In fiber lasers, operating in normal dispersion regime benefits high peak power operation thanks to no pulse breakup as in anomalous dispersion. However, the spectral range of Thulium (Tm) emission lies in anomalous dispersion regime for conventional optical fibers. Hence, a customized W-type step-index Normal Dispersion Thulium Fiber (NDTF) is designed to have strong waveguide dispersion at the Tm emission band. The dispersion of NDTF is -28.97 ps/nm.km at 1.9 μm wavelength. An all-fiber seed source based on a ring oscillator was built with the NDTF as the active fiber and produce mode-locked soliton pulses near 2 μm. Subsequently, the pulses are amplified through the NDTF in an all-fiber amplifier stage. The NDTF amplifier produced pulses of ~593 nJ pulse energy in a ~4.4 ps FWHM pulse width. The amplified pulse is then compressed to ~1.91 ps giving a peak power of ~310 kW in an all-fiber compressor consisting of SMF28 fiber. This represents a potential to generate high peak powers in ultrashort pulses at 2 μm wavelength in all-fiber configuration.
We demonstrate a 70 mol % GeO2 doped fiber for mid-infrared supercontinuum generation. Experiments ensure a highest output power for a broadest spectrum from 1000nm to 3000nm from this fiber, while being pumped by a broadband 4 stage Erbium fiber based MOPA. Our investigations reveal the unexploited potential of Germania doped fiber for mid-infrared supercontinuum generation. To the best of our knowledge, this is the record power, for an ultrabroadband, all-fiberized, and compact device size supercontinuum light source based on Silica and Germania fiber, ever demonstrated to the date.
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.
Near field optics concepts have introduced a paradigm shift in a wide variety of engineering fields in the recent past and the most significant applications of this fundamental physics concepts have been in the applied engineering problems such as improved broad band light absorption thereby enhancing the conversion efficiency of thin silicon solar cells. Also, for writing patterned structures or features using non contact optical methodologies have enabled near field optics assisted fabrication and related applications. The technology involving optics concepts and methodologies targeting energy sector have seen the impact of the same with a challenging trend to achieve smaller features or devices with micro- or nano-scale features. This demands automatically the need for achieving much smaller features beyond the forecasted sub- 30nm feature patterning methodologies. To meet such demands, a new branch of near- field optical concepts for improving patterning resolution has started developing which have been receiving considerable attention for its ability to produce high density sub-wavelength features that can find tremendous energy harvesting applications. This paper in this context mainly focuses on the review of different near field optical concepts and approaches developed for patterning by the author’s group at NTU. Different concepts were explored incorporating surface Plasmon waves ( LSPs, SPPs, LRSPs), gap modes as well as their interference in order to high resolution features and pattern dimensions at nano-scales. The absorbance of near band gap light is small and hence structuring of thin film solar cell is very important for increasing the absorbance by light trapping. The manuscript conclude by correlating the above said aspects and the challenges in achieving improved light conversion in thin film solar cells.
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.