JPH01273253A - Optical pickup - Google Patents

Abstract

PURPOSE:To eliminate the in-phase noise of magneto-optically modulated signals so as to improve the S/N of a signal and reliability of the reproducing operation of an optical pickup by making the ratio of the diameter of a light image on the light receiving surface to the width of the light receiving surface separating zone of each detector the same to another. CONSTITUTION:When the incident beam diameters and the widths of the light receiving surface separating zones 12 and 22 of detectors 1 and 2 are respectively represented by r1 and r2 and d1 and d2, the detector 2 is constituted so that d1/d2=r1/r2 can be established. Sum signals of the split detectors of each detector 1 and 2 are inputted to a differential amplifier 3 after they are respectively amplified by amplifiers 13 and 23. Then the quantity of variation of the incident light caused by the fluctuation of the reflectivity of a disk and the influence of a nonsensible zone goes to in-phase noise and canceled in a differential detecting signal C and modulated signal components from the disk are outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical pickup for a magneto-optical disk device capable of recording and reproducing.

2. Description of the Related Art First, the principle of reproduction of a magneto-optical disk device will be explained. In FIG. 3, 31 is a magneto-optical disk, and 1
'', 0° information is recorded in correspondence with the direction of the magnetic field (perpendicular magnetic field).For example, a laser beam 33 (parallel beam) having only a P-polarized component is applied to this minute magnetic domain. The lens 32 focuses the irradiation onto a minute spot.

The irradiated light is reflected by the disk recording film surface and passes through the objective lens 3 again.
However, as shown in Figure 4, the reflected light at this time returns by ±θ1 depending on the direction of magnetization due to the Kerr effect.
The light beam is emitted with its plane of polarization shifted by ζ (Kerr rotation angle). Reading (reproducing) signals by detecting this polarization shift
This is what we do.

Next, the actual pickup configuration and detection method will be explained. FIG. 5 shows the configuration of the pickup. The light emitted from the semiconductor laser light source 51 is converted into parallel light by the collimator lens 52, and further shaped into circular light by the anamorph prism 53 (because the light emitted from the semiconductor laser is an elliptical beam). This light is prism 54
The light enters the objective lens 55 through the lens, and forms a minute spot (1 to 2 μmφ) on the disk 56. The modulated reflected light from the disk returns to 55+54 again and passes through the λ7/2 plate 5.
After the polarization plane is rotated by 45 degrees at step 7, the light is separated into P-polarized light component and S-polarized light component by polarization beam splitter 58. The P-polarized light component passes through the astigmatism lens group 59 to the first photodetector 1, and the S-polarized light component passes directly to the second photodetector 2.
The amount of light incident on the beam is detected. Here, astigmatism lens group 59
The first detector 1 is an element constituting a servo error detection system for determining and controlling the spot light of the objective lens 55 in the focus direction or radial direction to the target track of the disk. Here, the generally well-known astigmatism method (focus direction) and push-pull method (radial direction) are used, and the first detector 1 has a light-receiving surface divided into four parts. The reason why two detectors, the first detector 1 and the second detector 2, are used to detect the information signal is by differentially detecting the P-polarized light component and the S-polarized light component, as shown in FIG. This is to remove in-phase component noise 66 due to variations in reflectance within the disk surface, etc., and increase the detection sensitivity of the modulated information signal (the information signal components are in opposite phases to each other).
.

FIG. 7 shows the configuration of the light receiving surface of the first detector 1.

81 to S4 are effective light-receiving surfaces 11, respectively, and when the objective lens correctly follows the target track, the incident light image becomes as shown by the broken line. If the amount of light received by each effective light receiving surface of 81 to S4 is directly expressed as 81 to S4, then (S 1 + 84) - (S
2+33) is the detection of focus error, (S1+82)
-(S3+84) becomes a tracking (radial direction) error detection signal, and the sum signal (S 1 +S2+S3+S4) is used to detect the information signal P polarization component. Reference numeral 12 in FIG. 7 is a light-receiving surface separation zone for separating the four light-receiving surfaces, and serves as a dead zone for incident light. The number of light-receiving surface separation bands 12 is determined by the manufacturing conditions of the detector, and is usually 10 to 2.
The width is 0 μm. Due to the detection principle and restrictions on optical components, the incident light image diameter is usually about 50 to 150 μm, and the light receiving surface separation zone 1
The proportion occupied by the dead zone due to 2 cannot be ignored.

As shown in FIG. 7, if the incident light is correctly incident on the first detector, it is possible to detect a signal with an excellent signal-to-noise ratio using the differential signal with the second detector 2 as described above. .

Problems to be Solved by the Invention However, in reality, during the operation of the device, the ideal incident light image (position ). For example, in the case of an optical image as shown in FIG. 8, the sum signal (S l+32+33+34), which is the total amount of incident light, changes due to the effect of the light-receiving surface separation band 12 in <a) and (b).

The second detector 2 shown in FIG. 5 is a detector with a single light-receiving surface without a light-receiving surface separation band, so the amount of incident light is always constant (minus the amount modulated by the readout information signal). As shown in the figure, common-mode noise removal by differential detection becomes insufficient, resulting in a problem that the S/N ratio of the reproduced signal decreases.

Means for Solving the Problem In order to solve this problem, the present invention provides that the second detector also has a multi-segment configuration, and the diameter of the incident light beam of the second detector and the width dimension of the light-receiving surface separation zone of the second detector are The ratio between the first and second detectors is set to be approximately the same as that of the first detector.

Operation When the second detector is constructed in this way, the movement (incidence position) and light intensity distribution of the incident light on the first detector and the second detector are almost the same even though the beam diameters are different.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1st
The figure shows the light receiving surfaces of the first detector 1 and the second detector 2. FIG. 1(a) shows the first detector, and FIG. 1(b) shows the second detector. Here, 11 and 21 are effective light-receiving surfaces, and 12 and 22 are light-receiving surface separation zones. Here, the incident beam diameter of the first detector 1 and the width of the light-receiving surface separation zone 12 are rl and
dl, and the incident beam diameter of the second detector 2 and the width of the light-receiving surface separation zone 22 are respectively r2. If d2 is approximately dl /
The second detector 2 is made so that d 2 = r 1/r 2 . FIG. 2 shows a circuit that outputs a readout signal using signals from the first detector 1 and the second detector 2. Since the configuration of the optical system is the same as that shown in FIG. 5, it will be omitted and only the detection section will be explained. 1.2 is a first detector and a second detector, respectively; 13.23 is a first amplifier and a second amplifier, respectively; and 3 is a differential amplifier. The sum signals of the divided detectors of each of the first detector 1 and the second detector 2 are transmitted to amplifiers 13 and 23, respectively.
is amplified. Since the sensitivities of the first detector l and the second detector 2 are generally different, if these signals are 81 and a2, and the gains of the amplifier 13.23 are k1 and K2, then al
・Amplifier 13.2 so that k 1 = 22・k2
Adjust the gains k 1 and k 2 of 3. These outputs b
1%b2 is applied to the differential amplifier 3.

At this time, the fluctuations in the incident light due to disc reflectivity variations and dead zones are common-mode noises, so they are canceled in the differential detection signal C of the differential amplifier 3, and the disc-specific modulation signal component shown in FIG. It is amplified and output.

Effects of the Invention According to the present invention, it is possible to remove the common mode noise of the magneto-optical modulation signal without complicating the configuration of the optical system or control circuit, and it is possible to improve the signal-to-noise ratio of the signal. Reliability of playback operation can be improved.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the light receiving surface of a photodetector according to an embodiment of the present invention, Figure S2 is a circuit diagram showing the configuration of the detection section of the present invention, Figures 3 and 4 are reproduction of a magneto-optical disk. A schematic diagram showing the principle; FIG. 5 is a block diagram of the configuration of the optical pickup optical system; FIG. 6 is a waveform diagram showing the principle of differential detection; FIG. 7 is a schematic diagram showing the light-receiving surface of the first detector; FIG. 8 is a schematic diagram showing an actual incident light image on the detector, and FIG. 9 is a waveform diagram showing waveforms when differential detection is inappropriate. 1...First detector 2...Second detector 3
... Differential amplifier 11.21 ... Effective light-receiving surface 12.22 ... Light-receiving surface separation band 13.23 ... Name of amplifier agent Patent attorney Toshio Nakao Haka1 Katsukei-O ! Fusuma ±4 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] An optical pickup for a magneto-optical disk device, comprising a first detector and a second detector that respectively detect a P-polarized signal component and an S-polarized signal component of reflected light from an optical disk, the first detector and The light-receiving surface of the second detector has a multi-divided configuration with a light-receiving surface separation band, and the ratio of the light image diameter on the light-receiving surface of the first detector to the width of the light-receiving surface separation band and the second
An optical pickup characterized in that the ratio of the optical image diameter on the light-receiving surface of a detector and the width of the light-receiving surface separation zone is approximately the same.