JPS63241734A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To detect a various kinds of signals generated by plural optical beams independently by a pair of photodetectors, by changing at least the light quantity of one optical beam periodically with a high frequency signal out of the plural optical beams. CONSTITUTION:On a laser driving circuit 30a, a signal of single frequency considerably higher than the frequency band area of an information signal recorded on an optical disk 10 is superposed by an oscillation circuit 31, thereby, the strength of the optical beam 50a emitted from a semiconductor laser 1a fluctuates periodically centering average strength. Meanwhile, the optical beam 50b from a semiconductor 1b keeps constant strength. When such optical beams are focused and reflected on the optical disk 10, each optical beam receives modulation independently. Those modulated components are detected by the photodetector 20. The output signal of the photodetector 20 is supplied to a signal separation/demodulation circuit 45, and the signal modulated independently at every beam on the disk 10 is separated and detected independently from the same detector 20.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical information recording/reproducing device (hereinafter referred to as an optical head) equipped with two or more semiconductor laser light sources.
Particularly reducing the number of parts in the optical head.

This invention relates to a circuit configuration suitable for miniaturization.

[Conventional technology]

Conventionally, two or more laser light sources are provided to irradiate a plurality of independent original spots on an optical information recording medium (hereinafter referred to as an optical disk), and each light spot is reflected from the optical disk or transmitted by a light beam. , a configuration for independently obtaining focus, traveking position iσ shift signals, information signals, etc. is disclosed in Japanese Patent Application Laid-Open No. 5A-103004,
As described in Japanese Unexamined Patent Publication No. 56-163531, there is a configuration in which multiple light beams reflected or transmitted through a single-source disk are spatially separated and a separate photodetection system is provided for each source beam. It had been done.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, it is necessary to provide separate photodetection systems for each of the plurality of light beams, which is a major problem in reducing the number of parts and downsizing the optical head.

An object of the present invention is to provide an optical head capable of independently detecting each signal from a plurality of reflected light beams using the same photodetector, in order to downsize and simplify the optical head. .

Means for Solving Problem c] The above object is to superimpose a high-frequency single frequency signal on the drive current of a semiconductor laser that emits at least one light beam among a plurality of light beams incident on the same photodetector. K to do
Therefore, the light intensity is periodically varied, and a signal component having a waveform that is amplitude-modulated from a carrier signal having the same frequency as the high-frequency signal that fluctuates the laser light intensity is separated from the output signal from the photodetector side. This is achieved by providing a demodulating circuit and a circuit that subtracts a signal having an amplitude proportional to the demodulated signal from the low frequency component of the original output signal.

[Effect]

As mentioned above, when at least one of the plurality of light beams incident on the same photodetector is periodically varied in light intensity using a high-frequency signal, passes through the optical disk, and enters the photodetector, The output signal includes a carrier wave having the same frequency as the frequency of one periodic light amount fluctuation, and a signal component whose amplitude is modulated by a signal obtained when the light beam is reflected or transmitted through the optical disk.

Therefore, as mentioned above, by providing a circuit that separates and detects this amplitude modulation component in the one-dimensional detection system and further demodulates the modulation signal by AM detection, the light beam whose light amount changes periodically can reflect or pass through the optical disk. It is possible to detect the focus, tracking position shift signal, information signal, etc. obtained when In addition, by providing a subtraction circuit that subtracts a signal with an appropriate amplitude proportional to the signal obtained by K from the low-frequency component signal of the output signal of the photodetector, it is possible to calculate the amount of light in one period. Various signals obtained when an unperturbed light beam reflects or passes through an optical disk can also be detected.

As described in 5 above, by periodically varying the light intensity of the light beam using a high-frequency signal, the signals from the optical disk contained in a plurality of original beams can be separately detected using the same photodetector.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure is a configuration diagram of an optical system and a circuit system for explaining one embodiment of the present invention. 1a and 1b are semiconductor laser light sources, and a laser drive circuit 30a.

30b emits light beams A 50a, 50b. 2a.

2b is a collimating lens, 3 is an optical element used to combine the two light beams SOA and SOB, such as 11-fumirror, 4 is a polarizing beam splitter, and 5 is 4
A half-wave plate, 6 an objective lens, and 7 a detection lens. Further, 10 is an optical disk, and 20 is a photodetector. The configuration of the above optical system and circuit system is as follows.

It has almost the same configuration as a conventional two-light source optical head.

On the other hand, the oscillation circuit 31. bypass filter 40,
Low pass filter 41. AM detection circuit 42. Amplifier 42
A signal separation/demodulation circuit 45 consisting of subtractor 44 and subtractor 44 is a newly provided circuit in the present invention.

The laser drive circuit 30a has a single frequency fo (for example, 20MHz to 50MHz) that is sufficiently high compared to the frequency band of the information signal recorded on the oscillator circuit 31 and the optical disk 10.
The intensity of the light beam 50a emitted from the semiconductor laser 1a is as follows.

As shown in FIG. 2(a), the average strength v11 changes periodically with respect to time t. (Hereinafter, this will be referred to as the light beam of channel 1.) On the other hand, since the semiconductor laser 1b is driven by direct current, the light beam 50b has a constant light intensity I2 as shown in FIG. 2(b). keep. (Hereinafter, this will be referred to as the channel 2 light beam.) When the channel 1 and channel 2 light beams are focused on the optical disk 10 and reflected, each beam is recorded on the optical disk 10. information signal or
Each party beam is subjected to intensity modulation or single phase modulation completely independently depending on the positional deviation in the focus direction and tracking direction of the condensed spot of each party beam with respect to the recording track of the information signal. This modulation component.

It is detected as an electrical signal by the photodetector 20.

Now, the average strength factor 1 amplitude A frequency f. After reflecting off the optical disk 10, the light beam of channel 1 whose light intensity periodically changes at
Then, V+ (t) can be expressed as a linear expression.

V+(tl = +-(Jl(t)・IA Cor(2
πfot)+11j= Kl −A−Ul (tl −
Cot (2π-f, t) + + -It -Ul
(t) (1) However, as described above, Ul(t) is the signal of the intensity or phase modulation component received when the optical beam of channel 1 reflects the optical disk 10,
Kl is a proportionality constant.

On the other hand, when the light beam of channel 2, which maintains a constant intensity 2, enters the photodetector 20 after reflecting off the optical disk 10, like the light beam of channel 1, the detected signal is V2 (1). + + is expressed by K as shown in the linear equation.

Vz(t) = K2- I2- U2 (+ri
−(2 square, [J2(tl is [Jl(t)
Similarly, the intensity received by the light beam of channel 2 when it is reflected from the optical disk 10.

or a signal of a phase modulation component, and k is a proportionality constant.

Therefore, as in the embodiment of FIG.
When the two light beams of channel 2 are simultaneously incident on the same photodetector 20 and photoelectrically converted.

The output signal V (tl is the signal obtained by linearly adding the signal V1(t) of channel 1 calculated using equation (1) and the signal Vz(t) of channel 2 calculated using equation (2). become.

Namely.

v(tl = V+(t) + Vz(t) = Kl・
A-Ul(+riCOt (2πft)+Kl・ENG1・U
l(2・I2・U2(t) at t1+
(3) Figure 3(a) shows an example of the output signal V(t) obtained by equation (3).The output signal 60 obtained by equation (3) V(t) is expressed as (1 ) channel 1 signal 61 (Fig. 3(b)) and channel 2 signal 62 (Fig. 3(c)) caused by V2(t) of 0) equation. It has a waveform that is added. Further, as shown in equation (1), the signal 61 is a carrier wave signal with a frequency f, a signal 63a (Fig. 3(d)) whose amplitude is modulated by the signal U1 (tl) of channel 1, and a signal (h(t)). It has a waveform in which a signal 63b (FIG. 3(e)) having an amplitude proportional to itself is added.Therefore, as shown in FIG. The spectrum 73b of the signal 63b having an amplitude proportional to the signal Ul(t) of channel 1 and the signal Uz of channel 2
Spectrum 72 of signal 62 with amplitude proportional to (t)
A spectrum 74 obtained by adding the line ff1K appears, and a spectrum 75a of a signal 65a obtained by amplitude modulating a carrier signal with a frequency of 1° with the signal Ul(t) on the high frequency side appears as a sideband of the spectrum of the carrier signal. .

From the above phenomenon, the output signal 60, the modulation signal U1(t) obtained by the channel 1 light beam from the optical disk IO, and the modulation signal U2(t) obtained from the optical disk 10 by the channel 2 light beam are each independently detected. for.

The photodetector 20 is provided with a signal separation and demodulation circuit 45 as shown in FIG. The operation of the signal separation and demodulation circuit 45 will be explained below with reference to FIG. FIG. 5 is an extracted diagram of the signal separation and demodulation circuit 45 shown in FIG.

From the output signal 60 sent from the photodetector 20, a signal 63a having a high frequency spectrum 73a is extracted by the bypass filter 40. As mentioned above, the signal 63a has a frequency f. Since the carrier signal of has a waveform whose amplitude is modulated by the signal U+ (t) of channel 1,
The AM detection circuit 42 can demodulate the signal 65b having an amplitude proportional to Ul(t).

On the other hand, a signal 64 having a spectrum 74 is also extracted from the output signal 60 by the low-pass filter 41 . As mentioned above, this signal is the channel 1 signal UI(t
) has a waveform in which a signal 65b with an amplitude proportional to K and a signal 62 with an amplitude proportional to channel 2 signal U2(t) are linearly added. Therefore, the output signal of the AM detection circuit 42 and the signal 64 extracted by the low-pass filter 41 are connected to amplifiers 45a and 4 with appropriate amplification factors, respectively.
3b and then subtracted by the subtracter 44,
By removing the signal component 63b having an amplitude proportional to Ul(f) included in the signal 64, the channel 20 signal U2(
A signal 62 can be extracted with an amplitude proportional to t). That is, the bypass filter 40. having a function as described above. Low pass filter 41. AM detection circuit 42
．． Channel 1. When the light beams of each channel 2 reflect off the optical disk 10, each light beam is intensity-modulated or phase-modulated completely independently, and a signal 0 is detected by the photodetector 20.
1(t) and U2(1) can be detected completely independently from the same photodetector 20.

Note that in this embodiment, the amplification factors of the amplifiers asa and a5b are fixed to a suitable combination of values.

In order to facilitate adjustment, the relative ratio of the amplification factors of each amplifier may be made variable.

FIG. 6 shows one embodiment thereof.

A signal separation and demodulation circuit 45 as shown in FIG. 6 is provided on the output side of the photodetector 2o of the optical system as shown in FIG. First, only the semiconductor laser 1a is turned on so that only the signal 61 of channel 1, which is calculated by V+(t) in equation (1), is added to the output signal 60 of the photodetector 20. Then, by moving the variable resistor 46, the amplitude of the signal output from the AM detection circuit 42, passed through the amplifier 43a, and inputted to the subtracter 44' is adjusted.
Make sure that the output signal from 4 becomes zero. By adjusting like this.

Lohas filter 41. After passing through the amplifier 43b, the subtracter 4
Channel 1 signal U included in the signal input to 4
+ a signal component whose amplitude is proportional to (t), and a bypass filter 40. AM detection circuit 42. Through amplifier 45a.

Since the signal whose amplitude is proportional to the signal U+(t) input to the subtracter 44 completely matches, the output signal of the subtracter 44 is.

A signal whose amplitude is proportional to channel 2 signal IJ2(t) can be correctly reproduced. Further, in addition to the embodiment shown in FIG. 6, for example, even in a configuration in which the amplification factor itself of the amplifier is made variable, adjustment is possible using exactly the same principle.

In the above embodiment, the number of semiconductor laser light sources is 2 (r!A), but of course, even if there are more light sources, separate detection of each signal is possible in the same way.In such a case, each semiconductor laser By superimposing signals of different frequencies on the drive current with a sufficiently wider interval than the frequency band of the recording signal of the optical disk 10, the amount of light is varied, and the detector side detects the amplitude of the carrier wave of each corresponding frequency. If separate signal separation and demodulation circuits 45 each equipped with a bandpass filter for separating and detecting modulated components are provided, signals of a plurality of light beams can be generated from one photodetector using the same operating principle as described above. Can be detected completely independently.

Note 1: A normal optical head generates focus and tracking servo signals from the reflected light from the optical disc.

To detect information signals, etc., one reflected light beam is divided into two
Photoelectric conversion is performed using two or more photodetectors or a multi-divided photodetector, and each of the obtained signals is subjected to arithmetic processing. Even in such a case, the light intensity of one of the two light beams can be varied using a high-frequency signal, and each photodetector can be
By separately providing signal separation and demodulation circuits 45 (not shown in the figure) and processing their output signals, it is possible to detect the focus, tracking servo signal, information signal, etc. of each of the two light beams completely independently. can.

FIG. 7 shows, as an example of the above configuration, a configuration in which the focus of the light spot irradiated on the original disk, the tracking servo signal, and the information signal are obtained by calculating the output signals of four sets of photodetectors. FIG. 2 is a configuration diagram showing an example. The same parts as in FIG. 1 are given the same reference numerals. The reflected light from the optical disk 10 is divided into two by the half mirror 8, one of which is irradiated onto the two-split photodetector 20a 17c by the detection lens 7a, and the other is
The knife edge 9 is removed, and the light is focused onto the two-split photodetector 20b by the detection lens 7b. Two-split photodetector 20a
The two output signals of are.

By subtraction, a tracking servo signal of the optical spot is output, and by addition, an information signal is obtained. Moreover, the two output signals of the two-divided source detector 20b are
By being subtracted, a focus servo signal for the optical spot is output. Even in an optical head having such a configuration, as shown in FIG.

By providing a separate signal separation and demodulation circuit 45 of the present invention, one for each output of the photodetector, two laser light channels 1. Focus and tracking servo signals for each channel 2 output signal.

Each information signal can be detected completely independently.

〔Effect of the invention〕

According to the present invention, each beam is focused by a set of photodetectors from the reflected or transmitted light from the optical disc of the plurality of light beams by reflecting or transmitting the optical disc.

Since each pole signal, such as tracking servo signals and information signals, can be detected completely independently, it is possible to reduce the number of components and simplify the size of an optical head that has multiple semiconductor laser light sources and irradiates multiple light spots independently onto an optical disk. It has a big effect.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram illustrating an embodiment of the present invention. Fig. 2 is an explanatory diagram showing the temporal change in the emission intensity of the semiconductor laser, Fig. 3 is an explanatory diagram showing an example of the waveform of the output signal of the photodetector, and Fig. 4 is an illustration of the frequency of the output signal. Fig. 5 is an explanatory diagram without showing the components, and Fig. 6 is a schematic diagram without showing the main parts of the embodiment shown in Fig. 1. FIG. 3 is a schematic diagram showing the main parts of another embodiment of the present invention. FIG. 7 is a block diagram illustrating another embodiment of the present invention. 1a, 1b--semiconductor laser light source, 30a,
50b-,, V-the drive circuit, 31... oscillation circuit, 40... bypass filter, 4+... low pass filter, 42... AM detection circuit. 44... Subtractor, 45... Signal separation and demodulation circuit.

Claims (1)

[Claims] 1. At least two or more semiconductor laser light sources, a focusing optical system that focuses mutually independent light beams emitted from each of the semiconductor laser light sources onto an optical information recording medium, and one of the semiconductor laser light sources. , an optical information recording/reproducing apparatus comprising a photodetector arranged such that reflected light beams from the optical information recording medium of light beams emitted from at least two or more light sources are incident together; Among the semiconductor laser light sources that emit a reflected light beam that enters the device, at least one semiconductor laser light source has an emission light intensity that is sufficiently higher than the frequency band of the information signal recorded on the optical information recording medium. A focus obtained when each light beam emitted from each of the semiconductor lasers is reflected or transmitted through the optical information recording medium based on the output signal of the photodetector and periodically varied by one high-frequency signal;
1. An optical information recording/reproducing apparatus characterized by comprising a signal separating/demodulating means for obtaining a tracking positional deviation signal and an information signal completely independently for each of the light beams.