Phase Modulation Of Wave Research Articles

Encryption Technology of Optical Communication Network Based on Artificial Intelligence Technology

At present, research on enhancing information transmission security by addressing the two key issues of time delay signal elimination and key space expansion in chaotic secure communication systems has become a hot topic. In order to improve the encryption effect of optical communication network, this paper analyzes the encryption technology of optical communication network with AIT (artificial intelligence technology), designs the encryption scheme of optical communication network with the help of AIT, and takes the digital random sequence as the key. Moreover, this paper uses the digital signal processor to control the arbitrary wave generator to generate multi-ary step square wave, modulate the optical feedback and realize the highly random change of external cavity delay, thus eliminating the long external cavity delay information. This article proposes a chaotic secure communication system using digital sequences as keys and external cavity optical feedback, a device for forming a chaotic source through arbitrary wave phase modulation and single loop feedback, and a chaotic secure communication system with single feedback key phase modulation and injection synchronization. At the same time, this paper proposes a system scheme using single-loop optical feedback phase modulation, the CS(chaotic signal) with complex dynamic behavior is output, and the time-delay signal is effectively eliminated. This paper analyzes the strength and phase information of CS by autocorrelation and mutual information technology, and verifies the effect of optical communication network encryption technology. Through the analysis of experimental results, it can be seen that the optical communication network encryption technology based on AIT proposed in this paper can effectively improve the encryption effect of optical communication network. The algorithm model camera proposed in this article can be used in subsequent practice to improve communication encryption performance

Single-channel acoustic vortex tweezer with attachable fan-shaped holographic lens

The utilization of acoustic vortices presents a promising technique for contactless particle manipulation. However, existing methods for generating acoustic vortices typically rely on complex active driving systems and array ultrasound transducers. Therefore, more simplified and robust approaches to inducing acoustic vortices should be considered. With inspiring the fact that acoustic vortices can be generated by the differences in the height of adjacent sectors in conventional four-panel transducers, we aim to develop a single-channel acoustic vortex tweezer with a simplified driving system by incorporating attachable fan-shaped polydimethylsiloxane (PDMS) holographic lens. This passive lens structure with different heights in adjacent sectors can generate phase-modulated ultrasonic waves. Therefore, the interaction of phase-modulated waves passing through the lens is expected to result in a vortex-like beam. The available materials of fan-shaped lens are not limited to the PDMS. This lens type can be appropriately fabricated with an understanding of the sound of speed within the desired material and predetermined thickness, inducing π/2 phase difference in the adjacent lobes. As a result, the excited acoustic waves propagated through the lens were under mutual interaction without any active electrical setup, forming a null pressure region enveloped by four distinct acoustic lobes. We systemically investigated the tweezing potential using vortex-like waves. Several types of bioparticles were utilized in these investigations: microbubbles, polystyrene (PS) beads, and cancer cells. Our findings demonstrate that the transducer with lens is sufficiently capable of spatial manipulation of bioparticles. Remarkably, the microbubbles traveling at a flow velocity of 32 cm/s in a blood vessel-mimicking phantom were feasibly trapped in the proposed transducer. Furthermore, the spatial control of PS and cells with higher acoustic impedance was also feasible in static conditions. Consequently, the proposed transducer offers an economically and practically viable solution for various biomedical applications, such as drug delivery and cell-based bioengineering.

On-chip manipulation of Bloch Surface Wave

Manipulation of optical surface wave is essential for diverse applications such as optical circuits, integrated optics, on-chip signal processing. One of the commonly used optical surface waves is the surface plasmon polariton (SPP), the intrinsic Ohmic loss introduced by the metal limits its potential for real applications especially for large scale on-chip devices. Bloch surface wave (BSW) is an alternative of SPP which propagates on multiple layers of dielectrics. Different from SPP, as dielectrics show nearly no Ohmic loss, the BSW is an excellent candidate for large scale optical circuits. In this paper, we propose a strategy to realize phase modulation of Bloch surface wave by adding additional dielectric boxes on top of the substrate. By carefully designing the positions as well as dimensions of these boxes, it is proved that beaming, focusing, specific beams generation such as Bessel beams or Airy beams is possible with this method, which shows great potential in on-chip electromagnetic field modulation and signal processing.

Flexible control of multi-focus with geometric phase encoded metalens based on the complex digital addition principle

A transmissive encoding metasurface based on the geometric phase principle is proposed. The encoding unit adopts an anisotropic Si dielectric strip and SiO2 substrate on the upper layer, and realizes the phase modulation of the incident wave in the span of 0–2π on the premise of achieving high polarization conversion efficiency. 1-bit, 2-bit and even multi-bit coding units are constructed by rotating surface units. In order to realize the multi-focus function of imaging space, we propose to introduce the principle of complex code addition into the design of metalens. Compared with traditional scalar encoding, complex encoding reveals the intrinsic connection between different encoded bits, thus closer to the essence of electromagnetism. The multi-angle control of multi-focus in free space is realized by the complex coding of four groups of single-focal metalenses and their addition operations. The multifocal metalens at this time also has the angular characteristics of the previous single focus lens, and multiple angles have no influence on each other. Our proposed complex additive multifocal metalens provides a new idea for future multifocal metalens design, especially the design of polarization-sensitive devices.

Space-time analogy and its application to design schemes borrowed from Fourier optics for processing ultrafast optical signals

Square-wave pulse generation with a variable duty ratio can be realized with the help of the ideas of Talbot array illuminators formulated for binary phase gratings. A binary temporal phase modulation of continuous wave (CW) laser field propagating through a group-delay-dispersion circuit of the fractional Talbot length results in a well defined sequence of square-wave-form pulses. When P = 1 a duty ratio of the pulses D is for Q = 4 and for Q = 3 and 6. Maximum intensity of the pulses doubles and triples compared to the CW intensity for and , respectively. These pulses can be used for return-to-zero laser field modulation in optical fiber communication. For extra features between the pulses are found originating from a finite rise and drop time of phase in a binary phase modulation. A similar effect to the benefit of the time-space analogy is predicted for binary phase gratings and interpreted as gleams produced by imperfect edges of the components of the rectangular phase gratings.

Spectral broadening of femtosecond pulses during SRS in hydrogen

It was shown that the spectral broadening of femtosecond laser pulses during stimulated Raman scattering (SRS) in hydrogen is determined by two nonlinear processes leading to phase modulation of the laser wave. Namely, the dependence of the refractive index of the gas on the intensity of laser radiation and the dependence of the refractive index on the ratio of the number of molecules at the ground and first vibrational levels of the hydrogen molecule, which changes during SRS.

STO/PDMS composite film achieving continuously tunable terahertz phase modulation via mechanical and thermal regulation

Phase is the basic property of electromagnetic waves, and controlling the phase is one of the eternal research topics in the field of electromagnetic waves. Here, a broadband terahertz phase shifter made of polydimethylsiloxane (PDMS) and strontium titanate (STO) has been theoretically proposed and experimentally demonstrated. The mixed material design gives the phase shifter the dual properties of PDMS and STO. Therefore, the phase shifter can not only change the thickness through stretching but also change the effective refractive index through temperature changes. The thickness and refractive index changes directly cause the transmission phase of the phase shifter to move synchronously. Because the material does not have frequency selection characteristics, the phase shifter realizes customized phase control in a wide range of the terahertz band. In the experiment, any phase shift can be achieved by adjusting the doping ratio, stretching ratio, and temperature. The proposed broadband phase shifter is simple to fabricate and has various control methods, which provides a variety of modes of terahertz wave phase modulation.

Dynamics of solutions of nonlinear functional differential equation of parabolic type

Purpose of this work is to study the initial-boundary value problem for a parabolic functional-differential equation in an annular region, which describes the dynamics of phase modulation of a light wave passing through a thin layer of a nonlinear Kerr-type medium in an optical system with a feedback loop, with a rotation transformation (corresponds the involution operator) and the Neumann conditions on the boundary in the class of periodic functions. A more detailed study is made of spatially inhomogeneous stationary solutions bifurcating from a spatially homogeneous stationary solution as a result of a bifurcation of the “fork” type and time-periodic solutions of the “traveling wave” type. Methods. To represent the original equation in the form of nonlinear integral equations, the Green’s function is used. The method of central manifolds is used to prove the theorem on the existence of solutions of the indicated equation in a neighborhood of the bifurcation parameter and to study their asymptotic form. Numerical modeling of spatially inhomogeneous solutions and traveling waves was carried out using the Galerkin method. Results. Integral representations of the considered problem are obtained depending on the form of the linearized operator. Using the method of central manifolds, a theorem on the existence and asymptotic form of solutions of the initial-boundary value problem for a functional-differential equation of parabolic type with an involution operator on an annulus is proved. As a result of numerical modeling based on Galerkin approximations, in the problem under consideration, approximate spatially inhomogeneous stationary solutions and time-periodic solutions of the traveling wave type are constructed. Conclusion. The proposed scheme is applicable not only to involutive rotation operators and Neumann conditions on the boundary of the ring, but also to other boundary conditions and circular domains. The representation of the initial-boundary value problem in the form of nonlinear integral equations of the second kind allows one to more simply find the coefficients of asymptotic expansions, prove existence and uniqueness theorems, and also use a different number of expansion coefficients of the nonlinear component in the right-hand side of the original equation in the neighborhood of the selected solution (for example, stationary). Visualization of the numerical solution confirms the theoretical calculations and shows the possibility of forming complex phase structures.

Coherent Square Pulses Generation Based on Continuous Wave Phase Modulation

Coherent Square Pulses Generation Based on Continuous Wave Phase Modulation

A review of terahertz phase modulation from free space to guided wave integrated devices

Abstract In the past ten years, terahertz technology has developed rapidly in wireless communications, spectroscopy, and imaging. Various functional devices have been developed, such as filters, absorbers, polarizers, mixers, and modulators. Among these, the terahertz phase modulation is a current research hotspot. It is the core technology to realize flexible control of the terahertz wavefront, beam scanning, focusing deflection. It is indispensable in terahertz wireless communication, high-resolution imaging, and radar systems. This review summarizes the research progress of terahertz phase modulators from the two major types: free space and guided wave integration. Among these, the free space terahertz phase modulator is realized by combining the tunable materials and artificial metasurfaces. Based on different types of tunable materials, the terahertz free space phase modulator combining the semiconductor, liquid crystal, phase change materials, graphene, and other two-dimensional materials are introduced, and the influence of different materials on the phase modulation performance is discussed and analyzed. The monolithic integration and waveguide embedding methods are introduced separately, and the characteristics of different forms of terahertz-guided wave phase modulation are also discussed. Finally, the development trends of terahertz phase modulators, possible new methods, and future application requirements are discussed.

Flexural wave control via the profile modulation of non-uniform Timoshenko beams

A methodology to control the flexural wave propagation via modulating the beam profile is presented in this paper. Firstly, the power series method is utilized to theoretically solve the flexural waves in a non-uniform Timoshenko beam with arbitrarily contoured profiles. It is demonstrated that this method is effective for most of inhomogeneous beams as long as the convergence criterion about the beam thickness is satisfied in advance. After validation by comparing the theoretical results with those from the finite element analysis for different thickness variations, lenses are designed by using the quadratic thickness variation pattern with the aim of focusing the wave emitted from a point source on one or two particular positions. Additionally, according to the generalized Snell's law, the thickness-induced phase modulation of the flexural wave is proved from the views of theoretical analysis and numerical simulations, based on which lenses for focusing a plane flexural wave are also realized. It is illustrated through systematic analysis in the frequency domain that all of the lenses designed can exhibit good performances with the evidently increased energy at actual focal positions and the focusing sizes smaller than one working wavelength, which has great potentials in versatile engineering applications.

Modified homodyne laser interferometer based on phase modulation for simultaneously measuring displacement and angle.

Many researchers from scientific and industrial fields have devoted their efforts to the laser interferometer, aiming to improve the measurement accuracy and extend the practical applications. Here, we present a modified homodyne laser interferometer based on phase modulation for simultaneously measuring displacement and angle. The active sawtooth wave phase modulation enhances immunity of this interferometer to the environmental fluctuations and laser power drift. Based on polarized optic theory and the sinusoidal measurement retro-reflector, a modified Michelson-type interferometer configuration is designed to simultaneously measure displacement and angle. Phase difference between the reference and measurement interference signals can be obtained using the sawtooth wave phase modulation and zero crossing detection technique, where the real-time displacement and angle values can be derived directly. Experimental results demonstrate our proposed interferometer has good static and dynamic performance.

Study on Acoustics Abnormal Refraction Based on Generalized Snell’s Law

In recent years, metamaterials have been used to manipulate wave fronts in various ways, affecting the propagation of waves, and exerting different its application values. Based on the generalized Snell’s law derived from Fermat’s principle, the article takes advantage of the high integration of metamaterials at the sub-wavelength scale to construct an acoustic metasurface artificial structure and expands it to a periodic type. Under the condition of ensuring the constant transmittance when acoustic wave passes through the interface of the two media, through the phase modulation of the acoustic wave on the surface of the structure, the strange phenomenon of abnormal refraction is generated, and the arbitrary manipulation of the wave is realized effectively.

Exact discrete spectrum of the Zakharov-Shabat scattering problem for a phase-modulated wave packet

The simple exact Zakharov-Shabat scattering problem discrete spectrum is presented for the special initial data of the nonlinear Schrödinger equation, having the form . The salient features of this solution and the issues of its stability are discussed.

Nonlinearity mitigation with a perturbation based neural network receiver

We propose a less complex neural network that estimates and equalizes the nonlinear distortion of single frequency dual polarization data transmitted through a single mode optical fiber. We then analyze the influence of the size of the input data symbol window on the neural network design and the enhancement of the quality factor (Q-factor) that can be achieved by integrating the neural network with a perturbative nonlinearity compensation model. We significantly reduce the complexity of the neural network by determining the most significant inputs for the neural network from the self-phase modulation terms (intra-cross phase modulation and intra-four wave mixing) in the model. The weight matrices of the neural network are determined without prior knowledge of the system parameters while the complexity of the network is reduced in two stages through weight trimming technique and principle component analysis (PCA). Applying our procedure to a 3200 km double polarization 16-QAM optical system yields a ≈ 0.85 dB Q-factor enhancement with a 35% smaller number of inputs compared to previous designs.

Theoretical study of coherent supercontinuum generation in chalcohalide glass photonic crystal fiber

Mid-infrared supercontinuum (SC) generation in normally dispersive photonic crystal fiber (PCF) made of GeS2-Ga2S3-CsI chalcohalide glass, is theoretically investigated. The finite difference method is employed to compute and optimize the different linear and nonlinear parameters of the fundamental guided mode. Simulation results indicate that the all-normal regime of dispersion over the entire wavelength range is achieved by properly reducing the diameter of the core neighboring air holes. The pulse propagation within the core of the proposed PCF and the SC generation process are accurately modelled and optimized, by numerically solving the generalized nonlinear Schrodinger equation. Both of Self Phase Modulation (SPM) and Optical Wave Breaking (OWB) effects are identified as the dominant nonlinear mechanisms involved in the pulse spectral broadening process. By launching at 3 μm, a 3 nJ energy and 50 fs duration input pulse into 15 mm long PCF, a broadband and highly coherent mid-infrared SC spectrum spanning the spectral region from 1.45 μm to 5.95 μm at 20 dB, is successfully generated.

Experimental observation of three-dimensional non-paraxial accelerating beams.

We experimentally realize three-dimensional non-paraxial accelerating beams associated with different coordinate systems. They are obtained by Fourier transforming a phase-modulated wave front in an aberration-compensated system. The phase pattern is encoded to include the phase and amplitude modulation for the accelerating beams with additional correction phase for the aberration compensation. These beams propagate along a circular trajectory, but they exhibit rather complex intensity patterns corresponding to the shape-invariant solutions in parabolic, prolate spheroidal and oblate spheroidal coordinate systems.

Second-harmonic generation spectroscopy in gold nanorod-based epsilon-near-zero metamaterials.

The interest in hyperbolic metamaterials is fueled by fascinating optical properties exhibited by this class of artificial media. Their optical features originate from hyperbolic dispersion emerging due to the shape anisotropy of the metal-dielectric composite. In this work, we study experimentally and numerically the second-harmonic generation (SHG) in ordered arrays of Au nanorods embedded in porous aluminum oxide. Strong increase of the SHG intensity in the vicinity of the epsilon-near-zero (ENZ) spectral point accompanied by dramatic phase modulation of the SHG wave is revealed. These effects are attributed to resonant enhancement of the electric field of the light wave and transition from the elliptical to hyperbolic dispersion law in hyperbolic metamaterials near the ENZ point.

Validation of full-f global gyrokinetic modeling results against the FT-2 tokamak Doppler reflectometry data using synthetic diagnostics

Two versions of the X-mode Doppler reflectometry (DR) synthetic diagnostics are developed within the framework of the ELMFIRE global gyrokinetic modeling of the FT-2 tokamak ohmic discharge. In the ‘fast’ version the DR signal is computed in the linear theory approximation using the reciprocity theorem, utilizing the probing wave field pattern provided by computation and taking into account the 2D plasma inhomogeneity effects; whereas the alternative ‘slow’ version DR synthetic diagnostic is based on the full-wave code IPF-FD3D describing the probing and scattered wave propagation in turbulent plasma. The DR signal frequency spectra and the dependence of their frequency shift, width and shape on the probing antenna position are computed and shown to be similar to those measured in the high-field side probing DR experiment at the FT-2 tokamak. The geodesic acoustic mode characteristics provided by the measurements and by the synthetic DR are close within a 12% accuracy. However, a substantial difference was found in the decay of the DR signal cross-correlation functions with growing frequency shift in the probing wave channels. The quick decrease in the radial correlation DR coherence observed in the experiment and full-wave synthetic diagnostic, compared to the fast synthetic DR, is attributed to the nonlinear effect of the probing wave phase modulation by the turbulence in the former two cases. The variation in the DR signal at a growing incidence angle in the experiment is also shown to be slower than predicted by both of the synthetic diagnostics, presumably due to underestimation of the probing wave phase modulation and consequent nonlinear saturation of the DR signal at lower incidence angles in modeling.

High-efficiency full-phase modulation of a terahertz wave based on a dielectric metasurface

In this paper, we propose a transmissive terahertz metasurface, consisting of periodically arranged subwavelength silicon cross resonators. Based on the theory of electromagnetic dipole resonance, and changing the structural parameters and directions of cross resonators; the phase modulation of a terahertz wave can be realized at a target terahertz frequency. By employing full-wave finite element numerical simulation, we utilize the metasurface to achieve an almost full phase 2π control in the terahertz band, and the transmission efficiency is over 90%. The proposed transmissive metasurface has potential applications in some terahertz functional devices, such as lenses, wave plates and optical vortex converters.