JPS63244336A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To improve the S/N of signal detection by making a beam splitter into a shape, which leads a ghost light in a direction intersecting approximately orthogonally with the arranging direction of plural photodetectors arranged nearly in a straight line. CONSTITUTION:A flux of light emitted from a semiconductor laser 1 is made into a parallel flux of light by a collimator lens 2 and is divided into three beams by a diffraction grating 3. The divided light beams are transmitted through a beam splitter 4 and converged on a disk 6 by an objective lens 5 and three beam spots are formed. The light beams reflected on the disk 6 pass through the objective lens 5 again and by being reflected by the beam splitter 4, they are separated from the incident beam. Here, in order to prevent the ghost light from being incident to the photodetectors 91-93, a face 41 opposing to the face facing toward the photodetector among the six faces constituting the beam splitter 4 is inclined so as to let the ghost light go in the direction intersecting approximately orthogonally the arranging direction of the photodetectors 91-93 and the S/N of the signal detection can be improved.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention has a semiconductor laser as a light source, and records and reproduces information by irradiating an information recording medium with a light beam from the semiconductor laser as a minute spot. The present invention relates to an optical recording/reproducing device that performs either or both of the following.

[Conventional technology]

A device that performs optical recording and/or reproduction uses an optical system to narrow down the light beam of a light source to a small size.
By irradiating the information recording medium and modulating the intensity of the light beam with a recording signal, the optical properties of the recording medium are changed and information is recorded. In addition, a light beam whose intensity is weaker than that during recording is narrowed down to a finely focused light beam, similar to that during recording, and irradiated onto the medium, optical changes in the medium are detected, and information is reproduced. This optical recording and reproducing device has many features such as being able to increase the density of information, but when recording and reproducing information, it is necessary to always focus and irradiate the information recording medium with a very small light beam. , focus control to keep the distance between the information recording medium and the optical system constant, and tracking control to follow the locus of recorded information are required. Generally, in an optical recording and reproducing device, in order to obtain an information signal when information is reproduced using a reflective disk, and to obtain a control signal when performing the above-mentioned focus control and tracking control. , it is necessary to extract the reflected light from the information recording medium.

A beam splitter is generally used to take out the reflected light from the information recording medium, and this beam splitter is inserted into the optical path from the light source to the recording medium to efficiently transmit the light from the light source to the recording medium and record the information. Information signals and control signals are detected by efficiently separating the light reflected by the medium from the optical path.

However, this conventional optical recording/reproducing apparatus using a beam splitter has the disadvantage that stray light, particularly ghost light, is generated at the beam splitter, which significantly reduces the S/N ratio of information signals and control signals.

In order to solve this drawback, for example, JP-A-59-15
No. 2549 (optical pickup) has been proposed. In this method, of the six surfaces that make up the beam splitter, the surface facing the photodetector is replaced with a surface that does not reflect the light beam from the light source toward the photodetector, i.e., the surface facing the photodetector. This method uses a surface that is inclined with respect to the direction to prevent the generation of ghost light. However, when the beam splitter used in this method uses multiple photodetectors arranged approximately in a straight line, it is not always possible to prevent the generation of ghost light because it is affected by the distribution shape of the reflected beam flux. However, there was a drawback that the S/N ratio of signal detection was lowered.

First, the astigmatism method is used for focus control, and the 3-way method is used for tracking control.
A conventional optical recording and reproducing apparatus using the beam system will be explained with reference to FIGS. 8 to 11. In FIG. 8, a light beam emitted from a semiconductor laser 1 is made into a parallel light beam by a collimator lens 2, and is divided into three beams by a diffraction grating 3. The divided light beams pass through a beam splitter 4 and are focused onto a disk 6 by an objective lens 5 to form three beam spots. The light beam reflected by the disk 6 passes through the objective lens 5 again, is reflected by the beam splitter 4, and is separated from the incident beam. This reflected beam then passes through the condensing lens 7.
, the light is focused by the cylindrical lens 8 and sent to the photodetector 9□,
It enters into 9□, 93. This photodetector 91°9°, 93
are arranged to receive light from three beam spots formed on the disk 6, respectively.

The light-receiving surface of the photodetector 9° is divided into four parts as shown in FIG. The astigmatism introduced is detected, and a focus control signal is obtained based on the principle of the known astigmatism method. Further, when reproducing information, a reproduction signal is obtained from this photodetector 92. Furthermore, the detection signals of the photodetectors 91+93 are differentiated to obtain a tracking control signal based on the principle of the well-known 3-beam system.

Here, in order to prevent ghost light from entering the photodetectors 91, 9□, 93, of the six surfaces forming the beam splitter 4, the surface 41 facing the direction of the photodetector is
Photodetectors 91, 9 when tilted in a direction substantially parallel to the arrangement direction of photodetectors 98, 9°, 93 so as to allow ghost light to escape
10 and 11 show the state of the reflected beam on the angles 93 and 93.

FIG. 10 shows a case where the surface 41 of the beam splitter is slightly tilted to allow ghost light to escape into the space between the photodetectors 91, 9□, and 93. In this case, there is a high possibility that ghost light will leak into the photodetectors 90, 9°, and 93, resulting in a poor S/N ratio of the signal. It is also possible to greatly tilt the beam splitter surface 41 to largely remove the ghost light from the photodetectors 93, 9°, 93, but if the tilt angle is too large (then it will be further reflected by the lens barrel wall etc. in the optical path). Photodetector 91,9°.

93 and may cause ghost light to occur. In order to prevent this, it is possible to secure a sufficiently large space in the optical path, but the optical head becomes thick (and the weight increases).

It goes without saying that the above-mentioned problems also occur when two photodetectors are used, such as in the well-known wedge prism method (focus control).

[Summary of the invention]

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned conventional devices, and to improve the S/N
An object of the present invention is to provide an optical recording/reproducing device capable of detecting signals with a high ratio.

The above-mentioned object of the present invention is to irradiate an information recording medium with a light beam from a semiconductor laser as a minute spot, and receive the reflected light from the information recording medium with a plurality of photodetectors arranged approximately in a straight line. In an optical recording and reproducing apparatus that performs recording and reproducing or only reproducing, a beam splitter is provided in an optical path from a light source to an information recording medium, and has a surface that separates reflected light from the information recording medium from the optical path, and the beam splitter This is achieved by shaping the ghost light caused by the separation surface in a direction substantially perpendicular to the direction in which the plurality of photodetectors are arranged.

〔Example〕

FIGS. 1 and 2 show an optical recording and reproducing apparatus of the present invention, which uses an astigmatism method for focus control and a three-beam method for tracking control. In FIG. 1, a beam emitted from a semiconductor laser 1 is made into a parallel beam by a collimator lens 2, and is divided into three beams by a diffraction grating 3. The split light beam passes through the beam splitter 4,
The light is focused onto the disk 6 by the objective lens 5 to form three beam spots. The light beam reflected on the disk 6 passes through the objective lens 5 again, is reflected by the beam splitter 4, and is separated from the incident beam.

This reflected beam is then condensed by a condensing lens 7 and a cylindrical lens 8 to a photodetector 91+'92+9.
3. The photodetectors 91, 9□, and 93 are arranged to receive light from three beam splitters formed on the disk 6, respectively.

The light-receiving surface of the photodetector 9□ is divided into four parts as shown in FIG. The astigmatism introduced is detected, and a focus control signal is obtained based on the principle of the known astigmatism method. Further, when reproducing information, a reproduction signal is obtained from this photodetector 9□. In addition, the photodetector 9. ．． The tracking control signal is obtained by subtracting the 93 detection signals and using the principle of the well-known 3-beam system.

Here, in order to prevent ghost light from entering the photodetectors 91+ 92+ 93, among the large surfaces constituting the beam splitter 4, a surface 4I opposite to the surface facing the photodetector is
The photodetector 9□ is tilted in a direction substantially perpendicular to the arrangement direction of the photodetectors 91, 9□, and 93 so as to allow ghost light to escape.
, 9□, and FIG. 3 shows the state of the reflected beams on 93. As is clear from the figure, by slightly tilting the surface 4□ of the beam splitter, the ghost light photodetector 9□ can be easily detected.

9° and 93 can be prevented and the S/N ratio of signal detection can be improved.

In the example of FIG. 1, the light beam emitted from the semiconductor laser 1 is divided into three beams by the diffraction grating, but a semiconductor laser l' having three light emitting points as shown in FIG. 4 may also be used. In this case, the number of parts is reduced.

FIGS. 5(A) and 5(B) show another embodiment of the present invention.

As in Japanese Patent Application Laid-Open No. 59-146449, the beam reflected by the beam splitter 4 is split into two by a prism 10, and the beam is divided into two by photodetectors 94, 9. It is designed to lead to.

As shown in the figure, by slightly tilting the surface 41 of the beam splitter, the ghost light generated in the beam splitter 4 can be easily transmitted to the photodetectors 94.9. It becomes possible to escape in a direction different from the arrangement direction of the .

The present invention is not limited to the above-described embodiments and can be applied in various ways. For example, as shown in Fig. 6, a beam splitter reflects the light beam emitted from a semiconductor laser and guides it onto the disk.As shown in Fig. 7, a beam splitter prevents ghost light from entering the detection means. In particular, a magneto-optical disk drive has a polarization characteristic that increases the Kerr rotation angle, which tends to generate ghost light (signal Although the present invention is effective because the components are minute, the same effect can be obtained even when applied to other optical recording and reproducing devices such as optical card recording and reproducing devices, digital audio disc devices, video disc devices, etc. It will be done.

〔Effect of the invention〕

As explained above, the present invention provides a conventional optical recording/reproducing device in which a beam splitter guides (shapes) ghost light in a direction substantially perpendicular to the arrangement direction of a plurality of photodetectors arranged substantially linearly. This has the effect of improving the S/N ratio of signal detection.

[Brief explanation of the drawing]

1 and 2 are diagrams for explaining an embodiment of the optical recording/reproducing device of the present invention, and FIG. 3 is a diagram for explaining the relationship between the photodetector and ghost light in the device shown in FIG. 4 to 7 are diagrams showing other embodiments of the optical recording and reproducing apparatus of the present invention, and FIGS. 8 to 11 are diagrams explaining a conventional optical recording and reproducing apparatus. 1・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・ Semiconductor laser 2・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・Collimator lens 3・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・Diffraction grating 4・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・Beam splitter 5・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・Objective lens 6・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・Disc 7・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・Condensing lens 8・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・Cylindrical lens 91.9□+9
3 +"4 +"5 ...... Photodetector (A
)(β)

Claims (1)

[Claims] (1) A light beam from a semiconductor laser is irradiated onto an information recording medium in the form of a minute spot, and the reflected light from the information recording medium is received by a plurality of photodetectors arranged approximately in a straight line to record or reproduce information. In an optical recording and reproducing device that performs only reproduction, a beam splitter is provided in an optical path from a light source to an information recording medium, and the beam splitter has a surface that separates reflected light from the information recording medium from the optical path, and the beam splitter is connected to the separating surface. An optical recording/reproducing device characterized in that the optical recording/reproducing device has a shape that guides ghost light caused by the above-mentioned light in a direction substantially perpendicular to the direction in which the plurality of photodetectors are arranged.