JP2762997B2 - Optical information processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an optical information processing apparatus using a semiconductor laser, and is suitable for an optical video player or an optical audio player. The present invention relates to a dynamic information processing device. 2. Description of the Related Art In an optical system using a semiconductor laser, when reflected light from an optical information disk on which a signal is recorded returns to the semiconductor laser, the semiconductor laser may generate noise. For this reason, conventionally, the reflected light is prevented from returning to the semiconductor laser mainly by optical means. FIG. 1 is a configuration diagram showing this conventional example. In FIG. 1, forward light 2a, 2b, 2c, 2d emitted from a semiconductor laser 1 passes through an optical system including a collimator lens 3, a mirror 4, a condenser lens 5 and the like, and an optical information panel 6 is provided. Focused on top. Generally, the laser light emitted from the semiconductor laser 1 is linearly polarized light, and by disposing the quarter-wave plate 7 in the optical path, the forward light 2d becomes circularly polarized light, and the reflected light from the optical information panel 6 9a
When the light passes through the quarter-wave plate 7 again, it becomes reflected light 9b of linearly polarized light whose polarization direction is different from the forward lights 2a, 2b and 2c by 90 °. Further, when the polarization beam splitter 8 is disposed between the quarter-wave plate 7 and the semiconductor laser 1, the reflected light 9b is reflected by the polarization beam splitter 8, becomes reflected light 9c, and enters the convex lens 10. Then, the light is guided to the detector 11 by the convex lens 10. Processing circuit 12
Processes information contained in the reflected light 9c. Processing circuit 1
2 is supplied to a video signal processing circuit and an audio signal processing circuit (not shown). Further, the backward light 13 emitted from the semiconductor laser 1 is incident on the monitor detector 14 and causes the laser drive circuit 15 to perform a feedback operation,
The configuration is such that the output of the semiconductor laser is kept constant. In the above-mentioned conventional example, the error of the emission wavelength of the semiconductor laser 1 and the quarter-wave plate 7, the retardation of the optical information panel 6, the polarization beam splitter 8
In general, it is inevitable that a small amount of reflected light passes through the polarizing beam splitter 8 and returns to the semiconductor laser 1 due to imperfection of the semiconductor laser 1. The light quantity may fluctuate and generate noise. When the semiconductor laser 1 generates noise, the output signal of the processing circuit 12 naturally includes noise. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned disadvantages of the prior art, and even if the light reflected by the optical information disk is again incident on the semiconductor laser, the reflected light is not reflected. An object of the present invention is to provide an optical information processing apparatus in which the influence of light does not substantially occur. In order to achieve the above object, according to the present invention, the output of a semiconductor laser is interrupted at a high speed, and the forward light emitted during the ON period is controlled by an optical information panel. In the time region where the light returns to the semiconductor laser after being reflected, the operation of the semiconductor laser is stopped. That is, the length of the optical path between the semiconductor laser and the optical information panel, the period of intermittent output of the semiconductor laser, and the length of the period during which the semiconductor laser is turned on during one period are appropriately set, and the reflection returning to the semiconductor laser is set. Eliminate the effects of light. Hereinafter, the present invention will be described based on embodiments. FIG. 2 is a configuration diagram of the optical system according to the present invention. The optical system such as the semiconductor laser 1, the collimator lens 3, the mirror 4, and the condenser lens 5 is substantially the same as that of the conventional example. The quarter-wave plate may be omitted, in which case a half mirror 16 is placed at the position of the polarizing beam splitter. Further, the semiconductor laser 1 is driven in a DC manner by a laser driving circuit 15 in which the backward light 13 is fed back via a monitor detector 14, so that the average output is kept constant and, at the same time, the high-frequency oscillation circuit 1
7, the laser light emitted from the semiconductor laser 1 is driven intermittently at high speed. FIG. 3 shows how the semiconductor laser 1 according to the present invention is intermittent and how light travels, with time t as the horizontal axis. FIG. 3A shows an optical path with the position of the semiconductor laser at position 0 and the position of the optical information panel with position P, and FIG. 3B shows the intermittent state of the semiconductor laser in two values, an ON state and an OFF state. The laser beam 2a emitted from the semiconductor laser 1 at time t0 travels at the speed of light c, is reflected by the optical information panel 6 at a distance of the optical path length L from the semiconductor laser 1, and is partially reflected by the half mirror 16 and reflected. It becomes light 9'c,
The remainder becomes return light 9'd and returns to the semiconductor laser 1 at time t2 (= 2 L / c). On the other hand, if the intermittent frequency of the laser beam 2'a emitted from the semiconductor laser 1 is the frequency f, and the ratio of the ON period to one cycle is a (0 <a≤0.5), the laser beam 2'a The time at which 'a is turned off is time t1 (= a / f), and the light emitted at time t1 is similarly turned on at time t3 (= a / f).
/ F + 2L / c). Further, the intermittent frequency is the frequency f, and the period in which the semiconductor laser 1 is in the off state continues from time t1 to time t4 (= 1 / f).
If the following equations (1) and (2) hold, the semiconductor laser 1 is turned off when the return light 9'd enters the semiconductor laser 1. A / f ≦ 2L / c (1) a / f + 2L / c ≦ 1 / f (2) When formulas (1) and (2) are arranged, formula (3) ac / ( 2f) ≦ L ≦ c (1-a) / 2f (3) where 0 <a ≦ 0.5. By the way, when a = 0.5 and f = 600 MHz, L = 12.5 cm, which is an optical path length suitable for practical use as an optical system. When the optical path length is set under the condition satisfying the equation (3) and the laser light emitted from the semiconductor laser 1 is interrupted at a high frequency, the semiconductor laser 1 substantially returns the return light 9 '.
The noise level does not increase due to a change in retardation of the optical information panel 6 without being affected by d. In the example shown in FIG. 2, since the half mirror 16 is used, the amount of light reaching the detector 11 is approximately one-fourth, that is, -12 dB as compared with the conventional example shown in FIG.
However, in the related art, the rise of the laser noise due to the return light 9d may reach 20 dB or more, so that the present invention does not hinder practically as compared with the conventional example. Incidentally, in the above embodiment, a quarter is used.
Although the wave plate is removed and the half mirror 16 is used instead of the polarizing beam splitter, a quarter wave plate and a polarizing beam splitter may be used as in the conventional case. Needless to say, the performance is further improved. When the distance between the semiconductor laser 1 and the optical information panel 6 is selected to be three times the optical path length L, the return light 9'd is generated at time t6 between time t5 and time t8.
Returns to the semiconductor laser 1 again from time t7.
Between the time t5 and the time t8, the semiconductor laser 1 is in the off state, so that the semiconductor laser 1 returns the return light 9 '.
Not affected by d. Therefore, generally, the optical path length L, frequency f,
If the ratio a of the ON period in the cycle is selected in the relationship as shown in the equation (4), the influence of the return light 9'd is eliminated. Ac / 2f ≦ L / (2n−1) ≦ c (1-a) / 2f (4) [n = 1, 2, 3, 4,...] FIG. The following shows an example. In this embodiment, the forward light 2 emitted from the semiconductor laser 1 reaches the optical information panel 6 via the collimator lens 3, the mirror 4, and the condenser lens 5. The reflected light 9a is condensed on the end face of the semiconductor laser 1 during the off-period through the above-described path in reverse. In this case, the semiconductor laser 1 functions as a light guide having a high refractive index, and a part of the return light 9 ′ d is guided to the rear of the semiconductor laser 1. Therefore, the backward light 13 is obtained by superimposing the intermittent light at a high frequency with the return light 9 ′ d having information received at the time of reflection at the optical information panel 6. The two output signals of the monitor detectors 14a and 14b divided into two regions by a boundary line parallel to a track (not shown) of the optical information panel 6 are added by an adder circuit 18, and the DC component is converted into a laser drive circuit. 15 and the RF band component is supplied to the RF processing circuit 19. The output signals of the two monitor detectors 14a and 14b are
The light is supplied to a tracking control circuit via the reference numeral 0 and used as tracking control of the condenser lens 5. FIG. 5 is a block diagram showing a further preferred circuit example when the monitor detectors 14a and 14b having the light receiving areas divided in this way are used. In this circuit example, in the substantially same configuration as the embodiment of FIG.
The output of the high-frequency oscillation circuit 17 is inverted by an inversion circuit 22, and the RF processing circuit 19
Of the gate circuits 23 and 24 inserted in the preceding stage of. According to this configuration, input signals to the RF signal processing circuit 19 and the tracking processing circuit 21 are only signals selected by the gate circuits 23 and 24 and given only from the rear light 13 when the semiconductor laser 1 is in the off state. Therefore, good signal processing can be performed. FIG. 6 shows an embodiment of the high-frequency oscillation circuit. In the figure, reference numeral 30 denotes a voltage control circuit, and 17 denotes a high-frequency oscillation circuit suitable for the present invention, which is a grounded base clap type oscillation circuit using a general shortened λ / 2 resonator. 3
Reference numeral 1 denotes a coupling capacitor, which is coupled to the semiconductor laser 1. The monitor detector 14 detects the backward light 13 of the semiconductor laser 1 and controls the laser drive circuit 15 via the Coke coil 32b.
Drives the semiconductor laser 1 in a DC manner. As described above, according to the present invention, there is no adverse effect on the semiconductor laser due to the return light from the optical information disk, and the occurrence of laser noise can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of a conventional example of an optical head. FIG. 2 is a configuration diagram according to the present invention. FIG. 3 is an explanatory diagram showing a time relationship between intermittent switching of a semiconductor laser due to high frequency and an optical path. FIG. 4 is a configuration diagram of a second embodiment of the present invention. FIG. 5 is a configuration diagram showing another example of the circuit configuration in the second embodiment. FIG. 6 is a circuit diagram of a high-frequency oscillation circuit suitable for implementing the present invention. [Description of Signs] 1 ... Semiconductor laser, 6 ... Optical information panel, 11 ... Detector, 14 ... Monitor detector, 15 ... Laser drive circuit, 17 ... High frequency oscillation circuit (laser light control means).

Claims (1)

(57) [Claims] A semiconductor laser that emits laser light, an optical device that focuses the laser light emitted from the semiconductor laser on an optical information panel, and a detector that detects the laser light reflected on the optical information panel When, an optical information processing apparatus having a signal processing circuit for processing the signals output by the detector, and a high-frequency oscillator for turning on / off light emission at a predetermined cycle of the semiconductor laser, the on During the period , the laser light emitted from the semiconductor laser is reflected on the optical information panel and returns to the off period.
Thus, the light from the semiconductor laser to the optical information panel
An optical information processing apparatus, wherein an optical distance is set .