JPS61936A - Optical reading device - Google Patents

Abstract

PURPOSE:To make focus control of high accuracy and to obtain a small-sized optical information reading device of good S/N ratio by feeding back proper quantity of light to a semiconductor laser and obtaining out-of-focus signals of good linearity. CONSTITUTION:A ray of light alpha irradiated on a part A shown by a broken line of a beam splitter 3 consisting of three rectangular prism from a semiconductor laser 1 returns to the laser 1, and the laser becomes multiple mode and reduces noise. A ray of light irradiated on a part B shown by solid line is light of P polarization, and made to circular polarized light by 1/4 wavelength wave 6, and irradiated on a disk 5. Light reflected by the disk 5 is made to S polarized light by 1/4 wavelength wave, and enters the beam splitter 3. At this time, reflected luminous flux that passes a half face that makes a plane made by the optical axis and track direction as a boundary and reflected luminous flux that passed another half face enter convergent lenses 7, 7' in the reverse direction to each other. Bisected photoelectric elements 9, 9' having parallel division lines are arranged in the track direction, and so adjusted that outputs of photoelectric elements become equal when in focus. Error output of photo-electric elements 9, 9' become very high in linearity.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical information reading device that reads information recorded on a VD, CD, etc. using a light beam, or an optical information reading device that reads information recorded on a VD, CD, etc. using a light beam. The present invention relates to an optical information writing device for writing information on, etc.

[Prior art]

When a semiconductor laser is used as the light source of the above-mentioned optical reading device, the B/N of the reproduced signal may be affected due to the generation of laser noise.
The ratio decreased, causing reading errors. Particularly, in the reproduction of analog recorded video signals, the image quality deteriorates. For this reason, conventional methods for reducing noise in semiconductor lasers have been proposed, such as using a half-mirror gold side to feed back the amount of returned light, and superimposing a high-frequency current on the semiconductor laser drive current. . However, in the former method, 50 cm of the incident light amount is lost due to the half mirror, so the light utilization efficiency is poor.
Therefore, it is not suitable for writing on magneto-optical disks, DRAV, etc., and is only applied to optical information reading devices for reproduction only. Furthermore, since different types of media have different reflectances, the amount of feedback light changes, making it impossible to create a car that can be used as is. In addition, the latter method requires the addition of a circuit to superimpose the high frequency current, and has the disadvantage that the high frequency tends to jump to other servo circuits, disturbing the servo signal and causing adverse effects. .

Furthermore, conventionally, methods such as an astigmatism method, a critical angle method, and an asymmetric method have been proposed for detecting defocus.

The astigmatism method uses an optical element that causes astigmatism in the light reflected from the disk to obtain a defocus signal 'jIc, but it has drawbacks such as a long optical path and a narrow focus detection range. was there.

The critical angle method is characterized by obtaining an unfocused T'L signal by identifying angular changes in reflected light using a critical angle prism, but the setting of the critical angle prism is delicate, and the sensitivity There were disadvantages such as low

The asymmetric method is characterized by placing a knife in the reflected optical path and using one knife to block a part of the beam to obtain a defocus signal. The S/N ratio of the - issue becomes low, and in addition,
The error detection curve for disk displacement near the in-focus state tends to be nonlinear, and highly accurate focus control is impossible.

Next, a conventional example of an asymmetric method using a half mirror for performing laser beam noise reduction, focus control, and tracking control will be described.

FIG. 1 is a diagram showing an example of a conventional optical information reading device in which an asymmetric detection method is used as a defocus detection method.

The light lf'' emitted from the semiconductor laser 1 is collimated by the collimator lens 2, passes through the half mirror 8, and the objective lens 4, and is converged onto the disk 5. It is reflected by the bit-shaped information track, passes through the objective lens 4, enters the half mirror 8, and is reflected in a direction perpendicular to the incident light flux.This reflected light blocks approximately half of the light flux. The reflected light beam is totally converged through a blinding plate 6 and a converging lens 7.The 4-split light receiving element 8 is focused on a non-imaging point B that is an appropriate distance away from the imaging point A in the focused state. In this state, the four-split light receiving element 8 is arranged so that the output of each light receiving element is the same.
The state of the luminous flux on the divided light receiving elements is shown. (α) The figure shows the in-focus state. ψ) The figure shows the state in which the disk 5 approaches. (C) shows a state in which the disk 5 is far away. Therefore, (8
A defocus signal can be obtained from cL+8d)-(8b+8c). However, in the conventional asymmetric method described above, although the focus detection range can be widened, half of the luminous flux is sacrificed due to the knife lens 7.
We introduced a large amount of light loss and a decrease in the RF multiplier signal B/N ratio. As shown in FIG. 8, the error output becomes non-linear with respect to the amount of n from the in-focus position, depending on whether the disk approaches or moves away. For this reason, it has been impossible to perform highly accurate focus control. Furthermore, since not all of the light beam incident on the objective lens is used, there is a drawback that, similar to using a lens with a small aperture, small digital bits cannot be read accurately due to diffraction phenomena. . or,
The disadvantage of the Naifetsuji 7 was that it was difficult to adjust.

The track deviation signal is detected as a change in the direction of the first-order diffracted light caused by a row of uneven pits on the track of the disk 5. Conventionally, as shown in Figs. 1 and 2, a knife 7 is arranged in a plane perpendicular to the plane formed by the tracking servo direction and the optical axis so that the light beam is divided into 1 part, and divided into 4 parts. The dividing line of the light-receiving element needs to be precisely aligned with the track direction and the tracking servo direction. A track deviation signal of (8α+8b)-(8c+8d) can be obtained, but as mentioned above, it is very difficult to adjust the knife 7 and the 4-division light receiving element 8.

Further, in order to reduce the noise of the semiconductor laser, a half mirror 8 is used to feed back the light to the semiconductor laser by about 5 to 10 inches of the total amount of light. However, half of the light quantity is lost in the half mirror 8, and furthermore, the light quantity is vignetted in the collimator lens 2 and the objective lens 4. It's already about 20%. For this reason, even if it is used for a playback-only optical pickup, it is not possible to return light with the half mirror 8 to a pickup for DRAW or for writing, such as an optical pickup for optical destruction. Ta. Furthermore, since the reflectance differs between different types of media, the amount of light returned to the semiconductor laser changes, necessitating readjustment.

[Purpose of the invention]

The purpose of the present invention is to eliminate these drawbacks, make the optical system extremely compact, and perform highly accurate focus control.
Furthermore, the present invention provides an optical information reading device for writing and reading in which the El/N ratio of the reproduced waveform is sufficiently good.

[Structure of the invention]

The optical information reading device of the present invention converges light emitted from a semiconductor laser to obtain a focal point when reading optical information from a track recorded on a disk or when recording information on a disk. In the control, the reflected light beam reflected by the disk and condensed by the objective lens is divided into two light beams with equal light intensity through a quarter-wave plate, with the plane where the optical axis and the track are separated as the boundary, three or three right-angle prisms are used. The beam splitter consists of 4 pieces, and on each beam 1h, there is a converging lens and at least 2 divided light receiving elements each having a dividing line in a direction parallel to the track direction. One is placed at the same distance from the image point, and one is placed on the side closer to the disk.
The other is disposed on the side far from the disk, and has a first difference component obtained by subtracting the output of the light receiving element that does not include the optical axis from the output of the light receiving element that does not include the optical axis, of one of the two split light receiving elements, and
The focal point (If"n signal is obtained from the sum signal of the second difference component obtained by subtracting the output of the light receiving element including the optical axis from the output of the other light receiving element not including the optical axis of the divided light receiving elements, and It is characterized in that a tracking deviation signal is obtained from the difference component of both of the above-mentioned light-receiving elements.The above-mentioned beam splitter also functions as a polarizing beam splitter for an appropriate amount of light near the optical axis emitted from the semiconductor laser. For the remaining light from the optical axis of the light emitted from the semiconductor laser, it acts as a half mirror or a total reflection mirror to return the light to the semiconductor laser via a collimator lens. characterized by things.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 4 is a diagram showing a beam splitter consisting of eight right angle prisms. In the broken line A section, a total reflection film or a semi-transparent film is deposited. In the solid line B section, a dielectric multilayer film is deposited, and 100% of the P-polarized light is transmitted and 100% of the 8-polarized light is reflected. Hereinafter, it is assumed that a total reflection film is applied to a portion A of the dotted line. The ratio of the solid line A section to the broken line B section is set so that the total amount of light from the semiconductor laser is about 8:2.

In FIG. 5, the light emitted from the semiconductor laser 1 is
The collimator lens 2 makes the parallel light 2t1 incident on the Heems blitter 8. This beam splitter 3 has the structure shown in FIG. The light ray .alpha. irradiated onto a portion A of the broken line in FIG. This return scene represents the peak of the total amount of light emitted by the semiconductor laser, resulting in a single
Semiconductor lasers with longitudinal mode oscillation can be made into multiple modes to reduce noise. On the other hand, the light rays irradiated onto the solid line B in FIG.
% transmitted, circularly polarized light with a quarter wavelength wave 6 is irradiated onto the disk 5 through the objective lens 4. The amount of light irradiated onto the disk is 80% of the total amount of light emitted from the semiconductor laser.

The light reflected by the disk 5 passes through the objective lens 4 and
Due to the action of /4 wavelength wave 6, it becomes S-polarized light, and beams 7
” is incident on the IJ footer. At this time, due to the action of the beam splitter 80, the reflected light beam that has passed through one half of the plane bordered by the plane formed by the optical axis and the track direction, and the reflected light flux that has passed through the other half are different from each other. In the opposite direction, it is divided into directions orthogonal to the incident light beam and enters the n1 converging lenses 7' and 71, respectively.If the focal lengths of both converging lenses are made approximately equal, the imaging points A and AI are as follows. The two come to a point equidistant from the beam splitter.The re-imaging point A is approximately equidistant away from Al, and the non-imaging point B, which is further away from the beam splitter.
.

, the other is a two-part light receiving element 9. having a dividing line parallel to the track direction at a non-imaging point BI near the beam splitter.
The two-split light-receiving elements 9"
Adjust g+.

Figure 6 shows the reflected light flux on the same optical axis, 1/4
FIG. 6 is a diagram showing a wavelength plate 6, a beam splitter 8t--omitted optical path diagram, and a beam state on each light receiving element 9, 91.

The figure (α) shows the state in focus, the figure (b) shows the state in which the disc 5 is approaching, and the figure (C) shows the state in which the disc 5 is far away. In reality, the half-light beams passing through the upper and lower parts of the lens are reflected by the beam splitter 8 into left and right parts as shown in FIG. 5, so that they do not affect each other. Now, at the time of focusing, the outputs of each light receiving element α, b, c, dld- are all the same, as shown in figure (α).

When the disk approaches, the state of the light receiving element 9 is the same as the state (C) when the disk is far away in FIG. 2, and the state of the light receiving element 91 is the same as the state (b) when the disk approaches in FIG. become. On the other hand, when the disc moves away,
The state of the light receiving element 9 is the same as the state ψ when the disk approaches in FIG.
The state is the same as the state (C) in which the disc is far away in the figure. Therefore, a defocus signal can be obtained from C9a 9h) (9'd-9'c).

That is, when the disc is in focus, it becomes 0, when the disc is close, it becomes negative, and when the disc is far away, it becomes positive. Furthermore, as for the output characteristics of each of the light-receiving elements 9 and 91, the error output is non-conforming with respect to the amount of disc as shown in FIG. As shown in FIG. 7, by selecting this method, an error output with extremely good linearity can be obtained with respect to the amount of disk.

The tracking deviation signal is (9α+
9b) It can be obtained from (9' 6+91 d). This is because the first-order diffracted light generated by the track is
This is because the light is deflected in a direction perpendicular to the track direction due to the track deviation rLVc, and therefore enters the light receiving elements 9 and 91 with different intensities. In addition, the RF signal is the sum of the outputs of each light receiving element,
That is, it can be obtained from (9α+96)+(9'c+9'd).

Incidentally, the converging lens 7.71 used in the above embodiment is as follows.

, the focal length may be different. Alternatively, as shown in FIG. 8, it may be formed integrally with the beam splitter.

In addition, the beam splitter 8 used in the above embodiment returns an appropriate amount of light to the semiconductor laser 1 to reduce laser noise during reproduction, and furthermore, uses the plane defined by the track direction and the optical axis as a boundary. Any structure may be used as long as it divides the luminous flux into two luminous fluxes with equal light intensity. For example, as shown in Fig. 9, the reflected light beam is divided into directions perpendicular to each other, and a mirror is attached to the input 9, or a total reflection film is deposited, and a portion of the incident light beam is returned to the entire semiconductor laser. You can let me.

〔Effect of the invention〕

As described above, according to the present invention, an appropriate amount of light is returned to the semiconductor laser, and the deterioration of the 8/N ratio of the reproduced signal due to the noise of the semiconductor laser is reduced. There is no need to readjust the amount of light, and the remaining light amount can be used effectively for 4-way recording, etc. In addition, the reflected light beam is divided into two light beams with equal light intensity using a plane including the track direction and the optical axis as a boundary, and two light beams are separated from each other by the same distance from the respective imaging points.
Since a focus shift signal with extremely good linearity can be obtained from complementary signals from the two two-split light receiving elements, highly accurate focus control can be performed.

Moreover, by widening the focus detection range, there is no loss of light quantity, and the S/N ratio of the RF multiplied signal during reproduction can be greatly improved. Furthermore, the optical system is small and simple.

[Brief explanation of the drawing]

Figure t81 A late diagram of the conventional asymmetric defocus detection method Figure 2 Optical path diagram and beam state diagram on the 4-split light receiving element in the conventional asymmetric defocus detection method (b) When in focus <b) When the disk approaches Figure 3: A diagram showing the relationship between the amount of defocus and the amount of error in the conventional asymmetric defocus detection method. Figure 4: A diagram of the beam splitter according to the present invention.
Diagram of the optical system according to the present invention, Figure 6. Optical path diagram in the defocus detection method according to the present invention and beam state diagram of the two-split light receiving element.1 (a) When in focus (b) When the disk approaches (Sometimes when the cl disk was far away, it was 1.7M) A diagram showing the relationship between the amount of defocus and the amount of error in the defocus detection method according to the present invention?i%8 diagram The beam splitter and converging lens according to the present invention FIG. 9 is a three-dimensional diagram showing an example of integration. Three-dimensional diagram 1 is a three-dimensional diagram showing an example of dividing a light beam into two in mutually healing directions and returning a part of the incident light to the semiconductor laser according to the present invention. 1: Semiconductor laser 2 : Collimator lens 3: Beam splitter 4: Objective lens 5: Disk 6: 1/4 wavelength plate 7: Converging lens 8: 4-split light-receiving element 9, 9': 2-split light-receiving element or more Applicant: Seiko 1JI Co., Ltd. Agent Co., Ltd. Patent Attorney/Iji Senior Affairs Figure 3 Figure 4 Figure 5

Claims (4)

[Claims] (1) In a device that optically detects information recorded on a disk in a non-contact manner, or in a device that aims to optically record information on a disk, a semiconductor laser is placed between the semiconductor laser and the disk. On the optical path, there is at least a collimator lens, a beam splitter, a quarter wavelength plate, and an objective lens, and between the light receiving element and the disk, from the disk,
On the optical path, there is at least an objective lens, a quarter-wave plate, a beam that divides the reflected light beam into two light beams with equal light intensity using the plane defined by the optical axis and the track as a boundary, and further returns a part of the incident light to the semiconductor laser. A splitter, and on each optical axis, a converging lens, and a light receiving element divided into at least two parts, each having a dividing line in a direction parallel to the track direction, separated by the same distance from the image forming point, one on the side closer to the disk. An optical reading device characterized in that the other is placed on the side far from the disk. (2) The defocus signal is transmitted from one of the two split light receiving elements.
A first difference component obtained by subtracting the output of the light receiving element that does not include the optical axis from the output of the light receiving element that includes the optical axis, and the output of the other of the two split light receiving elements that does not include the optical axis. The optical reading device according to claim 1, wherein the optical reading device can obtain a sum signal of a second difference component obtained by subtracting the output of the light receiving element including the axis. (3) The tracking deviation signal is obtained from the difference components of both of the light receiving elements.
1) The optical reading device described in item 1). (4) The beam splitter is made up of three or four right-angle prisms, and acts as a polarizing beam splitter for a suitable amount of light near the optical axis of the light emitted from the semiconductor laser. Claim (1) characterized in that the remaining light away from the optical axis of the emitted light acts as a half mirror or a total reflection mirror and returns the light to the semiconductor laser via a collimator lens. Optical reader as described.