JPS61192036A - Optical disk and reproduction method for reference signal - Google Patents

Abstract

PURPOSE:To reduce the effect of the crosstalk produced between address signals and to attain correctly the reproduction of address signals, by providing an optical recording layer on a groove forming a recording track and also modulating the depth of the groove with (n) types of frequencies to record a reference signal shown by an n-notation code signal. CONSTITUTION:A photodetector 10 converts the reflected light into electric signals and delivers them. A preamplifier 11 amplifies the output signal of the photodetector 10 and obtains a reproduction signal (p). A BPF 12 has a center frequency f0 of a pass band and detects the component of the frequency f0 from the signal (p). While a BPF 13 has a center frequency f1 of a pass band and detects the component of the frequency f1 from the signal (p). A comparator 14 compares the detection signal (q) of the BPF 12 with the detection signal (r) of the BPF 13 and decides whether the signal (p) is equal to '0' or '1' of a code signal for reproduction of an address signal (s). The comparison of the component intensity is carried out between both frequencies f0 and f1 contained in the signal (p) and therefore it is satisfactory if a difference exists between the ratios of contents of those two frequency components. Thus the amplitude of modulation can be reduced for the depth of the groove and the crosstalk is reduced between adjacent grooves.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical disc and a method of reproducing a reference signal by irradiating the optical disc with a laser.

2. Description of the Related Art In recent years, many optical disk memories have been proposed in which various types of information are recorded and reproduced on a disk using laser light. That-
For example, as a recording and reproducing method to improve recording density and transfer rate, a groove is formed on the surface of an optical disk so that the cross section in the disk radial direction is V-shaped, and signals are recorded and reproduced using the slope of this V groove as a track. A method is proposed.

(Patent Application No. 58-175259 and Japanese Patent Application No. 59-363
(No. 38 Publication) FIG. 2 shows a radial cross section of an optical disc having a V-groove. In FIG. 2, 1 is a substrate, and a large number of V
It has a groove 2 and is provided with a recording thin film 3. Tracks provided on two adjacent slopes, such as A and B or C and D, are irradiated with two laser spots 4 and 5 as shown in FIG. By driving these lasers independently of each other, independent signals can be recorded using the two slopes as tracks. The recording thin film 3 is made of, for example, TeO (X1.1), and signals are recorded by changing the reflectance according to changes in laser power.

When reproducing a signal recorded as described above, two adjacent slopes are irradiated with a laser as the reproducing power in the same manner as during recording, and the signals of two tracks are simultaneously reproduced. During this playback, if the shape of the groove is optimized, crosstalk from adjacent slopes can be sufficiently suppressed by mainly receiving the ±1st-order diffracted light of the reflected light from the disc, and
It is possible to play back the signals of two tracks individually.

Further, in order to search for a target track on the disc, an address is expressed in binary code and recorded on the track in advance. The address signal is recorded by forming bits 6 with grooves varying in depth, as shown in FIG. ■A disc with grooves is made by cutting a metal master disc with a cutting needle in the shape of a 7, and then molding a base resin with a stamper using the stamper. Address pits are created by vibrating a cutting needle in accordance with the bit position when cutting a metal master.

The address signal can be reproduced by utilizing the fact that the intensity of the diffracted light reflected from the disk changes as the depth of the V-groove changes depending on the bit.

Problems to be Solved by the Invention In the conventional address recording system as described above, as shown in FIG. Since the mountain ridgelines α and β shared with track E are modulated, address bit crosstalk occurs in the reproduced signals of tracks B and E.

■A cross section of the grooved disc is shown in Figure 6. Let the track pitch be pt, the depth of the V-groove be d, and the angle of the V-groove be θ. ■The following shape is used as an example of the groove shape.

When θ, tan (y) = P t /d=4nHere, because of the address bit, ■If the depth of the groove changes by Δd, the track pitch changes by Δpt, then from the above equation, θ Δpt −−Δd tan(T) ÷2n・Δd ・・・・・・・・・ (1)
becomes. When the refractive index of the base material is n = 1.5, according to equation (1), the change in rib depth Δd is three times the track pitch pt.
changes. At this time, the peak of the change in the ridge line is JPt
Therefore, the change in depth is six times the change in depth Δd. Further, the change in the intensity of the reproduced signal due to the presence or absence of bits becomes maximum when Δd=λ/4. At this time, ΔPt-
3λ/4, and adjacent tracks have a track width (pt
=λ) will be lost. In particular, when addresses overlap in adjacent V-grooves as shown in FIG. 6, there is a high possibility that the address signal will be misread due to the influence of the adjacent bits.

In addition, to reduce crosstalk, the bit depth d
If +dd) is made smaller, the amount of change in the reproduced signal will also be smaller, which will increase the occurrence of errors due to noise and the like.

The present invention has been made in view of the above, and an object of the present invention is to provide an optical disc and an address recording/reproducing method that can reduce the influence of crosstalk between address signals and reproduce address signals without error.

Means for Solving the Problem In the groove constituting the recording track, a frequency f0 corresponds to "0" of a binary code signal representing an address value, and another frequency f1 corresponds to "1". An address signal is provided by modulating the depth of each groove.

When reproducing the address signal, the trough of the optical disc,
A first band pass filter (hereinafter abbreviated as BPF) extracts a signal component of frequency f0 from the reproduced signal obtained by irradiating a laser spot on the top of the beam and receiving the reflected light with a photodetector. ) and the 20th BPF that extracts the signal component of frequency f1, each BPF
A comparison circuit that compares the magnitude of the output signals of the two output signals determines whether the reproduced binary code signal is "0" or "1".

Function: In the optical disc according to the present invention, the address signal is recorded using two frequencies f01f1, and the magnitudes of the two frequency components are compared during reproduction, so the magnitude of the reproduced signal can be reduced, and the presence or absence of pits can be reduced. Compared to the method of determining based on the change in the magnitude of the reproduced signal, the change in the depth of the groove can be made smaller. Thereby, crosstalk to adjacent grooves can be reduced.

In addition, since the address signal is reproduced by comparing the magnitudes of the reproduced signals of the frequencies assigned to "0" and 1", even if crosstalk from adjacent grooves occurs, the tracked groove If the address signal of
can be played correctly.

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

FIG. 7 shows the format of the disc in this embodiment. In FIG. 7, 7 represents the outermost circumference of the disk, 8 the innermost circumference of the disk, and 9 the center hole. In a portion surrounded by the outermost periphery 7 and the innermost periphery 8 (range indicated by a in the figure), grooves are formed in a concentric or spiral shape. Also,
Part b represents an address area. To access the address area,
■The address signal is recorded by modulating the depth of the groove.

The address signal includes a code signal representing the address value indicating each V-groove, an address mark signal indicating the start point of the address area, an error correction code for detecting and correcting errors that occur when reproducing the code signal, a clock synchronization signal, etc. configured.

The address signal recorded in the address area of the optical disc as described above will be explained using FIG. 1. FIG. 1 shows the case where an address signal is recorded only at the V-groove opening of the nine openings A and C of the V-groove.

6b is an address converter, and the depth of the groove is modulated by making frequency f0 correspond to "on" of the code signal and frequency f1 to "1". Let fl>fo. Recording of one pit of the code signal If the period is T, the depth of the groove is modulated at the frequency f0 or fl every T period and a signal is recorded.

For example, when recording the address value "101..." at the V bay mouth in FIG. 1, the period T0
The depth of the groove is modulated at the frequency f1 during the period T2 and at the frequency f0 during the period T1.

Next, the case where address signals are recorded in adjacent grooves will be described with reference to FIG. In Figure 8,
Address signals are recorded in each of the consecutive V grooves, E, and E by the method described above. In FIG. 8, coarse diagonal lines represent grooves whose depth is modulated at frequency f0°, and fine diagonal lines represent grooves whose depth is modulated at frequency f. If the recording period of one bit of the code signal is Tk (k-o, 1.2...), then the address values of each V-groove shown in FIG. 8 are as follows.

In this way, when address signals overlap in adjacent V-grooves, the ridgeline α and the ridgeline β in Fig. 8 shift according to the frequencies recorded in the V-grooves on both sides. (The transition of the ridgeline is not depicted.) This edge line shift causes crosstalk between address signals, but according to the present invention, this edge line shift can be reduced as will be explained later.

A method for reproducing address signals from an optical disc on which address signals have been recorded as described above will be explained. 9th
The figure shows a block diagram of an address signal reproducing circuit in this embodiment. In FIG. 9, 10 is a photodetector, 11 is a preamplifier, and 12 is a center frequency f. BPF, 13 is the center frequency f.

14 is a comparison circuit, 16 is an address area detection circuit, 16 is an address demodulation circuit, and 17 is an output terminal.

For example, assume that a laser spot is irradiated onto track C in FIG. The reflected light of the laser spot is received by a photodetector 10.

The photodetector 10 converts the reflected light into an electrical signal and outputs it. The preamplifier 11 amplifies the output signal of the photodetector 10 to obtain a reproduced signal p. Laser spot is track C
As we move over the recorded frequencies f0 and fl
The frequency components included in the reproduced signal p change. B
The center frequency of the passband of PFl2 is f. This is a bandpass filter that detects the frequency f0 component from the reproduced signal p.

In addition, BPFl 3 is a bandpass filter whose passband center frequency is fl, and from the reproduced signal p to the frequency f1.
Detect the components of The comparison circuit 14 compares the magnitude of the detection signal q of BPFl2 and the detection signal r of BPFls,
It is determined whether the reproduced signal p is the code signal "0" or "1", and the address signal date is reproduced. The address area detection circuit 16 detects an address mark signal from the reproduced address signal B and sends out an address gate signal t indicating the address area. The address demodulation circuit 16 detects an address code signal and an error correction code from the reproduced address signal S according to the address gate signalization, detects and corrects an error in the address code, and reproduces the address value U of the lost track C. , is sent from the output terminal 17.

By the way, in the conventional method of recording a code signal using the difference in strength of the reproduced signal depending on the presence or absence of bits, the depth of the pit cannot be made shallow because the difference in strength must be large to some extent. Ta. On the other hand, as explained above, in the address reproducing method according to □ of the present invention, the two frequencies f0 included in the reproduced signal p
In order to compare the intensities of the and fl components, it is sufficient that there is a difference in the proportions of the two frequency components, and the intensity of the reproduced signal itself may be small. Therefore, the modulation amplitude of the groove depth can be reduced, and crosstalk to adjacent grooves can be reduced.

Furthermore, as shown in FIG. 8, the reproduced signal p includes crosstalk components between the address signal on the track C illuminated by the laser spot and the address signals on the adjacent tracks B and D. ing. However, in an optical disc using a groove, the address signals on the two slopes on one groove are the same, so it is only necessary to consider the track on the adjacent V groove (track B in this case) as a crosstalk component. For example, FIG. 10 shows the spectrum of the reproduced signal p when the laser spot illuminates the period T0 in FIG. 8. In Figure 10, 18 is the 9th
The pass band of BPFl2 in the figure is shown, and 19 shows the signal strength of its detection signal q (component of frequency f0). Similarly, 20 indicates the passband of the BPF 13, and 21 indicates the signal strength of the detection signal r (component of frequency f1).

In this case, the detection signal r represents code 1# recorded on track C and track D, and the detection signal q represents the crosstalk component of code 0# recorded on track B. In order to reproduce a correct code from a reproduced signal containing a crosstalk component in this way, it is sufficient that there is a difference between the detection signal r and the detection signal q. This required difference is determined by the S/N of the reproduction system, etc. Reducing the a-stoke component to a level that satisfies this can be easily reproduced by reducing the modulation amplitude as described above.

In addition, in the embodiment, ① a method of simultaneously reproducing the slopes on the groove side was explained, but the Mizumoto EA is not limited to this method. It can also be implemented when the cross-sectional shape of is not V-shaped but trapezoidal or the like.

In addition, address signals are recorded on the optical disk in advance,
Although we have explained the case of reproducing this, it is not limited to address signals; it is also possible to record n-ary code signals by using a binary code signal x and modulation signals of n different frequencies. It is.

Effects of the Invention According to the present invention, two address signals are placed on the groove of an optical disc.
one frequency f0. f1 is used for recording, and during reproduction, the address signal is reproduced by comparing the proportions of two frequency components included in the reproduced signal. Therefore, the modulation amplitude of the groove depth can be reduced, and the Crosstalk components can be reduced. By using an optical disk on which such addresses are recorded and an address reproducing method, it is possible to more accurately reproduce the address values of the six grooves, which is extremely useful in practice.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an address signal recording portion of an optical disc according to an embodiment of the present invention, FIG. 2 is a radial cross-sectional view of an optical disc having a V-groove, and FIG. 3 is a schematic diagram showing a laser spot. Fig. 4 is a perspective view showing a conventional address signal recording method, Fig. 5 is a sectional view showing changes in the ridgeline of the V groove,
FIG. 6 is a perspective view showing a conventional address signal recording portion, FIG. 7 is a format diagram of an optical disc in an embodiment of the present invention, and FIG. 8 is a perspective view showing an address signal recording portion in another embodiment of the present invention. , FIG. 9 is a block diagram showing an address signal reproducing circuit in one embodiment of the present invention, and FIG.
The figure is a diagram showing a spectrum of a reproduced signal in an embodiment of the present invention. 6b...Address modulation section, A99B, C...
・・■Groove. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure VX V groove V groove Figure 2 Figure 3 Figure 4 Figure 5 Figure W&6 Figure BCDEF Figure 7 Figure 8

Claims (2)

[Claims] (1) A groove constituting a recording track is formed on the disk, a recording layer for optical recording is provided on the groove, and
An optical disc characterized in that a reference signal expressed as an n-ary code signal is recorded by modulating the depth of the groove at n different frequencies. (2) Grooves constituting recording tracks are formed on the disk, a recording layer for optical recording is provided on the grooves, and the depth of the grooves is modulated at n different frequencies. Using an optical disk on which a reference signal expressed as an n-ary code signal is recorded, a focused laser spot is irradiated onto the track, the reflected light from the optical disk is received by a photodetector, and the reference signal on the track is detected. During reproduction, the reference signal of the corresponding track is obtained by comparing detected signals obtained by extracting frequency components corresponding to each code signal from the reproduced signal and selecting a code value with a large number of frequency components. Reference signal reproduction method.