JPH06302007A - Optical head - Google Patents

Abstract

PURPOSE:To constitute the optical head to be a small size and to be capable of the exact detection of a reflected light beam. CONSTITUTION:This optical head 10 includes a light source 11 which emits a light beam, an objective lens 12 which irradiates the surface of the optical head with the light beam from this light source and receives the reflected light beam reflected by this surface and a photodetector 18 which receives this reflected light beam via a Wollaston prism 16. The optical head 10 is so constituted that this Wollaston prism 16 is formed out of lithium niobate LiNbO3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for irradiating a surface of an optical disc with a light beam for recording or reproducing information signals and detecting the reflected light through a Wollaston prism. It is about.

[0002]

2. Description of the Related Art Conventionally, for example, an optical head for a magneto-optical disk (MO) is constructed as shown in FIG. In the figure, an optical head 1 includes a laser light source 2 such as a semiconductor laser element, an objective lens 3 for focusing laser light emitted upward from the laser light source 2 on the surface of a magneto-optical disc MO, and an objective lens 3. This light source 2
It has a grating 4, a beam splitter 5, and a collimator lens 6 which are sequentially arranged between the lens and the objective lens 3.

Further, this optical head 1 is
The beam splitter 5 includes a Wollaston prism 7, a multi-lens 8 and a photodetector 9, which are sequentially arranged along the optical axis.

According to the optical head 1 thus constructed, the P-polarized light beam emitted from the laser light source 2 is
The surface of the magneto-optical disk MO, which passes through the objective lens 3 via the grating 4, the beam splitter 5 and the collimator lens 6, is refracted by the action of the objective lens 3 and is rotationally driven thereabove. Will be focused on.

The reflected light beam containing the MO component (that is, S-polarized light) reflected on the surface of the magneto-optical disk MO is
Again via the objective lens 3 and the collimator lens 6,
It advances toward the laser light source 2 and enters the beam splitter 5. In the beam splitter 5, the reflected light beam is reflected by the reflecting surface of the beam splitter 5.
The light is reflected laterally and is focused on the light receiving surface of the photodetector 9 via the Wollaston prism 7 and the multilens 8.

When the reflected light beam passes through the Wollaston prism 7, it is separated into three light beams of P-polarized light, S-polarized light and (P + S) -polarized light based on the birefringence effect. . As a result, the beams are focused on the light receiving surface of the photodetector 9 via the multilens 8, respectively. Thus, the photodetector 9 receives the three reflected light beams,
A focusing control signal, a tracking control signal, and a reproduction signal are detected.

[0007]

However, in the optical head 1 having such a structure, the Wollaston prism 7 is generally made of artificial quartz (SiO2). In the case of SiO2, the refractive index difference Δn is Δn≡ne −n0 = 0.0089 (@ λ = 780 nm)
It is a degree. Therefore, the ordinary light of the Wollaston prism 7
The separation angle of the extraordinary light is about 1 degree when the prism bonding angle is 45 degrees with respect to the crystal direction.

Therefore, when the incident reflected light beam has a beam diameter of 4 mm, the thickness of the Wollaston prism 7 in the optical axis direction is at least 4 mm or more. Thus, there is a problem that the optical path length to the photodetector 9 becomes long and the miniaturization is limited.

Further, when the reflected light beam incident on the Wollaston prism 7 is convergent light, the thickness of the Wollaston prism 7 causes aberration of each beam after separation, so that the optical design is There is a problem that it becomes difficult and accurate detection of the reflected light beam cannot be performed.

In view of the above points, an object of the present invention is to provide an optical head which is small in size and capable of accurately detecting a reflected light beam.

[0011]

According to the present invention, a light source for emitting a light beam, and a reflected light beam for irradiating the surface of an optical disk with the light beam from the light source and reflecting the light beam on the surface of the optical disk are provided. In the optical head, the Wollaston prism includes a lithium niobate (LiN
This is achieved by an optical head made of bO3).

[0012]

According to the above structure, since the Wollaston prism itself is formed of lithium niobate having a relatively large refractive index, it is relatively thin in order to obtain the same birefringence effect. .

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to FIGS. It should be noted that the examples described below are suitable specific examples of the present invention, and therefore, various technically preferable limitations are given, but the scope of the present invention particularly limits the present invention in the following description. Unless otherwise stated, the present invention is not limited to these modes.

FIG. 1 shows an embodiment of an optical head for a magneto-optical disk according to the present invention. In FIG. 1, an optical head 10 includes a laser light source 11 such as a semiconductor laser element, and an objective lens 12 for focusing laser light emitted upward from the laser light source 11 on the surface of a magneto-optical disk MO. , This laser light source 11
Grating 13, beam splitter 14, collimator lens 15 which are sequentially arranged between the objective lens 12 and the objective lens 12.
And have.

The optical head 10 includes a Wollaston prism 16 and a multi-lens 1 which are sequentially arranged along the optical axis on the side of the beam splitter 14 in FIG.
7 and a photo detector 18.

The above construction is the same as that of the conventional optical head 1 shown in FIG. 3, but in the optical head 10 according to this embodiment, the Wollaston prism 16 is
It is formed from lithium niobate LiNbO3. Here, the refractive indices ne and n0 of lithium niobate are
Since ne = 2.179 n0 = 2.259, respectively, the refractive index difference Δn is Δn≡ne −n0 = 0.08.

Therefore, this refractive index difference Δn is an order of magnitude larger than that in the case of the conventional artificial quartz (SiO 2).
Therefore, in the Wollaston prism 16, the apex angle of the two prism portions 16a and 16b attached together can be made extremely small, for example, 9 degrees as shown in FIG. As a result, this Wollaston prism 16
The thickness in the optical axis direction will be extremely thin.

Further, this Wollaston prism 16
2A, the prism part 16a on the incident side has its crystal optical axis rotated by 45 degrees as shown in FIG. 2B, and the prism part 16b on the exit side has a crystal optical axis as shown in FIG. 2C. The shaft is rotated 90 degrees.

The optical head 10 according to this embodiment is constructed as described above, and its operation is as follows. That is, the P-polarized light beam emitted from the laser light source 11 is transmitted through the grating 13, the beam splitter 14, and the collimator lens 15 to the objective lens 1
The light passes through 2 and is refracted by the action of the objective lens 12 at that time, so that it is focused on the surface of the magneto-optical disk MO which is rotationally driven above it.

The reflected light beam containing the MO component (that is, S-polarized light) reflected on the surface of the magneto-optical disk MO is
It again travels toward the laser light source 11 through the objective lens 12 and the collimator lens 15 and enters the beam splitter 14. In this beam splitter 14,
The reflected light beam is laterally reflected by the reflecting surface of the beam splitter 14, and the Wollaston prism 1
6 and the multi-lens 17 through the photo detector 1
Focus on the light-receiving surface of 8.

Here, when the reflected light beam passes through the Wollaston prism 16, it is separated into three light beams of P-polarized light, S-polarized light and (P + S) -polarized light based on its birefringence effect. . As a result, the beams are transmitted through the multi-lens 17 to the photodetector 1 respectively.
It will be focused on the light receiving surface of No. 8. Thus, the photodetector 18 detects the focusing control signal, the tracking control signal and the reproduction signal by receiving the three reflected light beams.

In this case, since the Wollaston prism 16 is made thin, the optical path length from the beam splitter 14 to the photodetector 18 is made relatively short. Therefore, the entire optical head 10 is made compact.

Further, since the Wollaston prism 16 is thin, even if the reflected light beam is convergent light,
The aberration of each reflected light beam separated by the Wollaston prism 16 is relatively small.

As described above, in this embodiment, since the Wollaston prism 16 itself is made thin by using lithium niobate having a relatively large refractive index, the Wollaston prism 16 through the photodetection section is provided. The optical path length will be relatively short. Therefore, the entire optical head 10 is made compact.

Further, since the Wollaston prism 16 is thin, the aberration of each reflected light beam separated by the Wollaston prism is relatively small even when the reflected light beam is convergent light. Therefore, the focusing control signal, the tracking control signal, and the reproduction signal can be accurately detected, the degree of freedom in optical design is large, and the design can be easily performed.

In the above embodiment, the case of the optical head 10 for a magneto-optical disk has been described.
Not limited to this, it is obvious that the present invention can be applied to optical heads for other optical disks, for example, optical disks such as CDs and LDs.

[0027]

As described above, according to the present invention, it is possible to provide an optical head which can be miniaturized and which can accurately detect a reflected light beam.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of an embodiment of an optical head according to the present invention.

2A is a side view of a Wollaston prism used in the optical head of FIG. 1, FIG. 2B is a front view of a prism section on an incident side, and FIG. 2C is a front view of a prism section on an exit side.

FIG. 3 is a schematic diagram showing a configuration of an example of a conventional optical head.

[Explanation of symbols]

 10 Optical Head 11 Laser Light Source 12 Objective Lens 13 Grating 14 Beam Splitter 15 Collimator Lens 16 Wollaston Prism 17 Multi-lens 18 Photo Detector

Claims (1)

[Claims] 1. A light source for emitting a light beam, an objective lens for irradiating the surface of an optical disk with the light beam from the light source and receiving a reflected light beam reflected by the surface, and a Wollaston for the reflected light beam. An optical head including a photodetector that receives light through a prism, wherein the Wollaston prism is lithium niobate (Li
An optical head formed of NbO3).