JP2001076384A - Optical recording medium, and method and device for reproducing optically recorded information - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the recording density, to stabilize the tracking and to make correctly reproducible multi-valued data by forming pits having two different depths no a substrate and making the wavelength of the light beams being used and the refractive index of the substrate of an optical recording medium satisfy prescribed relationships. SOLUTION: Pits having two different depths (D1 and D2) are formed on the substrate of an optical recording medium, and it is constituted so as to satisfy relationships 0<D1<λ/4n and λ/4n<D2<2n, where λ is the wavelength of the light beams used and n is the refractive index of the substrate of an optical recording medium. It is more desirable to make the depths of the pits D1 and D2 to satisfy relationships λ/8n<D1<λ/4n and λ/4n<D2<3λ/8n. Moreover, on the optical recording medium in which pits having at least two different depths are formed on the substrate, adjustment is made so that the amplitudes of tangential push-pull signals are made different and information is recorded by the magnitudes of the signal amplitudes of the tangential push-pull signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical recording medium on which multi-value digital data is recorded, and a reproducing method and a reproducing apparatus therefor.

[0002]

2. Description of the Related Art A conventional optical disk is binary recording in which binary data is associated with the presence or absence of a pit. In order to increase the density of a disk, the size of a pit is reduced, and a laser beam spot for reading the pit is also reduced. In addition, so-called multi-level recording in which one pit has multi-level data is also an effective means for increasing the density.

For example, Japanese Patent Laying-Open No. 58-215735 proposes an optical disk in which pit depth is set in a plurality of steps and the amount of reflected light is changed in multiple steps to record multi-value data. However, in this method, it is difficult to determine the level of the reflected light amount, and there is a problem that errors occur in reproduced data. In contrast, Japanese Patent Application Laid-Open No. 5-2052
No. 76 discloses a method of reproducing multi-valued recorded data by combining a reflected light amount level and a push-pull signal level.

[0004]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open No.
In the method disclosed in Japanese Patent No. 205276, a beam spot for obtaining a push-pull signal needs to be prepared separately from a beam spot for obtaining a reflected light amount.
One beam spot is required. In order to perform the operation with one beam spot, it is necessary to shift the beam spot from the center of the track or to wobble the track to cause relative displacement between the beam and the center of the track.

In such a case, there is a problem that the tracking control is not stable, and the track is easily shifted and a reproduction error is easily caused.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. The present invention has been made to improve the recording density, stabilize tracking, and correctly reproduce multi-valued data. And a playback device for optically recorded information.

[0007]

In order to solve the above-mentioned problems, according to the present invention, an optical recording medium is constituted as follows.

That is, an optical recording medium in which pits having two types (D1, D2) of depth are formed on a substrate, wherein the wavelength of light to be used is λ, and the refractive index of the substrate of the optical recording medium is n 0 <D1 <λ / 4n and λ / 4n <D2 <λ /
2n was satisfied.

Here, the pit depths D1 and D2
Are λ / 8n <D1 <λ / 4n and λ / 4n <D2 <3
It is preferable to be configured to satisfy λ / 8n.

An optical recording medium having pits having at least two types of depths formed on a substrate, wherein the magnitude of the tangential push-pull signal amplitude is adjusted to be different depending on each depth, and The information may be recorded with the magnitude of the amplitude of the initial push-pull signal.

Furthermore, an optical recording medium in which pits having at least three types of depths are formed on a substrate, wherein the magnitude of the tangential push-pull signal amplitude and the polarity of the tangential push-pull signal depends on each depth. At least one of them may be adjusted so as to be different, and information may be recorded in at least one of the magnitude of the amplitude of the tangential push-pull signal and the polarity of the tangential push-pull signal.

Here, the above three types of pits (D
1, D2, D3), when D1 <D2 <D3, and when the wavelength of the light to be used is λ and the refractive index of the substrate of the optical recording medium is n, 0 <D1 <λ / 4n and D2 ≒ λ / 4n and λ / 4n <D3 <λ / 2n.

Further, the pit depths D1, D2 and D3 are λ / 8n <D1 <λ / 4n and D2 ≒ λ / 4n.
Further, it is preferable that the configuration is such that λ / 4n <D3 <3λ / 8n.

In order to solve the above-mentioned problems, the present invention uses the following method for reproducing optically recorded information.

That is, in the method of reproducing optically recorded information according to the present invention, recorded data is reproduced by combining a signal based on the amount of reflected light from an optical recording medium and a tangential push-pull signal obtained from a pit.

Here, information may be reproduced based on the polarity of the tangential push-pull signal obtained from the pits on the optical recording medium, and ternary information may be reproduced.

Further, as one mode of the method of reproducing the optically recorded information, two sets of signals indicating that a tangential push-pull signal obtained from a pit on an optical recording medium exceeds a predetermined reference value in each of positive and negative polarities. The signal may be converted into a second binarized signal, each set of the second binarized signal may be added or subtracted as a positive or negative signal, and information may be reproduced based on the result of the addition or subtraction. A signal based on the amount of reflected light from the medium is converted into a first binarized signal, and a tangential push-pull signal obtained from the pit is converted into two sets of second signals indicating that the signal has exceeded a predetermined reference value with positive and negative polarities. And the information may be reproduced by observing the second binarized signal at the change point of the first binarized signal.

On the other hand, the method for reproducing optically recorded information according to the present invention reproduces information based on at least one of the magnitude and polarity of a tangential push-pull signal obtained from a pit on an optical recording medium. good.

Alternatively, information may be reproduced by combining a signal based on the amount of reflected light from the optical recording medium and at least one of the magnitude and polarity of a tangential push-pull signal obtained from a pit.

Here, as one mode of the method of reproducing the optically recorded information, information of three or more values based on at least one of the magnitude and the polarity of the tangential push-pull signal obtained from the pits on the optical recording medium. The tangential push-pull signal obtained from the pits on the optical recording medium may be reproduced, or two predetermined reference values may be provided with positive and negative polarities to indicate that these reference values have been exceeded. A set of binarized signals may be converted, and each set of these binarized signals may be added or subtracted as a positive or negative signal, and information may be reproduced based on the result of the addition or subtraction. A signal based on the amount of light is converted into a first binarized signal, and a tangential push-pull signal obtained from a pit is converted into a positive and negative signal at a change point of the first binarized signal. That exceeds a predetermined reference value in polarity,
Alternatively, it is converted into four sets of second binarized signals indicating that they do not exceed, and each set of these binarized signals is added and subtracted as positive and negative signals, and information is reproduced based on the result of the addition and subtraction. May be.

Further, the method for reproducing optically recorded information according to the present invention preferably uses the optical recording medium according to the present invention.

Further, in order to solve the above-mentioned problems, an optical recording information reproducing apparatus according to the present invention has the following configuration.

That is, the optical recording information reproducing apparatus according to the present invention is configured to reproduce recorded data by combining a signal based on the amount of reflected light from an optical recording medium and a tangential push-pull signal obtained from a pit.

Here, it is preferable to reproduce information based on the polarity of the tangential push-pull signal obtained from the pits on the optical recording medium, and it is more preferable to reproduce ternary information.

As one mode of the optical recording information reproducing apparatus, two sets of signals indicating that a tangential push-pull signal obtained from a pit on an optical recording medium exceeds a predetermined reference value in each of positive and negative polarities. A second conversion means for converting into a second binary signal, and an addition / subtraction means for adding / subtracting each set of the second binary signals as a positive / negative signal;
The information may be reproduced based on the result of the addition or subtraction, or a first conversion means for converting a signal based on the amount of reflected light of the optical recording medium into a first binary signal, and information obtained from the pits. And second conversion means for converting the tangential push-pull signal into two sets of second binary signals indicating that a predetermined reference value has been exceeded for each of the positive and negative polarities,
The information may be reproduced by observing the second binarized signal at the changing point of the first binarized signal.

Further, the optical recording information reproducing apparatus according to the present invention comprises an observation means for observing at least one of a polarity and a magnitude of a tangential push-pull signal obtained from a pit on the optical recording medium, The information is reproduced based on the polarity or size.

The information may be reproduced by combining at least one of the polarity and the magnitude of the signal based on the amount of reflected light from the optical recording medium and the tangential push-pull signal obtained from the pit.

Here, as one mode of the optical recording information reproducing apparatus, there is provided an observation means for observing the polarity or magnitude of a tangential push-pull signal obtained from a pit on an optical recording medium, Based on the information, three or more values of information may be reproduced, or a tangential push-pull signal obtained from a pit on an optical recording medium is provided with two predetermined reference values with positive and negative polarities, Conversion means for converting into four sets of binarized signals indicating that these reference values have been exceeded; and addition / subtraction means for adding / subtracting each set of these binarized signals as positive / negative signals. The information may be reproduced based on the result, or a first conversion means for converting a signal based on the amount of reflected light from the optical recording medium into a first binary signal;
4 sets of second binary values indicating that a tangential push-pull signal obtained from a pit at a transition point of the binarized signal has exceeded or has not exceeded a predetermined reference value with positive and negative polarities, respectively. It is also possible to provide a second converting means for converting the binary signal into a converted signal and an adding / subtracting means for adding / subtracting each set of these binary signals as a positive / negative signal, and to reproduce the information based on the result of the addition / subtraction.

Furthermore, it is preferable that the optical recording information reproducing apparatus according to the present invention uses the optical recording medium according to the present invention.

The above components can be combined with each other as much as possible.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. The track pitch is 0.74 μm using an optical system including a laser beam having a wavelength of 650 nm and a lens having an NA of 0.6.
Experiments were performed on disks having various pit depths.

The disc substrate was made of polycarbonate having a refractive index of 1.5, and the reflection film was made of Al. Discs with two different pit depths were made using the methods described in US Pat. No. 5,246,531 and Canadian Patent No. 2062840. In addition, tracking is Differentia
Using a 1 Phase Detection (DPD) method, the beam spot runs around the center of the track. Embodiment 1 FIGS. 1 to 5 show a first embodiment of the present invention.
This will be described with reference to FIG.

FIG. 1 shows the relationship between the pit depth, the tangential push-pull signal amplitude, and the RF signal amplitude. The horizontal axis represents the depth of the pit, which is expressed on the basis of the wavelength of the light used. In this experiment, λ / 8n = 54 nm, λ / 4n = 108 nm, 3λ
/ 8n = 162 nm and λ / 2n = 216 nm.

The amplitude of the RF signal takes the maximum value when the pit depth is λ / 4n, and the vertical axis on the right side of FIG. Tangential push-pull (TP
P) The signal amplitude is maximum when the pit depth is λ / 8n, and the vertical axis on the left side of FIG.

The polarity of the TPP signal is inverted at the pit depth λ / 4n, and FIG.
In the area of λ / 4n <pit depth <λ / 2n, the TPP
Is negative.

Next, the TPP signal and the RF signal will be described with reference to FIGS. FIG. 2A shows a state in which a beam spot travels on a pit, and FIG. 2B shows a state in which the reflected light is guided to a detector composed of two divided light receiving elements A and B. I have. TPP signal and RF signal are
It is obtained by the following calculation using the outputs of the divided light receiving elements A and B. TPP = AB RF = A + B In FIG. 1, D1 (80 nm), D2 (135 nm)
A pit having a depth represented by
The appearance of the F signal and the TPP signal will be described with reference to FIG.

Here, λ = 650 nm, n = 1.5
Therefore, D1 <λ / 4n and λ / 4n <D2.

The RF signal is a total signal of the amount of light returning to the light receiving elements A and B when the beam spot is irradiated on the disk as the optical recording medium. When the beam spot is located on the pit, the light is affected by diffraction by the pit,
Return light amount to light receiving element (may be rephrased as reflected light amount)
, The level of the RF signal decreases.

On the other hand, the TPP signal is a signal indicating the deviation of the amount of light in the pit length direction (tangential direction) of the reflected light when the beam spot is applied to the optical recording medium disk. When the beam spot approaches the edge of the pit, the diffraction direction of the light is deviated to the length direction of the pit, and the deviating direction differs depending on which edge is before or after the pit. When the difference is obtained, a pulse-like signal having different polarities at the front and rear edges of the pit is obtained.

However, which polarity signal appears at the leading and trailing edges of the pit also depends on the pit depth. For a pit having a depth D1 which satisfies the above conditions, the leading edge of the pit is in the forward direction and the trailing edge is the trailing edge. A signal is output in the negative direction at the edge, while the opposite is true for the pit having the depth D2.

As described above, the appearance of the signal at the leading and trailing edges of the pit is inverted between D1 and D2, and this is expressed in FIG. 1 as being different in the polarity of the tangential push-pull signal. .

Referring again to FIG. 1, the pits at the depths D1 and D2 satisfying the above conditions both have the RF signal amplitude,
The absolute values of the TPP signal amplitudes are substantially equal, and only the polarity of the TPP signal differs.

Hereinafter, a method of reproducing multi-value data using an RF signal and a TPP signal, and a configuration of a main part of the apparatus will be described with reference to FIGS. FIG. 4 is a block diagram showing a configuration of a main part of the reproducing apparatus, and FIG. 5 is a diagram for explaining a reproducing method and operation, and waveforms and timings at that time. First, consider the case where pits arranged as shown in FIG. 5A are reproduced. In FIG. 5, it is assumed that the pit depths are D1, D2, and D1 in order from the left. The output from the detector 1 comprising the light receiving elements A and B is calculated by the differential amplifier 2 to determine the difference between the two.
While the signal becomes a P signal (FIG. 5C), the sum is obtained by the addition amplifier 3 to become an RF signal (FIG. 5B). The RF signal is subjected to frequency characteristic correction and the like for a reproduced signal from a particularly short pit by the equalizing circuit 7, and is binarized by the binarizing circuit 8 (FIG. 5 (d)). Sent.

On the other hand, the TPP signal is compared with a positive reference value by the comparator 4, and when the TPP signal is larger than the reference value (the sign is positive and the absolute value is large), a pulse (+1) is output to the addition / subtraction circuit 6. (FIG. 5 (e)). Similarly, the comparator 5 compares the value with the negative reference value. If the value is smaller than the negative reference value (the sign is negative and the absolute value is large), the pulse (−1) is output to the addition / subtraction circuit 6 (FIG. 5). (F)). In the addition / subtraction circuit 6, the comparator 4,
Pulses from 5 are added, and the three states of -1, 0 and +1 are led to a demodulation circuit as a 2-bit output signal (FIG. 5 (g)).

That is, the adder / subtractor circuit 6 calculates two sets of pulse signals binarized by the comparators 4 and 5 from the tangential push-pull signal (in this example, addition is performed including the polarity thereof). Based on the result of the addition and subtraction, the pit portion can restore and reproduce two states of -1 and +1 in accordance with the pit depth (in other words, the order in which the positive and negative pulses on the tangential push-pull signal appear). In a non-pit portion where no pit is formed, a state of 0 can be restored, and a total of three values of recorded information can be reproduced depending on the presence and depth of the pit. Therefore, the recording density of information on an optical recording medium can be greatly improved as compared with the conventional case of so-called binary recording.

Incidentally, in order to reproduce recorded information in the same manner as the conventional binary recording / reproducing, all the pits should have the same depth. Referring to FIG. 5, for example, the depth D
In the pit 1, when the beam spot approaches the front edge, the tangential push-pull signal (T
The PP signal) (FIG. 5 (c)) appears positive and negative at the trailing edge. Therefore, if the pulse including the sign shown in FIGS. In the section, a state of 0 is obtained.

In other words, in the method or apparatus for reproducing recorded information according to the present invention, the binarized information is converted to the depth of the conventional binary-recorded optical recording medium having the same pit depth. The ternary information can be restored / reproduced for a new optical recording medium having a different size, and compatibility with a conventional optical recording medium on which binarized recording has been performed can be maintained. .

As described herein, the RF signal and TP
To perform multi-level recording by combining P signals, two types of depths D are sandwiched by a depth λ / 4n at which the polarity of the TPP signal is inverted.
The pits 1 and D2 may be formed on the optical recording medium.
As can be seen from FIG. 1, the conditions of 1, D2 only need to be configured to satisfy 0 <D1 <λ / 4n and λ / 4n <D2 <λ / 2n.

Further, from FIG. 1, the ranges of D1 and D2 are further limited, and λ / 8n <D1 <λ / 4n and λ / 4n <D2 <3λ /
8n, it can be seen that both the RF signal and the TPP signal can be obtained with good balance and a large amplitude.

That is, by obtaining a signal having a larger amplitude, it is possible to improve the signal quality and to reduce errors in reproducing recorded information.

As described above, binary information can be reproduced even with a conventional optical recording medium having a constant pit depth.
When an optical recording medium having a pit depth set as described above is used, it is possible to reproduce ternary information depending on the pit depth. Further, when the depth is further limited, both the RF signal and the TPP signal have a well-balanced and large amplitude. Therefore, the signal quality can be improved, and errors in reproducing information can be reduced, which is still more preferable. [Embodiment 2] In the first embodiment, two sets of binary signals corresponding to the positive and negative of the tangential push-pull signal (TPP signal) are generated, and the recorded information is reproduced from the result of addition / subtraction. Shows what to do. However, information on the same optical recording medium can be similarly reproduced by another method / configuration.

Returning first to FIG. 5, the RF signal (b) 2
Focusing on the relationship between the binarized signal (d) and the signals (e) and (f) obtained by binarizing the TPP signal (c) with positive and negative reference values, (e) or (f) at the change point of (d) ) Are almost the same, and (1) If (e) appears at the falling edge of (d), the reproduction information will be +1 if (f) appears at the falling edge of (d). It can be seen that if the reproduction information is always 0 at the rising edge of -1 (3) (d), the reproduction information exactly the same as that of the first embodiment can be obtained. FIG. 6 shows a configuration of a main part of a reproducing apparatus for reproducing the same information by this method / concept.

The structure is almost the same as that of the first embodiment shown in FIG. 4, except that the addition and subtraction circuit 6 is replaced by a latch 9.
10 are provided. Pulses ((e) and (f) in FIG. 5) output from the comparators 4 and 5 are given as inputs to the latches 9 and 10, and a binary signal of the RF signal ((b in FIG. 5) At the falling edge of)), these inputs are latched and output, while at the rising edge, the latches 9 and 10 are cleared and output 0 regardless of these inputs.

The outputs of the latches 9 and 10 are supplied to a demodulation circuit (not shown) together with a binarized RF signal (the output of the binarization circuit 8), and the output of the latch 9 is 1 in the demodulation circuit. If the reproduced information is +1 and the output of the latch 10 is 1, the reproduced information is -1 and the latch 9
If both outputs are 0, the reproduced information may be determined to be 0.

Also in the second embodiment, it is natural that the pit depth of the optical recording medium to be used is preferably the one described in the first embodiment, and the merit can be enjoyed as it is. [Embodiment 3] Next, a third embodiment of the present invention will be described. In FIG. 1, two types of pit depths are represented by D0
(60 nm) and a depth represented by D1 (80 nm), and the appearances of the RF signal and the TPP signal corresponding thereto are shown in FIG. As described above, the RF signal is applied to the light receiving element A when the beam spot is irradiated on the disk as the optical recording medium.
This is the sum signal of the amount of light returning to B. At the time when the beam spot is located on the pit, the light is affected by the diffraction by the pit, and the amount of light returning to the light receiving element (which may be referred to as the amount of reflected light) decreases, so that the level of the RF signal decreases. From FIG. 1, it can be seen that the pit having a depth D0
In the pit, the RF signal amplitude becomes larger. That is, the RF signal level is further reduced in the pit portion having the depth D1. On the other hand, as described above, the TPP signal is a signal that indicates a deviation in the amount of reflected light in the pit length direction (tangential direction) when a beam spot is applied to a disk as an optical recording medium. When the beam spot approaches the edge of the pit, the diffraction direction of the light is biased in the length direction of the pit, and the direction of the bias differs depending on which edge before or after the pit,
When the difference between the outputs of the light receiving elements A and B is obtained, a pulse-like signal having different signs at the front and rear edges of the pit is obtained. From FIG. 1, the TPP signal amplitude is smaller in the pit having the depth D1 than in the pit having the depth D0. Below, RF
A method for reproducing multi-value data using a signal and a TPP signal,
The configuration of the main part of the apparatus will be described with reference to FIGS. Here, FIG. 8 is a block diagram showing a configuration of a main part of the reproducing apparatus, and FIG. 9 is a view for explaining a reproducing method and operation, and waveforms and timings at that time. First, consider the case where pits arranged as shown in FIG. 9A are reproduced. In FIG. 9, it is assumed that the pit depths are D0, D1, and D0 in order from the left. The difference between the output from the detector 1 composed of the light receiving elements A and B is obtained by the differential amplifier 2 and the TPP signal (FIG. 9)
(C)), while the sum is obtained by the addition amplifier 3 to be an RF signal (FIG. 9 (b)). The RF signal is subjected to frequency characteristic correction for a reproduced signal from a particularly short pit by the equalizing circuit 7 and is binarized by the binarizing circuit 8 (FIG. 9 (d)). Sent to On the other hand, the TPP signal is compared with the second positive reference value by the comparator 11, and when the TPP signal is larger than the reference value (the sign is positive and the absolute value is large), a pulse (+1) is output to the addition / subtraction circuit 15. (FIG. 9 (e)). Similarly, the comparator 12 compares the value with the first positive reference value, and outputs a pulse (+1) to the addition / subtraction circuit 15 when the value is larger than the reference value (the sign is positive and the absolute value is large) (FIG. 9 (f)). Similarly, by the comparator 13,
The pulse is compared with the negative second reference value, and if it is smaller than the reference value (the sign is negative and the absolute value is large), a pulse (-1) is output to the addition / subtraction circuit 15 (FIG. 9 (g)). Similarly, the comparator 14 compares the pulse with the first negative reference value. If the first reference value is smaller than the reference value (the sign is negative and the absolute value is large), the pulse (−1) is output to the addition / subtraction circuit 15. (FIG. 9 (h)). In the addition / subtraction circuit 15, the comparator 1
Add the pulses from 1, 12, 13, 14 to get 0,
The three states 1 and 2 are led to a demodulation circuit as a 2-bit output signal (FIG. 9 (i)). That is, the adder / subtractor 15 calculates the tangential push-pull signal from the comparators 11, 1
Four sets of pulse signals binarized by 2, 13, and 14 are calculated, and the pit depth (in other words, the tangential push-pull signal) 2 of 1 and 2 depending on the magnitude of the amplitude)
The state can be restored and reproduced, and the state of 0 can be restored in the non-pit portion where no pit is formed.
Depending on the presence / absence and depth of the pits, a total of three values of recorded information can be reproduced. Therefore, the recording density of information on an optical recording medium can be greatly improved as compared with the conventional case of so-called binary recording. In this embodiment, the magnitude of the tangential push-pull signal is determined by two reference values, positive and negative, but the number of depths is increased, and the number of reference values is increased accordingly. The above-described multi-value recording becomes possible. [Embodiment 4] Next, a fourth embodiment of the present invention will be described with reference to FIG. 1 and FIGS. In this embodiment,
There are three types of pit depths, and D1 (80n
m), D3 (105 nm), and D4 (130 nm). RF signal and TPP corresponding to these
The appearance of the signal will be described with reference to FIG. From FIG.
In the pit of the depth D3 from the pit of the depth D1 and D4,
Accordingly, the RF signal amplitude increases. That is, the RF signal level is further reduced in the pit portion having the depth D3. On the other hand, as shown in FIG. 1, the TPP signal shows that signals having the same amplitude and different polarities are obtained between the pit having the depth D1 and the pit having the depth D4. In other words, in the pit having the depth D1, a signal is output in the positive direction at the leading edge of the pit, and in the negative direction at the trailing edge. As described above, the manner in which the signals at the leading and trailing edges of the pit are inverted at D1 and D4 is described as being different in the polarity of the tangential push-pull signal in FIG. It is as follows. Further, from FIG. 1, the TPP signal is almost 0 in the pit having the depth D3. Hereinafter, a method of reproducing multi-value data using an RF signal and a TPP signal, and a configuration of a main part of the apparatus will be described with reference to FIGS. FIG. 11 is a block diagram showing a configuration of a main part of the reproducing apparatus, and FIG. 12 is a view for explaining a reproducing method and operation, and waveforms and timings at that time. First, consider the case of reproducing pits arranged as shown in FIG. In FIG. 12, it is assumed that the pit depths are D1, D3, and D4 in order from the left. The output from the detector 1 composed of the light receiving elements A and B is determined by the differential amplifier 2 to obtain a TPP signal (FIG. 12C) while the sum is determined by the summing amplifier 3 and the RF signal (FIG. 12 (b)). The RF signal is subjected to frequency characteristic correction and the like for a reproduction signal from a particularly short pit by the equalizing circuit 7, and is binarized by the binarizing circuit 8 (FIG. 12 (d)). The signal is sent to a demodulation circuit (not shown). on the other hand,
The TPP signal is compared by the comparator 16 with a positive reference value. If the TPP signal is larger than the reference value (the sign is positive and the absolute value is large), a pulse (+1) is output to the data detection circuit 18 (FIG. e)). Similarly, the comparator 17
Is compared with the negative reference value, and when it is smaller than the negative reference value (the sign is negative and the absolute value is large), a pulse (−1) is output to the data detection circuit 18 (FIG. 12 (f)). It has become. The RF signal edge detection circuit 19
In the leading edge portion detected by
If there is no output from the comparators 6 and 17, a pulse (+2) is output in the data detection circuit 18 (FIG. 12 (g)). If there is no output from the comparators 16 and 17 at the trailing edge, the pulse (+2) is output. -2) is output in the data detection circuit 18 (FIG. 12 (h)). In the data detection circuit 18, the pulses output from the comparators 16 and 17 and the data detection circuit 18 are added, and -1, 0, +1 and +2 are added.
Are guided to the demodulation circuit as 2-bit output signals (FIG. 12 (i)). In the data detection circuit 18, the comparators 16 and 17 are converted from the tangential push-pull signal.
The two pulse signals binarized by the above operation, the two pulse signals binarized by combining the edge information of the RF signal and the tangential push-pull signal, that is, four pulse signals are calculated (in this example, four pulse signals are calculated). In addition, the pit portion can restore and reproduce three states of -1, +1 and +2 according to the pit depth based on the result of the addition and subtraction. In a non-pit portion where no pit is formed, a state of 0 can be restored, and a total of four levels of recorded information can be reproduced depending on the presence and depth of the pit. Therefore, the recording density of information on an optical recording medium can be greatly improved as compared with the conventional case of so-called binary recording. Incidentally, in order to reproduce the recorded information in the same manner as the conventional binary recording / reproducing, the depth of the pits may be the same for all D1, for example. At this time, a signal corresponding to FIG. 12 (e) at the leading edge of the pit and a signal corresponding to FIG. 12 (f) at the trailing edge are obtained from all the pits. It will be.
Alternatively, the pit depth for maintaining compatibility with the conventional binary recording / reproducing may be, for example, D3 or D4. At this time, referring to FIG. 12, in the former case, +2 and 0 are obtained, and in the latter case, -1 and 0 are obtained. In either case, binary information can be reproduced. In the data detection circuit 18 or the demodulation circuit receiving the output, it is easy to discriminate these binary states / information between zero and non-zero, and the compatibility can be maintained. Switching between determining such information as a binary value and determining it as a multi-valued value,
For example, it may be determined whether or not only the states of +2 and 0 or -1 and 0 appear over a certain time or from information recorded in a specific area on the recording medium. That is, in the method or apparatus for reproducing recorded information according to the present invention, a binarized information having a different depth is used for a conventional binary-recorded optical recording medium having the same pit depth. Thus, the quaternary information can be restored / reproduced with respect to such an optical recording medium, and the compatibility with the conventional optical recording medium on which the binarized recording is performed can be maintained. As described above, in order to perform multi-level recording by combining the RF signal and the TPP signal, the pit depth D1,
If the relationship between D3 and D4 is more generally expressed, two types of depths (D1 and D4) sandwiching the depth λ / 4n at which the polarity of the TPP signal is inverted, and the depth λ at which the TPP signal amplitude becomes extremely small A pit having a depth (D3) of around / 4n may be formed in the optical recording medium. The conditions of D1, D3, and D4 are, as can be seen from FIG. 1, 0 <D1 <λ / 4n and D3 ≒ λ / 4n and λ / 4n <
What is necessary is just to be comprised so that D4 <(lambda) / 2n may be satisfied.

Further, from FIG. 1, the ranges of D1, D3 and D4 are further limited, and λ / 8n <D1 <λ / 4n and D3 ≒ λ / 4n and λ /
If 4n <D4 <3λ / 8n, it can be seen that both the RF signal and the TPP signal are well-balanced and a large amplitude can be obtained. That is, it is possible to improve the signal quality by obtaining a signal having a larger amplitude, and to reduce an error when reproducing recorded information.

In this embodiment, the wavelength of 650 nm, NA0.
Although the optical system of No. 6 was used, it is obvious that the effect of the present invention is not limited to the optical system. Further, the value of the pit depth is not limited to the value shown in the above embodiment, and according to the gist of the present invention, it is possible that various combinations are possible within the width of the range described in the claims. Needless to say.

[0058]

First, in the optical recording medium according to the present invention, pits having two types (D1, D2) of depth are formed on the substrate, the wavelength of the light to be used is λ, the optical recording medium is When the refractive index of the substrate is n, 0 <D1 <λ / 4n and λ / 4n <D2 <λ / 2n are satisfied.

Therefore, since the polarity of the tangential push-pull signal is different due to the difference in the depth, by changing the pit depth, an optical recording medium on which higher density ternary recording has been performed instead of conventional binary recording. Can be realized.

The pit depths D1 and D2
Λ / 8n <D1 <λ / 4n and λ / 4n <D2 <3λ /
8n.

Accordingly, both the RF signal and the tangential push-pull signal can be obtained with a well-balanced and large amplitude, and the signal quality at the time of reproduction can be improved and the reproduction error can be reduced.

Further, pits having at least two kinds of depths are formed on the substrate, and the amplitude of the tangential push-pull signal amplitude is adjusted to be different depending on each depth.

Accordingly, since the amplitude of the tangential push-pull signal differs due to the difference in the depth,
By changing the pit depth, it is possible to realize an optical recording medium on which high-density ternary or higher-level recording is performed instead of conventional binary recording. Further, the apparatus for reproducing this medium may use only one beam spot, and since the beam spot runs around the center of the track, stable tracking control becomes possible.

Further, pits having at least two types of depths are formed on the substrate, and information is recorded by the magnitude of the tangential push-pull signal amplitude obtained from each pit.

Accordingly, it is possible to realize an optical recording medium on which a higher density ternary or higher recording is performed, instead of the conventional binary recording. In the device for reproducing this medium, the beam spot runs around the center of the track.
Stable tracking control becomes possible.

Further, three types (D1 <D2 <D
An optical recording medium in which pits having a depth of 3) are formed, where λ is the wavelength of light to be used and n is the refractive index of the substrate of the optical recording medium, 0 <D1 <λ / 4n and D2 ≒ λ / 4n and λ / 4n <
It is configured to satisfy D3 <λ / 2n.

Therefore, since the magnitude and polarity of the tangential push-pull signal differ due to the difference in the depth, by changing the pit depth, it is possible to carry out the light recording in which the higher density quaternary recording is performed instead of the conventional binary recording. It becomes possible to realize a recording medium. In the device for reproducing this medium, the beam spot runs around the center of the track.
Stable tracking control becomes possible.

The depths D1, D2 and D3 of the pits are λ / 8n <D1 <λ / 4n, D2ｎλ / 4n and λ /
4n <D3 <3λ / 8n.

Therefore, both the RF signal and the tangential push-pull signal can be obtained with a well-balanced and large amplitude, and the signal quality at the time of reproduction can be improved and the reproduction error can be reduced.

Next, a method for reproducing optically recorded information according to the present invention is characterized in that recorded data is reproduced by combining a signal based on the amount of reflected light from an optical recording medium and a tangential push-pull signal.

Therefore, it is possible to reproduce multi-valued recording data based on the amount of reflected light as in the related art, rather than reproducing binary recording data only from a so-called RF signal.

Further, information is reproduced based on the polarity of a tangential push-pull signal at a change point of a signal based on the amount of reflected light from the optical recording medium.

Therefore, it is possible to reproduce information from a conventional binary recording optical recording medium in which the polarity of the tangential push-pull signal, which varies according to the depth of the pit, is constant for each pit and does not change.

Further, it is characterized in that ternary information is reproduced based on the polarity of the tangential push-pull signal.

Accordingly, it is possible to reproduce information from a ternary recording optical recording medium capable of recording information at a higher density than conventional binary recording.

Further, the tangential push-pull signal on the optical recording medium is converted into two sets of binary signals indicating that each of the positive and negative reference values has been exceeded, and each set of these second binary signals is converted. Are added and subtracted as positive and negative signals, and information is reproduced based on the result of the addition and subtraction.

Therefore, it is possible to reproduce the information of the optical recording medium on which the ternary recording has been performed by a simple method.

A signal based on the amount of light reflected from the optical recording medium is converted into a first binary signal, and the tangential push-pull signal exceeds a predetermined reference value with positive and negative polarities. It is characterized in that it is converted into two sets of second binarized signals, and the information is reproduced by observing the second binarized signal at the changing point of the first binarized signal.

Therefore, it is possible to reproduce the information of the optical recording medium on which the ternary recording has been performed by another simple method.

Further, the method for reproducing optically recorded information according to the present invention reproduces information based on the magnitude and polarity of the tangential push-pull signal.

Therefore, it is possible to reproduce multi-valued recording data based on the amount of reflected light as in the related art, rather than reproducing binary recording data only from a so-called RF signal.

Further, information is reproduced by combining a signal based on the amount of reflected light from the optical recording medium and a tangential push-pull signal.

Therefore, it is possible to reproduce multi-valued recording data based on the amount of reflected light as in the related art, rather than reproducing binary recording data only from a so-called RF signal. Also, information of three or more values is reproduced based on the magnitude and polarity of the tangential push-pull signal. Therefore, it is possible to reproduce information from an optical recording medium of ternary recording or more capable of recording information at a higher density than conventional binary recording.

A tangential push-pull signal obtained from a pit on an optical recording medium is provided with two predetermined reference values with positive and negative polarities, and four sets of binarizations indicating that these reference values have been exceeded. Then, each pair of the binary signals is added and subtracted as positive and negative signals, and information is reproduced based on the result of the addition and subtraction.

Accordingly, information can be reproduced from a ternary recording optical recording medium capable of recording information at a higher density than conventional binary recording.

A signal based on the amount of reflected light from the optical recording medium is converted into a first binarized signal, and a tangential push-pull signal obtained from a pit at a change point of the first binarized signal. Are converted into four sets of second binarized signals indicating that a predetermined reference value is exceeded or not exceeded with positive and negative polarities, respectively, and each set of these binarized signals is used as a positive / negative signal. Addition and subtraction are performed, and information is reproduced based on the result of the addition and subtraction.

Therefore, it is possible to reproduce information from a quaternary recording optical recording medium capable of recording information at a higher density than conventional binary recording.

In the method for reproducing optically recorded information according to the present invention, the optical recording medium according to the present invention is used.

Therefore, the quality of a reproduction signal from an optical recording medium recorded with three or more achievable values can be improved, and a reproduction error can be reduced.

Next, the optical recording information reproducing apparatus according to the present invention is characterized in that the recording data is reproduced by combining the reflected light amount from the pits on the optical recording medium and the tangential push-pull signal.

Therefore, it is possible to realize a device that reproduces multi-valued recording data based on the amount of reflected light as in the related art, rather than reproducing binary recording data only from a so-called RF signal.

Further, information is reproduced based on the polarity of the tangential push-pull signal at the point of change of the signal based on the amount of light reflected from the optical recording medium.

Therefore, it is possible to reproduce the information of the conventional binary recording optical recording medium in which the polarity of the tangential push-pull signal is constant for each pit because the pit depth is constant and does not change. It is.

Further, the present invention is characterized in that ternary information is reproduced based on the polarity of the tangential push-pull signal at the change point of the signal based on the amount of reflected light from the optical recording medium.

Therefore, it is possible to reproduce information from a ternary recording optical recording medium capable of recording information at a higher density than conventional binary recording.

Further, the tangential push-pull signal on the optical recording medium is converted into two sets of binary signals indicating that each of the positive and negative reference values has been exceeded, and each set of these second binary signals is converted. Are added and subtracted as positive and negative signals, and information is reproduced based on the result of the addition and subtraction.

Therefore, it is possible to reproduce the information of the optical recording medium on which ternary recording has been performed with a simple configuration.

Further, in the optical recording information reproducing apparatus of the present invention, a signal based on the amount of light reflected from the optical recording medium is converted into a first binary signal, and the tangential push-pull signal is converted into positive and negative polarities. Are converted into two sets of second binarized signals indicating that a predetermined reference value has been exceeded.
It is characterized in that information is reproduced by observing a second binarized signal at a change point of the binarized signal.

Therefore, it is possible to reproduce the information of the optical recording medium on which the ternary recording has been performed with another simple structure. Further, in the optical recording information reproducing apparatus according to the present invention, the polarity or magnitude of the tangential push-pull signal obtained from the pits on the optical recording medium is observed, and the information is reproduced based on the polarity or magnitude. Therefore, it is possible to realize a device that reproduces multi-valued recording data rather than reproducing binary recording data only from a so-called RF signal based on the amount of reflected light as in the related art. Also, information is reproduced by combining a signal based on the amount of reflected light from the optical recording medium and the polarity or magnitude of the tangential push-pull signal obtained from the pit. Therefore, it is possible to realize a device that reproduces multi-valued recording data rather than reproducing binary recording data only from a so-called RF signal based on the amount of reflected light as in the related art. Also, the polarity or magnitude of the tangential push-pull signal obtained from the pits on the optical recording medium is observed, and information of three or more values is reproduced based on the polarity or magnitude. Therefore, it is possible to realize a device that reproduces multi-valued recording data rather than reproducing binary recording data only from a so-called RF signal based on the amount of reflected light as in the related art. Further, a tangential push-pull signal obtained from a pit on an optical recording medium is provided with two predetermined reference values with positive and negative polarities, and converted into four sets of binary signals indicating that these reference values have been exceeded. Then, each set of these binarized signals is added and subtracted as positive and negative signals, and information is reproduced based on the result of the addition and subtraction. Therefore, it is possible to reproduce the information of the optical recording medium on which ternary recording has been performed with a simple configuration. Further, a signal based on the amount of reflected light from the optical recording medium is converted into a first binarized signal, and a tangential push-pull signal obtained from a pit at a change point of the first binarized signal is converted into positive and negative signals. Are converted into four sets of second binarized signals indicating that the polarity exceeds or does not exceed a predetermined reference value, and each set of these binarized signals is added and subtracted as positive and negative signals;
The information is reproduced based on the result of the addition and subtraction. Therefore, it is possible to reproduce the information of the optical recording medium on which the quaternary data is recorded with a simple configuration. Further, an optical recording information reproducing apparatus according to the present invention is characterized by using the optical recording medium according to the present invention. Accordingly, the quality of a reproduction signal from an optical recording medium on which multi-level recording is possible can be improved, and a reproduction error can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between pit depth, tangential push-pull signal amplitude, and RF signal amplitude.

FIG. 2 is a diagram illustrating a tangential push-pull signal.

FIG. 3 is a diagram illustrating a pit depth, an RF signal, and a tangential push-pull signal.

FIG. 4 is a block diagram showing a configuration of a main part of an information reproducing apparatus in the first embodiment of the present invention.

FIG. 5 is a diagram illustrating waveforms and operations of the playback device having the configuration of FIG. 4;

FIG. 6 is a diagram showing another configuration of the main part of the information reproducing apparatus according to the second embodiment of the present invention.

FIG. 7 is a diagram illustrating a state of a pit depth, an RF signal, and a tangential push-pull signal amplitude.

FIG. 8 is a block diagram showing a configuration of a main part of an information reproducing apparatus according to a third embodiment of the present invention.

FIG. 9 is a diagram illustrating a waveform and an operation of an information reproducing apparatus according to a third embodiment of the present invention.

FIG. 10 is a diagram illustrating a state of a pit depth, an RF signal, a tangential push-pull signal amplitude, and a polarity.

FIG. 11 is a block diagram showing a configuration of a main part of an information reproducing apparatus according to a fourth embodiment of the present invention.

FIG. 12 is a diagram illustrating waveforms and operations of an information reproducing apparatus according to a fourth embodiment of the present invention.

[Explanation of symbols]

1 ··· Detector 2 ··· Differential amplifier 3 ··· Additional amplifier 4,5,11,12,13,14,16,17 ··· Comparator 6,15 ··· Addition and subtraction circuit 7 ··· Equalization circuit 8 · .Binarization circuit 18.Data detection circuit 19.Edge detection circuit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hitoshi Takeuchi 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka F-term (reference) 5D029 WA17 WB17 WC04 WC05 WD10 WD12 5D090 AA01 BB02 FF12 FF42 5D118 AA26 BB01 CA13 CD08 DA35

Claims (28)

[Claims] 1. An optical recording medium in which pits having two kinds of depths (D1, D2) are formed on a substrate, wherein a wavelength of light to be used is λ, and a refractive index of the substrate of the optical recording medium is n. An optical recording medium characterized by satisfying 0 <D1 <λ / 4n and λ / 4n <D2 <λ / 2n. 2. The pit depths D1 and D2 are λ / 8n <D1 <λ / 4n and λ / 4n <D2 <3λ /
The optical recording medium according to claim 1, wherein the optical recording medium is configured to satisfy 8n. 3. An optical recording medium in which pits having at least two types of depths are formed on a substrate, wherein the tangential push-pull signal amplitude is adjusted to be different depending on each depth, and An optical recording medium on which information is recorded with a magnitude of an amplitude of a push-pull signal. 4. An optical recording medium in which pits having at least three types of depths are formed on a substrate, wherein the magnitude of the tangential push-pull signal amplitude and the polarity of the tangential push-pull signal vary depending on the depth. An optical recording medium wherein at least one of them is adjusted to be different, and information is recorded in at least one of a magnitude of a tangential push-pull signal amplitude and a polarity of the tangential push-pull signal. 5. An optical recording medium in which pits having three kinds of depths (D1 <D2 <D3) are formed on a substrate, wherein a wavelength of light to be used is λ, a refractive index of the substrate of the optical recording medium. Is defined as n, 0 <D1 <λ / 4n and D2 ≒ λ / 4n and λ / 4n <
An optical recording medium characterized by satisfying D3 <λ / 2n. 6. The pit depths D1, D2 and D3.
Λ / 8n <D1 <λ / 4n and D2 ≒ λ / 4n and λ /
The optical recording medium according to claim 5, wherein 4n <D3 <3λ / 8n is satisfied. 7. An optical recording information reproducing method characterized by reproducing recorded data by combining a signal based on the amount of reflected light from an optical recording medium and a tangential push-pull signal obtained from a pit. 8. The method according to claim 7, wherein the information is reproduced based on the polarity of a tangential push-pull signal obtained from a pit on the optical recording medium. 9. The method according to claim 7, wherein the ternary information is reproduced based on the polarity of a tangential push-pull signal obtained from a pit on the optical recording medium. 10. A tangential push-pull signal obtained from a pit on an optical recording medium is converted into two sets of second binary signals indicating that a predetermined reference value has been exceeded for each of positive and negative polarities. 10. The method of reproducing optically recorded information according to claim 7, wherein each set of the second binarized signals is added and subtracted as positive and negative signals, and the information is reproduced based on the result of the addition and subtraction. 11. A signal based on the amount of reflected light from an optical recording medium is converted into a first binary signal, and a tangential push-pull signal obtained from a pit exceeds a predetermined reference value with positive and negative polarities. Are converted into two sets of second binarized signals, and at a change point of the first binarized signal,
10. The method for reproducing optically recorded information according to claim 7, wherein the information is reproduced by observing the binarized signal. 12. A method for reproducing optically recorded information, comprising reproducing information based on at least one of the magnitude and polarity of a tangential push-pull signal obtained from a pit on an optical recording medium. 13. An optical recording information reproducing method characterized in that information is reproduced by combining at least one of the magnitude and polarity of a tangential push-pull signal obtained from a pit and a signal based on the amount of reflected light from an optical recording medium. Method. 14. The light according to claim 12, wherein information of three or more values is reproduced based on at least one of a magnitude and a polarity of the tangential push-pull signal obtained from a pit on the optical recording medium. How to play recorded information. 15. A tangential push-pull signal obtained from a pit on an optical recording medium is provided with two predetermined reference values with positive and negative polarities, and four sets of binarization indicating that these reference values have been exceeded. 15. The reproduction of the optical recording information according to claim 12, wherein the signal is converted into a signal, each set of the binary signal is added and subtracted as a positive and negative signal, and the information is reproduced based on the result of the addition and subtraction. Method. 16. A tangential push-pull signal obtained from a pit at a changing point of the first binarized signal while converting a signal based on the amount of reflected light of the optical recording medium into a first binarized signal. The second set of four sets that indicate whether or not the predetermined reference value has been exceeded for each of the positive and negative polarities
The light according to any one of claims 12 to 14, wherein the signal is converted into a binary signal, and each set of the binary signals is added and subtracted as positive and negative signals, and information is reproduced based on a result of the addition and subtraction. How to play recorded information. 17. The method for reproducing optically recorded information according to claim 7, wherein the optical recording medium according to claim 1 is used. 18. An optical recording information reproducing apparatus for reproducing recorded data by combining a signal based on the amount of reflected light from an optical recording medium and a tangential push-pull signal obtained from pits. 19. The apparatus according to claim 18, wherein information is reproduced based on the polarity of a tangential push-pull signal obtained from a pit on the optical recording medium. 20. The optical recording information reproducing apparatus according to claim 18, wherein ternary information is reproduced based on the polarity of a tangential push-pull signal obtained from a pit on the optical recording medium. 21. A tangential push-pull signal obtained from a pit on an optical recording medium is converted into two sets of second binarized signals indicating that a predetermined reference value has been exceeded for each of positive and negative polarities. 20. An apparatus according to claim 19, further comprising: a conversion means for adding and subtracting each pair of the second binary signals as positive and negative signals, and reproducing information based on the result of the addition and subtraction. Item 21. An optical recording information reproducing apparatus according to item 20. 22. A first conversion means for converting a signal based on the amount of reflected light from an optical recording medium into a first binary signal, and a tangential push-pull signal obtained from a pit having a predetermined reference with positive and negative polarities. And a second set of conversion means for converting into two sets of second binarized signals indicating that the value has been exceeded, wherein a second binarized signal is provided at a change point of the first binarized signal. 2. The information is reproduced by observing a signal.
The optical recording information reproducing apparatus according to any one of claims 8 to 20. 23. A light characterized by observing at least one of the polarity and magnitude of a tangential push-pull signal obtained from a pit on an optical recording medium and reproducing information based on the polarity or magnitude. Playback device for recorded information. 24. A signal based on the amount of reflected light from the optical recording medium,
An optical recording information reproducing apparatus characterized in that information is reproduced by combining at least one of a polarity and a magnitude of a tangential push-pull signal obtained from a pit. 25. An observation means for observing the polarity or magnitude of a tangential push-pull signal obtained from a pit on an optical recording medium, and reproducing information of three or more values based on the polarity or magnitude. 25. The apparatus for reproducing optically recorded information according to claim 23 or claim 24. 26. A tangential push-pull signal obtained from a pit on an optical recording medium is provided with two predetermined reference values with positive and negative polarities and four sets of binarization indicating that these reference values have been exceeded. 24. A system according to claim 23, further comprising a conversion unit for converting the binary signal into a signal, and an addition / subtraction unit for adding / subtracting each set of the binary signals as a positive / negative signal, and reproducing information based on the result of the addition / subtraction. An optical recording information reproducing apparatus according to claim 25. 27. A first conversion means for converting a signal based on the amount of reflected light from an optical recording medium into a first binarized signal;
Indicates that the tangential push-pull signal obtained from the pit at the changing point of the digitized signal has exceeded or has not exceeded the predetermined reference value with positive and negative polarities.
A second conversion means for converting the set into a second binary signal, and an addition / subtraction means for adding / subtracting each set of these binary signals as a positive / negative signal, wherein information based on the result of the addition / subtraction is provided. 26. The optical recording information reproducing apparatus according to claim 23, wherein the optical recording information is reproduced. 28. An optical recording information reproducing apparatus according to claim 18, wherein the optical recording medium according to any one of claims 1 to 6 is used.