JPS6222243A - Optical head device - Google Patents

Abstract

PURPOSE:To improve the quality of a read signal by providing a correction optical element changing the position of an optical axis of a focusing lens and its direction between a light source and the focusing lens being an optical means so as to pass the optical axis of the focusing lens through the light source. CONSTITUTION:In providing the correction optical element 9 comprising a collimated glass plate with a tilt to the optical axis 8, the optical axis 8 is displaced by a quantity depending on the tilt angle of the correction optical element 9 while the direction is not changed. Through the utilization of the principles above, the tilt of the correction optical element 9 is adjusted to give a proper displacement to the optical axis 8 thereby correcting the deviation with the light source 1. As a result, the irradiated luminous flux 2 from the light source 1 becomes an axial object point light through the focusing lens 4 and an ideally small collected spot is irradiated on an information recording medium 3 without aberration. Thus, jitter of the read signal is decreased and the modulation is improved so as to improve the equality of the read signal.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical head device, and more specifically, to an optical head device for reading or writing multiple signals from an information recording medium such as an optical disk. The present invention relates to an optical head device.

[Conventional technology]

FIG. 3 shows a signal readout optical system of a conventional optical head device. In the figure, a light beam (2) emitted from a light source (1) such as a semiconductor laser is a track-shaped piece of information such as a digital audio signal or video signal. The light is emitted toward the recorded information recording medium (3), and is focused onto the information recording medium (3) by a focusing lens (4) placed near the focal point position. The reflected light beam (3) from the information recording medium (3) is separated from the emitted light beam (2) by a beam splitter (6) and detected by a photodetector. (r) is the optical axis of the focusing lens.

According to the above configuration, the light beam (-) emitted from the light source (1) passes through the beam splitter (6) and then passes through the focusing lens (4).
) is focused onto the information recording medium (3).

On the other hand, the reflected light flux o) containing information from the information recording medium (3)
passes through a focusing lens (ge) and is reflected by a beam splitter (6) to be separated from the output beam (, 2). This separated reflected light beam is received by a photodetector (W), and information can be obtained as an electrical signal.

In the above optical system, the focusing lens (represents its optical axis (r)
) is arranged so that it passes through the light source (1).

At this time, the focusing lens (RI) focuses the ideal small light spot on the information recording medium (the information storage medium) without producing aberrations.
3) Can be irradiated on.

[Problem that the invention seeks to solve]

In the conventional optical head device as described above, when arranging each optical element, errors often occur from the ideal arrangement position. Figure 1 shows an example in which the light source (1) is arranged at a position shifted from the optical axis (r) of the focusing lens (ri). In such an optical arrangement, the output light beam (2 ) is a so-called off-axis object point beam with respect to the focusing lens (RI), and when it passes through the focusing lens (II'>, comatic aberration mainly occurs, resulting in an ideal small focused spot on the information recording medium (3). Therefore, the jitter of the readout signal increases, the modulation rate decreases, and the quality of the readout signal deteriorates.

Regarding the causes of aberrations caused by focusing lenses for off-axis object point rays, please refer to Kazuo Miyake's ``Geometric Optics'', Kyoritsu Shuppan (/
q79) P? There are references such as , 7~.

This invention was made in order to solve the above problems, and is an optical system that can adjust the position and direction of the optical axis of a focusing lens so that the light source is located substantially on the optical axis of the focusing lens. The purpose is to obtain a head device.

[Means for solving problems]

The optical head device according to the present invention includes a correction optical element that can change the position and direction of the optical axis of the focusing lens between the light source and the focusing lens constituting the optical means.
! : The optical axis of the focusing lens passes through the light source.

[Effect]

In this invention, even if the light source position deviates from the optical axis of the focusing lens, the deviation is corrected by adjusting the correction optical element placed between the focusing lens and the light source.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention. In the figure, the optical axis (y) of the focusing lens (i.e., A correction optical element (9) using parallel flat glass is arranged to correct the optical axis (g) so that it passes through the optical axis (g).

With the above configuration, the outgoing light beam (2) emitted from the light source (1) is transmitted through a correction optical element made of parallel flat glass.
) and a beam splitter (6), the light is focused onto the information track of the information recording medium (3) by a focusing lens (4)K, and irradiates the information track. After reading the signal, the reflected light beam (5) passes through the focusing lens (ri) again, is reflected by the beam splitter (6), and is separated from the incident light beam (2). The separated reflected light beam (Y) is received by a photodetector (7), and a signal can be obtained as an electrical signal.

In fact, when constructing the optical system as described above, a misalignment occurs between the optical axis (g) of the condenser lens (Hiroshi) and the position of the light source (1). Here, we will explain how to correct the position of the optical axis (g) of the focusing lens.If the correction optical element (te) made of parallel flat glass is installed at an angle with respect to the optical axis (g), the optical axis Ct
) can be adjusted by adjusting the inclination of the correcting optical element (?) by taking advantage of the fact that the inclination of the correcting optical element (9) is displaced by an amount dependent on the angle without changing the direction; the optical axis Cg) An appropriate displacement is applied to the light source (1) to correct the deviation between the light source (1) and the light source (1). As a result, the light source (
The emitted light beam (2) from 1) is an axial object point light beam and can illuminate an ideally small focused spot on the information recording medium (3) without aberration. Therefore, the jitter of the read signal can be reduced, the modulation rate can be improved, and the quality of the read signal can be improved.

The method for adjusting the correction optical element is to adjust the correction optical element (9) while observing the focused spot by the focusing lens (ri).
The method of determining the inclination is to give an appropriate inclination to the optical axis of the lens so that the focused spot is the smallest, and while observing the signal output of the photodetector (7), the method of determining the inclination is to give an appropriate inclination to the optical axis. There are methods of determining the slope so that it becomes smaller.

FIG. 3 shows another embodiment using a wedge plate optical element as the correction optical element, in which the correction optical element (9a) made of the wedge plate optical element is installed with an appropriate inclination relative to the optical axis (g). In particular, both the position and direction of the optical axis can be changed. By using this fact, the optical axis (su) becomes the light source (1).
The inclination of the correction optical element (9a) is adjusted so that the correction optical element (9a) passes through, and the same effect as in the above embodiment is achieved.

In the above embodiments, a parallel plate glass or a wedge plate optical element was used as a correction optical element, but the beam splitter (6) may also be used as a correction optical element and be given an appropriate inclination. It has the same effect as.

In addition, in the above embodiment, the correction optical element is provided between the light source (1) and the beam splitter (B), but the same effect can be obtained by placing it between the beam splitter (X) and the focusing lens (B). play.

〔Effect of the invention〕

As is clear from the above description, this invention is equipped with a correction optical element and can be adjusted so that the positions of the optical axes of the light source and the condensing lens coincide, so that the condensing lens does not generate aberrations and information By irradiating an ideal small focused light spot onto the recording medium, it is possible to reduce the jitter of the read signal and improve the modulation rate, resulting in the effect of obtaining a high quality read signal.

[Brief explanation of the drawing]

FIG. 1 is an optical system diagram of one embodiment of the present invention, FIG. 2 is an optical system diagram of another embodiment, FIG. 3 is an optical system diagram of a conventional optical head device, and FIG. FIG. 3 is an optical system diagram for explaining the function of the object. (1)...Light source, (2)...Outgoing light flux, (3)...Information recording medium, (4)...Converging lens (optical means), Cs>
...Reflected light flux, (6)...Beam splitter (light beam separation means), (W)...Photodetector, (!:)...Optical axis, (9
)(ya)...Correction optical element. In each figure, the same reference numerals indicate the same or corresponding parts. -('J ("Lghψt's Procedural Amendment (Current 1. Indication of the case Patent Application No. 161219/1983 2, Name of the invention Optical) \ RAD device 3, Person making the amendment Relationship with the case Patent Applicant address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Name (601) Mitsubishi Electric Corporation Representative Moriya Shiki 4, Agent address 4th floor, Marunouchi Building, 2-4-1 Marunouchi, Chiyoda-ku, Tokyo 6. The statement of contents of the amendment shall be amended as follows.

Claims (4)

[Claims] (1) a light source, an optical means for irradiating an information track on an information recording medium with an emitted light beam from the light source, a light beam separating means for separating a reflected light beam from the information recording medium from the emitted light beam, and the reflected light beam An optical head device equipped with a photodetector for receiving light, characterized by comprising a correction optical element arranged between the light source and the optical means and adjusting the position and direction of the optical axis of the optical means. optical head device. (2) The optical head device according to claim 1, comprising a correction optical element made of a parallel plate optical element. (3) The optical head device according to claim 1, comprising a correction optical element formed of a wedge plate optical element. (4) The optical head device according to claim 1, wherein the light beam separating means has the function of a correction optical element.