JP2574916B2 - Optical device for reproducing magneto-optical recording media - Google Patents

Description

The present invention relates to an optical device for reproducing a magneto-optical recording medium,
In particular, the present invention relates to a reproducing optical device for differentially detecting a magneto-optical signal by utilizing a circular dichroism effect of a magnetic material.

[Conventional technology]

An optical disk using a rare earth transition metal alloy thin film as a recording medium has entered a practical stage as a digital memory. In order to reproduce information recorded on an optical disk, a method of irradiating a recording medium with linearly polarized light emitted by a semiconductor laser and converting the rotation of the plane of polarization of the reflected light into light intensity by an analyzer is usually employed.

To explain the principle of the reproducing method utilizing the so-called Kerr effect described above, as shown in FIG. 5, the reflected light R ₁₁ in the recording medium of the linearly polarized light by the semiconductor laser is emitted, the analyzer 31
It is led to. In the analyzer 31, the detection light D ₁₁ separated by the difference of the inclination of the polarization plane corresponding to the difference of the vertical magnetization direction of the recording medium and detecting light D ₁₂ is 32 - each photodetector
33 is converted into an electrical signal by the reproduced signal S ₁₁ and the reproduction signal S ₁₂ is obtained.

The specific direction of the perpendicular magnetization direction of the recording medium is (+), the opposite direction is (-), the reflected light vector of the recording bit magnetized in the (+) direction is α, and the recording bit magnetized in the (−) direction. Is a reflected light vector and γ is an incident light vector. As shown in FIG. 6, the reflected light vector α
Is the Kerr rotation angle + θ _{k with} respect to the incident light vector γ.
Is only spinning. The polarization plane of the reflected light vector β is rotated by the Kerr rotation angle −θ _{k with} respect to the incident light vector γ.

The reflected light vectors α and β are detected in two orthogonal polarization directions X and Y of the analyzer 31. For the polarization direction X, a signal corresponding to the component beta _X of the reflected light vector beta is output at a high level by the light detector 32, a signal corresponding to the component alpha _X of the reflected light vector alpha is the optical detector 32 Output at low level. Thus, high level (-) reproduced signal S ₁₁ corresponding to the recording, which is magnetized in the direction is output from the photodetector 32.

On the other hand, for the polarization direction Y, the component α _X
When it is outputted as a low level from the signal corresponding to the component alpha _Y of the reflected light vector alpha is output at a high level by the light detector 33. Further, when the component beta _X is output from the photodetector 32 as a high level, a signal corresponding to the component beta _Y of the reflected light vector beta is output at a low level by the light detector 33. Thereby, the output from the photodetector 32, a high level (-) and the reproduced signal S ₁₁ corresponding to the recording, which is magnetized in the direction, is output from the photodetector 33, a high level (+) is magnetized in a direction Playback signal S corresponding to the recorded
₁₂ is a signal whose phase is shifted by half a cycle from each other and whose polarities are inverted from each other.

The thus obtained reproduced signal S ₁₁ and the reproduced signal S
Numeral ₁₂ is a signal obtained based on the rotation of the plane of polarization of the reflected light, so that it is less affected by dust or the like attached to the optical disk and hardly contains disk noise. Further, in order to improve the S / N ratio, these are input to a differential amplifier, and information is reproduced based on the output signal.

However, the reproducing method utilizing the Kerr effect which is usually performed for magneto-optical recording as described above requires high accuracy in setting the analyzer 31, and has the problems of increasing the price of the reproducing apparatus. doing.

Therefore, as a method of simplifying the reproducing optical device without using an analyzer and reducing the cost of the reproducing device, a method of irradiating the recording medium with circularly polarized light and responding to the difference in the perpendicular magnetization direction of the recording medium. A reproduction method utilizing the so-called circular dichroism effect, which utilizes the occurrence of anisotropy in the intensity and phase of the reflected light, is also theoretically considered.

As shown in FIG. 7, the refractive index of the medium on the incident light side of the recording medium 34 is n ₀ , and the recording bit in the upward magnetization direction of the recording medium 34 is
The refractive index of 34a is n ₊ , the complex reflectivity is r ₊ , the refractive index of the recording bit 34b in the downward magnetization direction is n ₋ , and the complex reflectivity is r ₋ .
Such recording medium 34, for example, when irradiated with circularly polarized light L ₁₁ clockwise as you face the traveling direction of the light, reflected light is circularly polarized light L ₁₂ next to the left direction in the recording bit 34a, the recording bit 3
Light reflection at 4b is a circularly polarized light L ₁₃ small counterclockwise ^{_{strength, (r +) 2 - (}} r -) 2 reflected light intensity difference represented by the formula ... (1) can be obtained (the recording medium 34
When the counterclockwise circularly polarized light is irradiated, the reflected light becomes clockwise, and the relationship between the reflected light intensities of the recording bits 34a and 34b is opposite to the above. Note that r ₊ and r
_- it _{is, n 0, n +, n} - using _{a, r + = (n 0 -n} +) / (n 0 + n +) ...... (2) r - = (n 0 -n -) / (n ₀ + n _-) is expressed as? 3.

[Problems to be solved by the invention]

However, in the reproducing method using the circular dichroism effect, since the magnetization direction of the recording medium is detected based on the difference in reflected light intensity, foreign matter such as dust attached to the optical disk affects the reflected light intensity, and the reproduced signal is Will contain noise. As a result, there is a problem that the signal quality is more likely to be degraded than in the conventional reproducing method using the Kerr effect.

It is an object of the present invention to simplify the optical system by utilizing the circular dichroism effect without using the Kerr effect for reproducing information on a magneto-optical recording medium, and to enable differential amplification of a reproduction signal as in the related art. To provide an optical device for reproducing a magneto-optical recording medium.

[Means for solving the problem]

In order to solve the above-mentioned problems, an optical device for reproducing a magneto-optical recording medium according to the present invention irradiates a light beam to a magneto-optical recording medium made of, for example, a rare earth transition metal alloy thin film, and reflects the reflected light to a light detecting means. In the optical device for reproducing the magneto-optical recording medium, which reads information recorded on the magneto-optical recording medium by the difference in the magnetization direction by detecting
A first light source that emits S-polarized light, for example, a semiconductor laser;
A second light source that emits P-polarized light having a wavelength different from the S-polarized light, for example, a semiconductor laser; a quarter-wave plate that converts S-polarized light and P-polarized light into circularly polarized light and guides the circularly polarized light to the magneto-optical recording medium; And the phase of the drive signal of each second light source is shifted
And a second light source, which is turned on and off alternately, and a switching means such as an inverter and a high-frequency amplifier for alternately switching the emission of the S-polarized light and the emission of the P-polarized light. Separation means for separating and outputting a reproduction signal corresponding to a change in intensity is provided, for example, an inverter and a high-frequency amplifier, or a polarization beam splitter, and the reproduction signals are differentially amplified.

(Operation)

According to the above configuration, the S-polarized light emitted by the first light source is used as a quarter-wave plate (if the optical path difference between linearly polarized light vibrating in directions perpendicular to each other is within a quarter wavelength ± 20%). it can)
Then, the light is converted into, for example, right-handed circularly polarized light and irradiated on the magneto-optical recording medium. The second light source emits P-polarized light when the first light source is OFF by the operation of the switching means, and P-polarized light and S-polarized light are alternately emitted from each light source. Emitted P
The polarized light is converted to, for example, left-handed circularly polarized light by a quarter-wave plate, and is applied to the magneto-optical recording medium.

For example, a magneto-optical recording medium composed of a rare-earth transition metal alloy thin film has circular dichroism. Therefore, in a magnetic domain in which the magnetization direction of the magneto-optical recording medium is vertically downward, the irradiated right circularly polarized light has an intensity. Is reflected as a largely attenuated left circularly polarized light. On the other hand, the irradiated left circularly polarized light is reflected as right circularly polarized light having a small attenuation in intensity. Therefore, in the vertically downward magnetic domain, the reflected light intensity changes in synchronization with ON-OFF of the irradiated right circularly polarized light and left circularly polarized light, that is, ON-OFF of the P-polarized light and the S-polarized light.

In a magnetic domain in which the magnetization direction is vertically upward,
The irradiated left circularly polarized light is reflected as right circularly polarized light whose intensity is greatly attenuated. On the other hand, the irradiated right-handed circularly polarized light is reflected as left-handed circularly polarized light having a small attenuation in intensity. Therefore, in the vertically upward magnetic domain, the reflected light intensity is, on the contrary, ON-OFF of the irradiated left circular polarized light and right circular polarized light, that is, S polarized light and P polarized light.
It will change in synchronization with the polarization ON-OFF. After all,
The change in the intensity of the reflected light in the magneto-optical recording medium is symmetrical between a magnetic domain whose magnetization direction is vertically downward and a magnetic domain whose magnetization direction is vertically upward, so that its phase is shifted by a half cycle.

The separating means outputs the phase shift of the reflected light intensity change to the light detecting means as two kinds of reproduction signals having opposite polarities in synchronization with ON / OFF of the first light source and the second light source. Therefore, differential amplification becomes possible. The reproduced signal thus obtained changes in accordance with the magnetization direction of the recording medium, and the recorded information is read out digitally based on this. Even if each reproduction signal based on the intensity of the reflected light includes noise due to the influence of dust or the like, the noise is offset by differential amplification, so that a practical level of S / N ratio can be obtained.

Embodiment 1 An embodiment of the present invention is described below with reference to FIGS. 1 to 3.

As schematically shown in FIG. 1, a main part of the reproducing optical device according to the present invention includes a first light source and a second light source which emit laser beams having different wavelengths and having polarization directions orthogonal to each other. Semiconductor lasers 1 and 2, polarizing beam splitter 3, half mirror 4, collimating lens 5 for forming a parallel light beam, quarter-wave plate 6 for converting linearly polarized light to circularly polarized light, objective lens 7, photodetector as light detecting means 10, RF amplifier 11 and RF amplifier 12 as a separation means output the reproduced signal S ₁ and the reproduced signal S ₂ based on the output of the photodetector 10 when the input reference signal is at the high level, the output clock pulses Oscillator 13 superimposes a high-frequency signal on a laser drive current to reduce laser noise due to return light from optical disk 8, and oscillates laser light in semiconductor lasers 1 and 2 in a multi-longitudinal mode. It is composed of high-frequency amplifiers 14 and 15 as switching means for performing the switching and an inverter 16 as switching means for inverting the clock pulse output from the oscillator 13.

The polarization beam splitter 3 has a function of totally reflecting s-polarized light whose electric field vector is perpendicular to the incident surface and totally transmitting p-polarized light whose electric field vector is parallel to the incident surface. The linearly polarized light L _1S emitted from the semiconductor laser 1 becomes S-polarized with respect to the polarization beam splitter 3, and the linearly polarized light L _2P emitted from the semiconductor laser 2 becomes
(Therefore, the polarization directions of the linearly polarized light _L1S and the linearly polarized light _L2P are orthogonal to each other).

The quarter-wave plate 6 has a function of delaying the phase of the component of the electric field vector of the incident light in the direction of the main axis M by a quarter wavelength. Laying direction of the main axis M, as shown in FIG. 2, the polarization direction N _S of the linearly polarized light L _1S the incident has theta = Left 45 ° inclination with respect to the main axis M, also, the linearly polarized light L _2P polarization direction N _P is adapted to have a theta = right 45 ° tilt. Such linearly polarized light L
_1S is a quarter-wave plate 6 in which the phase of the component in the main axis M direction is 1/4.
If the wavelength is delayed, it changes to right circularly polarized light. On the other hand, when the phase of the component in the direction of the principal axis M is delayed by 1/4 wavelength, the linearly polarized light _L2P as described above changes to left circularly polarized light.

The recording medium 9 of the optical disk 8 is provided perpendicular to the optical axis of the objective lens 7 and is made of a rare earth transition metal alloy thin film. Information is recorded by the difference in the perpendicular magnetization direction of the recording medium 9. For example, as shown in FIGS. 3A and 3B, the magnetic domain 9b (↑) whose magnetization direction is vertically upward becomes a recording bit. I have.

Hereinafter, description will be made with reference to FIG. Oscillator 13
As shown in FIG. 3 (c), a high-frequency amplifier 14 and an inverter 16 generate a clock pulse train having a frequency of 10 to 100 MHz, which is 10 times or more the frequency of a normal recording / reproducing signal, based on an input high-frequency superimposition signal. Output to RF amplifier 14, as shown in FIG. 3 (d), in synchronism with the clock pulse, outputs a high frequency signal I ₁ to the semiconductor laser 1 as the drive current for the high-frequency superposition, to the high-frequency amplifier 11 Is also output as a reference signal. High frequency amplifier
15, as shown in FIG. 3 (e), in synchronism with the clock pulses inverted by the inverter 16 outputs a high frequency signal I ₂ to the semiconductor laser 2 as the drive current for the high-frequency superposition, frequency amplifier 12 Is also output as a reference signal. Thereby, the semiconductor laser 1 and the semiconductor laser 2 alternately _{turn on} and off the linearly polarized light L _1S and the linearly polarized light L _2P.
Fire while firing.

In the above configuration, since the linearly polarized light L _1S emitted from the semiconductor laser 1 is S-polarized, it is totally reflected by the polarization beam splitter 3 in the optical axis direction of the objective lens 7. Then, the linearly polarized light L _1S passes through the half mirror 4 and is converted into a parallel light beam by the collimating lens 5, and then, as described above, is changed to right circularly polarized light by the 既 に wavelength plate 6. The right circularly polarized light is condensed on a beam spot by the objective lens 7 and irradiates the recording medium 9 of the optical disk 8. The right circularly polarized light is reflected on the recording medium 9 as left circularly polarized light (as viewed from the recording medium 9) by the circular dichroism effect, as described with reference to FIG. However, magnetic domain 9b
In (↑), the attenuation of the reflected light intensity is small, but in the magnetic domain 9a (↓) whose magnetization direction is vertically downward, the attenuation of the reflected light intensity is large. The reflected left circularly polarized light is the objective lens 7
, Becomes a parallel ray bundle, and again the right circularly polarized light (1/4
(As viewed from the wave plate 6) and returns. In the 1/4 wavelength plate 6,
When the phase of the component in the direction of the principal axis M is delayed by 1/4 wavelength, the transmitted light of right circularly polarized light becomes linearly polarized light _L1P of P-polarized light. Linearly polarized light L _1P
The light is reflected by the half mirror 4 via the collimating lens 5 and is irradiated on the photodetector 10.

On the other hand, when the semiconductor laser 1 is OFF, the linearly polarized light L _2P emitted from the semiconductor laser ₂ (having a different wavelength from the linearly polarized light L _1S emitted from the semiconductor laser 1) is P
Since the light is polarized, it is completely transmitted through the polarization beam splitter 3. Then, similarly to the linearly polarized light L _1S , the linearly polarized light L _2P passes through the half mirror 4 and the
The light is changed to left circularly polarized light by the wave plate 6. The left circularly polarized light radiated onto the recording medium 9 via the objective lens 7 is reflected as right circularly polarized light (as viewed from the recording medium 9) on the recording medium 9 by the circular dichroism effect. However, magnetic domain 9b
In (↑), the intensity of the reflected light is greatly attenuated, but the magnetic domain 9a
In (↓), the attenuation of the reflected light intensity is small. The reflected left circularly polarized light passes through the objective lens 7 and returns to the quarter wavelength plate 6 again as left circularly polarized light (as viewed from the quarter wavelength plate 6). In the quarter-wave plate 6, the transmitted light of the left circularly polarized light is the linearly polarized light L _2S of the S polarized light.
Becomes The linearly polarized light L _2S is reflected by the half mirror 4 via the collimating lens 5 and is irradiated on the photodetector 10.

The change in the intensity of the reflected light (linearly polarized light L _1P , linearly polarized light L _2S ) applied to the photodetector 10 will be described. For example, the third
As shown in FIG. (D), the magnetic domain 9a (↓), the semiconductor laser 1 is turned ON by the high frequency signal I _1a, linearly polarized light L
Linear polarized light reflected by magnetic domain 9a (↓) when firing _1S
The intensity I _{R1a of} L _1P has been reduced by the above description, as shown in FIG. 3 (f). On the other hand, the semiconductor laser 1
Is OFF, and the semiconductor laser 2 is turned ON by the high-frequency signal I _2a as shown in FIG. 3 (e), and emits linearly polarized light L _2P , the linearly polarized light L reflected by the magnetic domain 9a (↓). _As shown in FIG. 3 (f), the intensity I _R2a of _2S has been relatively increased by the above description. Therefore, domain 9a
In (↓), the rising of the reflected light intensity I _R is high-frequency signal
Changes in synchronization with the rising edge of I _2.

Next, as shown in FIG. 3D, in the magnetic domain 9b (↑), when the semiconductor laser 1 is turned on by the high frequency signal I _1b and emits linearly polarized light L _1S , the semiconductor laser 1 is reflected by the magnetic domain 9b (↑). The intensity I _R1b of the obtained linearly polarized light L _1P has been relatively increased by the above description, as shown in FIG. 3 (f). On the other hand, when the semiconductor laser 1 is off,
Is turned on by the high-frequency signal I _2b and emits linearly polarized light L _2P as shown in FIG.
The intensity I _R2b of the linearly polarized light L _2S reflected at (↑) has been reduced by the above description, as shown in FIG. 3 (f). Thus, the magnetic domain 9b (↑), the rising of the reflected light intensity I _R will vary in synchronization with the rising edge of the high frequency signal I _1.

The above results, the reflected light intensity I _R is domain 9b (↑) and magnetic domain 9a
(↓) becomes symmetrical, and the phase changes by a half cycle.

Therefore, in the magnetic domain 9a (↓), the high-frequency amplifier 11
As shown in FIG. (G), in synchronization with the rise of high-frequency signals I _1a, the light detector 10 outputs a low level of the reproduced signal S _1a based on the intensity I _R1a of the reflected light received. Magnetic domain 9b
In (↑), the high-frequency amplifier 11 outputs a high-level reproduction signal S _1b based on the intensity I _R1b of the linearly polarized light L _1P received by the photodetector 10 in synchronization with the rising of the high-frequency signal I _2b . RF signal I ₁ is when OFF, the course, the reproduced signals S ₁ 0.

Thus reproduced signals S ₁ thus obtained is treated with an integrating circuit (not shown), as shown in FIG. 3 (i), integrated reproduced signal T ₁ is obtained. Integrated reproduced signal T ₁ is a high level in response to the magnetic domain 9b (↑) as a recording bit, the magnetic domain 9a
Low level corresponding to (↓).

Similarly, in the magnetic domain 9a (↓), the high-frequency amplifier 12
The linearly polarized light L _2S received by the photodetector 10 in synchronization with the rising of the high-frequency signal I _2a as shown in FIG.
And outputs a high-level reproduction signal _2a based on the intensity I _R2a of. In the magnetic domain 9b (↑), the high-frequency amplifier 12 outputs the high-frequency signal I
In synchronization with the rise of _2b, the light detector 10 outputs a low level of the reproduced signal S _2b based on the intensity I _R2b of the reflected light received. When the high-frequency signal I ₂ is OFF, the reproduction signal S ₂
Becomes 0.

Treatment The thus reproduced signal S ₂ obtained by the integration circuit, as shown in FIG. 3 (j), integrated reproduced signal T ₂ is obtained. The integration reproduction signal T ₂ has a phase shifted from that of the integration reproduction signal T ₁ by a half cycle and has the opposite polarity, and corresponds to the magnetic domain 9 b (↑) as a recording bit, and has a low level and a magnetic domain 9 a.
High level corresponding to (↓).

The above results, it is possible to be a differential amplifier and integrator reproduced signal T ₁ the integral reproduction signal T _2, as shown in FIG. 3 (k), the differential having a practical S / N ratio An amplified reproduction signal ΔT = T ₁ −T ₂ is obtained, and the information recorded on the recording medium 9 is read out digitally based on the intensity change. Further, the intensity of the reflected light is affected by foreign substances such as dust adhering to the substrate of the optical disk 8 and, for example, the reproduction signal S ₁
Becomes smaller than the original value, and the integrated reproduction signal T ₁
Even the strength of is reduced, the influence of the same foreign substance, also small signal intensity of the reproduced signal S _2, integrated reproduction signal
The strength of the T ₂ is reduced by the same amount. Therefore, the integral reproduction signal
If T ₁ and integrated reproduced signal T ₂ is a differential amplifier, decrease due to foreign matter is canceled. As a result, disc noise other than the reproduced signal of the recorded information is reduced.

Embodiment 2 Another embodiment of the present invention will be described with reference to FIG.
It is as follows. In addition, for convenience of explanation, the first embodiment is used.
The members having the same functions as the members shown in the drawings are denoted by the same reference numerals, and description thereof will be omitted.

In the first embodiment, the case where the reproduction signal based on the two reflected light intensities on the recording medium 9 is separated by the switching operation of the high frequency amplifiers 11 and 12 has been described. In the present embodiment, a case is shown in which reflected light is separated by using the polarization beam splitter 3 as a splitting unit using the difference in polarization direction.

In the optical device of this embodiment, as shown in FIG. 4, a half mirror 17 is provided between the semiconductor laser 1 and the polarization beam splitter 3, and a half mirror 17 is provided between the semiconductor laser 2 and the polarization beam splitter 3. 18 are arranged. On the optical axis of the objective lens 7, a collimator lens 5, a quarter-wave plate 6, an optical disk 8 and its recording medium 9 are provided as in FIG. As will be described later, after each reflected light on the recording medium 9 is separated by the polarization beam splitter 3, one is guided to a photodetector 19 by a half mirror 17, and the other is simultaneously detected by a half mirror 18 to a photodetector. It is led to 20. Further, as in the first embodiment, the high-frequency amplifier 14 outputs the high-frequency signal I ₁ to the semiconductor laser 1 in synchronization with the clock pulse output from the oscillator 13. The high-frequency amplifier 15 outputs a high-frequency signal I ₂ to the semiconductor laser 2 in synchronization with the clock pulse inverted by the inverter 16.

In the above configuration, since the linearly polarized light L _1S emitted from the semiconductor laser 1 is S-polarized light, the linearly polarized light L _1S is transmitted through the half mirror 13, is totally reflected by the polarization beam splitter 3, and has a collimating lens 5, a / 4 wavelength plate 6, and The recording medium 9 of the optical disk 8 is irradiated with right circularly polarized light via the objective lens 7. Then, the reflected light is 1/4 as in the first embodiment.
Since the light is converted into linearly polarized light _L1P of P polarization by the wave plate 6, the light is totally transmitted through the polarization beam splitter 3, is totally reflected by the half mirror 18, and is guided to the photodetector 20.

The linearly polarized light _{L2P of} P-polarized light emitted from the semiconductor laser 2 and having a different wavelength from the linearly-polarized light _L1S is also 1
The light is returned as S-polarized linearly polarized light L ₂ S by the action of the / 4 wavelength plate 6, and is totally reflected by the polarizing beam splitter 3, totally reflected by the half mirror 17, and guided to the photodetector 19. Thus, the reproduction signal S ₁ output from the photodetector 20
A photodetector 19 outputs a reproduction signal S ₂ is a high-frequency amplifier
Separated and extracted without the need for 11 and 12 switching operations.

The reproduction signals S ₁ is synchronized with the rising edge of the high frequency signal I _1, the intensity variation corresponding to the magnetic domain 9a (↓) and the magnetic domain 9b (↑) is exactly the same as in Example 1. The reproduction signal S ₂ is synchronized with the rising edge of the high-frequency signals I _2, the intensity change corresponding to the magnetic domain 9a (↓) and the magnetic domain 9b (↑) is exactly the same again as in Example 1. Hereinafter, the description of the reproduced signal obtained by the differential amplification is completely the same as that of the first embodiment, and therefore will be omitted.

〔The invention's effect〕

As described above, the reproducing optical device for a magneto-optical recording medium according to the present invention includes a first light source that emits S-polarized light, a second light source that emits P-polarized light having a different wavelength from the S-polarized light, S
A quarter-wave plate that converts the polarized light and p-polarized light into circularly polarized light and guides the light to the magneto-optical recording medium, and the first and second light sources by shifting the phases of the drive signals of the first and second light sources. Alternately ON-
A switching unit that turns off and alternately switches between emission of S-polarized light and emission of P-polarized light, and separation for the photodetection unit to separate and output a reproduction signal corresponding to the intensity change of each reflected light on the magneto-optical recording medium. Means for differentially amplifying each of the reproduced signals.

Accordingly, each circularly polarized light alternately guided to the recording medium changes due to the circular dichroism effect so that the polarities of the reflected light intensities are opposite to each other in accordance with the magnetization direction of the recording medium. It becomes possible to differentially amplify each reproduction signal output from the light detection means. As a result, the disk noise is canceled out by the differential amplification, and the S / N ratio at a practical level can be obtained by a simple optical system without using an expensive analyzer as in the past. Play.

[Brief description of the drawings]

1 to 3 show an embodiment of the present invention. FIG. 1 is a structural view of a main part of an optical device for reproducing a magneto-optical recording medium. FIG. 2 is an explanatory diagram relating to the operation of the quarter-wave plate. FIG. 3 is a timing chart of various signals corresponding to the magnetization direction of the recording medium. FIGS. 3A and 3B are diagrams showing the correspondence between recording bits and perpendicular magnetization directions. FIG. 3C is a waveform diagram of the clock pulse. FIGS. 3D and 3E are waveform diagrams of the high-frequency signal. FIG. 3 (f) is a waveform diagram of the reflected light intensity. 3 (g) and 3 (h) are waveform diagrams of the reproduced signal. FIGS. 3 (i) and (j) are waveform diagrams of the integrated reproduction signal. FIG. 3 (k) is a waveform diagram of the differential amplified reproduction signal. FIG. 4 shows another embodiment of the present invention and is a configuration diagram of a main part of an optical device for reproducing a magneto-optical recording medium. 5 to 7 show a conventional example. FIG. 5 is a configuration diagram of a main part of an optical device for reproducing a magneto-optical recording medium. FIG. 6 is an explanatory diagram showing the relationship between the Kerr effect and the polarity of the reproduced signal. FIG. 7 is an explanatory diagram relating to the circular dichroism effect in the magneto-optical recording medium. 1 is a semiconductor laser (first light source), 2 is a semiconductor laser (second light source), 3 is a polarizing beam splitter (separating means), 6 is a 1/4 wavelength plate, and 9 is a recording medium (magneto-optical recording medium) , 10, 19, and 20 are photodetectors (light detecting means), 11 and 12 are high-frequency amplifiers (separating means), 14 and 15 are high-frequency amplifiers (switching means), 16 is an inverter (separating means and switching means), L _1S is linearly polarized light (S polarized light), L _2P linearly polarized light (P polarized light), S ₁ · S ₂ is reproduced signal.

Claims (1)

(57) [Claims] 1. A magneto-optical recording medium which irradiates a magneto-optical recording medium with a light beam and detects reflected light thereof by a light detecting means to read information recorded on the magneto-optical recording medium due to a difference in magnetization direction. In the reproduction optical device, a first light source that emits S-polarized light, a second light source that emits P-polarized light having a different wavelength from the S-polarized light,
A quarter-wave plate that converts polarized light into circularly polarized light and guides it to the magneto-optical recording medium, and the first and second light sources are alternately turned on by shifting the phases of the drive signals of the first and second light sources. Switching means for turning off the S-polarized light and P-polarized light alternately, and a light detecting means for separating and outputting a reproduction signal corresponding to the intensity change of each reflected light on the magneto-optical recording medium; An optical device for reproducing a magneto-optical recording medium, comprising: a separating unit, wherein each of the reproduced signals is differentially amplified.