JPH03254451A - Reproduction optical device for magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain the S/N of practical use with a simple optical system by switching the emission of an S-polarized light and the emission of a P-polarized light alternately and applying differential amplification to each regenerative signal obtained through the separation of a regenerative signal in response to an intensity change in each reflected light in a recording medium. CONSTITUTION:This device is provided with a 1st light source 1 with an S-polarized light L1S outgoing therefrom, a 2nd light source 2 with a P-polarized light L2P whose wavelength differs from that of the S-polarized light L1S outgoing therefrom, and a 1/4 wavelength plate 6 converting the S-polarized light L1S and the P-polarized light L2P into a circularly polarized light, and switching means 14, 15 switching alter nately the emission of both the S-polarized light L1S and the P-polarized light L2P such as a high frequency amplifier. Moreover, the device is provided with separating means 11, 12 such as inverters to separately output regenerative signals S1, S2 outputted from photodetector means 10 in response to the intensity change in the reflected light in the recording medium 9 and the regenerative signals S1, S2 are differentially ampli fied. Thus, noise is cancelled by the differential amplification and the S/N of practical use is attained with the simple device.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical device for reproducing magneto-optical recording media, and in particular, to differential detection of magneto-optical signals using the circular dichroism effect of a magnetic material. This invention relates to a reproducing optical device.

[Prior Art] Optical disks using rare earth transition metal alloy thin films as recording media have entered the stage of practical use as digital memories. To reproduce information recorded on an optical disc, it is usually necessary to
A method has been adopted in which a recording medium is irradiated with linearly polarized light emitted by a semiconductor laser, and the rotation of the plane of polarization of the reflected light is converted into light intensity using an analyzer.

To explain the principle of the reproduction method using the so-called Kerr effect, as shown in FIG. 5, linearly polarized light RI 1 emitted by a semiconductor laser and reflected on a recording medium is guided to an analyzer 31. In the analyzer 31, the detection light Dll and the detection light I)+z, which are separated by the difference in the slope of the polarization plane corresponding to the difference in the perpendicular magnetization direction of the recording medium, are converted into electrical signals by the photodetectors 32 and 33, respectively. Then, a reproduced signal S11 and a reproduced signal S1□ are obtained.

The specific direction of the perpendicular magnetization direction of the recording medium is (+), the opposite direction is (-), the reflected light vector in the recording bit magnetized in the (+) direction is α, and the recording bit magnetized in the (-) direction. Let β be the reflected light vector and γ be the incident light vector. As shown in FIG. 6, the plane of polarization of the reflected light vector α is rotated with respect to the incident light vector T by the Kerr rotation angle θ. Further, the plane of polarization of the reflected light vector β is rotated by the Kerr rotation angle −0 with respect to the incident light vector T.

The reflected light vectors α and β are detected by three analyzers in two mutually orthogonal polarization directions X-Y. With respect to the polarization direction is output. As a result, the reproduction signal Sl corresponding to the recording in which the high level is magnetized in the (-) direction
+ is output from the photodetector 32.

On the other hand, for the polarization direction Y, the component α8 is detected by the photodetector 32.
When the signal corresponding to the component α7 of the reflected light vector α is output as a low level, the photodetector 33 outputs a signal as a high level. In addition, component β8 is detected by the photodetector 32.
When the signal corresponding to the component βY of the reflected light vector β is output as a high level, the photodetector 33 outputs a signal as a low level. As a result, the reproduction signal S11 corresponding to the recording is output from the photodetector 32 and the high level is magnetized in the (-) direction, and the reproduction signal S11 is output from the photodetector 33 and the high level is magnetized in the (+) direction. The reproduced signal S1□ corresponding to recording is a signal whose phase is shifted by half a cycle from each other and whose polarity is reversed from each other.

The reproduced signal S I+ and the reproduced signal S1□ obtained in this way are signals obtained based on the rotation of the plane of polarization of the reflected light, so they are less affected by dust attached to the optical disc and are less likely to contain disc noise. . Further, in order to improve the S/N ratio, these signals are input to a differential amplifier, and information is reproduced based on the output signal thereof.

However, as described above, the reproducing method using the Kerr effect, which is normally performed for magneto-optical recording, requires high precision in the setting of the analyzer 31, and also has the problem of causing an increase in the price of the reproducing device. are doing.

Therefore, as a method that can simplify the optical device for reproduction without using an analyzer and reduce the cost of the reproduction device, it is possible to irradiate the recording medium with circularly polarized light and to correspond to the difference in the perpendicular magnetization direction of the recording medium. A reproduction method that utilizes the so-called circular dichroism effect, which takes advantage of the anisotropy that occurs in the intensity and phase of reflected light, has also been theoretically considered.

As shown in FIG. 7, the refractive index of the medium on the incident light side of the recording medium 34 is no, the refractive index of the recording bin 34a in the upward magnetization direction of the recording medium 34 is n+, the complex reflectance is 4r, and the downward magnetization direction. It is assumed that the refractive index of the recorded bit 34b is n~, and the complex reflectance is r-. For example, when such a recording medium 34 is irradiated with right-handed circularly polarized light Ll+ directly facing the direction of travel of the light, the reflected light at the recording bit 34a becomes counterclockwise circularly polarized light L+z, and the reflected light at the recording bit 34b becomes It becomes counterclockwise circularly polarized light L13 with low intensity and becomes (r.)z
-(r→2 ・Old...The reflected light intensity difference expressed by the formula (1) is obtained. (When the recording medium 34 is irradiated with counterclockwise circularly polarized light, the reflected light becomes clockwise, and the recorded bit (The relationship between the reflected light intensity at the recording bit 34a and the recording bit 34b is opposite to the above). Note that r. and r- are no and n.

, n-, r, = (no n.)/(no + n,)...
・(2) r-= (no -n-)/(no +n-)
...It is expressed as in (3).

[Problem to be solved by the invention]

However, in the reproduction method using the circular dichroism effect, since the magnetization direction of the recording medium is detected by the difference in the intensity of reflected light, foreign matter such as dust attached to the optical disk affects the intensity of the reflected light, resulting in the reproduction signal being distorted. will include noise.

As a result, compared to the conventional reproduction method using the Kerr effect,
This has the problem that signal quality tends to deteriorate.

The purpose of the present invention is to simplify the optical system by using the circular dichroism effect without using the Kerr effect for information reproduction from a magneto-optical recording medium, and to enable differential amplification of the reproduced signal as in the conventional method. An object of the present invention is to provide an optical device for reproducing a magneto-optical recording medium.

[Means to solve 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 onto a magneto-optical recording medium, for example, from a rare earth transition metal alloy thin film, and optically detects the reflected light. In an optical device for reproducing a magneto-optical recording medium, which reads information recorded on the magneto-optical recording medium based on the difference in magnetization direction by detecting the difference in magnetization direction,
A first light source that emits polarized light, such as a semiconductor laser, and a second light source, such as a semiconductor laser that emits P-polarized light that has a different wavelength from the S-polarized light, converts the S-polarized light and the P-polarized light into circularly polarized light for magneto-optical recording. A 1/4 wavelength plate that guides the light to the medium, a switching device that alternately switches between outputting the S-polarized light and outputting the P-polarized light, such as an inverter and a high-frequency amplifier, and a photodetecting device that respond to changes in the intensity of each reflected light on the magneto-optical recording medium. It is characterized in that it is equipped with a separating means for separating and outputting corresponding reproduction signals, such as an inverter and a high-frequency amplifier, or a polarization beam splitter, and that each of the reproduction signals is differentially amplified.

[For production]

According to the above configuration, the S-polarized light emitted from the first light source is
The 1/4 wavelength trFi (can be used if the optical path difference between linearly polarized lights vibrating in directions perpendicular to each other is within 174 wavelengths ±20%) is converted into, for example, right-handed circularly polarized light and irradiated onto the magneto-optical recording medium. The second light source.

In this case, the first light source is switched to O by the operation of the switching means.
When in FF mode, P-polarized light is emitted, and P-polarized light and S-polarized light are emitted alternately from each light source. The emitted P-polarized light is converted into, for example, left-handed circularly polarized light by a 174-wave plate and is irradiated onto a magneto-optical recording medium.

For example, magneto-optical recording media made from rare earth transition metal alloy thin films have circular dichroism, so in a magnetic domain where the magnetization direction of the magneto-optical recording medium is vertically downward, the irradiated right-handed circularly polarized light is It is reflected as left-handed circularly polarized light with greatly attenuated intensity. On the other hand, the irradiated left-handed circularly polarized light is reflected as right-handed circularly polarized light whose intensity is less attenuated. Therefore, in a vertically downward magnetic domain, the reflected light intensity is ON-OFF of the right-handed circularly polarized light and left-handed circularly polarized light, that is, 0N-OFF of the P-polarized light and S-polarized light.
will change in sync with.

Furthermore, in a magnetic domain whose magnetization direction is vertically upward, the irradiated left-handed circularly polarized light is reflected as right-handed 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 whose intensity is less attenuated. Therefore, in a vertically upward magnetic domain, the intensity of reflected light changes, contrary to the above, in synchronization with the 0N-OFF of the irradiated left-handed circularly polarized light and right-handed circularly polarized light, that is, the 0N-OFF of the S-polarized light and the P-polarized light. become.

As a result, the intensity change of the reflected light in the magneto-optical recording medium is symmetrical between the magnetic domain whose magnetization direction is vertically downward and the magnetic domain whose magnetization direction is vertically upward, so that the phase thereof is shifted by half a period.

The separating means converts the phase shift of this reflected light intensity change into a first
In synchronization with ON-OFF of the light source and the second light source, two types of reproduction signals having opposite polarities are outputted to the light detection means, thereby making it possible to perform differential amplification. The reproduction signal obtained in this way changes in accordance with the magnetization direction of the recording medium,
Based on this, recorded information is read out digitally.

Even if each reproduced signal based on the reflected light intensity contains noise due to the influence of dust, etc., the noise is canceled out by differential amplification, so that a practical level S/N ratio can be obtained.

[Embodiment 1] An embodiment of the present invention will be described below based on FIGS. 1 to 3.

As schematically shown in FIG. 1, the main parts of the reproduction optical device of the present invention include a first light source and a second light source that emit laser beams having different wavelengths and whose polarization directions are orthogonal to each other. Semiconductor laser 2, polarizing beam splitter 3
, a half mirror 4, a collimating lens 5 that creates a bundle of parallel rays, a quarter-wave plate 6 that changes linearly polarized light into circularly polarized light, an objective lens 7, a photodetector 10 as a light detection means, and the input reference signal is at a high level. In this case, a high frequency amplifier 11 and a high frequency amplifier 12 are used as separation means to output a reproduced signal S1 and a reproduced signal S2 based on the output of the photodetector 10, respectively, an oscillator 13 that outputs a clock pulse, and a laser using return light from the optical disk 8. A high frequency signal is superimposed on the laser drive current to reduce noise, and the clock pulses output by the high frequency amplifiers 14 and 15 and the oscillator 13 are inverted as switching means for causing the semiconductor laser 2 to oscillate laser light in multiple longitudinal modes. It is composed of an inverter 16 as a switching means.

The polarizing beam splinter 3 has a function of totally reflecting S-polarized light whose electric field vector is perpendicular to the plane of incidence and completely transmitting P-polarized light whose electric field vector is parallel to the plane of incidence.

The linearly polarized light LI3 emitted by the semiconductor laser 1 becomes S-polarized light with respect to the polarization beam splitter 3, and the semiconductor laser 2
The linearly polarized light tzr emitted by the polarizing beam splitter 3
(Therefore, the polarization directions of the linearly polarized light LIS and the linearly polarized light Lzp are orthogonal to each other.)

The 1/4 wavelength plate 6 has a function of delaying the phase of the component in the direction of the principal axis M of the electric field vector of the incident light by 1/4 wavelength. As shown in FIG. 2, the direction of arrangement of the principal axis M is such that the polarization direction N of the incident linearly polarized light LI5 is θ=45 to the left with respect to the principal axis M.
degree, and the polarization direction N of the linearly polarized light LAF,
has an inclination of θ-45° to the right. Such linearly polarized light LI3 is polarized by a quarter-wave plate 6 with a main axis M.
When the phase of the directional component is delayed by 1/4 wavelength, it changes to right-handed circularly polarized light. On the other hand, the linearly polarized light LZF as described above changes to left-handed circularly polarized light when the phase of the component in the direction of the principal axis M is delayed by 1/4 wavelength.

Note that the recording medium 9 of the optical disk 8 is provided perpendicularly 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. 3(a) and (b), the magnetic domain 9b (↑) whose magnetization direction is vertically upward becomes the recording bit. There is.

The following description will be made with reference to FIG. 1 as appropriate. Oscillator 13
As shown in FIG. 3(C), based on the input signal for high frequency superimposition,
A clock pulse train with a frequency of 10-10-100, which is more than double the frequency, is output to the high frequency amplifier 14 and the inverter 16. As shown in FIG. 3(d), the high frequency amplifier 14 generates a high frequency signal 1.0 as a drive current for high frequency superimposition in synchronization with the above clock pulse. is outputted to the semiconductor laser 1 and also outputted to the high frequency amplifier 11 as a reference signal. As shown in FIG. 3(e), the high-frequency amplifier 15 outputs a high-frequency signal I2 to the semiconductor laser 2 as a drive current for high-frequency superimposition in synchronization with the clock pulse inverted by the inverter 16. 12 as a reference signal. As a result, the semiconductor laser 1 and the semiconductor laser 2 emit the linearly polarized light L13 and the linearly polarized light Lzp while being turned on and off alternately.

In the above configuration, since the linearly polarized light L Is emitted from the semiconductor laser 1 is S-polarized light, it is totally reflected by the polarizing beam splitter 3 in the optical axis direction of the objective lens 7 . And linearly polarized light.

The light passes through the half mirror 4, is made into a parallel beam by the collimating lens 5, and is then converted into right-handed circularly polarized light by the quarter-wave plate 6, as described above. For right circularly polarized light, objective lens 7
The light is focused into a beam spot and irradiated onto the recording medium 9 of the optical disc 8. This right-handed circularly polarized light is
As explained in the figure, due to the circular dichroism effect, the light is reflected from the recording medium 9 as left-handed circularly polarized light (as viewed from the recording medium 9). However, in the magnetic domain 9b (↑), the attenuation of the reflected light intensity is small, but in the magnetic domain 9a where the magnetization direction is vertically downward.
At (↓), the attenuation of the reflected light intensity becomes large. The reflected left-handed circularly polarized light becomes a parallel beam of light through the objective lens 7, and returns to the quarter-wave plate 6 again as right-handed circularly polarized light (as viewed from the quarter-wave plate 6).

In the 174 wavelength plate 6, when the transmitted light of right-handed circularly polarized light has a phase delay of 1/4 wavelength of the component in the direction of the principal axis M, it becomes linearly polarized light LI of P-polarized light.
It becomes F. The linearly polarized light LIF is reflected by the half mirror 4 via the collimating lens 5, and is irradiated onto the photodetector 10.

On the other hand, when the semiconductor laser 1 is OFF, the linearly polarized light L2. (It has a different wavelength from the linearly polarized light L Is emitted from the semiconductor laser 1)
is P-polarized light, so the polarizing beam splitter 3
Fully transparent. And the linearly polarized light LAF is the linearly polarized light L
Similar to Is, half mirror 4, collimating lens 5
The light is converted into left-handed circularly polarized light by the quarter-wave plate 6. The left-handed circularly polarized light irradiated onto the recording medium 9 through the objective lens 7 is reflected as right-handed circularly polarized light (as viewed from the recording medium 9) at the recording medium 9 due to the circular dichroism effect. However, the attenuation of the reflected light intensity is large in the magnetic domain 9b (↑), but the attenuation of the reflected light intensity is small in the magnetic domain 9a (↓). The reflected left-handed circularly polarized light passes through the objective lens 7 and returns to the quarter-wave plate 6 as left-handed circularly polarized light (as viewed from the 1/4-wave plate 6).At the quarter-wave plate 6, it becomes left-handed circularly polarized light. The transmitted light becomes S-polarized linearly polarized light Lzs. The linearly polarized light Lzs is
The light is reflected by the half mirror 4 through the collimating lens 5 and is irradiated onto the photodetector 10.

The intensity change of the reflected light (linearly polarized light LIF, linearly polarized light Lzs) irradiated onto the photodetector 10 will be explained.

For example, as shown in FIG. 3(d), in the magnetic domain 9a (↓), the semiconductor laser 1 is turned on by the high frequency signal IIs.
When it becomes N and emits linearly polarized light L Is, the magnetic domain 9a
The intensity of linearly polarized light LIF reflected by (↓) is 1.11,
As shown in FIG. 3(f), the size has been reduced by the above explanation. On the other hand, when the semiconductor laser 1 is OFF, the semiconductor laser 2 emits the high frequency signal 1 as shown in FIG. 3(e).
When the linearly polarized light LZF is turned on by 211 and the linearly polarized light LZF is emitted, the intensity 1112m of the linearly polarized light Lis reflected by the magnetic domain 9a (↓) is relatively large as shown in FIG. 3(f). It has become. Therefore, magnetic domain 9
In a (↓), the rise of the reflected light intensity IR changes in synchronization with the rise of the high frequency signal 1z.

Next, as shown in FIG. 3 (cl), when the semiconductor laser 1 is turned on by the high frequency signal 11m+ and emits linearly polarized light LIS in the magnetic domain 9b (↑), the magnetic domain 9b
The intensity of the linearly polarized light Ll reflected by (↑) is the third
As shown in Figure (f), it has become relatively large due to the above explanation. On the other hand, when the semiconductor laser 1 is OFF and the semiconductor laser 2 is turned ON by the high frequency signal rzb and emits linearly polarized light LAF, as shown in FIG. 3(e), it is reflected by the magnetic domain 9b (↑). The intensity I R2b of the linearly polarized light L2S is reduced by the above explanation, as shown in FIG. 3(f). Therefore, magnetic domain 9b (↑
), the reflected light intensity 1. The rising edge of the signal changes in synchronization with the rising edge of the high frequency signal.

As a result of the above, the reflected light intensity factor is magnetic domain 9b (↑) and magnetic domain 9
It becomes symmetrical with a (↓), and the phase changes by half a cycle.

Therefore, in the magnetic domain 9a (↓), the high frequency amplifier 11 detects the intensity 11 of the reflected light received by the photodetector 10 in synchronization with the rise of the high frequency signal I0, as shown in FIG. 3(g).
A low level reproduction signal S based on 118 is output.

In the magnetic domain 9b (↑), the high frequency amplifier 11 receives the high frequency signal I.
In synchronization with the rising edge of zb, the linearly polarized light received by the photodetector 10 outputs a reproduced signal S1b having a noise level of −intensity I II+b NIL. Naturally, when the high frequency signal 11 is OFF, the reproduced signal S1 becomes O.

When the reproduced signal S1 obtained in this manner is processed by an integrating circuit (not shown), an integral reproduced signal T1 is obtained as shown in FIG. 3(i). The integral reproduction signal T is at a high level corresponding to the magnetic domain 9b (↑) as a recording bit, and at a low level corresponding to the magnetic domain 9a (↓).

Similarly, in magnetic domain 9a (↓), high frequency amplifier
2 is a high frequency signal I'1m as shown in FIG.
In synchronization with the rising edge of , the photodetector 10 outputs a reproduction signal 52fi at a noise level based on the intensity I RZll of the linearly polarized light Lzs received. In the magnetic domain 9b (↑), the high frequency amplifier 12 synchronizes with the rising edge of the high frequency signal 1tb and detects the intensity 1. R□
A low level reproduction signal Sz++ based on ゎ is output.

Naturally, when the high frequency signal I2 is OFF, the reproduced signal S2
becomes O.

When the reproduced signal S2 obtained in this way is processed by an integrating circuit, an integrated reproduced signal T2 is obtained as shown in FIG. 3(j).
is obtained. The integral reproduction signal T2 is out of phase with the integral reproduction signal T1 by half a period and has opposite polarity, and has a low level corresponding to the magnetic domain 9b (↑) as a recording bit, and a low level corresponding to the magnetic domain 9a (↓) as a recording bit. It is at a high level.

From the above results, the integral reproduction signal T and the integral reproduction signal T2
As shown in Figure 3 (2), a differentially amplified reproduced signal ΔT = T + T z with a practical S/N ratio is obtained, and this intensity change The information recorded on the recording medium 9 is digitally read out based on the information. Furthermore, the reflected light intensity is affected by foreign matter such as dust attached to the substrate of the optical disk 8.
For example, even if the signal strength of the reproduced signal S1 becomes smaller than its original value and the intensity of the integral reproduced signal T becomes smaller, the signal strength of the reproduced signal S also decreases due to the influence of the same foreign object, and the integral reproduced signal T2 becomes smaller. the intensity of decreases by the same amount. Therefore, the integral reproduction signal T1 and the integral reproduction signal T
2 is differentially amplified, the decrease due to foreign matter is canceled out. As a result, disc noise other than the reproduction signal of recorded information is reduced.

[Embodiment 2] Another embodiment of the present invention will be described below based on FIG. For convenience of explanation, members having the same functions as those shown in the drawings of the first embodiment will be denoted by the same reference numerals, and the explanation thereof will be omitted.

In the first embodiment, a case was shown in which reproduction signals based on two reflected light intensities on the recording medium 9 are separated by the switching operation of the high frequency amplifiers 11 and 12. In this embodiment, a case is shown in which reflected light is separated by using a polarization beam splitter 3 as a separation means by utilizing a difference in polarization direction.

As shown in FIG. 4, the optical device of this embodiment includes a half mirror between a semiconductor laser 1 and a polarizing beam splitter 3.
17 is disposed, and a half mirror 18 is disposed between the semiconductor laser 2 and the polarizing beam splitter 3. On the optical axis of the objective lens 7, a collimating lens 5, a quarter wavelength plate 6, an optical disk 8 and its recording medium 9 are provided, as in FIG. Further, as will be described later, each reflected light beam on the recording medium 9 is separated by the polarizing beam splitter 3, and then one side is guided to the photodetector 19 by the half mirror 17, and at the same time, the other beam is guided to the photodetector 19 by the half mirror 17.
8 to a photodetector 20.

Further, similarly to the first embodiment, the high frequency amplifier 14 outputs the high frequency signal 11 to the semiconductor laser 1 in synchronization with the clock pulse output from the oscillator 13. The high frequency amplifier 15 is configured to output a high frequency signal 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+s emitted by the semiconductor laser 1 is S-polarized light, it is transmitted through half -13 and then totally reflected by the polarizing beam splitter 3, collimating lens 5, 1/4 wavelength plate 6, The light then becomes right-handed circularly polarized light and is irradiated onto the recording medium 9 of the optical disc 8 via the objective lens 7 . Then, as in Example 1, the reflected light is
Since the P-polarized light becomes linearly polarized light LIP at the quarter-wave plate 6,
Completely passes through the polarizing beam splitter 3 and passes through the half mirror 18.
After being totally reflected, the light is guided to the photodetector 20.

Similarly to Example 1, the P-polarized linearly polarized light I-zy' emitted from the semiconductor laser 2 and having a different wavelength from the linearly polarized light L-+s becomes the S-polarized linearly polarized light LZS by the action of the 174-wave plate 6. Then, the light is totally reflected by the polarizing beam splitter 3 and then by the half mirror 17, and then guided to the photodetector 19. In this way, the photodetector 20
The reproduced signal S1 outputted by the photodetector 19 and the reproduced signal S2 outputted by the photodetector 19 are separated and extracted without requiring switching operations of the high frequency amplifiers 11 and 12.

Note that the reproduced signal Sl is synchronized with the rise of the high frequency signal 11, and the intensity changes corresponding to the magnetic domain 9a (↓) and the magnetic domain 9b (↑) are exactly the same as in the first embodiment. Furthermore, the reproduced signal 'S t is synchronized with the rise of the high frequency signal I2, and the magnetic domain 9a (↓) and the magnetic domain 9b (↑
) is exactly the same as in Example 1. Hereinafter, the explanation of the reproduced signal obtained by differential amplification is also omitted since it is completely the same as in the first embodiment.

〔Effect of the invention〕

As described above, the optical device for reproducing 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; A quarter-wave plate that converts the S-polarized light and the P-polarized light into circularly polarized light and guides it to the magneto-optical recording medium, a switching means that alternately switches between outputting the S-polarized light and outputting the P-polarized light, and a photodetecting means that is magneto-optical. Separating means for separating and outputting reproduction signals corresponding to changes in the intensity of each reflected light on the recording medium,
This configuration is such that each of the reproduced signals described above is differentially amplified.

Therefore, due to the circular dichroism effect of each circularly polarized light that is alternately guided to the recording medium, the polarity of the reflected light intensity changes so that it becomes 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 optical detection means. As a result, disc noise is canceled out by differential amplification, making it possible to obtain a practical S/N ratio with a simple optical system without using an expensive analyzer as in the past. play.

[Brief explanation of drawings]

1 to 3 show one embodiment of the present invention. FIG. 1 shows the constituent countries of the main parts of an optical device for reproducing magneto-optical recording media. FIG. 2 is an explanatory diagram regarding the action of the quarter-wave plate. FIG. 3 is a timing chart of various signals corresponding to the magnetization direction of the recording medium. FIGS. 3(a) and 3(b) are diagrams showing the correspondence between recording bits and perpendicular magnetization directions. FIG. 3(C) is a waveform diagram of clock pulses. FIGS. 3(d) and 3(e) are waveform diagrams of high frequency signals. FIG. 3(f) is a waveform diagram of reflected light intensity. Figure 3 (b) is a waveform diagram of the reproduced signal. Figure 3 (i) and (j) are waveform diagrams of the integral reproduced signal. Figure 3 (g) is the differentially amplified reproduced signal. FIG. 4 shows another embodiment of the present invention, and shows the components of the main parts of an optical device for reproducing a magneto-optical recording medium. This shows a conventional example. Figure 5 shows the components of the main parts of an optical device for reproducing a magneto-optical recording medium. Figure 6 is an explanatory diagram showing the relationship between the Kerr effect and the polarity of a reproduced signal. 7 is an explanatory diagram regarding the circular dichroism effect in a magneto-optical recording medium. 1 is a semiconductor laser (first light a), 2 is a semiconductor laser (
3 is a polarized beam splinter (separation means)
, 6 is a quarter wavelength plate, 9 is a recording medium (magneto-optical recording medium)
, 1o, 19 and 2o are photodetectors (light detection means), 11 and 19 and 2o are photodetectors (photodetection means);
12 is a high frequency amplifier (separation means), 14 and 15 are high frequency amplifiers (switching means), 16 is an inverter (separation means and switching means), L's is a linearly polarized light (S
polarized light), L2P is linearly polarized light (P polarized light), and S, ·s2 is a reproduced signal.

Claims (1)

[Claims] 1. Magneto-optical technology that reads information recorded on a magneto-optical recording medium based on the difference in magnetization direction by irradiating the magneto-optical recording medium with a light beam and detecting the reflected light using a photodetector. In an optical device for reproducing a recording medium, 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, and a second light source that emits S-polarized light and P-polarized light,
A quarter-wave plate that converts polarized light into circularly polarized light and guides it to the magneto-optical recording medium, a switching means that alternately switches between outputting the S-polarized light and outputting the P-polarized light, and a photodetecting means, each of which is connected to the magneto-optical recording medium. 1. An optical device for reproducing a magneto-optical recording medium, comprising a separating means for separating and outputting a reproduction signal corresponding to a change in the intensity of reflected light, and wherein each of the reproduction signals is differentially amplified.