JPH07110941A - Method and apparatus for reproducing photon mode optical recording medium - Google Patents

Abstract

PURPOSE:To achieve reproduction without increasing an error rate by a method wherein the output corresponding to an average reflection factor during the reproduction of an optical recording medium is detected to change a reference voltage and a mark end rim is detected in comparison with the results to reproduce information. CONSTITUTION:An initial signal (indicated by the solid line) immediately after stored is digitized as shown in a signal 301 following a comparison. With the repetition of reproduction, the signal is shifted to the one indicated by the dotted line. After the repeated reproduction. a reference voltage is changed to V'b from Vb. The signal after the repeated reproduction is compared with the voltage V'b and can be detected as such the same as the initial signal as shown in a signal 302.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducing method and reproducing apparatus for a photon mode optical recording medium.

[0002]

2. Description of the Related Art As a next-generation optical recording technology, research is actively conducted on applying a photochromic material that reacts in a photon mode to an optical recording medium. Photochromic materials have the property that when irradiated with light of a specific wavelength, the molecular structure changes due to a photochemical reaction, the optical properties such as absorption rate also change accordingly, and the original molecular structure is restored by irradiation with light of another wavelength. is doing. In such photon mode recording, multiple recording is performed by making the best use of the degree of freedom of wavelength and polarization of light, enabling higher density recording than heat mode recording such as magneto-optical recording and phase change optical recording. Become.

By the way, in the photon mode recording, since there is no threshold value for recording, there is a problem that the recorded information is destroyed when the reproducing light having a wavelength capable of detecting the absorption change is repeatedly irradiated. In order to solve this problem, the present inventor has used ultra-low power reproduction light in the vicinity of P _rep (W) of the following formula (I) or within the range of P _rep (W) of the following formula (II). Proposing "ultra-low power reproduction method" for reproduction (Proceedings of the 40th Joint Lecture on Applied Physics-related N
o. 3,29p-B-13,1021 (1993)).

[0004]

[Equation 1]

(Here, SNR is the SN required for the system.
Power ratio (PP / rms), e is elementary electric power 1.6 × 10
^-19 (C), B is the system bandwidth (Hz), η is the sensitivity of the photodetector to a gain of 1 (A / W), γ is the pickup efficiency, R _ave is the average reflectance of the optical recording medium, and ΔR is The amount of change in reflectance between the recorded portion and the unrecorded portion of the optical recording medium is shown. )

[0006]

[Equation 2]

(Here, SNR is the SN required for the system.
Power ratio (PP / rms), e is elementary electric power 1.6 × 10
^-19 (C), B is the system bandwidth (Hz), η is the sensitivity of the photodetector to a gain of 1 (A / W), γ is the pickup efficiency, R _ave is the average reflectance of the optical recording medium, and ΔR is The amount of change in reflectance between the recorded portion and the unrecorded portion of the optical recording medium, k is Boltzmann's constant 1.38 × 10 ⁻²³ (J · K ⁻¹ ), T is absolute temperature (K), and I _{am p} is reproduction. The average noise current (A) and Z of the reproduction preamplifier indicate the impedance (Ω) of the reproduction preamplifier. ) According to the above ultra-low power reproduction method, reproduction can be performed 100,000 times or more.

By the way, in such a photon mode recording, a mark edge recording method is considered as a method capable of further increasing the recording density. The mark edge recording method has been variously studied as an effective means for high density recording even in magneto-optical recording. EFM
(Eight-fourteen modulatio
The mark edge recording method represented by n) is, for example,
ALAN B. MARCHANT "OPTICAL
RECORDING ”Chapter. 9 P. 241 etc. This method is a recording method in which 1 of a channel bit is associated with an edge portion of a recording mark,
As compared with mark position recording in which 1 is associated with the recording mark itself, the density can be increased by about 1.3 to 2 times. On the other hand, since the detection timing of the mark edge portion needs to be performed with high accuracy, the presence of edge fluctuation such as deformation of the recording mark caused by thermal diffusion in the heat mode recording increases the error rate. Therefore, in mark edge recording, it is desirable that such edge fluctuation be as small as possible. Unlike the heat mode recording, the photon mode recording has no mark edge fluctuation due to thermal diffusion, and in this sense, it is considered to be suitable for the mark edge recording. However, as a result of examining the influence of repeating the reproduction of the information recorded in the mark edge on the photon mode optical recording medium by the above-mentioned ultra-low power reproducing method, the present inventor has found that the mark edge portion is gradually reproduced by the repeated reproduction. I found a new problem of shifting.

FIG. 2 is a diagram for explaining such shift of the mark edge portion. Referring to FIG. 2A, the recording mark portion 1 has a length of about 2 μm in this case, and FIG. 2B shows the reflectance of the recording mark portion 1 in the relative movement direction. . The solid line indicates the recording mark part 1
Shows the initial reflectance immediately after recording in the relative movement direction X, and the dotted line shows the reflectance after 100,000 times reproduction by the ultra-low power reproduction method. The average of the reflectance of the non-marked portion where no recording is made and the reflectance of the center of the recorded mark portion 1 is shown as Ra ₁ at the initial stage (solid line) and as Ra ₂ after 100,000 times reproduction (broken line). There is.
If the mark edge portion of the recording mark portion 1 is defined as a portion where the reflectance has the values of Ra ₁ and Ra ₂ ,
As shown in (a), it is understood that the mark edge portion 102 after the recording mark portion 1 has been reproduced 100,000 times is shifted from the initial mark edge portion 101 by the width Δ. The width of Δ of this shift is about 0.05 to 0.1 μm.

Such a shift of the mark edge portion increases the error rate in reproduction. That is,
The reproduction signal irradiates the recording mark portion with the reproduction beam light,
It is obtained by converting the obtained reflected light into a photocurrent, and in the process of converting this into a digital signal, as shown in FIG. 3, the signals 301 and 302 that have been compared with an appropriate reference voltage Vb are obtained. Is converted to. The rising part and the falling part of this voltage correspond to the position of the mark edge part, and as shown in FIG. 3, due to the shift of the mark edge part, the signals 301,
The rising and falling portions of 302 are shifted by d.

The present invention solves the above-mentioned conventional problems and prevents an increase in the error rate due to the shift of the mark edge portion which occurs when the photon mode optical recording medium with mark edge recording is repeatedly reproduced. An object of the present invention is to provide a reproduction method and a reproduction device that can perform the reproduction.

[0012]

According to the reproducing method of the present invention, a photon mode optical recording medium having mark edge recording is irradiated with reproducing beam light, and an electric signal obtained is compared with a reference voltage so that the mark edge portion is compared. Of a photon mode optical recording medium for detecting recorded information and reproducing recorded information. The method is characterized in that the reference voltage is changed according to the output corresponding to the average reflectance during reproduction of the optical recording medium.

The reproducing apparatus of the present invention is an apparatus for reproducing the information recorded in the photon mode optical recording medium, and irradiates the reproducing beam light for reproducing the information recorded in the recording layer of the optical recording medium. A light source, a means for condensing the reproduction beam light emitted from the light source on the recording layer of the optical recording medium, and a means for photoelectrically converting the reproduction beam light passing through the recording layer of the optical recording medium into an electrical signal. A means for detecting an output corresponding to the average reflectance of the optical recording medium, a means for changing the reference voltage according to the output corresponding to the detected average reflectance, and an electric signal obtained by photoelectric conversion. It is characterized in that it is provided with a means for taking out information in comparison with the reference voltage.

[0014]

As described above, the photon mode optical recording medium is repeated.
The mark edge part shifts by performing playback again.
And the average reflectance of the optical recording medium is Ra₁To Ra
₂Changes to. In the present invention, the flatness of such an optical recording medium is
The output corresponding to the uniform reflectance is detected and the value is used as a reference
The voltage is changed for comparison. Servant
Therefore, the mark edge shifts due to repeated playback.
Plays without increasing the error rate even if it occurs
It becomes possible.

FIG. 1 is a diagram for explaining such an operation of the present invention. As shown in FIG. 1, the initial signal (solid line) immediately after recording is digitized as a post-comparing signal 301. By repeating the reproduction, the signal shifts to the signal shown by the dotted line, but in the present invention, the reference voltage after the repeated reproduction is changed from Vb to Vb ′, and the signal after the repeated reproduction is compared with the reference voltage Vb ′. Therefore, it can be detected as a signal similar to the initial signal 301 like the signal 302.

[0016]

FIG. 4 is a schematic diagram showing a reproducing apparatus according to an embodiment of the present invention. With reference to FIG. 4, as the light source 7 that emits the reproduction beam light, a visible light semiconductor laser that emits laser light having a wavelength whose reflectance change can be detected, or YA
A G laser second harmonic generation element or the like is used. The reproduction light beam emitted from the light source 7 is shaped into parallel light by the collimator lens 6 and several nW by the attenuation element 5.
The power is reduced to an ultra low power level of several μW. Next, the S-wave enters the polarization beam splitter 4 and is totally reflected. Next, it is converted into circularly polarized light by the λ / 4 plate 3,
Then, the light is focused on the photon-mode photochromic optical recording medium 100 by the objective lens system 2 which is a light focusing means.

The reflected light, the intensity of which is modulated according to the information recorded on the optical recording medium 100, passes through the objective lens 2 and the λ / 4 plate 3 again, and is polarized by the P wave into the polarization beam splitter 4.
Is passed through the lens 8 and is converted into an output voltage by the photodetector 9 and the IV conversion preamplifier 10 which are photoelectric conversion means. Here, as the photodetector 9, it is desirable to use an avalanche photodiode or the like having a photocurrent self-amplifying action. Next, the low-pass filter 11 obtains the average value of the amount of light reaching the photodetector 9, that is, the average voltage level corresponding to the average reflectance of the optical recording medium 100. This low pass filter 11
It is desirable that the cut-off frequency of is lower than the frequency band used for focus / tracking servo which is lower than the band of the recording signal.

The optical recording medium 10 obtained as described above
The voltage corresponding to the average reflectance level of 0 is applied to the amplifier unit 12
Is appropriately amplified or attenuated to become the reference voltage Vb. The signal voltage obtained from the preamplifier 10 is compared with this reference voltage Vb by the comparator 13 to obtain the comparator outputs 301 and 302 as shown in FIG. In the reproducing apparatus shown in FIG. 4, a known focus / tracking servo optical system / circuit system can be used, and in FIG. 4, such an optical system and circuit system are not shown.

As described above, by using the reproducing apparatus as shown in FIG. 4, the reference voltage is changed by the output corresponding to the average reflectance of the optical recording medium 100 at the time of reproducing, and the electric voltage obtained by photoelectric conversion is changed. By comparing (comparing) the target signals, it is possible to suppress the increase in the error rate due to the shift of the mark edge portion as in the conventional case.

In the above embodiment, the voltage level corresponding to the average reflectance is obtained from the output of the same reproduction light, but the present invention is not limited to such a structure, and the reproduction beam light is used. An output corresponding to the average reflectance of the optical recording medium may be detected by using light other than the above.

In the above embodiment, the combination of the low pass filter and the amplifier is used as the means for changing the reference voltage, but the present invention is not limited to such a configuration.

The amplifier section 12 does not have to have a linear amplification (attenuation) action, and may have a non-linear characteristic. Further, in the above-mentioned embodiment, the ultra-low power reproduction method of irradiating the reproduction light beam of ultra-low power as the reproduction light of the optical recording medium is adopted, but the present invention is not limited to this. It can also be applied to a method and apparatus for reproducing with normal power.

[0023]

According to the present invention, the output corresponding to the average reflectance during reproduction of the optical recording medium is detected, the reference voltage is changed by this, and the mark edge portion is detected by comparing with this reference voltage. , Playing information. Therefore, even if the mark edge portion shifts due to the repeated reproduction, the reproduction can be performed without increasing the error rate.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a reproducing method of the present invention.

FIG. 2 is a diagram for explaining a shift of a mark edge portion in a photon mode optical recording medium.

FIG. 3 is a diagram showing shifts of rising and falling portions of a comparator output according to a conventional reproducing method.

FIG. 4 is a schematic diagram showing a reproducing apparatus of an embodiment according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Recording mark part 2 ... Objective lens 3 ... (lambda) / 4 plate 4 ... Polarization beam splitter 5 ... Attenuation element 6 ... Collimating lens 7 ... Light source 8 ... Lens 9 ... Photodetector 10 ... IV conversion preamplifier 11 ... Low-pass filter 12 ... Amplifier section 13 ... Comparator 100 ... Optical recording medium 101 ... Mark edge section of initial recording mark section 102 ... Mark edge section of record mark section after repeated reproduction

Claims (2)

[Claims] 1. A photon mode optical recording medium on which mark edge recording is performed is irradiated with reproduction beam light, and an electric signal obtained is compared with a reference voltage to detect a mark edge portion and reproduce recorded information. A method of reproducing a photon-mode optical recording medium, wherein the reference voltage is changed according to an output corresponding to an average reflectance at the time of reproducing the optical recording medium. 2. An apparatus for reproducing information recorded in a recording layer of a photon mode optical recording medium, which emits a reproduction beam light for reproducing information recorded in the recording layer of the optical recording medium. A light source, a unit for condensing the reproduction beam light emitted from the light source on the recording layer of the optical recording medium, and the reproduction beam light that has passed through the recording layer of the optical recording medium into an electrical signal. Means for converting, means for detecting an output corresponding to the average reflectance of the optical recording medium, means for changing the reference voltage according to the output corresponding to the detected average reflectance, and the photoelectric conversion A reproducing device for a photon mode optical recording medium, comprising: means for extracting the information by comparing the obtained electric signal with the reference voltage.