JPH07105084B2 - Magneto-optical disk device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head of a magneto-optical disk device, and more particularly to a signal pair of a reproduced signal by integrating a photodetector for reproducing a magneto-optical signal and a preamplifier. The present invention relates to a magneto-optical disk device suitable for improving noise reduction.

[Conventional technology]

As described in JP-A-60-20340, the conventional device employs differential detection as a method for detecting a magneto-optical signal, and separates mutually orthogonal polarization components such as a Wollaston prism or a lotion prism as an analyzer. Use polarizing prisms that can be taken out, and use these prisms for the incident polarization direction.
Tilted at 45 °, or installed a λ / 2 plate (λ: wavelength used) in front of the prism, and set this to the incident polarization direction of the prism.
The light beam split by the prism while tilted at 45 ° is detected by the two-split photodetector. Usually, the output of the two-division photodetector is differentially obtained to obtain a magneto-optical signal, but in the conventional device, the detecting means is not specified.

[Problems to be solved by the invention]

The above-mentioned prior art relates to improvement of a signal-to-noise ratio of a magneto-optical signal,
No consideration is given to the optimum signal detection method from the photodetector, and it is said that a sufficient signal-to-noise ratio cannot be obtained due to stray capacitance and noise due to wiring simply by installing a preamplifier for current-voltage conversion. There was a problem.

An object of the present invention is to improve the signal-to-noise ratio and reduce the area occupied by the preamplifier by integrating a photodetector for signal detection and a preamplifier for converting its output into an electric signal.

[Means for solving problems]

The above object is achieved by incorporating a preamplifier for signal reproduction in the package of the two-divided photodetector.

[Action]

By providing preamplifiers in the photodetector, the problem of stray capacitance and the influence of disturbance are eliminated, and a high S / N signal can be obtained.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The light emitted from the semiconductor laser 1 passes through the coupling lens 2, becomes a circular parallel light at the beam shaping prism 3, and enters the first beam splitter 4 as p-polarized light. The light emitted from the first beam splitter 4 passes through a focusing lens 7 attached to a tracking galvano mirror 5 and a voice coil 6 for automatic focusing, and a perpendicular magnetic film 8 is formed on the disk by vapor deposition or sputtering. 9 is narrowed down to a spot shape of about 1 μm. The reflected light from the disk 9 enters the first beam splitter 4 through the same path as the incident light, the p-polarized reflectance component determined by the first beam splitter is reflected, and the optical path is separated. After that, the light is divided into two by the second beam splitter 10, the transmission side is used as a servo signal detection signal light beam for automatic focusing signal detection and tracking signal detection, and the reflection side is used as a magneto-optical signal detection light beam. . The transmitted light flux passes through the convex lens 11 and is split into two by the third beam splitter 12.
The transmission side is guided to the two-part photodetector 13 for tracking signal detection, and the reflection side is the cylindrical lens 14 and knife edge.
2-pass photodetector for automatic focusing signal detection after passing 15
Guided by 16. For tracking, a push-pull method is used for obtaining an error signal by differentially diffracting light from a disc with a guide groove. After being differentiated by a differential amplifier 17, the galvano mirror 5 is driven through a galvano mirror drive circuit 18. By doing. The automatic focusing is performed by driving the voice coil 6 through the voice coil drive circuit 20 after using the image rotation method described in Japanese Patent Application Laid-Open No. 57-108811, after being differentiated by the differential amplifier 19.

The magneto-optical signal detecting light beam reflected by the second beam sprinter 10 passes through the half-wave plate 21 and the convex lens 22 and enters the Wollaston prism or the lotion prism 23.
Each of these is a combination of crystal prisms,
The former can separate two polarized lights because the ordinary ray and the extraordinary ray go in different directions due to the birefringence at the boundary surface, and the latter can also separate the two polarized rays. The Wollaston prism has a larger angle. Since the two prisms have the same function in separating the two polarized lights, the Wollaston prism will be described below as a representative.

The direction of polarization incident on the stone prism 23 is determined by the wave plate 21.
When the angle is set to 45 °, the light quantities of the two separated light beams can be made equal. The same effect can be obtained by rotating the Wollaston prism itself by 45 ° without using the half-wave plate. The light flux divided by the Wollaston prism 23 is independently detected by the two-split photodetector 24. The light receiving elements 241 and 242 of the two-divided photodetector 24 are photoelectrically converted by the current-voltage converters 251 and 252 and then pass through the amplifiers 253 and 254 (however, not necessary when the outputs of 251, 252 are sufficient) and input to the differential amplifier 26. A magneto-optical signal is obtained, and an ID signal (sector mark, address information, CRC signal, etc.) in which concave and convex pits are previously formed on the disk 9 by being input to the summing amplifier 27 is obtained. Since the magneto-optical signal is smaller than the ordinary ID signal by 1 to 2 digits, the amplifier noise of the preamplifier used becomes a problem. For example, when preamplifiers (251, 252, 253, 254) are formed on the preamplifier board that is placed on the optical head by combining components, the stray capacitance of the wiring from the photodetector to the current-voltage converter 251, 252 and the stray capacitance of the feedback resistor Therefore, considering the frequency characteristics, the feedback resistance cannot be increased. Therefore, the signal light amount component becomes small, and the ampule noise becomes dominant in the noise component, and the signal-to-noise ratio (SN ratio) decreases. In order to solve the problem in the present invention,
The preamplifiers (251, 252, 253, 254), the differential amplifier 26, and the summing amplifier 27 are manufactured as a one-chip IC (a portion surrounded by a broken line in FIG. 1) and incorporated in a package containing a two-divided photodetector. The situation is shown in FIG. Package 31
A case of the standard of TO-18 or TO-5 is used, two-divided photodetectors 241 and 242 are arranged at the center of the case, and a chip 32, which is an IC of preampules, is arranged around it.
For simplicity, the wires and terminals are omitted in the figure).
In the above description, the method of assembling the two-division photodetector and the preamplifier IC is adopted, but the two-division photodetector and the preamplifier can be formed monolithically on the Si substrate.

Fig. 3 shows the frequency characteristics when the preamplifiers are integrated as an IC and when the preamplifier is assembled as a single component on a printed circuit board. In the figure, in the case of the present invention, the frequency characteristic does not deteriorate up to 20 MHz, and the amplifier noise becomes smaller than the calculated shot noise value, which is an ideal amplifier. In the conventional case, the frequency characteristic is 3 dB lower than 1
Although it is 2 MHz, the noise is 10 to 15 dB lower than the value in the present invention because the amplifier noise is dominant. As described above, according to the present invention, the signal-to-noise ratio of the magneto-optical signal can be sufficiently secured.

The magnetic field generator 30 for determining the magnetization direction of the perpendicular magnetization film during the recording / erasing operation is not related to the present invention in FIG.

〔The invention's effect〕

According to the present invention, since the photodetector of the photoelectric conversion unit and the preamplifiers are housed in the same package of the photodetector, the stray capacitance can be significantly reduced, the frequency characteristics are good, and the amplifier noise can be reduced. The signal-to-noise ratio of magnetic signals can be significantly improved. Also, a two-part photodetector,
Since the preamplifiers can be formed in pairs, the characteristics are the same and the gain variation between the two signals to be differentiated is eliminated, so that the common mode rejection ratio is also improved.

[Brief description of drawings]

FIG. 1 is a view showing an embodiment of the present invention, and FIGS. 2 and 3 are views for catching the embodiment. 4,10,12 …… Beam splitter, 21 …… 1/2 wave plate, 23…
… Wollaston prism, 24 …… 2 split photo detector, 251,
252 ... Current-voltage converter, 253,254 ... Amplifier, 26 ...
Differential amplifier, 27 ... Wadou amplifier

Claims (1)

[Claims] 1. A light source, an optical system for guiding light emitted from the light source onto an information recording medium made of a perpendicularly magnetized film, and a magneto-optical signal contained in reflected light from the information recording medium are differentially detected. In a magneto-optical disk device comprising a polarizing prism, a photodetector for receiving the light separated by the polarizing prism, and a magnetic field generator for applying a magnetic field to the information recording medium at the time of recording / erasing operation, Wollaston is used as the polarizing prism. A photodetector having a preamplifier for electrically converting the output of the photodetector is provided in the package of the photodetector using a prism or a lotion prism and a two-divided photodetector as the photodetector. A magneto-optical disk device characterized by.