JPH02158943A - Optical head device - Google Patents

Abstract

PURPOSE:To eliminate the need for the adjustment of the angle of attachment of a polarizer and to simplify assembling by providing the polarizer, which has such thickness that the polarization direction of a reflected beam is rotated at 45 deg., on the incidence face side of a polarizing beam splitter. CONSTITUTION:The reflected beam 12 of p-polarized light from a magneto- optical disk 11 is reflected on a beam splitter 9A and goes to a polarizing beam splitter 3A. This beam 12 is transmitted through an optical rotator 33 consisting of a crystal plate having a prescribed thickness, rotated at 45 deg. there, made incident on the splitter 3A, branched and made incident on photodetectors 4, 5 through lenses 39, 40. A regenerative signal is outputted from the photodetector 4, and a focus error signal and a tracking error signal are outputted from the photodetector 5. Thus, the adjustment of the angle of attachment of the optical rotator is unnecessary to simplify assembling, and the reliability of a head device is improved.

Description

[Detailed Description of the Invention] [Summary] The aim is to simplify the assembly of an optical head device for a magneto-optical disk device, and the beam reflected by a recording medium is divided into an S-polarized component and a P-polarized component. In an optical head device comprising a polarizing beam splitter that separates the beams into two beams and directs them to the photodetectors, the polarizing beam splitter has a thickness on the incident surface side that allows the reflected beam to pass therethrough, thereby changing the polarization direction of the reflected beam. It is constructed by providing an optical rotator sized to rotate the light by 45 degrees.

(Industrial Application Field) The present invention relates to an optical head device for a magneto-optical disk device.

The optical head device of a magneto-optical disk device is configured to read slight changes in the polarization plane of light reflected from the disk, and the polarization direction of the reflected beam from the non-recording portion of the magneto-optical disk is P( - It is necessary that the direction is 45 degrees with respect to the light direction.It is desirable that this optical head device has a configuration that is easy to assemble.

[Conventional technology]

FIG. 6 shows a conventional optical head device. 1 is a semiconductor laser, 2 is an objective lens, 3 is a polarizing beam splitter, 4.
5 is a photodetector. 6 is a 1/2 wavelength plate, which is used to set the polarization direction as described above.

The linearly polarized light in the P direction emitted from the semiconductor laser 1 is passed through a collimating lens 7 , a circular correction prism 8 , a beam splitter 91 , a reflecting mirror 10 . The light passes through the objective lens 2 and is focused onto the magneto-optical disk 11 . The reflected beam from the magneto-optical disk 11 returns along the path it came from, is reflected by the beam splitter 9, and is passed through a 1/2 wavelength plate before entering the polarizing beam splitter 3, as also shown in FIG. Pass 6.

The crystal axis 6a of this half-wave plate 6 is oriented at 22.5 degrees with respect to the P (Q light direction).The reflected beam 1
2 passes through this 1/2 wave root 6, and the seventh
As shown in the figure, the polarization direction is set at 45 degrees with respect to the P polarization direction.

This reflected beam 12A is split by the polarizing beam splitter 3 into P component light 12Ap and S component light 12As, which each pass through lenses 39 and 40 and reach a photodetector 4.5.

A differential amplifier 13 takes the differential output of each photodetector 4.5, and a reproduced signal is obtained from a terminal 14.

Further, a focus error signal and a tracking error signal are detected by one photodetector 4 and outputted from a terminal 15. The objective lens 2 is driven based on this error signal, and focus control and dragging control are performed.

Here, it is important that the polarization direction of the reflected beam 12A is exactly 45 degrees with respect to the P polarization direction. This is because, as shown by line 16 in FIG. 8, if the polarization direction of the reflected beam 12A deviates from 45 degrees with respect to the P polarization direction, the amount of deterioration of the reproduced signal increases.

[Problem to be solved by the invention]

Assuming that the signal degradation tolerance is approximately 1 dB, the reflected beam 1
The allowable deviation angle of the polarization direction of 2A is ±1 degree, which is 1/2
The deviation tolerance of the set angle of the wave plate 6 is as small as ±0.5 degrees. Further, at the stage of cutting out the half-wave plate from the base material, errors in the external shape of the crystal axis are likely to occur.

For this reason, it is actually difficult to adhesively fix the half-wave plate 6 to the side surface of the polarizing beam splitter 3 while accurately determining the angle of the crystal axis direction of the half-wave plate 6.

Therefore, in practice, an adjustment mechanism was provided, and the half-wave plate 6 was incorporated so that the direction of its crystal axis 6a could be adjusted.

That is, as shown in FIG. 9, the half-wave plate 6 is temporarily fixed to a ring-shaped holder 17, and this holder 17 is attached to a V-shaped plate provided between the beam splitter 9 and the polarizing beam splitter 3. The holder 17 is mounted on a pedestal 18, held down by a leaf spring member 19, adjusted by appropriately rotating the holder 17 with an adjustment iron 20, and fixed in place by adhesive.

For this reason, the number of assembly steps for the optical head device increases, and the number of parts also increases, resulting in higher manufacturing costs and insufficient reliability.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical head whose assembly can be simplified.

[Means to solve the problem]

The present invention converts the beam reflected by the recording medium into an S-polarized component and a P-polarized component.
In an optical head device comprising a polarizing beam splitter that separates polarized light components and directs them to a photodetector, the reflected beam has a thickness such that the reflected beam is transmitted through the incident surface side of the polarized beam splitter. The structure includes an optical rotator whose dimension is determined to rotate the polarization direction of the light by 45 degrees.

[Effect]

The attachment of the optical rotator to the polarizing beam splitter requires no position adjustment, and is easy to assemble.

〔Example〕

FIG. 1 shows an optical head device 30 according to an embodiment of the present invention. In the figure, the same reference numerals are given to the parts that substantially correspond to the constituent parts shown in FIG. 6, and the explanation thereof will be omitted.

The beam splitter 9A and the circular correction prism 8A are fixed with adhesive, and the polarizing beam splitter 3A and the prism 3
1 are fixed with adhesive, and both are fixed on the base 32.

33 is a crystal plate as an optical rotator, which is adhesively fixed to the beam splitter 9A and the polarizing beam splitter 3Δ;
It is placed between the two.

As shown in FIG. 4, the crystal plate 33 is cut out from a crystal base material in 17 predetermined directions perpendicular to its crystal axis 34.

The crystal plate 33 cut out in this manner loses birefringence and exhibits optical rotation instead. As shown in Figure 3,
When linearly polarized light whose polarization direction is the direction indicated by reference numeral 35 is incident on this crystal plate 33, the polarization direction is, for example, indicated by the arrow 36.
The polarization direction of the emitted beam becomes the direction indicated by reference numeral 37.

Optical rotation (rotation angle of polarization direction per unit thickness) depends on the wavelength of light, and this relationship in quartz crystal is as shown by the line in FIG. 5. At 380 nm, which is the wavelength of the laser from the semiconductor laser 1, the optical rotation is 10.7 degrees/m.

In this embodiment, the polarization direction is planned to be rotated by 45 degrees, and the thickness t of the crystal plate 33 is 45/10.7=4.
．． 2. It's Toshide.

In the above crystal plate 33, the rotation angle of the polarization direction is determined only by the thickness t, and the positional accuracy with respect to the polarization beam splitter 3A has no relation to the rotation angle of the polarization direction.

Therefore, in the optical head device 30 described above, the crystal plate 3
3 is not necessary, and the crystal plate 33 only needs to be fixed between the beam splitter 9A and the polarizing beam splitter 3A.

In the above-mentioned optical head device 30, the crystal plate 33 is adhesively fixed to the beam splitter 9A on one side and the polarizing beam splitter 3A on the opposite side, and is integrated with the beam splitter 9A and the polarizing beam splitter 3A. As shown by reference numeral 38, it is made into a composite optical element, and the number of parts is reduced. Furthermore, when assembling the composite optical element 38, there is no need to worry about the viscosity of the crystal plate 33 in the f-J direction, and assembly is simple.

The above-described optical head device 30 can be assembled simply by assembling the composite optical element 38 on the base 32, and is easier to assemble than in the past.

Next, the operation of the optical head device 30 described above will be explained with reference to FIGS. 1 and 2.

Pla, which is the reflected beam 12 from the magneto-optical disk 11;
The light beam is reflected by the beam splitter 9A and heads toward the polarizing beam splitter 3A.

This reflected beam 12 is transmitted through a crystal plate 33, where 45
As shown in FIG. 2, the beam 12A is turned into a beam 12A whose polarization direction 39 is at an angle of 45 degrees with respect to the P polarization direction, and enters the polarization beam splitter 3A, where it is split in the same manner as in Moeki, and is split into a beam 12A with a polarization direction 39 at an angle of 45 degrees with respect to the P polarization direction, as shown in FIG. 40 and reach the photodetectors 4 and 5. A reproduction signal is output from the terminal 14, and a focus error signal and a tracking error signal are output from the terminal 15.

Further, instead of the above-mentioned quartz plate 33, a plate made of another material having optical rotation may be used.

〔Effect of the invention〕

As explained above, according to the present invention, there is no need to adjust the angle at all when attaching the optical rotation -f, and the optical rotation only needs to be assembled to the instep, which simplifies the assembly of the optical head v device. I can do it. Further, since it is not necessary to adjust the angle of the optical rotator with respect to the polarizing beam splitter, it is possible to easily combine the optical components by adhesively fixing the optical rotator to the incident surface of the polarizing beam splitter. The number of parts can be reduced and the reliability of the optical head device can be improved.

[Brief explanation of the drawing]

1 is a diagram showing an embodiment of the optical head device of the present invention, FIG. 2 is a schematic diagram of a part of the optical head device of FIG. 1, FIG. 3 is a diagram illustrating optical rotation by an optical rotator, Figure 4 shows a quartz plate that controls the optical rotation, Figure 5 shows the wavelength dependence of the optical rotation of the quartz plate, Figure 6 shows a conventional optical head device, and Figure 7 shows the wavelength dependence of the optical rotation of the quartz plate. Fig. 6 is a schematic diagram of a part of the optical head device, Fig. 8 is a diagram showing the relationship between the crystal axis angle of the 1/2 wavelength plate and the amount of deterioration of the reproduced signal, and Fig. 9 is a diagram showing the relationship between the crystal axis angle of the 1/2 wavelength plate and the amount of deterioration of the reproduced signal. It is a figure showing attachment. In the figure, 3A is a polarizing beam splitter, 9A is a beam splitter, 11 is a magneto-optical disk, 12. 12A is a reflected beam, 30 is an optical head device, 32 is a base, 33 is a crystal plate, 94 is a crystal axis, and 38 is a compound An optical element is shown. Patent Applicant: Fuji Tsu Co., Ltd. Part of /) Figure 2 of the song 1-55 No. 4 of the 1-55 Zusai(h7(h7(h7(h7)'s 7th Yūo'kn 坏(Io) to the 2nd dormitory of the night sky. To 34 5.H4+shami←SeBnige)-1-
1Pi Gouf 1) Hahi J6ξ Mikonu 21 Fig. 7

Claims (1)

[Scope of Claims] An optical head device comprising a polarizing beam splitter that divides a beam reflected by a recording medium into an S-polarized component and a P-polarized component and directs the beam to a photodetector, comprising: the polarizing beam splitter (3A); The thickness (
t) is provided with an optical rotator (33) having a dimension that rotates the polarization direction of the reflected beam by 45 degrees when the reflected beam passes therethrough.