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Somnath Ghosh

Publications and source records attributed to Somnath Ghosh.

47 records · Page 3Linked to original sources
arXiv2017

Towards Ultra-Large Bandwidth and a New Class of Specialty Optical Fibers

We propose a scheme to enhance the effective photonic bandwidth exploiting bandgap overlapping of same order or different orders through judiciously chosen aperiodic geometries is spatial dimension. To implement the scheme, we design a specialty optical fiber with hybrid chirped-cladding. Our designed fiber provides an ultra-wide photonic bandwidth of ~ 3 micron. The less dispersive behavior of the structure carries the signature of zero dispersion at ~2.7micron. The proposed two material all-solid fiber geometry is based on thermally compatible chalcogenide glasses, GeAsSe and AsSe as low and high index respectively. The efficient delivery of short pulses with less distortion, and enhanced frequency broadening of specific pulses at certain conditions are demonstrated through these specialty fibers.

physics.optics↗
arXiv2017

Unconventional next nearest neighbor resonance coupling and states flipping mechanism in degenerate optical microcavities

We report a specially configured non-Hermitian optical microcavity, imposing spatially imbalanced gain-loss profile, to host an exclusively proposed next nearest neighbor resonances coupling scheme. Adopting scattering matrix (S-matrix) formalism, the effect of interplay between such proposed resonance interactions and the incorporated non-Hermiticity in the microcavity is analyzed drawing a special attention to the existence of hidden singularities, namely exceptional points (EPs); where at least two coupled resonances coalesce. We establish adiabatic flip-of-states phenomena of the coupled resonances in the complex frequency plane (k-plane) which is essentially an outcome of the fact that the respective EP is being encircled in system parameter plane. Encountering such multiple EPs, the robustness of flip-of-states phenomena have been analyzed via continuous tuning of coupling parameters along a special hidden singular line which connects all the EPs in the cavity. Such a numerically devised cavity, incorporating the exclusive next neighbor coupling scheme, have been designed for the first time to study the unconventional optical phenomena in the vicinity of EPs.

physics.optics↗
arXiv2016

Towards self-similar propagation in a dispersion tailored and highly nonlinear segmented bandgap fiber at 2.8 micron

We numerically demonstrate self-similar propagation of parabolic optical pulses through a highly nonlinear and passive specialty photonic bandgap fiber at 2.8 micron. In this context, we have proposed a scheme endowed with a rapidly varying, but of nearly-mean-zero longitudinal dispersion and modulated nonlinear profile in order to achieve self-similarity of the formed parabolic pulse propagating over longer distances. To implement the proposed scheme, we have designed a segmented bandgap fiber with suitably tapered counterparts to realize such customized dispersion with chalchogenide glass materials. A self-similar parabolic pulse with full-width-at-half-maxima of 4.12 ps and energy of ~ 39 pJ as been achieved at the output. Along with a linear chirp spanning over the entire pulse duration, 3dB spectral broadening of about 38 nm at the output has been reported.

physics.optics↗
arXiv2016

Unconventional optical microcavities hosting multiple exceptional points

Recently, presence of hidden singularities known as exceptional points (EPs) in non-Hermitian quantum systems has opened up a tremendous interest in different domains of physics owing to their unique unconventional physical effects. Effectively for such systems an EP appears as a fascinating topological defect where two mutually interacting eigenstates of the system coalesce. In this work, we report occurrence of EP via avoided crossing between coupled resonance states in an optical microcavity with spatially varying gain loss profile, an optical analogue of non-Hermitian system. With suitably tailored system openness and coupling strength, internally coupled resonances can exhibit EP in a medium with simultaneous presence of loss and gain. We explore the characteristics behaviors of energy eigenvalues in complex energy plane and corresponding eigenstates when the control parameters of the system are adiabatically changed, such a way that they encircle the EP. In this letter, we first ever exploit the above scheme to analyze the optical performance in terms of stability and rigidity of a microcavity simultaneously hosting such multiple EPs.

physics.optics↗
arXiv2016

Generation and Stability Analysis of Self Similar Pulses Through Specialty Microstructured Optical Fibers in Mid Infrared Regime

We report a numerical study on generation and stability of parabolic pulses during their propagation through highly nonlinear specialty optical fibers. Here, we have generated a parabolic pulse at 2.1 $μ$m wavelength from a Gaussian input pulse with 1.9 ps FWHM and 75 W peak power after travelling through only 20 cm length of a chalcogenide glass based microstructured optical fiber (MOF). Dependence on input pulse shapes towards most efficient conversion into self similar states is reported. The stability in terms of any deviation from dissipative self-similar nature of such pulses has been analyzed by introducing a variable longitudinal loss profile within the spectral loss window of the MOF, and detailed pulse shapes are captured. Moreover, three different dispersion regimes of propagation have been considered to study the suitability to support most stable propagation of the pulse.

physics.optics↗
arXiv2015

Quality enhancement with simultaneous suppression in excess noise of longer-lived states in non-uniformly pumped optical microcavities

We study the formation of longer lived states via internal coupling near a special avoided resonance crossing between the interacting states in an open optical system. Away from PT symmetry limit, we discuss the unconventional cavity resonance states created by a spatially varying gain/loss profile. Near certain avoided-resonant crossings (ARC), the parity symmetries of the chosen coupled states dictate the destructive interference resulting high Q, while avoided crossing in the imaginary part of the poles embraces the longer lived state. Now, via S-matrix formalism, we have numerically demonstrated that with suitably chosen system openness and coupling strengths, the excess noise generation among the interacting non-orthogonal states (calculated as Petermann factor K) can be suppressed close to the ideal value 1 with simultaneous order of magnitude enhancement in Q-factor of the longer lived state.

physics.optics↗
arXiv2014

Localization and adiabatic pumping in a generalized Aubry-André-Harper model

A generalization of the Aubry-André-Harper (AAH) model is developed, containing a tunable phase shift between on-site and off-diagonal modulations. A localization transition can be induced by varying just this phase, keeping all other model parameters constant. The complete localization phase diagram is obtained. Unlike the original AAH model, the generalized model can exhibit a transition between topologically trivial bandstructures and topologically non-trivial bandstructures containing protected boundary states. These boundary states can be pumped across the system by adiabatic variations in the phase shift parameter. The model can also be used to demonstrate the phenomenon of adiabatic pumping breakdown due to localization.

cond-mat.mes-hall↗
arXiv2013

Transverse localization of light in 1D disordered waveguide lattices with backbone photonic bandgap

The role of a prominent photonic bandgap (PBG) on the phenomenon of transverse localization of light in a semi-infinite lossless waveguide lattice consisting of evanescently coupled disordered one-dimensional optical waveguides has been investigated numerically. The interplay between the underlying photonic bandgap due to inherent periodicity of the optical system and various levels of deliberately induced transverse disorder in its refractive index periodicity has been studied. We show that the PBG indeed plays an important role and its simultaneous presence could catalyze realization of localized light even when strength of disorder is not sufficiently strong to independently cause localization of light. An important outcome of this study revealed that PBG could be gainfully exploited to tailor the spectral window for localization of light in potential applications like lasing in a disordered optical lattice.

physics.optics↗
arXiv2013

Ultra-large Mode Area Microstructured Core Chalcogenide Fiber Design for Mid-IR Beam Delivery

An all solid large modearea (LMA) chalcogenide based microstructured core optical fiber (MCOF) is designed and proposed for high power handling in the mid IR spectral regime, covering the entire second transparency window of the atmosphere (3 to 5 microns). The core of the proposed specialty fiber is composed of a few rings of high index rods arranged in a pattern of hexagon. Dependence of effective mode area on the pitch and radius of high index rods are studied. Ultra high effective mode area up to 75000 micron square can be achieved over this specific wavelength range while retaining its single mode characteristic. A negligible confinement loss along with a low dispersion slope (near 0.03 ps/km-nm square) and a good beam quality factor (M2 1.17) should make this LMA fiber design attractive for fabrication as a potential candidate suitable for high power, passive applications at the mid IR wavelength regime.

physics.optics↗
arXiv2012

Effect of a weak longitudinal modulation in refractive index on transverse localization of light in 1D disordered waveguide lattices

We report the enhancement of the effect of transverse localization of light (TL) in presence of a weak longitudinal modulation of refractive index in disordered waveguide lattices. In our chosen lattices, tunneling inhibition along length favors to achieve the diffraction-free propagation along with the simultaneous presence of transverse disorder. Results will be useful to tune the threshold value of disorder to achieve localized light.

physics.optics↗