Akhilesh Kumar Mishra

An SPR-based sensor with an extremely large dynamic range of refractive index measurements in the visible region

A promising GaP prism-based surface plasmon resonance sensor in the Kretschmann configuration with an extremely large dynamic range of refractive index detection is proposed. The prism base is coated with a gold layer and then a thin layer of silicon. The sensor is studied theoretically in terms of sensitivity and detection accuracy. The proposed sensor shows the potential of sensing media with a refractive index varying from gaseous to very dense liquid with appreciably high sensitivity.

Gas-Clad Two-Way Fiber Optic SPR Sensor: a Novel Approach for Refractive Index Sensing

We propose and study the characteristics of a novel gas-clad surface plasmon resonance (SPR)-based fiber optic sensor. The proposed fiber optic probe not only senses change in the refractive index of the environment surrounding the outer layer of the probe but also shows the potential of detecting different gases in cladding holes. We have carried out the study of sensing probe of gas-clad fiber with nitrogen gas filled in air holes of the primary cladding. Silica is used as a second cladding of the gas-clad fiber with ITO film over this secondary cladding as a plasmonic metal layer. To optimize the probe design, figure of merit (FOM) and detection accuracy (DA) are calculated for varying thicknesses of different layers.

MgF2 prism/rhodium/graphene: efficient refractive index sensing structure in optical domain

A theoretical study of a noble surface plasmon resonance (SPR) based sensing probe has been carried out. The sensing probe consists of a magnesium fluoride (MgF2) prism with its base coated with rarely used noble metal rhodium (Rh) and a bio-compatible layer of graphene. The refractive indices (RIs) of the sensing medium vary from 1.33 to 1.36 refractive index unit (RIU). The thickness of Rh and the number of graphene layers have been optimized for maximum sensitivity in a constraint set by the detection accuracy (DA). For the operating wavelength of 632 nm, the optimized sensing probe Rh (12 nm)/graphene (single layer) demonstrates sensitivity of ~259 degree/RIU with corresponding DA of ~0.32 degree-1 while for 532 nm of excitation, the optimized sensing probe Rh (12 nm)/graphene (three layer) exhibits sensitivity of ~240 degree/RIU and DA of ~0.27 degree-1.

Ultra-fast charge carrier dynamics across the spectrum of an optical gain media based on InAs/AlGaInAs/InP quantum dots

The charge carrier dynamics of improved InP-based InAs/AlGaInAs quantum dot (QD) semiconductor optical amplifiers are examined employing the multi-wavelength ultrafast pump-probe measurement technique. The transient transmission response of the continuous wave probe shows interesting dynamical processes during the initial 2-3 ps after the pump pulse, when carriers originating from two photon absorption contribute the least to the recovery. The effects of optical excitations and electrical bias levels on the recovery dynamics of the gain in energetically different QDs are quantified and discussed. The experimental observations are validated qualitatively using a comprehensive finite-difference time-domain model by recording the time evolution of the charge carriers in the QDs ensemble following the pulse.

Coherent control in room-temperature quantum dot semiconductor optical amplifiers using shaped pulses

We demonstrate the ability to control quantum coherent Rabi-oscillations in a room-temperature quantum dot semiconductor optical amplifier (SOA) by shaping the light pulses that trigger them. The experiments described here show that when the excitation is resonant with the short wavelength slope of the SOA gain spectrum, a linear frequency chirp affects its ability to trigger Rabi-oscillations within the SOA: A negative chirp inhibits Rabi-oscillations whereas a positive chirp can enhance them, relative to the interaction of a transform limited pulse. The experiments are confirmed by a numerical calculation that models the propagation of the experimentally shaped pulses through the SOA.

Coherent control in quantum dot gain media using shaped pulses: a numerical study

We present a numerical study of coherent control in a room temperature InAs/InP quantum dot (QD) semiconductor optical amplifier (SOA) using shaped ultra-short pulses. Both the gain and absorption regimes were analyzed for pulses with central wavelengths lying on either side of the inhomogeneously broadened gain spectrum. The numerical experiments predict that in the gain regime the coherent interactions between a QD SOA and a pulse can be controlled by incorporating a quadratic spectral phase (QSP) in the pulse profile. The sequential interaction with the gain medium of different spectral components of the pulse results in either suppression or enhancement of the coherent signatures on the pulse profile depending upon their proximity to the gain spectrum peak. In the absorption regime, positive QSP induces a negative chirp that adds up to that of a two photon absorption induced Kerr-like effect resulting in pulse compression while negative QSP enhances dispersive broadening of the pulse.

Analysis of free carrier effects on modulational instability in silicon-on-insulator nano-waveguides

We present a comprehensive theoretical study on the effects of two-photon absorption, free-carrier-induced loss, and high-order dispersion on the modulational instability (MI) at low-input powers in silicon-on-insulator nano-waveguides. The MI analysis is carried out in both the normal and anomalous dispersion regimes at telecommunication wavelength. To realize these two different kinds of dispersion, two different waveguide structures have been considered. Further, the effects of carrier lifetime and power dependence on MI gain spectra have also been delineated.

Cross-phase modulation induced modulation instability in negative index metamaterial with saturable nonlinear response

The influence of nonlinear dispersion (originating from the dispersive permeability as well as from the nonlinear polarization) on cross-phase modulation (XPM) induced modulational instability (MI) in the negative index domain of metamaterials (MMs) with saturable nonlinearity is investigated numerically. The study explores various possible regimes of normal and anomalous group velocity dispersion and their combinations, which the two copropagating waves could experience in the negative refractive index domain of a MM. It has been shown that, under certain conditions, the first-order nonlinear dispersion, i.e., self-steepening (SS) and the second-order nonlinear dispersion (SOND), may lead to a considerable change in the MI gain spectrum. In addition, it is shown that, at higher perturbation frequencies, the SS effect causes considerable structural changes in the MI gain spectrum.

Breakthroughs in Photonics 2014: Time-Scale-Dependent Nonlinear Dynamics in InAs/InP Quantum Dot Gain Media: From High-Speed Modulation to Coherent Light–Matter Interactions

The dynamical properties of InP-based quantum dot (QD) gain media are surveyed and analyzed for three time scales ranging from tens of picoseconds to less than 200 fs, where quantum coherent phenomena are observable. Each of these time scales determines the important properties of QD devices, i.e., modulation capabilities, nonlinear gain, and coherent light-matter interactions. Experimental investigations and modeling results are described, highlighting the state of the art in QD devices for the important 1550-nm telecom wavelength range.

Datacom multi-mode optical link using 850 nm VCSELs at 25 Gb/s

We present a numerically study of the transmission of 25Gb/s multimode optical signal comprising of 15 bit nonreturn-to-zero (NRZ) sequence over a length more than 50 meters in a graded index multi-mode (GI-MM) fiber with given specification at 850 nm of wavelength. Further, we study the wavelength dependence of relative delay (RD) and group velocity dispersion (GVD) parameters, and observe RD to be a major signal distorting factor in short distance communication links. The eye diagrams have been plotted at different communication wavelength and noticed that the eye remains open widely even after 50 meters of propagation only at 850 nm of wavelength and as the signal propagates further the eye starts to deteriorate.