Somnath Ghosh

Bio: Somnath Ghosh is an academic researcher from Indian Institute of Technology, Jodhpur. The author has contributed to research in topics: Microstructured optical fiber & Optical fiber. The author has an hindex of 28, co-authored 287 publications receiving 3318 citations. Previous affiliations of Somnath Ghosh include University of Calcutta & Indian Institute of Science.

Generation of a low divergent supercontinuum for mid-IR high power delivery through a large mode area photonic bandgap fiber

Abstract: We numerically report the feasibility of generating broadband low divergent supercontinuum covering the entire wavelength window of 1.5?3.5??m from a 2.25?m long effectively single mode all solid, soft glass based, photonic bandgap fiber with mode area as large as 1100??m2. Owing to its chosen fabrication, friendly geometry, and the chosen material composition, the proposed fiber-based light source should be useful as a mid-wave IR pulsed broadband light source for applications such as high power delivery, optical coherence tomography and mid-IR spectroscopy.

Generation of Low Divergent High Power Supercontinuum Through a Large Mode Area Photonic Bandgap Fiber

Abstract: We report generation of broadband low divergent supercontinuum over the entire wavelength window of 1.5 to 3.5 {\mu}m from a 2.25 meter long effective single moded photonic bandgap fiber with mode area of 1100 {\mu}m2.

Toward Self-Similar Propagation of Optical Pulses in a Dispersion Tailored, Nonlinear, and Segmented Bragg-Fiber at 2.8 $\mu$m

Abstract: We demonstrate self-similar stable propagation of parabolic optical pulses through a highly nonlinear specialty Bragg fiber at 2.8 $\mu$ m by a numerical approach. To obtain such propagation characteristics over a longer length of a Bragg fiber, we propose and verify a fiber design scheme that underpins passive introduction of a rapidly varying group-velocity dispersion around its zero dispersion wavelength and modulated nonlinear profile through suitable variation in its diameter. To implement the proposed scheme, we design a segmented and tapered chalcogenide Bragg fiber in which a Gaussian pulse is fed. Transformation of such a launched pulse to a self-similar parabolic pulse with full-width-at-half-maxima of 4.12 ps and energy of $\sim$ 39 pJ is obtained at the output. Furthermore, a linear chirp spanning across the entire pulse duration and 3 dB spectral broadening of about 38 nm at the output are reported. In principle, the proposed scheme could be implemented in any chosen set of materials.

C-H···O and C-H···X (X = Cl/Br) hydrogen bond tuned supramolecular assembly: a combined X-ray powder diffraction and Hirshfeld surface analysis

Abstract: Crystal structures of N -(2-chlorophenyl) acetamide ( 1 ) and phenyl (2-bromomethyl) benzoate ( 2 ) have been determined from laboratory X-ray powder diffraction data. In addition to intermolecular N–H···O and C–H···O hydrogen bonds, the crystal packing in ( 1 ) and ( 2 ) exhibits weak C–H···Cl/Br interactions, which facilitate formation of three-dimensional architectures. Hirshfeld surface analysis of compounds ( 1 ), ( 2 ), and a few related chloro- and bromo-phenyl derivatives retrieved from the CSD indicates that 83–97% of Hirshfeld surface areas in this class of compounds are due to H···H, H···π, H···O, and H···Cl/Br contacts.

A New Synthesis of Flavones and Pyranoflavone by Intramolecular Photochemical Wittig Reaction in Water.

Abstract: A new synthetic approach toward the synthesis of flavones and pyranoflavone has been developed by light induced intramolecular photochemical Wittig reaction in water onto aryloxycarbonyl groups and suitably substituted phosphonium bromides sans any phase transfer catalyst or promoter.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Exceptional points in optics and photonics.

Abstract: BACKGROUND Singularities are critical points for which the behavior of a mathematical model governing a physical system is of a fundamentally different nature compared to the neighboring points. Exceptional points are spectral singularities in the parameter space of a system in which two or more eigenvalues, and their corresponding eigenvectors, simultaneously coalesce. Such degeneracies are peculiar features of nonconservative systems that exchange energy with their surrounding environment. In the past two decades, there has been a growing interest in investigating such nonconservative systems, particularly in connection with the quantum mechanics notions of parity-time symmetry, after the realization that some non-Hermitian Hamiltonians exhibit entirely real spectra. Lately, non-Hermitian systems have raised considerable attention in photonics, given that optical gain and loss can be integrated as nonconservative ingredients to create artificial materials and structures with altogether new optical properties. ADVANCES As we introduce gain and loss in a nanophotonic system, the emergence of exceptional point singularities dramatically alters the overall response, leading to a range of exotic functionalities associated with abrupt phase transitions in the eigenvalue spectrum. Even though such a peculiar effect has been known theoretically for several years, its controllable realization has not been made possible until recently and with advances in exploiting gain and loss in guided-wave photonic systems. As shown in a range of recent theoretical and experimental works, this property creates opportunities for ultrasensitive measurements and for manipulating the modal content of multimode lasers. In addition, adiabatic parametric evolution around exceptional points provides interesting schemes for topological energy transfer and designing mode and polarization converters in photonics. Lately, non-Hermitian degeneracies have also been exploited for the design of laser systems, new nonlinear optics phenomena, and exotic scattering features in open systems. OUTLOOK Thus far, non-Hermitian systems have been largely disregarded owing to the dominance of the Hermitian theories in most areas of physics. Recent advances in the theory of non-Hermitian systems in connection with exceptional point singularities has revolutionized our understanding of such complex systems. In the context of optics and photonics, in particular, this topic is highly important because of the ubiquity of nonconservative elements of gain and loss. In this regard, the theoretical developments in the field of non-Hermitian physics have allowed us to revisit some of the well-established platforms with a new angle of utilizing gain and loss as new degrees of freedom, in stark contrast with the traditional approach of avoiding these elements. On the experimental front, progress in fabrication technologies has allowed for harnessing gain and loss in chip-scale photonic systems. These theoretical and experimental developments have put forward new schemes for controlling the functionality of micro- and nanophotonic devices. This is mainly based on the anomalous parameter dependence in the response of non-Hermitian systems when operating around exceptional point singularities. Such effects can have important ramifications in controlling light in new nanophotonic device designs, which are fundamentally based on engineering the interplay of coupling and dissipation and amplification mechanisms in multimode systems. Potential applications of such designs reside in coupled-cavity laser sources with better coherence properties, coupled nonlinear resonators with engineered dispersion, compact polarization and spatial mode converters, and highly efficient reconfigurable diffraction surfaces. In addition, the notion of the exceptional point provides opportunities to take advantage of the inevitable dissipation in environments such as plasmonic and semiconductor materials, which play a key role in optoelectronics. Finally, emerging platforms such as optomechanical cavities provide opportunities to investigate exceptional points and their associated phenomena in multiphysics systems.