RU2373558C1 - Method of modulating phase of light and optical modulator to this end - Google Patents

Abstract

FIELD: physics; optics.

SUBSTANCE: invention relates to optoelectronics. The method is based on electrically controlled variation of double refraction of a ferroelectric liquid crystal in a single-element electro-optic cell with a single pair of current-conducting coatings. When alternating electric field at low frequency (50 to 500 Hz) and at high frequency (500 to 8000 Hz) is simultaneously applied, three dimensional deformations arise in the liquid crystal layer, which lead to formation of small-scale spatially non-uniform and fast time-varying structures with random distribution of refractive index gradients in the said layer. In the optical modulator composition and thickness of the liquid crystal layer and mode of controlling the electro-optic cell with alternating electrical voltage are chosen from a condition which provides for the modulation speed and modulation depth of the phase of light required for suppressing speckles.

EFFECT: increased spatial resolution and faster modulation.

4 cl, 6 dwg, 1 ex

Description

Technical field

The invention relates to the field of optoelectronics and can be used in devices and systems for visualization and information display using LEDs and lasers, in particular in projection displays, including television, in spatial light modulators, in storage, conversion, visualization and image processing devices etc.

State of the art

Currently, devices and systems using coherent or partially coherent light emitted primarily by various types of LEDs and lasers are becoming increasingly common in the technique of visualizing and displaying information. When they illuminate randomly inhomogeneous objects, such as, for example, a rough surface of a screen or a transparent medium with a refractive index fluctuating in space, a spotted pattern or speckle structure is formed due to interference of scattered waves. In fact, it is noise, and this speckle noise significantly reduces image quality [1-3].

Figure 1 shows [3] an enlarged fragment of the speckle structure in the field of diffraction of a laser beam on a rough surface (a) and various optical schemes for observing speckle patterns (b, c) are shown. Here 1 is a light source (laser), 2 is a randomly inhomogeneous object or medium, 3 is a schematic view of the longitudinal section of a speckle layer, 4 is a randomly distorted wave front, 5 is an optical system. Note that speckles are also observed in imaging optical systems, in which the conditions of coherent illumination of an object are much less demanding. For example, such “subjective” speckle patterns are visible to the naked eye even in the polychromatic light of extended sources passing through a scattering medium (Figure 1c), which occurs when observing streetlights through a fogged or frozen vehicle window [3].

Devices and systems for visualization and display of information, as a rule, provide for the display of images on the screen for visual perception. Therefore, the urgent task is to reduce and eliminate (suppress) the speckle structure that creates noise in the image, or speckle modulation of a relatively low frequency, because the size of individual speckles is determined by the resolution of the eye [1-3]. The problem is solved in different ways based on the following two approaches, namely:

1 - the destruction of the speckle structure directly on the screen, and

2 - the destruction of phase relations leading to the creation of a speckle structure in a beam of light before it is projected onto the screen.

In both cases, speckle destruction is achieved by spatially temporal and randomly distributed (over the beam aperture) modulation of the phase of light with a sufficient depth of phase delay and a speed substantially greater than the reaction of the eye.

In the first approach, it is necessary to take into account the limiting angular resolution of the eye. It is taken equal to one minute or 20-30 lines / mm, but this value can vary depending on the lighting conditions, screen structure, image color. In practice, averaging and thereby eliminating the speckle structure is achieved by using a matte screen moving in the process of observing an image on it [4]. Obviously, the movement of the matte diffuser should be fast enough so that the eyes do not have time to track the shift of the speckle structure relative to the image. In [5], a method was proposed for eliminating the speckle structure using two opaque diffusers, one of which moves non-stop relative to the other. In this case, there is no dependence on the transfer function of the optical system, since the magnitude of the correlation function of the scatterer is usually much less than the pulse response of the output optical system.

The second approach to the elimination of speckle noise, based on the destruction of phase relationships and thereby the ability to interfere with the rays in the light beam, seems more compact and efficient, but the device implementing it should have a much higher resolution (of the order of hundreds or even thousands of 1 / mm) due to the need for subsequent expansion of the beam to the size of the screen, and also should not impair the intensity of the light beam and its directivity.

The problem of suppressing interference is solved using controlled spatial phase masks (in other words, filters, diffusers). An example of such a mask [1-3] is an illuminated using a diffuser (for example, frosted glass) and then bleached topographic plate, which provides spatial modulation of the phase of transmitted light with a random distribution of phase delay with a depth of the order of π or more over the area of the plate (over the beam aperture). Obviously, such a plate, as in the case of scattering screens considered above, must be quickly moved in the direction transverse to the beam, which is a significant drawback of this solution.

The mechanical motion of the phase mask can be avoided by using a spatio-temporal phase light modulator [7], for example, a liquid crystal one, which is a matrix of separately addressable liquid crystal cells. When controlling electric voltage or light according to a specially developed computer program, such a modulator in real time generates a variety of orthogonal phase shift matrices of 0 and pi (π) corresponding to the Hadamard, Walsh, or other orthogonal functions [7-9]. An example of a phase mask corresponding to the Hadamard matrix is given in [10] and shown in FIG. 2. Here, in matrix elements (pixels), conditionally shaded in black, there is no phase shift, and in unpainted ones, pi (π), or vice versa.

However, the use of an electro-optical medium, divided into light modulation channels (pixels), with an electronic addressing device for each channel, i.e. essentially an entire display (microdisplay), dramatically complicates and increases the cost of the optical speckle suppression system. Due to the decrease in the working aperture due to the presence of control electronic elements (usually thin-film transistors) and the gaps between the matrix elements, such a device has rather large light losses. Moreover, the periodic structure of the matrix introduces distortions of the wavefront of coherent light, which also leads to distortion of the image on the screen. Electronic control of a spatial light modulator is a separate and complex task.

Closest to the claimed is a method of modulating a phase of light, implemented in the device described in [11], namely, in a simple, without separation into modulation channels, light-modulating electro-optical cell filled with a liquid crystal (LC), namely, a smectic type liquid crystal with ferroelectric properties (FFA).

A physical model for modulating the phase of light in an electro-optical cell with FFA is shown in FIG. 3. In the FLC layer, the direction of the preferred orientation of the long axes of the molecules (director N) is determined by the polar angle θ, at which they are inclined relative to the normal to the smectic layers 3, and the azimuthal angle φ in the plane of the smectic layer. Due to the special stoichiometry of the molecules, each layer in the absence of external influences has a spontaneous polarization (P _s ), as a result of which FFAs are highly sensitive to the action of an electric field. The polarization vector lies in the plane of the smectic layer and is directed perpendicular to the polar axis, and the polar axes of various smectic layers separated from each other by a period of p ₀ are rotated relative to each other so that an equilibrium helically twisted structure (helicoid) is formed. Macroscopic polarization of the cell, however, is absent, because the angle φ in the smectic layers varies from 0 to pi (π) at a distance equal to the pitch of the spiral p ₀ .

FLC cells have various electro-optical properties [11, 12]. For example, they manifest the effect of electrically controlled birefringence, due to the deformation of the helicoid and therefore called the DHF effect (from deformed helix ferroelectric). It is observed along the direction of light propagation under the condition that the helix pitch is much smaller than the thickness of the LC layer (Figure 3). In addition, to observe the effect, it is important that the pitch of the spiral (usually 0.3–0.5 μm) is much smaller and the aperture of the light beam (almost always performed). This means that modulation is observed when averaging (over the beam cross section) the distribution of phase shifts occurring in the spatially modulated birefringent layer of the FLC. The effect has no threshold and is observed in small fields, which are less than the critical field of the helicoid's helix unwinding.

For the modulation of light in cells with FFA, the Clark – Lagerwol effect is widely used [11–13]. The necessary conditions for his observation are the previous requirement of the orientation of the smectic layer perpendicular to solid substrates and the inverse relationship for the helix pitch of the helicoid - it should be greater than the thickness of the LC layer (Figure 3). In practice, the spiral may be absent altogether (compensated by special additives with the reverse twist of the helicoid). In thin FLC layers, electro-optical switching is bistable due to the strong interaction of the layer with its bounding surfaces.

The principle of modulation of the phase of the light based on the Clark-Lagervol effect in the optical modulator - cell with FFA is illustrated in Fig.3. The modulator is controlled by an electric voltage source 4. The FLC layer is located between the substrates 1 with conductive coatings deposited on them 2. When an electric field is applied to the FLC cell, the polarization vector of each smectic layer is established along the field lines, and the long axes of the molecules are located in the plane of the FLC layer at an angle θ to the axis of the helicoid. When the field sign changes, the polarization vector reverses, and the long axes of the molecules as generators of the cone go to the position - θ in the same plane, i.e. are shifted by 2θ with respect to the previous position. The reorientation of the long axes of the molecules is accompanied by a change in the birefringence of the FLC layer, and, consequently, by phase modulation of the transmitted light, which can be converted into amplitude using polarizers.

Figure 3 also illustrates how amplitude modulation of light in an FLC cell is implemented in practice. Let natural non-polarized light fall on it, the intensity of which is I ₀ . Passing through the polarizer P, the light becomes linearly polarized in the direction of the transmission axis of the polarizer P. The direction of the director N in the cell depends on the sign of the voltage of source 4, that is, on the direction of the field E. The angle between the vectors N (+ E) and N (-E) is 2θ. If the FFA is in the + E field and the polaroid is oriented so that its axis is parallel to the N (+ E) vector, then the light propagates along the main optical axis of the FLC and therefore does not experience birefringence, and at β = π / 2 the cell does not transmit light. If the field direction changes by -E, the light will propagate at an angle of 2θ to the main optical axis of the FLC and, therefore, will experience birefringence, as a result of which the polarization of light from linear to elliptical is converted. In this case, at β = π / 2, the cell transmits light.

The transmitted light intensity I is determined by the ratio

I = I ₀ Sin ² 2θ + (N (-E), L) Sin ² (πΔnd / λ),

where Δn is the birefringence of the FLC layer; d is its thickness; λ is the wavelength of light; (N (-E), L) is the angle between the vectors N and L. The maximum possible light transmission of the cell T = I / I ₀ = 1 is achieved if

Δnd / λ = 1/2, θ + (N (-E), L) = π / 4.

A possible change in birefringence in the FLC layer is such that the phase shift by pi (π), corresponding to the first maximum of light intensity behind crossed polaroids, is achieved at a certain electric field strength at a layer thickness of 1.5-3.0 microns for the visible wavelength range, and in thick layers (of the order of and more than 10 μm), the phase shift can reach several pi (π) and, accordingly, lead to several light intensity maxima observed for crossed polaroids.

The circuit of an electrically controlled optical modulator of "transmitting" and "reflective" type is shown in Fig.4. In the first embodiment (Fig. 4a), light passes through the FLC cell through, and in the second (Fig. 4b) it passes twice, because reflected. The modulator contains two parallel-mounted dielectric plates (substrates) 1, of which both are transparent for option a, and at least one for option b. Antireflective coatings 2 are applied on the outer sides of the dielectric plates, and conductive coatings 3 (usually with antireflective sublayers) are applied on the inner sides, which are both transparent for option a, and one is transparent for option b, since the second is made reflective. At least one of the conductive coatings is covered with a layer of a transparent anisotropic dielectric substance (orientant) 4. The space between the plates is filled with a liquid crystal substance 5, which can change its optical anisotropy depending on the amplitude and / or pulse duration of alternating electrical voltage supplied to the conductive coatings from the source 7. The initial orientation of the long axes of the molecules of the liquid crystal substance in the absence of an external electric field sets anisotropic coating.

Due to the spontaneous polarization, FFAs are highly sensitive to the action of a control electric field. Therefore, the speed of electro-optical switching in them lies in the submillisecond range. Accordingly, optical modulators based on FLC cells provide a light modulation frequency of several units - tens of kilohertz. It is for such a modulation (amplitude or phase, depending on the presence or absence of polarizers) that the modulator considered above is applied in practice: either as an independent single-channel high-speed light modulator, or as one of many of the display cells of a high-speed FLC display, or as one of many light-modulation cells of a multichannel space-time light modulator, including one forming orthogonal functions.

Thus, an optical modulator based on an FLC cell provides a sufficiently high frequency of phase modulation of light in order to destroy the temporal component of the phasing (interference, coherence) of the light beam. However, the optical modulator based on the usual single-element (single-channel) electro-optical cell described in [12] and discussed in detail above cannot provide any spatial light modulation (especially with high spatial resolution) required to destroy the spatial coherence of the light beam, since cannot create the spatial structure of small-scale variations of the refractive index that are heterogeneous and randomly distributed over the entire aperture of the cell, leading to apertures non-uniform e phase modulation of light with a depth of the order of and more than pi (π).

The problem to be solved in the proposed method and device is the creation of an optical modulator based on an electro-optical ferroelectric liquid crystal cell of an electro-optical ferroelectric liquid crystal cell that is not divided into separately controlled elements (pixels) and provides an aperture inhomogeneous in it and implemented with high spatial resolution and high speed spatial-temporal modulation of the transmitted light with a depth of the order of and more than pi (π), which destroys the temporal and spatial phasing of the light beam and thereby ensures suppressing the speckle structure in the images formed by this beam.

SUMMARY OF THE INVENTION

The solution to this problem is ensured by the fact that in the known method of modulating the phase of light based on an electrically controlled birefringence of the FLC layer in a single cell electro-optical cell with FLC with a single pair of conductive coatings, the new is that an alternating electric field is simultaneously at a low frequency (50-500 Hz) and a high frequency (500-8000 Hz) applied from an electric voltage source in the FLC layer cause spatial deformations, which lead to the formation of small-scale ones in it (the size of the order of fractions - units of micrometers) of spatially inhomogeneous and rapidly changing in time structures with a random distribution of refractive index gradients, and as a result, to phase modulation of transmitted light spatially inhomogeneous over the aperture of the electro-optical cell.

To implement the method, an optical modulator based on an electro-optical ferroelectric liquid crystal cell is proposed, containing two parallel-mounted dielectric plates, at least one of which is made transparent, on the inside of which conductive coatings are applied, at least one of which is made transparent, a liquid crystal filling the space between conductive coatings, changing its optical anisotropy under the influence of an electric field, transparent anisotropic coating, specifying the initial orientation of the liquid crystal molecules in the absence of an external electric field, applied to at least one conductive coating from the side facing the liquid crystal, an electric voltage source in which the composition and thickness of the liquid crystal layer and the control mode of the electro-optical cell with alternating electrical voltage simultaneously at low and high frequency are selected based on the conditions of providing necessary to suppress with peckles of light phase modulation speed (more than 50 1 / s), depth of light phase modulation (π and more) and the ability to form small-scale (in the order of fractions - units of micrometers) spatially inhomogeneous structures with a random distribution of gradients in the FLC volume refractive index.

The liquid crystal layer thickness of 5-25 μm is selected from the condition of achromatic transmission in the entire visible wavelength range and reaching the depth of phase modulation necessary for suppressing speckles not less than pi (π) and the spatial deformation on-off rate of more than 50 1 / s.

Thus, the essence of the proposed method consists in the electrically controlled formation of small-scale spatially inhomogeneous and randomly distributed over the volume of the LC layer refractive index variations in a single-cell electro-optical cell with a ferroelectric LC, which provide phase modulation of the transmitted light random in the aperture of the optical modulator with an order of depth and more (π).

The technical result achieved in the claimed invention lies in the fact that in an optical modulator based on a single cell electro-optical cell with a ferroelectric LC, an aperture is inhomogeneous with high spatial resolution and speed, spatio-temporal modulation of the phase of transmitted light with a depth of the order of or more pi, destroying the temporal and spatial phasing of the light beam and thereby providing suppression of the speckle structure in the images formed by this beam.

The advantages of the proposed method and device for the spatio-temporal phase light modulation are realized by choosing the composition and thickness of the layer of liquid crystal material and a suitable power supply mode of the electro-optical cell with alternating voltage.

The main advantages of the proposed optical modulator, which ultimately reduces and suppresses speckle noise in images, are the simplicity of its construction, control and use, which becomes apparent when comparing such a single-element modulator with spatio-temporal light modulators used for the same purpose, for example, in in the form of a rotating phase diffuser [2] or a multi-element matrix forming orthogonal functions [9].

The composition of the FFA is selected based on its ability to form spatially inhomogeneous and rapidly changing in time structures with a random distribution of refractive index gradients in an electro-optical layer 5–25 μm thick under a certain mode of electric power supply to the optical modulator. Typically, such structures scatter transmitted light to a greater or lesser extent. In recent years, a large number of corresponding FLC compositions have been identified and conditions and physical mechanisms have been determined that facilitate the excitation of spatially inhomogeneous deformations in the FLC layer and, as a result, lead to light scattering with short (submillisecond) times of its on and off [14]. For example, the inversion of the sign of the electric field can lead to the excitation of such deformations and to light scattering if it induces the formation of the so-called transition domains and the associated refractive index gradients along the axis of the helicoid. It is the electric field-controlled variations of the refractive index over the area and depth of the FLC layer, initiated with the help of alternating electrical voltage of a special shape, that is the factor that allows the spatio-temporal phase modulation of light necessary for achieving the result to be achieved in the cell with FLC. Its depth is the greater, the greater the thickness of the FLC layer, and it can be several pi (π) with a layer thickness of 10–25 μm.

The choice of a suitable power regime for the optical modulator with alternating electrical voltage provides the conditions for the short-term inclusion of spatio-temporal deformations of the layer, leading to the formation of time-varying small-scale (in the order of fractions - units of micrometers) spatially inhomogeneous and randomly distributed over the volume of the layer refractive index variations. Note that short-term (by 100 μs or less) light scattering is not sensitive to the eyes, does not distort the structure of images, does not affect their perception and light losses on it are negligible (less than 10%).

The effect of spatially inhomogeneous phase modulation of light in the FLC layer is achieved by the simultaneous action of a low-frequency (hundreds of hertz) and high-frequency (kilohertz) pulsed supply voltage, since a significant increase (up to 90 °) of the angle between the plane of polarization of the incident light and the direction of the main optical axis of the FFA. In this case, the nature of the motion of the director of the FFA changes during its reorientation by the electric field, and spatial deformations of the layer arise, creating small-scale (in the order of fractions - units of micrometers) spatially inhomogeneous variations of the refractive index of the FFA randomly distributed over the volume of the layer.

Moreover, it is completely not obvious from the prior art that in an optical modulator based on a conventional electro-optical ferroelectric liquid crystal cell, it is possible to achieve effective spatio-temporal phase modulation of light only by choosing the composition and thickness of the liquid crystal layer and a suitable control mode of the electro-optical cell with alternating voltage, without cell division into separate elements and their separate control, without compromising stability and reliability of operation as a device Properties of light modulation.

To improve the characteristics of speckle-suppressing optical modulators, one can individually or collectively use various directions for their improvement, such as: changing the type and composition of the liquid crystal and the electro-optical effect in it, changing the control mode of the cell, modifying the design of the modulator, etc. For example:

- it is possible to use FLC with a spiral pitch greater or less than the wavelength of visible light, in order to reduce the visible background from scattered radiation;

- it is possible to use any other type of liquid crystals that can ensure the formation in its layer of spatial inhomogeneities with the above properties;

- it is possible to use polymer-liquid crystal compositions and dielectric plates in the form of thin and flexible films;

- conductive coatings may not be continuous and may have spatial inhomogeneities in thickness and resistance to create additional spatial phase inhomogeneities in the FLC layer;

- orienting coatings can be performed not continuous to create additional spatial phase inhomogeneities in the FLC layer;

- on top of one or both conductive coatings, protective dielectric films, for example, from alumina, can be additionally applied;

- control pulses can be additionally modulated in amplitude and / or frequency;

- one of the conductive layers is made mirror in order to ensure double passage of light through a layer of liquid crystal when it is reflected;

- to enhance the effect of suppressing speckle noise, the design of the modulator may include two sequentially located FLC cells, etc.

Thus, the use of the proposed method and device allows in the known optical modulator based on an electro-optical ferroelectric liquid crystal cell, without dividing it into separately controlled elements, to realize the functions of a fast and high-resolution spatio-temporal light phase modulator, which destroys the phasing of the transmitted light beam and thereby suppresses speckle structures in the images formed by him. In addition, such an optical modulator, being made in the wide-aperture version, can be used as an overwhelming speckle of the screen for displaying projected images on it.

Industrial applicability

The proposed optical modulator is a simple, compact, technological and effective device for suppressing speckle noise in images. This makes it possible to use it in many modern and promising information devices and systems for storing, converting, processing, visualizing and projecting information using LEDs and lasers. Moreover, its use will facilitate the simplification of the design and manufacturing technology of these devices and systems.

An example of the method

According to the proposed method and device, several experimental samples of optical modulators were made based on an electro-optical liquid crystal cell with FLC, which spatially temporal modulated the light beam, and the characteristics of such modulators were measured. The basic design of the manufactured modulators does not differ from that shown in FIG. 3.

In order to form a structure with spatial heterogeneity of optical anisotropy in the experimental cells, we used one of the helicoidal ferroelectric liquid crystal materials with an electric field controlled by birefringence and light scattering with the following material parameters: helicoid pitch p ₀ was 0.4 μm, spontaneous polarization Р _S = 50 nCl / cm ² ; the angle of inclination of the molecules θ ₀ = 25 °; coefficient of rotational viscosity γ _r = 0.7 poise; Δn = 0.17.

This material has a wide temperature range for the existence of the ferroelectric phase (-5 ... + 70 ° C) and has high speed: the on-off times of the electro-optical response lie in the submillisecond range. The aperture of the electro-optical cell was 2 × 2 cm. The thickness of the FLC layer in different cells was d≈13–16 μm, which satisfied the ratio d >> p ₀ .

The process of spatio-temporal modulation of a light beam using an electro-optical cell with an FLC can be described as follows. In the absence of an electric field, the helicoidal structure is not distorted - the pitch of the helicoid in the electro-optical cell coincides with the equilibrium pitch p ₀ . When an electric field E is applied perpendicular to the axis of the helicoid (FIG. 3), the dipole moments of a part of the FFA molecules are initially located along the direction of the field E (energetically favorable orientation). The domain in which the dipole moments are not in the direction of the field is unstable. Due to this, the appearance of regions (the so-called transition domains) [14] in which dipole moments are energetically favorable — in those smectic layers where the azimuthal angle φ had the maximum deviation from φ = 0 (or φ = π) occurs in it [14]. Transition domains are the bound state of two 180 ° domain walls of different signs. Under the influence of an electric field, the bound state grows and deforms, and when a certain critical field is reached, the walls begin to move, and walls of different signs move in opposite directions. The wall moves in such a way that the volume of the energetically favorable domain increases due to the domain of energetically unfavorable.

The movement of domain walls leads to an increase in the pitch of the helicoid in the electro-optical cell. After a certain period of time, the domain walls become infinitely distant - in all smectic layers, the azimuthal angle φ is the same, and the vector P _{s is} oriented in the direction of the field. Since the plane of polarization of the incident light lies along the direction of the director of the FLC (along the main optical axis), the light transmission of the electro-optical cell is maximized.

Inversion of the sign of the electric field (polarity of the control voltage) again induces the formation of transition domains, the movement of which ultimately leads to the restoration of the unperturbed helicoidal structure. In this case, the formation of transition domains causes the appearance of gradients of the refractive index along the axis of the helicoid, which may be accompanied by light scattering.

Figure 5 illustrates the formation in an experimental sample of an optical modulator manufactured by the proposed method and device of spatially heterogeneous structures with an almost random distribution of the refractive index along the beam cross section using alternating low-frequency voltage pulses shown on the lower waveform (meander amplitude ± 30 V with frequency repetition 450 Hz) modulated by short (about 100 μs) alternating pulses of high frequency (amplitude ± 20 V, repetition frequency 3.5 kHz). With the selected control voltage parameters in the FLC layer with a thickness of 16 μm, both the position of the main optical axis of the FLC (scattering indicatrix) is modulated and the phase of the light is modulated with a random time response up to 4π deep (upper waveform).

Evidence of the spatial-temporal modulation of the light beam in the same experimental sample of the optical modulator is shown in Fig. 6 photographs of the beam cross section with the original (a) and destroyed (b) speckle pattern. The speckle noise suppression efficiency was 50 percent and it can be improved with further optimization of the composition and thickness of the liquid crystal layer, the cell structure, and the mode of its supply with electric voltage.

Literary sources

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Claims (4)

1. A method of modulating a phase of light based on an electrically controlled birefringence change of a ferroelectric liquid crystal layer in a single-cell electro-optical cell with a single pair of conductive coatings, characterized in that an alternating electric field applied from the voltage source simultaneously at a low frequency (50-500 Hz) and high frequency (500-8000 Hz) in a layer of a liquid crystal cause spatial deformations, leading to the formation of small-scale (pore size Single fractions - micrometer units) spatially inhomogeneous and quickly changeable structures in time with a random distribution of the refractive index gradients, and as a result, the phase modulation of the transmitted light in spatially nonuniform aperture electrooptical cell. 2. The method of modulating the phase of light according to claim 1, characterized in that the phase shift value at any portion of the aperture of the modulating liquid crystal medium in a given mode (amplitude, shape, duration and frequency of alternating pulses) of the electric voltage is not exactly specified, but is in the range of values from 0 to the maximum, determined by the thickness of the liquid crystal, the wavelength and the maximum possible value of the change in birefringence in this section of the aperture. 3. An optical modulator based on an electro-optical ferroelectric liquid crystal cell, containing two parallel-mounted dielectric plates, at least one of which is made transparent, on the inner sides of which are conductive coatings, at least one of which is made transparent, a liquid crystal filling the space between the conductive coatings, changing its optical anisotropy under the influence of an electric field, a transparent anisotropic coating, the initial orientation of the liquid crystal molecules in the absence of an external electric field, applied to at least one conductive coating from the side facing the liquid crystal, an electric voltage source, characterized in that the electric voltage source is configured to supply the cell with an alternating electric field simultaneously at low and high frequencies, and the composition and thickness of the liquid crystal layer are selected from the condition of ensuring the formation of small-scale particles in the liquid crystal layer spatial heterogeneous and rapidly changing in time structures with a random distribution of refractive index gradients. 4. The optical modulator according to claim 3, characterized in that the thickness of the liquid crystal layer is selected within 5-25 μm from the condition of achromatic transmission in the entire visible range of wavelengths and reaching the phase modulation depth necessary for suppressing speckles not less than pi (π) and spatial deformation on-off rates of more than 50 1 / s.

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