WO2016151373A1

WO2016151373A1 - Process for controlling the state of light polarization and system for its implementation

Info

Publication number: WO2016151373A1
Application number: PCT/IB2015/056712
Authority: WO
Inventors: Szymon PUSTELNY; Przemysław WŁODARCZYK; Dmitry Budker; Derek F. Jackson KIMBALL; Valeriy YASHCHUK
Original assignee: Uniwersytet Jagielloński
Priority date: 2015-03-21
Filing date: 2015-09-03
Publication date: 2016-09-29
Also published as: PL411653A1; PL234906B1

Abstract

The invention relates to a process for controlling the state of light polarization, comprising directing linearly polarized light beams, of orthogonal polarizations, to appropriate acousto-optic modulators (AOM), their subsequent superposition resulting in a generation of an interference signal, and then directing the interference signal to a waveplate (2), wherein acousto-optic modulators (AOM) are excited with independent variable voltage of specific amplitude, frequency and phase parameters by the control system of the acousto-optic modulators (3). The present invention also relates to a system for the implementation of the process for the control of the state of light polarization.

Description

Process for controlling the state of light polarization and system for its implementation

The invention is related to a process for controlling the state of light polarization and a system to implement this process, permitting to produce the light of a particular polarization state and providing its dynamic modification in a continuous way. The objects of the inventions are applicable to optical detection systems for various physical quantities, in particular systems for the measurement of magnetic field (magnetometers).

The existing methods to control the state of light polarization can be divided into two main groups: passive and active. The basic components of the first group are birefringent crystals. Due to the different refractive indices of two orthogonal linear light polarizations of a birefringent crystal, after passing through a birefringent medium, a phase of light component, whose polarization is parallel to one crystal axis, is different from the phase of a component of polarization oriented along the second axis. Particular examples of passive elements are so- called waveplates, such as quarter-wave and half-wave plates offered by many commercial companies. Other examples of passive elements allowing for the control of the state of light polarization, which compete with crystals, are optical fiber systems. The principle of their operation is similar to the operation of birefringent crystals - the optical path in a bent optical fiber varies in the plane of the bend and perpendicularly thereto; therefore, it is possible to modify the state of light polarization by appropriate spatial orientation of this plane. For example, a system of three optical fiber loops allows for the generation of any state of light polarization. An example of such a system is the FPC030 fiber optic polarization controller offered by Thorlabs.

The second group of methods for polarization control comprises active methods, in which birefringence of a medium, e.g. a crystal, is controlled using external factors (e.g. electric field or mechanical stress). A particular example of a device which allows for dynamic modification of light polarization is an electro-optic modulator, such as the electro-optic modulator based on a lithium niobate offered, for example, by Thorlabs. This device uses a crystal made of special material, in which an electric field causes a spatial reorientation of crystal molecules - crystal molecules have an anisotropic structure; therefore, their spatial reorientation changes the optical properties (rotates a birefringence axis) of the crystal. Therefore, birefringence, and consequently the change in the state of light polarization, are controlled by an external electric field. This solution is used, among others, in liquid crystal displays, wherein an external electric field causes reorientation of liquid crystal molecules, thereby changing the optical anisotropy of the medium. The above-described systems have certain disadvantages. One of them is the limited rate of change in the polarization state. In passive methods, change of polarization is possible only by mechanical rotation of the birefnngent element. A frequency band of the polarization state of such a system is typically limited to only a few dozen of Hz. Further, mechanical rotation can be a source of vibrations, which can generate noise and lead to reduced performance of the device in which such a solution is used. In the case of electro-optic modulators, the situation is different. The modulation band in typical solutions can reach several hundred MHz, and in systems of the "Q-type", it can be as high as 100 GHz. However, this solution requires rapid on and off switching of the voltage, which in some modulators may vary from a few dozen to a few thousand volts. This requires the application of appropriate resonant loops, which optimize the operation of the device for the specified frequency range. Another limitation of traditional control systems of the polarization state is the lack of complete control over such changes. In particular, the introduction of linearly polarized light into an electro-optic modulator causes that the output light can have only elliptical polarization of a specified orientation of the main axis, or in two specific cases, circular polarization or linear polarization perpendicular to the polarization of the incident light. Greater control over the output polarization can be achieved either by the introduction of a mechanically rotated passive element or by the use of another electro-optical modulator, the output of which will be further equipped with a quarter-wave plate. Placing a quarter-wave plate at a right angle (45° relative to the axis of the electro-optically active crystal with no field) allows for full control over the output state of the light. While the band and full control over the state of light polarization can be reached e.g. using a system of electro-optic modulators, continuous change of the state of light polarization is not feasible on these devices. In particular, light polarization cannot continuously rotate in the specified direction, since this would require an infinite increase in voltage on the electro-optic crystal. A partial solution of this task would be stimulation of the electro-optic modulator using saw-tooth voltage. In such a case, the voltage applied to the crystal would increase as long as the phase difference between the components along the optical axes of the crystal would be equal to 2π or a multiplicity of this phase. In this case, the output light would reproduce the polarization state of the incident light. After reaching such a situation, the voltage on the crystal would be rapidly switched off, and the process of voltage growth would be repeated. Consequently, in order to achieve a quasi- continuous change in the state of light polarization, the electro-optic modulator would be stimulated by saw-tooth voltage. However, the disadvantage of this solution is the fact that the voltage must be switched off every time it reaches its maximal value. This process is not immediate, and it is characterized by a certain time constant. At the time when the voltage on the modulator decreases, light polarization "turns back". This is done within a much shorter time than the duration of the respective state of light polarization. However, said process can cause problems and disqualify the method for certain applications. Therefore, the technical problem for the present invention is to develop such a process for the control of the state of light polarization and a system for its implementation, which would allow for full control of polarization, enabling any light polarization, wherein the change in the polarization state can take place continuously (in the range from 0 to several MHz), allowing for, among others, the formation of rotating linear polarization, and at the same time, the process and the system would reduce signal interference, thereby increasing the accuracy of the control in a wide range of frequencies. The above-mentioned technical problems were solved by the present invention.

The first object of the invention is a process for controlling the state of light polarization, characterized in that it comprises the following steps: a) two linearly polarized light beams, of orthogonal polarizations, are directed into two acousto-optic modulators, wherein acousto-optic modulators are excited with independent alternating voltage of specified amplitude, frequency and phase parameters, supplied from the control system of acousto-optic modulators, b) after passing through acousto-optic modulators (AOM), light beams with at least one changed parameters, including phase, frequency and amplitude, superimpose on each other, giving rise to an interference signal, c) the interference signal formed in step b) (light beam) is directed to a quarter-wave plate (2), wherein the change of linear polarizations into orthogonal polarizations (right-handed and left-handed) takes place. In a preferred embodiment of the invention, linearly polarized light beams of orthogonal polarizations are obtained from a laser with a polarizing beam splitter or from two synchronized lasers. In a further preferred embodiment of the invention, the control system of acousto-optic modulators was selected from a group consisting of: a system of two synchronized generators, a system with a single sideband modulator. Preferably, acousto- optic modulators operate in the first order diffraction. Equally preferably, independent variable voltage signals to control acousto-optic modulators, generated by a control system of acousto-optic modulators, differ in frequency and/or amplitude and/or phase. In a further preferred embodiment of the invention, a phase of the signal split by means of a non- polarizing beam splitter is measured using a detector and a polarizer behind the quarter-wave plate, and it is compared to a variable voltage signal used to control acousto-optic modulators, and in case of a phase difference of the compared signals, it is compensated by means of a delay line introducing a compensating signal into a variable voltage signal used to control one of the acousto-optic modulators.

The second object of the invention is a system to control the state of light polarization, characterized in that it contains a light source which generates at least one light beam, behind which are disposed at least two acousto-optic modulators (AOM), controlled by independent variable voltage of specified amplitude, frequency and phase parameters from the control system of acousto-optic modulators, followed by a polarizer, on which at least two orthogonally polarized light beams from acousto-optic modulators fall, resulting in an interference signal which falls on a quarter-wave plate placed further in a line, changing the polarization of the incident interference signal. Preferably, the light source is in the form of a laser generating a linearly polarized light beam, which falls on a polarizing beam splitter, where it is split into two independent light beams of orthogonal polarizations, or it is in the form of two synchronized lasers generating two independent beams of orthogonal polarizations. Equally preferably, the control system of acousto-optic modulators was selected from a group consisting of: a system of two synchronized generators, a system with a single sideband modulator. In a preferred embodiment of the invention, acousto-optic modulators operate in the first order diffraction. In a further preferred embodiment of the invention, independent variable voltage signals to control acousto-optic modulators, generated by a control system of acousto-optic modulators, differ in frequency and/or amplitude and/or phase. In a further preferred embodiment of the invention, a non-polarizing beam splitter, which directs a part of the beam to a polarizer and a detector measuring the modulation phase of the interference signal intensity, are disposed behind the quarter-wave plate, and the control system of acousto-optic modulators comprises a comparator, which compares the variable voltage signal for the control of the acousto-optic modulators with a phase of the detected interference signal, and in case of a phase difference of the compared signals, it compensates it using a delay line introducing a compensating signal into one of the acousto-optic modulators. Preferably, the signal transmission between individual components of the system is performed using optical fibers.

Simple considerations on light polarization will help to understand the presented process and the control system of the polarization state. We assume two beams of left-handed and right- handed circularly polarized light:

E_B = cos(27ru₂t)— y sin(27ru₂t) wherein x and y are two linear versors in a Cartesian coordinate system, while υι and υ₂ are light frequencies for each of the circular polarizations. The addition of two quantities and trivial trigonometric transformations lead to the following equation:

which shows that the resultant polarization is a linear polarization rotating with a frequency (u₂— t>i)/2. However, in general, the above-described system allows for obtaining any state of polarization by controlling additional parameters of the system, such as phase and amplitude of the signals. In the embodiments, cases allowing for obtaining specific polarization states (static and dynamic) are illustratively discussed.

An important element of the present process and system for polarization control is to create two stable electrical waveforms of a frequency of several dozen/several hundred MHz of high mutual phase consistency, adjustable amplitude and phase difference. This kind of task can be accomplished using several ways in a control system of acousto-optic modulators. One embodiment of such a system is the use of two generators synchronized using one clock. Such synchronization can be accomplished in many ways, including an automatic frequency control loop, phase-locked loop, reproduction/frequency synthesis system, etc. Further, the use of systems for direct digital control enables generation of signals suitable to control said device. Exemplary control systems of acousto-optic modulators, suitable for use in the process and system according to the present invention, are described in the embodiments below. The present process for controlling the state of light polarization and the system for its implementation provides a possibility of precise control of the polarization state and a possibility of continuous changes of this state, especially of continuous rotation of linear polarization, within a broad band from 0 to several MHz. The use of two independently controlled acousto-optic modulators allows for obtaining any light polarization, even continuously variable polarization over time, e.g. linear polarization rotating over time. Elimination of all mechanical components significantly reduced vibrations in the whole system, contributing to a reduction in interference, thereby increasing the accuracy of polarization control. Furthermore, the present system and process allows for continuous changes of polarization over time, without the adverse effect of "light turning round".

Exemplary embodiments of the invention are presented in the illustration, wherein:

Fig. 1 presents a block diagram of the system to control the state of light polarization,

Fig. 2 presents a schematic diagram of the process for obtaining static light polarization,

Fig. 3 shows a schematic diagram of the process for the production of light with continuous change in polarization,

Fig. 4 shows a block diagram of a system of two synchronized generators,

Fig. 5 shows an electrical diagram of a system of a sideband modulator,

Fig. 6 shows a schematic diagram of a system for obtaining two coherent electric waveforms,

Fig. 7 shows a block diagram of a system to control the state of light polarization with a feedback loop,

Fig. 8 shows a block diagram of a system for stabilization of polarization phase stability,

Fig. 9 shows the waveforms of electric signals from a system for stabilization of linear polarization rotation.

Example 1 A block diagram of a system for controlling the state of polarization is shown in Fig. 1. In this system, the linearly polarized light of laser 1 illuminates on a polarizing beam splitter PBS, which directs two orthogonal light polarizations into two channels of an interferometer (of the Mach-Zehnder type). Polarization of the incident light is selected in such a way so that beam intensities in both channels are the same. Subsequently, each of the beams passes through the acousto-optic modulator AOM, operating in the first order diffraction. AOMs are excited by the control system of acousto-optic modulators 3 with sinusoidal signals of radio frequency (rf), wherein the signals can differ in phase and amplitude. Diffraction in the AOM produces changes in such light parameters as phase, frequency and intensity. In particular, the amplitude of the rf signal in each of the AOM modulators controls the beam intensities in the diffracted order and hence intensities of interfering beams. Behind the AOMs, beams are superimposed, which produces an interference pattern, and linear polarizations of each beam are converted into two orthogonal circular polarizations using a quarter-wave plate, or a birefringent crystal, which shifts the phase of one component of an electromagnetic wave, propagating through the plate, relative to the second component by 90°. The interference of two beams of different amplitudes and phases gives rise to a particular state of light polarization.

Control of the amplitude of the sinusoidal signals applied to the AOMs and control of the phase of one of these signals allows for the formation of any polarization state. In particular, the application of electrical signals to only one of the AOMs allows for generation of light of circular polarization of a helicity determined by the AOM which is used, while application of signals of equal amplitudes and frequencies to both AOMs allows for light of linear polarization of a spatial orientation dependent upon the phase difference between the signals applied to both AOMs. A schematic diagram allowing for the generation of linear polarization of light, oriented at a different angle than the initial polarization, is shown in Fig. 2. The above-discussed example allows for obtaining linear polarization rotated by an angle of 45° relative to the incident polarization angle in the system. Obtaining light with rotated polarization can be divided into the following steps: 1) the incident beam of linear polarization is separated on the PBS into two mutually perpendicular polarization components (beam ratio 50:50), 2) the beams split on the polarizing beam splitter PBS pass through acousto-optic modulators AOMs; both modulators are excited by a control system of acousto- optic modulators 3 with the same radio frequencies rf but shifted by 90° in phase of the signals, 3) subsequently, the beams are superimposed on a PI polarizer, which produces right- handed circular polarization, 4) the beams, after passing through a quarter-wave plate 2, are converted (linear polarization components turn into circular ones) into linear polarization, the axis of which was rotated by 45°.

Example 2 Further, the system presented in Example 1 allows for obtaining light of a polarization state which changes continuously over time. This was achieved by introducing frequency difference υ > 0 between two interfering beams (the frequency difference of rf signals, used to excite AOM modulators, obtained in the control system of the acousto-optic modulators 3). In this case, both polarization components interfere, but the phase of the two interfering beams changes over time, and thus the resultant polarization of light also changes. In a particular case, it is possible to produce light of continuous rotating linear polarization, as shown in Fig. 3. In the presented schematic diagram of a process for generating light with a continuous change in polarization, the following steps were indicated: 1) the linearly polarized beam of incident light from light source 1 in the form of a laser is separated using the PBS into two perpendicular linear components of different amplitudes, 2) the beams, after passing through the AOMs (one of the modulators introduces a frequency shift relative to the other one using a control system of acousto-optic modulators 3), are directed to appropriate mirrors M, 3) subsequently, the beams are superimposed in the PI modulators and undergo interference (the resultant polarization state changes continuously from linear polarization by right-handed circular polarization, linear polarization rotated by 90°, left-handed circular polarization to the initial linear polarization, etc.), 4) after passing through the quarter-wave plate 2, the components of linear polarization undergo conversion into two circular polarizations, which consequently leads to a linear polarization component of a polarization which rotates at a frequency determined by a frequency difference υ of both components, applied in the control system of acousto-optic modulators 3 (rotation at half of the frequency difference u).

Example 3

In the system used to control the polarization state presented in Fig. 1, used to obtain polarization states presented in Examples 1 and 2, a system of two synchronized generators G according to Fig. 4 was used as a control system of acousto-optic modulators 3 to provide two stable electrical waveforms of a frequency from several to several hundred MHz of a high mutual phase coherence, controlled amplitude and phase difference. This solution allows, among others, for control of signal amplitude and, in some cases, of the phase of the emitted waveform, which in turn allows for control of frequency, amplitude and phase of light in each of the branches of the interferometer used to generate a specified polarization. The use of commercial generators allows for the production of any electrical waveforms (modulation signal shapes: sinusoidal, rectangular, triangular, etc.) to excite the AOM modulators, as well as for control of other wave parameters (e.g. frequency, phase, amplitude modulation) and thus of the light. This allows for complex shaping of the parameters of the light leaving the device (modulation of amplitude, polarization, etc.). A further advantage is a possibility to control generators using a computer, which opens a possibility for simple integration of a device based on this solution with microprocessor systems.

However, the limitations of this solution are that the generated electrical waveforms should have a frequency from several to several hundred MHz, which, at the same time, reduces from the bottom frequency changes to which these waveforms may be subjected (in very sophisticated systems operating at a frequency of approx. 100 MHz, this is not less than 0.1 Hz).

Example 4

In the system used to control the polarization state presented in Fig. 1, used to obtain polarization states presented in Examples 1 and 2, a control system with a single sideband modulator MJ, presented in Fig. 5, instead of a system of two synchronized generators G, as described in Example 3, was used as a control system of acousto-optic modulators 3 to provide stable electrical waveforms controlling the operation of acousto-optic modulators. In the presented electrical schematic diagram of a single sideband modulator MJ, v_c is a carrier frequency of AOM (e.g. 80 MHz), while v_m represents the difference between waveforms used to excite the AOMs (e.g. from 0 to several MHz). A single sideband modulator allows for producing a waveform of a frequency which is a result of the addition or subtraction of the frequencies of initial signals. In particular, a Hartley modulator can be used, the operating principle of which is based on transfer of initial signals without distortions, thus preserving a very good phase stability of signals which excite the AOM modulators. For example, it is possible to use a signal of a high frequency, e.g. v_c = 80 MHz, to supply one of the AOM modulators and as an input signal of the single sideband modulator MJ (shown in Fig. 5). The second signal of a frequency v_m is applied to the second input of the modulator MJ. Consequently, signals of frequencies 80 MHz, 80 MHz - v_m or 80 MHz + v_m are generated. The use of signals of different frequencies to control the AOM modulators in the described system leads to a polarization change over time. In Fig. 6, a schematic diagram of a system for producing polarization of electrical signals used to generate polarization modulated in a continuous manner was presented. To the input of this system, using a system of a single sideband modulator, two electrical signals are applied: a signal of a radio frequency and a signal of a significantly lower frequency. Consequently, this system allows for obtaining two mutually coherent (without drifts and sudden phase shifts, but only with a linearly increasing phase difference) electrical systems. Further, the placement of a phase detection circuit in the system, with a controlled time delay circuit 6, allows for the compensation of phase drifts in the system (as shown in Fig. 8).

Example 5

In the system used to control the polarization state presented in Fig. 1, used to obtain polarization states presented in Examples 1 and 2, a feedback loop was used to control the relative phase and frequency between signals from the control system of the acousto-optic modulators 3 in order to, among others, eliminate the undesired drift of the interferometer. A block diagram of a control system of the state of light polarization with a feedback loop is presented in Fig. 7. In this case, in contrary to Examples 4 and 5, the absolute frequency of the generators is not controlled. The feedback signal can be obtained using a phase detector 4. Referring to the system of Fig. 7, the key element is the presence of a constant or well- controlled phase difference between two interfering beams. Such a difference is obtained by using the AOMs controlled with a control system of acousto-optic modulators 3, but this is also a result of a difference in the optical path of the beams in each of the branches of the interferometer. The result of the presence of this second factor is a lack of full control over the optical path, inducing possible phase differences variable over time in the system, resulting from e.g. the flow of the air in the branches of interferometer or from thermal changes in the size of the system (e.g. in crystals, in which the described system can be implemented). Changes in the phase of interfering beams are reflected in an uncontrolled change in the polarization state of the input light, which produces a so-called drift of the interference signal. In order to overcome this disadvantage the system (Fig. 7) was developed, which regularly controls the state of light polarization and adjusts the signals controlling the AOM modulators in a control system of the acousto-optic modulators 3 to compensate possible drifts and obtain light of a predetermined polarization. In the case of generating light of a dynamically variable polarization, presented in Example 2, a system with a single sideband modulator MJ, presented in Example 4, was used to generate light of a rotating polarization. In order to eliminate the phase drift, a measurement of intensity of the rotating beam, split from the main beam and transmitted by the polarizer P2 placed behind the interferometer (the beam split by a non-polarizing beam splitter BS) in relation to a forcing signal from the control system of the acousto-optic modulators 3, was used. The rotation of the polarization of light falling on the polarizer P2 causes a harmonic modulation of light intensity behind said polarizer P2, detected by the detector D. At a given time, the phase of this light is well defined relative to the phase of a slowly variable signal applied to the single sideband modulator MJ, and this depends both on the difference of optical paths in the branches of the interferometer and on the spatial setting of the polarizer P2. In particular, it may be changed by a rotation of a polarizer P2 in such a way that at a given time, both waveforms may have a mutually coherent phase. In this case, the signal from the detector D acts as an error signal - by comparing the modulation phase of the light intensity and a modulating signal, it is possible to close the feedback loop. The response to the increase in phase difference is a change of system parameters, e.g. shift of phase of the signal rf, which excites one of the AOMs.

The implementation of the stabilization system of the modulation phase, including a phase detector 4 and a control system of acousto-optic modulators 3, is schematically shown in Fig. 8. In this system, a low frequency signal v_m is applied to one of the inputs of a single sideband modulator MJ with a signal of high frequency v_c (e.g. 80 MHz). A comparison of a phase of the input signal and a phase of the rotating polarization signal in a comparator 5 (resulting from a mutual superimposition of light beams passing through the AOM modulators and obtained using the polarizer P2 placed behind the interferometer) allows for stabilization of phase differences between the two channels. The error signal obtained in a phase comparator 5 controls a radio frequency signal using a delay line 6 in one of the AOM modulators, which consequently changes the phase of the light and allows for stabilization of precession of the polarization. In the present solution, the delay line 6, controlled by an appropriately amplified error signal, which compares the signal controlling the polarization state from the phase detector 4 with a reference signal, was applied to control the signal phase rf. Fig. 9 presents the differences in waveforms of voltage signals between a non-stabilized and stabilized system, measured over a time of tens of seconds. Fig. 9 (a) presents an electrical signal which excites the system (bottom waveform) and a rotation signal recorded by measuring light intensity behind a linear polarizer (upper waveform). The signal was measured during tens of seconds - the afterglow shows earlier signals. As can be noticed, all the phase drifts of the rotating polarization were significantly reduced after the system was switched on. Fig. 9(b) presents a signal of phase difference between a low frequency signal, which excites the system, modulating frequency differences, and a phase rotation of polarization in a system of strong mechanical distortion of the system. According to the data shown in Fig. 9(b), switching on the stabilization system reduces the initial phase drifts from approx. 100° to approx. 1°, i.e., by 2 orders of magnitude. The results showing waveforms were registered for approx. one minute. The use of the phase stabilization system significantly reduced all phase drifts in the system.

Claims

1. A process for controlling the state of light polarization, characterized in that it comprises the following steps: a) two linearly polarized light beams, of orthogonal polarizations, are directed into two acousto-optic modulators (AOM), b) after passing through acousto-optic modulators (AOM), light beams are superimposed onto each other, giving rise to an interference signal, c) the interference signal formed in step b) is directed to a quarter-wave plate (2), wherein the change in polarization takes place, wherein acousto-optic modulators (AOM) are excited with independent alternating voltage of specified amplitude, frequency and phase parameters by the control system of the acousto-optic modulators (3).

2. The process of claim 1, characterized in that linearly polarized light beams of orthogonal polarizations are obtained using a laser with a polarizing beam splitter (PBS) or using two synchronized lasers.

3. The process of claim 1 or 2, characterized in that the control system of acousto-optic modulators (3) was selected from a group consisting of: a system of two synchronized generators (G), a system with a single sideband modulator (MJ).

4. The process of any of the claims from 1 to 3, characterized in that the acousto-optic modulators (AOM) operate in the first order diffraction.

5. The process of any of the claims from 1 to 4, characterized in that independent variable voltage signals to control acousto-optic modulators (AOM), generated by a control system of acousto-optic modulators (3), differ in frequency and/or amplitude and/or phase.

6. The process of any of the claims from 1 to 5, characterized in that a phase of the signal split by means of a non-polarizing beam splitter (BS) is measured using a detector (D) and a polarizer (P2), behind the quarter-wave plate (2), and it is compared to a variable voltage signal used to control acousto-optic modulators (AOM), and in case of a phase difference of the compared signals, it is compensated by means of a delay line (6) introducing a compensating signal into a variable voltage signal used to control one of the acousto-optic modulators (AOM).

7. A system to control the state of light polarization, characterized in that it contains a light source (1), which generates at least one light beam, behind which are disposed at least two acousto-optic modulators (AOM), controlled by independent variable voltage of specified amplitude, frequency and phase parameters, from the control system of acousto-optic modulators (AOM), followed by a polarizer (PI), on which at least two orthogonally polarized light beams from acousto-optic modulators (AOM) fall, resulting in an interference signal, which falls on a quarter-wave (2) plate placed further in a line, changing the polarization of the incident interference signal.

8. The system according to claim 7, characterized in that the light source (1) is in the form of a laser generating a linearly polarized light beam, which falls on a polarizing beam splitter

(PBS), where it is split into two independent light beams of orthogonal polarizations, or it is in the form of two synchronized lasers generating two independent beams of orthogonal polarizations.

9. The system according to claim 7 or 8, characterized in that the control system of acousto- optic modulators (3) was selected from a group consisting of: a system of two synchronized generators (G), a system with a single sideband modulator (MJ).

10. The system of any of the claims from 7 to 9, characterized in that acousto-optic modulators (AOM) operate in the first order diffraction.

11. The system of any of the claims from 7 to 10, characterized in that independent variable voltage signals to control acousto-optic modulators (AOM), generated by a control system of acousto-optic modulators (3), differ in frequency and/or amplitude and/or phase.

12. The system of any of the claims from 7 to 11, characterized in that a non-polarizing beam splitter (BS), which directs a part of the beam to a polarizer (P2) and a detector (D), measuring the modulation phase of the interference signal intensity are disposed behind the quarter-wave plate (2), and the control system of acousto-optic modulators (3) comprises a comparator (5), which compares the variable voltage signal for the control of the acousto- optic modulators (AOM) with a modulation phase of the interference signal, and in case of a phase difference of the compared signals, it compensates it using a delay line (6) introducing a compensating signal into one of the acousto-optic modulators (AOM).

13. The system of any of the claims from 7 to 12, characterized in that the signal transmission between individual components of the system is performed using optical fibers.