DESIGN AND MODELLING OF Ge11.5As24Se64.5 BASED MICROSTRUCTURED OPTICAL FIBER FOR SUPERCONTINUUM GENERATION

Abstract

Supercontinuum Generation (SCG) is a very exhilarating research field having multifarious applications in a variety of areas such as spectroscopy, medical imaging, telecommunication, high precision metrology and optical coherence tomography. The phenomenon of supercontinuum generation basically refers to the broadening of the spectrum of high intensity laser pulses as they traverse through a highly nonlinear medium. It was first reported in solid and gaseous nonlinear media by Alfano and Shapiro in the year 1970. The broadening of the spectra primarily takes place due to the interaction of linear effects such as dispersion as well as nonlinear phenomena involving self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM), stimulated Raman scattering (SRS), and soliton dynamics at pump wavelength. SCG in the mid-infrared realm of wavelengths can play a pivotal role because mid-infrared spectroscopy has the capability to provide a thorough knowledge of the composition of molecular structures of the matter and executing non-intrusive diagnostics of diverse chemical, physical and biological systems. In comparison to silica fibers, nonlinear materials like tellurite, bismuth, fluoride, and chalcogenides demonstrate significant optical nonlinearities and transparency in the near to mid-infrared realm of wavelengths which makes them quite apt for MIR supercontinuum generation. However, owing to optical transparency up to 25 µm in the infrared realm, chalcogenide glasses stand out as exceptional contenders for midinfrared supercontinuum generation. Chalcogenide glasses consist of elements in group VI of the periodic table such as S, Se, and Te (called chalcogens) combined with network forming elements including Si, As, Ge, P, and Sb. This project report aims at elucidating the various dispersion and nonlinear phenomena that lead to the generation of supercontinuum spectra. Further, as the prime objective of the project, a Ge11.5As24Se64.5 based microstructured optical fiber is designed and modelled for supercontinuum generation using ‘MATLAB’ and the finite element mode-solver ‘COMSOL Multiphysics’. The simulations performed suggest that the proposed Ch-MOF possesses a high non linearity of 1001 W-1/km and produces a broadband SC spectrum spanning from 1.4 μm to 16 μm at a pump wavelength of 3.1 μm with optical pulses having 4 kW peak power and 50 fs pulse width using only 20 mm of the fiber.