JPH0990299A - Polarized wave stabilizing optical circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To convert a polarized wave fluctuating timewisely into a linearly polarized wave and also to maintain a constant polarized state even though an input polarized state is fluctuated. SOLUTION: The polarized state of an input light beam whose polarization plane is timewisely fluctuated is adjusted by a variable polarization rotating means 11 and then an S-polarized wave and a P-polarized wave are separated by inputting the output light beam of the means 11 to an orthogonal polarized wave separating means 12. A polarization control means 20 detects light intensities of the S-polarized wave and the P-polarized wave and controls the variable polarization rotating means 11 so that the light intensity ratio becomes constant. The polarization rotating means 11 performs so that both polarized waves are lined up with each other at the time of combining two waves in a multiplexer means 14 by rotating either the S-polarized wave or the P-polarized wave by 90 degrees. Moreover, a variable phase adjusting means 16 adjusting a phase difference to be generated in between optical paths of the S-polarized wave and the P-polarized wave performs control so that phases of the S-polarized wave and the P-polarized wave coincide with each other by a phase control means 21 monitoring the output light beam of the multiplexer means 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization stabilizing optical circuit for converting input light whose polarization plane changes with time into stable linearly polarized light.

[0002]

2. Description of the Related Art FIG. 5 shows a first example of a conventional polarization stabilizing optical circuit.
An example of the configuration will be described. In the figure, the input light is input to the polarization beam splitter 51 and split into P polarization and S polarization. The P-polarized light and the S-polarized light thus separated are respectively transmitted through the polarization-maintaining optical fibers 52-1 and 52-2 to the polarization-maintaining coupler 5
Combined at 3. At this time, the polarization maintaining optical fiber 52-
By rotating one of 1, 52-2 by 90 degrees, the input light is converted into a linearly polarized wave and the polarization maintaining optical fiber 52-3
Sent to

FIG. 6 shows a second configuration example of a conventional polarization stabilization circuit. In the figure, two electro-optic crystals 54-
1, 54-2 are arranged at an angle of 45 degrees. The birefringence of each electro-optic crystal changes according to the applied voltage. Here, the first electro-optic crystal 54-1 converts an arbitrary elliptically polarized wave into an upright elliptically polarized wave. At the Cartesian coordinates (x ′, y ′) inclined by 45 ° with respect to this polarization state, the relationship of E _x ′ = E _y ′ is established between the components of the electric field. Therefore, by adjusting the birefringence of the second electro-optic crystal 54-2 tilted by 45 degrees with respect to the first electro-optic crystal 54-1, the polarization state is changed to the linear polarization in the x direction or the y direction. Can be converted to.

[0004]

SUMMARY OF THE INVENTION In the first conventional configuration,
When the input polarization state fluctuates with time, the phase of the two polarized waves changes with time, and the light intensity ratio of the two polarizations changes at the same time. Therefore, a coupler with a fixed coupling ratio cannot obtain a stable polarization state, and the output power fluctuates.

In the second conventional configuration, it is necessary to apply a voltage to the electro-optic crystal to convert an arbitrary elliptically polarized wave into an upright elliptically polarized wave. However, in order to control the polarization that fluctuates with time, the control method is complicated and the control is not easy. The present invention provides a polarization stabilizing optical circuit that can convert a polarization that changes with time into a linear polarization and that can maintain a stable polarization state even when the input polarization state changes. With the goal.

[0006]

The polarization stabilizing optical circuit of the present invention adjusts the polarization state of input light whose polarization plane fluctuates with time by a variable polarization rotating means, and outputs its output light by orthogonal polarization. It is input to the wave separation means and separated into S polarization and P polarization. The polarization control means detects the light intensities of the S polarization and the P polarization, and controls the variable polarization rotation means so that the light intensity ratio becomes constant. The polarization rotation means rotates either the S polarization or the P polarization by 90 degrees so that both polarizations are aligned when they are combined by the combining means. Further, the variable phase adjusting means for adjusting the phase difference generated between the optical paths of the S polarization or the P polarization is the phase control means for monitoring the output light of the combining means so that the phases of the S polarization and the P polarization coincide with each other. Control to do.

With such a configuration, even if the polarization plane of the input light fluctuates with time and the phase and light intensity ratio of the S polarization and P polarization separated by the orthogonal polarization change, the variable polarization rotation means. Further, the variable phase adjusting means can keep the light intensity ratio and phase of the S polarization and P polarization constant, and the stable linear polarization can be output from the combining means.

[0008]

1 shows a first embodiment of a polarization stabilizing optical circuit according to the present invention (claim 1). In the figure,
The input light whose plane of polarization fluctuates with time is input to the orthogonal polarization splitting means 12 via the variable polarization rotating means 11 and split into S polarization (vertical polarization) and P polarization (horizontal polarization). To be done. The separated S polarization and P polarization propagate in space,
The two optical paths are configured to be combined by the combining means 14 using the prism 13 or the mirror. S polarization or P
The polarization optical path (here, the S polarization optical path) has a polarization plane of 90
A polarization rotating means 15 for rotating the polarization is inserted, one polarization plane (S polarization) is aligned with the other polarization plane (P polarization), and one linear polarization (P polarization) from the multiplexing means 14 is obtained. It is output to the polarization maintaining optical fiber. In addition, the variable phase adjusting means 1 is provided in the optical path of S polarization or P polarization (here, the optical path of P polarization).
6 is inserted to correct the phase difference between the optical path and the other optical path (optical path of S polarization).

Beam splitters 17-1 and 17-2 are inserted in the respective optical paths of the S-polarized light and the P-polarized light, and the optical intensities of the branched polarizations are detected by the photodetectors 18-1 and 18-2. Each is converted into an electric signal. The two electric signals are input to the logarithmic amplifier 19, and a light intensity ratio signal corresponding to the light intensity ratio of each polarization is given to the polarization control circuit 20. The polarization control circuit 20 controls the polarization state of the input light by adjusting the polarization rotation angle of the variable polarization rotation means 11 so that the light intensity ratio of each polarization becomes constant. Further, the output light of the combining means 14 is converted into an electric signal by the photodetector 18-3 for monitoring and is given to the phase control means 21. The phase control means 21 is the multiplexing means 1
The variable phase adjusting means 16 is controlled so that the output light intensity of No. 4 becomes constant, and the phase difference generated between the optical paths of the S polarization and the P polarization is corrected.

With the above construction, even if the polarization plane of the input light fluctuates with time, and the phase and light intensity ratio of the S polarization and P polarization separated by the orthogonal polarization separating means 12 change, the variable polarization can be changed. The wave rotating means 11 and the variable phase adjusting means 16 keep the light intensity ratio and the phase of the S-polarized light and the P-polarized light constant, and the combining means 1
It is possible to output a stable linear polarized wave (P polarized wave) from No. 4.

FIG. 2 shows a second polarization stabilizing optical circuit according to the present invention.
(Claim 2) is shown. In the present embodiment, the optical paths of the S-polarized light and the P-polarized light separated by the orthogonal polarization are spatial systems in the first embodiment, whereas the polarization-maintaining light is the same as in the conventional configuration shown in FIG. Using fibers 52-1 and 52-2,
As the polarization rotation means 15, one polarization maintaining optical fiber is
It is rotated once and connected to the combining means 14. Moreover, a piezo element is inserted as the variable phase adjustment means 16 to perform phase adjustment utilizing expansion and contraction of the optical fiber. Further, polarization maintaining couplers 53-1, 53-2 and 53-3 are used as the beam splitters 17-1 and 17-2 and the combining means 14, and a part of each polarization is branched and the photodetector 18-. 1, 18-2, 18-
Enter 3

The other configurations and the functions of the respective parts are the same as those of the first embodiment. Even if the polarization plane of the input light fluctuates with time, a stable linearly polarized wave (P Polarization) can be output.

[0013]

EXAMPLE As the variable polarization rotating means 11, for example, a Faraday rotator can be used. In this case, the polarization control circuit 20 adjusts the magnetic field that changes the rotation angle of the Faraday rotator according to the light intensity ratio signal. As the orthogonal polarization separating means 12, for example, a polarization beam splitter or calcite can be used.

As the combining means 14, for example, a half mirror or a polarization maintaining coupler can be used. In addition,
When a half mirror is used, two output ports can be used as shown in FIG. Polarization rotation means 1
For example, a half-wave plate can be used as 5. As the variable phase adjusting means 16, for example, a rotary type phase adjusting plate or a piezo element shown in FIG. 2 can be used.

FIG. 3 shows an embodiment of the phase control means 21. In the figure, the control signal provided from the phase control unit 31 to the variable phase adjusting means 16 is a low frequency signal output from the oscillator 32 and is post-modulated. Photodetector 18-
The output signal of 3 is input to the synchronous detection circuit 33, and the oscillator 3
It is converted to a baseband signal by using the low frequency signal output from 2. This baseband signal is transferred to the phase controller 31.
The output light intensity of the combining means 14 is controlled to be constant by generating a control signal for determining the amount of phase adjustment of the variable phase adjusting means 16 by feeding back to.

FIG. 4 shows the configuration of another embodiment using the polarization stabilizing optical circuit of the present invention. In the figure, linearly polarized light (P polarized light or S polarized light) output from the polarization stabilizing optical circuit 40
Is input to the half-wave plate 41. Since the half-wave plate 41 is a simple tilt angle rotator for linearly polarized waves,
By adjusting the / 2 wavelength plate 41, it is possible to convert to an arbitrary linearly polarized wave.

By realizing each part constituting the polarization stabilizing optical circuit of the present invention described above by an integrated waveguide (PLC), it is possible to reduce the size and facilitate the phase adjustment.

[0018]

As described above, the polarization stabilizing optical circuit of the present invention can obtain stable linear polarization even if the polarization plane of the input light fluctuates with time. Further, it is possible to easily convert light whose polarization plane changes with time into arbitrary linearly polarized light.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a polarization stabilizing optical circuit of the present invention.

FIG. 2 is a diagram showing a second embodiment of a polarization stabilizing optical circuit of the present invention.

FIG. 3 is a block diagram showing the configuration of an embodiment of phase control means 21.

FIG. 4 is a block diagram showing the configuration of another embodiment using the polarization stabilizing optical circuit of the present invention.

FIG. 5 is a diagram showing a first configuration example of a conventional polarization stabilizing optical circuit.

FIG. 6 is a diagram showing a second configuration example of a conventional polarization stabilizing optical circuit.

[Explanation of symbols]

 11 variable polarization rotation means 12 orthogonal polarization separation means 13 prism 14 combining means 15 polarization rotation means 16 variable phase adjustment means 17 beam splitter 18 photodetector 19 logarithmic amplifier 20 polarization control circuit 21 phase control means 31 phase control Part 32 Oscillator 33 Synchronous detection circuit 40 Polarization stabilizing optical circuit 41 1/2 wavelength plate 51 Polarization beam splitter 52 Polarization maintaining optical fiber 53 Polarization maintaining coupler 54 Electro-optic crystal

Claims (5)

[Claims] 1. A variable polarization rotating means for adjusting the polarization state of input light whose polarization plane fluctuates with time, and output light of the variable polarization rotating means for S polarization (vertical polarization) and P polarization. Orthogonal polarization splitting means for splitting into waves (horizontal polarization) and light intensity of the S polarization and P polarization are detected, and the variable polarization rotation means is controlled so that the light intensity ratio becomes constant. Polarization control means, polarization rotation means for rotating one of the S polarization and P polarization by 90 degrees, and variable phase adjustment for adjusting the phase difference generated between the optical paths of the S polarization and P polarization. Means, a combining means for combining two polarized waves through the polarization rotating means and the variable phase adjusting means, and outputting as a linearly polarized wave; and an output light of the combining means for monitoring the S polarization. Wave and P
A polarization stabilizing optical circuit comprising: a phase control unit that controls the variable phase adjustment unit so that the phases of polarized waves match. 2. The polarization stabilizing optical circuit according to claim 1, wherein the polarization rotation means is a polarization maintaining optical fiber that propagates the S polarization and P polarization separated by the orthogonal polarization separation means. 90 for one
A polarization-stabilized optical circuit having a configuration in which the polarized waves at the output ends of each polarization-maintaining optical fiber are aligned by rotating the polarization-stable optical circuit. 3. The polarization stabilizing optical circuit according to claim 1, wherein the phase control means modulates the phase adjusted by the variable phase adjustment means with a low frequency signal, and outputs the output of the multiplexing means with the low frequency signal. A polarization stabilizing optical circuit having a configuration in which a signal is synchronously detected and a phase control amount is set. 4. The polarization stabilizing optical circuit according to claim 1, and a polarization rotation element for converting the S polarization or the P polarization output from the polarization stabilizing optical circuit into an arbitrary linear polarization. A polarization-stabilized optical circuit comprising: 5. A polarization stabilizing optical circuit, wherein each optical component of the polarization stabilizing optical circuit according to claim 1 is formed by an integrated waveguide.