JPH01143024A - Optical information processor - Google Patents

Abstract

PURPOSE:To short transition duration, which is needed at a switching time, by executing the switching of the optical intensity of a recording mode and a reproducing mode in an acoustic optical deflecting element. CONSTITUTION:A gain control amplifying circuit 24 is equipped and the signal level of a driving signal S1 to an acoustic optical deflecting element 3 is changed in correspondence to the recording mode and the reproducing mode. Then, by changing diffraction efficiency in the acoustic optical deflecting element 3, a scanning optical beam LB3 of the desired optical intensity can be obtained. Accordingly, since the optical intensity of an incoming optical beam LB1, which is emitted from a semiconductor laser LD, is always maintained to be constant regardless of a recording mode time and a reproducing mode time, the transition duration can be made short by evacuating the switching of the mode to be executed in a semiconductor laser driving circuit 10.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Field of Application The present invention relates to an optical information processing device, and in particular to recording optical information on an optical recording medium such as a card or tape using an acousto-optic deflection element (AOD). The present invention is suitable for application to devices that read and/or reproduce information (this is called an optical information processing device).

B. Summary of the Invention The present invention enables high-density recording in an optical information processing device by changing the signal level of a drive signal that drives the acousto-optic deflection element, thereby causing the acousto-optic deflection element to function as an attenuator of a laser beam. Alternatively, playback can be performed at high speed.

C. PRIOR TECHNOLOGY Conventionally, as shown in FIG. 4, this type of optical information processing apparatus uses a laser beam to form an image on, for example, a tape-shaped optical recording medium l in a scanning direction that crosses the running direction a of the optical recording medium l. A system has been proposed in which optical information is written on or read out from the recording track TR by scanning the written or read light spot 2 .

Here, the diameter of the light spot 2 can be converged to, for example, about l [μm] (for example, the wavelength is 780 (n
m) when using a laser beam).

Therefore, a large number of recording tracks TR can be stored in the gart band G, for example.
If optical recording information can be reproduced from each recording track TR while sandwiching B, optical information can be recorded and/or reproduced at a much higher density.

As a scanning means for scanning the light spot 2 across the optical recording medium 1 in this manner, a structure using an anisotropic Bragg diffraction type acousto-optic deflection element 3 has been proposed, as shown in FIG. (U.S. Patent No. 3.851,
No. 951).

Here, the acousto-optic deflection element 3 has a rectangular shape, and with respect to the transducer 3A provided at one end thereof, as shown in FIG. By supplying a drive signal S1 that repeatedly changes in the form of a sawtooth wave, the acousto-optic deflection element 3
forming a sound wave pattern 3B in which the density gradually changes,
As shown by arrow C, the absorbent material 3 provided at the other end
Proceed in direction C.

Here, the acoustic wave pattern 3B acts as a diffraction grating when a linearly polarized incident light beam LBI that is incident on the acousto-optic deflection element 3 from a laser light source made of, for example, a semiconductor laser device is transmitted. As a result, the light beam is diffracted by the sound wave pattern 3B, and the diffraction angle of the 1st-order diffracted light with respect to the 0th-order diffracted light LB2 changes as the density of the sound wave pattern 3B changes in accordance with the change in the frequency f of the drive signal S1. As a result, the scanning light beam LB3 consisting of the first-order diffracted light emitted from the acousto-optic deflection element 3 scans in the direction along the longitudinal direction of the acousto-optic deflection element 3 as shown by arrow d. Spot 2 (FIG. 4) can be obtained.

In an optical information processing device using the acousto-optic deflection element 3 having such a configuration, the output level of the semiconductor laser device used as a laser light source changes as the ambient temperature changes, so that the light onto the optical recording medium is Writing or reading information may become unstable.

In order to solve this problem, conventionally, as shown in Figure 3, the laser output is detected using a monitor photodiode etc. built into the semiconductor laser device and compared with a reference signal.
Based on this comparison result, automatic output control m (
A semiconductor laser drive circuit 10 having an APC) circuit configuration is used.

That is, in the semiconductor laser drive circuit 10,
A reference voltage for recording or reproduction V□17. Or V□.

One of them is selected and inputted to the addition input terminal of the subtraction circuit 16.

On the other hand, the monitoring photoelectric conversion element PD, which is a photodiode or the like built in the semiconductor laser device 13, is the semiconductor laser L.
Detect the light intensity of the output beam of D and monitor the current ■1
is converted into a monitor voltage in the current-voltage conversion amplifier circuit 14, and then passed through the low-pass filter 15 to the subtraction circuit 16.
The detection voltage ■ is input to the subtraction input terminal of .

The subtraction circuit 16 supplies the subtraction output SA to the voltage-current conversion amplifier circuit 19 via the amplifier circuit 17 and the variable characteristic loop filter 18, and generates a drive current (2). After converting the signal into 9, it is supplied as a drive output P to the semiconductor laser LD through the adder circuit 20.

Here, the variable characteristic loop filter 18 is connected to the switching circuit 1
8B is switched by the recording/reproduction mode switching signal ScH, and thereby the input resistor R-capacitor Ct loop and the input resistor R-buffer circuit ill 8A
The time constant of the variable characteristic loop filter 18 can be selected by - capacitor CI and the loop of capacitor C8.

(Constituting the APC circuit 22 as a whole,
Reference voltage V for recording or reproduction. 111 or V□. It is possible to obtain laser output according to the

In the above configuration, the recording track TR of the optical recording medium 1
When recording optical information, the reference voltage for recording ■□, , is obtained via the read/write switch circuit 12, and the laser output based on the reference voltage VERITK is applied to the recording pulse S. Corresponding optical information is recorded on the optical recording medium.

On the other hand, in the playback mode, the reading reference voltage V I
IEAD is obtained, the semiconductor laser LD is driven based on the reference voltage V READ, and optical information can thus be reproduced with the laser output determined by the reference voltage V REAll.

D Problems to be Solved by the Invention By the way, when attempting to switch the recording or reproducing mode of optical information at any timing as necessary using the semiconductor laser drive circuit 10 having the APC circuit configuration as described above,
Ideally, by shortening the transition time when switching the light intensity of the scanning light beam LB3 between recording and reproduction,
It is conceivable to enable high-speed and high-density recording or reproduction as a whole (FIG. 7(A)).

However, when trying to speed up the response of the feedback loop of the APC circuit in order to shorten the transient time, it also responds to the recording pulse S modulated during recording, so that the optical information 5IIX contained in the incident light beam LBI is (Figure 8 (A)
) has the problem of causing distortion (Fig. 8(B)).

Therefore, the response time constant in the feedback loop is recorded by the pulse S,
It is necessary to limit the number of pulses to several pulses or more, which causes the problem that the time required to switch between recording and reproduction modes increases accordingly, making it difficult to perform high-speed and high-density recording or reproduction.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose an optical information processing device that can minimize the transition time that occurs when switching between recording and playback modes.

E Means for Solving Problem E In order to solve this problem, in the present invention, the acousto-optic deflection element 3 is supplied with a drive signal S1 whose frequency changes in a sawtooth waveform. 3
Light that forms a sound wave pattern 3B that travels in a predetermined direction as time passes, and forms a scanning light beam LB3 that scans the recording track TR on the optical recording medium 1 by the diffraction effect of the sound wave pattern 3B. The information processing device 21 includes a gain control amplification circuit 24, and switches the light intensity of the scanning light beam LB3 by switching the signal level of the drive signal S1 according to the recording mode and the reproduction mode.

By changing the signal level of the drive signal S1 for the F-action acousto-optic deflection element 3 and changing the diffraction efficiency in the acousto-optic deflection element 3, a scanning light beam LB with a desired light intensity is produced.
You can get 3.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, in which parts corresponding to those in FIGS. 3 to 5 are given the same reference numerals, 21 indicates an optical information processing device as a whole, and in the semiconductor laser drive circuit 10, a photoelectric conversion device consisting of, for example, a photodiode, etc. AP the monitor output of the element PD
By feeding back to the C circuit 22, the reference voltage ■ is supplied from the semiconductor laser LD in both recording mode and reproduction mode. A laser beam having a light intensity corresponding to , a, is generated as an incident light beam LBI.

The incident light beam LB of the predetermined level obtained in this way
I is the scanning light beam LB3 by the acousto-optic deflection element 3.
The light beam is irradiated onto the optical recording medium 1, thereby recording or reproducing optical information.

Here, the light intensity of the scanning light beam LB3 emitted from the acousto-optic deflection element 3 during the recording and reproducing mode of optical information needs to be lower than the light intensity during the recording mode, and in this embodiment, the gain By changing the signal level of the drive signal s1 given to the acousto-optic deflection element 3 by the control amplifier circuit 24, the light intensity of the scanning light beam LB3 is controlled.

That is, the gain control amplifier circuit 24 is controlled to change its gain by the gain control signal S2, thereby changing the amplitude of the sawtooth frequency signal S3 sent from the voltage controlled oscillator (VCo) 23 depending on the recording and reproduction mode. The drive signal S1 is sent out, thus changing the signal level of the drive signal SL. In this embodiment, the gain control signal s2 is formed by voltage-to-frequency conversion of the sawtooth voltage signal S4.

In the above configuration, when the power W is applied to the acousto-optic deflection element 3 depending on the signal level of the drive signal Sl applied to the acousto-optic deflection element 3, the emitted light flux, that is, the scanning The relationship between the diffraction efficiency η of the light beam LB3 is expressed by the following equation, where the light wavelength λ, constants k and K are set, and in a region where the power W is below a predetermined level, the diffraction efficiency η increases as the power W increases. (Figure 2).

Therefore, when switching from the recording mode to the playback mode using this area, the signal level of the drive signal 31 is lowered to reduce the diffraction efficiency η of the acousto-optic deflection element 3, thereby reducing the light of the scanning light beam LB3. Suppress intensity.

In this way, the optical information processing device 21 transfers optical information to the optical recording medium 1.
In the case of recording on the top, the power W is such that the diffraction efficiency η in the acousto-optic deflection element 3 becomes a large value η8. (Figure 2)
By applying the drive signal S1 of a signal level that gives the acousto-optic deflection element 3, the scanning light beam L with high light intensity
Optical information is recorded on the optical recording medium 1 using B3.

On the other hand, when reproducing optical information recorded on the optical recording medium 1, the signal level that provides the powers W and I such that the diffraction efficiency η in the acousto-optic deflection element 3 becomes a small value η is determined. By applying the drive signal s1 to the acousto-optic deflection element 3, a scanning light beam LB3 is generated to the extent that the optical information on the optical recording medium 1 can be read out as a change in reflected light flux without damaging it.
Try to get the following.

Incidentally, for example, the power W of the drive signal S1 input to the acousto-optic deflection element 3 in the recording mode. is W. When = 1 (W),
Diffraction efficiency (η, = 70%) in acousto-optic deflection element 3
is obtained, the wavelength used is λ=780 (
nm), the above formula (1) is satisfied, and the constant = 0.
7, K=1.2X10-' can be obtained. Therefore, in the reproduction mode, the light intensity of the scanning light beam LB3 is attenuated to 10% of that in the recording mode, and the power Wl is reduced to Wl = 40.
(mW), the diffraction efficiency η = 7
%.

According to experiments, in the conventional semiconductor laser drive circuit 10, if the maximum laser output in recording mode is 20 [1], the required laser output in playback mode is about 2 [i], and in order to obtain this laser output, The current required is 100 (MA) in recording mode and 50 (MA) in playback mode.
+A), and the power consumption is about 200 yen in recording mode.
(e+W), 100100 (in playback mode).

In the conventional case, regardless of the recording or reproduction mode, the power consumption of the acousto-optic deflection element 3 is selected to be approximately 1 [W] so that the diffraction efficiency η is maximized. While the power consumption changes between the recording mode and the playback mode, in the above embodiment, the semiconductor laser drive circuit 1
0 power consumption is about 200 (mW) in the recording mode, whereas the power consumption on the acousto-optic deflection element 3 side changes between the recording mode and the reproduction mode.

Therefore, the acousto-optic deflection element 3 and the semiconductor laser drive circuit 10
The total power consumption of the conventional example is 1100 in playback mode.
(mW), whereas in this example it is 240 (mW
), making it possible to significantly reduce power consumption.

According to the above configuration, the light intensity of the incident light beam LBI emitted from the semiconductor laser LD only needs to be maintained at a constant value regardless of the recording mode and the reproduction mode. By avoiding switching between modes, it is possible to minimize the transition time that occurs when switching modes, and thus it is possible to realize an optical information processing device 21 that performs high-speed and high-density recording or reproduction with a simple configuration. can.

H Effects of the Invention As described above, according to the present invention, the light intensity of the recording mode and the reproduction mode is switched in the acousto-optic deflection element, so that the laser output can be adjusted using the feedback loop of the semiconductor laser drive circuit. It is possible to eliminate the need for switching between the recording mode and the playback mode, thus reducing the transition time required when switching between the recording mode and the playback mode as much as possible, and thus providing an optical information processing device that performs high-speed and high-density recording or playback with a simple configuration. Obtainable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the optical information processing device according to the present invention, FIG. 2 is a characteristic curve diagram showing the diffraction efficiency of the acousto-optic deflection element according to the embodiment, and FIG. 3 is a semiconductor laser drive circuit. 4 is a route map showing the recording pattern of the optical recording medium, FIG. 5 is a perspective view showing the configuration of the acousto-optic deflection element, FIG. 6 is a signal waveform diagram showing the drive signal, and FIG.
8 and 8 are characteristic curve diagrams showing drive output. DESCRIPTION OF SYMBOLS 1... Optical recording medium, 3... Acousto-optic deflection element, 10... Semiconductor laser drive circuit, 21
...Optical information processing device, 23... Voltage controlled oscillator, 24...≠In-control amplifier circuit, Sl... Drive signal.

Claims (1)

[Claims] By supplying a drive signal whose frequency changes in the form of a sawtooth wave to the acousto-optic deflection element, a sound wave pattern that progresses in a predetermined direction over time is created in the acousto-optic deflection element. An optical information processing device configured to form a scanning light beam that scans a recording track on an optical recording medium by the diffraction effect of the sound wave pattern, the optical information processing device comprising a gain control amplification circuit, which controls the recording mode and the reproduction mode. An optical information processing device characterized in that the light intensity of the scanning light beam is switched by switching the signal level of the drive signal in accordance with.