JPH0430342A - Optical disk device - Google Patents

Abstract

PURPOSE:To improve the quality of a reproducing signal while reproducing power is limited to a prescribed value by providing an optical amplifier in a signal reproduction optical path. CONSTITUTION:An optical amplifier 15 is inserted between a polarized beam splitter 8 and a photodetector 9 and between the polarized beam splitter 8 and a photodectector 10 respectively and amplifies a signal light separated into weak S and P polarized lights. Let an amplification factor of each optical amplifier be 10 and a level of a signal light outputted from the polarized beam splitter 8 be correspondent to a Kerr rotation angle of 0.5 degree. On the other hand, the output light level of each optical amplifier 15 is equivalent to 5-degree rotation and a value resulting from the calculation of a difference of outputs of the amplifiers 15 at a differential amplifier 11 is obtained at a signal output terminal 12. Thus it is possible to increase the C/N of the reproducing signal without increasing the reproduction power of the light source.

Description

[Detailed Description of the Invention] (Summary) Regarding improving the quality of the reproduced signal of an optical disc device, the objective is to provide a method for improving the quality of the reproduced signal while restricting the reproduction power emitted from the light source to a predetermined value. The light emitted from the light source is focused on the surface of the recording medium through an optical system having a beam splinter, and the return light containing the signal component that is reflected on the surface of the recording medium and has traveled backward through the forward optical system is collected as described above. A beam splitter separates the outgoing optical system into a signal reproducing optical path that is reflected and guided to a signal detecting system, and an optical amplifier provided in the signal reproducing optical path amplifies the signal component.

(Industrial Application Field) The present invention relates to improving the quality of reproduction signals of an optical disc device, which is a mass storage device.

With the recent demand for higher speed computer systems, higher performance optical disk devices are also required. In particular, it is important to improve the C/N ratio of optical disc reproduction signals.

[Prior Art] FIG. 4 shows a schematic configuration diagram of a conventional magneto-optical disk device. In the figure, ■ is a light source (for example, a semiconductor laser La5e
r Diode; hereinafter abbreviated as LD), 2 is LD
3 is a collimating lens that converts the emitted light from LI into parallel light; 3 is a beam splitter that transmits the incident light from LI 1 and reflects and separates the returned light; 4 is an objective lens; 5 is a beam focused by the objective lens 4; A recording medium receives the emitted light spot on a desired trunk, and 6 indicates a signal detection system for detecting the signal included in the signal reproduction optical path 6a separated by the beam splinter 3. 7 is a wavelength plate (for example, a 1/2 wavelength plate rotated by 45 degrees) for rotating the polarization direction of the returned light separated into the signal reproducing optical path 6a by a required angle; 8 is a wavelength plate for rotating the polarization direction of the returned light separated into the signal reproducing optical path 6a; A polarizing beam splitter separates the light into polarized components; 9 and 10 are light receiving elements that respectively receive and photoelectrically convert the S-polarized light component and the P-polarized light component separated by the polarized beam splitter 8; 11 is the output of each light-receiving element 9 and 10; A differential amplifier takes the difference, and 12 indicates a signal output terminal.

This FIG. 4 shows a schematic configuration diagram, and therefore, a circular correction prism to be inserted between the collimating lens 2 and the beam splitter 3, or a polarizing beam splitter 8 and the light receiving element 9, 10, respectively. The description of the condensing lens, etc. that should be used is omitted because it has no direct relation to the present invention.

The magneto-optical disk device makes linearly polarized light incident on the recording medium 5, and when the incident linearly polarized light is reflected by the recording medium 5,
A reproduced signal was obtained by utilizing the slight rotation of the plane of polarization due to the Kerr effect generated in response to the magnetism of information magnetically recorded on the recording medium 50 surface in advance. However, since the Kerr rotation angle is small, less than 1 degree, it has been difficult to improve signal quality. In order to improve the C/N ratio of the magneto-optical disk reproduction signal, it is sufficient to increase the reproduction power (the reproduction irradiation power of the laser beam onto the recording medium 5).

[Problem to be solved by the invention]

However, when the reproduction power is increased, there is a problem that when the same track is reproduced many times, the quality of the magnetic signal formed on the recording medium 5 deteriorates due to the reproduction power. Therefore, the conventional reproduction power is set to a value that does not deteriorate the quality of the reproduction signal formed on the recording medium 5. This problem is not limited to magneto-optical disks, but phase change type and write once type optical disk devices are also subject to similar restrictions.

Furthermore, if the reproduction power is set within a predetermined value, the signal level detected by the signal detection system becomes extremely weak, and in order to ensure the C/N ratio, an optical amplifier (for example, in a nonlinear optical system) is required. optical parametric amplifiers that utilize parametric interaction of light waves of different wavelengths)
However, since these conventional optical amplifiers require a relatively large installation space, it has been impossible to incorporate them into optical heads that require high-speed light spot position control.

The present invention has been made in view of the above conventional problems, and aims to provide a method for improving the quality of a reproduced signal while restricting the reproduction power emitted from a light source to a predetermined value.

[Means to solve the problem]

FIG. 1 is an explanatory diagram of an optical amplifier used in the present invention, FIG. 2 is a first embodiment of the present invention, and FIG. 3 is a second embodiment of the present invention. The light emitted from the light source 1 is focused onto the surface of the recording medium 5 through an optical system having a beam splitter 3, and the return light containing the signal component reflected from the surface of the recording medium travels backward through the outgoing optical system. The beam splitter 3 separates the outgoing optical system into a signal reproducing optical path 6a that is reflected and guided to a signal detecting system 6, and an optical amplifier is provided in the signal reproducing optical path 6a.

[For production]

An optical amplifier that uses excitation light can obtain output light that is amplified without depending on the polarization of input light, so that the reproduction power emitted from the light source during signal reproduction of an optical disk device is transmitted onto the recording medium 5. Even if it is regulated to a predetermined value that does not degrade the quality of the reproduced signal formed, the weak signal component contained in the returned light separated into the signal reproduction optical path 6a of the signal detection system 6 is inserted into the signal reproduction optical path 6a. optical amplifier 15
By amplifying the signal, the C/N can be increased and sufficient signal quality can be ensured.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

Note that, in order to make the explanation of the configuration and operation easier to understand, the same parts are given the same reference numerals throughout all the figures, and repeated explanation thereof will be omitted.

FIG. 1 is an explanatory diagram of the optical amplifier used in the present invention, and shows the function of the optical amplifier (for example, an optical parametric amplifier that uses parametric interaction of light waves of different wavelengths in a nonlinear optical system). . Recently, in the field of optical communication technology that uses optical fibers, optical amplification technology that uses pumping light for weak, attenuated light that accompanies optical fiber transmission has been put into practical use. In the figure, reference numeral 5 indicates an optical amplifier, and A indicates the direction of light incident on the optical amplifier 15 and the modulation waveform of the incident light. B shows the direction of pumping light (a light wave with a different wavelength from the incident light) to the optical amplifier 15 and the modulation waveform of the pumping light. This excitation light is input so as to be added to the modulated waveform of the incident light in a nonlinear optical system formed within the optical amplifier 15. C shows the direction of the output light of the optical amplifier 15 and the modulation waveform of the output light obtained by amplifying the incident light. Recently, in the field of optical communication technology that uses optical fibers, optical amplification technology that uses pumping light for weak, attenuated light that accompanies optical fiber transmission has been put into practical use. According to this optical amplifier 15, since the light is amplified without depending on the polarization direction of the light, this principle is utilized to improve the C/N ratio of the reproduction signal of the conventional optical disc device.

In recent years, optical heads in optical disk devices have a structure that can be separated into a main optical system fixed part having an optical detection system including a light source and a movable part having a light spot driver weft (for example, Japanese Patent Application Laid-Open No. 61-177651). is being developed. As a result, the detection of the optical signal becomes possible in the main optical system fixed part that has the optical detection system, so the restrictions on the installation space of the detection mechanism are relaxed, and the arrangement of the optical amplifier as in the present invention can be easily implemented. Ta.

FIG. 2 shows a first embodiment of the present invention, and FIG. 2 will be explained below with reference to FIG. 1. In both figures, optical amplifiers 15 are inserted between polarizing beam splitter 8 and light receiving elements 9 and 10, respectively, and amplify signal lights separated into al S-polarized light and P-polarized light according to the principle shown in FIG. 1. Assuming that the amplification factor of each optical amplifier 15 is 10 times and the level of the signal light output from the polarizing beam splitter 8 is a value corresponding to a Kerr rotation angle of 0.5 degrees, the output light level of each optical amplifier 15 is is equivalent to a rotation of 5 degrees, and a value calculated by the differential amplifier 11 from the difference between the outputs of the respective optical amplifiers 15 is obtained at the signal output terminal 12. That is, since the signal strength increases, the C/N ratio improves.

Further, it is also possible to insert only one optical amplifier 15 between the polarizing beam splitter 8 and the beam splitter 3 (which may be on the input side or the output side of the wave plate 7).

FIG. 3 shows a second embodiment of the present invention, and this example shows a configuration diagram when applied to a write once type and a phase change type optical disk device. In the figure, 5a indicates a recording medium used for write once type and phase change type.

The return light reflected by the recording medium 5a travels backward through the outgoing optical system, is reflected and separated by the beam splitter 3, and is guided to the signal reproduction light i6a of the signal detection system 6. By inserting the optical amplifier 15 into the signal reproducing optical path 6a, the signal strength increases as in the case of the magneto-optical disk device, and the C/N ratio improves.

[Effects of the Invention] As is clear from the above description, according to the present invention, there is an effect that the C/N ratio of the reproduced signal can be increased without increasing the reproduction power of the light source.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an optical amplifier used in the present invention, FIG. 2 is a first embodiment of the present invention, FIG. 3 is a second embodiment of the present invention, and FIG. 4 is a conventional magneto-optical disk device. A schematic configuration diagram is shown. In Figures 1 and 2, 1 is a light source (LD), 3 is a beam splitter, 5 is a recording medium, 6 is a signal detection system, and 6a
1 represents a signal regeneration optical path, and 15 represents an optical amplifier. Unexplained degree 7'1 Figure j

Claims (1)

[Claims] The light emitted from the light source (1) is focused on the surface of the recording medium (5) via an optical system having a beam splitter (3), and the signal is reflected by the surface of the recording medium and travels backward through the outgoing optical system. The beam splitter (3) separates the return light containing the component into a signal reproducing optical path (6a) which is reflected and guided from the outgoing optical system to the signal detecting system (6), and an optical amplifier (6a) provided in the signal reproducing optical path. 15) An optical disc device characterized in that the signal component is amplified by the above method.