Black phosphorus phase retarder based on anisotropic refractive index dispersion

Black phosphorus (BP) has gained wide interest as a promising layered material for its unique physical properties. In particular, the anisotropic optical property of BP can act as a retarder or a polarizer in nano-optoelectronic devices, for which quantitative qualification of the phase retardation and the anisotropic refractive index dispersion are essential. Here, we report the anisotropic refractive index and extinction coefficient dispersions of BP in the visible and near infrared range of 540–1500 nm, and then characterize optical phase retardation in a BP flake. Cauchy absorbent equations are provided for the refractive index dispersions along both armchair and zigzag directions, which well reproduce the experimentally measured reflectance and transmittance contrast spectra of BP flakes. Furthermore, we demonstrate that a linear polarized light through BP becomes elliptical, a finding that agrees well with simulation results using the obtained anisotropic refractive index dispersions. The two-dimensional phase retarder in this work is expected to find various applications in novel polarization-sensitive nano-optoelectronic devices.

An Improved Method for Determination of Refractive Index of Dielectric Films from Reflectance Spectrum by Using the Generalized Morse Wavelet

The Generalized Morse Wavelet (GMW) algorithm was adapted to determine the refractive index of dielectric film from the reflectance spectrum. A theoretically generated reflectance spectrum in the range of 300-1200 nm wavelength was analyzed by the Continuous Wavelet Transform (CWT) and the refractive index dispersion was obtained by the mentioned method. In addition, a noisy reflectance spectrum was analyzed to show the advantages of the CWT method. Refractive index dispersions calculated by the Morlet and the Paul wavelet were compared to GMW at the end of the study.

Effect of Cu Incorporation on Optoelectronic Properties of e-Beam Evaporated ZnO thin Films by Ellipsometric Investigations

Electron beam deposition technique has been used to deposit a series of Zn1-xCuxO nanocrystalline thin film on silica substrate with a variety of Cu concentrations. The microstructural, surface morphology and spectroscopic ellipsometry (SE) were used to examine the physical properties of the deposited films. The nanocrystalline nature of the Zn1-xCuxO (0.0≤x≤0.20) thin film has been confirmed by surface morphology studies. The XRD spectrum of the Zn1-xCuxO nanocrystalline film showed a hexagonal wurtzite type structure, and no extra phase was detected. Our results show that as the Cu content increases, the direct optical energy gap Eg decreases without any sign of solubility limit up to x≤0.2. The decrease in Eg can be attributed to the sp-d exchange coupling. In addition, exploring the spectral behavior of the refractive index dispersion from SE of the Cu-doped ZnO shows that as the Cu dopant increments; the refractive index of the deposited film enhances. Further, understand the refractive index dispersion of the deposited film has been performed using a single oscillator model proposed by Wemple-DiDomenico (WDD). Our calculations show that as the Cu concentration increases, the values of oscillator energy Eo decreases however, the dispersion energy Ed increases. As a result, the variation of the optical energy band gap and the tunability of the dispersive oscillator parameters values Eo, Ed, n0, e0, M-1 and M-3 with the increase of the Cu doping level confirm that Cu doped ZnO films are a good candidate for optoelectronic device applications.

The influence of oxygen deficiency on the dispersion parameters of TiO2 films

TiO2 thin films were deposited on quartz substrate by RF-magnetron sputtering technique. The effect of varying oxygen fraction [Formula: see text] on the surface morphology, structure, electrical and optical properties was investigated. Decreasing the oxygen fraction promotes phase transformation to the extent of isolating anatase phase with well oriented A(101) preferred crystal orientation at [Formula: see text] of 0.1%. The refractive index dispersion curves were utilized to estimate the single oscillator parameters. In addition, an enhancement in the electrical conductivity to [Formula: see text] at [Formula: see text]% was established. This enhancement was attributed to the deficiency of oxygen as well as the formation of anatase phase.

Bandgap and refractive index estimates of InAlN and related nitrides across their full composition ranges

III-Nitride bandgap and refractive index data are of direct relevance for the design of (In, Ga, Al)N-based photonic and electronic devices. The bandgaps and bandgap bowing parameters of III-nitrides across the full composition range are reviewed with a special emphasis on InxAl1−xN, where less consensus was reached in the literature previously. Considering the available InAlN data, including those recently reported for low indium contents, empirical formulae for InAlN bandgap and bandgap bowing parameter are proposed. Applying the generalised bandgap data, the refractive index dispersion data available in the literature for III-N alloys is fitted using the Adachi model. For this purpose, a formalism involving a parabolic dependence of the Adachi parameters on the dimensionless bandgap $${\xi }_{{E}_{\mathrm{g}}}=\left({E}_{\mathrm{g}, {\mathrm{A}}_{x}{\mathrm{B}}_{1-x}\mathrm{N}}-{E}_{\mathrm{g},\mathrm{ BN}}\right)/\left({E}_{\mathrm{g}, \mathrm{AN}}-{E}_{\mathrm{g},\mathrm{ BN}}\right)$$ ξ E g = E g , A x B 1 - x N - E g , BN / E g , AN - E g , BN of the corresponding ternary alloys is used rather than one directly invoking the alloy composition.

A Fiber-Optic Gas Sensor and Method for the Measurement of Refractive Index Dispersion in NIR

This paper presents a method for gas concentration determination based on the measurement of the refractive index dispersion of a gas near the gas resonance in the near-infrared region (NIR). The gas refractive index dispersion line shape is reconstructed from the variation in the spectral interference fringes’ periods, which are generated by a low-finesse Fabry-Perot interferometer during the DFB diode’s linear-over-time optical frequency sweep around the gas resonance frequency. The entire sensing system was modeled and then verified experimentally, for an example of a low concentration methane-air mixture. We demonstrate experimentally a refractive index dispersion measurement resolution of 2 × 10−9 refractive index units (RIU), which corresponds to a change in methane concentration in air of 0.04 vol% at the resonant frequency of 181.285 THz (1653.7 nm). The experimental and modeling results show an excellent agreement. The presented system utilizes a very simple optical design and has good potential for the realization of cost-efficient gas sensors that can be operated remotely through standard telecom optical fibers.