Nonlinear repolarization in optical fibers: polarization attraction with copropagating beams

We propose a type of lossless nonlinear polarizer, novel to our knowledge, a device that transforms any input state of polarization (SOP) of a signal beam into one and the same well-defined SOP toward the output, and perform this without any polarization-dependent losses. At the polarizer output end, the signal SOP appears to be locked to the input pump SOP. The polarizer is based on the nonlinear Kerr interaction of copropagating signal and pump beams in a telecom or randomly birefringent optical fiber.     

Cascaded dynamic eigenstates of polarization analysis for piezoelectric polarization control

We propose the cascaded dynamic eigenstates (DESs) of polarization to analyze multicomponent polarization control (PC) devices, and achieve the analytical expression of output state of polarization (SOP) as a function of voltage for piezoelectric polarization control (PPC). By measuring the DES at the output port of the device, the prestage DESs will rotate around subsequent ones. Experimental results in PPC confirm the validity of our analysis. The average error of our theoretical output SOP is 1.23 degrees, and the SOP response time is ~10 micros, which is promising to realize a quasi-open-loop high-speed PC.     

Uniformly high-speed semi-open loop polarization control and PMD suppression

We propose and demonstrate a novel scheme of semi-open-loop polarization control(SOL-PC), which controls the state of polarization(SOP) with high accuracy and uniform high speed. For any desired SOP, we first adjust the initial SOP using open-loop control(OLC) based on the matrix model of a three-unit piezoelectric polarization controller, and quickly move it close to the objective one. Then closed-loop control(CLC) is performed to reduce the error and reach precisely the desired SOP. The response time is three orders faster than that of the present closed-loop polarization control, while the average deviation is on par with it. Finally, the SOL-PC system is successfully applied to realize the suppression of the polarization mode dispersion(PMD) effect and reduce the first-order PMD to near zero. Due to its perfect performance, the SOL-PC energizes the present polarization control to pursue an ideal product that can meet the future requirements in ultrafast optical transmission and quantum communication.     

Visibility in magnetostrictive fiber-optic interferometric sensors and its dependence on the input SOP

The visibility in magnetostrictive fiber-optic interferometric sensors using a Gaussian laser beam is analyzed. It is shown that the conventional Gaussian laser beam has little influence on the visibility. The visibility depends strongly on the input state of polarization (SOP). We implement a cylindrical transducer and build a measurement setup with a polarization controller. The visibility dependent on the SOP of input light is measured. The estimated values are similar to the experiment results, which verifies the analysis.     

Spectroscopic polarimetry with a channeled spectrum

We describe a novel method for the spectroscopic measurement of the state of polarization (SOP) of light. A pair of thick birefringent retarders is incorporated into the spectroscopic polarimeter, so the generated channeled spectrum is composed of three quasi-cosinusoidal components carrying the information about the SOP of the light that is being measured. Fourier inversion of the channeled spectrum provides significant parameters for determination of the spectrally resolved Stokes parameters of light. No mechanically movable components for polarization control or active devices for polarization modulation are used, and all the Stokes parameters can be determined at once from only the single spectrum. The effectiveness of this method is demonstrated by the generation of elliptically polarized light whose SOP varies with wave number.     

Effects of polarization mode dispersion on cross-phase modulation in a WDM optical transmission system

The cross-phase modulation (XPM) changes the state-of-polarization (SOP) of various channels and leads to amplitude modulation of the propagating waves in a WDM system. Due to the presence of polarization mode dispersion (PMD), the angles between the SOP of the channels change randomly and cause the modulation amplitude fluctuation random in the perturbed channel. We analytically derive the dynamic equation of the perturbed channel, determine the combined probability density function of the random angle between the SOP of pumps and probe channel and evaluate the effects of PMD on XPM for a 4-channel IM-DD WDM system in terms of BER at bit rate of 10 Gb/s per channel. We also simulate the impact PMD on XPM for a 4-channel WDM system in terms of eye diagram and found that eye opening penalty is 1.85 dB higher when the fiber PMD coefficient increases from 0.5 to 1.5 ps/√km.     

Study of the stability of polarization mode dispersion in fibre

Polarization mode dispersion (PMD) is the ultimate limitation to high bit-rate fibre communication system. The stability of PMD is very important to its measurement and compensation. This paper puts forward a method to measure the stability of PMD by measuring the stability of the state of polarization (SOP) and introduces the conception of time evolution vector (TEV) of SOP. We observe the fact that the regularity of the principal state of polarization changing with time is the same as other SOPs‘‘, if we neglect the dependence of TEV on wavelength. We also measure the SOP‘‘s stability of some fibres with different lengths, and obtain results of PMD changing with time.     

Topological characterization of quantum phase transitions in a spin-1/2 model

We have introduced a novel Majorana representation of S=1/2 spins using the Jordan-Wigner transformation and have shown that a generalized spin model of Kitaev defined on a brick-wall lattice is equivalent to a model of noninteracting Majorana fermions with Z2 gauge fields without redundant degrees of freedom. The quantum phase transitions of the system at zero temperature are found to be of topological type and can be characterized by nonlocal string order parameters (SOP). In appropriate dual representations, these SOP become local order parameters and the basic concept of Landau theory of continuous phase transition can be applied.     

利用旋转波片组实现偏振变换器的两种新方法

偏振变换器作为一种重要的光学器件．以其高偏振变换精度、低成本、低插入损耗以及控制算法简单的特性在相干光纤通信和高速光纤通信领域具有十分重要的地位。提出了利用两个λ／4波片和一个λ／2波片的三波片组合实现任意偏振态变换的新方法。用改进的三维庞加莱球方法—偏振态投射平面的二维几何方法分别推导出了λ／4 λ／4 λ／2组合以及λ／2 λ／4 λ／4组合实现任意偏振态变换时每个波片的位置参量计算公式。研究结果表明：两个λ／4波片和一个λ／2波片的任意组合都可以实现任意偏振态的变换;用偏振态投射平面的几何方法处理偏振变换的相关问题比庞加莱球方法和矩阵处理方法简洁明了。研究结果为偏振变换器的设计提供了理论依据。     

The spin and pseudospin symmetries in the relativistic formalism: Similarities and differences

The effects of the symmetry breaking terms, spin-orbit potential (SOP) and pseudospin-orbit potential (PSOP), in the spin and pseudospin symmetries, respectively, are studied in a comparative way. The analytical properties of the small component F of the Dirac spinor for pseudospin doublets (PSDs) are investigated around the singularity point of the PSOP. We show that the PSOP and the pseudocentrifugal barrier must be appropriately related to each other to describe adequately the wave functions in the nuclear surface, whereas it is not the case for the centrifugal barrier and the SOP. We also determine a modified PSOP smaller than the PSOP when the parameter ˉ, appearing in it, is left to vary in the domain of real numbers. The inclusion of this modified PSOP allows us to define a continuous way that connects the two states of a PSD as ˉ varies continuously between the physical (integer) values of ˉ corresponding to these states. Our results indicate that whereas the SOP can be considered as a small spin symmetry breaking term that allows a simple explanation of the spin symmetry, the consideration of the PSOP as the pseudospin symmetry breaking term presents serious difficulties. Thus, we propose a new strategy to explain, in a simple way, the quasi-degeneracy of the PSDs.     

Stabilization of a channeled spectropolarimeter by self-calibration

A novel method to stabilize a channeled spectropolarimeter is described. The fluctuating retardations of the high-order retarders used in the spectropolarimeter are calibrated in parallel to the measurement of the wavenumber-dependent state of polarization (SOP) of light. Both the calibration of the retarders and the measurement of the SOP can be made simultaneously using a single light to be measured, and hence the resultant wavenumber-dependent SOP is almost immune to fluctuation of the retardations. The effectiveness of this method is experimentally demonstrated with retardation fluctuations induced by a temperature change up to 40 degrees C.     

全光学偏振自动控制器

本文报道新近研制的一种单模光纤偏振控制顺，该器件采用全光学的方法对光纤输出光信号的任意偏振态进行自动调整，使其成为一沿给定方向偏振的线偏振态，器件插入损耗小于１ｄＢ，与半导体激光放大器耦合损耗可小于５．５ｄＢ，其偏振灵敏度不大于０．５ｄＢ．     

Polarization properties of Rayleigh backscattering with a high degree of coherence in single-mode fibers

The state and degree of polarization (SOP, DOP) of Rayleigh backscattering (RB) are analyzed by using Jones calculus for the case the source coherent length is larger than the fiber length. It shows that the SOP of RB is the same as the SOP of input light, and the fiber disturbance does not influence the SOP of RB. The DOP of RB is also the same as that of input light. The corresponding experiments have been carried out, and the results agree well with all the predictions.     

Switchable multiple lasing oscillations in an erbium-doped fiber ring laser using a single stage of a Sagnac loop mirror

A simple scheme for a switchable multi-wavelength erbium-doped fiber (EDF) ring laser is investigated by using a single stage of a Sagnac loop mirror. The multiple lasing outputs are obtained and switched readily by controlling the state of polarization (SOP). Since the transmission characteristics of the Sagnac loop mirror in terms of peak wavelengths and peak powers strongly depend on the SOP, the switching performance of the proposed multi-wavelength EDF laser can be effectively obtained. The proposed multi-wavelength EDF laser has versatile lasing outputs in states of a single-, dual-, triple-, and quadruple-wavelength oscillations. The multiple outputs are effectively switchable by adjusting the SOP.     

Polarization shift keying (POLSK) phase diversity homodyne system with multiplying detection in coherent optical communications

We propose a Polarization Shift Keying (POLSK) phase diversity homo-dyne system with multiplying detection in coherent optical communications. The proposed system uses only one of three Stokes parameters, which is the phase difference between two orthogonal polarizations. Although such systems using only one Stokes parameter are very sensitive to polarization fluctuation, the proposed system becomes insensitive to the linear polarization fluctuation by using the multiplying detection with a combination of in-phase and quadrature optical signal components on two orthogonal polarizations. Furthermore, insensitivity to phase noise and offset frequency and attractiveness due to homodyne type in high-speed transmissions are maintained. The most attractive feature of the proposed system is that neither a polarization controller nor electronic feedback loop for matching the state of polarization (SOP) between transmitted and local oscillator (LO) optical signals is needed. We theoretically analyze the receiver sensitivity and the power penalties of the proposed system for the cases of the elliptical SOP of received optical signals and the imbalance optical 90° hybrid.     

Secrecy performance analysis of IRS-assisted D2D communication underlaying cellular network

In this paper, we evaluate the secrecy performance of an intelligent reflecting surface (IRS)-assisted device-to-device (D2D) communication in spectrum-shared cellular networks. To this end, we derive novel closed-form expressions for the secrecy outage probability (SOP) and the asymptotic SOP in the presence of multiple eavesdroppers. In the continue, in order to dynamically access the spectrum band of the licensed users, we define the optimization problem of secrecy spectrum resource allocation to minimize the SOP as a mixed-integer linear programming (MILP) problem. Then, the globally optimal solutions to this problem are obtained by using the Hungarian algorithm. Numerical analyses show that increasing the reflective elements of IRS can improve the secrecy performance.     

Physical layer secrecy analysis of HS-UAV NOMA network with spatially random eavesdroppers

This work investigates the physical layer secrecy performance of a hybrid satellite/unmanned aerial vehicle (HS-UAV) terrestrial non-orthogonal multiple access (NOMA) network, where one satellite source intends to make communication with destination users via a UAV relay using NOMA protocol in the existence of spatially random eavesdroppers. All the destination users randomly distributed on the ground comply with a homogeneous Poisson point process in the basis of stochastic geometry. Adopting Shadowed-Rician fading in satellite-to-UAV and satellite-to-eavesdroppers links while Rayleigh fading in both UAV-to-users and UAV-to-eavesdroppers links, the theoretical expressions for the secrecy outage probability (SOP) of the paired NOMA users are obtained based on the distance-determined path-loss. Also, the asymptotic behaviors of SOP expressions at high signal-to-noise ratio (SNR) regime are analyzed and the system throughputs of the paired NOMA users are examined for gaining further realization of the network. Moreover, numerical results are contrasted with simulation to validate the theoretical analysis. Investigation of this work shows the comparison of SOP performance for the far and near user, pointing out the SOP performance of the network depends on the channel fading, UAV coverage airspace, distribution of eavesdroppers and some other key parameters.     

Multiple re-configurable intelligent surfaces based physical layer eavesdropper detection for V2I communications

Inspired by the promising potential of re-configurable intelligent surface (RIS)-aided transmission in achieving the vision of 6th Generation (6G) network, we analyze the security model for a vehicular-to-infrastructure (V2I) network by considering multiple RISs (M-RIS) on buildings to act as passive relays at fixed distances from a source. In addition, multiple eavesdroppers are presented in the vicinity of the intended destination. Our aim is to enhance the secrecy capacity (SC) and to minimize secrecy outage probability (SOP) in presence of multiple eavesdroppers with the help of M-RIS in V2I communications. We propose a key-less physical layer security using beam-forming by exploiting M-RIS. The proposed approach assumes the concept of detecting eavesdroppers before the information can be transmitted via beam-forming by utilizing M-RIS. The results reveal that with consideration of M-RIS and beam-forming, the achievable SC and SOP performance is significantly improved while imposing minimum power consumption and fewer RIS reflectors.     

Detection of shear picosecond acoustic pulses by transient femtosecond polarimetry

Femtosecond transient polarimetry has been applied for the detection picosecond acoustic pulses generated in a thin film of zinc oxide (ZnO) deposited on an anisotropic zinc crystal surface. The measurements of the variations of the azimutal and the ellipticity angles describing the ultrafast variations of the state of polarisation (SOP) of the reflected light have been obtained. These polarimetric signals, interpreted as a SOP path on the Poincaré sphere, provide a sensitive method to detect acoustic echoes, particularly for shear acoustic pulses.     

光纤光栅辐射特性的研究

本文论述了光纤光栅辐射特性.通过耦合模理论首次给出了单模光纤偏振态(SOP)与光纤光栅远场辐射损失之间的关系.实验数据与理论分析基本吻合.利用光纤光栅这一关系可实现光纤偏振态在线检测.