JPH0376035A - Hologram system optical pickup - Google Patents

Abstract

PURPOSE:To execute the tracking servo by a three-beam method without wasting the light quantity by allowing an emitted light from a semiconductor laser and a feedback light to a photodetector to have each different optical axis, and also, providing a diffraction grating for separation of light into spectral components on the optical axis of the emitted light. CONSTITUTION:An emitted light from a semiconductor and a feedback light to a photodetector are made to have each different optical axis, and also, a diffraction grating for separation of light into spectral components is provided on the optical axis of the emitted light. That is, the emitted light from a laser 1, first of all, is divided into three pieces of beams by a hologram plate 6, and forms three pieces of spots on a disk 3. Three pieces of reflected light beams are subject to diffraction, respectively by a hologram plate 4, and condensed onto a servo detecting detector 5. In this case, it is only the emitted light that is diffracted by the hologram plate 6 and the feedback light is not subject to diffraction. In such a way, only the emitted light from the semiconductor laser is brought to separation of light into spectral components of three beams, and the feedback light is not brought to separation of light into spectral components, therefore, the tracking servo by a three-beam method can be executed without wasting the light quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a holographic optical pickup used in optical disk devices and the like.

BACKGROUND OF THE INVENTION In recent years, as optical pickups have become smaller, lighter, and cheaper, signal detection systems using holograms have been attracting attention. The conventional hologram optical pickup is the second
As shown in the figure. The light emitted from the semiconductor laser chip 1 is focused on the disk 3 by the lens 2, and on its way back after being reflected, it is separated by the hologram plate (A) 4 and focused on the servo detection detector 5. be illuminated.

Problems to be Solved by the Invention However, the above configuration has the following problems.

First of all, since it is not possible to perform tracking servo using the three-beam method that is currently the mainstream in optical pickup for compact discs, a general-purpose circuit cannot be used, and a dedicated servo circuit must be created. Is required. In addition, if another hologram plate (B) 6 is added in front of the hologram plate (A) 4 in order to use the three-beam method, both the emitted light and the returned light are separated and returned to the photodetector. The amount of light emitted by the sensor decreases significantly, and the detection sensitivity decreases.

Means for Solving the Problems In order to solve the above-mentioned problems, the hologram optical pickup of the present invention has a hologram optical pickup in which the emitted light from the semiconductor laser and the feedback light to the photodetector have different optical axes, and the emitted light It is characterized by having a diffraction grating for spectroscopy on the optical axis.

Effect With the above configuration, only the emitted light from the semiconductor laser is split into three beams, and the return light is not split, so tracking and tracking using the three-beam method can be performed without wasting the light amount.
Can do servo.

Example An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of the present invention, in which a semiconductor laser chip and a servo detection detector are mounted in the same package. In front of this package is a hologram plate (A) and a lens, and the feedback light from the disk is diffracted by the hologram plate (A) and focused onto a servo detection detector. A three-beam hologram plate (B) is located on the optical axis of the emitted light from the laser at a position that does not interfere with the optical axis of the return light to the detector, and divides the emitted light into three beams.

In the above configuration, the light emitted from the laser is first divided into three beams by the hologram plate (B) to form three spots on the disk.

This reflected light is diffracted by the hologram plate (A) and focused onto a servo detection detector. It is divided into 3 beams by the hologram plate (B), so 3
Tracking servo can be performed using the beam method. Further, since only the emitted light is diffracted by the hologram plate (B) and the returned light is not diffracted, the returned light can be focused on the detector without any loss of light.

In this embodiment, a finite system optical pickup using one lens has been described, but exactly the same effect can be obtained in an infinite system optical pickup using two or more lenses and a parallel beam. It goes without saying that the present invention is also effective in an integrated hologram type optical pickup in which the hologram plate (A) is also integrated.

As described above, the hologram optical pickup of the present invention has the following effects:
The light emitted from the semiconductor laser and the light returned to the photodetector have different optical axes, and by having a diffraction grating for dispersion on the optical axis of the emitted light, only the light emitted from the semiconductor laser can be divided into three beams. Since the returned light is not split, tracking servo can be performed using the three-beam method without wasting the amount of light, which has great practical effects.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a hologram type optical pickup according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional hologram type optical pickup. 1... Semiconductor laser chip, 4... Hologram plate (A), 6... Hologram plate (B)
.

Claims (1)

[Claims] A semiconductor laser chip and a signal detection photodetector are mounted in the same package, and the emitted light from the semiconductor laser chip and the feedback light to the photodetector have different optical axes, and the emitted light A holographic optical pickup characterized by having a diffraction grating for spectroscopy on the optical axis.