JPS6220148A - Optical recording/reproducing device - Google Patents

Abstract

PURPOSE:To improve specially the S/N of an optical signal obtained from a recording medium by providing an optical system to have a beam splitter in which one end plane interposed among the light source, the recording media and the reading means is formed so as to make a special angle specified beforehand. CONSTITUTION:A beam splitter 14 is formed so that one edge surface can form the special angle specified beforehand. From a laser device 11 to a beam splitter 14, the remaining laser beam, in which the laser beam made incident in the B2 direction of an arrow will not transmit, is reflected in the B3 direction of an arrow and made incident on an edge surface 27 by an incident angle thetab which is a Brewster angle. Consequently, the laser beam, which is a P polarized light, is all transmitted as shown in the arrow B7, the reflecting light in the direction of an arrow B3 is further reflected at the edge surface 27 and the reduction of S/N of the signal read can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical recording/reproducing apparatus including a beam splitter, such as a so-called optical disk recording/reproducing apparatus for recording or reproducing or recording and reproducing.

BACKGROUND ART FIG. 3 is a sectional view illustrating the operation of a beam splitter 1 used in a prior art optical disk recording/reproducing apparatus. The laser device 2 generates P-polarized laser light. This laser light enters the beam splitter 1 as shown by arrow A1, is partially transmitted through the semi-transparent surface 3, and is irradiated onto a recording medium 4 such as a disk. On the other hand, the remaining light is reflected by the semi-transparent surface 3, travels in the direction indicated by arrow A2, and travels from the end surface 5 to the outside of the beam splitter 1.

The reflected light from the recording medium 4 is reflected in the direction indicated by the arrow A3, is reflected by the semi-transparent surface 3 of the beam splitter 1, and travels in the direction indicated by the arrow A4. information is read.

Here, of the light reflected by the semi-transparent surface 3 and traveling in the direction of arrow A2, a portion of the light is reflected by the end surface 5 as shown by arrow A5. This reflected light mixes with the light indicated by the arrow A4, reducing the signal/noise ratio (hereinafter abbreviated as S/N) of the obtained optical signal.

Conventionally, in order to prevent such a drop in S/N, an antireflection film made of a dielectric material has been formed on the end surface 5 of the beam splitter 1. Even if the antireflection film is coated in this manner, the reflection at the end face 5 cannot be completely prevented.

For example, if the light reflectance of the end face 5 is 0.5%, and write!
Assuming that the light reflectance of the medium 4 is 20%, the ratio of noise light to the reflected light from the recording medium 4 is approximately 2.5%.

FIG. 4 is a beam splitter 1a explaining another prior art.
FIG. This prior art is similar to the prior art described above, and corresponding parts are given the same reference numerals. In this prior art, the end face 5 of the beam splitter 1a is formed to form an angle θ1 with the face 6 into which the laser beam from the laser device a2 is incident. Therefore, a portion of the laser beam from the laser device 2 that is reflected by the semi-transparent surface 3 is bent B as shown by arrow A6 at the end surface 5, resulting in beam splitting.
Go outside of Ri 1a.

On the other hand, the remaining light is θ2 with respect to the incident light in the direction of arrow A2.
It is reflected at an angle of . Although this light does not directly mix with the light in the direction of arrow A4, the light in the direction of arrow A5 becomes so-called stray light. ), and a portion of the light is mixed into the light directed in the direction of arrow A4. Therefore, again, the tt medium 4
This reduces the S/N of the optical signal from the source.

Further, a technique using Brewster's angle as a beam splitter is described in Japanese Patent Publication No. 17093/1983.

However, this prior art beam splitter uses an electro-optic crystal set such that the angle of incidence of the incident ray is Brewster's angle on the front or back surface, and the thickness of the crystal is the same as that of the ray incident on the surface. Polarization direction is 9 on the back side
It is characterized by being set to rotate by 0".

Therefore, it has the following drawbacks.

(2) When the above beam splitter is applied to an optical recording/reproducing device, it is not reasonable because it involves optical power loss.

■It is not possible to arbitrarily set the transmission/reverse ratio of the beam splitter.

(2) In an optical recording/reproducing device that utilizes the magneto-optic effect, the rotation of the polarization direction of light serves as an information signal, so the beam splitter described above cannot be used in principle.

■Since electro-optic crystal is used as the beam splitter material, it is expensive.

Problems to be Solved by the Invention An object of the present invention is to provide an optical recording/reproducing device that can solve the above-mentioned problems and significantly improve the S/N of an optical signal obtained from a recording medium. It is.

Means for Solving the Problems The present invention provides a light source that generates light polarized in a predetermined manner, a recording medium on which information is recorded or reproduced by the light from the light source, and light from the recording medium. An optical system comprising: means for reading a signal; and an optical system including a beam splitter interposed between a light source, a recording medium, and the reading means, and formed so that one end surface forms a predetermined specific angle. It is a recording/playback device.

The working light source generates light that is polarized in a predetermined manner. This light is irradiated onto the recording medium via the optical system,
Record or play back information.

For example, when reading information recorded on a recording medium, reflected light from the light source enters the information signal reading means via an optical system and is read. At this time, the optical system includes a beam splitter, and one end surface of the beam splitter is formed to form a predetermined specific angle. This specific angle is an angle at which all of the light incident on the one end surface out of the light incident on the beam splitter from the light source is transmitted. Therefore, the signal/noise ratio of the optical signal input to the information signal or servo system signal reading means through the optical system including such a beam splitter 7 is significantly improved.

Embodiment FIG. 1 is a block diagram illustrating the configuration of an optical disc recording/reproducing apparatus 10 according to an embodiment of the present invention.

A laser device 11, which is a light source, generates P-polarized laser light. This laser light is converted into parallel light by the frimate lens 12, and the cross section perpendicular to the traveling direction of the laser light is converted from an elliptical shape to a substantially circular shape by a prism 13. This laser light is applied to a magneto-optic disk 16, which is a recording medium, via a beam splitter 14 and an objective lens 7:15. Here, the beam splitter 1
4 is configured to transmit and reflect, for example, 50% of the incident light from the prism 13 and the reflected light from the magneto-optic disk 16, respectively.

The magneto-optic disk 16 is basically a disk substrate 18.
and an information recording layer 17. The disk substrate 18 is made of a synthetic resin material such as glass or polycarbonate (PC), and the information recording material 117 is made of a magnetic material that is an alloy of rare earths and transition metals. This magnetic material has a characteristic such that, for example, when the temperature rises, the coercive force decreases, and when the temperature falls, the coercive force increases. In addition, the objective lens 1 of the magneto-optical disk 16
A bias magnet 19 realized by, for example, an electromagnet is arranged on the side opposite to 5. This bias magnet 19 is configured to generate lines of magnetic force along a direction perpendicular to the surface of the magneto-optic disk 16 (vertical direction in FIG. 1).

The light reflected from the magneto-optical disk 16 and transmitted through the objective lens 15 has its traveling direction changed by the beam splitter 14 and enters the beam splitter 20 . A portion of the incident light passes through the beam splitter 20 as it is, and is focused through a spot lens 21 and a cylindrical lens 22 onto a servo system signal detector 23 realized by, for example, a charge-coupled device.

On the other hand, the remaining part of the light incident on the beam splitter 20 is reflected and has its traveling direction changed, and the spot lens 20
4 and an information signal detector 26 via a birefringent prism 25 realized for example from a Glan-Thompson prism or the like.
The light is focused on.

As mentioned above, the information is read by the servo system signal detector 23 and the information signal detector 26. a Configure the reading means. In addition, here reference numbers 12-15.20-22
, 24 and 25 constitute an optical system.

FIG. fiS2 is a front view illustrating the configuration of the beam splitter 14. FIG. 2 shows a simplified configuration of the optical disk recording/reproducing apparatus 10 shown in f1tJ1.

The operation of the optical disc recording/reproducing apparatus 10 will be explained with reference to FIGS. 1 and 2. The laser device 11 generates a P-polarized laser beam whose cross section perpendicular to the traveling direction is elliptical. Here, P-polarized light refers to light that is polarized such that the vibration direction of the light is only in the direction indicated by arrow B1 in FIG. 2, for example.

At this time, the direction of arrow B1 is determined as follows. That is, as shown by arrow B2, beam splitter 1
For example, 50% of the laser beam incident on the end face 2 is reflected by the semi-transparent surface 28 in the direction shown by the arrow B3.
7, the incident angle θb becomes the so-called Brewster's angle (or polarization angle), and at this time, arrow B1 is determined as the vibration direction such that all of the reflected light traveling in the direction of arrow B3 is transmitted through the end surface 27. It will be done.

Such a laser beam passes through a collimating lens 12 and a prism 13, and is converted into parallel light whose end face perpendicular to the traveling direction is approximately circular, and is incident on a beam splitter 14. At this time, for example, 50% of the incident laser light passes through as it is and is focused onto the magneto-optic disk 16 by the objective lens 15.

The information recording/117 of the magneto-optical disk 16 is made of a magnetic material as described above, and is uniformly magnetized along the thickness direction, for example, in the direction indicated by the arrow B5. When such an information recording layer 17 is irradiated with a laser beam, the temperature of the irradiated area increases and the coercive force decreases. At this time, the magnetization direction B
5, the irradiated area is magnetized in the direction of arrow B6 by the bias magnet 19 which generates lines of magnetic force in the direction shown by arrow B6. Therefore, the magnetization direction of each portion of the information recording layer 17 can be selectively reversed in a manner corresponding to the information recorded on the information recording layer 17. In this way, information is recorded on the magneto-optic disk I6.

The operation of reading information from the magneto-optical disk 16 will be described below. As mentioned above, the magneto-optical disk 16 on which information is recorded is equipped with a laser! The P-polarized laser beam is irradiated from 11. The reflected light of the laser beam focused on a predetermined location on the magneto-optic disk 16 by the objective lens 15 follows the above-described reversal of the magnetization direction of the information recording layer 17, and the rotation state of the polarization plane of the reflected light is changed. Change. In this way, the reflected light containing different states of rotation of the plane of polarization is transmitted to the semi-transparent surface 2 of the beam splitter 14.
8 and enters the beam splitter 20.

At this time, from the laser device 11 to the beam splitter 14,
The remaining laser light that does not pass through the laser light incident in the direction of arrow B2 in FIG. 2 is reflected in the direction of arrow B3 and enters the end face 27 at an incident angle θb, which is the Brewster's angle. Therefore, all of the P-polarized laser light is transmitted as shown by arrow B7. Therefore, as pointed out in the prior art, it is possible to prevent the reflected light in the direction of arrow B3 from being further reflected at the end face 27 and reducing the S/N of the read signal. Furthermore, since the laser beam directed in the direction of arrow B7 is obtained by transmitting all of the reflected light in the direction of arrow B3, it is necessary to easily process the laser beam so that it does not become so-called stray light. I can do it.

Note that the Brewster angle θb referred to herein can be determined as in the following formula.

θb=jan'-(1)
Here, 11 is the refractive index of air, and n2 is the refractive index of the material forming the beam or pre-lifter.

For example, about 50% of the laser light incident on the beam splinter 20 is transmitted as it is, and is incident on the servo system signal detector 23 via the sporatron r21 and the cylindrical lens 22. At this time, cylindrical lens 2
2 detects servo system signals such as the so-called focus F-M and the tractor signal. The seven-occurrence error signal will be explained below. Generally, the magneto-optical disk 16 is driven to rotate, and as a result of this rotation, vertical movement (displacement in the vertical direction in FIG. 1) occurs. Corresponding to this vertical movement, the focus of the laser beam by the objective lens 15 changes, for example, on the surface 17 of the information recording layer 17 facing the objective lens 15.
It is controlled to be located at a predetermined constant distance from a. That is, regarding the optical system including the objective lens 15, a servo system is provided to track the vertical movement of the magneto-optic disk 16.

On the other hand, regardless of the tracking operation using such a servo system,
Optical system including objective lens f: 15 and magneto-optic disk 16
When the difference between the distance and the preset distance increases,
The optical image on the servo system signal detector 23 becomes an ellipse whose eccentricity gradually increases.

On the other hand, as the distance approaches a predetermined distance, the eccentricity of this ellipse gradually decreases, and the shape becomes close to a perfect circle. By detecting such an optical image with the servo system signal detector 23, an error related to the distance between the optical system including the objective lens 15 and the magneto-optic disk 16 can be detected. Servo can be performed to bring this error close to zero.

The tracking error signal will be explained below. Grooves are formed in the magneto-optic disk 16 so that so-called tracking can be performed accurately. Laser device 1
If the reflected light of the laser beam irradiated from 1 is irradiated from directly above this groove, the intensity distribution of the light imaged on the servo system signal detector 23 located at a position conjugate to the magneto-optic disk 16 will be as follows. It becomes symmetrical and no tracking error signal occurs. On the other hand, if the light is irradiated from directly above the groove to a position that is perpendicular to the direction in which the groove extends, the intensity distribution of the light imaged on the servo system signal detector 23 will be asymmetrical. By detecting the intensity distribution of the light, it is possible to detect whether an error has occurred in tracking. therefore,
The optical system including the objective lens 15 is driven by a configuration not shown in the drawings so as to reduce the generated error to zero.

In this way, it is possible to realize a servo system that performs proper focusing and tracking of laser light on the magneto-optic disk 16.

Approximately 50% of the remaining reflected light from the magneto-optic disk 16 that is incident on the beam splitter 20 is changed in its traveling direction and passes through the spot lens 24 and the birefringent prism 2.
5 and enters the information signal detector 26. As described above, the reflected laser beam from the information recording layer 17 has a different rotational state of its polarization plane depending on the magnetization mode of the information recording layer 17. For example, the birefringent prism 25 realized by a Glan-Thompson prism can convert the degree of rotation of the plane of polarization into the amount of transmitted light. Therefore, by detecting this change in light amount using the information signal detector 26, the information recorded in the information record/[17] can be read.

As described above, by forming the end face 27 of the beam splitter 14 to have the Brewster angle θb, the S/N of the servo system signal from the magneto-optic disk 16 and the information signal from the information recording layer 17 is significantly improved. Thus, it was possible to obtain an optical disk recording/reproducing device 10 which is highly improved.

*As another embodiment of the present invention, the end surface 27 of the beam splitter 14 shown in FIG. It may also be set to a value.

Furthermore, although the incident angle θb shown in the second diagram is the so-called Brewster's angle determined by the first equation, an error of, for example, about ±0.5° is allowed for this incident angle θbl: . That is, the incident angle of the P-polarized light in the direction of arrow B3 and the degree of transmission at the end face 27 change continuously, and the incident angle θb is deviated from the Brewster angle by, for example, ±0.5°. Also, the reflectance of P-polarized light at this end face 27 is about 0.2%. Therefore, this degree of error in the angle of incidence is well within the spirit of the present invention.

In each of the above embodiments, the optical disc recording/reproducing device 1
2, the present invention can be widely implemented in optical systems of various optical recording/reproducing apparatuses that include a beam splitter as a component.

Effects As described above, according to the present invention, when recording or reproducing information on a recording medium using light polarized in a predetermined manner generated from a light source, a signal such as a servo system signal or an information signal is transmitted. It is read by a reading means. Here, an optical system is interposed between the light source, the recording medium, and the reading means, and this optical system includes a beam splitter. This beam splitter was formed so that one end surface formed a predetermined specific angle. Therefore, among the light incident on the beam splitter of the optical system from the light source,
Light traveling to the one end surface can be transmitted without being reflected. Therefore, this one end surface can prevent the light from the light source from being reflected and entering the reading means. Therefore, the light can be read by the reading means. The signal/noise ratio of the signal can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an optical disc recording/reproducing device RA10 according to an embodiment of the present invention, FIG. 2 is a sectional view showing the configuration of a beam splitter 14, and FIGS. FIG. 2 is a cross-sectional view showing the beam splitter 1°1a. 10... Optical disk recording/reproducing device, 11... Laser Vcra, 14.20... Beam splitter, 15
...Objective lens, 16...Magneto-optical disk, 17
... Information recording layer, 23 ... - Servo system signal detector, 2
6... Information (g detector, 27... end face, 28...
・Semi-transparent surface agent Patent attorney Number of strokes Kei part + 1 Figure 2 Figure 3 Figure 4 Procedure amendment document September 20, 1985 vfM 1986-159275 2. Name of the invention Optical recording/reproducing device 3. Amendment Relationship with the case of the applicant Applicant Address 22-22 Nagaike-cho, Abeno-ku, Osaka Name (50
4) Sharp Corporation Representative: Saeki Asahi 4, Agent address: 1-13-38 Nishihonmachi, Nishi-ku, Osaka Shinko Sangyo Building Country Equipment EX 0525-5985 INTAPT
J International FAX GIIl&Gn (06)538-
02476, "About 0.2%" in Column 7 of Detailed Description of the Invention of the Specification Subject to Amendment, Page 16, Line F514 of Inner Specification 3 of Amendment
Correct the statement to "RO, about 02%."that's all

Claims (1)

[Scope of Claims] A light source that generates light polarized in a predetermined manner; a recording medium on which information is recorded or reproduced by the light from the light source; and means for reading optical signals from the recording medium; An optical recording/reproducing apparatus comprising: a light source, an optical system including a beam splitter interposed between a recording medium and the reading means and formed so that one end surface forms a predetermined specific angle.