JPH0223538A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To perform a gain control for a focus control without being influenced by pressure by detecting a light quantity corresponding to a light beam prior to incidence upon a critical angular prism at the time of detecting a focus error in the method of critical angle of incidence and performing the gain control in the focus control based on this detecting output. CONSTITUTION:A light beam of P-polarization is emitted from a semiconductor laser 1, and the light beam is collimated by a collimator lens 2, and then its elliptical light is turned into round one by passing through a shaping prism 3. This transmitted light beam is turned into a round polarization by a 1/4 wavelength plate 4 and converged by an objective lens 5 to irradiate on a recording medium 6, and its reflected light is transmitted through the lens 5 and turned into S-polarization by the wavelength plate 4 and then reflected by the prism 3. This reflected light beam is branched by a semitransparent mirror 7, and the transmitted light is led to a bisected photodetector 8, and the reflected light beam is reflected by the critical angular prism 10 to be incident upon a bisected photodetector 11. An output of this detector 11 is calculated by a differential amplifier 12 to output a focus error signal relative to a focus position of the lens 5 with the medium 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus control device in an optical information recording/reproducing device, and particularly to a focus control device using a critical angle method.

[Prior Art] In recent years, optical recording and reproducing devices that can record information at high density using a light beam or reproduce information recorded at high density at high density are being put into practical use.

In an optical information recording/reproducing device, a light beam is irradiated onto a recording medium, and tracking control and focus control are performed in order to accurately record and reproduce information.

For example, Japanese Patent Publication No. 80-32264 discloses an example of tracking control, which eliminates the deviation of the light beam spot from the track according to the tracking error signal.
It is controlled to follow the truck. The tracking error signal is obtained from the transmitted/reflected light beam from the recording medium.

Therefore, if the intensity of the reflected light beam changes due to a change in the intensity of the laser light source that emits the light beam or a change in the transmittance or reflectance of the recording medium, the tracking error signal changes. In order to detect the deviation of the optical beam spot from the track as a track error signal without being affected by these changes, control is performed according to the sum output of the two-split photodetector to detect the track error signal by the difference output. It adjusts the gain of the circuit.

[Problems to be Solved by the Invention] In focus control, the focus error signal is obtained from the transmitted and reflected light beam from the recording medium, so it is effective to perform gain adjustment as shown in Japanese Patent Publication No. 60-32284. It is.

However, in the critical angle method, when the sum output of a photodetector for detecting a focus error signal is used for gain adjustment, the following problems occur.

Focus error detection using the critical angle method has high sensitivity, but it is easily affected by the surrounding pressure, because when the surrounding pressure changes, the refractive index of the air in contact with the boundary angle surface changes, so the critical angle changes. This is to do so. A specific example thereof is described in Japanese Patent Application Laid-Open No. 62-200538.

The sensitivity characteristic of the focus error signal with respect to pressure is opposite to the characteristic of the sum output of the photodetector for detecting the focus error signal with respect to pressure.

Therefore, if the sensitivity of the focus error signal decreases due to a change in pressure, for example, the gain must be adjusted to increase the sensitivity, but since the sum output of the photodetector increases with the opposite characteristic. Control works to reduce the gain. That is, there is a problem in that gain adjustment is reversed due to changes in pressure.

[Means for Solving the Problems] In order to solve the above problems, the present invention detects a light amount corresponding to the light beam before entering the critical angle prism using a photodetector in focus error detection using the critical angle method. hand,
Gain control in focus control is performed based on this detection output.

[Operation] If the above measures are taken, even if the critical angle of the critical angle prism changes due to a change in pressure, the amount of light corresponding to the light beam before entering the critical angle prism is used for gain control, so the pressure Performs gain control that is unaffected by changes in

[Example] The present invention will be described in detail below based on the drawings.

1 and 2 are diagrams showing a first embodiment of the present invention.

The semiconductor laser 1 emits a P-polarized light beam. The wavelength is, for example, 830 nm or 780 nm. The light beam emitted from the semiconductor laser 1 passes through the collimator lens 2
The light becomes parallel light at the shaping prism 3, and the elliptical light becomes sunlight and is transmitted through the shaping prism 3. The light beam transmitted through the shaping prism 3 is 1/
The light becomes circularly polarized light through the four-wavelength plate 4, is focused into a minute spot by the objective lens 5, and is irradiated onto the recording medium 6. The light beam reflected from the recording medium 6 passes through the objective lens 5 again, becomes S-polarized light by the quarter-wave plate 4, and is reflected by the polarization plane 33 of the shaping prism 3.

The light beam reflected by the polarization plane 33 passes through the semi-transparent mirror prism 7
The transmitted light beam is divided into two parts and is incident on a two-part photodetector 8. The reflected light beam passes through a critical angle prism 10
, and enters the two-split photodetector 11 . The output of the two-split photodetector 11 is used to obtain a differential output using a differential amplifier 12. This becomes a focus error signal indicating which direction and how much the distance between the objective lens 5 and the recording medium 6 has shifted from the in-focus position. Focus Nilla-i has AGC circuit 13
After the gain is adjusted by an auto-gain control circuit, it passes through a phase compensation circuit 14 and a drive circuit 15 to a focus coil 16, and then moves the objective lens 5 in the optical axis direction and holds it at a focusing position. On the other hand, the output of the two-split photodetector 8 is sent to a summing amplifier 17 to obtain a sum output, and a differential amplifier 18 to obtain a difference output. This sum output is the R6 signal (playback signal)
The difference output becomes a tracking error signal. The tracking error signal is similar to the focus error signal,
The light beam is added to the tracking coil 22 via the GC circuit 19, phase compensation circuit 20, and drive circuit 21, and is controlled by moving the objective lens in a direction perpendicular to the track so that the spot of the light beam is on-track on the medium 6. AGC circuit 13
．． 19 is controlled by the output of the summing amplifier 17.

FIG. 2 shows an example of an AGC circuit.

The output of the summing amplifier 17 is converted into a digital signal by an A/D conversion circuit 23. The output is sent to the CPU 24 and one of the analog switches 25 and 1 is selected with 8 bits, and the damping resistor 2
Select 6. A differential amplifier 27 has an inverting input terminal to which a focus error signal or a tracking error signal from the differential amplifier 12 or 18 is input, and a non-inverting input terminal to which an attenuation resistor 26 is connected. The output of the differential amplifier 27 is connected to a non-inverting input terminal through a feedback resistor 28, and the focus error signal or tracking error signal is amplified with an amplification factor determined by the feedback resistor 28 and the attenuation resistor 26.

With the above configuration, gain control is performed based on the light 111c of the light beam before entering the critical angle prism, so if the sensitivity of the focus error signal is large due to the influence of pressure etc. If it is small, it is possible to prevent adjustment in the opposite direction of making it even smaller.

Next, a second embodiment of the present invention will be described based on FIG.

The same parts as in FIG. 1 are given the same reference numerals and details are omitted.

Also, the parts not shown are the same as those in FIG. 1.

The difference from FIG. 1 is that the output of the summing amplifier 17 is used to
Rather than controlling the gain of the GC circuit 13, the sum output of the photodetector 9 and the sum output obtained by detecting the light transmitted through the critical angle prism 10 with the two-split photodetector 29 and using the summing amplifier 30 are combined into a summing amplifier. Two points are that gain control is performed based on the sum output combined at 31, and that the light transmitted through the semi-transparent mirror prism 7 is incident on the photodetector 8 via the single lens 32. The sum output obtained from the photodetector 11 fluctuates under the influence of pressure, and the amount of the fluctuation is represented by the amount of light transmitted through the critical angle prism 10. Therefore, if the sum output of the photodetector 11 and the amount of light transmitted through the critical angle prism 10 are combined, that is, the amount of light before entering the critical angle prism 10, it is a signal that does not include the influence of pressure on the critical angle prism 10. becomes. By controlling the gain using this signal, the gain can be set without being influenced by pressure.

In addition, since the light beam is focused using the single lens 32,
The photodetector 8 that receives light only needs to be small.

Next, a third embodiment of the present invention will be described using FIG. 4. This embodiment is an example of transmission type focus detection.

The light beam split by the polarized prism 3 and reflected by the semi-transparent prism 71 is focused through a single lens 32 and detected by the photodetector 8 to obtain an Rp times signal. On the other hand, semi-transparent mirror prism 7
The light beam passing through the critical angle prism 10 is refracted at its exit surface to change its direction, and then enters the critical angle prism 10. The light transmitted through the critical angle prism is received by a two-split photodetector 11, and the difference output obtained by a differential amplifier 12 is used as a focus error signal. Further, the light reflected by the critical angle prism 10 is detected by a two-split photodetector 29, and a sum output is obtained by a summing amplifier 30. The sum output of the summing amplifier 30 and the sum output of the photodetector 11 are obtained by the summing amplifier 31, and this signal is used to control the AGC circuit 1.
3 gain control is performed.

In this example, as in the second embodiment, the signal used for gain control corresponds to the signal before entering the critical angle prism 10, so gain control can be performed without being affected by pressure or the like.

It should be noted that the present invention is not limited to the above embodiment (various modifications can be made). It is used for the Rp multiplication signal and the tracking error signal, but it is not divided by the semi-transparent mirror prism, but enters the critical angle prism as it is, and the reflected light is received by the four-split photodetector, and the Rp signal is obtained from the total amount of light. A focus error signal and a tracking signal are obtained from the difference in the sum output of adjacent elements (however, when obtaining the focus error signal, the control signal for the AGC circuit is obtained from the total amount of light transmitted and reflected by the tracking prism. You can also use this as the third
The present invention may also be applied to the transmission type focus error detection shown in the figure.

[Effects of the Invention] As explained above, according to the present invention, in focus control using the critical angle method, the amount of light corresponding to the light beam before entering the critical angle prism is detected, and based on this detection output signal, Since the gain control for focus control is performed using
Even in focus control using the critical angle method, which is easily affected by pressure, gain control of focus control can be performed without being affected by pressure.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of the first embodiment of the present invention, Fig. 2 is a diagram showing an example of the AGC circuit used in the first embodiment, and Fig. 3 is a diagram showing the second embodiment. 4 are diagrams showing a third embodiment. 10... Critical angle prism, 8, 11.29... Photodetector 13.19... AGC [l, 1B... Focus coil patent applicant Olympus Optical Industry Co., Ltd.
Third Ward δ + 1. ．． 7I 4th Ward No. 21

Claims (1)

[Claims] A laser light source that emits a light beam, an optical system that guides the light beam emitted from the laser light source to a recording medium, and a part of the optical system that separates reflected light from the recording medium. In an optical information recording/reproducing device comprising a light splitting means and a critical angle prism into which at least a part of the light beam extracted by the light splitting means is incident, the light beam corresponds to the light beam before entering the critical angle prism. 1. An optical information recording/reproducing apparatus comprising a photodetector for detecting the amount of light, and performing gain control for focus control based on an output signal of the photodetector.