JPH0232691B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a recorded information reproducing apparatus that optically reproduces recorded patterns in a recording medium using an integrated optical structure.

2. Description of the Related Art Various methods for reproducing recorded patterns on a recording medium have been known. FIG. 1 shows a conventional optical system for optically reproducing a recorded pattern, and is composed of a light source 1, lenses 2a, 2b, 2c, a half mirror 3, and a photodetector 4. The light beam emitted from the light source 1 becomes a parallel light beam by the lens 2a, and is focused onto the recording medium 5 by the lens 2b. The reflected light from the recording medium 5 is modulated by information or signals on the recording medium 5. This reflected light is separated from the incident optical path by a half mirror 3, and is focused on a photodetector 4 via a lens 2c.
The information on the recording medium 5 will be output as an electrical signal. If the signal is formed on the recording medium 5 by pits or irregularities of a metal thin film, the reflected light is modulated in brightness and darkness by the signal. Recording medium 5
When is made of a magnetic material such as an amorphous magnetic thin film, the reflected light is modulated by the rotation of the plane of polarization, so by placing polarizing plates 6a and 6b in the optical path, the information from the rotation of the plane of polarization can be used to modulate brightness and darkness. It will be converted and guided to the photodetector 4.

An object of the present invention is to provide a recorded information reproducing device that has a compact optical system and can read signals at high speed by using an integrated optical structure. a light source that irradiates a linearly polarized light beam to the medium, a thin film optical waveguide that propagates the light beam reflected by the medium, an optical coupler that takes out the light beam propagated through the waveguide to the outside, and a light beam taken out from the optical coupler. It consists of a photodetector that receives light and an optical rotation mechanism provided in the optical path from the medium to the thin film optical waveguide, and the output angle of the light beam taken out from the optical coupler changes depending on the information recorded on the medium. The information is reproduced by detecting this with the photodetector.

The present invention will be explained in detail below based on the embodiments shown in FIG. 2 and below.

FIG. 2 shows an integrated optical structure 10 used in the present invention.
An optical coupler 14 made of a prism coupler is provided on a thin film waveguide 13 formed in a planar shape on a substrate 12 placed on an XZ plane. The incident light beam L ₁ is guided into the waveguide 13 via the optical coupler 14 as a light beam L ₂ to the end face 15 . To explain each component of the integrated optical structure 10 in more detail, the substrate 12 is made of LiNbO ₃ (lithium niobate), LiTaO ₃ (lithium tantalate), ZnO (zinc oxide), etc. teeth,
In the case of the substrate 12 of LiNbO ₃ , Ti is diffused at a high temperature of about 1000° C. to form a thickness of several μm on the substrate 12 . In addition, in the case of the LiTaO ₃ substrate 12, Nb or
Obtained by diffusing Ti. Although other combinations are also possible, the waveguide 13 has a high refractive index and the substrate 12
It is preferable to use a material that has a large refractive index difference between the waveguide 13 and the waveguide 13 and that can conduct light even if the waveguide 13 is made thin.

The integrated optical structure 10 receives a laser beam L ₁ from a light source 20 via an optical coupler 14 as shown in FIG.
is incident, and a light beam _L3 is emitted from the end face 15.
A lens system 21, a Faraday rotator 22, a lens system 23, and a magnetic recording medium 24 are arranged in this order on the end surface 15 side. The lens system 21 converts the light emitted from the end surface 15 of the integrated optical structure 10 into a Faraday rotator 22.
The lens system 23 focuses on the Faraday rotator 22.
It has a geometrical positional relationship such that an image of 1 is formed on the recording medium 24. A driving magnetic field circuit 25 is connected to the Faraday rotator 22, and the light beam is rotated by the magnetic field. Further, a photodetector 26 is arranged on the emission part side of the coupler 14.

As the magneto-optical recording medium 24, for example, MnBi, which can perform magnetic domain reversal recording by heat of optical energy,
Amorphous magnetic thin films having perpendicular magnetization characteristics such as GdCo, GdFe, TbFe, and GdTbFe can be used.
Generally, when a linearly polarized light beam is reflected by the magneto-optical recording medium 24 having perpendicular magnetization, the reflected light becomes elliptically polarized light, and at the same time, the plane of polarization rotates in proportion to the magnetization. Now, it is assumed that recording is to be performed on the magneto-optical recording medium 24 with the direction of magnetization either upward or downward with respect to the thickness direction. When the magneto-optical recording medium 24 recorded in these upward and downward states is irradiated with a linearly polarized beam of light, the polarization plane of the reflected light changes depending on the well-known Kerr effect. It rotates by +Θ _K or -Θ _K. That is, as shown in FIG. 4, if the polarization plane of the linearly polarized incident light beam is A, then the polarization planes of the reflected light are B and C with respect to the respective magnetization directions.

As the Faraday rotator 22, a YIG thin film or the like with a phase matching film that requires less driving magnetic field is suitable, and if this Faraday rotator 22 is used,
To obtain a Faraday rotator of about 40 degrees, approximately
It has the advantage of requiring only a small driving magnetic field of about 200 Oe.

In this embodiment, the magnitude of the magnetic field is adjusted by the drive magnetic field circuit 25 so that the plane of polarization of the light that has passed through the Faraday rotator 22 is rotated by Θ _K /2.

When reproducing information, a linearly polarized light beam (hereinafter referred to as a TE mode light beam) L ₁ whose electric field vibration direction is parallel to the end surface 15 of the waveguide 13 is emitted from the light source 20.
is guided to the waveguide 13 through the optical coupler 14.
The light beam L ₂ incident on the waveguide 13 is
The light propagates within the waveguide 13 and is emitted from the end face 15 of the waveguide 13. This luminous flux L ₃ emitted from the end face 15 is
It is a TE mode light beam, and its polarization direction is indicated by D in FIG. 5a. When this light beam L ₃ passes through the Faraday rotator 22, the plane of polarization rotates by Θ _K /2 as shown in E of FIG. 5A according to the above explanation. The light beam _L4 transmitted through the Faraday rotator 22 is reflected by the magneto-optical recording medium 24, and as shown in FIG. _K or -Θ _K rotation, F or G
reaches the state of When the reflected light L ₅ passes through the Faraday rotator 22 again, the plane of polarization is further rotated by Θ _K /2, so that the light flux returns to the end face 15 of the waveguide 13 again.
The polarization plane of L ₆ is determined by the recording medium 24 from the F and G states.
Depending on the direction of magnetization, the state becomes H or I as shown in FIG. 5c. That is, the polarization plane of the reflected light from the medium 24 whose magnetization direction is upward is as follows:
It is rotated by _2ΘK from the polarization plane corresponding to the TE mode, and the polarization plane of the reflected light from the downward state is the TE mode.
This will match the plane of polarization of the mode. Luminous flux L ₆
When entering the waveguide 13 again from the end surface 15 of the integrated optical structure 10, the TM component H' of the reflected light from the upward state is in the TM mode, and the reflected light is in the TM mode.
The TE component H'' and the reflected light I from the downward state propagate in the waveguide 13 as a light flux _L7 in the TE mode.
Since the TE mode light flux and the TM mode light flux have different propagation constants within the waveguide 13, the angles at which they exit from the optical coupler 14 are different. Also, photodetector 2
6 is placed in a position to receive the emitted light flux _L8 in the TM mode, the light flux enters the photodetector 26 only when the magnetization direction is upward on the magneto-optical recording medium 24, and the signal is detected. playback becomes possible. Further, the signal can also be reproduced by detecting a change in the power of the emitted light beam in the TE mode returning toward the light source 20.

In the above explanation, the plane of polarization was rotated by Θ _K /2 using the Faraday rotator 22.
Similar reproduction is possible by rotating by (π/4−Θ _K /2). In this case, as shown in Figure 6,
Corresponding to FIG. 5c, the polarization plane J of the reflected light from the medium 24 whose magnetization direction is in the upward state matches the polarization plane corresponding to the TM mode, and the polarization plane K of the reflected light from the downward state is It is located at an angle rotated by (π/2−2Θ _K ) from the plane corresponding to the TE mode.
When using this method, the signal can be regenerated by placing the photodetector 26 at a position where it receives the emitted light beam in the TM mode.

FIG. 7 shows another embodiment of the present invention, in which an integrated optical structure 10 has a comb tooth-like electrode 16 and a thin film lens 1 on its waveguide 13 for generating a surface acoustic wave W.
7 is provided. Now, when the parallel light beam l ₁ from the light source 20 is guided to the waveguide 13 via the optical coupler 14, the light beam l ₂ propagating through the waveguide 13 is
The surface acoustic wave W excited by the comb tooth-shaped electrode 16 provided on a part of the surface acoustic wave W causes a diffraction effect and is deflected. Furthermore, this deflected light beam l ₃ is focused by a thin film lens 17 so as to form a bright spot S on the end face 15 of the waveguide 13. The polarization angle is controlled by changing the frequency of the high-frequency voltage applied to the comb tooth-shaped electrode 16 to change the wavelength of the surface acoustic wave W on the waveguide 13, and bright spot scanning is performed on the end face 15. . In this embodiment, the bright spot S is
3, an image is formed on the magneto-optical recording medium 24, and the signal on the medium 24 is reproduced by the same means as in the previous embodiment.

Such a recorded information reproducing apparatus reads a signal by scanning the bright spot S on the magneto-optical recording medium 24, and therefore has the advantage of being able to perform high-speed reproduction. In addition, as in these embodiments, the means for returning the luminous flux onto the waveguide 13 is not limited to simply making the optical system smaller;
There is an advantage in that even if the beam is scanned, the light beam can be detected in a stationary state.

As described above, the recorded information reproducing apparatus according to the present invention reproduces information on a recording medium by reciprocating a light beam through an integrated optical structure, and has a simple configuration and enables high-speed reading.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional optical system for reproducing a recorded pattern on a recording medium. FIG. 2 and the following are examples of a recorded information reproducing apparatus according to the present invention. 3 is a configuration diagram of the first embodiment, FIG. 4 is an explanatory diagram of the Kerr effect due to the recording medium, FIGS. 5 and 6 are explanatory diagrams showing the state of the polarization plane during reproduction, and FIG. FIG. 7 is a configuration diagram of the second embodiment. 10 is an integrated optical structure, 12 is a substrate, 13
is a waveguide, 14 is an optical coupler, 15 is an end face, 17 is a thin film lens, 20 is a light source, 21 and 23 are lens systems, 22 is a Faraday rotator, 24 is a recording medium,
26 is a photodetector.

Claims (1)

[Claims] 1. A light source that irradiates a magneto-optical recording medium with a linearly polarized light beam, a thin film optical waveguide that propagates the light beam reflected by the medium, an optical coupler that extracts the light beam propagated through the waveguide to the outside, and the optical coupler. It consists of a photodetector that receives the light flux extracted from the optical coupler, and an optical rotation mechanism provided in the optical path from the medium to the thin-film optical waveguide, which detects the light flux extracted from the optical coupler according to the information recorded on the medium. A recorded information reproducing apparatus characterized in that the information is reproduced by detecting with the photodetector that the emission angle changes.