JPS6046914B2 - information recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an information recording device for recording signals on a recording medium, and particularly aims to reduce cross-modulation spectral components of carrier and audio that occur during reproduction.

Currently, for example, in video disk reproduction, cross-modulation (hereinafter referred to as I-M) of a video signal carrier and an audio signal carrier has become a problem as a factor that significantly reduces the S/N.

First, an example of video disc recording will be explained.

The master disk used as a recording medium is a glass disc with a diameter of about 30 crn coated with a positive photoresist with a thickness of 150 n7 TL, which is irradiated with argon laser or helium-cadmium laser light focused to a diameter of about 0.6 μm. Then, by developing it, pits are formed. The width of the pit is 0.6μ, and the track spacing is 1.6μ.
It is m. Experiments are also underway to use low-melting point metals or semiconductor materials instead of photo-1 resist.
In order to record using such bits, the recorded information can be subjected to signal processing as shown in FIG.

The video signal (4) of the video signal A, the audio signal 1B, and the audio signal C as recorded information is passed through a pre-emphasis circuit 1 and an FM modulator 2 to a center frequency ω. = Video FM with 8M pressure and frequency deviation of approximately 1.5MHz
The audio signal 1B and the audio signal ■C are converted into a carrier wave a, and the audio signal 1B and the audio signal ■C are respectively converted to a carrier wave frequency ω, I=2.
3M pressure, ω, ■=2.8MHz circumference pot number deviation ±100KH
The adder 7 adds the video FM carrier a and the audio FM carriers B and c, and the limiter 8 converts the signal into a rectangular wave. Therefore, a multiplexed signal whose repetition frequency is the same as that of the video FM carrier wave a and whose duty change corresponds to that of the audio FM carrier wave is input to the optical modulator 9 made of an electro-optic crystal. In this case, in consideration of linearity and cross-modulation, the addition ratio of the video FM carrier wave a and the audio FM carrier wave is set to about 10:1 in terms of amplitude. The bit on the disk is a recording of this rectangular wave. FIG. 2 shows an outline of the recording device.

10 is a rotatably mounted disk, 11 is a mirror that changes the optical path of the output of the optical modulator 9 toward the disk 10, and 12 is a focusing device disposed in the optical path between the mirror 11 and the disk 10 direction. The position is controlled by a servo device 13 to keep the focusing error within ±0.1 μm with respect to the vertical movement of the master as the disk 10 rotates, and exposes the disk 10 to form the bits. .

The optical modulator 9 turns on and off the laser beam 9A from the light source using the rectangular wave signal from the emitter 8, and uses the mirror 11 and the focusing device as described above to form a bit when the laser beam is on. Exposure is performed via 12.

In this way, the 8rS-4HZ video signal carrier and 2
When a 3MHZ audio signal carrier is recorded and played back, the C/N [carrier to noise ratio] is approximately 60 (11
B can be obtained throughout the entire circumference, but with respect to 1-M, conventionally only about 35C1B can be obtained. Therefore, when a normal image is recorded, heat corresponding to the audio/voice signal appears on the playback screen, significantly reducing the image quality. The amount of I-M generated due to bit duty-asyrrlmetry can be approximately calculated using the following equation.

However, Δ: amount of deviation from pit asymmetry, b
: Audio carrier level during recording, JO: Zero-order Bessel function, J1: -Next Bessel function Figure 3 shows the video signal carrier of 8M1Iz and 2.3MHZ.
The spectrum is shown when only the audio signal carrier of is subjected to Duty-Cycle modulation.

Theoretical calculations show that the IM component becomes zero when the bit duty is perfect. However, in reality, it is extremely difficult to maintain 40 dB due to distortion caused by the modulation circuit, exposure and development conditions on the recording medium, nonlinear components during readout, and other factors. In order to investigate the nonlinear state in the exposure and development process to the recording medium, we electrically controlled the asymmetry of the electrical signal supplied to the optical modulator 9, set conditions that were approximately duty-cycle after development, and conducted a recording/reproduction experiment. However, the result was that it was extremely difficult to reduce the I-M generation amount to 40 dB or less.

In addition, in order to investigate the S/N deterioration due to the amount of I-M generation, recording was performed without the audio signal carrier, and the reproduced image was almost the same as that of a broadcast video tape recorder. Additionally, a drift compensation servo for the optical modulator is essential when recording with such a system.

Without compensation, the extinction ratio cannot be obtained within a few minutes and recording becomes impossible. Therefore, various drift compensation servos have been considered, and one example will be explained next. FIG. 4 shows a principle diagram of operating point control, where the light modulation curve is I.

Sin2 [π/2 (■n/V+)], where IO is the maximum transmission amplitude of light, ■o is the input signal voltage, and ■usually is the half-wavelength voltage of the optical modulation element. When input signals of equal amplitude with different polarities [pulse P1, pulse P2] are input to operating points Hl and h2 located at symmetrical positions of the optical modulation characteristics, an output signal of equal amplitude [pulse P However, if the operating points Hl and h2 move from the symmetrical position due to temperature drift etc., the amplitude of the output signal will be different. Therefore, pulse P"1 and pulse P"2 By comparing the amplitudes of , it is possible to determine the moving direction of the operating points Hl and h2, and to control the operating points Hl and h2. However, this method uses AM modulation of a television signal etc. to optically record information. For example, this can be done by applying the pulses Pl and P2 shown in FIG. This is because, in the case of an FM signal, the electrical signal is a pulse train near the carrier frequency, and the pulse train is required as information even within the vertical synchronization interval.

The present invention has been made in view of the above-mentioned problems, and is an information recording system capable of compensating for the drift of an optical modulator in optical recording of FM signals and keeping the amount of I-M generation to a minimum. It provides equipment.

An embodiment of the present invention will be described below with reference to the drawings.

14 is a laser beam 14A from a light source according to an information signal.
An optical modulator 15 is a half mirror, which branches the output of the optical modulator 14 into a light beam 14B for information recording and a light beam 14C for drift monitoring.

16 is a photoelectric conversion element consisting of a PIN diode or an avalanche diode, and 17 and 18 are first and second photoelectric conversion elements.
As shown in FIG. 3, the center frequency of the first narrow band filter 17 is (ωo-ωs), and the center frequency of the second narrow band filter 18 is (ωo-ωs). ωo+ω,), and the band is both number 1
Approximately 0.00KHz is desirable.

A differential amplifier 19 inputs the outputs of the narrowband filters 17 and 18 via amplifiers 20 and 21, and detects a difference signal between the two.

22 is a light modulation element in the optical modulator 14 (not shown)
The drive circuit of the differential amplifier 19 via the amplifier 23
Using the output as a detection signal, a servo is applied so that the difference signal decreases, for example, to zero, and the operating point of the optical modulator 14 is controlled, and the information signal source 24 is brought to the controlled operating point of the optical modulator 14. Input information signal.

Note that when the recorded image is a single black screen, the signal after detecting the signal passed through the narrow band filters 17 and 18 is only the spectrum corresponding to the synchronization signal of the recorded image, so the narrow band filters 17 and 18 are One of the narrowband filters 1
However, in the case of color pars or television screens, which are the original purpose of recording, the influence of the recorded image on the detection outputs of narrowband filters 17 and 18 is negligible, so the detection output of narrowband filters 17 and 18 becomes large. The operating point of the optical modulator 14 can be controlled by applying servo so that the difference between the detection outputs of the bandpass filters 17 and 18 is always zero.

However, the information signal from the information signal source 24 supplied to the optical modulator 14 via the drive circuit 22 is subjected to a limiter so that the operating point of the optical modulator 14 does not exceed the half-wave voltage (■+). It is necessary to keep it. In addition, the narrow band filters 17 and 18
Since one output always increases and the other always decreases, it is necessary to apply servo within this range. When the detection output difference is zero, it means that the high-frequency component and the low-frequency component of the cross-modulation component are equal, and at this time, the total cross-modulation component is the minimum with respect to the entire recorded information spectrum.

Therefore, the optical modulator 14 is adjusted so that the detection output difference is minimized.
By recording while maintaining the operating point of , it is possible to record in a state where cross-modulation components are minimized. In the embodiment shown in FIG. 5, the servo of the optical modulator 14 is applied by detecting the difference between the two narrowband spectra on the low-frequency side and the high-frequency side.
As will be described in detail later, the same effect can be obtained by detecting the narrow band spectrum on the low frequency side and applying a servo so that this signal is always minimized.

In this case, as the narrow band spectrum on the low-frequency side, it is desirable to select a spectrum whose spectral components are least sensitive (ωo-ωs) depending on the recorded image. Regarding the servo to maintain the minimum signal value,
There are already many people. The law has been announced. By using the drift compensation device for the optical modulator 14 configured in this way, it is possible to prevent the shift of the optical modulation bias due to temperature drift of the optical modulation element over a long period of time, and it is possible to always maintain a signal with a constant spectonorum. It becomes possible to record.

Figures 6A and 6B are spectrum observation diagrams of information signals;
is an audio signal carrier, CVl and CV2 are a primary carrier and a secondary carrier of a video carrier, C and CH are I-M low-frequency components and high-frequency components. The information signal in FIG. 6a is a spectrum at a position where the operating bias position of the optical modulator 14 has theoretically the best symmetry (the position where the secondary carrier component is minimum). From this state, the optical modulator 14 generated by slightly moving the operating bias position while operating the drift compensation servo of the optical modulator 14
By utilizing the modulation distortion of , the spectrum signal shown in FIG. 6b can be obtained. Here, in Figure 6b, the lower frequency component CO of I●M is -8 dB1 higher frequency component C than in Figure 6a.
H becomes +2C1 manager, secondary carrier CV2 is about 30d
It can be seen that B is increasing. Figures 7A, b, and c show the modulation spectrum of the recording light and the M of the recording/reproducing lens, respectively.
The TF characteristics and the spectrum of the reproduced signal are shown.

Note that FIG. 7a is a spectrum distribution corresponding to FIG. 6b. Further, FIG. 7b shows the recording lens N. A=0.5 and reproduction lens N. A schematic diagram of a composite MTF characteristic with A=0.4 is shown, and FIG. 7c shows the spectrum distribution when a disc recorded as described above is optically reproduced after development. In comparison with Fig. 7a, the high frequency component CH of I-M
It can be seen that this decreases due to the MTF characteristics of the lens. As a result of such experiments, the operating point of the optical modulator 14 was moved slightly beyond the minimum position of the secondary carrier CV9 component of the monitoring light beam 14c, and the primary carrier C
The low frequency component CL is created in a state where an imbalance is caused between the high frequency component CH and the low frequency component CL of the cross-modulation component of the Vl and the audio signal.
By applying the servo so that the is minimized, the low frequency component of I-M shown as CL in Fig. 7c is compared with the carrier component! It has now become possible to constantly suppress -40c1B or more. Also, compared to the low-frequency components of I and M in the conventional recording method shown by the broken line A in FIG.
-M's multi-region component CL is? There is a difference of B or more. Note that the influence on the reproduced image by using the modulation distortion of the optical modulator 14 depends on the amount of modulation distortion and the MT of the recording and reproduction lenses.
It was found that by taking into consideration the amount of decrease in F, there was no adverse effect. As explained above, according to the present invention, it is possible to constantly suppress the cross-modulation component between the audio signal carrier and the video carrier to -40 dB or more in "information recording", which could conventionally be suppressed only to about -35 dB. This can significantly improve the reproduced image.

[Brief explanation of drawings]

Figures 1 and 2 are principle diagrams of the signal processing circuit and recording device, Figure 3 is an explanatory diagram of spectrum components, Figure 4 is an explanatory diagram of conventional optical modulator operating point control, and Figure 5 is an illustration of the present invention. FIGS. 6A, b and 7A, b, and c are diagrams illustrating the signal spectrum and spectrum changes through the recording and reproducing system. 14... Optical modulator, 14A... Luminous flux from a light source, 14B... Luminous flux for information recording, 14
c... Monitor light flux, 15... Half mirror [branching means], 17, 18... Narrow band filter, 19... Differential amplifier, 22... ... Drive circuit, 24 ... Information signal source, C, ...
Audio signal carrier, CVl...primary carrier of video carrier wave, CV2...secondary carrier of video carrier wave, CL...low frequency component of cross modulation component, CH...
・High frequency component of cross-modulation component.

Claims (1)

[Scope of Claims] 1. In an information recording device that performs FM modulation on a video signal and an audio signal, adds them together, and records an amplitude-limited information signal on a recording medium, a light beam from a light source is applied to the information signal. and a branching means for dispersing the output of the optical modulator into a light beam for information recording and a light beam for monitoring. It consists of a narrowband filter circuit for detecting the cross-modulation frequency component of the FM-modulated video signal and audio signal, and a supply means for supplying the detection signal of this filter circuit to the bias circuit of the optical modulator. An information recording device comprising a servo device that controls the optical modulator to maintain a constant operating point using a signal. 2 The servo device includes a high-frequency filter circuit that detects a cross-modulation frequency component corresponding to the sum frequency of the FM-modulated video signal and audio signal, and a high-frequency filter circuit that detects a cross-modulation frequency component corresponding to the difference frequency between them. 2. The information recording apparatus according to claim 1, further comprising a low-pass filter circuit for detecting a signal, and controlling the difference component of these detection signals to zero. 3 The servo device moves the monitor light beam slightly beyond the minimum position of the secondary carrier component of the video signal carrier wave, causing an imbalance in the high-frequency component and low-frequency component of the cross-modulation component of the video signal carrier wave and the audio signal carrier wave. In this state, the operating point of the optical modulator is controlled so that the low frequency component is minimized, and the recording lens is used to record the high frequency component near the resolution limit spatial frequency. An information recording device according to claim 1.