JPS5972659A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To attain stable control, by switching the operation of an optical beam intensity control means with the output of a focus detecting means to make the photo detecting amount of a photo detector constant at focusing state. CONSTITUTION:When no focus is set at the application of power supply, a temperature characteristic compensating optical power control circuit 21 is operated by the light of a semiconductor laser 103, a switch 22 is selected to the position (a) to make the luminous amount incident to a photo diode 20 constant. When the focus is set at the reproducing state, a reflecting factor changing compensating optical control circuit 26 is operated by the intensity of the light of the laser 103, the switch 22 is selected to position (b) with an output of a focus OK detecting circuit 27 and the reflected light from the disc is controlled to be constant. When the focus is set at the recording state, a power control error signal 104 just before recording is held for a recording period by a sample-and hold circuit 24, the switch 23 is turned off via a recording gate signal 105 and an inverter 18 to prevent the attenuation of the sample value. Thus, stable control is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention optically records information on a disc-shaped record carrier (disc) by focusing a light beam from a laser light source or the like.

The present invention relates to an optical recording/reproducing device for reproducing or erasing information, and in particular provides a means for keeping control loop gains such as focus and tracking control constant.

Conventional configuration and its problems In optical recording and reproducing devices using laser light, information is recorded and reproduced by focusing the laser light onto a minute spot on the disk using an aperture lens (objective lens).
Since a surface precipitate occurs when the disk is rotated, focus control is required to move the diaphragm lens in accordance with the surface preform so that the focus of the minute spot is always on the disk. Further, tracking control is required to follow the eccentricity of the track and always place the minute spot on the track.

For focus control, for example, a 7-lindrical lens is used to give astigmatism to the light reflected from the disk, and the shape of the reflected light at the 4-divided photodetector changes depending on the surface predetermined position of the disk. There is a known focus control method using astigmatism of reflected light to obtain a focus error signal. In the focus control method, a focus error signal is obtained by using the difference in the amount of light reflected from the disk that is incident on each of the four divided photodetectors, so for example, the light reflectance of the disk changes. However, the amount of light incident on the photodetector changes due to dirt or deterioration of optical parts such as lenses and mirrors used, resulting in a disadvantage that the total gain in the focus control loop changes. . The reflectance of the disk varies from 10 to 20 orders of magnitude before and after recording a signal.

It also changes depending on the groove width and depth of the guide track.

For example, when the reflectance of the disk decreases, the amount of reflected light decreases and the focus error signal decreases, resulting in a decrease in focus loop gain and a deterioration in the accuracy of tracking the surface wobbling of the disk. Moreover, when the reflectance of the disk increases, the focus loop gain increases, making the control system unstable, making it easier to oscillate, or oscillating when the reflectance is high and the loop gain reaches its maximum.

Purpose of the Invention The present invention solves the above-mentioned conventional problems, and includes detecting the amount of light incident on the photodetector and controlling the light beam intensity of a light source such as a laser so as to keep the amount of light constant. An object of the present invention is to provide an optical recording/reproducing device that can perform stable control by controlling the gains of the focus and l/racking servo control loops to a constant value.

Structure of the Invention The present invention comprises a light source such as a laser, an optical system for focusing a light beam from the light source into a minute spot, an information recording/reproducing disk, a photodetector for receiving reflected light from the disk, and the above-mentioned light source. An optical recording/reproducing device comprising a focus detection means for detecting that a minute spot is focused on the disk, and a light beam intensity control means for controlling the intensity of the light beam of the light source, the focus detection means Depending on the output, the operation of the light beam intensity control means is switched to keep the amount of light received by the photodetector constant in the focused state.

DESCRIPTION OF EMBODIMENTS The present invention will be explained in detail below with reference to the drawings. FIG. 1 shows an embodiment of an optical recording/reproducing apparatus incorporating a focusing and tracking device of the present invention. In FIG. 1, the optical system includes a light source 1 such as a semiconductor laser, a condenser lens 2 for condensing the light of the semiconductor laser, and a divergence angle of the semiconductor laser in the vertical and horizontal directions with respect to the cemented surface. To correct this, cylindrical lenses 3 and 4 having a lens action only in a direction parallel to the cemented surface are made of concave and convex cylindrical lenses.
, an aperture lens 6 that creates a minute spot light of about 1 μm in diameter on the disk 6, for example, a voice coil of a speaker. Control is performed so that the focus is always on the disk 5. The reflected light from the disk 5 that has passed through the wavelength plate 7 is reflected at right angles by the polarizing beam splitter 8 and enters the semi-convex lens 9.

The reflected light converged by the semi-convex lens 9 is split by a mirror 10, and one part enters a two-split photodetector 11 for detecting a focus signal, which is placed at the aperture point of the reflected light. The other light enters a two-split photodetector 12 for tracking signal detection placed in the far field of the reflected light. The focus signal is generated using the well-known Knifezi method, and a differential amplifier 15 uses the output of the two-split photodetector 11 for focus signal detection as a difference signal to generate a focus error signal FE, and an summing amplifier 16 uses it as a sum signal to generate a focus sum signal FS. The output of the two-split photodetector 12 for tracking signal detection is sent to a differential amplifier 13 to produce a tracking error signal TE as a difference signal, and an summing amplifier 14 to produce a tracking sum signal TS.

The focus error signal FE and the tracking error signal T
E is focus control and tiger respectively.

Used for king control.

FIG. 2 shows how the focus error signal FE changes depending on the defocus distance with respect to the disk. Focus control is applied at a point indicated by A in FIG. 2, and the slope of the focus error signal FE at this point becomes the focus gain.

This focus error signal FE is used for focus signal detection.
Since it is proportional to the amount of light received by the split photodetector 11, for example, when the reflectance of the disk 60 increases, the focus error signal FE increases from 100 to 101 in FIG.
Also, if the reflectance is low, it will be small as shown in 102 in FIG.

The above also applies to the tracking error signal TE, and the tracking gain changes.

In other words, the focus error signal FE and tracking error signal TE increase or decrease depending on the amount of light reflected from the disk, so the focus and tracking control loop gain changes each time, causing the focus and tracking control system to become unstable on the verge of oscillation. This may result in a system in which the aperture lens cannot follow the surface blur or eccentricity of the track.

In the present invention, in order to eliminate the drawbacks such as "double series", the light output of the light source is controlled so that the amount of reflected light from the disk 5 is constant, the focus and tracking control loop gains are kept constant, and the disk and optical To provide a new optical recording/reproducing device which can always achieve stable control regardless of changes in parts over time.

FIG. 3 is a block diagram of essential parts of an embodiment of the present invention. R
R2, R3, R4 are transistors Q1. This is the bias resistance of Q2. R5 is the load resistance of transistor Q1,
R6 is the emitter resistance of transistor Q3. A semiconductor laser 19 is connected to the collector of the transistor Q2.
．． The drive current d is the base voltage of the transistor Q3
Then, d=IvEE (■b-Vbe)l/R6
f given rel.

vbo is the base-emitter voltage of the transistor Q3, and EE is the power supply voltage on one side.

The current Id flowing through the semiconductor laser 19 changes to "High"/"Low" since the transistor Q1 is inverted and stops flowing when the output of the AND gate 1g becomes "High" level. The AND gate 17 ANDs the recording signal 106 and the recording gate signal 10F5, and modulates the semiconductor laser 19 only when the recording gate signal 106 is "High". A photodiode 20 photoelectrically converts the light beam 103 of the semiconductor laser 19, and is a photodetector forming part of a compensation circuit for compensating for temperature changes in the optical output of the semiconductor laser 19. Reference numeral 21 denotes a temperature characteristic compensation optical power control circuit that compensates for temperature changes in the optical output of the semiconductor laser 19. 22 is a two-person analog switch, 23 is a one-person analog switch, and 24 is a sample and hold circuit. 25 is a summing amplifier for the focus sum signal FS and the l.racking sum signal TS. 26 is a disk reflectance change compensation optical power control circuit. 18 is an inverter. 2A is a focus OK detection circuit that detects whether or not the focus is on the disc.

The operating states in Figure 3 include 1: power on and no focus, 2: focus and playback state, and 3: focus and recording state. be.

In operation mode 1, the light intensity of the light beam 103 of the semiconductor laser 19 is controlled by the temperature characteristic compensation optical power control circuit 21.
is activated, the analog switch 22 for two people is tilted to side a, and the analog switch 23 is on, thereby making the amount of light incident on the photodiode 20 constant.

In operation mode 2, the light intensity of the light beam 103 of the semiconductor laser 19 is controlled by the reflectance change compensation optical power control circuit 2.
6 is activated, the two-person analog switch 22 (focus ○) is tilted to the b side by the output of the detection circuit 2a, and the analog switch 23 is on, so that the amount of light reflected from the disk is constant. A two-person analog switch 22 (d) determines whether or not the disc is in focus by a detection circuit 27 that determines whether a tracking difference signal TE is present or not, and switches based on its output.

That is, when the focus is on, the two-person analog switch 22 is moved to the b side, and when the focus is on, the analog switch 22 is moved to the a side.

Operation mode 3 is when recording a signal, and the power control error signal 104 immediately before recording is held in the sample hold circuit 24 for a recording period. This operation mode improves the problem that the transient response time of the optical power control circuits 1 and 2 is long and the envelope of the modulated light intensity of the light beam 103 does not rise quickly. At this time, the analog switch 23 turns off the recording gate 105 using a signal inverted by the inverter 18 to prevent the sample value from attenuating.

In Figure 3, the reflectance change of the disk is expressed by the focus sum signal F.
Although the case where detection is performed using the sum of S and tracking sum signal TS has been shown, it goes without saying that either one of these signals may be used.

Effects of the Invention The optical recording/reproducing apparatus according to the present invention can achieve stable control by keeping the loop gain of focus control and tracking and king control constant by controlling changes in the amount of reflected light from the disk. Furthermore, the implementation effect is significant because the amplitude change of the read signal from the disk can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an overview of the optical system and servo signal detection section of an optical recording/reproducing apparatus to which the present invention is applied, FIG. 2 is a diagram showing changes in the focus error signal FE, and FIG. 3 is a diagram showing the invention FIG. 2 is a schematic diagram of a reflected light amount control circuit of an optical recording/reproducing apparatus according to an embodiment of the present invention. 1...Light source, 2...Condensing lens, 3,
4... Cylindrical lens, 6...
Disc, 6...Aperture lens, 7...
Wave plate, 8... Polarized beam printer, 9.
...Single lens, 10...Vera-111.
...Two-split photodetector for focus signal detection, 12
...Two-split photodetector for tracking signal detection,
13.115...Differential amplifier, 14. -16.
25...Summing amplifier, 17...AND
Gate, 1B... Inverter, 19...
・Semiconductor laser, 2o...photodiode,
21...Temperature characteristic compensation light (war control circuit, 2
2...2 people analogue Sui, Sochi, 23...
24...Sample hold circuit, 26...Reflectance change compensation light control circuit, 27...Focus OK
detection circuit.

Claims (1)

[Claims] (1) A light source that generates a light beam, an optical system that focuses the light beam into a minute spot, a disk that records and plays information on the minute spot, and detects the amount of light reflected from the minute spot from the disk. a control means for detecting a change in the amount of light received by the photodetector and controlling the minute spot so that it is on a track of the disk, and the amount of light received by the photodetector being constant. An optical recording/reproducing apparatus characterized in that it is provided with a light amount control means for varying the light beam intensity of the light source. (The light amount control means includes a focus detection means that detects that a minute spot light is focused on the disc, and a control duration of the control means that controls the light amount of the light source according to the output of the focus detection means. The invention is characterized in that the amount of light of the light beam is controlled to be constant in a focus-off state, and the amount of light received by the photodetector is controlled to be constant in a focus-on state. The optical recording/reproducing device according to scope 1.