JPS634430A - Optical head - Google Patents

Abstract

PURPOSE:To improve the S/N of an RF signal by providing a focusing actuator and a tracking actuator while a servo signal for focusing and tracking from light beams reflected in a recording medium. CONSTITUTION:The light beams reflected in a magneto-optical disk 8 follows the opposite path and the image is formed on a four-split PIN photo diode 14 through a knife edge 12 and a lens 13 to obtain a servo signal. The knife edge method is adopted for the focusing and the push-pull method is employed for the tracking, the focusing signal is fed back to the focusing actuator 7 to apply focusing servo. An optical system 15 of the tracking actuator is movable by a bearing 16 in a track perpendicular direction and driven by a bobbin 17 and a yoke 18.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to the structure of a transmissive optical head.

[Conventional technology]

In optical disk devices that have been actively put into practical use in recent years and are gradually becoming popular, the original head is an important element for recording and reproducing. There are two types of optical heads: reflective optical heads that obtain RIF signals from reflected light from a recording medium and transmissive optical heads that obtain RIF signals from transmitted light. Conventional examples of transmissive optical heads include PROCKED
INGSOF SP Engineering K), vol. 382, 240-24
4 pages, 1983. This is the original head for magnetic recording, and its configuration is shown in FIG.

The output light of the semiconductor laser 100 is collimated by the collimating lens 101.
．． 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, which then outputs a servo signal and RIF.
It is configured to obtain a 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. The first problem is the servo signal and R? The problem is that the differential detection method cannot be used when reproducing the RIF signal to obtain a doubled signal. FIG. 4 shows an example of a differential detection system. The light transmitted through the magneto-optical disk 103 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. You can get twice the signal. FIG. 5 is an example of a simplified differential detection method. 112 indicates the direction of the polarization plane of transmitted light. The transmitted light passes through an analyzer 115 and is received by a four-split photodetector. 113' and 114' are diagrams of the analyzer 113 and the 4-split photodetector 114 viewed from directly above. A differential amplifier 111 takes the difference between the diagonal sums of the outputs of the four-split photodetector to obtain Ry fj. Furthermore, analyzer 11
The diagonal line 3' indicates the direction of the transmission axis. In either differential detection method, common mode noise such as laser noise can be removed, and the S l N ratio of the Ry fu signal is improved by several dB. In the conventional example described above, this method cannot be adopted, so that the recording density cannot be increased or errors in reading the reproduced signal are likely to occur.

The second problem is that the incident side optical system and the transmission side optical system must be driven together for focusing and tracking, which places a large load on the head actuator. In particular, it is difficult to improve tracking accuracy,
As a result, track density cannot be increased. The track pitch of current optical discs is mainly 1.6 μm, but with this method, the track pitch has to be 4 to 10 μm. Therefore, there is a problem that the recording density becomes low.

Therefore, the present invention is intended to solve such problems.
The object of the present invention is to realize a transmissive optical head that has a high F-fold signal S/N ratio and can also narrow the track pitch.

[Means for solving problems]

The optical head according to the present invention has R from the light transmitted through the recording medium.
In a transmissive optical head that reproduces 7 signals, a) servo signals for 7 focusing and tracking are obtained from light reflected by the recording medium, and b) the objective lens of the incident side optical system is aligned perpendicular to the recording medium. (C) A tracking actuator that integrally drives the incident side optical system and the transmission side optical system in the tracking direction.

[Effect]

According to the above Uq configuration of the present invention, since the RA signal reproduction sensor and the servo signal sensor are different, a differential detection method can be used, and the RF multiplied signal S/N ratio is improved.

In addition, in 7-ocusing, only the objective lens of the entrance side optical system has a receiver, and only tracking is required for integral driving of the entrance side and transmission side optical systems, so the load on the head actuator is reduced and tracking accuracy is improved. It becomes possible to narrow the track pitch.

〔Example〕

FIG. 1 is a block diagram of this embodiment, particularly showing the optical system and focusing actuator. Explain the optical system. It is assumed that the polarization plane of the output light of the semicircular body laser 1 is in the direction 2. The output light is made parallel by a collimating lens 5, the optical path of the transmitted light from the beam splitter is bent at right angles by a mirror 5, and the optical path is converted to a magneto-optical disk 8 by an objective lens 6.
The light is focused on the recording surface. The transmitted light is an analyzer 9.4 division PX
R? by N photodiode 10? You can get twice the signal. The transmission-side optical system is shown in FIG. 5, and as a result, an RIF signal with a high S/N ratio can be obtained. The light reflected by the magneto-optical disk 8 follows the reverse path and reaches the knife 12. An image is formed by the lens 15 onto the 4-split P type N7 photodiode 14, and a servo signal is obtained. Focusing is by the Naifetsu method, and tracking is by the push-pull method. The focusing error signal is fed back to the focusing actuator 7, and the focusing servo is applied.

FIG. 2 shows a portion of the tracking actuator. 1
5 is a part of the optical system shown in FIG. The optical system 15 is movable in the direction perpendicular to the track by means of a bearing 16, and is movable in the direction perpendicular to the track by means of a bearing 16. Driven by yoke 18.

This actuator only receives tracking, improving tracking accuracy.

〔Effect of the invention〕

As described above, the present invention has the following effects.

The first effect is that the S/N ratio of the R7 signal is improved because a differential detection method can be employed. As a result, the recording wavelength can be shortened and the recording density can be improved. Furthermore, since noise jitter is reduced, there is an effect that reading errors are reduced.

The second effect is that the tracking accuracy is improved, so the dock pitch can be narrowed to about 1.6 μm, and the track density is improved. As a result, the recording density is improved.

It goes without saying that the present invention is not limited to the above-mentioned embodiments, but 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 the drawing]

FIG. 1 is a configuration diagram of an optical system according to an embodiment of the present invention. FIG. 2 is a configuration diagram of a tracking actuator according to an embodiment of the present invention. FIG. 5 is a configuration diagram of a conventional transmission type optical head. FIG. 4 is a configuration diagram of the differential detection system. FIG. 5 is a configuration diagram of a simplified differential detection system. 1... Semiconductor laser 2... Polarization plane 3... Collimating lens 4...
・・・Beam splitter 5・・・・・・・・・Mirror 6・・・・・・・・・Objective lens 7・・・・・・・・・7 Orcusing actuator 8
......Magneto-optical disk 9...Analyzer 10...Four-division P/N photodiode 11.
..... Bias magnetic field electromagnet 12 ..... knife 15 ..... lens 14 ..... 4-divided P/N photodiode 100
. . . Semiconductor laser 101 . Lens 108...Polarization beam splitter 109...Photodetector 110...1 111...Differential amplifier 112...Polarization plane 113...Analyzer 113'...Analyzer viewed from above Figure 114...Four-split photodetector 114'...One or more views of the four-split photodetector from above Applicant: Seiko Epson Co., Ltd. Representative Patent Attorney, Chief Patent Attorney (1 other person) 7 :Fuokashindeakunani-7 10: 4'i'f'J PIN7t)? '1”i
”-Do '144 Damaged PIN photodiode j&2 77〉7゛. 17: Main 18: Yaw 7 q

Claims (1)

[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. c) a focusing actuator that drives the objective lens of the system in a direction perpendicular to the recording medium, and c) a tracking actuator that drives the incident side optical system and the transmission side optical system together in the tracking direction. light head.