JPH0770097B2 - Magneto-optical recording / reproducing head - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magneto-optical recording / reproducing head using a magneto-optical recording medium, and particularly to a birefringence and an optical element of a medium substrate at the time of magneto-optical reproducing. The present invention relates to a magneto-optical recording / reproducing head configured to reduce the influence of retardation.

[Conventional technology]

A magneto-optical effect called Kerr effect or Faraday effect is used for reproducing magnetically recorded information from a magneto-optical recording medium on which an information signal is recorded.

In the magneto-optical recording / reproducing head shown in FIG. 6 (a), the reflected light from the recording medium 7 is amplitude-divided by the beam splitter 4, each analyzer 21a, 21b converts the information signal into a light amount change, and each photodetector. 2
This is a configuration in which a reproduction output is obtained by 3a and 23b and differential amplification is performed. On the other hand, in the magneto-optical recording / reproducing head shown in FIG. 6 (b), the polarization plane of the reflected light from the recording medium 7 is rotated by π / 4 by the half-wave plate 25, and the analyzer 21 splits the light at the same time. This is a configuration in which a signal is converted into a light amount change, a reproduction output is obtained by each of the detectors 23a and 23b, and differential amplification is performed. In FIGS. 6A and 6B, 1 is a semiconductor laser, 2 is a collimator lens, 3 is a polarizer, 4 is a beam splitter, 5 is an actuator,
Reference numeral 6 is an objective lens, 20 is a beam splitter, 22a and 22b are condenser lenses, and 24 is a differential amplifier.

[Problems to be solved by the invention]

In the case of the magneto-optical recording / reproducing head of FIG. 6 (a), it is necessary to use two expensive analyzers. In addition, there is a drawback in that it is difficult to make adjustment because it is necessary to set the set angle of each analyzer to an optimum angle. On the other hand, in the case of the magneto-optical recording / reproducing head shown in FIG. 6 (b), it is not necessary to set the analyzer at the optimum angle. However, FIG. 6 (a),
Since the configuration of (b) does not have the function of mitigating the effects of the birefringence of the medium substrate and the retardation of the optical element at the time of magneto-optical reproduction, the deterioration of the SN ratio of the reproduction signal and the envelope have a great influence. It has the drawback that it will be disturbed when it is received.

FIG. 3 illustrates the basic reproducing principle of magneto-optical recording using the magnetic Kerr effect. In the figure, P _i is the polarized light incident on the magneto-optical recording medium 7, R ⁺ is, for example, the polarized light reflected from the region magnetized below the medium film surface, and R ⁻ is the reflected from the region magnetized above the medium film surface. Each of the polarized lights is represented. Further, θ _k is called the Kerr rotation angle and represents the amount of rotation of the vibrating surface of light due to the magneto-optical effect. Fig. 6 (b)
Of the magneto-optical recording / reproducing head, the half-wave plate 25 is moved by θ / 2 from the extinction position of the analyzer 21 when the reproducing light spot scans the alternately magnetized areas of the magneto-optical recording medium 7. When the amount of transmitted light when it is rotated intentionally is P, modulated light having an intensity difference S represented by the following equation (1) is obtained and is regenerated by the photodetectors 23a and 23b.

S = Psin2θ _k Sin4θ (1) However, in the actual reproducing state, the reflected light is elliptically polarized light as shown in FIG. 4 due to the influence of the birefringence amount and the retardation of the medium substrate and the optical element itself. for that reason,
The absolute amount of the signal light amount is smaller than that of the equation (1) as represented by the following equation (2). Here, β is the ellipticity angle, and Δ is the retardation of the optical element.

S = P (cos2 | β | cosΔsin2θ _k + sin2 | β | sinΔ) sin4θ (2) That is, the noise component may increase due to the elliptically polarized light, and the signal-to-noise ratio (SN ratio) of the reproduced signal decreases. It has the drawback. Further, when a disk medium is used, the reproduced signal envelope is greatly disturbed due to the effect of birefringence in the circumferential direction. Disturbance of the envelope of the reproduced signal leads to erroneous reading of recorded information, leading to a drawback such as deterioration in the performance of the entire apparatus.

An object of the present invention is to provide a magneto-optical recording / reproducing head capable of improving the SN ratio of a reproduction signal and smoothing the envelope by alleviating the above-mentioned drawbacks, mitigating the effect of birefringence during magneto-optical reproduction. Especially.

[Means for Solving the Problems]

The magneto-optical recording / reproducing head of the present invention comprises a light source, an optical system for converging and irradiating a light flux emitted from the light source onto the surface of the magneto-optical recording medium, and extracting reflected light or transmitted light thereof, and the reflected light or transmitted light. , A phase compensator having a beam splitter provided in the optical path for amplitude-dividing the reflected light or the transmitted light, and a mechanism capable of rotating about the optical axis provided in the optical path of the reflected light from the beam splitter, the optical axis center A half-wave plate and an analyzer having a rotatable mechanism, photodetectors for receiving transmitted light and reflected light of the analyzer, and a differential amplifier for differentially amplifying the output of each photodetector. The differential amplifier is a frequency band for removing the disturbance of the envelope of the reproduced signal due to the birefringence of the reflected light or the transmitted light from the magneto-optical recording medium or the retardation of the optical element in the frequency space and smoothing it. It is characterized in that which has been subjected to limited.

[Action]

In order to bring the amount of signal light of the reproduction signal into the state of Expression (1), it is necessary to restore the polarization state of the elliptically polarized light by the medium substrate and the optical components to the linearly polarized light state. There is a quarter wavelength plate as an optical element for converting linearly polarized light into circularly polarized light and converting circularly polarized light into linearly polarized light. This quarter-wave plate has a different conversion method depending on the azimuth angle between the crystal axis direction and the polarization direction of the incident light. That is, when the azimuth angle is ± π / 4, linear polarization and circular polarization are converted, and in other cases, elliptically polarized light and linear polarization are related. Therefore, if the quarter-wave plate is inserted before the reflected light from the medium is incident on the analyzer, the polarization state of the elliptically polarized light by the medium substrate and the optical components can be returned to the linearly polarized state, Equation (1) for the signal light intensity
It will be improved to near the state of. Further, when the influence of birefringence or retardation due to the medium substrate or the optical element is great, the envelope of the reproduced signal is considerably disturbed as shown in FIG.

The period of this turbulence is about several Hz to 100 Hz because it depends on the rotation speed of the disk substrate. Therefore, for the filter characteristics of the differential amplifier, use the one configured with the filter specifications so that the disturbance of the reproduced signal envelope due to the birefringence of the reflected light from the medium and the retardation of the optical element is removed and smoothed in the frequency space. It will be good. This makes it possible to hold the signal light amount of the reproduction signal to the maximum and at the same time smooth the envelope of the reproduction signal.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the magneto-optical recording / reproducing head of the present invention. This magneto-optical recording / reproducing head uses a semiconductor laser 1 as a light source, and a light flux emitted from the light source passes through a collimator lens 2, a polarizer 3, a beam splitter 4, and an objective lens 6 provided in an actuator 5, and a magneto-optical recording medium 7 is provided. Then, the reflected light is split by the beam splitter 4. A phase compensating plate 8, a half-wave plate 9 and an analyzer 10 are provided in the optical path of the reflected light from the beam splitter 4, and a condenser lens 11a for condensing the transmitted light and the reflected light of the analyzer 10, 11b
And a photodetector 12a that receives the collected transmitted light and reflected light,
12b and a differential amplifier 13 that differentially amplifies each photodetector output
And a high-pass filter 14.

The phase compensating plate 8 is composed of a quarter wavelength plate and has a mechanism capable of rotating about the optical axis, the half wavelength plate 9 has a mechanism capable of rotating about the optical axis, and the differential amplifier 13 is a medium. The band limitation of the high-pass filter is applied to the filter so that the disturbance of the reproduced signal envelope due to the birefringence of the reflected light from 7 and the retardation of the optical element is removed in the frequency space and smoothed.

In FIG. 1, an optical system for obtaining a control signal for driving the actuator is omitted.

In the magneto-optical recording / reproducing head having the above structure, the light flux emitted from the semiconductor laser 1 is generated by the collimator lens 2, the polarizer 3,
The light is transmitted through the beam splitter 4 in this order, and is condensed and irradiated onto the surface of the magneto-optical recording medium 7 by the objective lens 6 installed in the actuator 5. A part of the light beam focused and irradiated is the medium 7
Is reflected by. The reflected light beam is reflected by the beam splitter 4
The light is divided by the phase compensating plate 8 according to the present invention and a half.
The polarization state of the reflected light flux is controlled by the wave plate 9, the signal component of the reflected light flux is amplitude-divided by the analyzer 10, and the condenser lens 11 is used.
It leads to two photodetectors 12a and 12b via a and 11b, and a differential amplifier
The signal is differentially amplified by 13, and the high-pass filter 14 smoothes the disturbance of the envelope of the reproduced signal due to the medium substrate or the optical element.

At this time, it is necessary to rotate the phase compensation plate 8 and the half-wave plate 9 independently. In FIG. 2, the phase compensating plates 8 and 2 are shown.
An example of a rotating mechanism that rotates the half-wave plate 9 about the optical axis will be shown. FIG. 2 (a) is a front view and FIG. 2 (b) is a side view. This rotating mechanism has a support base 15 having a through hole.
The gears 16 and 17 having an integral structure are inserted from both sides of the through hole, and these gears are rotatably supported. Through holes 18 and 19 are provided in the optical axis portions of the gears 16 and 17, respectively, and a phase compensation plate 8 is provided in the through hole 18 and a half-wave plate 9 is provided in the through hole 19. is set up. By rotating the gears 16 and 17, the phase compensating plate 8 and the half-wave plate 9 can be rotated.

In the above-described embodiments, the quarter-wave plate with the rotation mechanism is used as the phase compensating plate, but any phase compensator having a configuration capable of varying the phase can be applied.

In the above embodiments, the Kerr effect is used to output the signal corresponding to the magnetization state of the medium by the reflected light from the magneto-optical recording medium. However, when the Faraday effect is used, the magneto-optical recording is performed. A signal is output from the transmitted light of the medium.

〔The invention's effect〕

As described above, the magneto-optical recording / reproducing head of the present invention is
It has the effect of mitigating the effect of birefringence during magneto-optical reproduction, not only improving the signal-to-noise ratio of the reproduction signal, but also smoothing the envelope of the reproduction signal. Can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a magneto-optical recording / reproducing head of the present invention, and FIG. 2 is a diagram for explaining a rotation mechanism of a phase compensating plate and a half-wave plate according to the present invention. FIG. 4 is a diagram for explaining the basic principle of magneto-optical reproduction, FIG. 4 is a diagram for explaining the polarization state in the actual case of magneto-optical reproduction, and FIG. 5 is a description of disturbance of the envelope of the reproduction signal. FIG. 6 is a diagram showing an example of a conventional magneto-optical recording / reproducing head. 1 ... Semiconductor laser 2 ... Collimator lens 3 ... Polarizer 4 ... Beam splitter 5 ... Actuator 6 ... Objective lens 7 ... Magneto-optical recording medium 8 ... Phase compensator 9 ... Half wavelength Plate 10 …… Analyzer 11a, 11b …… Condensing lens 12a, 12b …… Photodetector 13 …… Differential amplifier 14 …… High-pass filter 15 …… Support stand 16,17 …… Gear 18,19 …… Penetration Hole

Claims (1)

[Claims] 1. A light source, an optical system for converging and irradiating a light flux emitted from the light source onto a surface of a magneto-optical recording medium and extracting reflected light or transmitted light thereof, and an optical system provided in the optical path of the reflected light or transmitted light. A beam splitter for amplitude-dividing the reflected light or the transmitted light, an analyzer provided in the optical path of the reflected light from the beam splitter, for amplitude-dividing the signal component of the reflected light flux, and the beam splitter and the analyzer. A phase compensating plate provided between the phase compensating plate and the analyzer, the half-wave plate having a mechanism capable of rotating about the optical axis; Each photodetector that receives the transmitted light and the reflected light of the analyzer, a differential amplifier that differentially amplifies the output of each photodetector, and a reflection from the magneto-optical recording medium in the output signal from the differential amplifier. Light or transmitted light The envelope of disturbance of the reproduced signal due to retardation of folding or optical element is removed in the frequency space, a magneto-optical recording and reproducing head, characterized in that a high-pass filter for smoothing.