Debashri Ghosh

Picosecond fiber MOPA pumped supercontinuum source with 39 W output power

We report picosecond fiber MOPA pumped supercontinuum source with 39W output, spanning at least 0.4–1.75µm with high and relatively uniform spectral power density of ∼31.7mW/nm corresponding to peak power density of ∼12.5W/nm in 20ps pulse.

Hypocycloid-shaped hollow-core photonic crystal fiber Part II: cladding effect on confinement and bend loss.

We report on numerical and experimental studies on the influence of cladding ring-number on the confinement and bend loss in hypocycloid-shaped Kagome hollow core photonic crystal fiber. The results show that beyond the second ring, the ring number has a minor effect on confinement loss whereas the bend loss is strongly reduced with the ring-number increase. Finally, the results show that the increase in the cladding ring-number improves the modal content of the fiber.

Ultra low-loss hypocycloid-core Kagome hollow-core photonic crystal fiber for green spectral-range applications

We report on the development of hypocycloidal-core kagome HC-PCF operating efficiently in the 450nm-650nm visible spectral range. Transmission loss as low as 70dB/km is achieved. Strong Raman comb generation and laser beam delivery are demonstrated.

Design of all-solid leakage channel fibers with large mode area and low bending loss

We investigate a novel design for all-solid large mode area (LMA) leakage channel fibers (LCFs) for high-power Yb-doped fiber lasers and amplifiers, based on a single down-doped-silica rod ring surrounding a seven-cell pure-silica core, aiming for effectively single-mode behavior and low bending loss characteristics. Through detailed numerical simulations based on the finite element method (FEM), we find that the proposed all-solid LMA-LCFs, having a seven-cell core and two different sizes of down-doped rods, can achieve sufficient differential mode loss and much lower bending loss, as compared with a previously-reported LCF with a one-cell core and six large down-doped-silica rods.

Limitation on Effective Area of Bent Large-Mode-Area Leakage Channel Fibers

We investigate the bending characteristics of leakage channel fibers (LCFs) to achieve large mode area (LMA) and effectively single-mode operation with a practically allowable bending radius for compact Yb-doped fiber applications. Through numerical simulations, carried by the full-vectorial finite-element method, we present the limitations on the effective area of LCFs under bent condition and compare their limits with that of conventional step-index LMA fibers. Due to a better controllability of the low numerical aperture and a large value of the differential bending loss (~20 dB/m) between the fundamental and higher order modes in LCFs, the LMA of ~500 μm2 (core diameter of ~36 μm) at 1064 nm can be achieved when the optimized LCF is bent into a 10 cm bending radius.

Blue-Extended Sub-Nanosecond Supercontinuum Generation in Simply Designed Nonlinear Microstructured Optical Fibers

We report experimentally observed extreme blue-enhanced supercontinuum (SC) generation down to 372 nm wavelength in simply designed and easily fabricated nonlinear microstructured optical fibers (MOFs). Three different MOFs of various core sizes and dispersion profiles are fabricated in order to optimize the parameters for achieving deeper blue components by group-index matching. The physical mechanism involved in the generation of extreme blue component is explained along with other nonlinear processes participating in the spectral broadening. We also explore the extent of applicability of the group-index matching technique for obtaining blue-enhanced SC and finally optimize the location of the zero dispersion wavelength (ZDW) with respect to the pump wavelength to achieve the maximum blue shift.

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.

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.

Strong infrared radiation through passive dispersive wave generation and its control

We observe strong infrared (IR) radiation as a result of passive dispersive wave generation for a realistic microstructured fiber having two zero-dispersion wavelengths. The IR radiation frequency can be suitably controlled by varying the operational wavelength, which falls in the first normal dispersion regime. The amplitude of the radiation can be significantly increased by introducing a suitable amount of chirp in the input pulse. This strong phase-matching radiation can be considered as an alternative solution for the IR laser for different applications.

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.