JPH0490137A - Optical system for optical information recording/ reproducing device - Google Patents

Abstract

PURPOSE:To attain stable APC control and AT (auto-tracking) control by a simple constitution by extracting a part of beams directed to a recording medium, detecting the extracted beams by a photodetector and obtaining a control signal. CONSTITUTION:Beams 21 radiated from a semiconductor laser are reflected by a galvanomirror 1 and turned to reflected beams 22 directed to the recording medium. A part of the incident beams 21 is transmitted through a transmitting aperture 4 formed on the mirror 1 as beams 24 directed to a spatial pattern 25 and the outputs 11, 12 of sensors 5, 6 are sent to a sum signal computing part 7 and a difference signal computing part 8. Since a sum signal 13 is changed when the light quantity of the incident beams 21 is changed, the sum signal 13 can be used as a stable APC signal. On the other hand, a difference signal 14 is sensitively changed in accordance with the rotation of the mirror 1, so that the rotational angle of the mirror 1 can be detected. Thus, the offset of an AT control signal due to the rotation of the galvanomirror 1 is removed by the simple constitution.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention records information by focusing light on an optical or magneto-optical recording medium such as an optical disk through an objective lens. The present invention relates to an optical system of an optical information recording/reproducing device that reproduces information using reflected light from a ray.

(Prior Art) Conventional optical information recording and reproducing devices employ, for example, an optical system as described below in order to record and reproduce information optically or magneto-optically. That is, as shown in FIG. 4, to explain this in the XYZ three-axis coordinate system, a diverging light beam 171 from the semiconductor laser 101 first becomes a parallel light beam 172 by the collimator lens 102, and is propagated in the positive direction of the X axis. . A part of the light beam is reflected by the polarizing beam splitter 103, becomes a light beam 173 directed in the negative direction of two axes, and reaches the APC sensor 104. The sensor 104 detects the amount of light emitted from the semiconductor laser 101 by detecting the amount of light beam 103.
If the amount of light emitted varies from the desired amount due to changes in ambient temperature, for example, the APC control circuit (not shown)
is used to control the amount of light emitted from the semiconductor laser 101 to a desired value.

On the other hand, the light beam 174 transmitted through the beam splitter 103
The traveling direction of the light beam is sequentially changed by a galvanometer mirror 105 and a mirror 106, and an image is formed as a light spot on the recording surface of a recording medium 109 such as a magneto-optical disk by an objective lens 107. The mirror 106 and objective lens 1
07 is unitized as a movable optical system 108 (the part surrounded by the broken line), and is arranged in the radial direction of the recording medium 1090 (arrow 1
51), forming a so-called separation optical system and enabling high-speed access operations.

The light beam 175 reflected from the recording medium 109 travels the optical path in the opposite direction, and passes through the beam splitter 103.
A part of the light beam is reflected as a light beam 176 heading in the positive direction of the two axes and directed toward the 1/2 wavelength plate 110 . In this case, the diverging light beam 171 from the semiconductor laser 101 is
Although it is linearly polarized light that vibrates within the Z plane, the 1/2 wavelength plate 110 is set so that the polarization direction of the transmitted light beam 177 forms an angle of approximately 45'' with respect to the XY plane. After the light beam 177 passes through the sensor lens system 111 consisting of a spherical lens and a cylindrical lens, it is sent to the light receiving section 113 by the polarizing beam splitter 112. ．． 113
．． ．． 113. and 1134, which are polarized and separated into a light beam 178 directed toward the sensor 113 and a light beam 179 directed toward the sensor 114.

In addition, in the conventional example listed here, autofocus control (
The AF control (hereinafter referred to as AF control) is performed using the astigmatism method. That is, the sum of the outputs from the light receiving sections 1131 and 1133, and 1
From the differential signal of the sum of outputs from 132 and 1134, A
An F control circuit (not shown) drives the objective lens 107 in the Y-axis direction.

On the other hand, auto-tracking control (hereinafter referred to as AT control) is performed using a push-pull method. That is, the light receiving section 113.
Based on the differential signal between the sum of the outputs from 113 and 113
It is rotated around a rotating shaft 115 that forms an angle of 45 degrees with the shaft (arrow 152). As a result, the light spot is directed on the recording medium 109 in its radial direction (arrow 153
).

In this way, in the separating optical system, by arranging the galvano mirror 105 on the fixed optical system side, the weight of the movable optical system can be reduced, which is extremely advantageous from the viewpoint of high-speed access.

Note that the magneto-optical signal is reproduced by the light receiving section 113. of the sensor 113. A differential signal between the sum of the outputs of 1134 to 1134 and the output from the sensor 114 is used.

(Problems to be Solved by the Invention) However, when performing APC control using the output of the sensor 104 as in the conventional example described above, there is a risk that an unstable element may be added to the control. That is, in order to perform accurate APC control, it is necessary to
Although the ratio of the light intensity to the light beam 174 directed toward the beam splitter 103 needs to be constant, the transmittance, reflectance, and absorption rate of the film of the beam splitter 103 change over time or are affected by the ambient temperature and humidity. Therefore, the above-mentioned light amount ratio changes because the light intensity ratio may vary, albeit slightly.

If APC control is performed in such an unfavorable state, the semiconductor laser 101 may exceed a predetermined value when recording information.
may emit light, which may shorten its lifespan.
Furthermore, there is a risk that the recorded information on the recording medium 109 will be destroyed when the information is reproduced. Alternatively, when recording information, if the semiconductor laser 101 emits light below a predetermined value, the recording medium 1
09 may not be able to secure the energy level necessary for recording, and sufficient C/N may not be obtained during subsequent playback, and the amount of light reaching the sensors 113 and 114 during information playback may be small. Similarly, there is a possibility that a sufficient C/N ratio cannot be obtained.

Further, when the galvanometer mirror 105 is rotated, the following problem occurs. That is, when the galvanomirror 105 is rotated in the direction of arrow 152 for AT sub-control, the light flux on the sensor 113 is accordingly displaced in the X direction, causing an offset in the signal for AT control.

Therefore, by limiting the rotation angle of the galvanometer mirror 105 to a minute angle, the quality of the reproduced signal is not substantially degraded. It is necessary to precisely control the movement of the light beam in the direction. It has also been considered to correct the AT control signal obtained from the sensor 113 by detecting the rotation angle of the galvanometer mirror 105 and knowing the amount of offset generated from the output thereof. FIG. 5 shows an example of means for detecting the rotation angle of the galvanometer mirror 105. Here, the galvanometer mirror 105 is rotated about a rotating shaft 152. Therefore, the incident light beam 174 is deflected from one state 181 to another state 182. The rotation angle detection means is a galvanometer mirror.
The light beam from the LED 121 is reflected on the back surface of the galvano mirror 105, and the traveling direction of the reflected light changes as the galvano mirror 105 rotates. Therefore, the two light receiving sections 1221 and 12
If a sensor 122 having a diameter of 2□ is placed in the optical path of the reflected light and attention is paid to the difference 123 between the respective outputs from the light receiving sections, the value of the difference 123 changes almost linearly with the rotation of the galvanometer mirror 105. . In this way, by providing the rotation angle detection means, it is possible to correct the offset amount to the AT control output, but a dedicated means for detecting this rotation angle must be prepared. Therefore, it is inevitable that the device as a whole becomes more complex, larger, and more expensive.

(Objective of the Invention) The present invention has been made based on the above circumstances, and aims to provide an optical system for an optical information recording/reproducing device that can realize stable APC control and A-child control with a relatively simple configuration. It is something.

Still another object of the present invention is to provide an optical system for an optical information recording/reproducing apparatus that can realize stable AT sub-control and stable APC control.

(Means for Solving the Problems) Therefore, in the present invention, when converging light onto an optical recording medium via an objective lens in order to optically or magneto-optically record or reproduce information, polarized light is emitted from a light source. Focuses the light onto the recording surface of the recording medium via a beam splitter and an objective lens,
Further, an optical system is configured to project the reflected light from the recording surface onto a photodetector via the objective lens and a polarizing beam splitter, and the polarized beam is projected based on the detection result of the photodetector. In an optical system of an optical information recording/reproducing device in which a galvano mirror provided between a splitter and an objective lens is rotationally controlled for auto-tracking control, the galvano mirror is provided with a predetermined direction perpendicular to its rotation axis. Provide a transmission aperture at a distance,
The light flux transmitted from the light source side through the aperture is received by a plurality of sensors, the rotation angle of the galvanomirror is set by the difference signal of the output of these sensors, and the light intensity of the light source is detected by the sum signal. I have to.

(Function) Therefore, since the light transmitted through the transmission aperture is a part of the light directed from the polarizing beam splitter to the recording medium, by measuring the amount of light from this, the film of the polarizing beam splitter can be measured. It is possible to obtain stable and accurate values without being affected by changes in transmittance, reflectance, or absorption over time or by ambient temperature or humidity. Furthermore, when the galvano mirror is tilted, the position of the transmission aperture is shifted, and a difference signal between the outputs of the sensor is obtained. You can make corrections for this.

(Example) An example of the present invention will be specifically described below with reference to FIG. Here, the explanation will be based on a three-axis coordinate system of XoY, Z, and axes. The galvanometer mirror 1 is controlled to rotate around a rotating shaft 2 (means for rotation are not shown)
. The luminous flux 2] from the semiconductor laser is X. A reflected light beam 2 travels in the negative direction of the axis, is reflected by the mirror surface 3 of the galvano mirror J, and heads toward the objective lens in the positive direction of the Ya axis.
It becomes 2. A rectangular transmission aperture 4 is formed in the region 23 used for reflection of the galvanometer mirror 1 at a required distance in a direction perpendicular to its rotation axis, and the incident light 2]
A part of the transmitted light passes through the transmission aperture 4 and becomes the light beam 24 of the aerial pattern 25. It is projected as if The photoelectrically converted outputs J] and 12 of each sensor are sent to a sum signal calculation unit 7 and a difference signal calculation unit 8, which generate a sum signal and a difference signal, respectively.

In such a configuration, when the galvanometer mirror 1 rotates around the rotation axis 2 for AT sub-control (about 30 minutes), the opposite light beam 22 is in a plane approximately parallel to the Y and Zo planes, It has an angle to the Y0 axis. On the other hand, since the galvano mirror 1 is made of a flat glass plate with a finite thickness, the refraction effect of the galvano mirror 1 works, and the transmitted light beam 24
has a component that shifts in the zo-axis direction. In other words, the aerial pattern 25 changes as the galvano mirror 1 rotates.
It has a component that moves in the Z0 axis direction on the two sensors 5.6. Therefore, the area of each sensor 5.6 is the aerial pattern 25
If the area is sufficiently larger than the area of
The sum signal 13 hardly changes. That is, the sum signal 13 changes when the light intensity of the incident light beam 21 changes, and can be used as a stable APC signal.On the other hand, the difference signal 14 becomes sensitive as the galvanometer mirror 1 rotates. Since it changes, it can be used as a signal for detecting the rotation angle of the galvanometer mirror 1.

FIG. 2 shows another embodiment of the invention, in which the mirror surface of the galvanometer mirror 1 has two transmitting mirrors located symmetrically and at equal distances in the direction orthogonal to its axis of rotation 2. Apertures 4.9 are formed - the transmitted light beams 24.26 from each transmission aperture 4.9 form an aerial pattern 25
．． 27, each portion of this aerial pattern is detected by a sensor 5.
It is designed to receive light at 6. And, as mentioned above,
APC from sum signal 13 of output 11 and 12 from each sensor
The rotation angle is detected from the difference signal 14 for control.

Note that if the intensity distribution of the incident light beam 21 is not uniform but has a Gaussian distribution, the sum signal 1 in the embodiment shown in FIG.
3, the influence of the intensity distribution in the 2° axis direction inside the aerial pattern 25 appears, but the embodiment of FIG. 2 is preferable because this influence is canceled out.

FIG. 3 shows the entire optical system using the galvanometer mirror 1 shown in FIG. 1, and here, the same parts shown in FIG. 4 are given the same reference numerals and their explanation will be omitted.

A light beam 21 from the semiconductor laser 101 is reflected by a galvanometer mirror 1 having a rotation axis 2, and becomes a light beam 22 directed toward an objective lens 107. Mirror surface 3 of galvano mirror 1
is provided with an aperture 4, through which a portion of the incident light beam 2I is transmitted to the sensor 5.6.

The sensor 5 detects the aerial pattern 25 of the transmitted light beam 24.
Output from each sensor 5.6 in area projected onto 6 11
．． 12 sum signal 13 and difference signal 14 are determined. and,
The area of the aerial pattern changes as the galvanometer mirror 1 rotates in the direction of arrow +52 about the rotation axis 2 for AT sub-control. In this way, the APC
Control and rotation valley detection of the galvanometer mirror 11 is performed.

(Effects of the Invention) The present invention has been described in detail above, and since a part of the light beam directed from the polarizing beam splitter to the recording medium is extracted and detected by a photodetector to obtain an APC control signal, the amount of light can be detected. Be accurate. In addition, without the need for a dedicated light source,
With a simple configuration, the rotation angle of the galvano mirror can be detected, the offset of the AT control signal caused by the rotation of the galvano mirror can be removed, and miniaturization and cost reduction can be realized.

[Brief Description of the Drawings] Fig. 1 is an optical path diagram of the main parts of an optical system showing one embodiment of the present invention, Fig. 2 is an optical path diagram of the main parts of another embodiment, and Fig. 3 is an optical path diagram of the main parts of an optical system showing one embodiment of the present invention. FIG. 4 is an optical path diagram of the system, FIG. 4 is an optical path diagram of a conventional example, and FIG. 5 is a side view of the main part thereof. l, , . 2. 3. 4. 5,6゜7, ,. 8. 25. Galvano mirror Rotation axis mirror surface transmission aperture9. Sensor sum signal difference A word, aerial pattern

Claims (1)

[Claims] When converging light onto an optical recording medium via an objective lens in order to optically or magneto-optically record or reproduce information, light is focused from a light source onto the recording surface of the recording medium via a polarizing beam splitter and an objective lens. The optical system is configured to emit light and project the reflected light from the recording surface onto a photodetector via the objective lens and the polarizing beam splitter, and based on the detection results of the photodetector, In an optical system of an optical information recording/reproducing device in which a galvanometer mirror provided between a polarizing beam splitter and an objective lens is rotationally controlled for auto-tracking control, the galvanometer mirror is rotated in a direction perpendicular to its rotation axis. A transmission aperture is provided at a predetermined distance, the light flux transmitted from the light source side through the aperture is received by a plurality of sensors, and the rotation angle of the galvanometer mirror is set by the difference signal of the output of the sensor, and the sum signal is 1. An optical system for an optical information recording/reproducing device, characterized in that the amount of light from a light source is detected.