JPS6342040A - Optical head - Google Patents

Abstract

PURPOSE:To improve the S/N of an RF signal to increase the recording density and to reduce a read error by obtaining servo signals for focusing and tracking from the light reflected from a recording medium. CONSTITUTION:The output light of a semiconductor laser 1 is converted to parallel rays by a collimator lens 3 and is transmitted through a beam splitter 4 and is turned orthogonally by a mirror and is condensed on a magneto-optical disk 7 by an objective lens 6. The RF signal is obtained from the light transmitted through the disk by an analyzer 8 and a 4-divided PTN photodiode 9. The light reflected on the magneto-optical disk 7 passes a reverse path, and servo signals are obtained by a knife edge 10, a lens 11, and a PIN photodiode. The knife edge method is used for focusing, and the push-pull method is used for tracking. Since the differential detection method is used in the transmission-side optical system in such a manner, the S/N of a reproduced signal is improved to increase the recording density, and the read error is reduced.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to the structure of an escape type original head.

[Conventional technology]

In the original disk drive, which has been actively put into practical use in recent years and is gradually becoming popular, the optical head is an important element for recording and reproducing.The single head is a reflective optical head that obtains an RF multiplied signal from the reflected light of the recording medium. There is also a transmission type optical head that obtains light from transmitted light. Conventional examples of transmissive optical heads include PROOF, PROOF
! KD Engineering NGS OIF 5PIF1i), 382
Vol., pp. 240-244, 1983. This is a source head for magneto-optical recording, the configuration of which is shown in FIG. The objective lens 102 is used to focus the light onto the magneto-optical disk 103 . The transmitted light passes through an analyzer 104 and is received by a 4-split photodiode 105 to obtain a servo signal and an RF multiplied signal. 106 is an electromagnet for applying a bias magnetic field.

[Problem that the invention seeks to solve]

However, the conventional example described above has the following problems. That is, since the servo signal and the R7 signal are obtained using one sensor, the differential detection method cannot be used when reproducing the RIF signal. FIG. 4 shows an example of a differential detection system, a magneto-optical disk 10.
The light that has passed through 3 is made almost parallel by a lens 107, split into two by a polarizing beam splitter 108, and the difference between the outputs of the two photodetectors 109 and 110 is taken by a differential amplifier 111 to obtain an R1' signal. . FIG. 5 is an example of a simplified differential detection method. Reference numeral 112 indicates the direction of the polarization plane of the transmitted light, and the transmitted light is passed through an analyzer 113 and received by a four-split photodetector. 113' and 114' are analyzers 113.
4 is a diagram of the four-split photodetector 114 viewed from directly above. FIG. A differential amplifier 111 takes the difference between the diagonal sums of the outputs of the four-split photodetectors to obtain an RIF signal. Note that the diagonal line on the analyzer 113' indicates the direction of the transmission axis. In either differential detection method, common mode noise such as laser noise can be removed, and R? The signal S/N ratio is improved by several df3. In the conventional example described above, since this method cannot be adopted, the recording density cannot be increased, and errors in reading the reproduced signal are likely to occur.

Therefore, the present invention is intended to solve such problems.
It is an object of the present invention to provide a transmissive optical head that has a high S/N ratio of an IF signal, can achieve high recording density, and can reduce reading errors.

[Means for solving problems]

The original head according to the present invention has an R
? In an optical head that reproduces double signals, α) servo signals for 7-focusing and tracking are obtained from the light reflected by the recording medium, and b) the incident side optical system and the transmission side optical system are aligned in the tracking direction and focusing. It is characterized by being equipped with an actuator that integrally drives it in the direction.

[Effect]

According to the above configuration of the present invention, 1. R? Since the sensor for signal reproduction and the sensor for servo signal are different, differential detection method can be used, and R? Double signal S/N ratio is improved.

〔Example〕

FIG. 1 is a configuration diagram of the optical system excluding the actuator of this embodiment. This embodiment is an original head for a magneto-optical disk. The optical system will be explained. The output light of the semiconductor laser 1 is made into parallel light by a collimator lens 3, transmitted through a beam splitter 4, the optical path is bent at right angles by a mirror, and the light is focused onto a magneto-optical disk 7 by an objective lens 6. The light transmitted through this is subjected to an analyzer 8.4-divided Pl''N photodiode 9 to obtain an R? times signal.The optical system on the transmission side is shown in FIG. The reflected light follows the reverse path and a servo signal is obtained by the Naifetsu 10. Lens 11. 4-split P/N photodiode.In this example, focusing is performed by the Naifetsu method and tracking is performed by the push-pull method. .In addition, Naifetsuji 10. Lens 11. 4 division P work N
The photodiode 12 is actually placed on the side perpendicular to the plane of the paper, and the differential detection method shown in FIG. 5 is used in the transmission side optical system, as in this embodiment, which has a thinner head. As a result, the S/N ratio of the reproduced signal is improved, the recording density is improved, and reading errors are reduced.

FIGS. 2(α) and (b) show a configuration diagram of an actuator for tracking and focusing, 14
1 is a magneto-optical disk, and 15 is the optical system shown in FIG. 16 is a leaf spring for 7 orcasing, and 17 is a magnet. 19 is a leaf spring for tracking, and 18 is a magnet.

The magnets 17, 18 are provided with a recess in which an electromagnetic coil is arranged. By passing a current through the electromagnetic coil, attractive force 9 and repulsive force act between the electromagnetic coil and the magnets 17 and 18, and the optical system 15 is driven in the focusing direction and the tracking direction. The optical system including this actuator is
It may be placed on a linear motor, a spin motor, or the like, and a two-stage turbo system (or two-stage access system) may be used for tracking.

[Effects of the Invention] As described above, according to the present invention, since the differential detection method can be adopted, R? Double signal S/N ratio is improved. As a result, the recording wavelength can be shortened and the recording density can be improved. Furthermore, since noise jitter is reduced, reading errors are reduced, which has one effect.

It goes without saying that the present invention is not limited to the embodiments described above, and may be modified in many ways. For example, the recording medium may not be a magneto-optical recording medium, and the shape may be card-shaped instead of disk-shaped. .

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an optical system according to an embodiment of the present invention. Figure 2 (α>, Cb> is a configuration diagram of an actuator according to an embodiment of the present invention. Figure 3 is a configuration diagram of a conventional transmissive optical head. Figure 4 is a configuration diagram of a differential detection system. Figure 5 is a simplified configuration diagram of the differential detection system. 1... Semiconductor laser 2... Polarization plane 3... Collimation Lens 4...
...Beam splitter 5...Mirror 6...Objective lens 7...Magneto-optical disk 8...・Analyzer 9・・・・・・4 division P N photodiode 1
0... Naifetsuji 11... Lens 12... 4-split P engineering N7 Otodiode 13.
...Bias magnetic field electromagnet 14...Magneto-optical disk 15...Optical system 16...Plate spring 17.18...Magnet 19. . . . Leaf spring 100 . . . Semiconductor laser 101 . Bias magnetic field electromagnet 107...Lens 108...Polarizing beam splitter 109...Photodetector 110...Photodetector 111...Differential amplifier 112...Polarization plane 113...Analyzer 113 '...Figure 114 when the analyzer is viewed from above...Four-split photodetector 114'...Figure 9 when the four-split photodetector is viewed from above:
Ima Branch = JPIN7 Otodayode+2:4/7I PIN7* Todaiodeonλ Figure 1 Flute Figure 3

Claims (2)

[Claims] (1) In a transmissive optical head that reproduces an RF signal from light transmitted through a recording medium, a) servo signals for focusing and tracking are obtained from light reflected by the recording medium, and b) incident side optics. An optical head comprising an actuator that integrally drives the system and the transmission side optical system in the tracking direction and the focusing direction. (2) The optical head according to claim 1, wherein the recording medium is a magneto-optical recording medium.