arXiv subjects

Partha Mondal

Publications and source records attributed to Partha Mondal.

9 recordsLinked to original sources

arXiv2026

Enhanced Third-Harmonic Generation in a Bound State in the Continuum Assisted Multiband All-Dielectric Metasurface

Multiband Fano resonances are demonstrated in the near-infrared (near-IR) using an all-dielectric metasurface whose unit cell consists of four silicon nanoblocks on a glass substrate. An in-plane asymmetry triggers symmetry-protected quasi-bound states in the continuum (QBICs), producing multiple high-Q resonances. Their origin is identified through multipolar decomposition of the scattering cross section and field distributions at the resonances. The strong field localization at these resonances enables efficient multiband third-harmonic (TH) generation in the ultraviolet (UV), with a maximum simulated conversion efficiency of $8.5 \times 10^{-3}$ at a peak pump intensity of $1.6\,\mathrm{GW/cm^{2}}$. The metasurface is fabricated in symmetric and asymmetric configurations, and its linear and nonlinear responses are measured under normal incidence. A TH conversion efficiency of $1.2 \times 10^{-6}$ is obtained at a peak pump intensity of $3.25\,\mathrm{GW/cm^{2}}$. These results establish a route to multiband photonic devices, including multiwavelength lasers, multiband harmonic generation, and single-photon sources for quantum photonics.

physics.optics↗

arXiv2026

A Single-Trace Surface Integral Equation Solver for Simulation of Open Bianisotropic Metasurfaces Described by Generalized Sheet Transition Conditions

A single-trace surface integral equation (SIE) solver incorporating generalized sheet transition conditions (GSTCs) is presented for the simulation of three-dimensional (3D) open bianisotropic metasurfaces. The metasurface is modeled as an infinitesimally thin, non-enclosing sheet across which the GSTCs enforce the electromagnetic field discontinuities through four surface susceptibility tensors. The proposed solver uses a single set of equivalent surface currents on the sheet, in place of the two sets used by prior multi-trace formulations. The scattered fields on both faces of the sheet, expressed through SIE operators acting on these currents, are substituted into the GSTCs. The resulting system of equations is then discretized using Rao--Wilton--Glisson basis functions. This solver models an open metasurface directly, without an artificial closure, and applies to both planar and curved geometries. It is validated against analytical solutions for polarization rotation and perfect reflection, and is used to model a realistic broadband absorber whose susceptibility tensors are retrieved from full-wave simulation data. A direct comparison shows that the single-trace formulation attains lower error than a multi-trace formulation while using significantly fewer unknowns.

physics.comp-ph↗

arXiv2026

Multiband Hybrid Metasurface for Enhanced Second-Harmonic Generation via Coupled Gap Surface Plasmon Modes

A multiband hybrid metasurface supporting multiple gap-surface plasmon (GSP) and localized surface plasmon (LSP) modes is presented. The structure adopts a metal-dielectric-metal configuration consisting of an aluminum bottom layer, a silicon dioxide spacer, and a bar-disc hybrid resonator patterned in the top aluminum layer. Optimized geometrical parameters yield four distinct resonances across the near-infrared and telecommunication bands, arising from the interplay between GSP modes and LSP excitations. The reflectance spectra are systematically analyzed as functions of geometric parameters and polarization, demonstrating tunable multiband operation. Experimental measurements of the fabricated metasurface show good agreement with numerical predictions. Furthermore, the second-harmonic generation (SHG) response is numerically investigated, revealing enhanced SH emission at the resonance wavelengths due to strong electromagnetic field confinement within the metal-dielectric-metal cavity. The proposed metasurface provides a compact platform for multiband and multifunctional nanophotonic applications.

physics.optics↗

arXiv2025

Enhanced Absorption in Thin-Film Silicon Solar Cells Using a Broadband Plasmonic Nanostructure

The design and fabrication of a metal-dielectric-metal absorber that achieves strong absorption from the ultraviolet (UV) to the near-infrared (near-IR) spectrum are presented. The proposed nanostructure consists of a periodic titanium (Ti) array as the top layer, a thin silicon dioxide (SiO2) spacer, and a continuous aluminum (Al) layer serving as the back reflector. Comprehensive optimization of structural parameters results in an average absorptance of 96% in the 280-1000 nm wavelength range. The proposed design exhibits polarization insensitivity and maintains high absorption efficiency under oblique incidence. Fabrication is carried out using electron beam lithography followed by a lift-off process, ensuring both high performance and manufacturing simplicity. Experimental measurements show strong agreement with numerical simulations, validating the effectiveness of the design. Furthermore, integration of the absorber into a thin-film silicon (Si) solar cell is analyzed, revealing significant enhancement in light absorption within the active layer. Owing to its broadband response, angular robustness, and structural simplicity, the proposed absorber shows strong potential for applications in solar energy harvesting, thermal emission, and advanced photovoltaic technologies.

physics.optics↗

arXiv2022

Linear and Nonlinear Characterization of broadband integrated Si-rich silicon nitride racetrack ring resonator for on-chip applications

We demonstrate the linear and nonlinear characterization of plasma-enhanced chemical vapor deposited silicon-rich silicon nitride (SRSN) racetrack ring resonator for on-chip application within the telecommunication wavelength range. The SRN waveguide parameters are optimized by employing the refractive index profile measured by ellipsometry to achieve flat dispersion in the telecom band. Furthermore, we measure the thermo-optic coefficient (TOC) of the micro-resonator by analyzing the temperature-dependent transmission spectra and assessing it to be $3.2825$ $\times$ $10^{-5}$ $^o{} C^{-1}$. Additionally, we perform power-dependent transmission spectra to investigate the effect of local heating and nonlinear absorption. The power-dependent transmission spectra exhibit a blue-shifting of the resonance peak in the visible and near-IR regions, which indicates the presence of nonlinear losses in that range. The power-dependent transmission spectra almost remain unchanged in the telecom band, revealing the absence of nonlinear losses and excellent thermal stability in that wavelength range. Our experimental results reveal that the SRSN-based structure can be employed potentially to realize linear and nonlinear applications in the telecom band.

physics.optics↗

arXiv2020

Competition Between Intermodal Modulation Instability and Kerr Beam Self-cleaning in Graded-index Multimode Fiber

We report the suppression of intermodal modulation instability peaks as a consequence of Kerr induced self beam-cleaning in a 90m long graded-index multimode optical fiber under various specific launching conditions. The output spectrum and the modal beam profiles for three modes (LP01, LP11, and LP21) have been recorded for several values of pump pulse energy. Experimental findings establish that the nonlinear coupling among the guided modes leads to reshaping the output speckle pattern into a bell shape or higher-order spatially clean beam profile as the pump peak power increases, whereas in spectral-domain intermodal modulation instability peaks are observed whose amplitude increases gradually to its maximum value and beyond certain threshold power, the intermodal modulation instability peaks diminish. This suggests the possibility to generate intermodal modulation instability free broadband spectra at high pump peak powers.

physics.optics↗

arXiv2019

Phase Synchronization of Stimulated Raman Process in Optical Fiber For Long Pulse Regime

We investigate the evolution of coherence property of noise-seeded Stokes wave in short (< 1 ps) and long pulse (> 1 ps) regimes. Nonlinear equations expressing the evolution of pump and Stokes wave are solved numerically for both the regions. The simulations include quantum noise by incorporating noise seed in the pump field where one photon per mode with random phase. The spectral phase fluctuations of the Stokes wave for both the regions, are characterized by performing multiple simulations and finally, the degrees of first-order mutual coherence are calculated as a function of wavelength for different conditions. Our statistical analysis proclaim that noise-seeded stimulated Raman process, which plays the role in degradation of coherence in short pulse region, exhibits strong phase synchronization in long pulse regime. The manifestation of phase synchronization occurs by the transition of the Stokes wave from incoherent to coherent spectra in long pulse regime.

physics.optics↗

arXiv2019

Modal Group Velocity Mismatch Induced Intermodal Modulation Instability in Step-index Fiber

We present detailed experimental study on noise-seeded intermodal modulation instability (IM-MI) in normal dispersion region of a conventional step-index fiber. The sharp refractive index contrast between core and cladding leads to large group velocity mismatch between the spatial modes, coaxing to efficient IM-MI and generation of multiple spectral peaks along with Raman peaks. Evolution of the spectrum with pump powers and fiber lengths are observed. Experimental findings are well supported with the theoretical framework based on bimodal-MI model considering the distinct dispersion parameters of the participating modes.

physics.optics↗

arXiv2018

Generalized Mathematical Formalism Governing Free-carrier Driven Kerr Frequency Comb in Optical Micro-cavities

Continuous-wave pumped optical microresonators have been vastly exploited to generate frequency comb (FC) utilizing the Kerr nonlinearity. Most of the nonlinear materials used to build photonic platforms exhibit nonlinear losses such as multi-photon absorption, free-carrier absorption (FCA), and free-carrier dispersion (FCD) which can strongly affect the nonlinear characteristics of the devices made out of these materials. In this work, we model the Kerr FC based on modified Lugiato-Lefever Equation (LLE) along with the rate equation and develop analytical formulations to make quick estimations of the steady-state, modulation instability (MI) gain, bandwidth and the dynamics of Kerr Frequency-Comb (FC) in presence of nonlinear losses. Our analytical model is valid over a broad wavelength range of interest as it includes the effects of all nonlinear losses. Higher order (>3) characteristic polynomial of intra-cavity power describing the steady-state homogeneous solution of the modified LLE are discussed in detail. We derive the generalized analytical expressions for the threshold of normalized pump detuning to initiate the optical bistability which is a necessary condition for the FC generation. Free-carrier dispersion-led nonlinear cavity detuning is observed through the reverse Kerr-tilt of the resonant-peaks. We further deduce the expressions for the threshold pump intensity and the range of possible cavity detuning for the initiation of the MI when all the nonlinear losses are present. To corroborate our analytical findings, LLE along with the rate equations are solved numerically through split-step Fourier method. Our theoretical study can explain several experimental results which are previously reported and thereby is able to provide a better understanding of the comb dynamics.

physics.optics↗