JP3070125B2 - Optical disk recording and playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk apparatus for optically recording and reproducing information, and more particularly to a signal recording and reproducing method.

[0002]

2. Description of the Related Art A conventional information signal of an optical disc is recorded on an optical disk in an optically identifiable form of unevenness, light and dark pits, and phase change pit magneto-optical domains.

The lengths of the pits and domains have been determined by the characteristics of the optical system for reproducing the pits and domains. That is, the reproduction capability of the optical system is determined by the NA (numerical aperture) of the objective lens and the wavelength λ of the laser used, and is expressed by using the spatial frequency, which is the reciprocal of the pitch of the grating that can resolve the resolution capability. A spatial frequency that cannot be resolved is called a cutoff spatial frequency Fc. Under the above conditions, normally, Fc = 2NA / λ (Equation 1).

Therefore, hitherto, the pitch length of the pits and domains representing information has not been made shorter than the grating pitch determined by the cutoff spatial frequency.

[0005]

Therefore, the recording density of information is limited by the resolution of the optical system. An object of the present invention is to further reduce the pitch of pits and domains representing information than the limit grating pitch determined by the resolution of the conventional optical system, and to further improve the recording density compared to the related art.

[0006]

In order to achieve the above object, in advance vinegar for this
Guide grooves with a specific periodic structure optically in the direction of pot travel
Provided, recording information pits and domains with a pitch shorter than the limit grating pitch determined by the resolution of the optical system along the said guide groove. Alternatively, the guide groove and the information pit may be formed at the same time. The signal detected by the optical system is multiplied by a signal synchronized with the guide groove.

[0007]

When a light spot is applied to the guide groove, the information pits and the domains, the light is reflected by the spatial resolution of the guide grooves, the information pits and the domains due to optical interference such as diffraction and Kerr effect. Light returns to the objective lens. At this time, the angle of reflection from the disk corresponds to the spatial frequency. The objective lens allows reflected light from the disc to pass through within an angle determined by the numerical aperture of the lens. That is, from the standpoint of signal transmission, the objective lens is a low-pass filter.

For example, taking a light and dark pit as an example, the reflection characteristic of the guide groove is F1 (x) and the reflection characteristic of the information pit is F2.
Assuming that (x), the total reflection characteristic when both the guide groove and the information pit exist are F1 (x) · F2 (x).
Assuming that the spatial frequency component of F1 is H1 (y) and the spatial frequency component of F2 is H2 (y), the spatial frequency component H of the reflected light is
(F) is a convolution of H1 and H2. Now, when the guide groove is changed in the depth direction by a sine wave having a constant period p1 as shown in FIG. 1, the spatial frequency component of the groove is only a single frequency y1 (y1 is a cut-off spatial frequency or more). I have nothing. Y2 of information pit (y2 is cut-off spatial frequency
Frequency components of more and larger) is shifted to the frequency of y1 + y2 and y1-y2 by convolution. Since the spatial frequency component of y1 + y2 does not pass through the pass band of the lens, only the frequency component of y1-y2 passes through the lens. The amount of reflected light passing through the lens is guided to one photodetector in the same manner as in a conventional optical disc, converted into a photocurrent, and converted into an electric signal. This electric signal has f1-f2 corresponding to y1-y2 determined from the linear velocity and the spatial frequency.
Only the signal frequency component of Therefore, when this electric signal is electrically multiplied by a sine wave having a frequency of f1, a signal component having a frequency of f2 and a signal component having a frequency of 2 · f1-f2 are obtained. When the former signal component and the latter signal component are separated by electric signal processing using a frequency, a phase, or the like, only a signal component having an electric frequency corresponding to the spatial frequency of the information pit can be extracted. As a result, information pits and domains having a higher frequency than the cutoff spatial frequency determined by the optical system that could not be reproduced conventionally can be reproduced, and high-density recording can be performed. Further, by modulating the groove at a spatial frequency higher than the cutoff spatial frequency of the optical system, it is possible to solve various problems which have conventionally occurred according to the thermal recording principle of the optical disk. For example, when recording is repeatedly performed on a phase change medium as a recording medium, the phase change film becomes fluid and the quality of a reproduced signal deteriorates, so that the number of repetitions is limited. On the other hand, by modulating the grooves as described above, the number of repetitions can be improved by increasing the resistance to fluidization between the base and the fluidization. Also, since the magneto-optical recording film has better heat conductivity than other recording films, the pit shape and its position change due to thermal interference from the front and rear domains. However, according to this guide groove, the effective heat transmission distance can be extended, and the effect can be reduced.

[0009]

FIG. 1 shows the concept of the present invention. The guide groove 1 is changed sinusoidally in the depth direction at a constant period p1.
The recording film 5 is provided on the guide groove by vapor deposition or the like. The light and dark pits 2-1 to 2-9 recorded thereon slightly change around the average pit pitch p2. p2 is shorter than p1. The irradiation spot diameter Ws3 formed on the disk surface by the objective lens 6 (for example, when the intensity 4 is 1
/ E * 2) is twice or more p1. The linear velocity is v [mm / s] and the spatial frequency is y [lines / m
m], the electric frequency f [Hz] is f = y ·
There is a relationship v. Since there is a linear relationship between y and f at the same linear velocity, the following description will be made using electric frequencies for simplicity. FIG. 2 shows the signal band of the present invention. As a signal, a so-called video disk in which an NTSC television signal is directly FM-modulated and recorded on an optical disk is taken as an example. Conventionally, the modulation frequency of the shining chip of the video signal corresponds to 7.6 MHz, the white peak frequency corresponds to 9.3 MHz, and the 3.8 MHz video signal band is FM-modulated. The FM signal occupied band is about 7.5 MHz. At this time, the cutoff frequency of the optical system is 12 MHz. This time, the frequency of the guide groove is selected to be 12 MHz. FM
A signal having a modulation center frequency of 18 MHz and an FM signal occupied band of 11 MHz is recorded in the form of light and shade pits. Then, when a light spot is irradiated on the disk to detect the transmitted light from the objective lens, the photoelectrically converted signal has an FM modulation center frequency of 18 MHz to 12 MHz, that is, 6 MHz, and becomes an FM wave having an occupied band of 11 MHz. When this is multiplied by a 12 MHz sine wave signal synchronized with the frequency of the guide groove, an FM signal in a band of 11 MHz with a center frequency of FM modulation of 18 MHz and a signal component in an occupied band of 11 MHz centering on 6 MHz are generated. Where 12MHz
A required FM signal can be detected by using a filter that cuts off the signal. Here, in order to obtain an electrically synchronized signal of 12 MHz, this signal cannot be optically resolved, so that a pit having a spatial frequency corresponding to half of 6 MHz is formed simultaneously with the guide groove. When creating 12 MHz, the frequency is doubled from the 6 MHz pit. At this time 1
Since the phase of 2 MHz is not determined, two series of signals whose phases are shifted by π radians are generated, and one of the series may be selected based on the result of multiplication of these signals and the detection signal. At this time, a pilot signal for determining this may be added to the information modulation signal.

FIG. 3 is a block diagram of a specific recording / reproducing apparatus. A video signal 11 photographed by the camera 10 has a center frequency of 18 MHz and a modulation signal band of 1 by an FM modulator 12.
The signal is converted into an FM signal of 1 MHz, input to a modulator 13 for driving a laser light source 14, and modulates the light source 14. Although not described in detail in this apparatus, an automatic focus servo and tracking are performed in the same manner as in a normal optical disk apparatus, and a light beam 17 emitted from a light source is condensed by an objective lens 6 into a light spot 17.
Is guided along the guide groove to perform recording and reproduction. Disk 16
Is rotated by the rotation drive mechanism 18. In the signal reproduction, the light spot 17 is guided to the guide groove 1 as in the recording, and the recorded pits are read out along the light spot 17. Objective lens 6
The reflected light flux that has passed through is separated into incident light and reflected light by the light beam separating element 19, and the reflected light 18 is made incident on the photodetector 20. The electric signal photoelectrically converted by the photodetector 20 has a signal component of 11 MHz as a band. This signal is input to a synchronization signal detector 21 for detecting a signal synchronized with the modulation frequency of the guide groove of 12 MHz. When the synchronization signal is detected, the timing is transmitted to the synchronization reference signal generator, and the same signal synchronized with the modulation frequency of the groove of 12 MHz is transmitted. A synchronization reference signal 23 which is a frequency signal is generated. The signal 23 is electrically operated by the multiplier 24 by the photoelectrically converted electric signal, and only the necessary FM signal is extracted by the bandpass filter 25, and the video signal 11 is extracted by the FM demodulator 26.
Demodulated to This can be put into a receiver to watch a higher quality television image than before.

In another embodiment, a 12M synchronous with a guide groove is used.
Instead of electrically multiplying the Hz signal, the laser may be intensity-modulated during reproduction. For this purpose, the signal 23 from the synchronizing signal generator is input to the modulator 13, and the reproduced light of the laser is modulated by the same frequency synchronized with the modulation frequency of the groove of 12 MHz. As a result, the signal from the photodetector has the same signal band components as those appearing after the multiplier 24 shown in the above embodiment. In this embodiment, the multiplier 24 becomes unnecessary.

[0012]

As described above, the FM modulation signal band of 7.5 M, which was conventionally limited by the optical limit frequency of 12 MHz.
Even if the same optical system is used for the Hz, it can be expanded to 11 MHz and a video signal having a signal band about 1.5 times that of the conventional one can be recorded on an optical disc and reproduced. As a result, a conventional video disc can record and reproduce an HDTV in combination with an EDTV and other functions.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between spots, grooves, and pits representing the concept of the present invention.

FIG. 2 is a diagram showing a relationship on a frequency axis of a signal according to the present invention.

FIG. 3 is a block diagram of a recording / reproducing apparatus.

[Explanation of symbols]

 1 ... Annai groove, 5 ... Recording film.

Claims (7)

(57) [Claims] 1. A reproduction optical system having Fc = 2NA / λ on a disk- shaped recording medium having a guide groove whose shape changes in the depth direction at a constant period.
Means for recording an information recording mark having a first spatial frequency component higher than a cut-off spatial frequency Fc defined by a formula (NA: numerical aperture of an objective lens, λ: light frequency), and the disc-shaped recording medium Of the reflected light of the light spot
Spatial frequency components are converted to frequency component
And a second frequency component below the cut-off spatial frequency
Means for shifting the reflected light shifted to the second spatial frequency component
Converting into an electrical signal corresponding to the second spatial frequency component,
The electric signal is converted to an electric signal corresponding to the first spatial frequency component.
An optical disk recording / reproducing apparatus , comprising: an electric signal converting means for shifting to an air signal . 2. The electric signal conversion means according to claim 1 , wherein said electric signal and said detection signal are recorded using an electric signal synchronized with a period determined by said constant period of said guide groove generated by said constant period structure and a linear velocity on said disk. 2. The optical disk recording / reproducing apparatus according to claim 1, wherein the information signal is reproduced. 3. A reproduction optical system having Fc = 2NA / λ (N) on a disc-shaped recording medium having a guide groove whose optical characteristics change at a constant cycle.
A: means for recording an information recording mark having a first spatial frequency component higher than the cut-off spatial frequency Fc defined by the formula of A: numerical aperture of the objective lens, λ: frequency of light, a light source, and an output from the light source An objective lens for irradiating a light spot on the disc-shaped recording medium by condensing a light beam to be emitted and extracting reflected light of the light spot, and reproducing the information on the disc-shaped recording medium, Means for modulating the light source with an electric signal synchronized with a frequency corresponding to a certain cycle. 4. An information having a first spatial frequency component higher than a cut-off spatial frequency Fc defined by a formula of Fc = 2NA / λ (NA: numerical aperture of an objective lens, λ: frequency of light) of a reproducing optical system. The first frequency component of the reflected light of the light spot applied to the disc-shaped recording medium having the guide groove whose optical characteristics change at a constant period in which
An optical system that passes only a second spatial frequency component equal to or lower than the cutoff spatial frequency shifted by a wave number component, and converts the passed light into an electric signal corresponding to the second spatial frequency component, and converts the electric signal into an electric signal. And an electric signal converting means for shifting the signal to an electric signal corresponding to the first spatial frequency component. 5. Information having a first spatial frequency component higher than a cut-off spatial frequency Fc defined by a formula of Fc = 2NA / λ (NA: numerical aperture of an objective lens, λ: frequency of light) of a reproducing optical system. the but the spatial frequency component of the reflected light of the light spot irradiated on a disc-shaped recording medium having a guide groove in which the optical characteristics are changed in the recorded fixed period, the fixed said first spatial frequency component
An optical converting means for shifting the frequency component corresponding to the cycle to the cut-off spatial frequency or less, converting the reflected light having the spatial frequency component shifted into an electric signal, and converting the electric signal into the first space. An optical signal reproducing device having an electric signal converting means for shifting to an electric signal corresponding to a frequency component. 6. Information having a first spatial frequency component higher than a cut-off spatial frequency Fc defined by a formula of Fc = 2NA / λ (NA: numerical aperture of an objective lens, λ: frequency of light) of a reproducing optical system. Irradiating a light spot on a groove of a disk-shaped recording medium whose optical characteristics change at a constant period in which is held, shifts a spatial frequency component of the reflected light to a frequency component corresponding to the constant period, and The information reproducing method includes: shifting the light to pass through a reproducing optical system; converting the light passing therethrough into an electric signal; and shifting the electric signal to an electric signal corresponding to the first spatial frequency component. Method. 7. A groove whose optical characteristics change at a constant period, and Fc = 2NA / λ (NA: numerical aperture of an objective lens, λ:
Irradiating a light spot on a groove of a disc-shaped recording medium in which an information pit row corresponding to information having a first spatial frequency component higher than the cut-off spatial frequency Fc defined by the equation (light frequency) is formed. The spatial frequency component of the reflected light is shifted by a frequency component corresponding to the above-mentioned fixed period, shifted below the cut-off spatial frequency and passed through a reproducing optical system, and the passed light is converted into an electric signal. An information reproducing method comprising: shifting a signal to an electric signal corresponding to the first spatial frequency component.