A broadband quantum noise source based on detection of shot noise of a balanced photodetector is demonstrated. Precise electro-optical tuning of the balanced photodetector circuit was carried out by an integrated optical beam splitter constructed in the form of the dual output Mach-Zehnder interferometer on a lithium niobate substrate. The classical component of the detected noise related to the relative intensity noise of a laser diode was suppressed by more than 15 dB. At the maximum laser power of 100 mW, the power spectral density of detected shot noise was 12 dB higher than the level of technical noise of the measuring system in the frequency band above 3 GHz. Keywords: quantum random number generator, vacuum fluctuations, shot noise measurements, integrated optics, lithium niobate

A numerical method for approximating the equations of dynamics of a polymer solution flow is proposed. The proposed technique is based on a hybrid approach. The hydrodynamic component of the flow is described by a system of Navier–Stokes equations and is numerically approximated using the linearized Godunov method. The polymer component of the flow is described by a system of equations for the polymer stretching vector 𝐑 and is numerically approximated by the Kurganov–Tadmor method. Using this scheme, stability of the polymer solution flow at low Reynolds numbers Re∼ 10 in a square cell under the action of an external periodic force is investigated. The instability of this type of flow characterized by a violation of its laminarity is studied by means of a numerical experiment. The spectral characteristics of the polymer solution at low Reynolds numbers are constructed.

Two methods for compensation of polarization fading in microwave photonic links have been studied. Comparison of noise characteristics has been performed and factors limiting the dynamic range of microwave photonic link have been analyzed on an example of a link with an external remote electrooptic modulator. The possibility of reaching spurious-free dynamic range close to the shot-noise limit SFDR3~116 dB Hz-2/3 has been demonstrated for 1000 m microwave photonic link. Keywords: Optical polarization, polarization fading, fiber-optic links, optical noise, dynamic range, balanced detection, microwave photonics, integrated optical modulator, polarization control

The diffraction of a light wave by fluctuations in the refractive index in a turbulent medium leads to its distortions. Their analysis allows one to extract the main parameters of turbulence. In this paper, we propose a new method based on measurements of the correlation function of the gradients of the light wave phase, which allows us to independently find the Fried parameter r0 and, then, the outer scale of turbulence L0. The method has been successfully tested on measurement data obtained during the passage of laser radiation through a gaseous medium with artificially created turbulence.

The problem of two-dimensional flow of a viscous weakly compressible fluid in a square cell under excitation by a spatially periodic static external force (Kolmogorov flow) is considered. A new method for determining the flow structure is presented. It is based on the analysis of the vorticity field at different times. This method is used to classify types of flows the characteristics of which were obtained by numerical simulation. The main flow regimes are identified depending on the values of the friction coefficient against the bottom and the pumping force: laminar, chaotic and vortex regimes. Transitional types of flow are studied separately: the quasi-periodic regime, which arises through a sequence of bifurcations when the laminar and chaotic flow regimes change, and the alternation regime, which occurs during the transition from the chaotic to vortex flow. Phase diagrams are constructed in the space the amplitude of the external force–the friction coefficient against the bottom, which made it possible to classify the type of flow on the basis of the values of the friction coefficient against the bottom and the pumping force.

We examine statistics of fluctuations of the light beam intensity at its propagating in a turbulent atmosphere. We are interested in the probability of relatively large values of the beam intensity. The model of a phase screen is considered. We find the tail of the probability density function characterized by the stretched exponent with power 7/12. Conditions of realizing the tail are established. The general picture is discussed.

A two-dimensional flow of a viscous fluid in a cell of finite size is studied numerically. The flow arises as a result of an inverse cascade supported by a constant pumping. Several distinct states are observed. One of them is dominated by a large eddy with a well-defined average velocity profile. In the second state, strong chaotic large-scale fluctuations predominate. A laminar flow is observed in the third state. The nature of the resulting state depends on the fluid kinematic viscosity coefficient, the magnitude of the external pumping force wave vector, and the value of the bottom friction factor. When the values of the kinematic viscosity and wave vector are fixed, a small value of the bottom friction factor leads to the appearance of the first state. As the coefficient of the bottom friction factor increases, there occurs a transition from a flow with one large vortex to a laminar flow through a series of states with several unstable vortices, which we call chaotic motion. The paper presents the results of numerical simulation of a weakly compressible viscous fluid flow in a closed cell with no-slip boundary conditions on the walls. Pumping is carried out by a static force periodic in space in two directions. The simulation is carried out for various values of the bottom friction factor.

We investigate fluctuations of vorticity inside a coherent vortex generated by the inverse energy cascade in two-dimensional turbulence. Temporal and spatial correlations can be characterized by the pair correlation function. The interaction of fluctuations leads to a nonzero third moment of vorticity. We analyze the pair correlation function and the third moment using a model in which the pumping is short-correlated in time and derive explicit expressions for the Gaussian spatial correlation function for the pumping force.

We study the correlations of vorticity fluctuations inside a coherent vortex resulting from the inverse energy cascade in two-dimensional turbulence. The presence of a coherent flow, which is a differential rotation, suppresses small-scale fluctuations of the flow, which are created by an external force, and lead to the fact that these fluctuations can be considered as non-interacting and, therefore, examined in a linear approximation. We calculate the pair correlation function of vorticity and demonstrate that it has a power-law behavior both in space and in time. The obtained results allow us to start a systematic study of the effects associated with the nonlinear interaction of fluctuations, which play an essential role on the periphery of a coherent vortex. Our results are also applicable to the statistics of a passive scalar in a strong shear flow.

We examine statistics of fluctuations of the laser beam intensity at its propagating in turbulent atmosphere. We are interested in relatively large propagating distances and the remote tail of the probability density function. The tail is determined by the stretched exponent, we find its index.

This article presents a methodology for calculating extreme loads (positive and negative) acting on an object during the direct impact of a tsunami wave. The methodology is based on an analysis of the results of physical modeling of the interaction of long tsunami-type waves with a storage unit of compressed natural gas for various parameters of the object and external influence being studied.

We present nonlinear dynamic equations for nematic and smectic A liquid crystals in the presence of an alternating electric field and explain their derivation in detail. The local electric field acting in any liquid-crystalline system is expressed as a sum of external electric field, the fields originating from feedback of liquid crystal order parameter, and a field, created by charged impurities. The system tends to decrease the total electric field, because it lowers the energy density. This basically nonlinear problem is not a pure academic interest. In the realm of liquid crystals and their applications, utilized nowadays modern experimental techniques have progressed to the point where even small deviations from the linear behavior can be observed and measured with a high accuracy. We follow hydrodynamic approach which is the macroscopic description of condensed matter systems in the low frequency and long wavelength limit. Nonlinear hydrodynamic equations are well established to describe simple fluids. Similar approaches (with degrees of freedom related to the broken orientational or translational symmetry included) have been used also for liquid crystals. However to study behavior of strongly perturbed (well above the thresholds of various electro-hydrodynamic instabilities) liquid crystals, the nonlinear equations should include soft electromagnetic degrees of freedom as well. There are many examples of such instabilities, e.g., classical Carr-Helfrich instability triggered by the competitive electric and viscous torques, flexoelectric instability, and so one. Therefore the self-consistent derivation of the complete set of the nonlinear electro-hydrodynamic equations for liquid crystals became an actual task. The aim of our work is to present these equations, which is a mandatory step to handle any nonlinear phenomenon in liquid crystals.

This work presents the results of experiments on the physical modeling of the interaction of long tsunami-type waves with floating gas storage. Loads under wave action are assessed, and the results are analyzed. Conclusions are drawn on the nature of the load dependence on the floating object orientation relative to the impact direction of the tsunami wave and the maximum tsunami height.

For the first time, the theory and practical realization of a broadband quantum noise generator based on original integrated optical beam splitter in the form of a Mach-Zehnder interferometer is demonstrated. The beam splitter with a double output, made on a lithium niobate substrate, provided accurate electro-optical balancing of the homodyne quantum noise detection circuit. According to our knowledge, the experimentally obtained excess of quantum noise over classical noise by 12 dB in the frequency band over 4 GHz, which is the best parameters of quantum noise generators known from the literature.

A novel operating point stabilization method for fiber-optic Mach-Zehnder interferometers using optical frequency shifters is proposed. The method is capable of continuous reset-free compensation of an unbounded phase drift in arms of an interferometer with rates up to hundreds radians per millisecond.

The aim of this work is to revisit the phenomenological theory of the interaction between membrane inclusions, mediated by the membrane fluctuations. We consider the case where the inclusions are separated by distances larger than their characteristic size. Within our macroscopic approach a physical nature of such inclusions is not essential. However, we have always in mind two prototypes of such inclusions: proteins and RNA macromolecules. Because the interaction is driven by the membrane fluctuations and the coupling between inclusions and the membrane, it is possible to change the interaction potential by external actions affecting these factors. As an example of such external action we consider an electric field. Under external electric field (both dc or ac), we propose a new coupling mechanism between inclusions possessing dipole moments (as it is the case for most protein macromolecules) and the membrane. We found, quite unexpected and presumably for the first time, that the new coupling mechanism yields to giant enhancement of the pairwise potential of the inclusions. This result opens up a way to handle purposefully the interaction energy, and as well to test of the theory set forth in our article.

We examine analytically and numerically the state of a two-dimensional fluid in a finite box appearing as a result of the inverse cascade supported by a permanent pumping. We argue that there are two different states. One of the states is dominated by big coherent vortices with a well-defined mean profile. The other state is dominated by strong chaotic large-scale fluctuations. The character of the realized state depends on the ratio νkf2/α where ν is the kinematic viscosity coefficient, kf is the characteristic wave vector of the pumping force and α the bottom friction coefficient. If the ratio νkf2/α is large then one expects to observe the first state, whereas in the opposite state the second (chaotic) state is expected. To check the prediction we performed the direct numerical simulations of hydrodynamics of a weakly compressible two-dimensional fluid with no-slip boundary conditions. The pumping force is static and contains some spacial harmonics. The simulations are performed for different values of pumping and of the ratio νkf2/α. We introduce the criterion based on presence/absence of long time correlations to distinguish two above states. The numerical results confirm the analytical predictions.

Broadband integrated optical modulators are key elements of modern optical information systems. The three main technological material platforms for their manufacture are considered: lithium niobate, III-V semiconductors, and silicon. Progress achieved in the development of integrated optical modulators is analyzed, and the main parameters of modulators obtained for various materials are compared with requirements for practical applications. Directions in the further development of the technology of modulators related to new problems in optical information systems are discussed.

We investigate the coherent vortex produced by two-dimensional turbulence excited in a finite box. We establish analytically the mean velocity profile of the vortex for the case where the bottom friction is negligible and express its characteristics via the parameters of pumping. Our theoretical predictions are verified and confirmed by direct numerical simulations in the framework of two-dimensional weakly compressible hydrodynamics with zero boundary conditions.