Design of Polarization-independent Wavelength-interleave Coupler in Fluorinated Polyimide Waveguide

Based on the measurement of dispersion characteristic and birefractive index of the fluorinated polyimide film,a statistical optimum design method is proposed and used to realize the design of 32- and 36-wavelengths optical waveguide wavelength-interleave coupler(i,e.,interleaver) with the optimization of polarization fluctuation and wavelength interval of 0.8 nm at 1 550 nm.The largest cross coupling ratios of the two interleavers are respectively less than 1.8% and 3.5%,while the least through coupling ratios are respectively greater than 98.2% and 96.5%.The output differences due to polarization fluctuation are less than ±1.7% and ±3.2%.

Excellent polarization-independent reflector based on guided mode resonance effect

A broad band polarization-independent reflector working in the telecommunication C＋L band is proposed using the guided mode resonance effect of a periodic surface relief element deposited by a layer of silicon medium. It is shown that this structure can provide high reflection （R 〉 99.5%） and wide angular bandwidth （θ≈ 20°, R 〉 98%） for both TE and TM polarizations over a wide spectrum band 1.5 μm-l.6 μm. Furthermore, it is found by rigorous coupled wave analysis that the polarization-independent reflector proposed here is tolerant of a deviation of grating thickness, which makes it very easy to fabricate in experiments.

Polarization-Independent Metamaterial Sensing Based on Electromagnetically Induced Transparency

We propose a metamaterial structure that can achieve electromagnetically induced transparency and polarization—independent of the incident wave. The structure consists of a regular octagonal frame and four L-shaped metal wires arranged periodically. There is a strong transparent window at 4.28 GHz. Our calculation results are in good agreement with the simulation results. When changing the excitation polarization of the incident wave, the transmission spectrum remains stable. Furthermore, when we adjust the permittivity of the medium in front of the metamaterial, the frequency of the transmission valley shifts linearly with the change in permittivity. This structure can be independent of the polarization of the incident wave and has potential inspiration in fields such as sensing.

Bidirectional visible light absorber based on nanodisk arrays

A perfect bidirectional broadband visible light absorber composed of titanium nitride and tungsten nanodisk arrays is proposed.The average absorption of the absorber exceeds 89%at 400 nm–800 nm when light is normally incident on the front-side.Illumination from the opposite direction(back-side)results in absorption of more than 75%.Through the theoretical analysis of the electric and magnetic fields,the physical mechanism of the broadband perfect absorption is attributed to the synergy of localized surface plasmons,propagating surface plasmons,and plasmonic resonant cavity modes.Furthermore,the absorber also exhibits excellent polarization-independence performance and a high angular tolerance of~30°for both front-and back-side incidence.The designed bidirectional broadband visible light absorber here has wide application prospects in the fields of solar cells and ink-free printing.

Ultra-wideband low radar cross-section metasurface and its application on waveguide slot antenna array

A novel approach devoted to achieving ultra-wideband radar cross section reduction（RCSR） of a waveguide slot antenna array（WGSAA） while maintaining its radiation performance is proposed. Three kinds of artificial magnetic conductors（AMCs） tiles consisting of three types of basic units resonant at different frequencies are designed and arranged in a novel quadruple-triangle-type configuration to create a composite planar metasurface. The proposed metasurface is characterized by low radar feature over an ultra-wideband based on the principle of phase cancellation. Both simulated and measured results demonstrate that after the composite metasurface is used to cover part of the antenna array, an ultrawideband RCSR involving in-band and out-of-band is achieved for co-and cross-polarized incident waves based on energy cancellation, while the radiation performance is well retained. The proposed method is simple, low-cost, and easy-tofabricate, providing a new method for ultra-wideband RCSR of an antenna array. Moreover, the method proposed in this paper can easily be applied to other antenna architectures.

Ultra-broadband absorber based on cascaded nanodisk arrays

An ultra-broadband perfect absorber consisting of cascaded nanodisk arrays is demonstrated by placing insulatormetal-insulator-metal nanodisks on insulator-metal film stacks.The absorber shows over 90% absorption in a wavelength range between 600 nm and 4000 nm under transverse magnetic(TM) polarization,with an average absorptivity of 91.5%and a relative absorption bandwidth of 147.8%.The analysis of the electric field and magnetic field show that the synergy of localized surface plasmons,propagating surface plasmons,and plasmonic resonant cavity modes leads to the ultrabroadband perfect absorption,which accords well with the results of impedance-matched analysis.The influences of structural parameters and different metal materials on absorption performance are discussed.Furthermore,the absorber is polarization-independent,and the absorption remains more than 90% at a wide incident angle up to 400 under TE polarization and TM polarization.The designed ultra-broadband absorber has promising prospects in photoelectric detection and imaging.

Simulated and experimental studies of a multi-band symmetric metamaterial absorber with polarization independence for radar applications

We develop a simple new design for a multi-band metamaterial absorber(MTMA)for radar applications.Computer Simulation Technology(CST)Studio Suite 2018 was used for the numerical analysis and absorption study.The simulated results show four high peaks at 5.6 GHz,7.6 GHz,10.98 GHz,and 11.29 GHz corresponding to absorption characteristics of 100%,100%,99%,and 99%,respectively.Furthermore,two different structures were designed and compared with the proposed MTMA.The proposed structure remained insensitive for any incident angle and polarization angle from 0°to60°.Moreover,negative constitutive parameters were retrieved numerically.To support the simulated results,the proposed design was fabricated by using a computer numerical control-based printed circuit board prototyping machine and tested experimentally in a microwave laboratory.The absorption mechanism of the proposed MTMA is presented through the surface current and electric field distributions.The novelties of the proposed structure are a simple and new design,ease of fabrication,low cost,durability,suitability for real-time applications and long-term stability given the fabrication technique and non-destructive measurement method and very high absorption.The proposed structure has potential applications in C and X band frequency ranges.

Polarization-insensitive complementary metamaterial structure based on graphene for independently tuning multiple transparency windows

Polarization-insensitive multiple transparency windows are obtained with a graphene-based complementary metamaterial structure in terahertz regions,which is composed of two kinds of monolayer graphene perforated in shapes of a cross and four identical split rings that construct a resonator.The geometric parameters of resonators are different from each other.Numerical and theoretical results show that the quantum effect of Autler-Townes splitting is the key factor for appearance of transparency windows within the resonant dips.Further investigation demonstrates that by employing the fourfold-symmetry graphene complementary structure,polarization-independent transparency windows can be achieved.Moreover,multiple transparency windows can be separately manipulated over a broad frequency range via adjusting the chemical potential of the corresponding graphene resonators,and the bandwidth as well as resonance strength can also be tuned by changing the relative displacement between resonators each consisting of a cross and four split rings.The proposed metamaterial structure may be utilized in some practical applications with requirements of no polarization-varied loss and slowing the light speed.

Polarization-independent two-dimensional beam steering using liquid crystal optical phased arrays

A polarization-independent nonmechanical laser beam steering scheme is proposed to realize continuous two-dimensional（2 D） scanning with high efficiency, where the core components are two polarization-dependent devices, which are called liquid crystal optical phased arrays（LC-OPAs）. These two one-dimensional（1D） devices are orthogonally cascaded to work on the state of azimuthal and elevation steering, respectively. Properties of polarization independence as well as 2D beam steering are mathematically and experimentally verified with a good agreement. Based on the experimental setup, linearly polarized beams with different polarization angles are steered with high accuracy. The measured angular deviations are less than 5 μrad, which is on the same order of the accuracy of the measurement system. This polarization-independent 2 D laser beam steering scheme has potential application for nonmechanical laser communication, lidar, and other LC-based systems.

Visible-near infrared ultra-broadband polarization-independent metamaterial perfect absorber involving phase-change materials

We numerically demonstrate a novel ultra-broadband polarization-independent metamaterial perfect absorber in the visible and near-infrared region involving the phase-change material Ge_2Sb_2Te_5(GST).The novel perfect absorber scheme consists of an array of high-index strong-absorbance GST square resonators separated from a continuous Au substrate by a low-index lossless dielectric layer(silica)and a high-index GST planar cavity.Three absorption peaks with the maximal absorbance up to 99.94% are achieved,owing to the excitation of plasmon-like dipolar or quadrupole resonances from the high-index GST resonators and cavity resonances generated by the GST planar cavity.The intensities and positions of the absorption peaks show strong dependence on structural parameters.A heat transfer model is used to investigate the temporal variation of temperature within the GST region.The results show that the temperature of amorphous GST can reach up to 433 K of the phase transition temperature from room temperature in just 0.37 ns with a relatively low incident light intensity of 1.11×10~8W∕m^2,due to the enhanced ultra-broadband light absorbance through strong plasmon resonances and cavity resonance in the absorber.The study suggests a feasible means to lower the power requirements for photonic devices based on a thermal phase change via engineering ultra-broadband light absorbers.

Binary blazed grating-based on silicon polarization-independent filter on insulator

In this paper, a binary blazed grating-based polarization independent filter on silicon on insulator （SOI） under full conical incidence is presented. The properties of the grating filter are investigated by rigorous coupled-wave analysis. It＇s shown that the filter demonstrates high reflectivity （R 〉 99%） at its resonant wavelength, which stays the same under three different polarization states. It indicates that this grating filter is polarization-independent. The final data shows its polarization-dependent loss （PDL） is only 0.04 dB and the full width at half maximums （FWHMs） of the transverse electric （TE-） and transverse magnetic （TM-） polarized light are 0.24 and 0.46nm, respectively.

Broadband NIR absorber based on square lattice arrangement in metallic and dielectric state VO2

In this Letter, we propose a broadband near-infrared(NIR) absorber based on the phase transition material VO2.By designing different arrangements of the VO2 square lattice at high and low temperatures on fused silica substrates, the absorption rate reaches more than 90% in the entire 1.4–2.4 μm range. Using a finite-difference time-domain simulation method and thermal field analysis, the results prove that the absorber is polarizationindependent and has wide-angle absorption for incident angles of 0°–70°. The proposed absorber has a smoother absorption curve and is superior in performance, and it has many application prospects in remote sensing geology.

Polarization independent superconducting nanowire detector with high-detection efficiency

The superconducting nanowire single photon detector（SNSPD） draws much attention because of its attractive performance at ultra violet, visible, and nearinfrared wavelengths, and it can be widespread in quantum information technologies. However, how to increase the absorption which can dramatically increase the quantum efficiency of the SNSPD is still a top research issue. In this study, the effect of incident medium and cavity material on the optical absorptance of cavity-integrated SNSPDs was systematically investigated using finite-element method. The simulation results demonstrate that for photons polarized parallel to nanowire orientation, even though the maximum absorptance of the nanowire is insensitive to cavity material,it does increase when the refractive index of incident medium decreases. For perpendicularly polarized photons, both incident medium and cavity material play significant roles,and the absorptance curves get closer to the parallel case as the refractive index of cavity material increases. Based on these results, two cavity-integrated SNSPDs with frontillumination structure which can enhance the absorptance for both parallel and perpendicular photons are proposed.Finally, a design to realize polarization-independent SNSPDs with high absorptance is presented.