JPS63112832A - Optical head - Google Patents

Abstract

PURPOSE:To shorten the moving distance of a lens by providing plural lenses on a movable head at a roughly equal interval in the radial direction of an optical disk. CONSTITUTION:Dichroic mirrors 10A-10C are provided on a movable head at a roughly equal interval in the radial direction of an optical disk 15, and in accordance with it, lenses 11A-11C and 1/4 wavelength plates 12A-12C are also provided at a roughly equal interval in the same direction. Comparing with the case of one pieces of lens 11, the maximum moving distance can be shortened to 1/3, and also, its height can be made to same as the case of one piece of lens 11, therefore, the weight increase can be suppressed to the minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical head for an optical disc device, and more particularly to an optical head suitable for speeding up access, which is equipped with a plurality of lenses in the semi-column direction of an optical disc.

[Conventional technology]

Conventionally, as an optical disk device, there is a device in which a plurality of lens actuators for forming and tracking a minute optical spot are provided in the semi-column direction of an optical disk, as disclosed in Japanese Patent Laid-Open No. 58-1374.
It is disclosed in Publication No. 2.

In this device, the light beam input section from the light source and the light beam output section to the detection optical system are separated, and the output sections from each lens are also different.

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional technology, the size of the entire optical head becomes large and it becomes difficult to reduce the weight, and therefore, there is a problem that a sufficiently high speed of access cannot be obtained.

Furthermore, if the number of lens actuators installed in the semi-column direction is increased, the area through which the light beam must pass increases, resulting in the problem that high-speed access cannot be achieved, as described above.

An object of the present invention is to provide an optical head that can shorten the moving distance.

[Means for solving problems]

To achieve this object, an optical head according to the present invention includes a light source that emits light beams of a plurality of wavelengths on a common optical axis, and a light source that emits light beams of a plurality of wavelengths on a common optical axis at the intersection of the light beams emitted from the light source and the common optical axis. and dichroic mirrors arranged at approximately equal intervals in the same number as the plurality of wavelengths, and which reflect a light beam of a wavelength matching a specific wavelength among the plurality of wavelengths and allow light beams of other wavelengths to pass, and from the dichroic mirror. A lens that is provided with a detector that detects the light beam that is emitted and reflected on the optical disk surface, focuses the light beam reflected by the dichroic mirror to a minute spot on the optical disk surface, and has an actuator for focusing and track position tracking. An actuator is provided corresponding to the dichroic mirror.

[Effect]

According to the above configuration, the incident light beam to the optical head and the output light beam from the optical head are provided on a common optical axis, and the incident light beam on the common optical axis is incident on a predetermined lens actuator, and the output light beam is The beam is detected by a detector. Further, the selection of the lens actuator is performed by a dichroic mirror provided for each lens actuator that reflects different wavelengths, thereby switching the wavelength of the light beam emitted from the light source.

〔Example〕

The present invention will be explained below based on embodiments shown in the drawings.

FIG. 1 shows a first embodiment of the present invention, and an optical head 1 is roughly divided into a fixed part and a movable part. The fixed unit includes a plurality of fixed heads 2, for example, three fixed heads 2A, 2B, and 2C, and each fixed head 2 includes a light source 3 (3A, 3B, 3G
) and the corresponding deflection beam splitter 5 (5A,
5B, 5C) and the detection optical system 6 (6A, 6
B, 6C). Optical axis L of each fixed head 2
At the intersection of A, LB, and LC with the common optical axis LO, there is a dichroic mirror 8 (8
A, 8B) are provided. On the other hand, the movable part includes a movable head 9, and the movable head 9 has a fixed head 2.
Similarly, dichroic mirrors 10 (IOA, IOB, 1
0C), lenses 11 (IIA, IIB, 11C) and 174 corresponding to the dichroic mirror 10, respectively.
The optical axis of the movable head 9 is always aligned with the common light by a guide 14 via a plurality of rollers 13 rotatably supported on the lower surface of the movable head 9. It is guided so as to coincide with the axis L○.

The center of the dichroic mirror 10 is set so that it is always located on the common optical axis LO even if the movable head 9 moves in the radial direction of the optical disk 15 for access. The dichroic mirrors IOA, 10B, and 10C are provided on the movable head 9 at approximately equal intervals in the radial direction of the optical disk 15, and corresponding lenses 11A, 11B, and 11
C and quarter wavelength plates 12A, 12B, and 12G are also provided at approximately equal intervals in the same direction. In addition, the movable head 9 has
A later-described lens actuator 31 (see FIG. 3) that drives the dichroic mirror 10 and the lens 11, the quarter-wave plate 12 and the lens 11, and the lens 11, respectively.
is provided. Further, the center of the optical disc 15 is fixed to a rotating shaft 16, so that the optical disc 15 rotates in the direction of arrow A.

Next, the operation of the first embodiment of the present invention will be explained.

The light beams emitted from the light sources 3A, 3B, and 3C pass through the polarizing beam splitters 5A, 5B, and 5C, respectively, are reflected by the dichroic mirrors 8A, 8B, and enter the movable head 9 along the common optical axis LO. The light beams reflected by the dichroic mirrors IOA, IOB, and 10G pass through quarter-wave plates 12A, 12B, and 12C, and the linearly polarized light changes to circularly polarized light, and the lenses IIA, IIB,
11C, a minute light spot is formed on the surface of the optical disc 15.

The light beam reflected by the optical disk 15 travels backward through the same path again. At this time, by passing through the quarter-wave plate 12 again, the circularly polarized light is changed into linearly polarized light in a direction perpendicular to the linearly polarized light at the time of incidence. Therefore, this linearly polarized light is reflected by the polarizing beam splitter 5 and enters the detection optical system 6, which then outputs a focusing error signal and a track positioning error signal to the optical disc 1.
Read the data signal on the 5th side.

Operations such as correcting the position of the lens 11 by the lens actuator 31 by feeding back the focusing error signal and the track positioning error signal, and moving the movable head 9 in the radial direction of the optical disk 15 to access the optical disk 15 are carried out in general. This is similar to the optical disc device.

Since the lenses IIA, IIB, and 11C are provided on the movable head 9 at approximately equal intervals in the radial direction of the optical disk 15 as described above, the maximum movement distance can be shortened to 173 compared to the case where only one lens 11 is provided. Can be done. Moreover, since the height can be the same as when there is only one lens 11, the weight increase can be kept to a minimum. Furthermore, since each set of optical and detection optical systems 6 is configured completely independently, it is possible to perform writing or reading operations simultaneously using the lens actuator 31.

In FIG. 1, a dichroic mirror 8 is arranged for each fixed head 2, but it is not necessary to select the outermost fixed head 2C and the innermost lens 11C of the optical disk 15. Therefore, by installing the light source 3C on the common optical axis LO, one dichroic mirror 8 can be omitted, and the dichroic mirror 10C of the movable head 9 can be replaced with a total reflection mirror.

2 to 4 relate to a second embodiment of the present invention, and are examples in which a light source 3 in which a plurality of semiconductor lasers with different wavelengths are formed on the same chip is used. Same-
Alternatively, substantially the same components will be described with the same reference numerals.

Figure 2 is a system diagram of optical head 1, Figure 3 is optical head 1
FIG. 3 is a perspective view specifically showing one example, and the following description will be mainly based on FIG. 3.

The fixed head 2 includes a multi-wavelength laser light source 3, a collimator lens 21, a prism 22, a polarizing beam splitter 5, a lens 23, a half mirror 25, and a cylindrical lens 26.
, a knife 28, a tracking sensor 29, and a focus sensor 30.

The movable head 9 includes a plurality of, for example, two, dichroic mirrors 10 (IOA, 10B) and corresponding two-dimensional lens actuators 31 (31A, 31B, 31B).
) and 174 wavelength plates 12 (12A, 12B), and a head moving coil 32. Further, the movable head 9 is formed with a hole 9a through which the light beam from the fixed head 2 is incident. The lens actuator 31 is the lens 11 (IIA, 11B)
The lens 11 connects to the bottle 3 through the groove 31a.
3. Move straight along (33A, 33B).

In addition, in FIG. 3, 35 is the lens actuator 3.
It is a coil-shaped elastic body to elastically hold 1.

Next, the operation of the second embodiment of the present invention will be explained.

A light beam emitted from a light source 3, which is a multi-wavelength laser in which a plurality of lasers with different wavelengths are arranged on the same chip at intervals of, for example, about 100 μm, is converted into parallel light by a collimator lens 21, and the cross-sectional shape is changed from an ellipse to an ellipse by a prism 22. The light is shaped into a substantially circular shape, exits the fixed head 2 through the polarizing beam splitter 5, and enters the movable head 9 through the hole 9a of the movable head 9. The light beam reflected by the dichroic mirror 10 that matches the reflected wavelength is converted from linearly polarized light to circularly polarized light by the quarter-wave plate 12 that matches the wavelength,
The light enters the lens actuator 31. Here, the lens 11 is moved straight along the pin 33 to focus, and a light spot is formed on the recording surface of the optical disc 15.

Further, by rotating the lens 11 around the pin 33, the lens 11 is displaced and its position in the tracking direction is finely adjusted.

As shown in FIG. 3, the lens actuator 31 has no member disposed directly below the lens 11 to drive the lens 11, so the dichroic mirror 10
Also, the quarter wavelength plate 12 can be provided directly below the lens 11, and the movable head 9 can be made thin. Although this lens actuator 31 has already been disclosed in Japanese Patent Application No. 61-48343 by the same applicant, the lens actuator 31 used in the present invention is not limited to this embodiment.

The light beam reflected by the optical disk 15 passes through the lens 11 and is converted by the quarter-wave plate 12 from circularly polarized light to linearly polarized light having a polarization plane 90° different from that at the time of incidence. The light beam reflected by the dichroic mirror 10 and re-injected from the movable head 9 to the fixed head 2 is reflected by the polarizing beam splitter 5, passes through the lens 23 and the half mirror 25, and is split into a light spot by the tracking sensor 29 on the surface of the optical disk 15. The amount of track deviation of a track guide groove (not shown) is detected, and a control circuit is used to drive the lens actuator 31 and head moving coil 32 so as to reduce the amount to zero. The tracking sensor 29 also reads out data signals recorded on the surface of the optical disc 15 at the same time.

On the other hand, the light beam reflected by the half mirror 25 uses a detection optical system consisting of a combination of a cylindrical lens 26, a knife lens 28, and the lens 23 that passed through it first, and a focus sensor 30 to detect the defocusing voltage between the optical disk 15 surface and the light spot. The lens actuator 31 is driven by the control circuit so that this becomes zero. The above detection method was developed for recording and reproducing optical discs that are already in practical use, and details can be found in Hitachi Review Vol. 65, 10.
It is described on pages 23-28 of the monthly issue.

Although FIG. 3 does not illustrate the fixed guide 14 and the magnetic circuit paired with the head moving coil 32,
Their configuration can be easily determined by those skilled in the art.

Since the lasers of the light source 3 are separated by about 100 μm, the angle at which the lasers are emitted from the collimator lens 21 is different for each laser. A method for correcting this will be explained below.

On the semiconductor laser chip 40 are lasers 41A and 41B.
Assume that the laser 41B is on the optical axis of the collimator lens 21. The light beam (indicated by a broken line) emitted from the laser 41A provided at a distance d from the laser 41B is tilted by θ with respect to the light beam emitted from on the optical axis. If the focal length of the collimator lens 21 is f, then θ=-.

When the inclination of the light beam incident on the movable head 9 is large,
As the movable head 9 moves, the dichroic mirror 1
The light beam incident on the dichroic mirror 10 deviates from the center of the dichroic mirror 10,
There is a risk of being kicked. Furthermore, there is a risk that the light spot formed by the lens 11 will deviate from the optical axis of the lens 11, resulting in increased comatic aberration. In order to keep these values below tolerance, the chromatic aberration of the prism 22 is utilized. Snell's law holds true for the incident angle a of the light beam and the angle β of the refracted light with respect to the normal line on the incident side of the light beam of the prism 22.

That is, the following formula holds true.

sinβ I S 1 n α n Since the refractive index n differs depending on the wavelength of light, the wavelength of the laser 41A is λA, and the wavelength of the laser 41B is λB.

When the refractive index at the wavelength λA is n and the refractive index at the wavelength λB is n', the prism 22 may be made of a material that satisfies the following formula.

sin β 1 sin (α 10) n Comparing the influence of the inclination of the light incident on the lens 11 in the tracking direction, which is the radial direction of the optical disk 15, and the jitter direction, which is perpendicular to the tracking direction, the tracking direction has a track pitch of 1.6 μm. Since the amount of jitter is extremely small, adverse effects such as increased crosstalk from adjacent tracks are more likely to occur than in the jitter direction. Therefore, when the lasers 41A and 41B are disposed in a plane parallel to the surface of the optical disk 15 and the wavelength is changed, the direction in which the light spot moves due to the remaining correction is made to be the jitter direction. is desirable.

〔Effect of the invention〕

As described above, according to the present invention, the movable part can be made compact and lightweight, and the movable part can be provided with a plurality of lenses to shorten the distance of movement of the lenses. This has the effect that it can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an optical head according to a first embodiment of the present invention, FIGS. 2 to 4 are a system diagram of an optical head according to a second embodiment of the present invention, and FIG. 2 is a system diagram of an optical head. 4 is a perspective view of an optical head showing a specific configuration, and FIG. 4 is an explanatory diagram showing the action of a light beam. 1... Optical head, 3 (3A, 3B, 3G)... Light source, 6 (6A,
6B, 6G)...Detector, 8(8A, 8B, s
c) , 10 (IOA, 10B, 10C)...
- Dichroic mirror, 15... Optical disk, 31 (31A, 31B)... Lens actuator L○... Common optical axis.

Claims (4)

[Claims] (1) a light source that emits light beams of a plurality of wavelengths on a common optical axis; and a light source that emits light beams of a plurality of wavelengths on a common optical axis, and the same number of light beams as the plurality of wavelengths are arranged at approximately equal intervals at the intersections of the light beams emitted from the light source and the common optical axis,
A dichroic mirror that reflects a light beam with a wavelength that matches a specific wavelength among the plurality of wavelengths and passes light beams with other wavelengths is provided, and a light beam that is emitted from the dichroic mirror and reflected on an optical disk is reflected. A detector is provided for detection, and a lens actuator is provided corresponding to the dichroic mirror to focus the light beam reflected by the dichroic mirror into a minute spot on the surface of the optical disk, and has an actuator for focusing and track position tracking. light head. (2) The optical head according to claim 1, wherein the light source and the detector are individually provided corresponding to a plurality of wavelengths. (3) Claim 1, wherein the light source is a single light source capable of emitting a plurality of wavelengths, and the detector is one or more.
Optical head described in section. (4) The optical head according to claim 1, wherein the light source has a plurality of semiconductor lasers having different oscillation wavelengths formed close to each other on the same chip.