The results of the research in the field of the electro-optics of nematic and smectic (ferroelectric) liquid crystals, performed at the Lebedev Physical Institute of the Russian Academy of Sciences (FIAN), as well as their applications in modulation of the amplitude, phase, or scattering of laser radiation in electrically and optically controlled transparencies (spatial light modulators); holographic memory devices; wave-field formers and image converters (including three-dimensional ones); and recognition, sensor, and other laser technique devices, are presented.

Speckles in images formed by a laser beam are interference noise arising due to coherent nature of laser radiation. As the number of projection systems using laser light sources increases, new methods and devices appear for reducing the contrast of speckle-noise and thereby suppressing it. Taking into account the long-standing nature of the problem and the continuing relev-ance of its solution, this review discusses modern practical methods and de-vices—despecklers, used to reduce the speckle contrast and to achieve high quality of projected images. The review discusses the nature of the speckles appearance, considers their statistical properties, and describes the measurement of the speckle contrast. The requirements for despecklers are considered, the most important of which are speckle suppression efficiency, sim-plicity of design and compactness, low power consumption and low optical loss. The characteristics of different types of despecklers, including diffusers, devices based on electroactive polymers, optical waveguides, colloidal solutions and liquid crystals, as well as orthogonal phase matrices and diffraction gratings proposed as despeckers, are examined in detail. It is shown that despecklers with decorrelation of the phase front based on the mirror deformation and optical fiber have less light losses. Electro-optical-liquid crystal despecklers do not have mechanically deformable or moving elements that reduce the reliability and durability of operation, and are more compact and simple in design. A comparative table of characteristics of the most effective despecklers in which the speckle contrast is reduced to ten percent or less, with an indication of their advantages and disadvantages, is given.

Fast transient times of ferroelectric liquid crystal (FLC) modulators (shutters) provide accurate selection of pulse light fluxes, for example, the active selection of view images in the stereoscopic applications. The problem of the electronic control of the FLC shutter appears in the case of unequal durations of its alternating open and closed optical states. Corresponding unequal portions of control electrical power during positive and negative polarities of the control voltage cause the degradation of the FLC performance. Main reason of the degradation is the inequality of the volume ion charges induced into the FLC layer by positive and negative control voltage. In this paper, the concept of solution to this problem is suggested with the corresponding experimental verification. Our method allows to equalize the positive and negative control electrical power values without affecting the optical response of the FLC shutter by introducing the short time gaps into a longer control voltage waveform to lower the corresponding integral electrical power value.

In a known display cell with the nematic liquid crystal (NLC) and interdigital electrodes on one of the glass substrates, the “In-Plane Switching” (IPS) mode is implemented, in which the NLC main optical axis reorients in a plane parallel to substrates, providing the most correct color reproduction at different angles view, up to 178 ° horizontally and vertically. Unfortunately, the creation of interdigital metal electrodes complicates and increases the technological process cost and causes a decrease in image contrast. At the same time, experimental results and calculations based on classical electro-optics of crystals indicate that electrooptical switching in the IPS mode is a natural and intrinsic feature of a conventional (with continuous electrodes) display cell with a planar-oriented layer of the ferroelectric liquid crystal (FLC), in which the effect of the deformed (by the electric field) helix FLC nanostructure is realized (DHF effect). In such a cell, the reorientation of the main optical axis under the influence of a weak electric field also occurs in the substrate plane if the FLC has a small pitch (about 100 nm or less) and a large tilt angle of molecules in the layer (about 38 ° or more). The dependences of the FLC cell light transmittance measured in this work, confirmed the achievement of the IPS electro-optical mode in the DHF FLC cell; moreover, the light modulation frequency was 1 kHz. Thus, while maintaining all the advantages of the IPS mode known in NLC, its implementation in FLC allows additionally obtaining technological advantages and multiple increase in modulation frequency.

Optical shutters based on ferroelectric liquid crystal (FLC) possess small transition times and provide accurate selection of pulsed light fluxes of millisecond duration. However, when an optical FLC-shutter must work with unequal duration of the open and closed optical states, the use of the traditional method of electronic control causes dysfunction. In this case, an average (during the control period) direct current begins to flow through the FLC shutter creating a residual volumetric ion charge in the FLC layer. The electric field of this charge distorts the action of the control electric field on the FLC molecules. The article describes the proposed method of solving the indicated problem. The essence of the method: the control electrical signal corresponding to the longer optical state of the FLC shutter is composed of a sequence of short pulses. This provides mutual equalization of the average energy of positive and negative control signals and, as a consequence-minimizing (zeroing) the direct current. The relations between the time parameters of the FLC shutter and the additional pulses, ensuring the required action of them with preservation of a given (initial) form of the temporal optical response of the FLC shutter are given. The principal operability of the method was experimentally tested. Physical properties and the substance of the FLC shutter layer used in the experiment are described.

The dynamics of the director reorientation in new helix-free ferroelectric liquid crystals (FLC) is considered. These materials are specially designed helix-free FLCs with a rather low value of the spontaneous polarization (less than 50 nC/cm2) and high viscosity (from 0.3 to 1.0 Poise), which are characterized by a spatial periodic deformation of smectic layers in the absence of an electric field. FLC director reorientation is due to the motion of solitons – spatially localized waves of a stationary profile that arise in an alternating electric field upon transition to the Maxwellian mechanism of energy dissipation. A theoretical model is proposed for describing the spatial-periodic deformation of FLC and reorientation of its director. The frequency and field experimental dependences of FLC electro-optical response time are presented for the modulation of the light transmission with fastest response among all LC materials. The novel helix-free FLC are able to efficiently modulate the visible and near IR radiation at frequencies up to 7 kHz at the electric field strength of the order of 1-2 V/μm. The conditions for the continuous hysteresis-free electro-optical response were determined, and such a response was realized for the first time in the frequency range up to 6 kHz.

In-plane electro-optical switching (IPS) is a natural feature of a conventional planar-aligned display cell based on the deformed helix ferroelectric liquid crystal effect (DHFLC-effect) with a sub-wavelength helix pitch, if the tilt angle is close to 40 degrees.

These materials are the helix-free ferroelectric liquid crystals (FLCs) with small spontaneous polarization (less than 50 nC / cm(2)) and high viscosity (from 0.3 to 1.0 Poise). They were specially designed for fast low-voltage displays and light modulators operating in transparent or scattering mode. The FLC director reorientation is due to motion of solitons at the transition to Maxwellian mechanism of energy dissipation. Such FLCs are able to efficiently modulate the visible and near IR radiation at frequencies up to 7 kHz at the electric field strength of the order of 1-2 V/mu m. The hysteresis-free and smooth dependence of the optical response on the external electric field is in the frequency range up to 6 kHz. In the bistable light scattering mode one can memorize an optical state for the time exceeding the switching time up to six orders of magnitude. Besides, the spatially inhomogeneous modulation of the light phase delay is demonstrated that is able to suppress the speckle-noise in images formed by a laser beam. Novel FLC- materials are compatible with FLCOS, 3D and FSC technologies.

We discuss cryptographic data protection network schemes combining the approaches of quantum cryptography with advanced computer information processing methods. The use of the latter is due to the presence of a number of unsolved problems in the existing quantum key distribution systems and is also associated with projects for the development of network-centric quantum communications and photonic networks, which involves the employment of multi-agent control models. Developments based on the Y-00 protocol with data encoding by the quantum noise of a transmitting laser are considered, and achievements in the field of quantum-optical random number generators are presented. The latter can be also used to design secure multi-valued logic encoding schemes that are promising for increasing the dimension of the key space in the 'one-time pad' method, for solving the tasks of position-dependent cryptography and for implementing multi-agent models.

The novel helix‐free ferroelectric liquid crystals developed at the Lebedev Physical Institute are characterized with the spatial deformation of smectic layers and soliton mechanism of director reorientation and show fastest electro‐optical response at lowest control voltage. The conditions are studied to increase the frequency interval of hysteresis‐free modulation (was extended to 6 kHz) and the temperature interval, in which the response time is practically constant (it is from 12 to 52 °C now). These FLC materials are very promise for future Field Sequential Color and 3D displays.

This is a review of results from studying ferroelectric liquid crystals (FLCs) of a new type developed for fast low-voltage displays and light modulators. These materials are helix-free FLCs, which are characterized by spatially periodic deformation of smectic layers and a small value of spontaneous polarization (less than 50 nC/cm(2)). The FLC director is reoriented due to the motion of solitons at the transition to the Maxwellian mechanism of energy dissipation. A theoretical model is proposed for describing the FLC deformation and director reorientation. The frequency and field dependences of the optical response time are studied experimentally for modulation of light transmission, scattering, and phase delay with a high rate. The hysteresis-free nature and smooth dependence of the optical response on the external electric field in the frequency range up to 6 kHz is demonstrated, as well as bistable light scattering with memorization of an optical state for a time exceeding the switching time by up to 6 orders of magnitude. Due to the spatially inhomogeneous light phase delay, the ability of a laser beam to cause interference is effectively suppressed. The fastest FLCs under study are compatible with 3D, FLC on Silicon (FLCoS), and Field Sequential Colors (FSC) technologies.

Spatially inhomogeneous modulation of a phase delay with the depth of the order π or more makes it possible to destroy phase relations in a laser beam passing through an electro-optical cell with the ferroelectric liquid crystal (FLC) and, as a consequence, to suppress speckle noise in images formed by this beam. Such a modulation is a consequence of chaotic changes in the position of the scattering indicatrix of helix-free FLC, when an electro-optical cell is simultaneously supplied with a low-frequency and high-frequency bipolar control voltage. In this work, the phase modulation and effective suppressing of the speckles are realized using a new type of helix-free FLC material with periodic deformations of smectic layers.

In an experimental sample of a despeckler, consisting of an electrooptic cell with a 20-mu m-thick helix-free liquid ferroelectric, to which an electric field with a strength of similar to 3V mu m(-1) and a frequency of 2 kHz is applied, we obtained spatially nonuniform phase modulation of a laser beam with a value exceeding pi. The effect allows the implementation of speckle noise suppression with an efficiency of 10.7 dB.

The characteristics of modern microdisplays based on liquid crystals and electromechanical micromirrors are considered. These displays, being spatial light modulators, can rapidly generate large optical data arrays to be recorded as holograms and used for data processing. The potential of microdisplays for visualising digital holograms in real time is estimated.

We suggest a simple and effective method of suppressing the speckle-noise in the laser-generated images using the high-speed electro-optical cell with the ferroelectric liquid crystal (FLC), in which the helix is absent (compensated). The nature of deformations of FLC smectic layers in the electric field is indicated, and the mechanism of spatially inhomogeneous phase modulation of the laser beam passing through a cell is considered. The results of destruction of the phase relationships in a laser beam and speckle-noise suppressing are presented in comparison with earlier results, when helix FLC was used.

A new type of ferroelectric liquid crystal (FLC) is considered, where the reorientation of the director (main optical axes) at the interaction of an electric field with the FLC's spontaneous polarization is due to the movement of spatially localized waves with a stationary profile: solitons arise at the transition due to the Maxwellian mechanism of energy dissipation. Under certain conditions, the appearance of such waves leads to the formation of a structure of transient domains, and as a consequence, to the scattering of light. The Maxwellian mechanism of energy dissipation allows one to reduce the electric field strength at which the maximum efficiency of light scattering is achieved down to 2-3 V/μm and to increase the frequency of light modulation up to 3-5 kHz. Intensive bistable light scattering in an electro-optical cell filled with a specially designed helix-free FLC was studied, and a stable scattering state can be switched on and off for a few tens of microseconds and memorized for a few tens of seconds.

The authors develop an original and promising method of suppressing the speckle-noise in images generated by a laser beam by means of a compact despeckler based on an electro-optical cell with the smectic ferroelectric liquid crystal (FLC), realizing spatially inhomogeneous phase modulation of light. The mechanisms of destruction of the phase relations in the laser beam passing through a cell with helix-free FLC are discussed. The electric field induces the light scattering and small-scale randomly distributed gradients of the refractive index in FLC layer. The features and benefits of a despeckler using helix- free FLC compared to helix FLC are indicated.

The characteristics of modern micro-displays are considered and compared. These devices in principle are capable not only to display the computer generated information blocks on the projection screen but also to send them into the holograms, and even to form these blocks as the digital holograms reconstructed from a micro-display screen.

AbstractWe present results of studying the intensive bistable light scattering in an electro‐optical cell filled with a specially designed helix‐free ferroelectric liquid crystal (FLC). A stable scattering state can be switched on and off for 70–100 μs and memorized for a few tens of seconds.

Results of the research of experimental samples of electro-optical cells based on ferroelectric liquid crystals (FLC) fulfilled in recent years show that display screens produced on the base of FLC-technology will significantly surpass in performance the modern screens both on the basis of the widely used nematic liquid crystals (NLC) and the known bistable FLC. With respect to the devices with NLC this will provide with a guarantee the better visualization of 3D and 2D images due to an increasing 5 and more times the frame rate (600 Hz or more), reducing 4-5 times the optical response time (till less than 0,1 ms) and increasing at least 2 times the image brightness at the energy consumption reduced by more than half.Till now FLC are limitedly used in helmet-mounted displays, but potentially FLC-technology is suitable for a wide range of high-speed low-voltage screens of smartphones and gadgets, microdisplays and projection displays on their base, including three-dimensional displays, shutters for stereo glasses, spatial light modulators, elements and devices for information processing, adaptive optics, holography, sensors and others, in which the increased speed of FLC not only provides superiority of parameters but new functional properties also.