Objective: Fabrication of silica-based hollow core photonic crystal fibers (HC-PCFs); Photonic Band Gap (PBG) fiber having diameter 125 – 150 µm; Simulation of gas-filled HC-PCFs for pressure dependent dispersion and nonlinearity tailoring to identify pump wavelength and estimate SC bandwidth; Design of gas cells for pressurized filling of gases (H, He, Ar or Xe) in HC-PCFs and pressure control inside the HC-PCFs for tuning of dispersion and nonlinearity; Demonstration of SC generation in the range of 2-5 µm by utilizing the gas-filled HC-PCF pumped by the developed Thulium/Holmium doped pulsed fiber laser; Comparative study of the characteristics of the SC and selection of the best possible combination of the filled gas and its pressure to obtain maximum possible SC bandwidth and output power; Study of the coherence properties of the visible-near-IR SC source to obtain ultrahigh (sub-micron) axial resolution in the order of 0.7-0.9 µm for efficient imaging in OCT Summary: The project aims to develop supercontinuum (SC) light sources in two separate spectral domains - mid-IR region from 2-5 µm using hollow core photonic crystal fiber (HC-PCF) and the visible-near-IR spectral region from 0.5 µm to 1.7 µm using microstructured optical fiber (MOF), for application in deep-penetration ultrahigh-resolution OCT in the two spectral regimes. The axial resolution of an OCT system is inversely proportional to the bandwidth of the source. Hence PCF-generated supercontinuum having octave-spanning bandwidth is advantageous as it largely exceeds the bandwidth of conventional sources. HC-PCFs and MOFs will be designed and fabricated by the stack and draw method to generate SC for possible application as OCT light source.
Visible-near-IR SC from 0.5-1.7 µm will be generated by pumping the developed nonlinear MOFs around 1 µm which is the zero dispersion wavelength (ZDW) of water, one of the main constituents of biological tissues. OCT with central wavelength around 1 µm is advantageous since it removes any imbalance in dispersion in the reference and sample arms caused due to the influence of dispersion of water on that of the sample and helps to obtain ultrahigh axial resolution. The SC spectra and its coherence property will be optimized to achieve sub-micron axial resolution in the order of 0.7-0.9 µm which will be a stark improvement compared to the existing commercial sources with axial resolution limit of 5 µm. | 
