JPS63148448A - Magneto-optical head device - Google Patents

Abstract

PURPOSE:To obtain a compact magneto-optical head device by using a thin film waveguide element containing a grating coupler which leads only the polar ized component of a specific direction among those reflected beams received from an optical system and a recording medium to a thin film waveguide path and a photodetector which detects the quantity of reflected light of the recording medium connected to the thin film waveguide path. CONSTITUTION:The magneto-optical head device consists of a semiconductor laser 1, a collimator lens 2, a beam splitter 3, a capacitor lens 4, a thin film waveguide element 6 containing a grating coupler 10 which leads only the polar ized component of a specific direction to a thin film waveguide path 9, a photo detector 7 connected to the end face of the path 9, and an error detecting optical system 8. The light emitted from the laser 1 is converged on a recording medi um 5 in the form of a minute spot via the lenses 2 and 4. Only a specific polar ized component is led to the path 9 by the coupler 10 out of the reflected light received from the medium 5. Then the light emitted through the end face is detected by the photodetector 7. While the light separated by the splitter 3 is led to the system 8. In such a constitution, a compact magneto-optical head device is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical optical head device that uses light to record on and reproduce information from a magnetic recording medium.

[Conventional technology]

Magneto-optical recording has both the high density of optical recording and the rewritability of magnetic recording, so it is a useful means for producing large-capacity files.

In magneto-optical recording, as a recording bit detection method, a recording medium is irradiated with linearly polarized light, and the presence or absence of focus is detected by utilizing the rotation of the polarization plane of the reflected light due to the Kerr effect.

FIG. 5 shows the configuration of a conventionally used optical head device. The emitted light from the semiconductor laser 1 is transmitted through a collimating lens 2 and a beam splinter 3a.

3b, the light is focused onto the recording medium 5 as a minute spot via the condensing lens 4. Here, since the laser emitted light is linearly polarized light, the focused spot also becomes linearly polarized light. A portion of the reflected light from this spot is separated by a beam splinter 3b, and is detected by a photodetector 17 through an analyzer.

At this time, by setting the angle of the analyzer to an angle of about 45 to 80' with respect to the direction of the incident polarized light,
Rotation of the plane of polarization can be detected. The reflected light separated by the other beam splinter 3a is guided to an error detection optical system 8 that detects spot position errors.

As shown in FIG. 6, another method for detecting the rotation of the plane of polarization is to combine a half-wave plate 13 and a polarizing beam splitter 14 to detect the reflected light in the polarization direction of ±45@, There is a method of taking the difference between the outputs of 17a and 17b, and according to this method, the SiN of the detection signal can be improved.

[Problem that the invention seeks to solve]

Conventional systems for detecting the rotation of the plane of polarization use an analyzer and a polarization beam splitter, making the optical system large and making it difficult to downsize the entire optical head device. This has caused problems in miniaturizing the entire optical disk device and improving data access time.

An object of the present invention is to provide a magneto-optical optical head device that can be miniaturized without causing the above problems.

[Means for solving problems]

The magneto-optical optical head device of the present invention includes an optical system that focuses emitted light from a laser light source on a recording medium as a minute spot of linearly polarized light, and a polarized light component in a specific direction in the light reflected from the recording medium. The present invention is characterized by comprising a thin film waveguide element equipped with a grating coupler that guides only the light to the thin film waveguide, and a photodetector that detects the amount of reflected light from the recording medium coupled to the thin film waveguide.

[Effect]

As shown in FIG. 2, the grating coupler used in the present invention is composed of a grating pattern periodically configured on a thin film waveguide 9 on a thin film waveguide element 6, and has a grating coupling having a periodic refractive index distribution. It is a vessel. In this grating coupler, the periodic structure is formed on the thin film waveguide 9, but the periodic structure functions similarly even if it is inside the thin film waveguide 9.

In the thin film waveguide 9, by appropriately selecting the film thickness and material, the TE mode, which has an electric field component only in the lateral direction within the film plane, and the 7M mode, which has an electric field component only in other directions, can have significantly different propagation. Can have constants.

Since the grating coupler 10 causes coupling only between modes having electric field components in the same direction with respect to the incident light beam, the incident light with an electric field parallel to the grating becomes the TE mode, and the incident light with an electric field perpendicular to the grating becomes the TE mode. Join mode.

On the other hand, as mentioned above, since the propagation constants of the TE mode and the 7M mode are different, the angle of incidence of the incident light coupled to the propagation mode by the grating is different between the two modes. Therefore, by selecting the incident angle, only the polarized component in a specific direction of the incident light can be coupled to the thin film waveguide 9, providing the same effect as an analyzer.

A grating coupler exhibiting the above-mentioned characteristics can be manufactured by, for example, forming a thin film of Corning 7059 on a Pyrex glass substrate by sputtering or the like, and forming a grating pattern thereon using ethog such as SiN. If the thickness of each layer is about 0.6 μm for the wavelength, the waveguide thickness is 0.6 μm.
Sufficient characteristics can be obtained with a grating layer thickness of about 5 μm and a grating layer thickness of about 0.02 μm.

〔Example〕

FIG. 1 shows an embodiment of the invention. This magneto-optical optical head device includes a semiconductor laser 1, a collimating lens 2,
A beam splitter 3, a condensing lens 4, a thin film waveguide element 6 equipped with a grating coupler lO shown in FIG. It is composed of a photodetector 7 coupled to the end face of the sensor, and an error detection optical system 8.

In the optical head device having the above configuration, the light emitted from the semiconductor laser 1 is transmitted through the collimating lens 2. The light is focused as a minute spot on the recording medium 5 via the condenser lens 4 . Of the light reflected from the recording medium 5, only a specific polarized component is guided to the thin film waveguide 9 by the grating coupler 10, and the end-emitted light is detected by the photodetector 7. On the other hand, the light separated by the beam splitter 3 is guided to an error detection optical system 8.

In the above embodiment, the photodetector 7 is provided coupled to the end face of the thin film waveguide 9, but it may be integrated on the thin film waveguide element. Further, in the above embodiments, the thin film waveguide element is provided between the beam splitter 3 and the condenser lens 4, but the thin film waveguide element may be used for the reflected light from the beam splitter 3.

In this case, the optical system 8 for error detection can also be integrated on the thin film waveguide element.

FIG. 3 shows an optical system for error detection integrated on a thin film waveguide element 9. In FIG. A grating coupler 10 and a demultiplexer 11 having light condensing properties are formed on the thin film waveguide 6 on the thin film waveguide element 6, and two
Separate photodetectors 7a and 7b are provided, respectively. The light guided to the waveguide 9 by the grating coupler 10 is split into two by the condensing demultiplexer 11 and sent to the photodetector 7.
a, and 7b, respectively. The photodetector 7a detects the amount of reflected light from the recording medium 5, and the photodetector 7b detects the amount of reflected light from the recording medium 5.
Error detection is performed using the Foucault method.

FIG. 4 shows thin film waveguides 9a, 9b and grating couplers 10a, 10 on the front and back sides of the substrate constituting the thin film waveguide element 6.
b is provided to couple to the TE and TM modes, respectively, and photodetectors 15a and 15b are coupled to the thin film waveguides 9a and 9b, respectively. This makes it possible to detect polarized light components at ±45°, similar to the detection method shown in FIG.

〔Effect of the invention〕

According to the present invention, unlike conventional optical head devices, an analyzer and a polarization beam splitter are not used in the system for detecting the rotation of the plane of polarization, so it is possible to provide a compact optical head device for magneto-optical use. .

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIGS. 2 to 4 are diagrams showing a configuration example of a thin film waveguide element used in the present invention, and FIG. 5 is a diagram showing a conventional optical head device. FIG. 6 is a diagram showing another example of a method for detecting rotation of a polarization plane in a conventional optical head device. l... Semiconductor laser 2... Collimating lens 3...
...... Beam splitter 4 ...... Condensing lens 5 ...... Recording medium 6 ...... Thin film waveguide element 7 , 7a, 7b, 15a, 15b. 17, 17a, 17b...Photodetector 8...
・・・・・・Error detection optical system 9・・・・・・・・・
・Thin film waveguides 10, 10a, 10b... Grating coupler 11... Light condensing demultiplexer 12...
・・・・・・Analyzer 13・・・・・・・・・・
Half-wave plate 14...Polarizing beam splitter representative Patent attorney Yoshiyuki Iwasa Figure 1 Figure 2 1ob Mi-trend/rW4 Figure 5

Claims (1)

[Claims] (1) An optical system that focuses the emitted light from a light source on a recording medium as a minute spot of linearly polarized light, and a grating coupling that guides only the polarized component in a specific direction of the light reflected from the recording medium to a thin film waveguide. What is claimed is: 1. A magneto-optical optical head device comprising: a thin film waveguide element having a waveguide; and a photodetector for detecting the amount of light reflected from a recording medium coupled to the thin film waveguide.