JPH02294942A - Optical memory device - Google Patents

Abstract

PURPOSE:To reduce optical beam shifting quantity attended with the rotation of a galvanomirror and to stabilize the operation by providing an afocal optical system composed of the two groups of optical systems having the positive refracting power between an objective lens and the galvanomirror. CONSTITUTION:Light emitted from a semiconductor laser 201 is in parallel light by a collimator 202 and transmitted through a prism 204 for servo signal separation. Then, the optical path of the light is bent by a reflecting mirror 205 and bent almost in a seeking direction by a galvanomirror 206. The light passes through the afocal optical system where the light is condensed by a first group optical system 102 and goes to the parallel light again by a second group optical system 103, guided to an objective lens 105 by a reflecting mirror 207 and condensed on an optical storing medium 106. Since the rotational angle of the mirror 206 can be reduced by prolonging the focal distance of the optical system 102 rather than that of the optical system 103, a medium 106 can be rotated at high speed and a distributed optical memory device can be easily manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical memory device using a separate optical system in the field of optical storage.

[Conventional technology]

Conventional optical memory devices use an integrated optical head in which all optical systems, a focus actuator, and a track actuator are mounted on a single chassis, and seek is performed on all of them. However, since the moving mass is large, the seek time cannot be shortened. In order to solve this problem, an optical memory device has a separate optical system in which the objective lens and the reflector focus actuator are allowed to seek, but the other optical systems and the tracking actuator, so-called galvanometer mirrors, are not allowed to seek. has been devised.

FIG. 3 shows an example of a side view of a conventional optical memory device.

The light emitted from the semiconductor laser 201 becomes a traveling light by a collimator lens 202, passes through prisms 203 and 204, has its optical path bent by a reflecting mirror 205, and enters a galvano mirror 206. The light travels approximately in the sea and evening direction, and its optical path is bent by the reflecting mirror 207 and passes through the objective lens 105.
The light is focused on the optical storage medium 106.

[Problem to be solved by the invention]

However, in the above-mentioned conventional technology, as shown in FIG.
As the galvanometer mirror 206 rotates, the objective lens 10
5 has the problem that the light beam incident on it is shifted.

Specific adverse effects include the following items.

- The amount of light incident on the objective lens changes, the accuracy of the energy density on the optical storage medium deteriorates, and writing errors occur.

- The distribution of light incident on the objective lens changes, the shape of the focused spot becomes unstable, and reading errors occur.

- In order to avoid vignetting caused by the objective lens, the diameter of the collimated beam must be increased, which reduces the light utilization efficiency and requires the use of expensive high-power semiconductor lasers.

- Output light beam 501 as shown in the cross-sectional view of the light beam in Figure 5
The position of the returned light beam moves from 502 in the case of the initial position of the galvano mirror to 503, and the light beam moves on the servo signal detection sensor, making it impossible to obtain an accurate servo signal. This is especially serious in the case of the track error detection method using the push-pull method.

This is because the moving direction 504 of the light beam and the direction of the dividing line 505 of the two-part sensor used in the push-pull method are perpendicular to each other.

The present invention is intended to solve the above-mentioned problems, and its purpose is to provide an optical memory device capable of stable operation by reducing the amount of optical beam shift 1 caused by the rotation of the Galhano mirror. That's true.

[Means to solve the problem]

The optical memory device of the present invention includes an objective lens and a separate optical system using a Galhano mirror that drives a reflecting mirror for tracking, in which a positive It is characterized by the installation of an afocal optical system consisting of a first group optical system that has refractive power and is installed on the galvano mirror side, and a second group optical system that has positive refractive power and is installed on the objective lens side. do.

[Effect]

The effects of the afocal optical system in the present invention are as follows.

As shown in Fig. 1, the optical axis 101 is
The light beam incident on the first group optical system 1o2 at an angle of θ1 with respect to This leads to the second group optical system 103 installed at the position.

This first group optical system 102 and second group optical system 103 are connected at a distance f
The system installed at a distance of l+f2 is the afocal optical system of the present invention.

The angle θ2 of the output beam from the second group optical system 103 is
It is given by θ2−θ1*(fl/f2). At this time, the objective lens 1 is placed at the position where the principal ray 104 intersects with the optical axis 101.
If 05 is placed, no light beam shift will occur. in fact,
Since the objective lens 105 moves with seeking, the center of the seek area is at position d in Figure 1.
Minimizes optical beam shift. 106 is an optical storage medium.

〔Example〕

FIG. 2 is a side view of an embodiment of the present invention, which is an example applied to a 5.25-inch magneto-optical disk drive.

The light emitted from the semiconductor laser 201 passes through the collimator 202
The servo signal separation prism 203
, passes through the magneto-optical signal separation prism 204 and passes through the reflecting mirror 20
5, the optical path is bent by the galvano mirror 206, and the light is bent almost in the direction of the sky. The light beam is once condensed by the first group optical system 102, and then becomes parallel light again by the second group optical system 103. The light beam is then guided by a reflecting mirror 207 to the objective lens 105 and focused onto the optical storage medium 106.

The direction of rotation of the Galhano mirror is opposite to the conventional one.

Each parameter in this example is as follows.

First group optical system focal length 17.3mm Second group optical system focal length g'li 15.4mm Objective lens focal length 3mm Objective lens numerical aperture 0.55 Distance from Garhano mirror to first group optical system 4mm First group optical Distance from the system to the second group optical system: 32.7 mm Distance from the second group optical system to the objective lens placed in the center of the seek area: 33 mm Seek area: 32 mm Large light beam diameter to the afocal optical system: 5 mm From the afocal optical system Output light beam diameter 4. 45
mm The parameters for moving the optical spot by 50 μm on the optical storage medium are as follows.

Rotation angle of the Galhano mirror: 0.42 degrees Incident angle to the afocal optical system: 0.85 degrees Output angle from the afocal optical system: 0.95 degrees Since the present invention does not use a new reflective surface, the polarization characteristics of the light can be adjusted without any problem. Magnetic recording was possible.

Furthermore, by using achromatic lenses in each of the first group optical system and the second group optical system, it was possible to adapt to changes in the wavelength of the semiconductor laser.

Furthermore, by proactively increasing the difference in focal length between the first group optical system and the second group optical system, it is possible to further reduce the required rotation amount of the Garno A mirror.

Of course, the present invention can also be applied to 3.5-inch optical disk drives.

〔Effect of the invention〕

If an optical memory device equivalent to the above embodiment is configured using the conventional technology and an attempt is made to move the optical spot by 50 μm, the optical beam will shift by a maximum of 1.43 mm at the objective lens position. This is 43.3% of the pupil diameter of the objective lens, which is very unacceptable.

On the other hand, according to the present invention, the light beam shift amount is at most 0. 27 mm, which is 8% of the objective lens pupil diameter, was actually reduced to 175.3 mm.

Furthermore, in this example, the focal length of the first group optical system was made longer than the focal length of the second group optical system, and the angular magnification was set to 1.12, making it possible to reduce the rotation angle of the Galhano mirror by 11%. This effect is effective in the design of Garhano Mirror when the optical memory body is rotated at high speed in one temple.

In addition, conventional problems such as fluctuations in energy density on optical storage media, fluctuations in the shape of the focused spot, and reductions in light utilization efficiency,
Deterioration of the focus servo signal is no longer a practical problem.

The deterioration of the track error signal caused by the push-pull method, which has been the most problematic conventional method, has been corrected by the conventional mirror hold method, or by combining it with a glasses-type sensor, the signal can be returned to a sufficiently high quality.

As described above, the present invention is a very important invention that makes it possible to manufacture a separate optical memory device, which has been difficult to manufacture in the past.
It greatly contributed to the development of external storage devices for computers, especially to speeding them up.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the principle of the present invention. FIG. 2 is a side view of an embodiment of the present invention. FIG. 3 is a side view of a conventional optical memory device. FIG. 4 is an explanatory diagram of a conventional optical memory device. Cross-sectional view of light beams of conventional optical memory device Optical system Second group Optical system Principal ray Objective lens Optical storage medium Semiconductor laser Collimator Lens Servo signal separation prism Optical magnetic signal separation prism 7...Reflector Galvano mirror Above Applicant Seiko Epson Hayashi Shiki Company agent Patent attorney Kisaburo Suzuki and 1 other person

Claims (1)

[Claims] In an optical memory device having a separate optical system using an objective lens and a galvano mirror that drives a reflecting mirror for tracking, a galvano mirror with positive refractive power is provided in the optical path between the objective lens and the galvano mirror. An optical memory device comprising an afocal optical system consisting of a first group optical system installed on the mirror side and a second group optical system having positive refractive power and installed on the objective lens side.