JP2523469B2 - Optical recording / playback head - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing head most suitable for an apparatus for recording or reproducing data or images by accessing a predetermined address at high speed on a recordable or reproducible optical disk. It is a thing.

Structure of Conventional Example and Problems Thereof FIG. 1 shows the Japanese Patent Laid-Open No. 56-1124 previously proposed by the present inventors.
The optical system of the optical recording / reproducing head described in No. 72 is shown. This optical system has been proposed for the purpose of increasing the dynamic range in a recording / reproducing head of a tracking servo system that follows an information track formed by an information signal 13 on an information carrier 12.

In this method, a so-called far-field tracking method (or push-pull tracking method) is used, and a photodetector 8 for detecting this tracking signal is provided with an objective lens 7, a quarter-wave plate 6 and a beam splitter 5. Comprised of a movable optical system having a two-dimensionally or three-dimensionally movable structure, a light source 1, a coupling lens 2, a beam shaping optical system 3, a beam splitter 4, a mirror 9, a single lens 10 and a focusing detector 11. And a fixed optical system that is used.

With the above configuration, the dynamic range of the tracking servo can be substantially tripled or more than the tracking control range in which the far field signal is received by the detector provided on the fixed optical system to perform the tracking servo. . However, this type of recording head
When performing track access at random, it is necessary to move the entire recording / reproducing head including the movable optical system and the fixed optical system, which is disadvantageous in terms of weight. The weight of the recording / reproducing head manufactured by this method actually manufactured is less than 100 g, but it is desirable to reduce the weight as much as possible in consideration of shortening the random access time of the optical disk memory in the future. Further, in the above method, the number of power sources and signal lines supplied to the light source, the photodetector for detecting the servo signal and the information signal, and the number of signal lines are increased, and it is inevitable that the spring effect of this wire material has an adverse effect on the linear motor for access. .

An object of the present invention is an optical recording / reproducing head which is suitable for high-speed access of an optical disk memory and can secure a wide servo dynamic range while avoiding the weight and wiring system which are disadvantageous in high-speed access seen in the above-mentioned conventional example. Is provided.

Structure of the Invention The present invention is to reflect a part or almost all of the light amount of a substantially parallel light beam reflected from an optical disc which is an information carrier,
A movable optical system including a beam splitter that spatially divides the light beam into at least two, and the plurality of light beams emitted from the beam splitter are located in the vicinity of the focal point of a lens provided in the fixed optical system. By making the light incident on a plurality of second photodetectors corresponding to the light beams, the weight of the movable optical system can be reduced, and the optical parts mounted on the movable part can be made as small as possible and the number of parts can be reduced. And Further, in order to reduce the influence of the wiring on the movable part, the detector for detecting the servo signal and the information signal is incorporated in a complete fixed optical system.

Description of Embodiments The configuration of an embodiment of the present invention will be described below with reference to FIG.

A light beam emitted from a light source 14 such as a semiconductor laser on the fixed optical system 30 is reflected by a polarization beam splitter 17 through a coupling lens 15 and an anamorphic optical system 16 that performs wavefront shaping of the light beam, and movable optical. Go to Series 29.
Here, the light beam is a substantially parallel beam, and a substantially constant light beam is incident on the movable optical system 29 regardless of the movement of the movable optical system 9 in the optical axis direction. Mirror 18 on movable optics 29
The light beam reflected by is transmitted through the special polarization beam splitter 19, the λ / 4 plate 20, and the objective lens 21, and is focused on the signal element 28 on the disk 27. Signal element 28
Is such that it changes the phase and / or the amplitude of the light beam. The light beam modulated by this signal element is reflected and a part of the light beam is reflected by the polarization beam splitter 19. The polarization beam splitter 19 has a structure capable of spatially separating half of the light beam as shown in FIGS. 3 and 4, and the P-polarized light beam transmits almost the entire light amount. , S-polarized light beams have high reflection and low transmission. Practically, the transmittance of P-polarized light is 98% or more, the reflection of S-polarized light is 70 ± 5%,
It is easy to use those with a transmission of 30 ± 5%. The spatially separated light beam is converged by the convex lens 22 and enters the two-divided photodetector 23 at the focal position.

Here, even if the movable optical system 29 moves in the optical axis direction, the position of the light beam on the photodetector 23 remains substantially stationary.
Substantially means here a polarizing beam splitter
This is because the condensing position of the light beam changes due to the inclination of 19 or the aberration of the convex lens 22, but this change amount can be made smaller than half the separation distance of the light beam on the photodetector 23. Therefore, it is possible to individually detect the far-field light beams spatially separated by the polarization beam splitter 19 by the photodetector 23. The beam splitter 19 spatially splits the light beam and splits it into directions having a constant angle. At this time, the photodetector
Since 23 is approximately at the focal position of the lens 22, the center position of the light beam focused on the photodetector 23 is immovable, and the light beam has a constant shape regardless of the movement of the movable optical system. There is. The insertion of this lens 22 has the advantage that the photodetector 23 can be made smaller, but it can be omitted depending on the application. Since the beam splitter 19 is for spatially splitting the light beam and detecting the tracking signal, various forms other than the embodiment of the present invention are conceivable. The far field tracking signal can be detected using the above principle. The meaning of the far field tracking signal is clear in the above-mentioned Japanese Patent Laid-Open No. 56-112472, etc., and will not be mentioned here.

On the other hand, the light beam that passes through the polarization beam splitter 19 is reflected by the mirror 18, passes through the polarization beam splitter 17, and only half of the light beam is reflected by the edge mirror 24.
It is incident on the two-part photodetector 26 located at the focal position of the lens 25. A focusing signal by the knife edge method can be obtained by using this edge mirror and the two-divided photodetector.

EFFECTS OF THE INVENTION As is clear from the above description, by using the present invention, it is possible to provide an optical recording / reproducing head most suitable for a device that performs high-speed access.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical recording / reproducing head previously proposed by the present inventors, FIG. 2 is a block diagram showing the arrangement of an optical system in one embodiment of the present invention, and FIGS. 3 and 4 are polarized beams. It is a perspective view showing an example of a splitter. 14 …… Light source, 17,19 …… Polarizing beam splitter, 20 ……
λ / 4 plate, 23 ... Two-part photodetector, 26 ... Photodetector, 27 ...
… Discs, 29… movable optics, 30… fixed optics.

Claims (2)

(57) [Claims] 1. A first light receiving at least one or a plurality of radiation light sources, an optical system for making a light beam emitted from the radiation light source substantially parallel light, and a light beam reflected and returned on an information carrier. A fixed optical system including a detection unit, an objective lens system that receives the light beam emitted from the fixed optical system, and converges the light beam onto an information carrier, and a part or almost all of the light amount of the substantially parallel light beam reflected from the information carrier. A movable optical system that is a beam splitter that reflects all light and spatially divides the tracking signal into at least two, and a plurality of light beams emitted from the beam splitter are provided in the fixed optical system. A tracking signal is obtained by causing the light beams to be incident on a plurality of second photodetectors corresponding to the plurality of light beams in the vicinity of the focal point of the lens and by the second photodetectors. The optical write head according to claim. 2. A polarization beam splitter is used as a beam splitter in a movable optical system, and the polarization beam splitter transmits all P polarized waves and 60% S polarized waves.
Patent that 90% is reflected and 10-40% is transmitted, and half of the light beam emitted from the polarization beam splitter is spatially separable from the other half and is incident on two corresponding photodetectors The optical recording / reproducing head according to claim 1.