JPH01307726A - Beam splitter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to the configuration of optical components, particularly to the configuration of polarizing elements used in information recording and reading devices on optical discs.

(Prior Art) In recent years, with the increasing sophistication and mass increase in information, various types of data have been stored using magnetic media such as 70-pin discs, magnetic tapes, and optical recording media such as optical discs.
Among these, optical disks have a much larger storage capacity than other storage media, and are therefore popular as various storage media including compact disks.

FIG. 5 (at is a block diagram showing the configuration of optical components of a conventionally used optical disc recording device.

In the figure, reference numeral 1 denotes a laser light source, and a beam of light with an elliptical cross section emitted from the laser light source passes through a beam shaping prism 2. The light enters the beam splitter 3, and a portion of the incident light is reflected by the junction surface of the polarizing beam splitter 3 and enters the monitor light receiver 4.

Most of the P-polarized light that has passed through the polarizing beam splitter 3 becomes circularly polarized light when it passes through the 174-wave plate 5 in the next stage and is irradiated onto the optical disk 6.

Further, the reflected circularly polarized light is reflected based on the information stored in the original disk, and the reflected circularly polarized light passes through the quarter-wave plate 5 again and becomes S.
It becomes polarized light.

Therefore, it is reflected at the joint surface of the polarizing beam splitter 3 in the next stage, enters the reading or servo light receiver 7, and reads the information on the disk.

In the optical system constructed in this way, the above-mentioned monitoring light receiver is used to control the output of the semiconductor laser, and cannot be used with the output tracking device for the laser.

However, the spectral characteristics of a polarizing beam splitter are
The one shown in figure (bl) is common.

In order to obtain the monitor output mentioned above, the transmittance of P-polarized light must be 1.
00% cannot be used.

For example, using a wavelength λ at which the transmittance is about 95%,
This is to obtain the reflected light at the polarizing beam splitter.

Therefore, since the wavelength of the light source is not necessarily constant due to temperature changes, manufacturing variations, etc., the Vi%niter output will fluctuate due to the 1-spectral characteristics where the transmittance varies extremely widely with respect to the wavelength. It was necessary to adjust the monitor output control circuit.

Furthermore, since the spectral characteristics of the polarizing beam splitter vary depending on the manufacturing process, for example, the deposition state of the contact force, there may be a point where the monitor output fluctuates even when the wavelength is constant. Ta.

In order to avoid the above problem, there is also a method of measuring a small amount of light output from the non-emitting side end face opposite to the light emitting end face of the semiconductor laser and using it as a monitor signal for output control, etc. However, there was a drawback in that the reflected light from the nine disks etc. entered the sensor that measured the light from the non-emission side end face of the semiconductor laser, making it impossible to make accurate measurements.

(Object of the invention) The present invention has been made in view of the above-mentioned problems, and includes:
It is an object of the present invention to provide a polarizing beam splitter that can obtain reflections for use in monitor output, etc. by simply adding inexpensive optical components and using a portion of the polarizing beam splitter that is more stable in terms of spectral characteristics.

(Summary of the Invention) In order to achieve the above-mentioned object, the present invention is a beam splitter used for reading optical discs, etc., which has a polarizing element that transmits P-polarized light and reflects S-polarized light. In a polarizing device of the type that obtains a branched output of P-polarized light by reflection at the element, it is configured to include an optical rotator or a wavelength plate for rotating the plane of polarization on the incident optical axis and on the incident side of the polarizing element. do.

(Examples) The present invention will be described in detail below based on the embodiments shown in the drawings.

FIG. 1(a) is a diagram showing the configuration of the present invention. .

In the figure, a 10Fi laser light source, 11 is a beam shaping prism, and a polarizing beam splitter 13 and a polarizing beam splitter 13 and 1/2
4 wavelength plate 14vk: equipped.

A monitor light receiver 15 and an information reading light receiver 16 are provided approximately perpendicularly to the polarizing beam splitter 13.

In the optical system configured in this manner, when P-polarized light having an elliptical cross-section is emitted from the light source 1, the P-polarized light passes through the beam shaping prism 11, where the cross-section becomes circular, and then the optical rotator in the next stage 12 and the output of the optical rotator 12 is shown in Fig. 1(b).
As shown by K, it becomes linearly polarized light rotated by σ. (Here σ
is expressed as θ=ρ·t, where ρ is the optical rotation power of the optical rotator and t is the thickness of the optical rotator in the optical axis direction. ) Therefore, when linearly polarized light having a light intensity of 10 rotated by 0 is incident on the primary stage polarizing beam splitter, Io3
The amount of light i6''t is reflected and enters the light receiver 15.

On the other hand, the next Io-
P with a light amount of Iosin"θ (if is 1/4 of the next stage
A polarizing beam splitter that transmits the 174 wavelength plate 14 and becomes circularly polarized light, which is irradiated onto the optical disc 17, reflected based on the information recorded on the optical disc 17, and then transmitted through the 174 wavelength plate 14 again, which becomes S polarized light. It is reflected by the junction surface of 13 and enters the light receiver 16.

As mentioned above, by rotating the P-polarized light incident on the polarizing beam splitter 13 by θ, reflection as a simulator output is obtained, so a part of the polarizing beam splitter with unstable spectral characteristics is used as conventionally used. No need for second
It can be used with stable wavelength-transmittance characteristics as shown by the solid line in the figure.

Therefore, even if the wavelength of the light source fluctuates by several nanometers due to temperature changes, the amount of reflected light that becomes the monitor output and the amount of light that passes through the polarizing beam splitter are stable, and the manufacturing process of the polarizing beam splitter is also stable.

For example, even if the spectral characteristics vary relative to the wavelength, as shown by the broken line in Figure 3, due to the vapor deposition state or adhesion state of the bonding surface, the transmittance is stable in the range when the wavelength to be used is set. Some λ. If it is set to , it will not be affected by the above-mentioned variations in spectral characteristics due to the manufacturing process of the polarizing beam splitter.

FIG. 4(a) is a diagram showing the configuration of another embodiment of the present invention, and the difference from the embodiment described above is that an optical rotator is replaced with a
This is because a 72 wavelength plate 18 is provided. The 1/2 wavelength plate 18
As shown in Figure 4 (bl).

The optical axis is rotated by α with respect to the polarization axis of the incident P-polarized light, and the polarization plane of the light emitted from the 172-wave plate is a (here θ
= α) Something that rotates it.

Therefore, when light whose polarization plane is σ-rotated and the amount of light I<1 is incident on the first stage polarizing beam splitter 13, l0su''
The amount of light corresponding to σ is reflected at the joint surface, and Io-I@s
The amount of light corresponding to in"θ is transmitted.

Thereafter, since the same operation as in the above-mentioned embodiment is performed, it is possible to obtain the same radiation in the polarizing beam splitter without using a region where the spectral characteristics of the splitter are unstable.

9 In the detailed explanation of the present invention, a polarizing beam splitter was used as a spectroscopic means, but the invention is not limited to this, and a prism or other spectroscopic means may also be used. It is self-evident that the spectrometer is not limited to only the reading unit, but may be used as long as it is used to obtain a P-polarized reflected output used for monitor output, etc. when irradiating 1cP-polarized light with a spectroscopic means having the characteristic of transmitting P-polarized light and reflecting S-polarized light. It is.

(Effects of the Invention) Since the present invention is configured and functions as described above, stable reflected output can be obtained by adding optical components at low cost even if P-polarized light is irradiated onto a spectroscopic means such as a beam splitter. It is possible.

This is more than enough to compensate for the increase in the number of optical parts.

[Brief explanation of the drawing]

FIG. 1(a) is a diagram showing one embodiment of the present invention, and FIG.
) is a diagram showing the optical axis in the optical rotator, Figures 2 and 3 are diagrams showing the relationship between transmittance and wavelength in a polarizing beam splitter, and Figure 4 (a) is a modified embodiment of the present invention. FIG. 4(b) is a diagram showing the human output optical axis and optical axis in a 172-wavelength plate, and FIG. 5(a) is a diagram showing the configuration of a conventionally used device. Figure 5 (bl H is a diagram showing the relationship between transmittance and wavelength in a conventionally used polarizing beam splitter. 1.10......Light source, 2.11...・
...Beam shaping prism, 3.13...
...Polarizing beam splitter, 4,7,
15.16......Receiver, 5.1
4・・・・・・・・・1/4 wavelength plate. 6.17...Optical disc, 12.
・・・・・・・・・Polarization, 18・・・・・・・・・
・1/2 wavelength plate. Patent applicant: Toyo Tsushinki Co., Ltd. Figure 2 Figure 3 vR Conclusion) Figure 3

Claims (1)

[Claims] In a polarizing device of a type that has a polarizing element that transmits P-polarized light and reflects S-polarized light, and obtains a P-polarized light branched output by reflection in the polarizing element, on the incident optical axis and on the incident side of the polarizing element. A beam splitter characterized in that it is equipped with an optical rotator or a wavelength plate for rotating the plane of polarization.