JP2879278B2 - Optical head of magneto-optical recording device - Google Patents

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 apparatus.

[0002]

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

In the light modulation method, a magnetic field capable of reversing the direction of magnetization is applied to a magneto-optical recording layer, and laser light irradiation is turned on / off in accordance with information to be recorded, and the magneto-optical recording layer is selected. This is to heat up to the Curie point to reverse the direction of magnetization. In the conventional light modulation method, on / off of laser light irradiation is performed by directly turning on / off the output of a laser diode, so that a laser whose oscillation wavelength is originally unstable is further destabilized. There was a problem. Further, there is a problem that noise is generated due to laser switching, and the laser is deteriorated due to excessive switching.

Incidentally, an optical shutter itself using an electro-optical element such as PLZT, a polarizer and an analyzer is known in the field of optical communication and the like, but an example in which this is used for an optical head of a magneto-optical recording apparatus. There is no. Also, Japanese Patent Application Laid-Open No. Sho 61-77823
Japanese Patent Application Laid-Open Publication No. H11-163,878 proposes an optical head in which the above-described optical shutter group and optical fiber group are combined. Is an unrelated technology.

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

[0006] Therefore, by inserting a wavelength selection filter having a peak wavelength equal to the laser oscillation peak wavelength between the semiconductor laser of the optical head and the objective lens, the adverse effect of the return light is prevented, and the lens has chromatic aberration. It is described that the fluctuation of the laser oscillation wavelength can be prevented even in the case where it is present (Japanese Patent Laid-Open No. Hei 3-209638).

Further, since the semiconductor laser has a different aspect ratio of a light emitting region and a divergent angle of a 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 system in which a laser beam is obliquely incident on an incident surface of a shaping prism and a direct incidence system in which a laser beam is incident at a right angle.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical head capable of writing information by a light modulation method without turning on and off a laser light source.

[0009]

The optical head of the magneto-optical recording apparatus according to the present invention is provided between a laser light source and an objective lens.
Combination of shaping prism made of electro-optic material and analyzer
Equipped with an optical shutter and a wavelength selective transmission filter
The optical shutter operates according to the magnitude of the applied voltage.
Light modulating means for turning on and off the light flux from the laser light source
The wavelength selective transmission filter is used for the laser light.
A transmission peak wavelength approximately equal to the oscillation peak wavelength of the
The half-value width of the transmission characteristic does not have the wavelength selective transmission filter
Using a laser light source narrower than the half width
It is characterized by that.

[0010]

FIG. 1 is an explanatory view showing an embodiment of an optical head according to the present invention. A conventional magneto-optical device except that an optical shutter 31 utilizing a shaping prism 41 is inserted after a collimator lens 13 is shown. It has the same configuration as the optical head in the recording apparatus. The detailed configuration is shown in FIG.
did.

The laser light output from the laser diode 11 (semiconductor laser) is applied to the collimator lens 1.
At 3, the light beam is converted into a parallel light beam and enters the optical shutter 31. The laser beam is corrected by the shaping prism 41 which forms a part of the optical shutter 31 so that the cross section of the beam becomes a perfect circle, and the light passing through the optical shutter 31 is spot-irradiated to the magneto-optical disk 61 by the objective lens 17 via the beam splitter 15. Is done.

The shaping prism 41 is made of an electro-optic material, unlike the shaping prism of a conventional optical head made of general optical glass. The effect of correcting to a circle is the same as that of a conventional shaping prism.

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

At the time of writing information, the direction of magnetization of the recording pits (magnetic domains) of the magneto-optical disk 61 is previously aligned, and a magnetic field in the opposite direction to the direction of the magnetization is applied to the magneto-optical disk 61 while the laser diode is being written. 11 irradiates the signal light, heats the recording pit of the light irradiation part to the Curie point,
Reverses 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 is turned on.
Controls ON / OFF of light irradiation on the magneto-optical disk 61. 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 interposed therebetween. A comb-shaped electrode 45 is formed on the emission surface of the shaping prism 41 made of an electro-optic material, and ON / OFF of a signal voltage to the comb-shaped electrode 45 is performed.
Is controlled by the control power supply circuit 43.

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

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

FIG. 3 shows a detailed embodiment of the optical head according to the present invention. FIGS. 1 and 2 are similar to FIGS. It is the same as the optical head shown.

FIG. 4 shows the transmission characteristics of the wavelength selective transmission filter 47. FIG. 5A shows the effect of the wavelength selective transmission filter 47 on the laser diode output on the return light quantity 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)
(A)) is a narrow band transmission filter showing the maximum transmittance at the same wavelength as that of (a). The half-value width W ₂ of the square transmission characteristics obtained by the square of the transmittance at each wavelength in the wavelength characteristic of the filter 47, the spectral characteristics of the light returning to the laser diode 11 in the absence of the filter 47 (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, and FIG.
As shown in (B), the center wavelength of the return light becomes constant, and fluctuation of the oscillation wavelength of the laser diode 11 is prevented.

The reason why the square transmission characteristic is one index is that the laser beam passes through the filter 47 twice before and after the reflection on the magneto-optical disk 61 and becomes return light.

As described above, the filter 47 having a high transmittance at a specific wavelength and having a narrower transmission band than the wavelength band of the return light,
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, an optical shutter can be configured so that the laser beam is transmitted when the signal voltage (current) is turned off.

The shaping prism 41 made of an electro-optical material and the wavelength selective transmission filter 47 may be inserted between the laser diode 11 and the objective lens 17, and the wavelength selective transmission filter 47 is shaped. It may be formed 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, switching of light modulation recording can be performed 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 the switching noise of the laser light source and the deterioration of the laser due to excessive switching.

Further, since the shaping prism, which is essential for the optical head, is used as the electro-optical element necessary for the configuration of the optical shutter, an increase in the number of parts, an increase in the weight and an increase in the size of the optical head can be minimized. Can be.

Further, by using the wavelength selective transmission filter, it is possible to prevent the oscillation wavelength of the laser diode from becoming unstable due to the influence of the return light.

[Brief description of the drawings]

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

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

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

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

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

[Explanation of symbols]

 Reference Signs List 11 laser light source 13 collimator lens 15 beam splitter 17 objective lens 19 half-wave plate 21 condenser 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-shaped electrode 47 wavelength selection Transmission filter 61 Magneto-optical disk

Claims (1)

(57) [Claims] 1. An electric power source between a laser light source and an objective lens.
Combination of shaping prism made of aero-optic material and analyzer
An optical shutter, and a wavelength selective transmission filter, wherein the optical shutter is configured to control the laser by the magnitude of an applied voltage.
-Used as a light modulation means for turning on and off the light beam from the light source
The wavelength selective transmission filter is provided for oscillating the laser light source.
The transmission peak wavelength approximately equal to the peak wavelength
Before the absence of the wavelength selective transmission filter
Use a laser light source that is narrower than the half width
An optical head for a magneto-optical recording device.