JPH05282698A - Optical head of magneto-optical recording device - Google Patents

Abstract

PURPOSE:To stabilize an oscillation wavelength by turning ON a laser diode all the time, to prevent the occurrence of a switching noise and laser degradation and to reduce the number of parts by using a shaping prism. CONSTITUTION:A luminous flux from a laser diode 11 is spot irradiated on a magneto-optical disk 61 by an objective lens 17 through an optical shutter 31. During an optical modulation recording, a write magnetic field is applied to the disk 61 and the direction of magnetization of a recording pit is selectively reversed by turning on-off the shutter 31 and irradiating. The shutter 31 consists of a polarizer 33, an analyzer 35 and a shaping prism 41 which are held between the polarizer and analyzer and is made of an electro-optical material. The prism 41 is made of lithium niobate and a light transmission is turned ON-OFF by turning ON-OFF the voltage of interdigital electrodes formed on a light emitting surface by controlling a control power supply circuit 43.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head in an optical modulation type magneto-optical recording device.

[0002]

2. Description of the Related Art Magneto-optical recording is to detect the direction of the magnetization of a recording pit by utilizing the magneto-optical effect such as Kerr effect and read the recorded information. A modulation method and a magnetic field modulation method are known.

In the optical modulation method, a magnetic field capable of reversing the direction of magnetization is applied to the magneto-optical recording layer, laser light irradiation is turned on / off according to the information to be recorded, and the magneto-optical recording layer is selected. It is intended to reverse the direction of magnetization by heating to the Curie point. In the conventional optical modulation method, since the irradiation of the laser light is turned on and off by directly turning on and off the output of the laser diode, it is said that the laser whose oscillation wavelength is originally unstable is further destabilized. There was a problem. In addition, there is a problem that noise is generated due to switching of the laser and the laser is deteriorated due to excessive switching.

An optical shutter itself using an electro-optical element such as PLZT, a polarizer and an analyzer is well known in the field of optical communication and the like. An example in which this is used for an optical head of a magneto-optical recording device. There is no. Also, JP-A-61-77823
In the publication, there is proposed an optical head in which the above-mentioned optical shutter group and an optical fiber group are combined. This is a printer head, a color number display plate, etc. even if it is called an optical head. Is an unrelated technology.

Further, in the optical head for magneto-optical recording, it is inevitable that a part of the reflected light from the magneto-optical recording disk returns to the laser, and the returned light makes the oscillation wavelength unstable (hopping). It causes noise.

Therefore, by inserting a wavelength selection filter having a peak wavelength equal to the oscillation peak wavelength of the laser between the semiconductor laser of the optical head and the objective lens, the adverse effect of the returning light is prevented and chromatic aberration is caused in the lens. It is described that the fluctuation of the oscillation wavelength of the laser can be prevented even if there is such a case (Japanese Patent Laid-Open No. 3-209638).

Further, since the semiconductor laser has a different aspect ratio in the light emitting region and the divergence angle of the beam is anisotropic,
Correction is performed using a shaping prism (Japanese Patent Publication No. 63-1652). As the correction optical system, there are known an oblique incidence method in which a laser light beam is obliquely incident on an incident surface of a shaping prism and a direct incidence method in which a laser light beam is incident at a right angle.

[0008]

SUMMARY OF THE INVENTION The present invention provides an optical head capable of writing information by an optical modulation method without turning on / off a laser light source.

[0009]

An optical head of a magneto-optical recording apparatus according to the present invention comprises an optical shutter in which a shaping prism made of an electro-optical material and an analyzer are combined, and an optical shutter for turning a light beam from a laser light source on and off. It is characterized by being provided as a modulation means.

[0010]

FIG. 1 is an explanatory view showing an embodiment of an optical head of the present invention, except that an optical shutter 31 using a shaping prism 41 is inserted in a rear stage of a collimator lens 13 and a conventional magneto-optical device. It has the same configuration as the optical head in the recording apparatus.

Laser light output from the laser diode 11 (semiconductor laser) is collimator lens 1
The light beam is collimated by 3 and enters the optical shutter 31. The laser light flux is corrected by the shaping prism 41 forming a part of the optical shutter 31, and the cross section of the light flux becomes a perfect circle, and the light passing through the optical shutter 31 passes through the beam splitter 15 and spot illuminates the magneto-optical disk 61 by the objective lens 17. To be done.

The shaping prism 41 is made of an electro-optical material, unlike the shaping prism of a conventional optical head made of general optical glass. However, the shaping prism 41 is a laser beam having an elliptical cross section. The function of correcting to a circle is similar to that of the conventional shaping prism.

The reflected light from the magneto-optical disk 61 enters the objective lens 17 again, and is guided to the detection system 23 via the beam splitter 15, the half-wave plate 19 and the condenser lens 21.
A focus error signal and a tracking error signal are detected, and a recording signal is detected during reproduction.

When writing information, the directions of magnetization of the recording pits (magnetic domains) of the magneto-optical disk 61 are aligned in advance, and then a laser diode is applied while applying a magnetic field in the direction opposite to this direction of magnetization to the magneto-optical disk 61. The signal light is irradiated by 11 to heat the recording pit of the light irradiation portion to the Curie point,
Reverse the direction of magnetization.

In the optical head of the present invention, the laser diode 11 is continuously turned on at this time, and the optical shutter 31
The ON / OFF of the light irradiation to the magneto-optical disk 61 is controlled by. The optical shutter 31 includes a polarizer 33 and an analyzer 35 whose transmission axes 37 are orthogonal to each other as shown in FIG.
And a shaping prism 41 made of an electro-optical material and interposed between the shaping prism 41 and the shaping prism 41. A comb-shaped electrode 45 is formed on the exit surface of the shaping prism 41 made of an electro-optical material, and a signal voltage to the comb-shaped electrode 45 is turned on and off.
Is controlled by the control power supply circuit 43.

The electro-optical material is one in which the plane of polarization of transmitted light is rotated by the action of an electric field or magnetic field on the spectral lines, and the magnitude of the rotation angle is proportional to the optical density and the strength of the electric field or magnetic field. ing. Therefore, by appropriately setting the optical path length of the shaping prism 41 made of an electro-optical material and the magnitude of the applied voltage, when the signal voltage is applied (ON) by the control power supply circuit 43, the polarization plane of the transmitted light is set to 9 degrees.
It can be rotated by 0 degrees to pass the analyzer 35,
It is possible to control ON / OFF of the light irradiation to the magneto-optical disk 61. Since the laser light from the laser diode 11 can be regarded as linearly polarized light, the polarizer 3
3 can be omitted.

The electro-optical material utilizes the Faraday effect,
The presence of an unpaired electron pair causes an interaction as the light passes through, rotating the light in a manner that depends on the number and arrangement of the unpaired electron pairs. As the electro-optical material, a lithium niobate single crystal or a europium aluminate single crystal is preferable in terms of translucency and switching speed, and it is particularly preferable to form the shaping prism 41 with a lithium niobate single crystal. Lithium niobate is about 10 against PLZT
In addition, europium aluminate (aluminate europium) has a switching speed about 10 times that of PLZT.

FIG. 3 shows another embodiment of the optical head of the present invention, which is shown in FIGS. 1 and 2 except that a wavelength selective transmission filter 47 is formed on the incident surface of a shaping prism 41 made of an electro-optical material. It is the same as the optical head shown.

FIG. 4 shows the transmission characteristics of the wavelength selective transmission filter 47. Further, FIG. 5A shows the influence of the wavelength selective transmission filter 47 which gives the laser diode output to the returning light amount in FIG. 5B.

As shown in FIG. 4, the wavelength selection filter 47
Is the oscillation wavelength peak λ ₁ of the laser diode (Fig. 5
(See (A)) is a narrow band transmission filter that exhibits the maximum transmittance at the same wavelength. Then, the full width at half maximum W ₂ of the square transmission characteristic obtained by squaring the transmittance at each wavelength of the wavelength characteristic of the filter 47 is the spectral characteristic of the return light to the laser diode 11 when the filter 47 is not provided (see FIG. 5). (See (B)). in this way,
Since the wavelength selectivity of the filter 47 is large, the return light to the laser diode 11 is efficiently cut off, and the light shown in FIG.
As shown in (B), the central wavelength of the returning light becomes constant, and the fluctuation of the oscillation wavelength of the laser diode 11 is prevented.

Here, the square transmission characteristic is one index because the laser light flux passes through the filter 47 twice before and after reflection on the magneto-optical disk 61 and becomes return light.

As described above, the filter 47 having a high transmittance for a specific wavelength and a narrower transmission band than the wavelength band of the return light is
For example, it can be obtained by forming a multilayer film in which a low-refractive-index dielectric thin film such as silicon dioxide and a high-refractive-index dielectric thin film such as titanium dioxide are laminated with a predetermined thickness by a vacuum deposition method or the like.

By adjusting the transmission axes of the analyzer 35 and the polarizer 33, it is possible to configure the optical shutter so that the laser light is transmitted when the signal voltage (current) is turned off.

Further, the shaping prism 41 and the wavelength selective transmission filter 47 made of an electro-optical material may be inserted anywhere between the laser diode 11 and the objective lens 17, and the wavelength selective transmission filter 47 is shaped. It may be formed on a surface other than the exit surface of the prism 41. Further, as the shaping prism 41, a direct incidence type may be used instead of the oblique incidence type shown in FIGS.

[0025]

According to the optical head of the present invention, optical modulation recording can be switched by the optical shutter without switching the laser light source, and instability of the oscillation wavelength of the laser light source can be avoided. .. Further, it is possible to prevent deterioration of the laser due to switching noise of the laser light source or excessive switching.

Moreover, since the shaping prism, which can be said to be essential to the optical head, is used as the electro-optical element necessary for the construction of the optical shutter, the increase in the number of parts, the increase in the weight of the optical head, and the increase in size can be minimized. You can

Further, by using the wavelength selective transmission filter, it is possible to prevent the oscillation wavelength of the laser diode from being destabilized due to the influence of the returning light.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of an optical system of an optical head of the present invention.

FIG. 2 is an explanatory diagram showing an example of an optical shutter.

FIG. 3 is an explanatory diagram showing another embodiment of the optical system of the optical head of the present invention.

FIG. 4 is a graph showing a transmission characteristic of a wavelength selective transmission filter and its square transmission characteristic.

FIG. 5A is a spectral characteristic of laser diode output,
(B) is a graph showing the spectral characteristics of the amount of return light (effect of the selected wavelength transmission filter).

[Explanation of symbols]

 11 Laser Light Source 13 Collimator Lens 15 Beam Splitter 17 Objective Lens 19 Half-wave Plate 21 Condensing Lens 23 Signal Detection System 31 Optical Shutter 33 Polarizer 35 Analyzer 37 Transmission Axis 41 Shaping Prism 43 Control Power Supply Circuit 45 Comb Electrode 47 Wavelength Selection Transmission filter 61 Magneto-optical disk

Claims (3)

[Claims] 1. Optical of a magneto-optical recording apparatus, comprising an optical shutter, which is a combination of a shaping prism made of an electro-optical material and an analyzer, as an optical modulation means for turning on and off a light beam from a laser light source. head. 2. The optical head of a magneto-optical recording apparatus according to claim 1, wherein the electro-optical material is lithium niobate or europium aluminate. 3. Between the semiconductor laser and the objective lens,
The optical head of a magneto-optical recording apparatus according to claim 1, wherein a wavelength selective transmission filter having a transmission peak wavelength substantially equal to the oscillation peak wavelength of the semiconductor laser is inserted.