arXiv subjects

Shreesha Rao D. S.

Publications and source records attributed to Shreesha Rao D. S..

8 recordsLinked to original sources

arXiv2026

Measured group birefringence and group velocity dispersion of elliptical-core ZBLAN fibres for mid-infrared supercontinuum generation

Polarisation-maintaining ZBLAN optical fibres with small elliptical cores are attractive for nonlinear frequency conversion, for example in supercontinuum generation (SCG), and for dispersion management in ultrafast fibre laser systems operating in the mid-infrared (MIR) spectral region. Accurate characterisation of group birefringence and group velocity dispersion (GVD) is essential for modelling ultrafast pulse propagation in such fibres, yet experimental data remain scarce. Here, we present broadband measurements of group birefringence and GVD in four elliptical-core ZBLAN fibres, selected for their potential for low-noise MIR SCG, over the wavelength range 1.4 to 4.3 μm. Using polarisation-resolved white-light spectral interferometry, we quantify the dispersion characteristics of both fundamental modes in each fibre. Measurement uncertainties are evaluated using a combined uncertainty analysis that includes the spread between repeated measurements and the uncertainty in the measured fibre length. This work aims to support the development of MIR supercontinuum sources and to facilitate the understanding of nonlinear optical phenomena in ZBLAN fibres.

physics.optics↗

arXiv2026

Ultra-low-noise supercontinuum in normal-dispersion ZBLAN fibres pumped at 1.85 $μ$m

We demonstrate, for the first time to our knowledge, ultra-low-noise supercontinuum (SC) generation in normal-dispersion fluoride fibres pumped by femtosecond (fs) pulses. We have investigated two elliptical-core polarisation-maintaining (PM) ZBLAN fibres with core dimensions 6.7$\times$2.7 $μ$m and 8.9$\times$4.1 $μ$m, experimentally measured to have normal dispersion up to 3.77 $μ$m and 3.25 $μ$m, respectively; the smaller-core fibre yields ultra-low-noise SC spanning 1.537-2.196 $μ$m with a minimum relative-intensity noise (RIN) of 0.22% at 1.7 $μ$m, and the larger-core fibre yields 1.507-2.250 $μ$m with 0.36% at 2.0 $μ$m. To aid the generation of low-noise SC, we developed an all-PM thulium chirped-pulse amplifier delivering 58 fs pulses at 1.85 $μ$m, 210 mW average power at 40 MHz, with 0.41% RIN, seeded by a part of an ultra-low-noise SC using a 1.55 $μ$m fs laser and an all-normal-dispersion (ANDi) silica fibre for precise seed control. These results establish a robust, alignment-free pathway to extend ultra-low-noise ANDi-fibre SC towards the mid-infrared using PM fluoride fibres.

physics.optics↗

arXiv2022

AMC 12 atomic mass compilation data extrapolated for atomic masses of nuclei far from the valley of stability

The experimental mass data from the Atomic Mass Compilation - 2012 (AMC12) has been analyzed for two-neutron separation energies (S$_{2n}$), two-proton separation energies (S$_{2p}$), double-beta decay energies (Q$_{2β^-}$), and four-beta decay energies (Q$_{4β^-}$) and plotted against neutron number and mass number, respectively. A new weighted slope method of extrapolation, tested for known and new mass measurements, has been used to obtain the extrapolated mass values with better precision for more than 1100 nuclei far from the valley of stability, out of which more than 100 are being reported for the first time. A comparison has been made with five of the popular mass models with reference to experimental extrapolated masses from the present work and the Atomic Mass Evaluation 2016 (AME16). The extrapolated experimental atomic mass data will be very useful for both experimentalists and mass-model theoreticians, as well as in simulations of astrophysical r-processes.

physics.atom-ph↗

arXiv2022

Noise in supercontinuum generated using PM and non-PM tellurite glass all-normal dispersion fibers

Intensity fluctuations in supercontinuum generation are studied in polarization-maintaining (PM) and non-PM all-normal dispersion tellurite photonic crystal fibers. Dispersive Fourier transformation is used to resolve the shot-to-shot spectra generated using 225 fs pump pulses at 1.55 μm, with experimental results well reproduced by vector and scalar numerical simulations. By comparing the relative intensity noise for the PM and non-PM cases, supported by simulations, we demonstrate the advantage of the polarization-maintaining property of the PM fibers in preserving low-noise dynamics. We associate the low-noise in the PM case with the suppression of polarization modulation instability.

physics.optics↗

arXiv2020

Shot-noise limited, supercontinuum based optical coherence tomography

We present the first demonstration of shot-noise limited supercontinuum-based spectral domain optical coherence tomography (SD-OCT) with axial resolution of 5.9 $μ$m at a center wavelength of 1370 nm. Current supercontinuum-based SD-OCT systems cannot be operated in the shot-noise limited detection regime because of severe pulse-to-pulse relative intensity noise of the supercontinuum source. To overcome this disadvantage we have developed a low-noise supercontinuum source based on an all-normal dispersion (ANDi) fiber, pumped by a femtosecond laser. The noise performance of our 90 MHz ANDi supercontinuum source is compared to that of two commercial sources operating at 80 and 320 MHz repetition rate. We show that the low noise of the ANDi supercontinuum source improves the OCT images significantly in terms of both higher contrast, better sensitivity, and improved penetration. From SD-OCT imaging of skin, retina, and multi-layer stacks we conclude that supercontinuum-based SD-OCT can enter the domain of shot-noise limited detection.

physics.optics↗

arXiv2019

Ultra-low-noise supercontinuum generation with a flat near-zero normal dispersion fiber

A pure silica photonic crystal fiber with a group velocity dispersion ($β_2$) of 4 ps$^2$/km at 1.55 $μ$m and less than 7 ps$^2$/km from 1.32 $μ$m to the zero dispersion wavelength (ZDW) 1.80 $μ$m was designed and fabricated. The dispersion of the fiber was measured experimentally and found to agree with the fiber design, which also provides low loss below 1.83 $μ$m due to eight outer rings with increased hole diameter. The fiber was pumped with a 1.55 $μ$m, 125 fs laser and, at the maximum in-coupled peak power (P$_0$) of 9 kW, a 1.34$-$1.82 $μ$m low-noise spectrum with a relative intensity noise below 2.2\% was measured. The numerical modeling agreed very well with the experiments and showed that P$_0$ could be increased to 26 kW before noise from solitons above the ZDW started to influence the spectrum by pushing high-noise dispersive waves through the spectrum.

physics.optics↗

arXiv2019

Directional supercontinuum generation: the role of the soliton

In this paper we numerically study supercontinuum generation by pumping a silicon nitride waveguide, with two zero-dispersion wavelengths, with femtosecond pulses. The waveguide dispersion is designed so that the pump pulse is in the normal-dispersion regime. We show that because of self-phase modulation, the initial pulse broadens into the anomalous-dispersion regime, which is sandwiched between the two normal-dispersion regimes, and here a soliton is formed. The interaction of the soliton and the broadened pulse in the normal-dispersion regime causes additional spectral broadening through formation of dispersive waves by non-degenerate four-wave mixing and cross-phase modulation. This broadening occurs mainly towards the second normal-dispersion regime. We show that pumping in either normal-dispersion regime allows broadening towards the other normal-dispersion regime. This ability to steer the continuum extension towards the direction of the other normal-dispersion regime beyond the sandwiched anomalous-dispersion regime underlies the directional supercontinuum notation. We numerically confirm the approach in a standard silica microstructured fiber geometry with two zero-dispersion wavelengths.

physics.optics↗

arXiv2018

A Heuristic Algorithm for Network Optimization of OTN over DWDM Network

While the network traffic has seen exponential increase, the revenues have not maintained the same pace. New methods have to be explored to reduce this gap between traffic and revenue. One such method is convergence in networking layers. In this work, we study the convergence of OTN and DWDM layer from a network planning perspective. We compare the costs of planning networks without and with convergence and show that the multilayer planning offers least cost for higher traffic volumes.

cs.NI↗