JPS6114573B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention uses a converged light beam to FM-modulate information such as audio signals and video signals on a recording medium and record the information bit by bit at high density. The present invention relates to an optical recording/reproducing device for reproducing the signal, and particularly to a device for improving the reduction in S/N of the reproduced signal due to dirt, dust, etc. adhering to the recording medium.

Conventionally, in order to record information at high density, a light beam is focused into a minute spot (for example, 1 μm in diameter).
There is an apparatus for optically recording and reproducing by irradiating a recording material. In the device, information such as audio signals and video signals is used to improve the S/N of the reproduced signal.
Alternatively, FM modulation is often performed due to the properties of the recording material, and recording methods include bit-by-bit recording using the light transmittance or light reflectance of the recording material; In most cases, the recording material is deposited on a transparent disk. In the device described above, which narrows the optical spot to about 1 μm in diameter and records FM-modulated high-frequency signals bit by bit at high density, the size of one bit recorded on the recording material is at least 1 μm. Even microscopic dirt and dust, which are as small as 1μ and floating in the air, adhere to a recording medium and are reproduced as impulsive noise during reproduction, resulting in a reduction in S/N. However, even if the dirt or dust adheres to the recording medium, the dirt or dust adhering to the recording area exhibiting properties equivalent to their optical properties during reproduction does not appear in the reproduction signal as noise. For example, in an optical recording/reproducing device that records information bit by bit by using the magnitude of the light transmittance of a recording material and reads out a signal depending on the magnitude of the amount of light transmitted through the recording medium, a recording portion with a low light transmittance,
Dirt and dusty areas with low light transmittance (most dust and debris are light-blocking properties) exhibit optically equivalent properties during playback, so
Dirt and dust attached to the recording area with low light transmittance are not detected as noise after FM demodulation.

FIG. 1 shows an example of a conventional optical recording/reproducing device. A light source 11 such as a laser generates a light beam a. Reference numeral 12 denotes an optical modulator that uses, for example, Bragg reflection caused by ultrasonic waves, and the light beam a is divided into the zero-order light b and the first order light according to the electrical signal input to the terminal I.
It is divided into the following light d. That is, during recording, the optical modulator irradiates the recording site of the recording material with the total amount (100%) of the light beam a as zero-order light b. Also, when reproducing an unrecorded area or a recorded signal, for example, about 10% of the total amount of light beam a becomes 0th order light b, and the remaining about 90% becomes 1st order light d.
10% of the light has the function of irradiating the recording material. 13
is a slit, which allows only the 0th-order light b to pass through.
A projection lens 14 magnifies the light beam b and projects it onto the objective lens 17. A total reflection mirror 15 changes the optical path of the light beam b. This total reflection mirror rotates slightly around the axis x in the direction of the arrow. As a result, the light beam is swung in the direction of the arrow X and is held so as to be irradiated onto the information track 19. 1
A beam splitter 6 changes the optical path of the light c reflected on the information track 19 as shown in the figure. 17
is an objective lens, for example, a microscope objective lens is used. The light b incident on the objective lens 17 is focused to a minute spot (for example, 1 μm) and is irradiated onto the information track 19 at a point P. Reference numeral 18 denotes an objective lens driving device for keeping the distance between the objective lens 17 and point P on the information track 19 constant.
Move up and down in the direction of the arrow y. Reference numeral 19 indicates an information track recorded on the recording material. 20, 21
is a photodetector which detects the transmitted light d of the information track 19, reproduces the recorded signal, and compares the amount of received light incident on each photodetector 20, 21 to detect the minute light spot. It has a function of determining whether P is accurately irradiated onto the information track 19.

Its functions will be explained below with reference to FIG. In FIG. 1, reference numerals 22 and 23 are amplifiers for the photodetector 2.
The output signals of 0 and 21 are respectively amplified. A differential amplifier 24 calculates and amplifies the difference between the outputs of the amplifiers 22 and 23. Therefore, a signal is generated at the terminal J which indicates how much the minute light spot P has shifted in the direction of the arrow X with respect to the information track 19. This signal causes the total reflection mirror driving device 25 to slightly rotate the total reflection mirror in the direction of the arrow around the axis
Control so that the light is irradiated upward (tracking control). Reference numeral 25 denotes a total reflection mirror drive device which has the function of rotating the total reflection mirror around the axis x in the direction of the arrow by the output signal of the differential amplifier 24, and uses a device based on the principle of a galvanometer, for example. The light c reflected by the information track 19 is reflected by the beam splitter 16 and sent to a pair of photodetectors 2.
6,27. The irradiation position of this reflected light c on the photodetectors 26 and 27 is determined by the objective lens 17.
and moves in the direction of arrow Y according to the distance from point P on the information track 19. For example, in the configuration shown in FIG. 1, as the distance between the objective lens 17 and point P approaches, the irradiation position of the reflected light on the photodetector surface changes in the direction of the photodetector 27, as shown by c'. Moving. 28 is a device that slightly moves the pair of photodetectors 26 and 27 in the Y direction. Thereby, when the distance between the objective lens 17 and the point P is at a desired position, the amount of light received by the photodetectors 26 and 27 can be set to be equal to each other. 29 and 30 are the photodetectors 2;
An amplifier 31 is a differential amplifier for amplifying the outputs of the amplifiers 6 and 27, respectively, and the difference between the outputs of the amplifiers 29 and 30 is taken and amplified. Therefore, when the distance between the objective lens 17 and the recording material is at a desired value, the output of the differential amplifier can be made zero. 32 is a drive circuit for driving the objective lens 18. If the objective lens driving device 18 drives the objective lens 17 so that the output of the differential amplifier 31 is always zero, the distance between the objective lens 17 and the point P can be adjusted regardless of the unevenness of the recording material or the displacement due to warping. It can be held constant, that is, the focus can be controlled.

In FIG. 1, information (input signals) such as audio signals and video signals is input from terminal K during recording. 33 is an FM modulator, and the input signal from terminal K is FM modulated. 34 is an optical modulator drive circuit, and according to the output signal from the FM modulator 34,
As described above, the optical modulator outputs from the terminal I a drive signal for dividing the light beam a into the zero-order light b and the first-order light c. On the other hand, during reproduction, as described above, a weak continuous zero-order light b, which is approximately 10% of the total light intensity of the light beam a, is generated by the optical modulator (reading light). The recording signal on the information track 19 is reproduced on the photodetectors 20 and 21 by the readout light. 35
is an amplifier which sums and amplifies the outputs of the photodetectors 20 and 21. Therefore, at the terminal L, a reproduced signal of the recorded signal on the information track 19 is obtained. A limiter 36 keeps the amplitude of the reproduced signal constant. Reference numeral 37 denotes an FM modulator, by demodulating the FM modulated reproduction signal, information such as an audio signal or a video signal input from terminal K can be obtained from terminal M. In No. 38, a material that becomes sensitive to strong light (for example, the amount of light when the total amount of light beam a is focused to about 1 μ) and exhibits light-blocking properties is deposited on a transparent disc-shaped base. It is a recording medium.

In view of the above-mentioned prior art, the present invention provides an S/
In order to improve Length) 1 of the FM modulated signal so that it can be recorded for a longer time.
Provide a device that changes the duty ratio during the cycle (for example, the length of the recorded area with low light transmittance is 70%, and the length of the unrecorded area with high light transmittance is 30%), and adheres to the recording medium. The purpose is to prevent the S/N of recording/reproducing signals from decreasing due to dirt, dust, or scratches.

The details of the present invention will be explained below together with the embodiments shown in FIGS. 4, 5, and 10, but before that, examples of improvements that led to the present invention will be explained. Figure 2 is a block diagram showing an improved example in which the duty ratio during one cycle of the FM modulator output signal is shifted from 50% by using a monostable multivibrator, and Figure 3 is the output of each part in Figure 2. FIG. 3 is a diagram showing changes in signals and light amount. The device shown in FIG. 2 is a replacement for those shown in FIG.
The output from terminal Q in the figure is input to terminal I in FIG. Figure 3 is a waveform diagram of each part of Figure 2.
In the figure, an audio signal, a video signal, etc. to be recorded are input from a terminal N. Reference numeral 51 indicates an FM modulator, and its output signal is shown in FIG. 3a. Reference numeral 54 indicates a monostable multivibrator, which is triggered by the falling edge of the FM modulator output signal and generates a single pulse with a constant time width (t ₀ seconds). FIG. 3b shows the signal of the single pulse. Reference numeral 52 in FIG. 2 indicates an OR circuit, which takes the logical sum of the FM modulator output and the single pulse. FIG. 3c shows the output signal of the OR circuit 52. Reference numeral 53 in FIG. 2 indicates an optical modulator drive circuit, and the output from terminal Q is the first
The signal is input to 12 optical modulators in the figure. d in FIG. 3 shows a change in the amount of zero-order light (b in FIG. 1), which is generated from the output signal of the OR circuit. Here the third
The direction of arrow Y in d in the figure is the direction in which the amount of light increases.
The method for changing the duty ratio of the FM modulated signal by adding a single pulse of a fixed time to the FM modulator output signal and the change in the amount of zero-order light at that time have been described above.

FIG. 4 shows the improved example shown in FIG.
This is an embodiment of the present invention showing an example in which the shift ratio of the duty ratio during one cycle of an FM modulated signal is changed according to the amplitude of the input voltage to the FM modulator, and FIG. 5 is similar to FIG. FIG. 3 is a diagram showing changes in the output signals and light amount of each part of FIG. In addition, the fourth
The device shown in the figure is an alternative to the devices 33 and 34 in FIG. 1, and the output from the terminal U in FIG. 4 is input to the terminal I in FIG. 1. In FIG. 4, 51' indicates an FM modulator, and its output signal is shown in FIG. 5a. 54'
is a monostable multivibrator which is triggered by the falling edge of the FM modulator output signal and generates a single pulse with a different time width depending on the voltage of the information 55 input from the terminal T. FIG. 5b shows the output of the monostable multivibrator. That is, when the voltage of the signal input from terminal T is high (when the frequency of the FM modulator output signal is high), the generated single pulse is short (t ₁ second), and when the voltage of the signal is low (when the frequency of the FM modulator output signal is high), the generated single pulse is short (t 1 second). When the frequency of the device output signal is low), the time width of the single pulse generated becomes long (t ₂ seconds)
The monostable multivibrator 54 operates as follows. an output b of the monostable multivibrator;
The OR circuit 52' calculates the logical sum with the FM modulator output a, and the output c of the OR circuit is used as the optical modulator drive circuit 5.
3' to obtain an output signal from terminal U. (3'c). The output signal from the terminal U drives the 12 optical modulators shown in FIG. 1 to obtain a change in the amount of 0th-order light (d in FIG. 5) (b in FIG. 1). In FIG. 3d, the direction of arrow Y is the direction in which the amount of light increases. The method for changing the duty ratio of the FM modulated signal by changing the time width of a single pulse added to the FM modulator output signal and the change in the amount of zero-order light using the FM modulator input voltage has been described above.

Note that in order to obtain a single pulse with a time width that varies depending on the input voltage as shown in Figure 5b, the time constant of a capacitor or resistor, etc. that determines the time width of a single pulse, or the power supply voltage, etc. must be adjusted to the input voltage. You can change it accordingly. Generally, a variable capacitance diode or the like whose capacitance changes depending on the voltage can be used.

Figure 6 shows an improved example in which the duty ratio during one cycle of the FM modulator output signal is shifted from 50% by using a delay circuit, and Figure 7 shows the output signals and light intensity of each part of Figure 6. FIG. The device shown in FIG. 6 is similar to FIGS. 2 and 4 in place of the devices 33 and 34 in FIG. 1, and the output from terminal S in FIG. 6 is input to terminal I in FIG. In FIG. 6, audio signals, video signals, etc. to be recorded are input from terminal R.
60 is an FM modulator, the output signal of which is indicated by a in FIG. Reference numeral 61 indicates a delay circuit, and its output signal is shown in FIG. 7b. That is, the delay circuit delays the output signal of the FM modulator for a certain period of time (t ₀
(seconds) Create a signal with the same waveform as the delayed FM modulator output signal. 62 is the OR circuit and the FM
The output signal a of the modulator 60 and the signal b from the delay circuit 61 are logically summed to obtain an output signal c. Reference numeral 63 in FIG. 4 is an optical modulator driving circuit, and the output obtained from the terminal S is applied to the optical modulator 12 in FIG. FIG. 5 d shows the change in the amount of the zero-order light (FIG. 1 b) generated by the signal from the terminal S. In d of FIG. 5, arrow Y indicates the direction of increasing light intensity. Note that if a delay line or a combination of a CR integration circuit and a waveform shaping circuit is used for the delay circuit 61 in FIG. 6, the method will operate more stably than the method using the monostable multivibrator.

Next, the effects obtained when the circuits shown in FIGS. 2, 4, and 6 are added to the configuration shown in FIG. 1 will be explained while comparing with the conventional example. FIG. 8 is a diagram showing an example of the output signals of each part and the recording state of the recording material during recording and reproduction in the conventional optical recording/reproducing apparatus of FIG. 1. Figure 8 a, b,
c is a diagram for explaining the time of recording, and the horizontal axes are written in correspondence with each other. Further, c, d, and e in FIG. 6 are diagrams for explaining reproduction, and are drawn corresponding to the horizontal axis. a in Figure 8 is the FM modulator (first
The figure which showed the output signal of 33) of a figure. FIG. 8b is a diagram showing changes in the amount of the zero-order light (b in FIG. 1), and the direction of arrow Y is the direction in which the amount of light increases. FIG. 8c shows a cross section of one information track of the recording medium in the track direction, 68 is a disc-shaped base made of a transparent material, 69 is vapor deposited on the base 68, and is exposed to light and becomes black. It is a recording material. Reference numerals 70 and 71 indicate the recording portions recorded on the recording material, which have light blocking properties. 7
2, 73 indicates the unrecorded portion of the recording material,
It has a light-transmitting property. Reference numerals 75 and 76 indicate the above-mentioned dirt and dust having a light-blocking property or scratches having a light-scattering property attached to the recording material.
It shows bits smaller than recording bits such as 70 and 72. d in FIG. 8 shows the pair of photodetectors (the first one) when the track in c in FIG.
This shows the output of the sum of 20 and 21) in the figure. d in Figure 8
, the direction of the arrow Y is the direction in which the amount of detected light increases, for example, the recording portions 70 and 71 and the recording portions 75 and 75,
The dirt and dust portion 76 exhibits light-blocking properties, making it difficult for light to pass therethrough, and the output of the photodetector is also small. On the other hand, since the unrecorded portions 72 and 73 exhibit a light-transmitting property, the amount of light transmitted therethrough increases, and the output of the photodetector also increases. 8 shows the output of the limiter (36 in FIG. 1), that is, the reproduced signal. Looking at e in Fig. 8, we can see that the above-mentioned 75 dirt and dust adhered to the recording area (70, 71 in c in Fig. 8) which exhibits properties optically equivalent to dirt and dust during playback. Although it is not affected by
The dirt and dust of 76 adhering to the unrecorded area (72, 73 in Figure 8c) that exhibits the opposite property to the above property generates impulsive noise such as 78, which reduces the S/N of the reproduced signal. I can see it getting worse. 7
Reference numerals 7 and 78 indicate noise appearing in the reproduced signal due to the dirt, dust, etc.

9 and 10, as explained in FIGS. 2 to 7, by shifting the duty ratio of the FM modulated signal from 50%, that is,
FIG. 3 is a diagram illustrating how the S/N of a reproduced signal is improved according to the present invention. Note that each of the figures a to e in FIG. 9 is the same as each figure a to e in FIG.
77' corresponds to 68 to 77 in FIG. 8, respectively. a in FIG. 9 is the FM modulator output signal,
Create a change in the amount of light as shown in b. In other words, compared to b in Fig. 8, the time when the amount of 0th-order light is large is t ₀
seconds longer, and the duty ratio during one cycle has changed. FIG. 9c is a diagram showing a cross section of the recording medium recorded with the zero-order light shown in FIG. 9b in the recording track direction. Compared to the recording regions 70 and 71 shown in FIG. 8C, the recording regions 70' and 71' shown in FIG. 9C are longer _l0 . 9d shows the pair of photodetectors (20 and 2 in FIG. 1) when the track in FIG. 9c is read out from the transmitted light.
1) shows the output of the sum. 9. e in FIG. 9 shows the output of the limiter (36 in FIG. 1), that is, the reproduced signal. As can be seen by comparing e in Fig. 9 and e in Fig. 8, as shown in c in Fig. 9, a portion (7
0', 71' blackened part) is lengthened and recorded.
The impulsive noise caused by the dirt and dust, etc., as shown in 77' of e in Fig. 7, is reduced,
The S/N of the reproduced signal is improved.

Compared to the improved example shown in FIG. 9, FIG. 10 is an explanatory diagram of the present invention for recording and reproducing when the configurations shown in FIGS. 4 and 5 are used. FIG. 7 is a diagram illustrating how the S/N of the reproduced signal is improved even more than in the improved example by shifting. Note that a in Figure 10
Each of the figures from ~e corresponds to each of figures a to e in Figure 9, and 68'' to 77'' in Figure 10 correspond to 68' to 77' in Figure 9, so they represent the same thing. A detailed explanation will be omitted, and only the improvements will be explained. In c of FIG. 9, the length of the recording part is 70', 7
1' is always one constant width _l0 longer than the original length (70, 71 in c in FIG. 8), regardless of the frequency of the FM modulator output. However, in c of Figure 10,
The width increases depending on the frequency of the FM modulator output.
It changes as l ₁ , l ₂ , l ₃ . In other words, when the frequency of the FM modulator output is high, the length is also short, l ₁ ,
When the frequency of the FM modulator output is low, the width becomes longer l ₂ , and as a result, there are more blackened parts 70'' and 71'' in c of Fig. 10 than in c of Fig. 9. . As mentioned above, dirt and dust attached to the recording area will not appear as noise in the playback signal, so
As can be seen by comparing e in Figure 9 and e in Figure 10, when recording as in c in Figure 10, the impulsive noise generated in the reproduced signal due to the dirt and dust is further reduced compared to the improved example. As a result, the S/N of the basic signal becomes even better.

In addition, to demodulate an FM modulation output signal whose duty ratio during one cycle is not 50%, use a general FM
Although demodulation can be performed using a modulator, FIG. 11 shows an example of an FM demodulator. 70 is a delay circuit, 71 is a balance modulator, and 72 is a low-pass filter. A terminal V provides an FM modulated signal, and a terminal W provides an FM demodulated signal. The band of the low-pass filter is the band of the modulated signal (information).

As described above, the present invention, when reproducing a signal recorded bit by bit, increases the length of the part that exhibits the same characteristics as dirt or dust according to its original length (by changing the duty ratio). This has the effect of significantly reducing the influence of impulsive noise caused by dust and scratches.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical recording/reproducing apparatus according to a conventional embodiment, and FIGS. 2 to 7 are block circuit diagrams and waveform diagrams of main parts of optical recording/reproducing apparatuses according to different embodiments of the present invention. FIG. 8 is an explanatory diagram of signal recording and reproducing in a conventional device, FIGS. 9 and 10 are explanatory diagrams of signal recording and reproducing in different embodiments of the present invention, and FIG. 11 is an example of a circuit for reproducing signals recorded according to the present invention. FIG. 11... Laser light source, 12... Optical modulator, 17
...Objective lens, 19...Information track, 20,
21...Photodetector, 33...FM modulator, 34...
... Optical modulator drive circuit, 51 ... FM modulator, 52
...OR circuit, 54...mono multi.

Claims (1)

[Claims] 1. In an optical recording and reproducing device that records an electrical information signal bit by bit on a recording medium using a converged light beam and reproduces the recorded signal using the converged light beam, dust on the recording medium is The length of a part (bit) on a recording medium that exhibits optically equivalent properties during playback to dust, dirt, etc.
An optical recording/reproducing device having means for recording a part longer than the original length thereof and changing the length according to the original length.