Ghosh, Somnath

We report a dual-core gain-loss assisted optical fiber-segment to host an exceptional point between two quasi-guided hybrid-modes, and study the adiabatic mode conversion phenomenon by a stroboscopic gain-loss variation around the identified EP.

We investigate an anti-parity-time (APT)-symmetric gain-loss assisted microcavity system based on scattering (S)-matrix formalism and report the fascinating aspects of encircled exceptional points (EPs) toward topological state-transfer applications.

We report the correlated characteristics of enhanced nonreciprocal light guidance with chirality-drove asymmetric mode conversions in two complementary waveguides with T-symmetric gain-loss profiles, which individually host two dynamically encircled conjugate exceptional points (EPs).

We present a quasi-periodically modulated coupled multicore fiber based on Aubry-Andre-Harper model to exhibit a sharp localization phase transition that is explicitly dependent on modulation strength and core arrangement radius of the geometry.

We report the hosting higher order conjugate exceptional points (EPs) in gain-loss assisted multi-mode supported optical waveguides and explore the selective mode conversion phenomenon assisted by parametrically encircled multiple exceptional points.

We report a planar 1D photonic bandgap waveguide exhibiting four second-order exceptional points (EP2s). The interactions between the selective pairs of supported quasi-guided TE modes are modulated by spatial distribution of transverse in-homogeneous gain-loss profile.

We present an unconventional way to manipulate light dynamics in photonic time crystals by introducing isolated temporal defects as a new degree of control over the amplification of propagating pulse with momentum lying within bandgap.

Topological photonics provides a new platform to control and manipulate the flow of light in photonic devices that exhibit topological phase transitions. One way to introduce such transition of geometric phases in photonic waveguides is to modulate the structure of the photonic crystals, array waveguides, or the metamaterials in such a way that it eventually changes the bulk topology. Such topological waveguides localize the light at the boundary of the two distinct bulk systems with different topological invariant. Based on this fundamental physics, we demonstrate a robust and controlled propagation of light in a class of specialty optical fiber which exhibits the topological phase transition between a nontrivial one-dimensional (1D) periodic cylinder and its topologically trivial counterpart. The key idea is to explore the possibility of topological phase transition of 1D photonic bands over the momentum space by tuning the unit-cell dimension and its individual thicknesses. We have systematically computed the trivial and the nontrivial topological invariants, the Zak phase, of designed cylindrical 1D lattices with inversion symmetry over the first Brillouin zone. To establish the presence and the robustness of the localized edge mode, we have studied the reflectance of the geometry in the presence of disorder. Also, the simulated field profile and the back-reflectionless propagation of the edge mode through the fiber have been shown. Besides conventional fibers, such topological optical fibers are definitely a waveguide geometry for robust delivery of light and thus would be very significant to open up a new paradigm in guided wave photonics.