Polarization-independent Broadband Research Articles

Raman signatures of strong Kitaev exchange correlations in (Na1−xLix)2IrO3: Experiments and theory

Inelastic light scattering studies on single crystals of (Na1−xLix)2IrO3 ( and 0.15) show a polarization-independent broad band at ∼ 2750 cm−1 with a large band-width . For Na2IrO3 the broad band is seen for temperatures and persists inside the magnetically ordered state. For Li samples, the intensity of this mode increases, shifts to lower wave numbers, and persists to higher temperatures. Such a mode has recently been predicted (by Knolle et al.) as a signature of the Kitaev spin liquid. We assign the observation of the broad band to be a signature of strong Kitaev exchange correlations. The fact that the broad band persists even inside the magnetically ordered state suggests that dynamically fluctuating moments survive even below TN. This is further supported by our mean-field calculations. The Raman response calculated in mean-field theory shows that the broad band predicted for the SL state survives in the magnetically ordered state near the zigzag-spin liquid phase boundary. A comparison with the theoretical model gives an estimate of the Kitaev exchange interaction parameter to be .

Polarization-independent broadband plasmonic absorber based on a silicon-nanowire array decorated by gold nanoparticles at the optical regime.

We present a design for a plasmonic absorber that is composed of a hexagonal-packed silicon nanowires (SiNWs) array with gold nanoparticles (AuNPs) decoration. Simulations and experiments demonstrated that the proposed absorber achieves a broadband absorption. Its bandwidth over an absorption of 80% ranges from 400 nm to 1000 nm at 0 degree to 30 degrees incidence. It was also demonstrated that the plasmonic absorber is polarization-insensitive. Analyzing the field distributions in the structure, we find that the wideband absorption is ascribed to the formation of cavity modes in the SiNWs and surface plasmon polaritons on the AuNPs. Such a designed plasmonic structure with high-efficiency absorption can be served as a good optical absorber.

Polarization independent broadband metamaterial absorber based on tapered helical structure

This communication presents a tapered helical structure as absorber, made of unconventional material i.e. metamaterial. Modeling, analytical study and the optimization of the absorber have been done. Quad helical optimized structure gives almost unity absorption at 499nm wavelength and gives the absorption more than 75% from 300nm to 1650nm which is a very wide operating region with, average absorbance of 91.32%. Whereas, triple helical structure gives 85% average absorbance with the operating range from 300nm to 1350nm. Also, it is analyzed that the presented structures are polarization independent and broadband. Comparison of the proposed quad helical absorber with the existing metamaterial absorbers is done and found it is most eligible.

Polarization independent broadband terahertz antireflection by deep‐subwavelength thin metallic mesh

AbstractBroadband antireflection coatings for passive terahertz (THz) components are extremely important in the application of THz technology. Metallic nano‐films are commonly used for this purpose. Here a new approach to realize polarization independent broadband antireflection in THz range, based on a meta‐surface design is experimentally demonstrated. The internal reflection of a broadband THz pulse (spectral bandwidth of 0.06 – 4 THz) at a Si/air interface can be fully suppressed with a Cr square mesh with deep‐subwavelength dimensions. Small nonuniformity of the meta‐surface structure can enhance the tolerance on structural parameters for achieving the AR condition. The design concept is applicable to other metals and frequency ranges as well, which opens a new window for future AR coatings.

Polarization independent broadband femtosecond optical gating using transient Kerr lens effect

A convenient polarization independent, broadband femtosecond optical gating technique utilizing transient Kerr lens effect is demonstrated by measuring the chirp structure of linearly polarized or non-polarized white light continuum generated in water and a photonic crystal fiber, respectively. Comparing with previous time-resolved spectroscopic techniques, this Kerr lens gating method is not limited by the requirement of specific nonlinear media with broadband response, critical phase-matching conditions, and especially the pump-probe polarization relationship. By replacing the white light continuum with other broadband light signals of interest, this method can be exploited in other femtosecond time-resolved spectroscopy, e.g., femtosecond photoluminescence.

Transparent and Flexible Polarization-Independent Microwave Broadband Absorber

We present an optically transparent, flexible, and polarization-independent broadband microwave absorber. It is designed to possess two spectrally overlapped resonances of a bow-tie array, which originates from the fundamental resonance mode and the coupling between the neighboring units. An Al wire gird is used to construct the bow-tie array to induce high ohmic loss and broaden the bandwidth of the resonances. As a result, the combined resonances lead to more than 90% total absorption covering a wide frequency range from 5.8 to 12.2 GHz. The transparent and flexible properties provide more flexibility for absorber applications. The optical transmittance of the whole structure is more than 62%.

Triple-core collinear and noncollinear plasmonic photonic crystal fiber couplers

Numerical analysis of single and multiple gold nanowires embedded in triple cores arranged in collinear and noncollinear configurations in photonic crystal fibers (PCFs) is reported. A full-vectorial finite element method is used to achieve coupling characteristics of plasmonic PCF couplers for both x and y polarizations. It is demonstrated numerically that the PCF plasmonic couplers exhibit polarization-independent tunable broadband filter characteristics that can be tuned according to the diameter of the embedded gold rod(s).

Optically thin composite resonant absorber at the near-infrared band: a polarization independent and spectrally broadband configuration

We designed, fabricated, and experimentally characterized thin absorbers utilizing both electrical and magnetic impedance matching at the near-infrared regime. The absorbers consist of four main layers: a metal back plate, dielectric spacer, and two artificial layers. One of the artificial layers provides electrical resonance and the other one provides magnetic resonance yielding a polarization independent broadband perfect absorption. The structure response remains similar for the wide angle of incidence due to the sub-wavelength unit cell size of the constituting artificial layers. The design is useful for applications such as thermal photovoltaics, sensors, and camouflage.

Polarization independent broadband reflectors based on cross-stacked gratings

We report here a broadband reflector based on a two cross-stacked grating structure. This type of broadband reflector is polarization-independent, with ~100% reflectance over a designed spectral range of 1.4 to 1.6 μm. The reflection phase differences between TE and TM polarizations remain almost a constant value of 1.2π over the same high reflection spectral range. The reflector performance tolerance was also investigated by varying the grating structure parameters. Two types of Fabry-Perot cavities can be configured based on two cross-stacked grating structures, for both polarization independent and polarization dependent resonance cavity mode control. All these characteristics associated with the cross-stacked grating reflectors enable a new type of resonant cavity or wave plate design for a large range of photonic applications.

A liquid lens-based broadband variable fiber optical attenuator

To the best of our knowledge, proposed is the first variable fiber optical attenuator (VFOA) using an electronically controlled variable focus liquid lens. The approach uses the changes in the radius of curvature of the liquid lens edge to enable an electronically controlled optical wedge that produces a varying beam tilt angle. In effect, changing beam tilt within a single mode fiber (SMF) lens free space coupling assembly leads to a polarization independent broadband VFOA design. The demonstrated VFOA experiment shows broadband operation over the 1530–1560 nm C-Band with a 40 dB dynamic range, <0.5 dB resolution, 0.3 dB polarization dependant loss, 4.3 dB fiber-to-fiber optical loss, 3 dB optical bandwidth from 1510 nm to 1700 nm, and switching time of <100 ms. Applications for this VFOA include use in hand held test and measurement equipment.