Samudra Roy

Self-frequency blueshift of dissipative solitons in silicon-based waveguides

We analyze the dynamics of dissipative solitons in silicon on insulator waveguides embedded in a gain medium. The optical propagation is modeled through a cubic Ginzburg-Landau equation for the field envelope coupled with an ordinary differential equation accounting for the generation of free carriers owing to two-photon absorption. Our numerical simulations clearly indicate that dissipative solitons accelerate due to the carrier-induced index change and experience a considerable blue-shift, which is mainly hampered by the gain dispersion of the active material. Numerical results are fully explained by analytical predictions based on soliton perturbation theory.

Chemically deposited magnesium hydroxide thin film

Abstract Here we report for the first time to the best of our knowledge the processing techniques, nucleation kinetics and the nanoindentation behaviour of a 1·5 μm magnesium hydroxide thin film chemically deposited on a commercially available soda lime silica glass substrate at room temperature. The phase and microstructure of the films were analysed by X-ray diffraction, scanning electron microscopy, field emission scanning electron microscopy as well as transmission electron microscopy. An exponential nucleation kinetics was identified for the growth of the thin films. The nanomechanical properties, e.g. nanohardness and Young’s modulus of the films were measured by the nanoindentation technique at ultralow loads of 50, 70 and 100 μN. Finally, the nature of deformation of the thin film was analysed in terms of the energetics of the nanoindentation process and the microstructure.

Generation of supercontinuum and its theoretical study in three-ring silica microstructured optical fibers.

We report supercontinuum generation in nonlinear microstructured optical fibers (MOFs) especially fabricated in a two-step stack and draw process having three rings of airholes. High air-filling fraction (>0.9) is obtained in a simple and straightforward way during the drawing process which is essential to enhance nonlinearity. Two of the fabricated samples are characterized and zero dispersion wavelength is tailored to achieve efficient pumping in the anomalous group velocity dispersion regime. The characteristics of the supercontinuum band as observed experimentally show good agreement with the predicted numerically simulated results, where soliton mediated dispersive waves are distinctly observed.

Study of nonlinear dynamics in silver-nanoparticle-doped photonic crystal fiber

Linear and nonlinear properties of silver-nanoparticle-doped photonic crystal fibers (SNPCFs) are explored to obtain exciting nonlinear pulse dynamics. SNPCF offers additional control over the Kerr nonlinearity of the core glass. Unlike traditional PCFs, these composite fibers offer a significantly large negative nonlinearity at lower wavelengths. The interplay between large negative nonlinearity and dispersion leads to interesting dynamics of ultrashort pulse evolution where blueshifted Raman solitons are generated along with phase-matched radiations. Further, it is observed that the numeric sign of self-steepening coefficient provides an additional tool in harnessing the dispersive wave generation.

High-energy, shock-front-assisted resonant radiation in the normal dispersion regime

We present a simple yet effective theory that predicts the existence of resonant radiation bands in the deep normal group-velocity dispersion region of a medium, even in the absence of a zero-group-velocity dispersion point. This radiation is evident when the medium is pumped with high-energy ultrashort pulses, and it is driven by the interplay between the Kerr and the shock terms in the nonlinear Schrodinger equation. Accurate experiments performed in bulk silica fully support the theoretical phase-matching condition found by our theory.

Efficient Supercontinuum Sources Based on Suspended Core Microstructured Fibers

We fabricate uniform silica microstructured optical fibers (MOFs) having very simple geometry with only three rings of air holes in order to generate efficient supercontinuum (SC). The fabricated MOFs possess suspended core with comparatively larger pitch and are the most active component in a SC source. We use the suspension factor as a design parameter which significantly influences the nonlinear and dispersion properties of the MOFs. It is experimentally shown that our fabricated MOFs generate efficient SC both in femtosecond and picosecond pumping domain. We also numerically model the nonlinear dynamics for SC sources in order to identify the nonlinear processes and illustrate the spectral broadening mechanisms.

Solving Soliton Perturbation Problems by Introducing Rayleigh's Dissipation Function

We solve soliton perturbation problem in nonlinear optical system by introducing Rayleighs dissipation function in the framework of variational approach. The adopted process facilitates variational approach to be applied on dissipative system where the Lagrangian and Hamiltonian are difficult to form. Exploiting the idea, loss and filtering problems are evaluated with convincing results. Considering other perturbing terms like two soliton interactions, intrapulse Raman scattering, self-steepening, and two-photon absorption in extended nonlinear Schrodinger equation, Rayleighs dissipation function is configured intuitively so that the generalized Euler-Lagrange equation converges to the related governing equation of the pulse propagation. The process evolves a set of differential equations exploiting the dynamics of different pulse parameters under the influence of perturbations. The obtained analytical results are verified with generalized Kantorovich approach and compared with previous reported results. Numerical simulations based on the split-step beam propagation method are employed to calculate the pulse evolution parameters and the derived results are found to be corroborated well with the analytical predictions.

Implications of a zero-nonlinearity wavelength in photonic crystal fibers doped with silver nanoparticles

Photonic crystal fibers doped with silver nanoparticles exhibit a Kerr nonlinearity that can be positive or negative depending on the input wavelength and which vanishes at a specific wavelength. The existence of negative nonlinearity allows soliton formation even in the normal-dispersion region of the fiber, and the zero-nonlinearity wavelength (ZNW) acts as a barrier for the Raman-induced redshift of solitons. We adopted the variational principle to understand the role of the zero-nonlinearity point on Raman redshift and verified its prediction numerically for fundamental and higher-order solitons. We show how the simultaneous presence of a ZNW and a zero-dispersion wavelength affects soliton evolution inside such fibers and find a number of unique features such as the position and the spectral bandwidth of the dispersive wave that change with the location of the ZNW.

Experimental and theoretical study of red-shifted solitonic resonant radiation in photonic crystal fibers and generation of radiation seeded Raman soliton

Redshifted solitonic resonant radiation (RR) is a fascinating phase-matching phenomenon that occurs when an optical pulse, launched in the normal dispersion regime of photonic crystal fiber, radiates across the zero-dispersion point. The formation of such phase-matched radiation is independent of the generation of any optical soliton and mainly governed by the leading edge of an input pump which forms a shock front. The radiation is generated at the anomalous dispersion regime and found to be confined both in the time and frequency domain. We experimentally investigate the formation of such radiation in fabricated photonic crystal fiber for two different pulse width regimes (femtosecond and picosecond) with detailed theoretical analyses. Theoretically predicted results corroborate well with experimental results and confirm the existence of such unique radiation which is robust in nature. Further, we extend the study to long-length fiber and investigate the interplay between redshifted solitonic RR and intrapulse Raman scattering (IPRS). The consequence of the formation of such solitonic RR in an anomalous dispersion domain is found to be very interesting where it seeds a series of Raman solitons and behaves like a secondary source. These Raman solitons are now continuously redshifted and open up the possibility of wideband supercontinuum generation even in normal dispersion pumping. We fabricate a suitable photonic crystal fiber and experimentally demonstrate the RR-seeded IPRS process.

Optical analog of spontaneous symmetry breaking induced by tachyon condensation in amplifying plasmonic arrays

We study analytically and numerically an optical analogue of tachyon condensation in amplifying plasmonic arrays. Optical propagation is modeled through coupled-mode equations, which in the continuous limit can be converted into a nonlinear one-dimensional Dirac-like equation for fermionic particles with imaginary mass, i.e. fermionic tachyons. We demonstrate that the vacuum state is unstable and acquires an expectation value with broken chiral symmetry, corresponding to the homogeneous nonlinear stationary solution of the system. The quantum field theory analogue of this process is the condensation of unstable fermionic tachyons into massive particles. This paves the way for using amplifying plasmonic arrays as a classical laboratory for spontaneous symmetry breaking effects in quantum field theory.