R. Sidharthan

Surface plasmon enhancement in gold nanoparticles in the presence of an optical gain medium: an analysis

The localized surface plasmon (LSP) enhancement in a gold nanoparticle is demonstrated in this paper. The enhancement of LSP is influenced by both size and the dielectric gain medium surrounding the nanoparticles. The nanoparticle is found to induce plasmonic enhancement of varying degrees depending on its size, and it is inferred that a gold nanoparticle of size 60 nm exhibits the maximum LSP for 532 nm excitation. Singularity due to cancellation of SP loss by an infinite gain medium and LSP enhancement are studied using a pump-probe Rayleigh scattering experiment. Gold nanoparticles of average size 60 nm exhibit the lowest threshold power to observe Rayleigh scattering. Furthermore, compared with the bare nanoparticles, a 12.5 fold enhancement of LSP is observed when the nanoparticle of average size 60 nm is kept in the gain medium.

Gap modes assisted enhanced broadband light absorption in plasmonic thin film solar cell

In this paper, gap modes assisted enhanced broadband light localization and possible absorption in a thin film silicon solar cell is presented. The existence of gap modes in metal particle-surface based thin film silicon solar cell is numerically investigated for improved light absorption. About 10.2% increment in light absorption compared to bare thin film silicon solar cell is obtained and enhanced light absorption at longer wavelength range is observed. The enhancement is due to the modification of localized surface plasmon modes around the nanoparticles via exciting the gap modes in the space between the nanoparticle and the surface.

Record power, ultra-broadband supercontinuum source based on highly GeO 2 doped silica fiber

We demonstrate highly germania doped fibers for mid-infrared supercontinuum generation. Experiments ensure a highest output power of 1.44 W for a broadest spectrum from 700 nm to 3200 nm and 6.4 W for 800 nm to 2700 nm from these fibers, while being pumped by a broadband Erbium-Ytterbium doped fiber based master oscillator power amplifier. The effect of repetition frequency of pump source and length of germania-doped fiber has also been investigated. Further, germania doped fiber has been pumped by conventional supercontinuum source based on silica photonic crystal fiber supercontinuum source. At low power, a considerable broadening of 200-300 nm was observed. Further broadening of spectrum was limited due to limited power of pump source. Our investigations reveal the unexploited potential of germania doped fiber for mid-infrared supercontinuum generation. These measurements ensure the potential of germania based photonic crystal fiber or a step-index fiber supercontinuum source for high power ultra-broad band emission being by pumped a 1060 nm or a 1550 nm laser source. To the best of our knowledge, this is the record power, ultra-broadband, and all-fiberized supercontinuum light source based on silica and germania fiber ever demonstrated to the date.

Optical orbital angular momentum amplifier based on an air-core erbium doped fiber

We present for the first time wideband operation of an optical orbital angular momentum amplifier with topological charge |l|=1. An air-core erbium-doped fiber is fabricated and up to 15.7dB gain is obtained with a cladding-pumped configuration.

Stress-Loss Correlation and Dispersion Control in Highly GeO 2 -Doped Fibers

We report a fabrication route to achieve highly GeO2-doped silica fibers with GeO2 molar concentration as high as 74% using the conventional modified chemical vapor deposition (MCVD) process. The dependence of background loss on fiber frozen-in stress in these highly doped fibers is investigated. A central dip of refractive index in the core is found to introduce stress variation, and contribute to the background loss. Dispersion control and supercontinuum generation in 2.1-2.8-μm region using the 74-mol% fiber are also presented.

High power, ultra-broadband supercontinuum source based on highly GeO2 doped silica fiber

We demonstrate a 74 mol % GeO2 doped fiber for mid-infrared supercontinuum generation. Experiments ensure a highest output power for a broadest spectrum from 700nm to 3200nm from this fiber, while being pumped by a broadband 4 stage Erbium fiber based MOPA. The effect of repetition rate of pump source and length of Germania-doped fiber has also been investigated. Further, Germania doped fiber has been pumped by conventional Silica based photonic crystal fiber supercontinuum source. At low power, a considerable broadening of 200-300nm was observed. Further broadening of spectrum was limited due to limited power of pump source. Our investigations reveal the unexploited potential of Germania doped fiber for mid-infrared supercontinuum generation. This measurement ensures a possibility of Germania based photonic crystal fiber or a step-index fiber supercontinuum source for high power ultra-broad band emission being pumped a 1060nm or a 1550nm laser source. To the best of our knowledge, this is the record power, ultra-broadband, and all-fiberized SC light source based on Silica and Germania fiber ever demonstrated to the date.

Multimode-pumped Raman amplification of a higher order mode in a large mode area fiber

We report the first demonstration of Raman amplification in a fiber of a single Bessel-like higher order mode using a multimode pump source. We amplify the LP08-mode with a 559-µm2 effective mode area at a signal wavelength of 1115 nm in a pure-silica-core step-index fiber. A maximum of 18 dB average power gain is achieved in a 9-m long gain fiber, with output pulse energy of 115 µJ. The Raman pump source comprises a pulsed 1060 nm ytterbium-doped fiber amplifier with V-value ~30, which is matched to the Raman gain fiber. The pump depletion as averaged over the signal pulses reaches 36.7%. The conversion of power from the multimode pump into the signal mode demonstrates the potential for efficient brightness enhancement with low amplification-induced signal mode purity degradation.

Ultra-wideband Operation of a Tunable Thulium Fibre Laser offering Tunability from 1679–1992 nm

We demonstrate a tuneable thulium-doped fibre laser incorporating in-house fabricated Tm/Ge co-doped fibre capable of accessing the sub 1700nm wavelength band. An ultra-wide operating bandwidth of over 310nm is realized using an external cavity grating.

Asymmetric large mode area fibres

Asymmetric core is an alternative approach for mode scalability and better heat dissipation, thus being expected for suppressed mode instability. This talk will present stretched core fibres in aspects of its mode area scalability and mode instability.

Nanoring patterning using surface plasmon assisted photolithography

Achievable resolution of nano-rings, fabricated using commonly employed conventional mask based photolithography, is limited by diffraction of light. In this work conventional photolithography is modified to incorporate the phenomenon of surface plasmons to overcome the diffraction limit and thus to fabricate nano rings. Here, an embedded-amplitude mask based surface plasmon lithography is numerically investigated to conceptalize a noval methodology to fabricate the proposed nano-ring structure. Results of FDTD simulation shows sharp transmission peaks at the hole edges which could be recorded using suitable thinned photoresist to obtain nano ring structures.