JPH0389209A - Polarization controller - Google Patents

Abstract

PURPOSE:To obtain the polarization controller which consists of a small number of components and has good controllability by providing an analyzer whose transmission axis direction is set as specified and a photodetector which photodetects its transmitted light and controlling phase compensators so that the quantity of photodetection is maximum and minimum. CONSTITUTION:This polarization controller is provided with the analyzer 4 which is arranged without having its transmission axis direction in the main-axis direction of the phase compensators 1 and 2, the photodetector 5 which detects monitor light 13 passed through the analyzer 4, and a controller 6 which inputs its detection output and controls the compensators 1 and 2 to maximize and minimize the output of the detector 5. In this constitution, the polarization main axis azimuth angle of incident light 11 is put on an X or Y axis by eliminating a phase difference given by the compensator 2 firstly, photodetecting the quantity of the monitor light 13 transmitted through the analyzer 4 by the detector 5, and controlling the compensator 1 by the controller 6 so as to give a phase difference deltamax or deltamin maximizing or minimizing the quantity of light.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a polarization control device that converts incident light whose polarization is unknown into polarization whose polarization is known.

[Conventional technology] Next, the elliptical diagram of the conventional device will be explained with reference to FIG.

1 and 2 in Fig. 2 are phase compensators, 3 is a beam splitter,
11 is incident light, 12 is output light, 13 is monitor light, 21 is beam splitter, 22 is Wollaston prism, 23
and 24 are photodetectors, 25 is a controller, 31 is a 174 wavelength plate, 32 is a Wollaston prism, 33 and 34 are photodetectors, and 35 is a controller.

After passing through the phase compensators 1 and 2, the incident light 11 is separated by the beam splitter 3 into an output light 12 and a monitor light 13.

The phase compensators 1 and 2 include those that give a phase difference to light components in the same direction as the two orthogonal birefringence axes of the birefringent crystal by passing through the birefringent crystal, and those that give distortion to glass, etc. A device that provides a phase difference using the photoelastic effect caused by this is used.

Those using birefringent crystals change the phase difference by changing the thickness of the crystal. These include Babinet-Soleil compensators and the like. Those using the photoelastic effect change the phase difference by changing the amount of strain. This includes a Rayleigh compensator and the like.

The monitor light 13 is further split into two monitor lights 14 and 15 by a beam splitter 21.

The monitor light 14 is separated into two orthogonal polarization components by the Wollaston prism 22, and the photodetectors 23 and 24 and the control unit 25 detect the power difference between the orthogonal polarization components to control the phase compensator 1.

The monitor light 15 passes through the quarter-wave plate 31, is separated into two orthogonal polarization components by the Wollaston prism 32, and the power difference between the orthogonal polarization components is detected by the photodetectors 33 and 34 and the control unit 35. to control the phase compensator 2.

The principal axes of the two phase compensators 1 and 2 are arranged at an angle of 45° with respect to each other.

Further, the main axis directions of the two Wollaston prisms 22 and 32 are also arranged at an angle of 45° with respect to each other, and the main axis direction of the Wollaston prism 22 is arranged to coincide with the main axis direction of the quarter-wave plate 31.

The outputs of the photodetectors 23 and 24 are input to the control unit 8, and the output difference between them is made to be "0".

That is, the phase compensator 1 is controlled so that the difference between the orthogonal polarization components of the completed monitor 4 becomes r□.

Thereby, the direction of the principal axis of polarization of the incident light 11 can be made to match the direction of the principal axis of the Wollaston prism 32.

The outputs of the photodetectors 33 and 34 enter the control section 35, which controls the phase compensator 2 so that the output difference becomes r□. Thereby, the incident light 11 is controlled to be linearly polarized light.

[Problems to be Solved by the Invention] In the prior art shown in FIG. 2, since the axial directions of the prisms, etc. are fixed, it is difficult to adjust the optical system.

Furthermore, since many beam splitters and Wollaston prisms are used, the input power to the photodetector is considerably smaller than the power of the incident light 11, resulting in problems such as poor control accuracy.

As a system for detecting changes in the polarization state, this invention includes an analyzer whose transmission axis direction is arranged so as not to overlap the main axis direction of two phase compensators, and a photodetector that receives the light transmitted by the analyzer. The present invention aims to provide a polarization control device with a simple configuration by adjusting two phase compensators so that the amount of received light becomes maximum and minimum.

[Means for Solving the Problems] In order to achieve this object, in the present invention, the incident light 11
a first phase compensator l that gives a phase difference to the first phase compensator 1; a phase compensator 2, and a beam splitter 3 that separates the incident light 11 that has passed through the second phase compensator 2 into output light 12 and monitor light 13.
In a polarization control device having 2
an analyzer 4 that converts the polarization control state by the phase compensator 2 into a light amount; a photodetector 5 that detects the monitor light 13 that has passed through the analyzer 4; By controlling the phase compensator 1 and the second phase compensator 2, the photodetector 5
and a controller 6 that maximizes and minimizes the output of t3.

Next, an elliptical diagram of the polarization control device according to the present invention will be explained with reference to FIG.

1 is an analyzer, 5 is a photodetector, 6 is a controller, and the other parts are the same as in FIG. 2.

In FIG. 1 as well, after the incident light 11 passes through the phase compensator 1.2, the beam splitter 3 separates the output light 12 and the monitor light 13.
It can be divided into

After the monitor light 13 passes through the analyzer 4, it is photoelectrically converted by the photodetector 5, enters the control section 6, and is outputted to the phase compensators 1 and 2 by the control section 6.
is controlled.

[Operation] Next, the operation of the phase compensators 1 and 2 will be explained with reference to FIG.

FIG. 3 shows the direction of the birefringence axis of the phase compensator 1 in the X-axis direction,
The birefringence axis direction of the phase compensator 2 is set at 145° with respect to the birefringence axis direction of the phase compensator 1, and the transmission axis direction of the analyzer 4 is set at α° with respect to the X-axis direction.

However, the birefringence axis direction of the phase compensator 2 is
It may be +45° with respect to the birefringence axis direction.

Furthermore, the direction α° of the transmission axis of the analyzer 4 is determined by the phase compensator 1.
Any value may be used as long as it does not overlap with the direction of the birefringence axis of No. 2. The reason for this will be explained with reference to FIG.

FIG. 4 shows part of the process of change in polarization state when the amount of phase compensation of a phase compensator having a birefringence axis on the X axis is changed.

At this time, the amount of light transmitted through the analyzer 4 is proportional to the square of the component in the transmission axis direction of the analyzer 4.

For example, in polarization state A, it is "OA", and in polarization state B, it is proportional to the square of rOB.

Therefore, when the transmission axis of the analyzer 4 overlaps with the X axis, that is, when it overlaps with the birefringence axis of the phase compensator, the amount of light passing through the analyzer 4 is always constant and does not change.
The transmission axis direction of the analyzer 4 and the birefringence axis direction of the phase compensator are
It is necessary to avoid overlapping.

[Example] Next, the transmission axis direction of the analyzer 4 in FIG.
The effect when fixed within a range of 5° is shown in Figure 1 from Figure 5.
This will be explained using Figure 1.

FIG. 5 is an example in which the incident light 11 is arbitrary elliptically polarized light.

FIG. 6 shows the polarization state when the phase difference of the incident light 11 is changed by the phase compensator l, and the polarization state is controlled so that the principal axis azimuth of the polarized light is overlapped on the X axis or the Y axis, and FIG. It is a figure which shows the example of a change of the light quantity of the monitor light 13 at that time.

To superimpose the polarization principal axis azimuth of the incident light 11 on the X-axis or the Y-axis, first, the phase difference given by the phase compensator 2 is set to zero, and the light intensity of the monitor light 13 transmitted through the analyzer 4 is measured by the photodetector 5. The control unit 6 controls the phase compensator 1 so as to provide a phase difference δ□8 that maximizes the amount of light or a phase difference δ0 that minimizes the amount of light.

At this time, the polarization state of the incident light 11 becomes linearly polarized light as shown in FIG. 8 when the amount of light received by the photodetector 5 is the maximum, and becomes linearly polarized light as shown in FIG. 9 when the amount of light received by the photodetector 5 is the minimum.

Next, when the amount of light received by the photodetector 5 is maximum, that is, when the polarization state is linearly polarized light as shown in FIG.
The phase difference given by is set to (δ□8−π/2).

In addition, in the minimum case, the given phase difference is (δ□9+π
/2), it is possible to obtain clockwise elliptically polarized light whose principal axis of polarization azimuth overlaps on the X-axis or the Y-axis as shown in FIG.

However, assuming that the phase difference given when the output of the photodetector 5 is maximum is (δIIIAX+π/2) and the phase difference given when it is minimum is (δ, 9−π/2), the polarization principal axis azimuth is on the X axis. Alternatively, it may be a counterclockwise elliptically polarized light that overlaps on the Y axis.

FIG. 10 shows that the phase compensator 2 gives a phase difference in the direction of +45° or -45° to the incident light 11 controlled as shown in FIG. light 11
This figure shows part of the process by which the polarization of light changes.

For example, if the birefringence axis direction of the phase compensator 2 is -45°,
As the phase difference is increased by the phase compensator 2 from the polarization state shown in FIG. The light becomes linearly polarized in the X-axis direction.

However, when decreasing the phase difference with phase compensator 2,
The polarization state changes from the state shown in FIG. 6 to the state shown in FIG. 11, and when the amount of light reaches the minimum, the light becomes right-edge polarized in the Y-axis direction.

[Effect of the invention] According to this invention, there are the following effects.

(a) The configuration becomes easier.

(a) The optical system requires only an analyzer and a beam splitter, and its axial adjustment is not difficult.

(1) It has a small number of parts and is inexpensive.

(1) Since the detection system includes only an analyzer and a photodetector, the amount of light split into monitor light by the beam splitter may be small.

[Brief explanation of drawings]

FIG. 1 is a polarization control device according to the present invention, FIG. 2 is a configuration diagram of a conventional device, and FIG. 3 is an explanatory diagram of the operation of phase compensators 1 and 2.
Figure 4 is a diagram of how the polarization state changes when the phase compensation amount of a phase compensator with a birefringence axis on the Axial direction is Oo
It is an explanatory view of the effect in the case of 45 degrees. 1... Phase compensator, 2... Phase compensator, 3... Beam splitter, 4... Analyzer, 5... Light Detector, 6... Control section.

Claims (1)

[Claims] 1. A first phase compensator (1) that provides a phase difference to the incident light (11); and a first phase compensator (1) that provides a phase difference to the incident light (11); A second phase compensator (2) provides a phase difference of 45° with respect to the first phase compensator (1), and the incident light (11) that has passed through the second phase compensator (2) is converted into output light. (12) and a beam splitter (3) that separates the monitor light (13) into The first phase compensator (1) and the second phase compensator (2) are arranged at positions where the transmission axis directions do not overlap.
A photodetector (5) that detects the monitor light (13) that has passed through the analyzer (4), and inputs the output of the photodetector (5). and the first phase compensator (
1) and the second phase compensator (2) to control the photodetector (5).
) and a controller (6) that maximizes and minimizes the output of the polarization controller.