Dynamic phase assembled terahertz metalens for reversible conversion between linear polarization and arbitrary circular polarization

If a metalens integrates the circular polarization(CP)conversion function,the focusing lens together with circular-polariz-ing lens(CPL)in traditional cameras may be replaced by a metalens.However,in terahertz(THz)band,the reported metalenses still do not obtain the perfect and strict single-handed CP,because they were constructed via Pancharatnam-Berry phase so that CP conversion contained both left-handed CP(LCP)and right-handed CP(RCP)components.In this paper,a silicon based THz metalens is constructed using dynamic phase to obtain single-handed CP conversion.Also,we can rotate the whole metalens at a certain angle to control the conversion of multi-polarization states,which can simply manipulate the focusing for incident linear polarization(LP)THz wave in three polarization conversion states,in-cluding LP without conversion,LCP and RCP.Moreover,the polarization conversion behavior is reversible,that is,the THz metalens can convert not only the LP into arbitrary single-handed CP,but also the LCP and RCP into two perpen-dicular LP,respectively.The metalens is expected to be used in advanced THz camera,as a great candidate for tradi-tional CPL and focusing lens group,and also shows potential application in polarization imaging with discriminating LCP and RCP.

Circular Polarization Hologram Realized by Pancharatnam-Berry Phase in Microwave Frequency

Metasurfaces have shown great potential in controlling the propagation of electromagnetic waves, making them suitable for holographic beam-shaping elements. Using the principle of array synthesis, holograms have been realized in microwave frequency to manipulate electromagnetic waves to generate specific field patterns. However, current research is almost based on linear polarization and has little analysis on the circular polarization microwave hologram. Herein, we propose a circular polarization hologram realized by sub-wavelength units with self-adaptively phase profiles of electromagnetic waves. The full, continuous control of the phase is achieved by using a single structure unit based on the Pancharatnam-Berry phase. The inhomogeneity of wave-front is considered through amplitude and phase compensation which are essential to improve the quality of microwave hologram. The model achieves circular polarization hologram in microwave frequency and the clear field pattern is generated. The circular polarization hologram enriched the research field of microwave imaging, thus providing more inspirations for the development of various related techniques.

Polarization and phase control of two-photon absorption in an isotropic molecular system

We theoretically and experimentally study the polarization and phase control of two-photon absorption in an isotropic molecular system. We theoretically show that the two-photon transition probability decreases when the laser polarization changes from linear through elliptical to circular, and the laser polarization does not affect the control efficiency of two-photon transition probability by shaping the spectral phase. These theoretical results are experimentally confirmed in coumarin 480. Furthermore, we propose that the combination of the laser polarization with the spectral phase modulation can further increase the control efficiency of the two-photon absorption.

Design of broad angular phase retarders for the complete polarization analysis of extreme ultraviolet radiation

A method of designing broad angular phase retarders in the extreme ultraviolet （EUV） region is presented. The design is based on a standard Levenberg-Marquardt algorithm combined with a common merit function. Using this method, a series of broad angular EUV phase retarders were designed using aperiodic Mo/Si multilayers. At photon energy of 90 eV, broad angular phase retarders with 30°, 60°, and 90° phase retardations have been realized in the angular range of 39°-51°. By analyzing and comparing the performances of the designed broad angular phase retarders, we found that the Mo/Si multilayer with more layers could obtain higher phase retardation in broader angular range when used to design the broad angular phase retarder. Broad angular phase retarders possess lower sensitivity toward changing incident angle compared with the traditional phase retarders designed with transmission periodic multilayers, and can be used for the polarization control of broad angular EUV sources.

Behavior of Vacuum Polarization of Gauge-Boson and Wavefunction Renormalization Factor of Fermion in Different Phases of QED3

We investigate the behavior of the vacuum polarization of the gauge-boson Ⅱ and the wave-function renormalization factor of the fermion A in QEDs, using the coupled Dyson-Schwinger equations for the gauge-boson and fermion propagator. Using several different ansatze for the fermion-gauge-boson vertex, we find that the wave-function renormalization factor .4 and especially the vacuum polarization Ⅱ have different behaviors in the dynamical chiral symmetry breaking phase and in the chiral symmetric phase and hence in the phenomenological applications of QED3 one should choose different forms of gauge-boson propagator for these two phases. We also find that when adopting a specific ansatze of the fermion-gauge-boson vertex （ansatze （3）） the vacuum polarization function equals its one-loop perturbative result in the chiral symmetric phase. This fact suggests that in QEDs the Wigner vacuum corresponds to the perturbative vacuum.

Polarization readout analysis for multilevel phase change recording by crystallization degree modulation

Four different states of Si15Sb85 and Ge2Sb2Te5 phase change memory thin films are obtained by crystallization degree modulation through laser initialization at different powers or annealing at different temperatures. The polarization characteristics of these two four-level phase change recording media are analyzed systematically. A simple and effective readout scheme is then proposed, and the readout signal is numerically simulated. The results show that a high-contrast polarization readout can be obtained in an extensive wavelength range for the four-level phase change recording media using common phase change materials. This study will help in-depth understanding of the physical mechanisms and provide technical approaches to multilevel phase change recording.

Fifth-order phase-sensitive detection of ultrafast polarization beats in cascade four-level system

We study the colour-locked twin-noisy-field correlation effects in the fifth-order nonlinear susceptibility of ultrafast polarization beats in a cascade four-level system. More importantly, the fifth-order phase-sensitive heterodyne detection of ultrafast polarization beats has been exploited. The fifth-order nonlinear optical response can be controlled and modified through the colour-locked correlation of twin noisy fields. Thus, this method with the phase dispersion information is a good way to measure the real and imaginary parts of the fifth-order nonlinear susceptibility.

Understanding the effect of elliptical polarization in surface nuclear magnetic resonance method

Currently, surface nuclear magnetic resonance （SNMR） method is the only geophysical method that detects groundwater directly. In this paper, we investigate the effect of elliptical polarization in the perpendicular excitation magnetic field. The effect of elliptical polarization is clearly visible in our ellipticity calculation and it can cause strong distortion to the excitation field in the presence of high subsurface conductivities. By examining the co-rotating and counter-rotating components of the field, we show that elliptical polarization affects transmitting and receiving processes differently and that a clear phase lag exists between transmitter loop and receiver loop. Finally, we derive the response function of coincident loops and calculate proton tip angles, the kernel function and SNMR response curves of a 1D aquifer model. Based on the simulations, we conclude that the elliptical polarization and phase lag can significantly affect SNMR response and it is essential to include elliptical polarization in SNMR modeling and data interpretation.

Twisted microdomains in liquid crystals for polarization-insensitive phase modulation

Polarization-independent phase modulators based upon liquid crystals(LCs)with a simple device architecture have long been desired for a range of optical applications.Recently,researchers have demonstrated a novel fabrication procedure using cholesteric LCs as a primer for achieving low polarization dependence coupled with a large phase modulation depth.

Four-dimensional direct detection receiver enabling Jones-space field recovery with phase and polarization diversity

Data centers,the engines of the global Internet,rely on powerful high-speed optical interconnects.In optical fiber communication,classic direct detection captures only the intensity of the optical field,while the coherent detection counterpart utilizes both phase and polarization diversities at the expense of requiring a narrow-linewidth and high-stability local oscillator(LO).Herein,we propose and demonstrate a four-dimensional Jones-space optical field recovery(4-D JSFR)scheme without an LO.The polarization-diverse full-field receiver structure captures information encoded in the intensity and phase of both polarizations,which can be subsequently extracted digitally.To our knowledge,our proposed receiver achieves the highest electrical spectral efficiency among existing direct detection systems and potentially provides similar electrical spectral efficiency as standard intradyne coherent detection systems.The fully recovered optical field extends the transmission distance beyond the limitations imposed by fiber chromatic dispersion.Moreover,the LO-free advantage makes 4-D JSFR suitable for photonic integration,offering a spectrally efficient and cost-effective solution for massively parallel data center interconnects.Our results may contribute to the ongoing developments in the theory of optical field recovery and the potential design considerations for future high-speed optical transceivers.

Mitigation of cross-eye jamming using a dual-polarization array

This paper presents an approach for mitigating the cross-eye jamming using a dual-polarization array. By transmitting a sum beam and a difference beam in two orthogonal polarimetric channels, a synthesized transmitted beam with spatially varying polarization is produced, such that the polarization of the transmitted radar wave varies in azimuth or elevation. Thus, the phases of the signals received on the two antennas of a cross-eye jammer become unequal, and an additional phase difference is introduced to disrupt the 180？ phase shifting in the retrodirective loop of the jammer. By means of beam scanning in a small angular range,the optimal beam steering configuration can be found to maximize the phase error for the mitigation of cross-eye jamming. As a result, the jamming performance of the cross-eye jammer degrades largely. Theoretical analysis and simulation results indicate that the proposed method is valid and feasible.

Three-dimensional modulations on the states of polarization of light fields

Light fields with spatially structured states of polarization（SoPs） are gathering increasing attention because of their potential applications from optical imaging and micromanipulation to classical and quantum communications. Meanwhile,the concepts within structured light fields have been extended and applied to acoustic, electron, and matter waves. In this article, we review recent developments of the SoP modulation of light fields, especially focusing on three-dimensional（3 D） modulations on the SoPs of light fields. The recent progress and novel implementations based on 3 D spin-dependent separation are discussed. Following the discussions to this physical phenomenon, we then describe recent developments on the vector fields with 3 D structured SoP and intensity distributions, namely, 3 D vector fields. The discussed phenomena inspire us to explore other structured light fields for the expansion of applications in biomedical, information science,quantum optics, and so on.

Ellipsometric configurations using a phase retarder and a rotating polarizer and analyzer at any speed ratio

In this paper, we propose an ellipsometer using a phase retarder and rotating polarizer and analyzer at a speed ratio I：N. Different ellipsometric configurations are presented by assuming N = 1, 2, and 3. Moreover, two values of the offset angle of the retarder are considered for each ellipsometric configuration. The Mueller formalism is employed to extract the Stokes parameters, from which the intensity received by the detector is obtained. The optical properties of c-Si are calculated using all configurations. A comparison between different configurations is carried out considering the effect of the noise on the results and the uncertainties in the ellipsometric parameters as functions of the uncertainties of the Fourier coefficients. It is found that the alignment of the phase retarder has a crucial impact on the results and the ellipsometric configuration with speed ratio 1：1 is preferred over the other configurations.

Tight focusing of partially polarized vortex beams by binary phase Fresnel zone plates

Based on vectorial Debye theory, the focusing properties of partially polarized vortex beam by high numerical aperture Fresnel zone plate are investigated. The effects of the numerical apertures of and the phase difference of binary phase Fresnel zone plates, the topological charge of vortex beam and the degree of polarization of incident beam on the intensity distribution and degree of coherence in the focal plane are investigated in detail. It is shown that elliptical light spots and the flat top beam can be obtained by selecting certain parameters. Studies of degree of coherence reveal that the degree of coherence between x and y components of the electric field, which is zero in the source plane, is improved in the focal plane for vortex beam, but it is hardly changed for the nonvortex beam. It is also proved that any two of the three electric field components Ex, Ey and Ez are completely coherent everywhere in the focal region if the incident light beam is linearly polarized.

Ultra-thin single-layer transparent geometrical phase gradient metasurface and its application to high-gain circularly-polarized lens antenna

A new method to design an ultra-thin high-gain circularly-polarized antenna system with high efficiency is proposed based on the geometrical phase gradient metasurface（GPGM）.With an accuracy control of the transmission phase and also the high transmission amplitude,the GPGM is capable of manipulating an electromagnetic wave arbitrarily.A focusing transmission lens working at Ku band is well optimized with the F /D of 0.32.A good focusing effect is demonstrated clearly by theoretical calculation and electromagnetic simulation.For further application,an ultra-thin single-layer transmissive lens antenna based on the proposed focusing metasurface operating at 13 GHz is implemented and launched by an original patch antenna from the perspective of high integration,simple structure,and low cost.Numerical and experimental results coincide well,indicating the advantages of the antenna system,such as a high gain of 17.6 d B,the axis ratio better than 2 d B,a high aperture efficiency of 41%,and also a simple fabrication process based on the convenient print circuit board technology.The good performance of the proposed antenna indicates promising applications in portable communication systems.

Sacrificial Anode Stability and Polarization Potential Variation in a Ternary Al-xZn-xMg Alloy in a Seawater-Marine Environment

In this paper, the effects of zinc （Zn） and magnesium （Mg） addition on the performance of an aluminum-based sacrificial anode in seawater were investigated using a potential measurement method. Anodic efficiency, protection efficiency, and polarized potential were the parameters used. The percentages of Zn and Mg in the anodes were varied from 2% to 8% Zn and 1% to 4% Mg. The alloys produced were tested as sacrificial anodes for the protection of mild steel in seawater at room temperature. Current efficiency as high as 88.36% was obtained in alloys containing 6% Zn and 1% Mg. The polarization potentials obtained for the coupled （steel/Al-based alloys） are as given in the Pourbaix diagrams, with steel lying within the immunity region/cathodic region and the sacrificial anodes within the anodic region. The protection offered by the sacrificial anodes to the steel after the 7th and 8th week was measured and protection efficiency values as high as 99.66% and 99.47% were achieved for the A1-6%Zn-l%Mg cast anode. The microstructures of the cast anodes comprise of intermetallic structures of hexagonal Mg3Zn2 and body-centered cubic A12Mg3Zn3. These are probably responsible for the breakdown of the passive alumina film, thus enhancing the anode efficiency.

Simultaneous polarization separation and switching for 100-Gbps DP-QPSK signals in backbone networks

We propose a novel scheme of simultaneous polarization separation and switching, based on the orthogonallypolarized four-wave mixing(FWM) effect, for ultra-high-speed polarization multiplexing(Pol-MUX) fiber networks such as 100-Gbps and 400-Gbps backbone networks. We use theoretical and experimental analysis of the vector theory of FWM to successfully achieve polarization separation and all-optical switching by utilizing a 100-Gbps dual polarizationquadrature phase shift keying(DP-QPSK) signal and two orthogonally-polarized pumps. Both of the polarization-separated QPSK signals have clear constellation diagrams, with root mean square(RMS) error vector magnitudes(EVMs) of 14.32%and 14.11% respectively. The wavelengths of idlers can be created at 30 different wavelengths, which are consistent with International Telecommunication Union-Telecommunication(ITU-T) wavelengths, by flexibly changing the wavelength of the pump light. Moreover, the idlers that have distinct wavelengths have power distributed in a range from-10 dBm to-15 dBm, which can support error-free transmission. The power penaltyis 5 d B lower than that of back-to-back(BTB)signal for both the X-and Y-polarization components measured at a bit error ratio(BER) of 3.8×10^(-3). Our experimental results indicate that this scheme has promising applications in future backbone networks.

Phase and direction dependence of photorefraction in a low-frequency strong circular-polarized plane wave

Contrary to the superposition principle, it is well known that photorefraction exists in the vacuum with the presence of a strong static field, a laser field, or a rotational magnetic field. Different from the classical optical crystals, the refractive index also depends on the phase of the strong electromagnetic field. We obtain the phase and direction dependence of the refractive index of a probe wave incident in the strong field of a circular-polarized plane wave by solving the Maxwell equations corrected by the effective Lagrangian. It may provide a valuable theoretical basis to calculate the polarization evolution of waves in the strong electromagnetic circumstances of pulsar or neutron stars.

Beam pointing correction of variable polarization MMW/IR combined detection

A kind of beam-scanning algorithm of variable polarization millimeter array antenna based on the phased array technology is put forward in this paper. The algorithm can be successfully applied to deal with beam directivities inconsistency of millimeter wave/infrared（ MMW/IR ） multimode detector, it can keep electric axis and optical axis coincident. Accordingly, this method can decrease the data fusion difficulty and improve the accuracy of angle measurement. Simulation results show that variable polarization millimeter array antenna has flexible beam-scanning abibility within ±0.5° after the algorithm was adopted, simultaneously, antenna polarization purity is better than 20 dB within the half power beamwidth, sidelobe imbalance keeps high available and antenna gain of the sum beam is over 26.8 dB.

Creation of Multiple Subwavelength Focal Spot Segments Using Phase Modulated Radially Polarized Multi Gaussian Beam

Based on the vector diffraction theory, the effect of complex phase filters on intensity distribution of a radially polarized multi Gaussian beam in the focal region of high NA lens is theoretically investigated. It is observed that a properly designed multi belt complex phase filter can generate subwavelength novel focal patterns including splitting of focal spots and generation of multiple focal spot segments such as eight, six and four focal spots along the optical axis are obtained. We expect that such an investigation is useful for optical manipulation and material processing, multiple high refractive index particle trapping technologies.