JPH01189052A - Optical head of magneto-optical recording device - Google Patents

Abstract

PURPOSE:To separate an abnormal optical component from a normal optical component and to obtain a differential output by providing a polarizing prism consisting of birefringent materials at a light receiving system so that the optical axis of a crystal may be parallel with reading light. CONSTITUTION:The light from a semiconductor laser 10 linearly polarized by a lens 12 and an analyzer 14, passes through a prism 16 and a lens 18, and irradiates the prescribed position of a magneto-optical disk 20. The polarizing surface of the reflected light rotates according to the direction of magnetization, the reflected light reverses, and it is divided into two mutually orthogonal light pathes by a prism 24. The transmitted light progresses, without being separated to the respective normal and abnormal components, into a polarizing prism 40, which consists of direfringent materials and whose optical axis of the crystal is parallel with the normal direction of an incident surface, and it is totally reflected by an oblique surface. The reflected light is separated to abnormal and normal optical components, they passes through light receiving elements 42 and 44 and a differential amplifier 46, and their differential output corresponding to recording information is taken out.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical head used in a magneto-optical recording device.
More specifically, a polarizing prism made of a uniaxial crystal birefringent material is used, and the readout light from the magneto-optical recording medium is made incident on the polarizing prism, where it is totally reflected on its slope and separated into ordinary light components and extraordinary light components. The present invention relates to an optical head that reproduces recorded information by detecting a differential output between the two.

[Prior art] Information recorded on magneto-optical materials is reproduced by utilizing the phenomenon that when a magnetic material is irradiated with linearly polarized light, the plane of polarization of reflected or transmitted light rotates in accordance with the direction of magnetization. The case of zero reflection is the Kerr effect, and the case of transmission is the Faraday effect.
Kerr effect is often used.

An example of an optical head in a conventional magneto-optical recording device is shown in the fourth example.
As shown in the figure, light from a semiconductor laser 10 is focused by a collimating lens 12, and linearly polarized light is extracted by an analyzer 14. This linearly polarized light passes through the first half prism 16, is focused by the objective lens 18, and illuminates the magneto-optical disk 20. When such linearly polarized light irradiates the magneto-optical disk 20, the plane of polarization of the reflected light is rotated due to the Kerr effect. For example, if the irradiation spot is magnetized downward and rotated by -8 with respect to the polarization plane 22 of the incident light, if the irradiation spot is magnetized upward it is rotated by -8. The plane of polarization rotates by 〇.

Therefore, by detecting the degree of polarization of this reflected light, a modulation signal corresponding to the Kerr rotation angle can be read.

The reflected light from the magneto-optical disk 20 is reflected by the objective lens 18.
This light is reflected by the first half prism 16 and directed toward the light receiving system.The second half prism 24 separates the light into two paths perpendicular to each other, and the reflected light is sent to the servo signal detection system (not shown). Opposite, the transmitted light passes through the λ/2 plate 26 and reaches P.
toward the BS (polarizing beam splitter) prism 28,
The combination of the λ/2 plate 26 and the PBS prism 28 further separates the optical path.

One passes through the condensing lens 29 and is detected by the first light receiving element 30 and converted into an electrical signal, and the other passes through the condensing lens 31 and is converted into an electrical signal by the second light receiving element 32. The detection outputs of the first light receiving element 30 and the second light receiving element 32 are applied to the input terminal of a differential amplifier 34 to obtain a differential output signal. By employing such a differential detection method, it is possible to reduce noise caused by variations in light amount.

[Problems to be Solved by the Invention] In the prior art, a PBS prism is used to extract the differential output signal as described above.

However, the Kerr rotation angle on the magneto-optical disk 20 is usually 1''.
In contrast, the extinction ratio of a normal PBS prism is about 30 dB, making it difficult to obtain a high C/N ratio.

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved optical head for a magneto-optical recording device that eliminates the drawbacks of the prior art as described above, is easy to downsize, and improves the C/N ratio. .

[Means for Solving the Problems] The present invention, which can achieve the above objects, includes a polarizing prism made of a uniaxial crystal birefringent material in a light receiving system that detects light from a magneto-optical recording medium. The optical head is configured to provide a differential output signal and thereby obtain a differential output signal.

The basic configuration of the present invention is shown in FIG.
In the optical head according to the present invention, a polarizing prism 40 is used in the light receiving system.
is located. The polarizing prism 40 is made of a birefringent uniaxial crystal material such as quartz, rutile single crystal, or calcite, and the optical axis of the crystal is approximately parallel to the normal direction of the surface on which the read light from the magneto-optical recording medium is incident. It is a triangular prism made parallel to each other.

Further, a first light receiving element 42 detects an ordinary light component which is totally reflected on the slope of the polarizing prism 40 and separated, a second light receiving element 44 detects an extraordinary light component, and both light receiving elements 42.
A differential amplifier 46 is provided in which the detection signal at 44 is manually input.

[Operation] In the optical head configured as described above, the continuous light emitted from the magneto-optical recording medium is incident on the polarizing prism 40. Since the optical axis of the polarizing prism 40 made of a uniaxial crystal birefringent material is parallel to the normal direction of the incident surface, the incident light is polarized as it is without being separated into extraordinary light components and ordinary light components. It passes through a prism 40. It is then totally reflected on that slope. The totally reflected light is separated into an ordinary light component and an extraordinary light component and then emitted.In the present invention, a larger separation angle can be obtained through total reflection compared to a normal double refraction prism.For example, the angle of incidence on an inclined surface is θ is set as follows.

θ-tan visit (n, /n,) Here, n: extraordinary refractive index no: ordinary refractive index.

This separated emitted light is used to reproduce recorded information. This will be explained with reference to FIG. Assume that the polarization plane of linearly polarized light incident on the magneto-optical recording medium is represented by the symbol U. The light reflected by the magneto-optical recording medium is rotated by 10 degrees or -8 degrees depending on the direction of magnetization of the light irradiation spot. The light totally reflected on the slope of the polarizing prism 40 is separated into two components: an ordinary light component and an extraordinary light component.

For example, considering the polarization plane V rotated by 103, the ordinary light component and the extraordinary light component are obtained as al+ bl respectively, so the differential output is (a+ bl ).On the other hand, the polarization plane W rotated by 101 , the ordinary light component is at and the extraordinary light component is bt, so the differential output is (az bz ).As a result, the differential output of the polarization plane V rotated by 03 and the polarization plane W rotated by -θ3 The differential output difference for is (a+bl) (az 'z)=as”bs
becomes. In other words, depending on the direction of magnetization of the magneto-optical recording medium,
This difference in size (as + bs) occurs, and this makes it possible to read the recorded information on the magneto-optical recording medium.

[Embodiment] FIG. 3 is an explanatory diagram showing an embodiment of the optical head according to the present invention. The incident path of the read light from the semiconductor laser 10 to the magneto-optical disk 20 is the same as that of the prior art shown in FIG. 4, and most of the configuration of the light receiving system is the same as the basic configuration diagram shown in FIG. For simplicity, corresponding parts are given the same reference numerals.

The readout light from the semiconductor laser 10 is transmitted through the collimating lens 1
After the light is focused by 2 and linearly polarized light is taken out by an analyzer 14, the light passes through a half prism 16 and is focused by an objective lens 18 to illuminate a predetermined position on the magneto-optical disk 20.

The plane of polarization of the reflected light from the magneto-optical disk 20 is rotated by 10 or -0 depending on the direction of magnetization at the irradiation spot. After this reflected light passes through the objective lens 18 and is reflected by the half prism 16, it is separated into two optical paths perpendicular to each other by the second half prism 24, and the reflected light is directed toward the servo signal detection system, toward the position of the optical head. '421
used for.

The transmitted light passes through a condenser lens 39 and reaches a polarizing prism 40 . As mentioned above, the polarizing prism 40 is made of a birefringent material, and the optical axis of the crystal is parallel to the normal direction of the incident surface, so that the polarizing prism 40 is not separated into the ordinary light component and the extraordinary light component, but is directly transmitted inside. , and is totally reflected on that slope. The totally reflected light is separated into an ordinary light component and an extraordinary light component. The light then reaches the corresponding light receiving elements 42 and 44, where it is converted into an electrical signal. These electrical signals are input to the differential amplifier 46 and amplified, and then output to the optical disk 20.
A differential output corresponding to the recorded information is extracted.

As the polarizing prism 40, for example, rutile single crystal, quartz, calcite, etc. are used. First and second light receiving elements 4
Although 2.44 may be separate photodetectors, a two-split photodetector is preferable because the ordinary light component and the extraordinary light component are close to each other.

[Effects of the Invention] As described above, the present invention provides a polarizing prism made of a birefringent material in the light receiving system for the read light from the magneto-optical recording medium so that the optical axis of the crystal is substantially parallel to the read light.
By performing total reflection, the separation angle is increased, the extraordinary light component and the ordinary light component are separated, and a differential output can be obtained.

In particular, in the present invention, since the separated ordinary light component and extraordinary light component are emitted in almost the same direction, two light receiving elements can be arranged in parallel.
Since a split photodetector can be used and a large separation angle can be obtained due to total reflection, the optical path length after separation can be shortened, making it easy to downsize.

Furthermore, since the polarizing prism used in the present invention has a higher extinction ratio (approximately 50 dB) than a normal PBS prism, it is possible to improve the C/N ratio.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the basic configuration of the present invention, FIG. 2 is an explanatory diagram of its operation, and FIG. 3 is an explanatory diagram showing an embodiment of the optical head according to the present invention. Further, FIG. 4 is an explanatory diagram showing an example of the prior art. 40... Polarizing prism, 42.44... Light receiving element,
46...Differential amplifier. Patent applicant Fuji Electrochemical Co., Ltd. Agent Shigeru Estimate Figure 1 Figure 2 Figure 3 Figure 2Q-〒 Figure 4

Claims (1)

[Claims] 1. A polarizing prism made of a uniaxial crystal birefringent material, two light-receiving elements that separately detect ordinary light components and extraordinary light components that are totally reflected on the slope of the polarizing prism and separated, and detection of both light-receiving elements. A magneto-optical recording device comprising a differential amplifier that receives an output as an input, and wherein the polarizing prism has an optical axis of a crystal substantially parallel to a normal direction of a plane on which read light from a magneto-optical recording medium is incident. optical head.