JP2586641B2 - Optical head device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical head device used for an information input / output device for recording and reproducing information using light.

[Conventional technology]

At present, in an optical head device that records and reproduces information using light, for the purpose of increasing the transfer speed of a reproduction signal,
Development of optical heads that irradiate multiple tracks on different tracks of a recording medium (for example, Yoshiwara, Katayama et al .: Parallel recording / reproduction of magneto-optical disks with multi-beam optical heads, '88 Akiyoshi 4p -ZD-2).

FIG. 7 schematically shows a configuration of a conventional multi-beam optical head using an array laser as a light source. A plurality of light beams emitted from the semiconductor laser array 1, which can be driven independently, pass through a collimator lens 2 and a condenser lens 4, and as shown in FIG.
Irradiated to 83,84. At the time of recording, recording is performed independently for each track by independently modulating the intensity of each light beam. In the figure, recording pits are indicated by 86. At the time of reproduction, each reflected light beam from the recording medium surface is split by the beam splitter 3 and made incident on different photodetectors on the photodetector array 11 via the condenser lens 10. The output signal from each detector is input to the signal processing circuit 13. Further, in the error detection system, each reflected light beam from the recording medium surface is split by the beam splitter 6 and is incident on a different photodetector on the error signal detection photodetector array 8 via the condenser lens 7. An output signal from each detector is input to an error signal processing circuit 9.

With the above configuration, independent reproduction of the information signal of each track and independent detection of the error signal are enabled.

[Problems to be solved by the invention]

In the configuration of the conventional optical head device described above, there is a problem that, in the information reproducing system, when a wraparound from an adjacent light beam or interference from an adjacent pit occurs, a reproduced signal characteristic is deteriorated.

An object of the present invention is to provide an optical head device capable of removing such crosstalk between light beams and interference from adjacent pits and improving reproduction signal characteristics.

[Means for solving the problem]

The present invention is directed to an optical head device having a light detection unit that irradiates a plurality of light beams on different tracks of a recording medium and reproduces a signal independently from reflected light from each track, wherein each of the light beams output from the light detection unit A plurality of frequency converters each of which is capable of inputting a reproduction signal for each track and capable of changing a frequency characteristic; and a predetermined frequency converter based on an output signal of a predetermined frequency converter among the plurality of frequency converters. Signal processing means for adjusting the frequency characteristics of the remaining frequency converters different from the above and reducing output signals from the remaining frequency converters.

[Action]

According to the present invention, a plurality of photodetector outputs including crosstalk and intersymbol interference are independently input to a frequency converter having a variable frequency characteristic to detect a light beam signal modulated by information to be reproduced. The output signal of the frequency converter connected to another photodetector is subtracted from the output of the frequency converter connected to the detector. With such a configuration, the frequency converter connected to the photodetector that detects the signal of the light beam modulated by the information to be reproduced mainly removes intersymbol interference from adjacent pits, Crosstalk can be mainly removed using the output signal of the frequency converter connected to the photodetector.

The frequency characteristics of these frequency converters include, for example, a predetermined preamble signal as a reference signal, and a frequency converter output connected to a photodetector that detects a signal of a light beam modulated by information to be reproduced. It can be determined by controlling the frequency characteristics of each frequency converter so that the power of the error signal from the reference signal is minimized.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment in which a semiconductor laser array 1 having three light sources is used. In a signal reproducing system, a reproduced signal detecting photodetector array 11 and an information reproducing signal processing circuit 13 are shown.
A frequency converter group 12 is provided between. The signal reproducing circuit 13 is the same as the conventional one shown in FIG. 7, and the error detection system has the same configuration as the conventional one. In FIG.
Components that are the same as the components in the figure are given the same reference numerals.

FIG. 2 shows an example of a configuration of the photodetector array 11 for detecting a reproduction signal and the frequency converter group 12. The photodetector array 11
Photodetector for signal reproduction 300, photodetectors for interference signal detection 301 and 3
The frequency converter group 12 is composed of frequency characteristic variable filters 310 to 312, an adder 320, a reference signal generation circuit 321, an error signal detection circuit 322, and a frequency characteristic variable filter control circuit 323. .

In the optical head device having the above-described configuration, the light emitted from the semiconductor laser array 1 is collimated by the collimating lens 2 and is irradiated on the recording medium 5 by the focusing lens 4. FIG. 3 shows a schematic diagram of the positional relationship between the condensed spot and the track on the recording medium surface at this time. Each of the beams 24a, 24b, 24c irradiates a separate track 21, 22, 23, respectively. The spot 24b at the center is for signal reproduction, and the spots 24a and 24c at both ends are for detecting a wraparound signal to the center beam. In the figure, reference numeral 25 denotes a recording pit.

At the time of writing, recording can be performed for each track by modulating the light intensity. Further, at the time of reproduction, the reflected light from the recording medium surface is split by the beam splitter 3,
Each beam on the photodetector array 11 is condensed by a condensing lens 10 on separate detectors 300, 301, 302.

The signal reproducing photodetector 300 mainly detects the reflected light from the center track 22 in FIG. The photodetectors 301 and 302 for detecting interference signals mainly include the tracks 21 and
The reflected light from 23 is detected. From these photodetectors 300 to 302, signals including crosstalk and intersymbol interference from adjacent pits are output, and input to frequency characteristic variable filters 310 to 312, respectively. Frequency characteristic variable filter 31
The output signals 0 to 312 are input to the adder 320, and the respective signals are added. The added signal is input to the error signal detection circuit 322 together with the reference signal generated from the reference signal generation circuit 321. The error signal detection circuit 322 detects an error signal of these signals, and converts the detected error signal into a frequency characteristic variable filter control circuit 323.
Output to The frequency characteristic variable filter control circuit 323 independently controls the frequency characteristics of the frequency characteristic variable filters 310 to 312 using the input error signal by, for example, a gradient method so that the error signal power is minimized. .

On the other hand, the output of the adder 320 is input to the information reproduction signal processing circuit 13 at the next stage, and a reproduction signal from which crosstalk between light beams and interference from adjacent pits are removed is obtained.

FIG. 4 shows an embodiment in which a semiconductor laser having a single light source and a diffraction grating are used, and components equivalent to those in FIG. 1 are denoted by the same reference numerals. One outgoing light beam from the semiconductor laser 1 passes through the diffraction grating 41 and is converted into a plurality of light beams (a total of three diffracted lights of 0th order and ± 1st order in this example). A focused spot similar to that shown in the figure is formed. That is, the central spot is for signal reproduction, and the spots at both ends are for detecting a wraparound signal to the central beam. The operation of the signal reproducing system is the same as that of the embodiment shown in FIG. 1. Also in this embodiment, it is possible to eliminate crosstalk between light beams and interference from adjacent pits, thereby improving reproduction signal characteristics.

FIG. 5A shows an embodiment in which a semiconductor laser array having four light sources is used. The same components as those in the embodiment of FIG. 1 are denoted by the same reference numerals. The positional relationship between the focused spot and the track is the same as in FIG. Focused spots 852 and 853 can be used for signal reproduction. Signals from the focused spots 851 and 853 are used for interference removal for reproduction from the focused spot 852, and signals from the focused spots 852 and 854 are used for interference removal for reproduction from the focused spot 853.

FIG. 5B shows a signal flow in the signal reproducing system in the present embodiment. Since there are two signal-reproducing condensing spots, two frequency converter groups having the configuration shown in FIG. 2 are used. 520 and 521 are these frequency converter groups. Track 8
The reflected lights from the converging spots 851,852,853,854 on 1,82,83,84 enter the four photodetectors of the photodetector array 11 for signal detection, respectively, and output photodetection signals 500,501,502,503. Signal 501 is input to frequency converter group 520 for signal reproduction, and signals 500 and 502 are input for interference removal. In addition, the signal 502 is input to the frequency converter group 521 for a signal reproduction signal, and the signals 501 and 503 are input for interference removal. The output from each frequency converter group is input to the information reproduction signal processing circuit 13 at the subsequent stage. From the signal processing circuit 13, two pieces of reproduction information from which crosstalk and interference have been removed are obtained.

FIG. 6 shows a semiconductor laser array 1 having three light sources.
A single photodetector 8 ', 11' is used as a photodetecting means without using a photodetector array, and a circuit 14 for temporarily storing a reproduction signal from each track is provided with a frequency converter. It is provided immediately before the group 12. The positional relationship between the focused spot and the track on the recording medium surface is the same as in FIG.
In signal reproduction, the light source that emits light is switched for each round, and a signal from a track to be reproduced and a signal for removing code interference are separately reproduced. It takes time for three rotations of the disk to obtain all the signals necessary for signal reproduction and interference removal. Therefore, the reproduced signal from each track is temporarily stored in the circuit 14. The configuration of the present embodiment has an advantage that the optical system is reduced in size as compared with the case where the photodetector array is used.

〔The invention's effect〕

According to the present invention, in a signal reproducing system of an optical head device that irradiates a plurality of light beams onto a recording medium surface, a roundabout between adjacent light beams and an interference between adjacent pits are removed to obtain a good reproduced signal. It became possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment in which a semiconductor laser array having three light sources is used, FIG. 2 is a diagram showing one configuration example of a frequency converter group, and FIG. FIG. 4 is a diagram showing a positional relationship between a spot and a track. FIG. 4 is a diagram showing an embodiment in which a plurality of light beams are obtained using a diffraction grating. FIG. 5 is a diagram showing a case in which a semiconductor laser array having four light sources is used. FIG. 6 is a diagram showing an embodiment, FIG. 6 is a diagram showing an embodiment in which a single photodetector is used without using a photodetector array as a photodetector, and FIG. FIG. 8 is a diagram showing a configuration example of the optical head device, and FIG. 8 is a diagram showing a relationship between the converging spots and tracks when four converging spots are irradiated. DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser array 2 ... Collimating lens 3 ... Beam splitter 4 ... Condensing lens 5 ... Recording medium 6 ... Beam splitter 7 ... Condensing lens 8 ... Error signal detection photodetector array 9 ... Error signal processing circuit 10 ... Condenser lens 11 ... Photodetector array for reproduction signal detection 12 ... Frequency converter group 13 ... Signal processing circuit for information reproduction 14 ... Reproduction signal is temporarily stored. Circuits with functions 21 to 23 Track 24 Focus spot 25 Recording pit 300 Photodetectors for signal reproduction 301 and 302 Photodetectors for interference removal 310 to 312 Frequency variable filter 320 … Adder 321 …… Reference signal generating circuit 322 …… Error signal detecting circuit 323 …… Frequency characteristic variable filter control circuit 41 …… Diffraction grating 500-503 …… Light detection signal 520,521 …… Frequency characteristic converter group 81-84 …… Tracks 851-854 ... focused spot 86 ...... recording pits

Claims (1)

(57) [Claims] 1. An optical head device having light detecting means for irradiating a plurality of light beams on different tracks of a recording medium and reproducing signals independently from light reflected from each track, wherein the light output from the light detecting means is provided. A plurality of frequency converters, each of which is capable of inputting a reproduction signal for each track and capable of changing a frequency characteristic; and outputting the predetermined frequency conversion from an output signal of a predetermined frequency converter among the plurality of frequency converters. An optical head device comprising: signal processing means for adjusting the frequency characteristics of the remaining frequency converters different from the frequency converter to reduce output signals from the remaining frequency converters.