JPH0254434A - Optical head - Google Patents

Abstract

PURPOSE:To obtain a miniaturized and light optical head by arranging a hologram element between an objective lens which converges light from plural light sources with different wavelength on a recording medium and the light source, and introducing the light diffracted by the hologram element to a photodetector. CONSTITUTION:Semiconductor lasers 1a and 1b with different wavelength are arranged adjacently, and the emission light of them are made incident on a transmission type diffraction grating 2, and 0th-order light transmitting the diffraction grating are converged on a magnetic film that is the recording medium 5 formed on a disk substrate 4 by the objective lens as spots 6a and 6b, respectively. And information on the recording medium 5 can be erased by lighting the laser 1b and changing the direction of the magnetic field of a thin film magnetic head 7, and also, new information can be recorded. Meanwhile, the spot 6a by the laser 1a is used for the readout of the information. The light reflected on the recording medium 5 is made incident on the diffraction grating 2, and 1st-order diffracted light is introduced to photodiodes 8a and 8b, then, is used in the detection of a focusing error signal, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of an optical head for recording, erasing, and reproducing information using light.

[Prior Art] In an optical head for magneto-optical recording that uses light to record and reproduce information on a magnetic layer, which is a recording medium, a structure that allows information to be rewritten at high speed was proposed in the 1986 IEICE National As shown in Conference Lecture No. C-587, a device has been devised in which a plurality of spots are formed on a recording medium using semiconductor lasers with different wavelengths as a light source, and each spot is provided with a recording or reproducing function.

[Problems to be Solved by the Invention] However, in the conventional optical head described above, a wavelength separation filter is used to separate the reflected light from the recording medium into wavelengths, which increases the number of parts and increases costs. It has the problem of being expensive. The present invention is intended to solve these problems, and its purpose is to eliminate the need to add a new element such as a wavelength separation filter in order to separate the wavelengths of reflected light from a recording medium. ,
The aim is to provide a small and lightweight optical head.

[Means for Solving the Problems] An optical head of the present invention includes a plurality of light sources with different oscillation wavelengths, an objective lens that focuses light from the plurality of light sources onto a recording medium, and a combination of the light sources and the objective lens. It is characterized by including a hologram element located therebetween, and a light receiving element that detects light diffracted by the hologram element.

[Operation] Light emitted from a plurality of semiconductor lasers arranged in a direction perpendicular to the optical axis, each with a different oscillation wavelength, enters a hologram element such as a transmission or reflection type diffraction grating, and the 0th order diffracted light is reflected by an objective lens. The light is focused on the recording medium, and a plurality of spots are formed on the recording medium corresponding to the positions of the semiconductor laser serving as the light source.

The reflected light at each spot position passes through the objective lens again and enters the hologram element. This time we will use first-order diffracted light, but since the diffraction angle depends on the wavelength, it is possible to separate the diffraction directions of each wavelength by appropriately selecting the period of the grating that makes up the hologram element. can. By arranging the light-receiving elements in the separated diffraction directions, each light-receiving element can detect diffracted light corresponding to one wavelength, and wavelength separation can be performed.

Further, it is possible to cause astigmatism in the diffracted light by the hologram element, and it is also possible to detect a focusing error signal by appropriately dividing a photodiode, which is a light receiving element.

Hereinafter, the details of the present invention will be shown by examples.

[Example] FIG. 1 is a main sectional view of the optical head of the present invention.

Semiconductor laser 1a with oscillation wavelength of 780 nm, oscillation wavelength of 83
A 0 nm semiconductor laser 1b is arranged closely.

These emitted lights enter a transmission type diffraction grating 2 formed by etching the surface of glass, and the zero-order light transmitted through the diffraction grating is transmitted through an objective lens 3 to a recording medium 5 formed on a disk substrate 4. The light is focused on the magnetic layer. At this time, the lights emitted from the semiconductor lasers 1a and 1b are spots 6a and 6b, respectively.
becomes.

A thin film magnetic head 7 is arranged close to the recording medium 5 so that a magnetic field can be applied to the position of the 830 nm spot 6b. By adjusting the information, information on the recording medium 5 can be erased and new information can be recorded.

On the other hand, a spot 6a produced by the semiconductor laser 1a having a wavelength of 780 nm is used for reading information.

The light reflected by the recording medium 5 passes through the objective lens 3 again and enters the diffraction grating 2. This time, we will use the first-order diffracted light. The direction in which light is diffracted by a diffraction grating depends on the incident wavelength, and for the same grating period, the longer the wavelength, the more the light will be diffracted. Therefore, 830 nm is diffracted more greatly, and 780 nm is diffracted less than 830 nm.

The diffracted 780 nm light enters a photodiode 8a having a polarizing plate 9 attached to its surface. The orders of diffraction are +1st and -1, and photodiode 8 is used to utilize the orders of diffraction.
a are arranged on both sides of the central axis AA.

The arrangement of the polarizing plate 9 will be explained with reference to FIG. The polarization direction of the light emitted from the semiconductor laser 1a is assumed to be the 110 direction. The polarization direction with the highest transmittance in the polarizing plate 9 attached to the front surface of the photodiode 8a is designated as 12. The two polarizing plates 9 are arranged so that their polarization directions 12 are orthogonal to each other and make an angle of 45 degrees with the polarization direction 11 of the light from the semiconductor laser.

The polarization direction 11 of the light reflected by the recording medium 5 on which information is recorded as the direction of magnetization is rotated depending on the direction of magnetization, and the direction of rotation can be determined by taking the differential output from each of the photodiodes 8a. can know,
Information on the recording medium 5 can be reproduced.

The optical head requires a servo mechanism to ensure that the spot created by the objective lens is always irradiated onto the required position on the recording medium. Astigmatism that occurs in the order diffraction light can be used, and a push-pull method can be used to detect the tracking error signal. In this case, the photodiode 8a is divided into appropriate regions and an error signal is obtained from the differential signal of the region. Based on this error signal, the objective lens 3 is moved by the lens actuator 10 to align the spots 6a and 6b to desired positions on the recording medium. Even if the photodiode 8a is divided into several regions, the signal on the recording medium 5 can be read as described above by taking the differential of all the phases.

On the other hand, the 830 nm light is diffracted more than the 780 nm light and enters the photodiode 8b. It may be used to monitor optical power or to detect error signals.

What is necessary is to separate the 830 nm light and the 780 nm light using the diffraction grating 2 so that the 830 nm light used for recording and erasing does not enter the photodiode 8a that detects reproduction and error signals.

If such a function can be realized, the grating pattern of the diffraction grating 2 may consist of a group of straight lines or a group of curves.Also, as shown in FIG.
may also be used. FIG. 3 and FIG. 4 are cross-sectional views of FIG. 1 taken from the side. In FIG. 4, a collimator lens 15 and a mirror 16 are arranged between a diffraction grating 14 and an objective lens 17. Semiconductor laser 1
a.

1b, photodiodes 8a, 8b, diffraction grating] 4. Record the objective lens 17 and mirror 16 as one unit while keeping the collimator lens 15 fixed #111tJJ
It becomes possible to move the A-body 5 in the cross-track direction, and the access time can be shortened.

Although the embodiments have been described above, the present invention erases and records information with 830 nm light as in the above embodiments, and
It is not limited to reading information with 830 nm light, and depending on the method of rewriting information, it may be erased with 830 nm light,
It can also be applied to optical heads for recording with nm light.

In this case, a semiconductor laser having a different wavelength and a photodiode for receiving the diffracted light may be further arranged for readout. Furthermore, although the embodiments show an optical head for magneto-optical recording, the present invention can also be applied to an optical head for optical disks that utilizes the phase change of a recording medium.

[Effects of the Invention] As described above, according to the present invention, in an optical head having a light source with different wavelengths for rewriting information on a recording medium, reflected light from the recording medium is separated into wavelengths by a diffraction grating. By making it incident on the photodiode, the diffraction grating has a beam splitter function, an error signal generation function,
This has the effect of consolidating wavelength separation functions, reducing the number of parts, and configuring a small, low-cost optical head.

[Brief explanation of the drawing]

FIG. 1 is a diagram representing the optical head of the present invention, and is a main sectional view including a disk substrate. FIG. 2 is a diagram illustrating a method of reading magneto-optical signals in the optical head of the present invention. 3 and 4 are main sectional views showing an example of application of the present invention. la, Ib...Semiconductor laser 2...Transmission type diffraction grating...Objective lens...Disk substrate...Recording medium 6b...Spot...Thin film magnetic head 8b...Photodiode polarizing plate Lens actuator Polarization direction Polarization direction Reflective diffraction grating Transmissive diffraction grating Collimator Lens Mirror Objective lens 8 a. 9 ... 0 ... 1 ... 2 ... 3 ... 4 ... 5 ... 6 ... 7 ... That's all

Claims (1)

[Claims] A plurality of light sources with different oscillation wavelengths, an objective lens that focuses light from the plurality of light sources onto a recording medium, a hologram element located between the light source and the objective lens, and a hologram element that collects light diffracted by the hologram element. An optical head characterized by including a light receiving element for detection.