JPS63100645A - Magneto-optical information reproducing device - Google Patents

Abstract

PURPOSE:To improve the C/N of a signal detection by using a polarizing beam splitter having an optimum polarizing characteristic as a means to divide a luminous flux for detecting the magneto-optical signal and for detecting the servo signal of a magneto-optical information reproducing device. CONSTITUTION:The luminous flux ejected as the straight line polarization of a P polarizing direction from a semiconductor laser 21 goes to a parallel luminous flux by a collimator lens 22, transmits a first polarizing beam splitter 34 and is image-formed as a fine spot on recording media 25 by an objective lens 24. A reflecting light magneto-optically modulated in accordance with the information recorded magnetically on the recording medium 25 is made into the parallel luminous flux again by the objective lens 2, reflected by the splitter 34, and thereafter, passes through a converging lens 25, goes to a convergent luminous flux and is made incident on a second polarizing beam splitter 15. The luminous flux to transmit the splitter 15 is detected by a detector 37 detected by a photodetector 36. On the other hand, the luminous flux reflected by the splitter 15 is detected by a detector 38 and a focus servo signal and a tracking servo signal are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a magneto-optical information reproducing device that reproduces information magnetically recorded on a recording medium by utilizing the magneto-optical effect.

[Prior art]

BACKGROUND ART In recent years, optical memories that perform recording and reproduction using semiconductor laser light have been actively researched and developed for practical use as high-density recording memories. Among these, in addition to read-only optical disks and DRAW type optical disks such as compact disks that have already been commercialized, magneto-optical disks that are erasable and rewritable are particularly promising. Magneto-optical disks magnetically record information using the local temperature rise of a magnetic thin film caused by laser spot irradiation, and reproduce the information using the magneto-optic effect (particularly the Kerr effect).

The Kerr effect here refers to a phenomenon in which the plane of polarization rotates when light is reflected by a magnetic recording medium.

The basic configuration of a conventional magneto-optical disk device is shown in FIG. In FIG. 6, l is a semiconductor laser, 2 is a collimator lens, 14 is a polarizing beam splitter, 4 is an objective lens, 5 is a magneto-optical information recording medium, 6 is a condenser lens, 20 is a half mirror, 116 is an analyzer, 17 18 is a detector for detecting magneto-optical information, and 18 is a detector for focus and tracking servo. It is assumed that the P polarization direction is also parallel to the paper surface, and the S polarization direction is perpendicular to the paper surface.

The light beam emitted from the semiconductor laser 1 as linearly polarized light in the P polarization direction is made into a parallel light beam by the collimator lens 2,
It passes through the polarizing beam splitter 14.

14 has polarization characteristics of approximately 80% transmittance in the P polarization direction and S
It is known that if the reflectance in the polarization direction is 100%, the laser light usage efficiency is also moderate and a magneto-optical signal with a good C/N ratio can be obtained. The light beam is imaged as a minute spot on the recording medium 5 by the objective lens 4.

When a magnetic domain (focus) is previously formed on the recording medium 5, the reflected light from the medium 5 is affected by the Kerr effect (when light is reflected by the magnetic recording medium, as shown in FIG. 7),
±θ depending on the magnetization direction (upward or downward) of the spot irradiation area (a phenomenon in which the plane of polarization rotates).
undergoes rotation of the plane of polarization. Here, if the P polarization component of the amplitude reflectance of the recording medium is R and the S polarization component is K, the following equation holds true.

The magneto-optically modulated reflected light is again converted into a parallel beam by the objective lens 4, and is reflected by the polarizing beam splitter 14.
It passes through the condensing lens 6 and becomes a convergent beam.

The half mirror 20 is provided to divide the light beam into a detector 17 for detecting a magneto-optical signal and a detector 18 for detecting a servo signal. Servo signal band (~10KHz
) is significantly different.

The light beam that has passed through the half mirror 20 is analyzed by an analyzer 16 and detected by a detector 17 as an intensity-modulated light beam. On the other hand, the light beam reflected by the half mirror 20 is
It is detected by a detector 16, and a focus servo signal and a tracking servo signal are obtained by a known method.

Assuming that the amplitude after being reflected by the polarizing beam splitter 14 is α, the angle of the optical axis of the A1 analyzer from the P analysis direction is α, and the transmittance is 1, the amplitude reflected by the polarizing beam splitter 14 is as shown in FIG. The apparent Kerr rotation angle of the luminous flux increases to ±θ', and the amplitude of each luminous flux after being divided by the half mirror 20 becomes A/V'2.

On the transmission side of the half mirror 20, as shown in FIG. 8(A),
This rotation of the plane of polarization is analyzed by the analyzer 16 as an orthogonal projection of the amplitude onto the analyzer optical axis, and a magneto-optical signal is obtained.

On the other hand, on the reflection side, the same is true as in (A), but in order to obtain a servo signal, no magneto-optical modulation component is required at all, and as shown in Figure 8 (B), detection is performed without using an analyzer. be done.

The amount of light incident on the output of the semiconductor laser I to the IO1 magneto-optical signal detection detector 17 and the servo signal detection detector 18 is I RF .

If Is, then from the above, IRF cc2I (, (l Rl "cos" a±
IRI lK15in2(Z) (2) l5ec-1
, IRI” (3)
and make a hail. (2) The second term in parentheses is the magneto-optical modulation component, and the sign corresponds to the sign of the Kerr rotation angle ±θ.

However, in the conventional device that uses the half mirror 20 to divide and guide the light flux to the detector for detecting the magneto-optical signal and the detector for detecting the servo signal, the magneto-optical modulation component is transferred to the transmission side in the half mirror 20. It is divided into 1/2 on the reflection side, resulting in a good C/N.
(ratio of carrier wave to noise) was difficult to obtain.

[Summary of the Invention] It is an object of the present invention to provide a magneto-optical information reproducing device which improves the drawbacks of the above-mentioned prior art and is capable of reproducing magneto-optical signals with a simple configuration and a good C/N ratio.

The above-mentioned object of the present invention is to provide a magneto-optical information reproducing device with means for focusing a light beam polarized in a predetermined direction onto a track on a recording medium on which information is magnetically recorded as a minute spot;
a polarizing beam splitter that splits a reflected or transmitted light flux from the recording medium whose polarization state has been modulated according to the information by a magneto-optical effect at a predetermined ratio according to the polarization component; and the polarizing beam splitter. a first detecting information recorded on the recording medium from one of the light beams;
and a second detection means for detecting both defocus information and track deviation information of the light beam irradiated onto the recording medium from the other divided light beam.

〔Example〕

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a schematic configuration diagram showing a first embodiment of a magneto-optical information reproducing apparatus based on the present invention.

In FIG. 1, 21 is a semiconductor laser, 22 is a collimator lens, 34 is a first polarizing beam splitter, 24 is an objective lens, 25 is a magneto-optical information reproducing device, 26 is a condenser lens, and 15 is a second polarized beam 36 is an analyzer, 37 is a detector for detecting magneto-optical information, and 38 is a focus and tracking servo detector. P
It is assumed that the polarization direction is parallel to the paper surface and the S polarization direction is perpendicular to the paper surface.

The light beam emitted from the semiconductor laser 21 as linearly polarized light in the P polarization direction is made into a parallel light beam by the collimator lens 22, transmitted through the first polarizing beam splitter 34, and focused as a minute spot on the recording medium 25 by the objective lens 24. imaged. The reflected light, which has been magneto-optically modulated according to the information magnetically recorded on the recording medium 25, is turned into a parallel light beam again by the objective lens 24, reflected by the first polarizing beam splitter 34, and then focused. passes through the optical lens 26,
The light becomes a convergent beam and enters the second polarizing beam splitter 15.

The light beam transmitted through the second polarizing beam splitter 15 is analyzed by an analyzer 36, and detected by a detector 37 as an intensity-modulated light beam. On the other hand, polarizing beam splitter 1
The light beam reflected by the detector 5 is detected by a detector 16, and a focus servo signal and a tracking servo signal are obtained by a known method. The polarization characteristics of the polarization beam splitter 15 are as follows: tp is the amplitude transmittance in the P polarization direction, and rps is the reflectance.
If the amplitude transmittance in the S polarization direction is ts and the reflectance is rs, then l tp l"> I rp I"
(4) l ts l”> l rs l”
(5). That is, it is sufficient to divide the minimum amount of light necessary to obtain a sufficient S/N to the servo signal detection detector 38, and since no magneto-optical modulation component is required, l ts l''= 1. l rs l”=o
(6) may also be used.

If a polarizing beam splitter with such polarization characteristics is used, as shown in FIG. 2(A), the polarizing beam splitter 15
On the transmission side of the polarizing beam splitters 34 and 15
Therefore, the apparent Kerr rotation angle increases to ±θ′,
Also, the amplitude is Ar5in"θ' g + I tp l"cos2θ
' (however, 1tsj''=1). Also, on the reflection side, as shown in Figure 2 (B), the S polarization component, that is, the magneto-optical modulation component, becomes 0, and the amplitude is the Arpco polarization component of only the P polarization component.
It becomes sθ'.

If the output of the semiconductor laser 21 is 10, and the amounts of light incident on the magneto-optical signal detection detector 37 and the servo signal detection detector 38 are I' RF and I' s, then 1.
'RF@C1o(ltpl"lR1"cos"α soil
t[)l 1tsl IRI lK15in2α)1'
S cX:Iolrpl"lR1"
(8) It will rain. Here, for example, 1t
If p 12 = o, 81 rp l'' = 0.2, the strength of the magneto-optical signal will be improved by 3.2 times, and the carrier level will be improved by 5 dB, compared to the conventional case using a half mirror.

FIG. 3 is a schematic configuration diagram of an optical system showing a second embodiment of the present invention. This embodiment is a modification of the first embodiment described above so that magneto-optical information is detected from the transmitted light beam of the polarizing beam splitter 15. In FIG. 3, the same members as in FIG. 1 are denoted by the same symbols. The detailed explanation will be omitted. The polarization characteristic of the polarizing beam splitter 15 is l rp 12> l tp l”
(9) l rs 12> l ts l”
(10), and care is taken so that a sufficient amount of magneto-optical modulation component enters the magneto-optical signal detection detector 37. Also, l rs l””1. l ts l”=0
(11) may also be used. Figure 2 and (7),
In equation (8), tp and ps, js and rs may be replaced.

Furthermore, although FIGS. 1 and 3 show the dividing plane of the polarizing beam splitter within the paper for convenience of explanation, the present invention is not limited to this.

FIGS. 4(A) and 4(B) are schematic views showing a third embodiment of the present invention, and FIG. 4(B) shows a view of FIG. 4(A) viewed from the direction of the arrow. In FIGS. 4(A) and 4(B), the same members as in FIG. 1 are denoted by the same reference numerals, and detailed explanations will be omitted.

In this embodiment, the polarizing beam splitter 34 of the first embodiment is
Instead, a polarizing beam splitter 23 having a beam shaping function is used. As a result, the light beam of the semiconductor laser 21 having an elliptical far-field pattern is transferred to the recording medium 26.
The image can be efficiently formed as a circular spot. Further, the surface a is tilted again in a predetermined manner so that stray light does not enter the photodetector 29.

Further, the magneto-optical detection light transmitted through the polarizing beam splitter 15 is sent to the λ/2 plate 42 and the third polarizing beam splitter 3.
9, differential detection is performed by detectors 4o and 41. The polarization characteristic of this polarization beam splitter 39 is l tp
Both l'' and lrs l'' are 100%.

The beam splitting surface of the polarizing beam splitter 15 is not within the plane of the paper. The polarization characteristics of this polarizing beam splitter 15 are l tp=100% and 1ts=80% in the transmission direction, and 1rp=o and 1rs=20% in the reflection direction. However, P and S are relative to the splitting plane of the polarizing beam splitter 15, and are different from the P and S polarization directions determined in the embodiment of FIG. Manufacturing such a polarizing beam splitter is easy, and it was confirmed that the carrier level was improved by 5 dB or more in this example.

FIG. 5 is a schematic diagram showing a fourth embodiment of the present invention.

In FIG. 5, the same members as in FIG. 4 are denoted by the same reference numerals, and detailed explanations will be omitted. In this example, the second
It is configured to obtain magneto-optical information from the reflected light of the polarizing beam splitter 15.
The polarization characteristic of is l t in the transmission direction, l”=20%1t
sl”=o, 1rp12=80% in reflection direction, 1rsl
”=loO%. However, p and s are P1S defined at the beginning.
Matches polarization. Such a polarizing beam splitter is easy to manufacture, and a good C/N can be obtained in this embodiment as well.

The present invention can be applied in various ways in addition to the embodiments explained and explained above. For example, in the embodiment, reflected light from the magneto-optical recording medium is detected, but it may be configured to detect a light flux that passes through the magneto-optical recording medium and is modulated by the Faraday effect.

〔Effect of the invention〕

As explained above, the present invention uses a polarizing beam splitter with optimal polarization characteristics as a means for splitting a light flux into magneto-optical signal detection and servo signal detection in a conventional magneto-optical information reproducing device. , signal detection C/
It has the effect of improving N.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of a magneto-optical information reproducing apparatus based on the present invention, FIGS. 2(A) and (B) are diagrams showing polarization states of detection light in the present invention, and FIG. 3, respectively. 4(A), 5(B) and 5 are schematic diagrams showing other embodiments of the present invention, FIG. 6 is a schematic diagram illustrating an example of a conventional magneto-optical information reproducing device, and FIG. Figure 8(A). (B) is a diagram showing the principle of general opto-magnetic signal detection. 15... Second polarizing beam splitter 21... Semiconductor laser 22... Collimator lens 24... Objective lens 25... Magneto-optical information reproducing recording medium 26... Condensing lens 36... analyzer

Claims (2)

[Claims] (1) A means for focusing a light flux polarized in a predetermined direction onto a track on a recording medium on which information is magnetically recorded as a minute spot, and modulating the polarization state according to the information by the magneto-optic effect. a polarizing beam splitter that splits the reflected or transmitted light beam from the recording medium at a predetermined ratio according to its polarization component; and information recorded on the recording medium from one of the light beams split by the polarizing beam splitter. A magneto-optical information reproducing device comprising a first detecting means for detecting, and a second detecting means for detecting at least one of defocus information and track misalignment information of a light beam irradiated onto the recording medium from the other divided light beam. . (2) A characteristic in which the polarizing beam splitter increases the polarization component in the direction perpendicular to the predetermined direction, of the light flux detected by the first detection means, relative to the polarization component in the predetermined direction. A magneto-optical information reproducing device according to claim 1.