JPH07134831A - Optical head - Google Patents

Abstract

PURPOSE:To eliminate a DC offset of a servo signal due to a stray light generated in an optical head and to obtain a stable error signal. CONSTITUTION:Peripheral light-receiving areas 12i and 12j are provided in the vicinity of signal detecting light-receiving areas 12e and 12f of a photodetector, and a differential between signals obtained in the signal detecting lightreceiving areas 12e and 12f and signals obtained in the peripheral light- receiving areas 12i and 12j is taken. Thereby a DC offset due to a stray light is canceled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for recording and reproducing by irradiating a recording medium with a light beam.

[0002]

2. Description of the Related Art In recent years, an optical head for reproducing a recording medium having a low reflection such as magneto-optical property has been developed, and it is required to detect a minute signal.

A conventional optical head will be described below with reference to the drawings. FIG. 4 is a diagram showing an optical system of a conventional optical head, FIG. 5 is a diagram showing an optical path rising portion of the optical system, and FIG. 6 is a diagram showing a signal detection light receiving region of a photodetector of the optical system.

In FIG. 4, reference numeral 1 is a semiconductor laser which is a light source, and 2 is a grating, and a diffraction grating is formed on one surface thereof to form a tracking beam by diffraction. Reference numeral 3 denotes a collimating lens for collimating the light emitted from the light source 1 into a parallel light flux, 4 a beam splitter for branching the reflected light flux from the recording medium to the photodetector 12, 4a a reflecting surface of the beam splitter 4, and 5 a reflection. A front-light photodetector for detecting the light reflected by the surface 4a, 6 a rising mirror for reflecting a parallel light beam toward the recording medium, 7 an objective lens for converging a light spot on the recording medium, and 8 an The reflected light beam from the recording medium split by the beam splitter is P-polarized and P + S
Wollaston prism that separates polarized light and S polarized light,
Reference numeral 9 is a reflection mirror for bending the optical axis by 90 °, 9a is a reflection surface, 10 is a detection lens for collecting the reflected light flux from the recording medium on the photodetector 12, and 11 is for generating a focus error signal. Cylindrical lens, 12 is a resin-molded photodetector for detecting information signals and servo signals, 13 is a base for fixing parts of an optical head, and 13a
Is a hole for guiding the front light of the semiconductor laser 1 to the front light photodetector 5, 14 is an effective light beam emitted from the collimator lens 3,
15 is a light beam condensed on the recording medium, 16a, 16b,
16 c and 16 d are light beams 14 scattered by the base 13.

In FIG. 5, reference numeral 17 designates the objective lens 7 in the focus direction and the tracking direction (perpendicular to the paper surface).
The actuator 18 is a recording medium that is moved to focus on the recording medium 18. 16e and 16f are light beams 14 scattered by the actuator 17.

In FIG. 6, 12a, 12b, 12c,
Reference numeral 12d is a signal detection light receiving area for detecting a focus error signal, 12e and 12f are signal detection light receiving areas for detecting a tracking error signal, 12g and 12h are signal detection light receiving areas for detecting a polarization separated information signal, 19n, 19o,
Reference numeral 19p is a differential circuit, and 19q is an addition circuit.

The operation of the conventional optical head having the above structure will be described below.

In FIGS. 4 and 5, the light emitted from the semiconductor laser 1 is incident on the grating 2 and is diffracted in the direction perpendicular to the paper surface, and the three light beams necessary for detecting the tracking error signals of the 0th order light and the ± 1st order light are detected. It is split into light beams (only the 0th order light is shown in the figure). The three light beams pass through the beam splitter 4, are reflected by the rising mirror 6, and the objective lens 7 collects a light spot for information detection in the center on the recording medium 18 and a light spot for a tracking error signal on both sides thereof. It
The reflected light beam from the recording medium 18 enters the beam splitter 4 through the objective lens 7 and the rising mirror 6 and is reflected by the reflection surface 4
It is reflected by a and enters the Wollaston prism 8. In the Wollaston prism 8, the reflected light beam is separated into three light beams in the direction orthogonal to the above three beams: an information detecting P-polarized light beam, a focus error signal P + S-polarized light beam, and an information-detecting S-polarized light beam. The light is reflected by the reflecting surface 9 a of 9 and enters the detection lens 10. The detection lens 10 converges the reflected light flux from the recording medium 18, which is a substantially parallel light flux, and the cylindrical lens 11 generates astigmatism corresponding to the surface wobbling of the recording medium 18 to form a light spot on the photodetector 12. .

On the other hand, the light beam collimated by the collimator lens 3 is reflected by the reflecting surface 4a, passes through the hole 13a of the base and enters the photodetector 5 for front light, and is obtained from this photodetector 5. The signal is controlled so that the emission power of the semiconductor laser 1 becomes constant.

In FIG. 6, the light spots for focus error signals are signal detection light receiving regions 12a, 12b, 12c,
The photocurrent generated in each area is 12a.
And 12c and 12b and 12d are added together, and then subjected to IV conversion, and further differentiated by the differential circuit 19o to obtain a focus error signal (12a + 12c)-(12b + 12d). The optical spot for the tracking error signal is formed on the signal detection light receiving regions 12e and 12f, and the photocurrent generated in this region is differentially converted by the differential circuit 19n after the IV conversion to obtain the tracking error signal (12e-12f). Is obtained. Further, the information light spots are the signal detection light receiving regions 12g, 12
After being formed on h, the photocurrent generated in this region is IV converted, and then, in the case of a magneto-optical disk (MO), it is differentiated by a differential circuit 19p to generate an information signal (12g-12h).
In the case of a ROM disc, the addition circuit 19q performs addition to obtain an information signal (12g + 12h).

[0011]

In the optical head having the above structure, the objective lens 7 moves in the tracking direction,
Further, in order to allow a margin for various component assembly errors, it is necessary to secure the light flux 14 having a diameter larger than that of the light flux 15 actually condensed on the recording medium 18. Therefore, the extra luminous flux hits the base 13 and the actuator 17 and scatters the light (16
a, 16b, 16c, 16d, 16e, 16f), which become stray light in the optical head and enter the photodetector 12 directly or after passing through optical components. These lights do not form a small spot on the photodetector 12, but a blurred image having a non-uniform intensity distribution.

This image has a substantially equal amount of stray light at adjacent locations, but has a different amount of stray light at distant locations. Further, in FIG. 6, even if a differential operation is performed on the difference in stray light, a DC component of the difference in stray light remains. Therefore, DC offset occurs in the focus error signal and the tracking error signal. In addition, in an optical head that records / reproduces a low-reflection recording medium, the amount of stray light is larger than the amount of reflected light from the recording medium, so that the proportion of DC offset is large and accurate servo cannot be applied. Had a point.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an optical head resistant to stray light.

[0014]

In order to achieve this object, the present invention provides an objective lens for converging a light beam emitted from a light source on a recording medium, and a light beam reflected from the recording medium on a photodetector. An optical head having a detection lens for detecting the condensed light flux as an information signal and a servo signal, wherein the photodetector is a reflection including the information signal and the servo signal from the recording medium. It is provided with a signal detection light receiving region on which a light beam is incident and a peripheral light receiving region provided near each of the signal detection light receiving regions.

The photodetector is a photodetector with a built-in circuit that has a built-in circuit such as an IV converter.

The areas of the signal detection light receiving area and the peripheral light receiving area are substantially the same.

Further, the area of the peripheral light receiving area is 1 / n of the area of the signal detecting light receiving area, and the signal generated in the peripheral light receiving area is amplified by n times.

[0018]

With the above-described structure, the present invention has an effect on the focus / tracking error signal detection by taking the signal difference between each signal detection light receiving area and the peripheral light receiving area even if stray light is generated. It is possible to prevent this, and it is possible to stably detect the focus error signal and the tracking error signal.

[0019]

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

FIG. 1 shows a photodetector of an optical head according to the first embodiment of the present invention. In FIG. 1, 19a, 19
b, 19c, 19d and 19e are differential circuits, 19f is an adder circuit, 12i is a peripheral light receiving area provided near the signal detection light receiving area 12e, and 12j is a peripheral light receiving area provided near the signal detection light receiving area 12f. The signal detection light-receiving region and the peripheral light-receiving region have the same area. The other parts have basically the same structure as the signal detection light receiving area of the photodetector of the conventional optical head shown in FIG. 6, and therefore, the same parts are designated by the same reference numerals and detailed description thereof will be omitted. .

The optical operation of the optical head constructed as described above is the same as that of the conventional example shown in FIG. 4, and therefore its description is omitted, and only the operation of the photodetector 12 will be described.

In this embodiment, the peripheral light receiving regions 12i, 12j
Are arranged in the vicinity of the signal detection light receiving regions 12e and 12f, respectively, and have the same area. Therefore, 12i and 12e,
The photocurrents generated by stray light in 12j and 12f are almost equal. Therefore, the stray light components are canceled by IV converting the respective photocurrents and taking the differential in the differential circuits 19a and 19d. Therefore, the differential circuit 1
There is no DC offset of the tracking error signal obtained by 9b, and an optical head capable of detecting a stable tracking error signal can be realized.

FIG. 2 shows a photodetector of an optical head according to the second embodiment of the present invention. In FIG. 2, 19g, 19
h, 19i, 19j, 19m are differential circuits, 19k, 19
l is an adder circuit, and 12k, 12l, 12m and 12n are signal detection light receiving regions 12a, 12b, 12c and 12d, respectively.
Is a peripheral light receiving region provided in the vicinity of, and has the same area as each signal detection light receiving region. In this embodiment, the photocurrents generated by stray light are substantially equal in the signal detection light receiving regions 12a, 12b, 12c, 12d and the peripheral light receiving regions 12k, 12l, 12m, 12n. Therefore, the respective photocurrents are subjected to IV conversion and differential circuits 19g, 19h, 19i,
The stray light component is canceled by taking the differential at 19j. Therefore, the DC offset of the focus error signal obtained by the differential circuit 19m is eliminated, so that an optical head capable of detecting the stable focus error signal can be realized.

FIG. 3 shows a photodetector of an optical head according to the third embodiment of the present invention. In FIG. 3, the peripheral light receiving regions 12i and 12j are one of the signal detection light receiving regions 12e and 12f.
/ N area. Therefore, the amount of stray light detected is also 1 / n, so that the peripheral light receiving regions 12i, 12j
After the photocurrent generated in IV is converted into IV, the amplifiers 20a and 20b are converted.
After being amplified by n times, the differential can be taken to cancel the stray light. As a result, an optical head capable of detecting a stable tracking error signal can be realized. Also, the first
The photodetector can be configured with a smaller signal detection light receiving area than that in the above embodiment.

[0025]

As described above, according to the present invention, the peripheral light receiving area is provided in the vicinity of the signal detecting light receiving area, and the signal detecting light receiving area and the peripheral light receiving area are differentiated to obtain a uniform intensity distribution. The effect of non-blurred stray light can be eliminated. As a result, it is possible to realize an optical head that can stably detect the focus error signal, the tracking error signal, and the information signal.

Further, in the structure of a normal photodetector, since the area other than the light receiving area is shielded by aluminum or the like, the stray light incident on the area other than the signal detecting light receiving area is reflected on the surface and internally reflected in the resin mold of the photodetector. Is repeated and it becomes more likely to become stray light. In the present invention, since another light receiving area is provided around the signal detection light receiving area, stray light can be absorbed to some extent and internal reflection of stray light can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing a photodetector of an optical head according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a photodetector of an optical head according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a photodetector of an optical head according to a third embodiment of the present invention.

FIG. 4 is a plan view showing an optical system of a conventional optical head.

FIG. 5 is a side view showing an optical path rising portion of an optical system of a conventional optical head.

FIG. 6 is a block diagram showing a signal detection light receiving area of a photodetector of an optical system of a conventional optical head.

[Explanation of symbols]

12a to 12d Focus error signal detection light receiving area 12e, 12f Tracking error signal detection light receiving area 12g, 12h Information signal detection light receiving area 12i to 12n Peripheral light receiving area 19a, 19b, 19d, 19e, 19g to 19j, 1
9m to 19p Differential circuit 19f, 19k, 19l, 19q Adder circuit

Front page continuation (72) Hideki Nakata, 1006 Kadoma, Kadoma City, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd. (72) Hiroyuki Nakamura, 1006, Kadoma, Kadoma City, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. An objective lens for converging a light beam emitted from a light source on a recording medium, a detection lens for condensing a reflected light beam from the recording medium on a photodetector, and an information signal or servo for the condensed light beam. An optical head having a photodetector for detecting as a signal, wherein the photodetector has a signal detection light receiving region on which a reflected light flux including the information signal and the servo signal from the recording medium enters, and the signal detection light receiving region. An optical head having a peripheral light receiving area provided in the vicinity of. 2. The optical head according to claim 1, wherein the photodetector is a photodetector with a built-in circuit such as an IV converter. 3. The optical head according to claim 1, wherein the signal detection light receiving area and the peripheral light receiving area have substantially the same area. 4. The optical head according to claim 1, wherein the area of the peripheral light receiving area is 1 / n of the area of the signal detection light receiving area, and the signal generated in the peripheral light receiving area is amplified n times.