RU2725144C1 - Method of controlling a fiber-optic polarization controller - Google Patents

Abstract

FIELD: fiber optic equipment.SUBSTANCE: invention relates to fiber-optic equipment. According to the method of controlling a fiber-optic polarization controller, optical radiation is supplied to the input of the optical fiber, into which three birefringent elements of the fiber-optic polarization controller are connected in series, to each of which a mechanical load is applied, which is controlled by signals coming from the control unit, a feedback signal is sent to the input of the control unit, which is formed by selecting a portion of the optical radiation passing through the fiber-optic polarization controller, for which from the output of the fiber-optic polarization controller using an optical coupler, selecting a portion of the optical radiation, said extracted part of optical radiation is supplied to a linear optical polariser, from the output of which optical radiation is supplied to the input of the photodetector, in which a feedback signal is generated, which is transmitted to the input of the control unit, where the polarization state of the optical radiation at the output of the fiber-optic polarization controller is controlled, and based on the results of processing signals coming from the feedback circuit, generating signals which control the mechanical load applied to the birefringent elements of the fiber-optic polarization controller so as to provide a given polarization state of the optical radiation at the output of the fiber-optic polarization controller, note here that birefringent elements of fiber-optic polarization controller are calibrated.EFFECT: invention is intended to control polarization state of optical radiation at output of fiber-optic polarization controller.1 cl, 1 dwg

Description

The invention relates to fiber optic technology and is intended to control the state of polarization of optical radiation at the output of a fiber optic polarization controller and can be used to determine the polarization state of optical radiation at its input.

A known method of controlling a fiber-optic polarization controller [1], which consists in the fact that optical radiation is fed to the input of the optical fiber, to three sections of which are applied radial loads from the unit for forming and monitoring the load applied to the optical fiber, control these radial loads, control the state polarization at the output of the fiber optic polarization controller and change the radial loads applied to the optical fiber according to the results of monitoring the state of polarization at the output of the fiber optic polarization controller. This method does not allow to determine the polarization state at the input of the fiber-optic polarization controller, as well as the influence of the voltage applied to a separate section on the polarization state of the optical radiation at the output of the fiber-optic polarization controller from the radial load applied to one of the three sections of the optical fiber. As a result, a given state of polarization of the optical radiation at the output of the fiber-optic polarization controller is obtained by sorting out the combinations of radial loads applied to the three above-mentioned sections of the optical fiber of the fiber-optic controller.

A known method of controlling a fiber-optic polarization controller [2], which consists in the fact that the optical radiation is fed to the input of the optical fiber, which consistently includes three birefringent elements of the fiber-optic polarization controller, to each of which a mechanical load is applied, which is controlled by signals, coming from the control unit, and feedback signals are fed to the inputs of the control unit, which form, isolating part of the optical radiation passing through the fiber-optic polarization controller. To this end, from the output of each of the birefringent elements of the fiber-optic polarization controller using an optical coupler, a part of the optical radiation is extracted, this extracted part of the optical radiation is fed to a linear optical polarizer, from the output of which the optical radiation is fed to the input of the photodetector, in which a feedback signal is generated, which is fed to the corresponding input of the control unit, where changes in the state of polarization of optical radiation are monitored at the output of each of the birefringent elements of the fiber-optic polarization controller, and according to the results of processing these changes, signals are generated that regulate the mechanical load applied to the birefringent elements of the fiber-optic polarization controller , so as to provide a given state of polarization of the optical radiation at the output of the fiber optic polarization controller. To implement this method, three feedback circuits are required, and, accordingly, an optical coupler, three linear optical polarizers and three photodetectors, which significantly complicates the implementation of the method, increases its cost, and, as a result, limits its scope.

The essence of the alleged invention is the expansion of the scope.

на каждом из двулучепреломляющих элементов от уровня сигнала блока управления, регулирующего механическую нагрузку, прикладываемую к этому двулучепреломляющему элементу, и запоминают их, затем последовательно устанавливают следующие восемь комбинаций значений фазовых сдвигов оптического излучения на двулучепреломляющих элементах

– (0, 0, 0), (0, π, 0), (0, π/2, π/2), (0, π/2, 3π/2), (π/2, π/2,0), (π/2, 3π/2, 0), (0, 3π/2, 0), (0, π/2, 0), определяют и запоминают значения оптической мощности, поступающей на фотоприемник для каждой из указанных комбинаций, после чего определяют состояние поляризации оптического излучения на входе волоконно-оптического контроллера поляризации, вычисляя ориентацию оси линейного поляризатора и параметры вектора стокса по формулам:This essence is achieved by the fact that, according to the method of controlling the fiber-optic polarization controller, which means that the optical radiation is fed to the input of the optical fiber, in which three birefringent elements of the fiber-optic polarization controller are sequentially connected, to each of which a mechanical load is applied, which is regulated by signals from the control unit, a feedback signal is supplied to the input of the control unit, which form a part of the optical radiation that passes through the fiber-optic polarization controller, for which part of the optical radiation is isolated from the output of the fiber-optic polarization controller using an optical coupler , this selected part of the optical radiation is fed to a linear optical polarizer, from the output of which optical radiation is fed to the input of the photodetector, in which a feedback signal is generated, which is fed to the input of the control unit, where the measurement the state of the polarization of optical radiation at the output of the fiber-optic polarization controller and, based on the results of processing the signals received from the feedback circuit, form signals that regulate the mechanical load applied to the birefringent elements of the fiber-optic polarization controller so as to provide a given state of polarization of the optical radiation at the output of the fiber-optic polarization controller, at the same time, the birefringent elements of the fiber-optic polarization controller are pre-calibrated, for which, successively for each birefringent element of the fiber-optic polarization controller, at fixed signal levels of the control unit that regulate the mechanical load applied to the other two birefringent elements, they are removed the dependence of the optical power supplied to the photodetector on the signal level of the control unit that regulates the mechanical load applied to this two refractive element, which is used to construct the dependences of the phase shift of optical radiation

on each of the birefringent elements from the signal level of the control unit that regulates the mechanical load applied to this birefringent element, and remember them, then sequentially establish the following eight combinations of values of the phase shifts of the optical radiation on the birefringent elements

- (0, 0, 0), (0, π, 0), (0, π / 2, π / 2), (0, π / 2, 3π / 2), (π / 2, π / 2, 0), (π / 2, 3π / 2, 0), (0, 3π / 2, 0), (0, π / 2, 0), determine and store the values of optical power supplied to the photodetector for each of these combinations and then determine the polarization state of the optical radiation at the input of the fiber-optic polarization controller, calculating the orientation of the axis of the linear polarizer and the parameters of the Stokes vector by the formulas:

, $$2\varphi =\arctan \left(\frac{P\left\{0\pi /2,\pi /2\right\}-P\left\{0\pi /2,3\pi /2\right\}}{P\left\{\mathrm{0,0,0}\right\}-P\left\{0\pi 0\right\}}\right)$$

,

, $${\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_1=\frac{P\left\{\mathrm{0,0,0}\right\}-P\left\{0\pi 0\right\}}{\cos \left(2\varphi \right)}$$

,

, $${\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_2=\frac{P\left\{\pi /2,\pi /20\right\}-P\left\{\pi /2,3\pi /20\right\}}{\cos \left(2\varphi \right)}$$

,

, $${\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_3=\frac{P\left\{03\pi /20\right\}-P\left\{0\pi /20\right\}}{\cos \left(2\varphi \right)}$$

,

- мощность на входе фотоприемника для соответствующей комбинации фазовых задержек на элементах двулучепреломления

, - затем, решая систему уравнений:Where $$P\left\{{\theta }_1,{\mathrm{<figure-callout\; id="2"\; label="\theta "\; filenames="00000026.png"\; state="\{\{state\}\}">\theta </figure-callout>}}_2,{\theta }_3\right\}$$

- power at the input of the photodetector for the corresponding combination of phase delays on the elements of birefringence

, - then, solving the system of equations:

, определяют значения фазовой задержки двулучепреломляющих элементов контроллера поляризации, при которых исходное состояние поляризации оптического излучения $$S_{}^{вх}=\left[s_0^{вх},s_1^{вх},s_2^{вх},s_3^{вх}\right]$$

преобразуется в требуемое $$S_{}^{вых}=\left[s_0^{вых},s_1^{вых},s_2^{вых},s_3^{вых}\right]$$

, по результатам калибровки определяют уровни сигнала блока управления, которые соответствуют этим значениям фазовой задержки двулучепреломляющих элементов контроллера поляризации, и устанавливают их. $$\{\begin{array}{l}{\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_1^{\mathrm{in}sx}={\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_1^{\mathrm{in}x}\cos \left({\theta }_2\right)+{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_2^{\mathrm{in}x}\sin \left({\theta }_1\right)\sin \left({\theta }_2\right)-{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_3^{\mathrm{in}x}\cos \left({\theta }_1\right)\sin \left({\theta }_2\right)\\ {\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_2^{\mathrm{in}sx}={\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_1^{\mathrm{in}x}\sin \left({\theta }_2\right)\sin \left({\theta }_3\right)+{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_2^{\mathrm{in}x}\left[\cos \left({\theta }_1\right)\cos \left({\theta }_3\right)-\sin \left({\theta }_1\right)\cos \left({\theta }_2\right)\sin \left({\theta }_3\right)\right]+\\ +{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_3^{\mathrm{in}x}\left[\sin \left({\theta }_1\right)\cos \left({\theta }_3\right)+\cos \left({\theta }_1\right)\cos \left({\theta }_2\right)\sin \left({\theta }_3\right)\right]\\ {\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_3^{\mathrm{in}sx}={\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_1^{\mathrm{in}x}\sin \left({\theta }_2\right)\cos \left({\theta }_3\right)-{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_2^{\mathrm{in}x}\left[\cos \left({\theta }_1\right)\sin \left({\theta }_3\right)+\sin \left({\theta }_1\right)\cos \left({\theta }_2\right)\cos \left({\theta }_3\right)\right]+\\ +{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_3^{\mathrm{in}x}\left[\cos \left({\theta }_1\right)\cos \left({\theta }_2\right)\cos \left({\theta }_3\right)-\sin \left({\theta }_1\right)\sin \left({\theta }_3\right)\right]\end{array}$$

determine the phase delay values of birefringent elements of the polarization controller, at which the initial state of polarization of the optical radiation $$S_{}^{\mathrm{in}x}=\left[s_0^{\mathrm{in}x},{\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_1^{\mathrm{in}x},{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_2^{\mathrm{in}x},{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_3^{\mathrm{in}x}\right]$$

converted to required $$S_{}^{\mathrm{in}sx}=\left[s_0^{\mathrm{in}sx},{\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_1^{\mathrm{in}sx},{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_2^{\mathrm{in}sx},{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_3^{\mathrm{in}sx}\right]$$

, the calibration results determine the signal levels of the control unit, which correspond to these phase delay values of birefringent elements of the polarization controller, and set them.

The drawing shows a structural diagram of a device for implementing the proposed method.

The device contains a fiber-optic polarization controller 1, the optical fiber 2 of which is connected in series with the first 3, second 4, and third 5 birefringent elements connected, respectively, with the first 6, second 7, and third 8 elements that convert electrical signals to mechanical load, a control unit 9, an optical coupler 10, a linear polarizer 11 and a photodetector 12. Moreover, the first birefringent element 3 is connected to the first element 6 that converts the electrical signals into mechanical load, the second birefringent element 4 is connected to the second element 7 that converts the electrical signals into mechanical load, and the third birefringent element 5 is connected to the third element 8, which converts the electrical signals into mechanical load. In this case, the optical fiber 2 of the optical fiber polarization controller 1 at the output of the optical fiber polarization controller 1 is connected to the input of the optical coupler 10, the second output of which is connected to the input of the linear polarizer 11, and the output of the linear polarizer 11 is connected to the input of the photodetector 12. Photodetector output 12 is connected to the input of the control unit 9, the first, second and third outputs of which are connected, respectively, to the inputs of the first 6, second 7 and third 8 elements that convert electrical signals into mechanical load.

– (0, 0, 0), (0, π, 0), (0, π/2, π/2), (0, π/2, 3π/2), (π/2, π/2,0), (π/2, 3π/2, 0), (0, 3π/2, 0), (0, π/2, 0), при этом определяются и запоминаются значения оптической мощности, поступающей на фотоприемник для каждой из указанных комбинаций, после чего определяется состояние поляризации оптического излучения на входе волоконно-оптического контроллера поляризации в результате вычислений в блоке управления 9 ориентации оси линейного поляризатора и параметров вектора Стокса по формулам:The method is as follows. Optical radiation through the optical fiber 2 of the optical fiber polarization controller 1 is supplied sequentially through the first 3, second 4 and third 5 birefringent elements, and then through the optical fiber 2 of the optical fiber polarization controller 1 and the optical coupler 10 to the first output of the optical coupler 10, which is the output of the fiber-optic polarization controller 1. A part of the optical radiation (up to 5% of the total power) in the optical coupler 10 is coupled to the second output of the optical coupler 10 and through the linear polarizer 11 to the input of the photodetector 12, which converts the optical signal into electrical. An electrical signal from the output of the photodetector is fed to the input of the photodetector 12 and fed to the input of the control unit 9, in which, as a result of processing this signal, the value of the optical radiation power level at the input of the photodetector 12 is determined and stored. Previously, the fiber optic birefringent elements are calibrated according to the program of the control unit optical polarization controller. At the same time, for each birefringent element of the fiber-optic polarization controller at fixed signal levels of the control unit that regulate the mechanical load applied to the other two birefringent elements, the dependence of the optical power supplied to the photodetector on the signal level of the control unit that regulates the mechanical load applied to this birefringent element, which is used to construct and memorize the dependences of the phase shift of the optical radiation θ _i on each of the birefringent elements on the signal level of the control unit that regulates the mechanical load applied to this birefringent element. Then, the following eight combinations of phase shifts of the optical radiation on birefringent elements are sequentially established

- (0, 0, 0), (0, π, 0), (0, π / 2, π / 2), (0, π / 2, 3π / 2), (π / 2, π / 2, 0), (π / 2, 3π / 2, 0), (0, 3π / 2, 0), (0, π / 2, 0), and the values of the optical power supplied to the photodetector for each of them are determined and stored these combinations, after which the polarization state of the optical radiation at the input of the fiber-optic polarization controller is determined as a result of calculations in the control unit 9 of the orientation of the axis of the linear polarizer and the parameters of the Stokes vector according to the formulas:

, $$2\varphi =\arctan \left(\frac{P\left\{0\pi /2,\pi /2\right\}-P\left\{0\pi /2,3\pi /2\right\}}{P\left\{\mathrm{0,0,0}\right\}-P\left\{0\pi 0\right\}}\right)$$

,

, $${\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_1=\frac{P\left\{\mathrm{0,0,0}\right\}-P\left\{0\pi 0\right\}}{\cos \left(2\varphi \right)}$$

,

, $${\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_2=\frac{P\left\{\pi /2,\pi /20\right\}-P\left\{\pi /2,3\pi /20\right\}}{\cos \left(2\varphi \right)}$$

,

, $${\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_3=\frac{P\left\{03\pi /20\right\}-P\left\{0\pi /20\right\}}{\cos \left(2\varphi \right)}$$

,

- мощность на входе фотоприемника для соответствующей комбинации фазовых задержек на элементах двулучепреломления

, затем, путем решения системы уравнений:Where $$P\left\{{\theta }_1,{\mathrm{<figure-callout\; id="2"\; label="\theta "\; filenames="00000026.png"\; state="\{\{state\}\}">\theta </figure-callout>}}_2,{\theta }_3\right\}$$

- power at the input of the photodetector for the corresponding combination of phase delays on the elements of birefringence

, then, by solving the system of equations:

, определяются значения фазовой задержки двулучепреломляющих элементов контроллера поляризации, при которых исходное состояние поляризации оптического излучения $$S_{}^{вх}=\left[s_0^{вх},s_1^{вх},s_2^{вх},s_3^{вх}\right]$$

преобразуется в требуемое $$S_{}^{вых}=\left[s_0^{вых},s_1^{вых},s_2^{вых},s_3^{вых}\right]$$

, по результатам калибровки определяются уровни сигнала блока управления, которые соответствуют этим значениям фазовой задержки двулучепреломляющих элементов контроллера поляризации, после чего устанавливаются эти уровни сигналов блока управления. $$\{\begin{array}{l}{\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_1^{\mathrm{in}sx}={\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_1^{\mathrm{in}x}\cos \left({\theta }_2\right)+{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_2^{\mathrm{in}x}\sin \left({\theta }_1\right)\sin \left({\theta }_2\right)-{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_3^{\mathrm{in}x}\cos \left({\theta }_1\right)\sin \left({\theta }_2\right)\\ {\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_2^{\mathrm{in}sx}={\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_1^{\mathrm{in}x}\sin \left({\theta }_2\right)\sin \left({\theta }_3\right)+{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_2^{\mathrm{in}x}\left[\cos \left({\theta }_1\right)\cos \left({\theta }_3\right)-\sin \left({\theta }_1\right)\cos \left({\theta }_2\right)\sin \left({\theta }_3\right)\right]+\\ +{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_3^{\mathrm{in}x}\left[\sin \left({\theta }_1\right)\cos \left({\theta }_3\right)+\cos \left({\theta }_1\right)\cos \left({\theta }_2\right)\sin \left({\theta }_3\right)\right]\\ {\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_3^{\mathrm{in}sx}={\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_1^{\mathrm{in}x}\sin \left({\theta }_2\right)\cos \left({\theta }_3\right)-{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_2^{\mathrm{in}x}\left[\cos \left({\theta }_1\right)\sin \left({\theta }_3\right)+\sin \left({\theta }_1\right)\cos \left({\theta }_2\right)\cos \left({\theta }_3\right)\right]+\\ +{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_3^{\mathrm{in}x}\left[\cos \left({\theta }_1\right)\cos \left({\theta }_2\right)\cos \left({\theta }_3\right)-\sin \left({\theta }_1\right)\sin \left({\theta }_3\right)\right]\end{array}$$

, the phase delay values of birefringent elements of the polarization controller are determined, at which the initial state of polarization of the optical radiation $$S_{}^{\mathrm{in}x}=\left[s_0^{\mathrm{in}x},{\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_1^{\mathrm{in}x},{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_2^{\mathrm{in}x},{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_3^{\mathrm{in}x}\right]$$

converted to required $$S_{}^{\mathrm{in}sx}=\left[s_0^{\mathrm{in}sx},{\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_1^{\mathrm{in}sx},{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_2^{\mathrm{in}sx},{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="00000026.png"\; state="\{\{state\}\}">s</figure-callout>}}_3^{\mathrm{in}sx}\right]$$

, the calibration results determine the signal levels of the control unit that correspond to these phase delay values of the birefringent elements of the polarization controller, after which these signal levels of the control unit are set.

In contrast to the known method, which is the prototype, to implement the method requires three times less elements such as optical couplers, linear polarizers and photodetectors, and a less complex scheme is used. This simplifies the implementation of the method and reduces its cost in comparison with the prototype, which, as a result, expands the scope of the method.

LITERATURE

1. US 6885782 B2.

2US 6552836 B2.

Claims (7)

A method of controlling a fiber-optic polarization controller, namely, that optical radiation is supplied to the input of an optical fiber, in which three birefringent elements of a fiber-optic polarization controller are sequentially connected, to each of which a mechanical load is applied, which is regulated by signals from the control unit , a feedback signal is fed to the input of the control unit, which is formed by extracting part of the optical radiation passing through the fiber-optic polarization controller, for which a part of the optical radiation is extracted from the output of the fiber-optic polarization controller using an optical coupler, this distinguished part of the optical radiation is fed to a linear optical polarizer, from the output of which optical radiation is fed to the input of the photodetector, in which a feedback signal is generated, which is fed to the input of the control unit, where changes in the polarization state of the optical radiation are controlled At the output of the fiber-optic polarization controller and, based on the results of processing the signals received from the feedback circuit, signals are generated that control the mechanical load applied to the birefringent elements of the fiber-optic polarization controller so as to provide a given state of polarization of the optical radiation at the output of the fiber-optic polarization controller, characterized in that the birefringent elements of the fiber-optic polarization controller are pre-calibrated, for which, successively for each birefringent element of the fiber-optic polarization controller, at fixed signal levels of the control unit that regulate the mechanical load applied to the two other birefringent elements, the dependence of the optical the power supplied to the photodetector from the signal level of the control unit that regulates the mechanical load applied to this birefringent element, according to To build the dependence of the phase shift of the optical radiation

on each of the birefringent elements from the signal level of the control unit that regulates the mechanical load applied to this birefringent element, and remember them, then sequentially establish the following eight combinations of values of the phase shifts of the optical radiation on the birefringent elements

- (0,0,0), (0, $$\pi$$

, 0), (0, $$\pi$$

/ 2, $$\pi$$

/20, $$\pi$$

/ 2, 3 $$\pi$$

/ 2), ( $$\pi$$

/ 2, $$\pi$$

/20), ( $$\pi$$

/ 2, 3 $$\pi$$

/ 2, 0), (0, 3 $$\pi$$

/ 2, 0), (0, $$\pi$$

/ 2, 0), determine and store the values of the optical power supplied to the photodetector for each of these combinations, after which the polarization state of the optical radiation at the input of the fiber-optic polarization controller is determined by calculating the orientation of the linear polarizer axis and the Stokes vector parameters using the formulas: $$2\varphi =\arctan \left(\frac{P\left\{0\pi /2,\pi /2\right\}-P\left\{0\pi /2,3\pi /2\right\}}{P\left\{\mathrm{0,0,0}\right\}-P\left\{0\pi 0\right\}}\right)$$

, $$s_1=\frac{P\left\{\mathrm{0,0,0}\right\}-P\left\{0\pi 0\right\}}{\cos \left(2\varphi \right)}$$

, $$s_2=\frac{P\left\{\pi /2,\pi /20\right\}-P\left\{\pi /2,3\pi /20\right\}}{\cos \left(2\varphi \right)}$$

, $$s_3=\frac{P\left\{03\pi /20\right\}-P\left\{0\pi /20\right\}}{\cos \left(2\varphi \right)}$$

, Where $$P\left\{{\theta }_1,{\theta }_2,{\theta }_3\right\}$$

- power at the input of the photodetector for the corresponding combination of phase delays on the elements of birefringence

, then, solving the system of equations: $$\{\begin{array}{l}{s}_1^{\mathrm{in}sx}=s_1^{\mathrm{in}x}\cos \left({\theta }_2\right)+s_2^{\mathrm{in}x}\sin \left({\theta }_1\right)\sin \left({\theta }_2\right)-s_3^{\mathrm{in}x}\cos \left({\theta }_1\right)\sin \left({\theta }_2\right)\\ s_2^{\mathrm{in}sx}=s_1^{\mathrm{in}x}\sin \left({\theta }_2\right)\sin \left({\theta }_3\right)+s_2^{\mathrm{in}x}\left[\cos \left({\theta }_1\right)\cos \left({\theta }_3\right)-\sin \left({\theta }_1\right)\cos \left({\theta }_2\right)\sin \left({\theta }_3\right)\right]+\\ +s_3^{\mathrm{in}x}\left[\sin \left({\theta }_1\right)\cos \left({\theta }_3\right)+\cos \left({\theta }_1\right)\cos \left({\theta }_2\right)\sin \left({\theta }_3\right)\right]\\ s_3^{\mathrm{in}sx}=s_1^{\mathrm{in}x}\sin \left({\theta }_2\right)\cos \left({\theta }_3\right)-s_2^{\mathrm{in}x}\left[\cos \left({\theta }_1\right)\sin \left({\theta }_3\right)+\sin \left({\theta }_1\right)\cos \left({\theta }_2\right)\cos \left({\theta }_3\right)\right]+\\ +s_3^{\mathrm{in}x}\left[\cos \left({\theta }_1\right)\cos \left({\theta }_2\right)\cos \left({\theta }_3\right)-\sin \left({\theta }_1\right)\sin \left({\theta }_3\right)\right]\end{array}$$

determine the phase delay values of birefringent elements of the polarization controller, at which the initial state of polarization of the optical radiation $$S_{}^{\mathrm{in}x}=\left[s_0^{\mathrm{in}x},s_1^{\mathrm{in}x},s_2^{\mathrm{in}x},s_3^{\mathrm{in}x}\right]$$

converted to required $$S_{}^{\mathrm{in}sx}=\left[s_0^{\mathrm{in}sx},s_1^{\mathrm{in}sx},s_2^{\mathrm{in}sx},s_3^{\mathrm{in}sx}\right]$$

, the calibration results determine the signal levels of the control unit, which correspond to these phase delay values of birefringent elements of the polarization controller, and set them.

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