JPS621125A - Optical disk recording and reproducing method - Google Patents

Abstract

PURPOSE:To improve the recording linear density, even when a conventional optical system or semiconductor laser is used, by representing the information by using plural kinds of marks having an equal length and each different shape, and recording and reproducing this mark on an optical disk recording medium. CONSTITUTION:When an output of comparators 15, 16 and an output of a D flip-flop are inputted to a logical circuit constituted by using AND circuits 27, 29 and NOR circuits 30, 31, signals of output terminals 36-39 are varied as shown by figures (N)-(Q). That is, by a waveform 9, an output of an AND circuit 28 becomes a high level as shown by a figure (O), and by a waveform 10, an output of the AND circuit 27 becomes a high level as shown by a figure (N), and by a waveform 11, an output of the AND circuit 29 becomes a high level as shown by a figure (P), and by a waveform 12, an output of the NOR circuit 30 becomes a high level as shown by a figure (Q). In this way, four kinds of different mark shapes provided on an optical disk can be detected, and an information quantity of 2 bits can be assigned with regard to one mark, therefore, a linear density of the optical disk can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical disc recording and reproducing method in which information is recorded and reproduced by irradiating a focused laser beam onto an optical disc.

2. Description of the Related Art A method of recording and reproducing information by providing a recording thin film on the surface of an optical disk and irradiating it with focused laser light has been developed, and is expected to be used as a large-capacity optical memory.

Signals on an optical disc are recorded as irregularities or bulges in a recording thin film, or changes in reflectance.

These changes cause changes in the amount of light reflected from the optical disk, and by detecting these changes, signals are reproduced.

In such optical discs, the numerical aperture (hereinafter referred to as IN, A) of the objective lens is used to focus the laser beam onto the optical disc.
The size of the smallest mark that can be recorded and reproduced is determined by the wavelength λ of the laser beam and the wavelength λ of the laser beam. Therefore, it is necessary to increase the recording surface density of the optical disc or shorten λ. However, if N and A are made too large, the depth of focus becomes too large and the tolerance for optical disc tilt and thickness unevenness decreases, so currently N and A
, up to about 0.6 are used for optical disc applications. Furthermore, the wavelength of semiconductor lasers used in optical discs is currently around 780n1, and lasers with wavelengths shorter than that have not yet been available for practical use. It has been difficult to improve the linear density using the method that expresses this.

SUMMARY OF THE INVENTION The present invention aims to eliminate the above-mentioned conventional drawbacks, and aims to provide an optical disk recording and reproducing method that can improve recording linear density even when using conventional optical systems and semiconductor lasers.

Means for Solving the Problems In order to solve the above-mentioned problems, the optical disc recording and reproducing method of the present invention expresses information using a plurality of types of marks of equal length and different shapes, and uses the marks to record information on an optical disc recording medium. This is what is recorded and played back on.

Effect According to the above method, when N types of marks (N is an integer of 2 or more) with different shapes provided at regular intervals on an optical disk recording medium are reproduced with a narrowed laser beam, each mark causes a rise or Different playback waveforms such as falling edges can be obtained.

Therefore, by detecting the characteristics of this reproduced waveform, N
The type of mark can be determined, and more information can be obtained than just the presence or absence of a mark.

EXAMPLE Hereinafter, an example of the present invention will be described based on FIGS. 1 to 7.

FIG. 1 is an explanatory diagram of a mark shape on an optical disk as an optical disk recording medium used in an optical disk recording and reproducing method according to an embodiment of the present invention. In FIG. 1, S is the rotational direction of the optical disk, and the circumferential direction is and the king indicates the radial direction. L indicates a fixed period in which marks are provided. FIG. 1 shows an nth track and an (n+1)th track. Marks 1 to 3 represent information, which have the same length and different shapes, and are either recorded on the optical disk in advance, or by driving a laser with a recording pulse as shown in FIG. Recording is performed on a recording medium *m<for example, Te Ox, X<2> on an optical disc. That is, in order to record marks 1 to 3 as shown in FIG. 1, the laser is driven using recording pulses 5 to 7 as shown in FIG. 2, respectively, as recording pulses. For example, to record a series of marks as shown in FIG. 3(A), the laser is driven with a series of pulses as shown in FIG. 3(B). To record marks at regular intervals,
A driving laser pulse is driven at a constant period T. Here, the relationship between L and T is, if the linear velocity of the optical disc is ■, then L-
It is V-T.

In the above example, in order to allocate 2 bits of information to one mark, as in mark 4 in FIG.
Even if there is no mark between L, it is considered as one mark. In other words, consider four types of marks: marks 1, 2, 3, and 4. For this purpose, it is important that the marks on the optical disk are recorded and reproduced in synchronized periodic fashion. In order to record and play back signals synchronously in this way,
A synchronization signal is required, but in this embodiment, a mark for obtaining a synchronization signal is recorded on the optical disc in advance.
Reproduction is performed using a laser different from the recording/reproduction laser, and a synchronization signal is obtained.

Next, let us consider the case where the marks recorded as described above are reproduced as a series of marks as shown in Fig. 4 <A) using a focused laser beam. In Figure 4<A),
(L△) indicates a laser beam used for recording and reproduction, and R indicates the rotation direction of the optical disc. Figure 4 (B) 9~
Reference numeral 12 indicates a reproduced waveform when marks 1 to 4 in FIG. 2A are reproduced.

In this way, the rising and falling edges of the reproduced waveforms 9 to 12 change depending on the shape of the mark. Therefore, the reproduced waveforms 9 to 1
By detecting the inclination of mark 2, it is possible to detect which mark among marks 1 to 4 it is.

A circuit for detecting this waveform and reproducing the signal is shown in FIG. In FIG. 5, 13 to 16 are comparators, each having a transfer characteristic shown in FIGS. 6(A) to 6(D). 17 to 19 are R-8 flip 70 blocks, 20 is a D flip 70 block, 21.22 is an integrator, 23 and 24 are peak hold circuits, 25 is a differential amplifier, 26 is a sample hold circuit, and 21 to 29 are AND circuit, 30 and 31 are NOR circuits, 32 to 34 are inverters, 35 is an input terminal, 3
6 to 39 are output terminals.

The case where the signal of FIG. 7(C), which is a waveform obtained by reproducing FIG. 4(A), is input to the input terminal 35 of FIG. 5 will be explained based on the time chart shown in FIG. 7. Figure 7 (A)
is a synchronization signal, obtained in the manner described above. FIG. 7(B) is a clear signal that initializes the R-8 flip 70 knobs 17 to 19, integrators 21 to 22, and peak hold circuits 23 and 24 in FIG. That is, the outputs Q of the R-S flip-flops 17 to 19, the outputs of the integrators 21 and 22, and the outputs of the peak hold circuits 23 and 24 are brought to O level. Fig. 7(C) shows the signal of Fig. 4(8) which is the signal reproduced from the mark on the optical disk shown in Fig. 4(A>). Fig. 7(D) and (E) Outputs of RS flip-flops 17 and 18, respectively, FIG. 7 (F) (G)
are the outputs of the peak hold circuits 23 and 24, Fig. 7 (H)
is the output of the differential amplifier 25, and FIG. 7(r) is the output of the sample hole loop 26. The output of the differential amplifier 25 is sampled and held at the rising edge of O.

Figure 7 (J) and (K) are comparators 15°1G, respectively.
7(L) is the output of the RS flip-flop 19, FIG. 7(M) is the output of the D flip 70 tube 2°, and FIG. 7(N) to (P) are the AND circuits 27 to 29, respectively. The output of FIG. 7 (Q) is the output of the NOR circuit 3o.

Next, the operation of the circuit shown in FIG. 5 will be explained with reference to FIG. The reproduced waveform as shown in Fig. 7(C) is the fifth
The signals are input to the input terminal 35 in the figure, and their levels are compared by comparators 13 and 14. The threshold levels of comparators 13 and 14 are shown in Fig. 6 (A) (B) 17)
Since the settings are as follows: Vl, V2 (Vt < V2) (7), the output of the comparator 13 rises, thereby setting the R-8 flip 70 knob 17,
Next, the output of the comparator 14 rises, and this rise resets the RS flip 70 knob 18. In this way, the R-S flip 70 knob 1 as shown in FIG. 7(D) is generated by the rise of the reproduced waveform input shown in FIG. 7(C).
7 outputs are obtained. Next, when the reproduced waveform falls and becomes smaller than the threshold level 2 of the comparator 14, the comparator 14 falls to the O level, and the R-8
Flip 70 knob 18 is set. Next, when the reproduced waveform becomes smaller than vl, the comparator 13 falls to the O level, thereby resetting the R-8 flip-flop 18. In this way, the output of the R-8 flip 70 tube 18 as shown in FIG. 7(E) is obtained. R-
The 8 flip-flops 17 and 18 are respectively shown in Fig. 7(C).
The output pulse width is changed depending on the rise and fall speed of the reproduced waveform. Therefore, the rise and fall of the reproduced waveform can be detected by the outputs of the R-8 flip 70 tabs 17 and 18 shown in FIGS. 7(D) and 7(E). R-8
The outputs of the seven lip-flops 17 and 18 pass through integrators 21 and 22 and peak hold circuits 23 and 24, respectively.
It is input to the differential amplifier 25. The output of this differential amplifier 25 is as shown in FIG. 7(H). The output of the differential amplifier 25 is input to the sample hold circuit 26 and latched at the rising edge of the clock. This situation is shown in FIG. 7<1). The output of the sample and hold circuit 26 is input to comparators 15 and 16. Comparator 15.1
6 has a transfer characteristic as shown in FIG. 6(C) ([)). Therefore, when the output of the sample and hold circuit 26 is input to the comparators 15 and 16, the output changes as shown in FIGS. 7(J) and 7(K). On the other hand, the R-8 flip-flop Otub 19 changes as shown in FIG. 7(L) by the outputs of the comparators 13 and 14. The output of the R-8 flip-flop 19 is latched into the D flip-flop 70 block 20 at the rising edge of the recovered clock. The situation is shown in FIG. 7(M). When the output of the D-flip 70 knob 20 is at high level, it indicates that marks 1 to 3 in FIG.
(actually there is no mark). As can be seen from the above explanation and FIG.
The output of the comparator Is, 16 of J) (K) and the output of the D flip 70 tube 20 of FIG. 7(M) are delayed by one clock. Marks 1 to 4 in FIG. 1 can be detected using the signals shown in FIGS. 7(J), 7(K), and 7(M). That is, as shown in FIG. 5, a logic circuit is constructed using AND circuits 27, 29 and NOR circuits 30, 31. A comparator 15.1 is added to such a logic circuit.
6 and the output of the D flip-flop 20, the signals at the output terminals 36 to 39 become as shown in FIG.
). That is, in waveform 9, the output of the AND circuit 28 becomes high level as shown in FIG. 7(0), in waveform 10, the output of the AND circuit 27 becomes high level as shown in FIG. 7(N), and in waveform 11. Now, AND circuit 29
The output of the NOR circuit 30 becomes high level as shown in FIG. 7 (P), and in waveform 12, the output of the NOR circuit 30 becomes high level as shown in FIG. 7 (<Q).

With this circuit configuration, it is possible to detect four different mark shapes provided on the optical disc, and it is possible to allocate 2 bits of information to each mark, improving the linear density of the optical disc. can be done.

In the above embodiment, for the sake of simplicity, the recording/reproduction synchronization signal was obtained from a signal provided in advance on the optical disc, but it goes without saying that the method for obtaining the synchronization signal is not limited to this method.

Effects of the Invention As described above, according to the present invention, the linear density of an optical disc can be improved, and its industrial utility value is extremely large.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a mark shape used in an optical disc recording/reproducing method in an embodiment of the present invention, FIG. 2 is a waveform diagram of a recording pulse applied to a laser drive circuit to record the mark shown in FIG. 1, and FIG. Figure 3 is an explanatory diagram of the relationship between the recording drive pulse and the mark recorded on the optical disc, Figure 4 is an explanatory diagram of the relationship between the mark recorded on the optical disc and the waveform that reproduced it, and Figure 5 is the reproduction diagram. A circuit diagram of a detection circuit for detecting the types of marks provided on an optical disk according to waveforms, Fig. 6 is an explanatory diagram of the characteristics of the comparator in the circuit, and Fig. 7 shows the operation of the circuit shown in Fig. 5. It is a time chart for explanation. 1 to 3...marks, 5 to 7...laser drive pulses,
9-11... Mark playback waveform agent Yoshihiro Morimoto Figure 1

Claims (1)

[Scope of Claims] 1. An optical disc recording and reproducing method in which information is expressed using multiple types of marks of equal length and different shapes, and the marks are recorded and reproduced on an optical disc recording medium. 2. A plurality of types of marks of equal length and different shapes are provided on an optical disc recording medium, and a focused laser beam is irradiated onto the optical disc recording medium, and the laser beam is diffracted by the marks on the optical disc recording medium. 2. The optical disc recording and reproducing method according to claim 1, wherein the signal is determined based on the rising and falling slopes of the reproduced signal waveform when the signal is reproduced by receiving the reflected light. 3. When recording marks representing signals by narrowing and irradiating a laser beam onto an optical disk recording medium, different mark shapes are recorded by keeping the recording laser power constant or increasing or decreasing the recording laser power during the recording period. An optical disc recording and reproducing method according to claim 1.