Polarization-independent Performance Research Articles

Plasmonic bound states in the continuum for unpolarized weak spatially coherent light

Plasmonic resonances empowered by bound states in the continuum (BICs) offer unprecedented opportunities to tailor light–matter interaction. However, excitation of high quality-factor ( Q -factor) quasi-BICs is often limited to collimated light at specific polarization and incident directions, rendering challenges for unpolarized focused light. The major hurdle is the lack of robustness against weak spatial coherence and poor polarization of incident light. Here, addressing this limitation, we demonstrate sharp resonances in symmetric plasmonic metasurfaces by exploiting BICs in the parameter space, offering ultraweak angular dispersion effect and polarization-independent performance. Specifically, a high- Q ( ≈ 71 ) resonance with near-perfect absorption ( > 90 % ) is obtained for the input of unpolarized focused light covering wide incident angles (from 0° to 30°). Also, giant electric and magnetic field enhancement simultaneously occurs in quasi-BICs. These results provide a way to achieve efficient near-field enhancement using focused light produced by high numerical aperture objectives.

Ultra-broadband metamaterial absorber in the visible and near-infrared range based on silicon carbide hemisphere arrays

In this paper, we theoretically study the broadband optical metamaterial absorber composed of silicon carbide (SiC) hemisphere array placed atop a tungsten substrate, where high average absorptivity reaching 93.5% is obtained in a broad range from ultraviolet to near-infrared frequency. The presented broadband metamaterial absorber exhibits good tolerance to incidence angle up to 40° and shows polarization-independent performance. The underlying mechanism of the broadband absorption is attributed to the magnetic dipole resonance stimulated inside SiC hemispheres as well as the intense field trapping caused by lattice resonances. The presented structure is simple and efficient, and also offers promising applications in broadband thermophotovoltaic devices.

Ultrabroadband, compact, polarization independent and efficient metasurface-based power splitter on lithium niobate waveguides.

We propose a metasurface-based Lithium Niobate waveguide power splitter with an ultrabroadband and polarization independent performance. The design consists of an array of amorphous silicon nanoantennas that partially converts the input mode to multiple output modes creating multimode interference such that the input power is equally split and directed to two branching waveguides. FDTD simulation results show that the power splitter operates with low insertion loss (< 1dB) over a bandwidth of approximately 800 nm in the near-infrared range, far exceeding the O, E, S, C, L and U optical communication bands. The metasurface is ultracompact with a total length of 2.7 µm. The power splitter demonstrates a power imbalance of less than 0.16 dB for both fundamental TE and TM modes. Our simulations show that the device efficiency exhibits high tolerance to possible fabrication imperfections.

Convoluted FSS Structure For Shielding Application In X-Band Frequency Response

A compact single-layer frequency-selective surface (FSS) covering X-band frequency range for shielding application is presented in this study. The proposed FSS structure, constructed with a convoluted element printed on both sides of FR4 material, exhibits band-stop response covering a frequency spectrum of 8–12 GHz at 10 dB level of insertion loss. The designed FSS provides polarization-independent performance and good angular stability. The simulated result and the measured results seem to be in a good agreement.

A Spectrally Tunable Dielectric Subwavelength Grating based Broadband Planar Light Concentrator

Energy consumption of buildings is increasing at a rapid pace due to urbanization, while net-zero energy buildings offer a green and sustainable solution. However, limited rooftop availability on multi-story buildings poses a challenge for large-scale integration of photovoltaics. Conventional silicon solar panels block visible light making them unfeasible to cover all the surfaces of a building. Here, we demonstrate a novel dielectric grating based planar light concentrator. We integrate this functional device onto a window glass transmitting visible light while simultaneously guiding near infrared (NIR) portion of sunlight to edges of the glass window where it is converted to electricity by a photovoltaic cell. Gratings are designed to guide NIR region and realize polarization independent performance. Experimentally, we observe 0.72% optical guiding efficiency in the NIR region (700–1000 nm), transmitting majority of the visible portion for natural room lighting. Integrating solar cell at the window edge, we find an electrical conversion efficiency of about 0.65% of NIR light with a 25 mm2 prototype. Major losses are coupling and guiding losses arising from non-uniformity in fabrication over a large area. Such a functional window combining energy generation, natural room lighting and heat load reduction could mitigate urban heat island effect in modern cities.

Silicon nitride based polarization-independent 4 × 4 optical matrix switch

A polarization-independent 4 × 4 optical matrix switch based on a 580-nm-thick silicon nitride platform is designed and experimentally demonstrated. The switch is composed of four 2 × 2 Mach-Zehnder interferometers, with each integrated with a pair of Ti/Pt resistive micro-heaters. Polarization-independent performance can be realized with the power consumption for a single switching operation of less than 130 mW. The measured rise/fall time of the switch upon electrical tuning is about 24.5/30.5 μs, corresponding to a maximum switching speed of about 20 kHz. The insertion loss is about 7.2 dB for transverse electric light or 5.7 dB for transverse magnetic wave, with a polarization dependent loss of about 0.65 dB. The device performance can be further optimized and even large-scale silicon nitride polarization-insensitive electro-optical matrix switches can be expected for future optical communication applications.

A Single-Layer UWB Frequency-Selective Surface With Band-Stop Response

A single-layer compact frequency-selective surface (FSS) covering ultra-wideband application is presented in this letter. The proposed FSS constructed with convoluted elements exhibit band-stop response covering a frequency spectrum of 3.1–13.3 GHz at 10 dB. The prototype of the FSS is fabricated and the measured results seem to be in good agreement with the simulated result. Also, the designed FSS manifest polarization independent performance and good angular stability.

SERS polarization-independent performance of two-dimensional sinusoidal silver grating

This letter demonstrates a possibility to overcome the polarization-dependent problem in surface enhanced Raman scattering (SERS) performance by two-dimensional (2D) sinusoidal silver grating. A reproducible SERS substrate with a large area can be easily fabricated by maskless laser interference photolithography. The polarization-independent SERS performance and SERS enhancement factor (EF) of this substrate are deduced by finite difference time domain and demonstrated by R6G SERS detection experiments. SERS performance of 2D sinusoidal grating is polarization-independent over the whole 360° and EF can be 5 orders of magnitude as possible. Moreover, this long-range SERS substrate can realize label-free SERS detection of 2,4,6-Trinitrotoluene (TNT).

Spontaneous pump depolarization in ultralong cavity Raman fiber laser amplifiers.

We present an experimental demonstration of polarization-independent performance in a forward and backward-pumped 2nd-order ultralong cavity Raman laser amplifiers with highly polarized pumps. Our findings show that the depolarization of the Stokes component due to gain saturation leads to polarization-insensitive performance in terms of output gain and relative intensity noise in the signal. These results pave the way for the use of individual highly polarized low-RIN semiconductor laser diodes in Raman-amplified optical communications.

Low-Scattering Tri-Band Metasurface Using Combination of Diffusion, Absorption and Cancellation

In this paper, we proposed for the first time a novel mechanism to design a tri-band low-scattering metasurface. The radar cross section (RCS) reduction in the three operational bands relies on scattering diffusion, absorption, and scattering cancellation, respectively. The diffusion metasurface was realized by distributing scattering unit cells with different rotation angles. For the absorption, four units operating at different frequencies were combined to achieve a broadband absorption. The scattering cancellation was realized by arranging two out of phase elements in a chessboard configuration. The tri-band metasurface was constructed by directly combining the three metasurfaces in a single assembly. The simulated and measured results have a good agreement. The tri-band RCS reduction is well preserved up to 45° with polarization-independent performance. This paper provides an alternative approach to design the multi-band metasurface for stealth application.

Experimental Demonstration of Metasurface‐Based Ultrathin Carpet Cloaks for Millimeter Waves

A metasurface carpet cloak for millimeter-wave range with polarization-independent performance is experimentally demonstrated. It is shown that the cloak is able to mimic the ground plane by fully restoring the amplitude and phase distributions for both transverse electric and transverse magnetic polarizations, with a relatively wide frequency and angular widths response. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Scattering engineering in continuously shaped metasurface: An approach for electromagnetic illusion.

The control of electromagnetic waves scattering is critical in wireless communications and stealth technology. Discrete metasurfaces not only increase the design and fabrication complex but also cause difficulties in obtaining simultaneous electric and optical functionality. On the other hand, discontinuous phase profiles fostered by discrete systems inevitably introduce phase noises to the scattering fields. Here we propose the principle of a scattering-harness mechanism by utilizing continuous gradient phase stemming from the spin-orbit interaction via sinusoidal metallic strips. Furthermore, by adjusting the amplitude and period of the sinusoidal metallic strip, the scattering characteristics of the underneath object can be greatly changed and thus result in electromagnetic illusion. The proposal is validated by full-wave simulations and experiment characterization in microwave band. Our approach featured by continuous phase profile, polarization independent performance and facile implementation may find widespread applications in electromagnetic wave manipulation.

Reflective gradient metasurfaces for polarization-independent light focusing at normal or oblique incidence

Reflective gradient metasurfaces are reported as flat, ultra-thin light focusers using a cross-resonator array with spatially varied geometric parameters atop a continuous gold ground plane spaced by a layer of SiO2. The sub-wavelength cross-shaped building element offers polarization-independent performance and full 2π phase tuning range by varying its width and length, which is explained by an analytical model based on harmonically oscillating dipole antenna. With a radial phase gradient, a metasurface is demonstrated to function as a parabolic reflector at 1.47 μm wavelength with the measured efficiency of 44%. In addition, by elaborately engineering the planar distribution of different building elements, another two focusing reflectors are designed and experimentally verified to anomalously reflect and concentrate light along normal direction but with oblique incident angles of 30° and 60°, respectively.

Non-uniform annular rings-based metasurfaces for high-efficient and polarization-independent focusing

A reflection metasurface, composed of metallic annular rings, is presented for realizing high-efficient and polarization-independent focusing. By varying the inner and outer radii of the isotropic rings, we can achieve a full modulation on the phase from −180° to 180°. By properly arranging the annular rings, we design gradient metasurfaces for focusing without polarization sensitivity by finite element method simulations and further demonstrate the focusing effect with high-efficient and polarization-independent performance experimentally in the microwave domain. In addition, the structure is also proved applicable in the optical domain by simulations. This work expands the capabilities of metasurfaces to focusing and imaging applications without polarization limitations.

Design and Simulation of a Polarization-Independent Active Metamaterial Terahertz Modulator

The design and simulation of a polarization-independent active metamaterial terahertz modulator is presented in this work. The device incorporates an array of gold triple SRRs on an n-doped gallium arsenide layer to create an active metamaterial terahertz modulator with a high modulation depth, a high modulation speed and an especial polarization-independent performance for use in terahertz communication, imaging and sense.We established the theoretical model and simulatedthe key performances of the device with Ansoft HFSS.The results showed that the device exhibits a polarization-insensitivebehavior with a maximum amplitude modulation depth of 71% and a modulation rate of3.2Mbps at the resonance frequency of0.86 THz.

Negligible birefringence in dual-mode ion-exchanged glass waveguide gratings

Polarization dependence of UV-written Bragg gratings in buried ion-exchanged glass waveguides is investigated. A polarization-dependent shift in Bragg wavelength of less than 0.02 nm is measured, both for the even and the odd modes of a laterally dual-mode waveguide. The measured wavelength shift corresponds to a waveguide birefringence of the order of 10(-5), which is negligible for most applications in optical communications. It is observed that the UV-induced birefringence is small, within the limits of the measurement accuracy. The thermal stability of the fabricated gratings is also very good. The results are of particular importance for devices considered here since they require a polarization-independent mode-converting waveguide Bragg grating. Polarization-independent performance of these gratings enables the fabrication of a new class of integrated optical devices for telecommunication applications.

Zeroth-order half-wave plates of LiNbO3 for integrated optics applications at 1.55 μm

Reports on fabrication and characterization of the first zeroth-order half-wave plates of LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> obtained by crystal ion slicing (CIS). Polarization rotation was demonstrated in 10-μm-thick freestanding LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> films with 30-dB conversion ratios and negligible material loss. Polarization-independent performance was demonstrated in a hybrid-optic device comprising a CIS wave plate integrated with single-mode silica-based channel waveguides.

Scattering from wedge-tapered absorbers

The scattering of a plane electromagnetic wave, arbitrarily polarized and normally impinging on a wedge-tapered absorbing structure, is theoretically and experimentally studied. The theoretical solution is found in two asymptotic cases: spacing between consecutive edges, small and large with respect to the incident wavelength. In the former case, a transmission line analogy is set up; in the latter, quasi-optical techniques are applied. Numerical and experimental results are presented; the latter are in good agreement with the theory. The possibility of using the studied structure as an absorbing termination is discussed in some detail, and optimizing criteria, as well as the possibility of obtaining polarization-independent performance, are indicated.