Surajit Bose

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.

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.

Design and Fabrication of Microstructured Optical Fibers With Optimized Core Suspension for Enhanced Supercontinuum Generation

Nonlinear microstructured optical fibers (MOFs) offer better prospects in various interdisciplinary fields than conventional nonlinear fibers. High air filling fraction and small core are necessary to ensure high nonlinearity of MOFs. The air holes adjacent to the core can be elongated and tapered into the core in a controlled way during fiber drawing so that the solid core seems to be suspended in air with very thin silica struts connecting it to the matrix. This reduces the effective core area thereby increasing nonlinearity. In this study, the effect of core suspension on the nonlinearity and dispersion of MOFs are systematically investigated on the basis of a geometrical design parameter called suspension factor (SF). Detailed study reveals that MOF designs with enhanced nonlinearity can be obtained even with larger pitch and such MOF structures are easier to fabricate. Fiber drawing parameters which control the SF are precisely identified and optimized. Several fiber samples were drawn at different drawing conditions under constant monitoring and it was observed that high furnace temperature and high drawing speed are the two key parameters that ensure high SF. Further, the role of SF on nonlinear spectral broadening was experimentally investigated and it was found that MOF having high SF offers almost two octave-spanning supercontinuum.

Effect of zero-nonlinearity point on optical event horizon in defocused nonlinear media

We numerically show that a pump pulse close to the zero dispersion wavelength on the anomalous dispersion side in a self-defocusing (negative) nonlinear medium can excite resonant radiation due to shock wave formation. This shock wave is responsible for pulse splitting, and subsequently blue solitons are generated when the leading edge of pump pulse hits the zero dispersion wavelength. The interaction of this soliton with one of the pulse component (interpreted as control pulse) generates a reflected wave upon collision, which may be viewed as an optical event horizon like situation. The collision length is controlled by the zero nonlinearity wavelength (the wavelength at which the nonlinear index coefficient, n2 becomes zero) of silver nanoparticle doped photonic crystal fiber. Interaction of control pulses with solitonic pulse modifies the trajectory of the soliton.

Experimental study of solitonic dispersive wave in photonic crystal fiber

We experimentally observed the emission of phase-matched resonant radiation in the form of solitonic dispersive wave in a fabricated photonic crystal fiber by pumping picosecond and femtosecond pulses close to zero-dispersion wavelength in normal dispersion regime. The generation of such phase matched radiation does not require a soliton to be formed and red-shifted in nature. Shock front from the leading edge of the input pump initiates the resonant radiation. The radiation develops in the anomalous dispersion domain and found to be confined both in spectral and temporal domain. The resonance mechanism can be well explained from the numerical simulation governed by generalized nonlinear Schrödinger equation.

Supercontinuum generation in silver doped photonic crystal fiber

Silver doped photonic crystal fibers offer an additional control over the Kerr nonlinearity of core glass. We investigated numerically the optical properties and found an octave-spanning super continum where the visible region is dominated by Raman induced blue shifting and longer wavelength edge by dispersive wave generation.

Multimodal characteristics of supercontinuum light generated in nonlinear photonic crystal fiber

We report supercontinuum generation in nonlinear photonic crystal fiber, where first higher-order mode is excited in the visible part of the spectrum by selectively coupling pump light in normal dispersion regime.

Polarization characteristics of metal filled suspended core photonic crystal fiber

We present the study of polarization characteristics of metal filled suspended core photonic crystal fiber. The numerical calculation shows that modal birefringence increases with the increase in core suspension factor.

Effect of dispersion on supercontinuum generation of suspended core photonic crystal fiber

Supercontinuum generation in suspended core photonic crystal fiber is experimentally reported pumped with picosecond pulse at 30mW. Three different dimensions of fabricated fibers with distinct dispersion properties are employed to generate broadband white light source.