Due to their unique optical properties, plasmonic materials are widely used in nonlinear optics, nanophotonics, optoelectronics, photocatalysis, biosensing, information storage, etc. Researchers usually need to know the detailed permittivity behavior at the vicinity of surface plasmons’ excitation wavelengths, which in turn are located near the zero points of the real part of the permittivity called epsilon-near-zero (ENZ). We hereby introduce a spectral fitting method to quickly obtain the materials' permittivity at the ENZ region and summarize the experiences of selecting dispersion models and optimizing model parameters. Specifically, we have made a detailed description of the optical constant fitting process for a series of plasmonic materials such as heavily doped semiconductors, transparent conductive oxides, organic conductive materials, two-dimensional materials, and sandwiched composites. Hopefully, to provide specific data and theoretical support for researchers in the field of photoelectric properties of plasmonic materials.
The unique performances of Epsilon-near-zero (ENZ) materials allow them to play a crucial role in many optoelectronic devices and have spawned a wide range of inventive uses. In this paper, we found that the modified PEDOT:PSS film formed with a kind of so-called “Metastable liquid-liquid Contact (MLLC)” solution treatment method can achieve a wide tuning of ENZ wavelength from 1270 nm to 1550 nm in the near-infrared region. We further analyzed the variation trend of imaginary permittivity for these samples with different ENZ wavelengths. The Berreman mode was successfully excited by a simple structural design to realize a tunable polarization absorber.
A novel Si/In2O3 hybrid plasmonic waveguide modulator was experimentally realized by using an asymmetric directional coupler (ADC), which consists of a silicon photonic waveguide and a Si/In2O3 hybrid plasmonic waveguide. All the silicon cores are covered with a silica layer, above which there is a metal-oxide-semiconductor (MOS) capacitor consisting of the In2O3/HfO2/Au layers. The Au layer sitting on the top of the MOS capacitor works as the top-electrode while the In2O3 thin film covers the sidewall and contacts with the Au bottom-electrode. When the bias voltage is not applied, light launched from the silicon photonic waveguide is weakly coupled into the Si/In2O3 hybrid plasmonic waveguide, and thus one has a high transmission at the through port of the ADC. On the other hand, when the bias voltage is applied, the carrier density in the In2O3 layer is changed, which introduces some modification to the refractive index of the In2O3 thin film. As a result, light is strongly cross-coupled from the silicon photonic waveguide to a Si/In2O3 hybrid plasmonic waveguide, and one has low transmission at the through port. In this paper, an ultra-compact Si/In2O3 hybrid plasmonic waveguide modulator is realized with a 3.5-μm-long ADC. In the experiments, the fabricated waveguide modulator works well and exhibits a high modulation bandwidth of >40 GHz for the first time.
light absorption is a substantial problem that profoundly influences a wide range of disciplines. Whereas it is fundamentally restricted by the bandgap energy of the involved materials. Herein, we study the sub-bandgap light absorption in germanium films via Berreman mode (BE) and its enhancement through weak coupling to Fabry-Perot cavity mode. This enhancement is performed by integrating the semiconductor film into a microcavity structure and tune its resonance frequency to match the epsilon-near-zero (ENZ) wavelength of the film material in a planar multilayer structure. We ascertained that our approach of electric field confinement in the semiconductor layer could perform significant light absorption at large incidence angles. That provides a novel, general, and simple method to enhance the optical and optoelectronic responses of any ENZ material, especially semiconductors below their bandgap energies.
Optical performances of epsilon near zero (ENZ) material gallium doped zinc oxide (GZO) can be effectively tuned by modulating substrate types, substrate heating temperatures, as well as post-annealing procedures. Four GZO film samples with imaginary part of permittivity at their ENZ wavelengths of εENZ ′′ = 0.26, 0.32, 0.50, 0.68 were deposited with radio frequency magnetron sputtering technology, all samples could reach perfect absorption at a certain incident angle and wavelength. A smaller εENZ ′′ of GZO film provides narrower bandwidth of near perfect absorption peak (higher Q-factor), while a larger εENZ ′′ tends to have a broader bandwidth. Furthermore, the incident angle allowed to achieve perfect absorption is also influenced by εENZ ′′ of GZO films. To realize near perfect absorption (reflectivity below 5%), larger εENZ ′′ provides a wider near perfect absorption window (Δθ); smaller εENZ ′′ tends to have an easier condition to achieve perfect absorption.
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