JPH0668470A - Method and device for reproducing optical information - Google Patents

Abstract

PURPOSE:To obtain a satisfactory S/N even with low power by dividing a deflected beam from a single light source into two beams, detecting the two beams obtained by performing optical mixing on them after applying prescribed processing by an optical detector independently, and obtaining a reproducing signal by performing subtraction between the two beams. CONSTITUTION:The deflected beam 11a emitted from the single light source is divided into a first beam 11b and a second beam 11d by a first beam splitter 13. The first beam 11b is made incident on an optical recording medium 23, and a reflected beam whose deflecting surface is modulated corresponding to information recorded on the medium 23 is fetched from the medium 23. The optical mixing of the reflected beam 11c and the second beam 11d is performed, and a third beam 11e and a fourth beam 11f (number 11f is not shown in figure) generated by such mixing are detected independently by the optical detectors 221, 222 via analyzers 201, 202. The subtraction between two detection signals obtained by such detection is performed by a differential amplifier 24, and the reproducing signal can be obtained, then, it is OUT-PUTed.

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 an reproducing apparatus for an optical recording medium capable of recording information at high density.

[0002]

2. Description of the Related Art In recent years, researches for applying a photochromic material as a rewritable optical recording medium have been actively pursued. When this photochromic material is irradiated with light of a predetermined wavelength, the structure of the molecule changes due to a photochemical reaction, which causes a change in optical characteristics such as absorbance and refractive index with respect to light of a specific wavelength. It has the property that the changed molecular structure returns to its original state when heat is applied.

Therefore, recording on the photochromic optical recording medium is performed by a change in molecular structure caused by irradiation with light of a specific wavelength, and reproduction is performed by detecting a change in optical characteristics associated therewith, particularly a difference in absorbance.

By the way, as a problem of the photochromic medium, it is well known that reproduction output is lowered due to repeated reproduction. This is because the reaction of the medium molecule proceeds in the photon mode, so that the reaction of the photochromic molecule slightly progresses even when reproducing at relatively low power, and by repeating this, the reproduction output also decreases. . Therefore, in order to obtain a good reproduction output after the maximum number of reproductions, it is easy to understand that the reaction accompanying the reproduction should be suppressed as small as possible, that is, the reproduction should be performed with the smallest optical power.

However, as the reproducing power is reduced, the amplifier noise (or thermal noise) of the reproducing circuit system becomes dominant and the SN ratio is extremely deteriorated.

In order to prevent such deterioration of the SN ratio during low power reproduction, there is a technique disclosed in Japanese Patent Publication No. 4-3575 as a reproduction method for a magneto-optical recording medium. FIG. 14 shows the structure of the optical pickup disclosed in the embodiment of this publication. In the figure, 11a to 11e are reproduction light beams, 12 is a polarizer, and 13 is the light beam 11
A first beam splitter that splits a into a first beam 11b and a second beam 11d with an appropriate amount of light and polarization, 14 is a second beam splitter, 15 is an objective lens, 16 is a mirror, and 17 is polarized light of 11d. Λ / 2 plate for changing the direction, 1
Reference numeral 8 denotes a phase plate for phase adjustment, reference numeral 19 denotes a third beam 11c of the reflected light from the medium 23 which is reflected by the second beam splitter 14, and second beam 11c which is separated by the first beam splitter 13. A third beam splitter for optically mixing and interfering with the beam 11d, 20 is an analyzer for detecting the polarization of the mixed beam 11e, 21 is a condenser lens,
Reference numeral 22 is a photodetector as a detector.

According to the above-mentioned publication, the intensity I detected by the detector 22 after being mixed by the third beam splitter 19 is detected.
Is given by the following equation 1.

[0008]

[Equation 1]

According to this equation 1, by adjusting the characteristic of the first beam splitter 13 to increase the power P _{1 of the} beam 11d, a large signal component (the above-mentioned signal is generated even if the power of the reproducing beam 11b (11c) is small). It can be seen that it is possible to obtain a term depending on θ _k of Equation 1.

[0010]

However, the above-mentioned conventional method has the following problems.

1. To obtain a large reproduction output, it is necessary to make P ₁ sufficiently large. However, it is known that intensity fluctuations, that is, laser noise also exists in laser light that is normally emitted with a constant power, and that this noise is proportional to the magnitude of P ₁ (P ₁ >> P ₀ ). Signal components as can be seen from Equation 1 thus increases in proportion to the square root of P _1, but laser noise increases in proportion to a substantially P _1, an increase in the noise component from the even signal components to increase the P ₁ Since it becomes large, there is a problem that P ₁ cannot be unnecessarily increased.

2. Since the beam splitter 19 is a half mirror, only half the power of the beams 11c and 11d reaches the photodetector 22, which is inefficient.

3. The above method cannot be directly applied to the low power reproduction of the photochromic medium. Because the reproduction of the photochromic medium is performed by detecting the change in reflectance, the signal is included as a change in P ₀ , and there is no rotation of the plane of polarization like the Kerr rotation angle θ _{k in} this example. Therefore, the second term of Equation 1 = 0, and the effect of enhancing the output signal due to the increase of P ₁ is completely absent.

In view of the above problems of the conventional method, it is an object of the present invention to provide an optical reproducing method capable of obtaining a good SN ratio even at low power.

[0015]

As a method of the present invention, a polarized beam emitted from a single light source is divided into first and second beams, and the first beam is incident on an optical recording medium,
A reflected beam whose polarization plane is modulated according to the information recorded on the medium is extracted from the medium, the reflected beam and the second beam are optically mixed, and the third and fourth beams generated by this mixing are generated. Each of the beams is independently detected by a photodetector through an analyzer, and two detection signals obtained as a result of this detection are subtracted from each other to obtain a reproduction signal.

Alternatively, the present invention splits a polarized beam emitted from a single light source into a first beam and a second beam, irradiates the optical recording medium with the first beam, and changes the information recorded on the medium. Accordingly, the reflected beam whose light intensity is modulated is extracted by the reflection by the medium, the reflected beam and the second beam are mixed, and the intensities of the third and fourth beams generated by this mixing are detected by a photodetector, respectively. Is detected independently, and a reproduction signal is obtained by subtracting between two detection signals obtained as a result of the detection.

Further, the apparatus of the present invention comprises a single light source, an optical separation element for separating the beam from the light source into first and second beams, and condensing the first beam on an optical recording medium. Lens system, an optical mixing element that optically mixes the reflected beam from the medium and the second beam, and a photodetector that independently detects the third and fourth beams generated by this mixing, A circuit that performs a subtraction between two signals obtained from the detector and outputs the result as a reproduction output, or a single light source, and a polarized beam from the light source with first and second orthogonal beams. A polarization splitting element for splitting into a component and a first λ / 4 for converting the first beam into circularly polarized light
Plate, a lens system for converging the first beam converted into circularly polarized light on the optical recording medium, a second λ / 4 plate for converting the second beam into circularly polarized light, and a first λ / 4 plate converted into circularly polarized light. A mirror for reflecting the two beams, a light mixing element for mixing the beam reflected by the mirror and the reflected beam from the medium,
And a photodetector for detecting a single mixed light beam obtained by this mixing element.

In the above optical information reproducing method, the phase of at least one of the first beam, the reflected beam from the medium, and the second beam is modulated at a frequency higher than the maximum frequency of the information signal for reproducing. Alternatively, in the above optical information reproducing apparatus, a phase modulating means for modulating the phase of at least one of the two beams incident on the optical mixing element at a frequency higher than the highest frequency of the information signal for reproducing. Is desirable.

[0019]

In the above structure, the mixed light beam contains the respective signal components in the opposite phase and the laser noise component in the same phase, and by subtracting between the detection signals of these beams, Laser noise is canceled and signal components are enhanced.

Further, if at least one of the mixed beams is phase-modulated, it is possible to suppress the fluctuation of the reproduction output due to the surface wobbling of the optical recording medium.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical information reproducing method and apparatus according to the present invention will be described below with reference to the drawings. [First Embodiment] First, FIG. 1 is a block diagram showing a first embodiment in which the present method and apparatus are applied to a magneto-optical recording medium. Components having the same functions as those in FIG. is doing. In the apparatus of FIG. 4, the third beam splitter 19
While only one beam 11e of the two light-mixed beams generated by is detected by the analyzer 20, the lens 21, and the detector 22, in FIG. 1, the two light-mixed beams, that is, the third and fourth beams 11e are detected. , 11f for analyzer 2 respectively
01, lens 211, detector 221, and analyzer 202,
The lens 212 and the detector 222 detect independently, and the differential amplifier 2 detects between the detection signals of the detectors 221 and 222.
The difference is that the subtraction is performed by 4.

Now, the third mixed light beam 1 having passed through the third beam splitter 19 as described in the section of the prior art.
1e has a light intensity expressed by the following equation 2 after passing through the analyzer 201.

[0023]

[Equation 2]

In the embodiment of FIG. 1, since the beam splitter 19 is a half mirror, the optical field intensities E ₁ 'and E _{1 of} Eq.
₀ 'is first pre-light mixing, the second beam 11c, using the beam intensity 11d is expressed by the following equation 3.

[0025]

[Equation 3]

When the optical electric field VE of the third light mixed beam 11e is expressed as a vector with respect to the two polarization components, it is expressed by the following equation 4.

[0027]

[Equation 4]

On the other hand, regarding the optical electric field VE _d of the second beam 11 _d after passing through the λ / 2 plate 17 and the phase plate 18, the following expression 5 is obtained by using the same expression as the above expression 4.

[0029]

[Equation 5]

Further, reproduction light, that is, the first beam 11c
Similarly, the optical electric field VE _c can be expressed as in Equation 6.

[0031]

[Equation 6]

The optical field V of the fourth light mixed beam 11f
E ′ is obtained by the following Equation 7 by using the above Equations 4 to 6 and conserving the optical energy before and after passing through the beam splitter 19 for each polarization component.

[0033]

[Equation 7]

Here, the azimuth angle of the second analyzer 202 is ψ ′.
Then, the light detection intensity I ′ of the fourth mixed light beam 11 f can be obtained as shown in Expression 8 in a form similar to Expression 2 above.

[0035]

[Equation 8]

When the analyzer azimuth ψ ′ is made to coincide with ψ of the above equation 1, the component proportional to P ₁ has the same sign and the laser noise contained in P ₁ is in-phase when compared with the equation 1. It becomes clear that the signal component proportional to θ _k is included in the opposite sign, that is, in the opposite phase. Therefore, by taking the difference between these detection signals I and I'in the differential amplifier 24, the following equation 9 is obtained.

[0037]

[Equation 9]

It can be seen from Equation 9 that laser noise is effectively removed and the signal component is doubled. That is, it is possible to improve the SN ratio by increasing P ₁ without the influence of laser noise. [Second Embodiment] Next, an example in which the present invention is applied to low power reproduction of a photochromic medium will be described with reference to FIG. Elements having the same functions as those in FIG. 1 are designated by the same reference numerals. In the figure, a radiation beam 1 from the reproduction light source
1a is linearly polarized light, and its polarization direction is adjusted by the λ / 2 plate 25. Reference numeral 13 denotes a polarization beam splitter that totally transmits the P component of the polarized beam and totally reflects the S component. The polarized beam splitter 13 divides the polarized component into two beams 1 according to the polarization azimuth angle.
It is separated into 1b (first beam) and 11d (second beam). Since the first beam 11b is irradiated onto the photochromic medium, it is as weak as possible.
Since the beam 11d is involved in the signal amplifying action, it is desirable that the beam 11d be as strong as possible. The polarization direction of the λ / 2 plate 25 is set so as to satisfy these conditions.

Now, the first beam 11b is totally transmitted as a P wave to the second polarization beam splitter 26, and the λ / 4 plate 27 is used.
It is converted into circularly polarized light by and is irradiated onto the medium 23 by the objective lens 15. The intensity of the reflected light from the medium 23 is modulated according to the recorded information. The reflected light again includes the objective lens 15 and the λ / 4 plate 27.
This time, it passes through as S-polarized light and enters the polarization beam splitter 26, where it is totally reflected to become a reflected beam 11c,
It reaches the third polarization beam splitter 19.

On the other hand, the first polarization beam splitter 13
After being reflected by and adjusting its phase by the phase plate 18,
It reaches the third beam splitter 19. Since both of these beams 11c and 11d are S-polarized beams, they are optically mixed by the third beam splitter 13 to generate two light mixing beams 11e (third beam) and 11f (fourth beam).

The thus-obtained third and fourth beams 11e and 11f after light mixing are respectively lenses 211 and
The light is focused on the photodetectors 221 and 222 by 212, and two signals are independently obtained, and then subtracted by the differential amplifier 24.

Next, in the structure shown in FIG. 2, the numerical analysis is performed as in the first embodiment. Among the components decomposed by the first polarization beam splitter 13, the optical electric field VE ₀ of the beam 11b is expressed by the following formula 10.

[0043]

[Equation 10]

This VE ₀ is applied to the medium 23, and the optical field VE _{0 of} the beam 11c reflected by the second polarization beam splitter 26 is reflected after being intensity-modulated by the change of the energy reflectance R of the medium 23. 'Is like Equation 11.

[0045]

[Equation 11]

On the other hand, the optical electric field VE _{1 of the} component of the other beam 11d separated by the first polarization beam splitter 13 is given by equation 12.

[0047]

[Equation 12]

Therefore, the third beam splitter 1
The intensity I of the third beam 11e generated by the light mixing by 9 can be expressed as in Equation 13 when the transmittance of the third beam splitter 19 is ε.

[0049]

[Equation 13]

Considering that the power is normally set so that P ₀ << P _{1 in the} formula 13, the formula 13 can be expressed as the following formula 14.

[0051]

[Equation 14]

Looking at this equation (14), a component depending on the medium reflectance R is obtained in the second term, and even if P ₀ is small, P
_It can be seen that the signal intensity can be increased by increasing ₁ and therefore the present analysis can be applied to a medium of a type that detects a change in reflectance such as a photochromic medium.

Also, with respect to the other fourth beam 11f generated by the light mixing, similarly, the formula 15 can be obtained for the power intensity I '.

[0054]

[Equation 15]

Here, if the third beam splitter 19 is set to ε = ½ and the subtraction is performed between the detection signals I and I ′, the result of Expression 16 is obtained.

[0056]

[Equation 16]

As is clear from this equation 16, the first
Similar to the embodiment, the signal component is doubled, laser noise can be effectively reduced, and a large SN ratio can be obtained even if the reproduction power is small. This is effective as a method of reproducing the photochromic medium with low power and high SN ratio as described above, and for example, it is possible to obtain the number of times of reproduction of about 100,000 times with ultra-low power of about several tens nW.

As described above, according to the reproducing method and apparatus of the first and second embodiments, it is possible to effectively reduce the influence of laser noise and thermal noise and obtain a good SN ratio even at low power. By applying this configuration to the photochromic recording medium, the number of reproducible times with a good SN ratio can be greatly improved.

By the way, according to the above-mentioned two embodiments, although the problem at the time of reproducing at a large signal level found in the technique of Japanese Patent Publication No. 4-3575 is improved, a plurality of problems can be solved as in these embodiments. In a reproducing method using light interference, there is a problem that a sufficient improvement of the SN ratio cannot be seen unless the phase relationship of the light to be interfered with is kept constant. That is, due to surface wobbling on the surface of the optical recording medium 23, the phase of the reflected beam 11c from the medium 23 changes irregularly in practice, and as a result, the reproduction output level also largely changes. For this reason, the range to which the above-mentioned two embodiments can be applied is limited to a medium system / optical system having a highly reduced surface wobbling, and it is difficult to apply it to an optical system of a normal optical disk.

Therefore, a method for preventing the fluctuation of the reproduction signal output caused by the phase fluctuation of the reflected light due to the surface deviation of the medium 23 will be described below.

Conceptually, this method modulates the phase of at least one of the two reproduction beams separated by a frequency higher than the maximum frequency contained in the reproduced information signal, and then performs optical mixing. Then, it is detected by a photodetector.

When this concept is analyzed by a mathematical expression, first, in the case of the optical system having the structure shown in FIG.
When the beam 11d is expressed by including the phase factor of light, its electric field e _LO can be expressed as in Expression 17.

[0063]

[Equation 17]

Similarly, the electric field e _S of the beam 11c which is radiated to the medium 23 and reflected is as shown in Eq.

[0065]

[Equation 18]

In the equation (18), P _S represents the intensity of light. Since the reproduction of the photochromic medium is usually performed by detecting the change in reflectance, the information signal to be reproduced is included in P _S. For example, when a signal of angular frequency ω is reproduced, P _S has the form shown in the following Expression 19.

[0067]

[Formula 19]

Further, the light intensity P ₁ of the third beam 11e after being mixed and re-separated by the half mirror 19 is given by the following formula 20 when the transmittance of the half mirror 19 is ε.

[0069]

[Equation 20]

Then, the photocurrent I ₁ flowing through the photodetector 221
Is proportional to the light intensity P ₁ , but the bandwidth capability of the photodetector 221 does not reach the optical frequency range, so
The first and second terms of 0 and the first term in {} are averaged, respectively, and the third term in {}, which is a relatively low frequency component, remains unchanged. That is, equation 21 is obtained.

[0071]

[Equation 21]

Photocurrent I ₂ flowing through one photodetector 222
Has the same form as Equation 21, but the sign of the third term is negative, and ε is replaced by 1-ε.
This is expressed in Equation 22.

[0073]

[Equation 22]

Here, ε = 1/2 as the half mirror 19.
And the differential amplifier 24 is used to calculate
Create 2 to get the resulting output (OUTPUT
T) becomes equation (23).

[0075]

[Equation 23]

As is apparent from the above equation 23, the output can be amplified by increasing P _LO , but the output is a waveform as shown in FIG. 3A due to the irregular phase change factor φ (t). Is obtained. Looking at this waveform, the absolute value of the envelope changes according to the value of cosφ (t).
(T) is a value of π / 2, 3 / 2π, etc. and cosφ (t) = 0
Therefore, there is a point (A) where the output becomes 0. Further, it can be seen that the phase of the signal is inverted before and after cosφ (t) = 0.

Next, consider the case where the phase of the second beam 11d or the reflected beam 11c of FIG. 2 is modulated by the above method. First, when the second beam 11d is phase-modulated with the angular frequency ρ, the electric field e _LO can be expressed by, for example, the following Expression 24 instead of the above Expression 17.

[0078]

[Equation 24]

By using this equation 24 and performing the same calculations as the equations 17 to 22, an output (OUTPUT) as in the following equation 25 can be obtained.

[0080]

[Equation 25]

As described above, φ (t) is a phase variation of a relatively low frequency as compared with the recording signal.
A factor of π cos ρt is included, and cos (φ (t) is obtained by comparing ρ with the recording signal and selecting a sufficiently high frequency.
+ Π cos ρt) oscillates within a range of ± 1 at a frequency sufficiently higher than that of the recording signal. This makes OUTPUT
The waveform of T is almost unaffected by φ (t).
The waveform is as shown in (b). In this case, what is important is to set the phase modulation frequency higher than the highest frequency of the recording signal band.

On the contrary, the reflected beam 1 is not the beam 11d.
Considering the case where the phase modulation of 1c is performed, in this case, the above e _LO remains the same as the _equation 17, and the following equation 26 is used instead of the equation 18.

[0083]

[Equation 26]

Then, using this formula 26,
By performing the same calculation as in 2, playback output (OUTPUT
T) is obtained in the same manner as the equation 25.

Of course, the same result can be obtained by phase-modulating both the beams 11c and 11d. In this case, however, it is desirable that the phases are opposite to each other so that the modulation effects do not cancel each other when the light is mixed. .

In this way, the OUTPUT in FIG.
The signal obtained with such a waveform becomes a waveform as shown in FIG. 4A by, for example, rectification processing, and then a low-frequency transmission filter that transmits the recording signal and cuts the modulation frequency ρ is used as shown in FIG. The waveform becomes as shown in b), and the signal that should be originally reproduced can be restored.

An optical system pickup device for carrying out the above method will be described with some examples. [Third Embodiment] FIG. 5 shows a third embodiment in which the present method is applied to the pickup device of the type shown in FIG. 2. The reproducing beam 11a is divided into two by the beam splitter 13, and the first beam The beam 11b is the polarization beam splitter 2
6. After passing through the λ / 4 plate 27, the medium 23 is irradiated with the objective lens system 15.

When the medium 23 is a photochromic medium and an ultra-low power reproducing system is used, a power adjusting element such as an ND filter is provided between the two beam splitters 13 and 26 so that the power applied to the medium 23 is several tens nW. Set to a degree.

The reflected light from the medium 23 is again reflected by the lens 15,
It passes through the λ / 4 plate 27 and is reflected by the polarization beam splitter 26. On the other hand, the other second beam 11d split into two by the beam splitter 13 is reflected by the mirror 16,
The mirror 16 is connected to the pickup 250 itself through the piezoelectric element 25a, and the piezoelectric element 25a is vibrated at high speed by the driving source 25b.

As a result, the beam 11d reflected by the mirror 16 is phase-modulated at a frequency higher than the maximum frequency of the reproduced recording signal as shown in the equation 25.
The beam 11d is mixed with the reflected light 11c (corresponding to the equation 19) from the medium by the half mirror 19, and is separated again to be the third beam 11e and the fourth beam 11.
yield f. Here, the half mirror 16 has ε = 1/2
Is set to.

The beams 11e and 11f are collected by the lenses 211 and 212 onto the photodetectors 221 and 222, photoelectrically converted, and subtracted through the differential amplifier 24 to obtain OUTPUT shown in Formula 26. To be This OUTPUT output waveform has a waveform as shown in FIG. 3B, but this waveform can be transformed into the waveform shown in FIG. 4B by the low frequency equivalent filter circuit shown in FIG. 6, for example.
Note that points B, C, and D in FIG. 6 are respectively shown in FIG.
It corresponds to (b) and FIG. 4 (a), and a buffer may be provided at point C if necessary. [Fourth Embodiment] FIG. 7 is a view showing another embodiment corresponding to the third embodiment of FIG. 5, and the main structure is the same as that of FIG. 5, but the mirror 16 is fixed in FIG. The difference is that the electro-optical element 26a is provided therein as an element for phase-modulating the second beam 11d. The electro-optical element 26a has a property that the refractive index changes with the application of a voltage, and the second beam 11d is phase-modulated by applying a high frequency voltage by the driving source 26b. [Fifth Embodiment] FIG. 8 is a view showing still another embodiment corresponding to the third embodiment of FIG. 5, of the beams bisected by the beam splitter 13, the beam for irradiating the medium. The difference is that (that is, the reflected beam 11b) is phase-modulated. The phase modulation method here is shown in FIG.
Although it is the same as the method shown in, the method of FIG. 5 may of course be used.

Further, the phase modulation is performed by the medium 2 as shown in FIG.
It may be performed before irradiating the light on the medium 3, or may be performed on the reflected light of the medium 23. In the latter case, an element that performs phase modulation is provided between the polarization beam splitter 26 and the half mirror 19.

The beam 11d and the beam 11c in this embodiment are represented by equation 18 and equation 27, respectively.
Is in the form represented by Equation 24. [Sixth Embodiment] FIG. 9 shows a sixth embodiment in which the present invention is applied to a reproducing apparatus for detecting the rotation of the polarization plane of a magneto-optical recording medium or the like. The optical system in this example is an application of the optical system of Japanese Patent Publication No. 4-3575 described in the Related Art section, and the second beam 11d is applied to the electro-optical element systems 26a and 26.
Phase modulation is performed at a frequency higher than the highest frequency of the signal to be reproduced by b. [Seventh Embodiment] FIG. 10 shows a seventh embodiment applied to the magneto-optical recording medium reproducing apparatus shown in FIG.
Compared with the device of FIG. 9, it is characterized in that it is attenuated by the differential amplifier system 24 of the second beam 11d and a high SN ratio can be obtained. Of course, the phase modulation is executed by the electro-optical element systems 26a and 26b as in the case of the sixth embodiment.

As described above, it is possible to prevent the irregular fluctuation of the reproduction output level caused by the phase fluctuation of the reflected light due to the surface wobbling of the optical recording medium, and to obtain the stable reproduction output.

[0095]

As described above, according to the present invention, the effects of laser noise and thermal noise can be effectively reduced, and a good SN ratio can be obtained even at low power.

By applying the present invention to a photochromic medium, the number of times reproduction is possible with a good SN ratio can be greatly improved.

Further, according to the present invention, it is possible to prevent an irregular fluctuation of the reproduction output level caused by the phase fluctuation of the reflected light due to the surface deviation of the surface of the optical recording medium, and to obtain a stable reproduction output.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system of a reproducing device according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of an optical system of a reproducing apparatus showing a second embodiment of the present invention.

FIG. 3A is a waveform diagram showing a variation in reproduction output in a conventional reproduction device, and FIG. 3B is a waveform diagram when phase modulation according to the present invention is performed.

4A is a waveform diagram when the waveform of FIG. 3B is subjected to rectification, and FIG. 4B is a waveform diagram when the waveform of FIG. 3A is passed through a low frequency filter. .

FIG. 5 is an optical system configuration diagram of a reproducing apparatus showing a third embodiment of the present invention.

FIG. 6 is a circuit diagram of a low frequency equivalent filter.

FIG. 7 is an optical system configuration diagram of a reproducing apparatus showing a fourth embodiment of the present invention.

FIG. 8 is a configuration diagram of an optical system of a reproducing apparatus showing a fifth embodiment of the present invention.

FIG. 9 is an optical system configuration diagram of a reproducing apparatus showing a sixth embodiment of the present invention.

FIG. 10 is a configuration diagram of an optical system of a reproducing apparatus showing a seventh embodiment of the present invention.

FIG. 11 is a diagram showing an optical system configuration of a conventional reproducing apparatus.

[Explanation of symbols]

 12 Polarizer 13 First Beam Splitter 14 Second Beam Splitter 15 Objective Lens 16 Mirror 17, 25 λ / 2 Plate 18 Phase Plate 19 Third Beam Splitter 20, 201, 202 Analyzer 21, 211, 212 Lens 22, 221, 222 photodetector 23 medium 24 differential amplifier 11a to 11f beam

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G11B 7/135 Z 7247-5D

Claims (5)

[Claims] 1. A polarized light beam emitted from a single light source is divided into a first beam and a second beam, the first beam is incident on an optical recording medium, and the first beam is responsive to information recorded on the medium. A reflected beam whose polarization plane is modulated is taken out from the medium, the reflected beam and the second beam are optically mixed, and the third and fourth beams generated by this mixing are respectively photodetected via an analyzer. Is detected independently of each other and subtracted between two detection signals obtained as a result of this detection to obtain a reproduction signal. 2. A light source, an optical separation element for separating a beam from the light source into first and second beams, a lens system for converging the first beam on an optical recording medium, and the medium. Optical mixing element for optically mixing the reflected beam and the second beam, a photodetector for independently detecting the third and fourth beams generated by this mixing, and two photodetectors obtained from the detector. An optical information reproducing apparatus including a circuit for performing subtraction between signals and reproducing the result as a reproduction output. 3. A polarized beam emitted from a single light source is divided into a first beam and a second beam, the optical beam is irradiated with the first beam, and the beam is responsive to information recorded on the medium. A reflected beam having a modulated light intensity is extracted by reflection by the medium, the reflected beam and the second beam are mixed, and the intensities of the third and fourth beams generated by this mixing are independently detected by a photodetector. Detected in
A method of reproducing optical information, characterized in that a reproduction signal is obtained by performing a subtraction between two detection signals obtained as a result of the detection. 4. The method for reproducing optical information according to claim 1 or 3, wherein the phase of at least one of the first beam, the reflected beam from the medium and the second beam is the maximum of the information signal to be reproduced. A method for reproducing optical information, characterized by modulating at a frequency higher than the frequency. 5. The optical information reproducing apparatus according to claim 2, wherein the phase of at least one of the two beams incident on the optical mixing element is modulated at a frequency higher than the maximum frequency of the information signal for reproducing. A device for reproducing optical information, characterized in that a phase modulating means for performing the operation is provided.