JPS62223823A - Optical information processor - Google Patents

Abstract

PURPOSE:To prevent reflecting light from an optical disk from overlapping and the reflecting light of a 1/4 wavelength plate surface on a light detecting device by including the 1/4 wavelength plate in parallel to the direction in which the normal line of a crystal shaft is inclined to an optical axis and forming a plate thickness in which a linear polarization is converted to a circular polarization by the inclining angle. CONSTITUTION:A light path 9 of the light reflected on the surface of a 1/4 waveform plate 4 has the angle to a reflecting light path from an optical disk 6 since the 1/4 waveform plate 4 is inclined. Consequently, the light path 9 does not come onto a light detecting device 8 at the surface of the light detecting device 8. For the inclination, in order to use the performance of the 1/4 wavelength plate 4 to the maximum, the 1/4 wavelength plate 4 is inclined in the direction parallel to the direction of a crystal shaft 10, then, a plate thickness (t) is set optimumly so that the converting capacity of the linear polarization and the circular polarization can be maximum, thereby, eliminating the need for adjusting.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is a method for optically reading information recorded in a spiral shape on a disc-shaped information distribution carrier such as a digital audio disc or a video disc. The present invention relates to an optical information processing device used for writing.

[Background Art and Problems Therewith] Conventionally, an optical information processing device, such as an optical big-ag device, is configured as shown in FIG.
, collimator lens 2, polarizing beam splitter 3, I/
A four-wavelength plate 4, an objective lens 5, and an optical disk (information recording carrier) 6 are sequentially arranged at predetermined intervals on a straight line, and the polarizing beam splitter 3 is focused on a straight line perpendicular to the straight line. A track deviation detection optical system 7 and a photodetector 8 are also provided.

During operation, the diffused light H1f emitted from the light source 1
The n1 polarized beam splitter 3 is converted into a parallel beam by the flJ7'-tarlens 2, and sequentially transmitted through the 1/4 wavelength plate 4.
An optical disk 6 which is an information recording carrier is formed by an objective lens 5.
The light is focused as a minute spot on the information recording surface. The information recording surface has information recorded as minute bit strings, and reflected light is diffracted by these bits. The content of the information can be read by changing the amount of light depending on the presence or absence of diffraction of the reflected light. That is, the reflected light from the optical disk 6 travels backwards, is focused by the objective lens 5, is converted into a parallel beam, is transmitted through the quarter-wave plate 4, and then is reflected by the polarizing beam splitter 3, causing defocus and tracking. It reaches the optical hanger 8 via the deviation detection optical system 2, and the information recorded on the optical disk 6 is read.

1/2 used in the above optical pickup device
The four-wavelength plate 4 has the function of converting linearly polarized light into circularly polarized light, but since its optical surface is highly polished, reflection of incident light cannot be suppressed. Therefore, when the three-beam method is used as a tracking error detection method, when the reflected light of the sub-beam and the reflected light of the 1/4 wavelength plate 4 overlap on the photodetector 8, the light intensity ratio is the same. level, this poses a performance problem.

That is, in the case of the three-beam method, since the difference in light amount between the main beam and the sub beam is about 10=1, the difference in light amount with the light reflected from the 1/4 wavelength plate 4 is not very large. If the reflected light overlaps one of the two sub-beams, it will be narrowed as an offset to the tracking error signal, and in order to remove this offset, a great effort will be required in the subsequent electrical circuit design, and in the worst case, the offset will not work properly. Occasionally, it may not be removed.

In order to compensate for the above-mentioned drawbacks, it was proposed in Japanese Patent Application Laid-Open No. 60 (1982) to set aside the 174-wavelength version so that it does not overlap with the reflected light from the optical disk or land on the same photodetector.
It is described in the publication No.-177444. This is the fourth
As shown in the figure, the reflected light 13 reflected on the surface of the quarter-wave plate 40 has an angle with respect to the reflected optical path from the optical disk 6 because the quarter-wave plate 4 is tilted.
On the photodetector 8 side, there is no rice on the photodetector 8.

However, this inclination significantly impairs the function of the quarter-wave plate 4. This problem is particularly exacerbated when the normal line of the quarter-wave plate 4 is tilted parallel to the tilt direction of the crystal axis. Even in the orthogonal direction, the degree of deterioration is slightly less, but it gets worse. In other words,
The original function of the quarter-wave plate 4, the conversion of linearly polarized light into 6 circularly polarized lights, is no longer performed normally, resulting in conversion of related polarized light 4+elliptically polarized light.

As a result, after passing through the polarizing beam splitter 3, the amount of transmitted light increases and the amount of reflected light decreases. Therefore, light'IM
The amount of light that returns to 1 increases, and the amount of light that reaches the photodetector 8 decreases. An increase in the amount of light returning to the light source 1 has an adverse effect as return light noise when a semiconductor laser is used as the light source 1. A decrease in the amount of light to the photodetector 8 deteriorates the S/N of the detection signal.

Then, the reflected light from the surface of the 1/4 wavelength plate 4 is transferred to the optical disc 6.
The optimal angle to prevent the reflected light from overlapping on the photodetector 8 depends on the focal length and position of the optical components used,
It is determined by the pattern of the photodetector 8, etc. Generally speaking, if you tilt the photodetector 8 by about 2 degrees, the amount of light that reaches the photodetector 8 will be 1
0ch goes down. In order to prevent this decrease, it is necessary to make adjustments such as by rotating the quarter-wave plate 4.

[Objective of the Invention] The object of the present invention is to improve the performance of the quarter-wave plate, f, maximum, so that the reflected light on the surface of the quarter-wave plate does not have an adverse effect on the performance of the device, and the work efficiency is not deteriorated. The object of the present invention is to provide an optical information processing device that can perform to the maximum extent possible.

[Summary of the Invention] In order to achieve the above object, the present invention tilts a 174-wave plate so that its normal line is parallel to the direction in which the crystal axis is tilted with respect to the optical axis, and when the tilt angle is set, linearly polarized light is generated. This is an optical information processing device in which the thickness of the plate is such that the light is converted into circularly polarized light, and the light reflected from the optical disk and the light reflected from the surface of the quarter-wave plate do not overlap on the photodetector.

[Embodiments of the Invention] An optical information processing device, such as an optical pickup device, according to the present invention is constructed as shown in FIG.
The same parts as in Figure) are given the same reference numerals.

That is, a light source 1, a collimator lens 2, a polarizing beam splitter 3, a 1/4 wavelength plate 4, an objective lens 5, and an optical disk (information recording carrier) 6 are sequentially arranged on a straight line at predetermined intervals, and the polarized beam In the splitter 30 portion, a focus shift and track shift detection optical system 7 and a photodetector 8 are sequentially provided at a predetermined interval on a straight line orthogonal to the above-mentioned straight line.

In the above case, the 1/4 wavelength plate 4 is made of crystal, and as shown in FIG.
As shown in a) and (b), the crystal is arranged so that its normal 11 is parallel to the direction in which the crystal axis 10 is tilted with respect to the optical axis, and at that tilt angle, linearly polarized light becomes circularly polarized light. The plate thickness is set to be converted. In addition, in Figure 2 (b), 1
2 indicates the direction of incident linear polarization.

Now, during operation, the light emitted from the light source 1 is converted into parallel light by the collimator lens 2, passed through the polarizing beam splitter 3 (F), is converted from linearly polarized light to circularly polarized light by the 174 wavelength plate 4, and is converted into parallel light by the objective lens 5. It is focused onto the optical disc 6. The information-containing light reflected by the optical disk 6 passes through the objective lens 5 and is converted into linearly polarized light in a direction perpendicular to the polarization direction of the light source 1 by the 174-wave plate 4 . Therefore, the polarized beam is reflected by the f-litter 3, its optical path is bent, passes through the entire focus shift and track shift detection optical system 7, is incident on the photodetector 8, and is converted into an electrical signal.

The optical path 9 of the light reflected on the surface of the 1/4 wavelength plate 4 is 1/4
Since the four-wavelength plate 4 is tilted, it has an angle with respect to the reflected optical path from the optical disk 6, as shown in FIG. . In order to maximize the performance of the 1/4 wavelength plate 4 even if it is tilted, the 1/4 wavelength plate 4 is tilted in a direction parallel to the crystal axis 10 direction as described above, and at that time, linearly polarized light changes to circularly polarized light. The plate thickness t is optimally set so that the conversion capacity of the plate is maximized, and there is no need to adjust it (see Fig. 2).

Note that in the case of vertical incidence to the quarter-wave plate 4, the retarding amount is calculated using the following formula.

However, λ: Length t: Plate thickness no: Extraordinary ray refractive index no: Ordinary ray refractive index i: Crystal optical axis tilt angle = retardation In normal QM', it is set so that r' = 174. When λ = 780 nm, the plate thickness t is approximately 0.
, 5 m, the crystal axis is tilted by about 13°.

In the case of non-perpendicular incidence, if the angle of incidence is Δi, it can be transformed as follows. By setting the value of Δ1 to a certain value and changing only the plate thickness t, sufficient performance as the quarter-wave plate 4 can be achieved.

As the value of Δl increases, tolerances for tilt errors and thickness errors become stricter.
There is an acceptable value. This is the focal length in the detection system, 1/
The distance to the 4-wavelength plate 4 and its mounting vary depending on accuracy, etc.

Generally speaking, it is better for the light to be incident at a direction closer to the two crystal axes.
It is also the direction in which the plate thickness t becomes thinner, which is advantageous in terms of resources.
It can be kept sufficiently away from the reflected light from the optical disc 6.

[Effect of the invention] According to the invention, the reflected light on the quarter-wave plate 4 is
It is possible to provide an optical information processing device that satisfies the function of the 1/4 wavelength plate 4 without overlapping the reflected light containing information from the optical disk 6 on the photodetector 8.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an optical information processing device (optical pickup device) according to an embodiment of the present invention, and FIG.
a) j (b) is a plan view and side view showing the vicinity of the main part (1/4 wavelength plate) of the present invention, FIG. 3 is a schematic configuration diagram showing a conventional optical information processing device, and FIG. 4 is a conventional optical information processing device. FIG. 2 is a schematic configuration diagram showing an example of a case where a 174-wavelength plate is tilted in an optical information processing device of FIG. DESCRIPTION OF SYMBOLS 1...Light source, 2...Collimating lens, 3...Polarizing heam splitter, 4...1/4 wavelength plate, 5...
Objective lens, 6... Optical disk (information recording carrier), ?
...Optical system for detecting focus deviation and track deviation, 8...
・Photodetector. Applicant's agent Patent attorney Takeshi Suzue 2 Figure 1 Figure 3

Claims (2)

[Claims] (1) At least a light source, a collimator lens that transforms the light emitted from the light source into parallel light, a polarizing beam splitter and a quarter-wave plate that transmit the parallel light, and a light that has passed through the quarter-wave plate. An objective lens condenses the light as a minute spot on the information recording carrier, and the light reflected by the information recording carrier and transmitted through a quarter-wave plate and a polarizing beam splitter is photoelectrically converted through an optical system for detecting focus shift and track shift. a photodetector that moves the objective lens in a focal direction and a track deviation direction;
In an optical information processing device where the wave plate is a quarter-wave plate made of quartz crystal and whose crystal axis is inclined with respect to the propagation line on the plate surface, the normal line of the quarter-wave plate is set to the optical axis. optical information processing, characterized in that the quarter-wave plate is tilted parallel to the direction in which the crystal axis is tilted, and the thickness of the quarter-wave plate is set such that linearly polarized light is converted to circularly polarized light at that tilt angle. Device. (2) The optical information processing device according to claim 1, wherein the inclination angle between the normal line and the optical axis is set to about 2 degrees.