JPS63257945A - Optical head - Google Patents

Abstract

PURPOSE:To obtain an optical head which can magneto-optically record and reproduce information with simple constitution by detecting a magneto-optical change in a recording medium by means of the strength difference of two beams whose strength change in accordance with a polarization state, and detecting the change in the reflection factor of the recording medium and an error signal for servo control by means of the unchanged beam. CONSTITUTION:A lambda/2 (lambda is wavelength) phase plate 41 which is turnably arranged in a way that it is orthogonal to a reflection light or a transmitted light optical axis between a Wollaston prism 33 separating into two beams whose strength change in accordance with the deflection state and into one beam without a change in the optical strength due to deflection and an objective lens 3, and a photo detector 34 in which elements separating three beams which have transmitted through the Wollaston prism 33 and receiving light beams are arranged on a same surface are supplied. The magneto-optical change in the recording medium is detected by the strength difference of two beams whose strength changes in accordance with the deflection state, and the change in the reflection factor of the recording medium and the error signal for servo control are detected by the beam without the strength change due to deflection. Thus, two detecting optical system are made into one, and miniaturization is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical disk device for magneto-optically recording and reproducing information, and particularly to an optical head.

[Conventional technology]

Conventionally, this type of optical head has required both a servo roller detection optical system and a read signal detection optical system as shown in FIG.

Nine lights emitted from the semiconductor laser 1 are sent to the collimating lens 2
After passing through the first beam splitter 20i, the parallel light passes through the second beam splitter 20. A part of the light that has passed through the beam splitter 20i is focused onto the recording medium 100 by the objective lens 3. The light reflected by the recording medium 100 travels backward through the objective lens 3 and is partially reflected by the second beam splitter 20 . The partially reflected beam passes through the condensing lens 21 and is separated by the Wallaston prism 23 according to the polarization state. It is done. The light that has passed through the second beam splitter 20 is partially reflected by the first beam splitter 10 and enters the condenser lens 11 .

A portion of the t light collected by the condensing lens 11 is blocked by the knife 12 and enters the detection sensor 13, where an error detection signal such as a focus error signal is obtained by the knife method or the like.

[Problem that the invention seeks to solve]

Since the conventional optical head described above has two detection optical systems, it has the disadvantage that it is difficult to miniaturize due to its large shape.

[Means for solving problems]

The optical head of the present invention is arranged in the optical path of reflected light or transmitted light on a recording medium, and the reflected light and the transmitted light are divided into two beams whose intensity changes depending on their polarization state, and a change in light intensity due to polarization. a Wollaston prism that separates the beam into one beam without a λ/2 beam, and a λ/2 prism that is rotatably arranged orthogonal to the optical axis of the reflected or transmitted light between the Wollaston prism and the objective lens. It is equipped with a phase plate and a multiplication table detector in which an element that separates and receives all three beams after passing through the Wallaston prism is arranged on the same plane, and the intensity changes depending on the polarization state. It is configured to detect all magneto-optical changes in the recording medium due to the intensity difference between the two generated beams, and to detect changes in the reflectance of the recording medium and error signals for servo control using a beam with no intensity change due to polarization. Characterized by a friend.

〔Example〕

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

FIG. 1 is a configuration diagram showing a first embodiment of the present invention, and FIG. 2 is a partial perspective explanatory diagram of FIG. 1.

In FIG. 1, the light beam emitted from the semiconductor laser 1 becomes a parallel light beam at the collimating lens 2, and the transmittance is 70%.
The light passes through a beam splitter 30 configured to have a reflectance of 30%, and is focused onto a recording medium 100 by an objective lens 3. The light beam reflected by the recording medium 100 travels backward through the objective lens and enters the beam splitter 30 again. The light beam reflected by the beam splitter 30 passes through the condenser lens 31, the λ/2 phase plate 41, and the cylindrical lens 3.
2t- transmitted and enters the Wallaston prism 33.

As shown in FIG. 2, the Wollaston prism 33 is perpendicular to the central axis 200 of the light beam after passing through the cylindrical lens 32, and has an optical axis 510 aligned with the polarization direction.
A first prism 500 made of a uniaxial crystal such as quartz having an inclination of @45°, a luminous flux central axis 200, and a direct firing optical axis 610.
is composed of the optical axis of the first prism 500 and the second prism 600 which is substantially crystalline.

As shown in FIG. 2, the Wollaston prism 33 separates the beam into beams 700 and 900 whose intensity changes depending on the incident polarization state, and beam 800 whose intensity does not change depending on the incident polarization state.

The beam 800 with no change in intensity is incident on the four-divided detection sensor section of the photodetector 34, and a focus error detection signal is obtained by the astigmatism method. Intensity change lasuru beam 700
and 901j, tW@ recorded on the recording medium 100
At the pit part, the entire polarization direction is slightly changed due to the optical effect of the outgoing air.

The sensor 34 detects the intensity change caused by the incidence of these light beams at 3 parts and 0 parts of the light detection center t34. Reading of the recorded information is performed using a differential signal of the a section output and the C section output.

The λ/2 phase plate 41 adjusts the direction of polarization of light incident on the Wollaston prism 33 (at 45° with respect to the optical axis of the prism A300 in FIG. 2) so that the differential output is minimum in the non-recording area. By adjusting the rotation to fine-tune the information, the minute changes in the intensity of the recorded information pit area can be fully reproduced.

Note that the transmittance of the beam splitter in this embodiment row and the focus detection means based on the astigmatism method are not limited to this groove configuration.

It is also possible to make changes such as adding corrections based on reflectance and optical output fluctuations to the b output iC of the differential detection of the a output and C output of the sensor+j34 in this embodiment.

Instead of the cylindrical lens 32, it is also possible to insert a parallel plane glass plate at an angle to the light beam. Furthermore, it is also possible to form the Corinaught lens 2 and the objective lens 3 as one body and eliminate the Izumimoto lens 31.

Furthermore, the position of the λ/2 phase 41 is not limited to the present example, and can be moved to just before the incident light to the Foraston prism. Dog is λ/
It is also possible to arrange the two-phase plate 41t71J between the drical lens 32 and the Forlaston prism 33.

[Effect of Kabuto]

As explained above, according to the present invention, an optical head capable of recording information magnetically and optically with a simple structure can be obtained.

[Brief explanation of the drawing]

No. it! ii3 is a configuration diagram of an optical head according to an embodiment of the present invention; FIG. 2 is a perspective view showing a part of the optical head shown in FIG. 1; FIG. 3 is a configuration diagram of a conventional optical head. l...Semiconductor laser, 2...Collimating lens, 3...Objective lens, 11, 21.3
1...Condensing lens, lO...A beam splitter, 20...B beam splitter, 3
0... Beam splitter. 12... Naiue, Tsuji, 13, 24. 34.
...Light a out - + = nbu, 23.33...
・Forlaston prism, 32...Cylindrical lens, 41...λ/2 phase plate, 20θ
...... Center of luminous flux (ψ, 50[) ...... Ki-
Prism, 600...Second prism. 510.610...Optical axis.

Claims (1)

[Claims] In an optical head that irradiates a recording medium on which information is recorded magneto-optically with focused light and detects information recorded magneto-optically by changing the polarization state of reflected light or transmitted light from the recording medium, Disposed on the optical path of reflected light or transmitted light, the reflected light or transmitted light is separated into first and second beams whose intensity changes depending on the polarization state and a third beam whose light intensity does not change due to polarization. a λ/2 phase plate rotatably disposed between the Wollaston prism and the objective lens perpendicular to the optical axis of the reflected light or the transmitted light; and the Wollaston prism. and a photodetector having elements disposed on the same surface to separate and receive the first, second, and third beams that have passed, and detect the recording medium by the difference in intensity between the first and second beams. An optical head characterized in that it detects a magneto-optical change, and detects a reflectance change of a recording medium and an error signal for servo control using the third beam.