JPH0419825A - Reproduction of optical information - Google Patents

Abstract

PURPOSE:To reproduce the optical information with high reliability even though the arranging intervals reduced among the information marks and the recording density of an optical information recording medium is increased by performing a digital operation to increase the contrast of a detection signal. CONSTITUTION:The clock signals C are produced in accordance with the discrete times ti-1, ti, ti+1... respectively on the basis of the detection time of a timing mark 3. Then an electric signal (b) is sampled by the clock signal, and a detection signal S(ti) is obtained according to each discrete time ti. Then an equation I is solved based on the detection values S(ti-1), S(ti), S(ti+1), S(ti+2)... with (n) defined as one or more integers, (k) as an interference coefficient which satisfies the conditions 0<k<1, and (a) as the number which satisfies 0<a<1 and a k respectively. Thus the presence or absence of an information mark is decided at the time ti. As a result, the arranging intervals can be reduced among the information marks and the interference of the noise component can be reduced.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for reproducing optical information.

[Prior Art] A light spot scans an information track of an optical information recording medium on which an information mark is formed at a predetermined period from a position a predetermined distance from the timing mark as a starting point at a predetermined scanning speed. A well-known method is to scan, detect physical changes in reflected light or transmitted light from an optical information recording medium due to the timing mark/information mark, and reproduce optical information depending on the presence or absence of the information mark.

Recently, attempts have been made to improve the recording density of such optical information recording media.

The first method of increasing the recording density of an optical information recording medium is to reduce the spacing between the information marks, second to reduce the spacing between the information tracks, and third to reduce the spacing between the information tracks and One possible method is to reduce the arrangement interval of information marks. Of these three methods, the second and third methods require changes from the specifications of the optical information recording medium itself and are difficult to implement easily. However, the first method can be easily realized by using a conventional optical information recording medium as is and simply changing the specifications for recording optical information.

However, although it is relatively easy to reduce the arrangement interval of the information marks, it is not necessarily easy to reduce the size of the information marks themselves or the diameter of the light spot for reproduction scanning accordingly.

When the arrangement interval of the information marks becomes smaller than the diameter of the light spot, when the light spot illuminates the information mark to be reproduced, part of the other information marks before and after the information mark on the information track are also partially illuminated. This interferes with the detection signal of the information mark as a noise component, reducing the accuracy of reproduction.

As a method to remove such interference from noise components, a method is known that uses an analog circuit to perform linear calculations on the reproduced signal and its second differential signal, then detects the zero-crossing time, and reproduces information by reducing jitter. (Japanese Unexamined Patent Application Publication No. 1983-1999)
107 Gore Publication).

[Problems to be Solved by the Invention] The conventional method described above uses an analog circuit, so it takes time for adjustment, and even when integrated circuits are used, there are problems in that it is difficult to obtain high reliability at a low cost.

The present invention was made in view of the above-mentioned circumstances, and
It is an object of the present invention to provide a novel method for reproducing optical information that can reduce the arrangement interval of information marks and effectively reduce the interference of noise components.

[Means to solve the problem] The present invention will be explained below.

The present invention relates to an optical information recording medium in which information marks are formed at a predetermined cycle from a position at a predetermined distance starting from the timing mark on an information track on which the timing mark is formed.
The information track is scanned by a light spot at a predetermined scanning speed, physical changes in the reflected light or transmitted light from the optical information recording medium due to the timing mark/information mark are detected, and the optical This method is a method for reproducing digital information, and has the following features.

That is, starting from the timing mark detection time, discrete times 0, . + , j + -1+ j + + j + Gin1
．． t, Yu21. ,,.

Detected values according to, , S (t knee +), 5 (tt), S (t; ++)
,S(t knee 2),,.

Based on, n is an integer of 1 or 2 or more, k is an interference coefficient that satisfies the condition O<k<1, and a is 0<a<1. a# As a number that satisfies k, S”(t,)=S(t:)+Σ(-a)Is
(t;-1)+5(tr,J))J21 To compare the result S''(tl) with a reference value or mutually compare the values of S''(t, ). Accordingly, the presence or absence of the information mark at time t is determined.

The above n and a are determined experimentally from those satisfying the above conditions. Of course, k can be found experimentally.

"Physical changes" in the above "physical changes due to timing marks and information marks in reflected light or transmitted light from optical information recording media" include not only changes in intensity but also changes in polarization characteristics such as Kerr rotation and Faraday rotation. .

[Function] Referring to FIG. 1(a), numeral 1 is an information track, numeral 2 is a light spot, numeral 3 is a timing mark, and numeral 4 is an information track.
indicates the information mark.

A plurality of information tracks 1 are formed concentrically, spirally, or parallel to each other.

When the information tracks are concentric or parallel, the timing mark/73 is formed for each individual track, and when the information tracks are spiral, the timing mark/73 is formed for each 1' column in the direction orthogonal to the track arrangement direction. Formed in multiple rows.

The light spot 2 is used for scanning, and is generally a laser beam focused into a spot shape, and its intensity is set to "a size that does not destroy timing marks and information marks during scanning."

The timing mark 3 and the information mark 4 are formed on the information track of the optical information recording medium, and when the light spot 2 is irradiated, they give the reflected light or the transmitted light the physical change as described above. Therefore, these marks are specifically reflective marks provided on a transparent optical information recording medium substrate, transparent marks provided on a reflective optical information recording medium substrate, or reflected or transmitted light. This is a mark or the like that has the property of rotating the plane of polarization.

Information marks 4, which express information depending on their presence or absence, are arranged on the information track 1 at a predetermined period from a position at a predetermined distance from the timing mark 3. In other words,
The position where the information mark 4 is to be formed on the information track 1 is predetermined in relation to the timing mark 3, and the information mark may or may not be formed at this position, but it is formed. The exponent position is determined by the above-mentioned predetermined period.

Therefore, for example, when the information track 1 is scanned at a constant scanning speed in the direction of the arrow 5 by the optical spot 2 as shown in the figure, the position of the information mark on the information track will change after a certain period of time after the pressure of the timing mark is detected. , discrete times 91., separated by predetermined intervals. .

1;-+, 1. ．． 1. Ya192. corresponds to

The above discrete times, , ti-1, ti, ti. 111
．． is determined depending on the "scanning speed and information mark formation period".

Therefore, in the following explanation, for example, the position on the information track determined by the discrete time t will be referred to as the position of timing t.

Here, for the sake of concreteness of the explanation, the optical information recording medium is reflective,
Assuming that the information mark is optically transparent and that the information track is scanned by the optical spot 2 to detect the intensity of the reflected light, the first electric signal is photoelectrically converted according to the intensity of the reflected light accompanying optical scanning. The signal shown in Figure (b) is changed.

On the other hand, based on the detection time of the timing mark 3, the discrete times are +, ti-1, ti+ti+1 . ．． ．． A lock signal as shown in Fig. 1(C) is generated in accordance with A detection signal S(t,) is obtained according to time t.

In the same figure, the symbol C indicates the difference in the detection signal depending on the presence or absence of the information mark. big. However, when the arrangement interval of the information marks is made smaller, the difference C gradually becomes smaller, the contrast of the pressure detection signal decreases, and the reliability of optical information reproduction decreases.

As mentioned above, when the arrangement interval of information marks becomes smaller, when one information mark is irradiated with a light spot, some of the adjacent information marks before and after the information mark on the information track are also irradiated with light, and these adjacent information This is because changes in reflected light intensity due to marks interfere as noise components.

The influence of adjacent information marks as noise is expressed by an interference coefficient.

Referring to FIG. 3, the vertical axis of this figure shows the level of the pressure detection signal, and the horizontal axis shows the position according to timing. The timing is timing 1 for the information mark. ,．． 1.
．． 1. , , is shown.

Curve 10 shows the change in the pressure detection signal when the light spot is at position J with timing 1, and the position of the information mark that should be at this position is centered on the timing and deviates from it.The detection signal is Light spot center and timing t1
The level is normalized to 1 when the centers of the information marks that should be at the positions coincide.

The interference coefficients include the timings 11-, , 1 of curve 10. ,,
It is defined as the value at the position of , and gives the ratio of signal mixing from adjacent information marks, but it is thought to be determined by the arrangement interval of the information marks, the size of the information marks, and the size of the light spot, and O<k Takes a value in the range <1.

Now, considering an arbitrary information mark on an information track, there are 0 to 2 adjacent marks before and after this information mark.

If the detection signal obtained when the light spot illuminates the position of timing t is S(t,), then in general, S(t+
)=S'(t; )+ and -3'(t; -, )+ and -3' (ti, I) (1) holds true.

Here, s'(t,) represents the detection signal obtained when the position of timing t1 is irradiated with a light spot when there is no information mark at the position of timing ji-1sti+1,
The value when there is an information mark at the position of timing t1 is 1.
Standardize to. The S'(ti) value is O when there is no information spot at the position of timing t.

Therefore, if an information mark exists at the position of timing t1 and no adjacent information marks exist before or after it, the level of the detection signal will be 1+0+0=1 according to equation (1).

On the other hand, when there is no information mark at the position of timing t1 and two adjacent information marks exist before and after it, the level of the detection signal becomes O++k·2.

The contrast of the detection signal depending on the presence or absence of the information mark changes depending on the combination of the presence or absence of the information mark at the timing position illuminated by the light spot and the presence or absence of the adjacent information mark. The contrast depending on the combination of cases (1-2
k).

Further, when the adjacent information mark is O, the ideal contrast is obtained in a combination of the presence and absence of the information mark at the position of timing t, and its value is 1.

The combination of information mark arrays that minimizes the contrast of the detection signal is called the "worst combination."

Now, in the present invention, as mentioned above, the detected value...
(t;-+), S(t;), S(t;, +), S(
t;,2),,,.

Based on, n is an integer of 1 or 2 or more, k is an interference coefficient that satisfies the condition 0<k<1, and a is O<a<1. a# As a number that satisfies k, S''(t;)=S(t;)+Σ(-a)'(S
(t knee;)+S(t;,=)) (2) The following calculation is performed to determine the presence or absence of the information mark at time t1.

Using equation (1), when n=, equation (2) is S'(t+)
=S'(t:)+a-3' (t knee+)+a-3'
(t;++)→Σ(-a)'(S'(t;-=)"
a's'(tl-,,-+)+a-3' (ti-,
++l)"S'(ti+j)"a"S' (ti+j
-1)+a's' (t+,=,yu)) (3)
Therefore, the noise component due to the adjacent information mark is -s' (t
It can be seen that -s' (t+4+) is reduced to ;-+)+. By reducing the noise component in this way, the contrast can be increased to C' as shown in FIG. 1(e).

The effect of increasing contrast according to equation (3) increases as the value of n increases; however, in consideration of the complexity of calculation, the smaller the value of n, the better. In fact, a sufficient effect can be obtained even if n=1.

Also, a is O<a<1. Although it can be selected as appropriate within the range of a#k, the case where n= will be explained here.

In equation (3), n=1. When n=, S'(t;)・
S' (t,) - to 2 (2S' (t,) ÷ 63 + 64
) (4) is obtained. Here s'(t,) · 0 (there is an information mark at the position of timing t1) · 1 (there is no information mark at the position of timing t1)
δ3. δ4 = 1 (there is an information mark at the position of timing ti-1+ti+1) - 0 (there is no information mark at the position of timing ji-11ji.1).

Incidentally, in this notation, the above equation (1) becomes S''(tl)・
S'(t:)+k(δ3+64) (5).

The worst combination described above, ie, the information mark arrangement where there is an information mark at the position of timing t1 and no adjacent information marks before and after it, and the case where there is no information mark at the above position and two adjacent information marks before and after it. The level of the pressure detection signal, that is, the contrast of the standardized pressure detection signal, for the combination j of information mark arrays when there is Figure 4 shows the result of calculation using formula (5), and (b) the result of calculation using formula (4).
It can be seen that the method of the present invention using equation 4) effectively improves the contrast of the pressure detection signal in the "worst combination" even if the interference coefficient is somewhat large compared to the conventional method using equation (5). . That is, in the conventional method, as shown in Fig. 4(a)
As shown in the figure, the contrast linearly approaches 0 as k increases, whereas according to the method of the present invention, the contrast slowly approaches 0 as k increases.

In addition, in the present invention, it is basically preferable that the numerical value a is set to a=, but depending on the selected value of the numerical value n or the characteristics of the recording medium, it is preferable to select the value of a so that the contrast is most improved. Be practical. At this time, the value of a may deviate from the value of k to some extent, but this does not deviate from the spirit of the present invention.

Also, if n is changed in equation (3), the contrast in the worst combination becomes (1-(2k)"), so n
Expressing the change in contrast using the parameter, the fourth
As shown in Figure (C), a significant improvement in contrast is obtained for k<0.5. In addition, in Fig. 4(c), n=
o indicates the case of the conventional method.

[Example] Specific examples will be described below.

FIG. 2 shows, as a block diagram, one example of a circuit for implementing the present invention.

When the detection signal 10 detected by the optical spot in the optical pickup 20 is applied to the synchronization signal detector 21, the timing mark (reference numeral 3 in FIG. 1) is detected by the synchronization signal detector 21.
is detected. The detector 21 activates the Glock generator 22 based on the timing mark detection time, and the A/D converter 23 generates the predetermined time j4. j2
+---1ji-1, ti+ti. +9. The detection signal at is sampled and converted into a digital signal as a detection value S(t,).

The converted detection value S(t,) is input to the digital calculator 24. The digital calculator 24 performs the calculation according to the above-mentioned equation (4) (generally, equation (3)) on each timing mark based on three successive detected values.

The result of the calculation is sent to the judgment circuit 25, and the judgment circuit 25 judges the calculation result by comparing it with an appropriate threshold value or by relatively comparing the values before and after the information mark 4. The presence or absence is outputted as a reproduction signal 26.

[Effects of the Invention] As described above, according to the present invention, a novel method for reproducing optical information can be provided. This method is configured as described above, and because the calculation for increasing the contrast of the detection signal is performed digitally, even if the arrangement interval of the information marks is reduced and the recording density of the optical information recording medium is increased, the information can be transmitted with high reliability. Can be played.

Furthermore, even if the frequency or bit rate of the reproduced signal changes, in the case of analog circuits, complicated readjustment of circuit constants is required, but with the method of the present invention, the second
This can be handled by simply changing the clock frequency of the A/D converter illustrated in the figure, increasing system flexibility.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the present invention, Fig. 2 is a diagram for explaining an embodiment, Fig. 3 is a diagram for explaining the present invention in detail, and Fig. 4 is a diagram for explaining the effects of the embodiment. It is a diagram. Yu00. Information track, 200. Light spot, 311.
Tai Honda Akira Chiananfung, 1st Fukukura 謬謬学Q-Niyagu H cry♀oPQtsun life 10 stories (-as νM90. GiLIi Ward A

Claims (1)

[Claims] The information track of an optical information recording medium on which information marks are formed at a predetermined period from a position at a predetermined distance from the timing mark as a starting point is scanned by a predetermined optical spot. A method of scanning at a scanning speed, detecting a physical change in reflected light or transmitted light from an optical information recording medium due to the timing mark/information mark, and reproducing optical information according to the presence or absence of the information mark. , Discrete times starting from the timing mark detection time and corresponding to the scanning speed and the information mark formation period. ．． ．． , t_i_−_1, t_i, t_i_+_1, t
_i_+_2,. ．． ．． ．． Detected value according to. ．． ．． , S(t_i_−_1), S(t_i), S(t
_i_+_1), S(t_i_+_2), . ．． , where n is an integer of 1 or 2 or more, k is an interference coefficient that satisfies the condition 0<k<1, and a is a number that satisfies 0<a<1 and a≒k, S^*(t_i)= S(t_i)+▲There are mathematical formulas, chemical formulas, tables, etc.▼(-a)^j{S(t_i_-_j)+
A method for reproducing optical information, characterized in that the presence or absence of an information mark at time t_i is determined by performing the calculation: S(t_i_+_j)}.