photodetector 18 are in phase and have approximately the same amplitude. Therefore, the output of the adder 22 which adds the electrical signals detected by the two-split photodetector 16 and the output of the four-split photodetector 1
By adding the electrical signals detected in step 8 and the output of adder 21 in adder 24, it is possible to efficiently reproduce the information signal.

Effects of the Invention As described above, the present invention can be applied to magneto-optical disks,
It is possible to obtain an optical recording and reproducing apparatus that can reproduce discs such as compact discs on which information is recorded in a concave and convex manner, discs on which information is recorded by changes in reflectance, and the like.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a conventional optical head for magneto-optical TiSF.
FIG. 2 is a block diagram of an optical recording/reproducing apparatus according to an embodiment of the present invention. 1... Semiconductor laser, 2... Collimating lens, 3 - Half mirror 14... Objective lens, 5... Information recording medium, 6... No--
Fmirror, 7... Convex lens, 8... Analyzer,
9... Photodetector, 10... Optical device for error signal detection, 11... Divided photodetector, 12...
Objective lens actuator, 13... Difference wavelength plate, 14 - Polarization beam splinter, 16... Two-split photodetector, 16.17... Convex cylindrical lens, 18...・4-split photodetector, 19.20.2
3.--Subtractor, 21, 22.24... Adder. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2

Claims (1)

[Claims] a semiconductor laser, a collimating lens that converts the diverging light from the semiconductor laser into parallel light, an objective lens that focuses the parallel light on an information recording medium as a minute light spot, and between the objective lens and the collimating lens. and separates the reflected light from the information recording medium. The polarization direction of the separated reflected light is approximately 45 degrees
A wavelength plate installed to rotate, a polarizing beam splitter that separates the light transmitted through the A wavelength plate into two mutually orthogonal polarization components, and one of the two polarization components, the objective lens and the information. an optical means for detecting a focus error signal between recording media; a first split-type photodetector for receiving light that has passed through the optical means for detecting the focus error signal; and the other of the two polarized light components; A second split-type photodetector arranged to detect a tracking error between an information track on an information recording medium and the minute light spot, and an electric signal generated in each light-receiving area of the first split-type photodetector. A first adder that takes the sum of the electric signals generated in each light receiving area of the second split type photodetector, and a second adder that takes the sum of the electric signals generated in each light receiving area of the second split type photodetector.
an adder, a subtracter that takes the difference between the output of the first adder and the output of the second adder, and the sum of the output of the first adder and the output of the second adder. An optical recording/reproducing device characterized by comprising a third adder that takes .