W-type co-axial chalcogenide optical fiber for coherent mid-IR supercontinuum generation

A W-type co-axial chalcogenide optical fiber structure is designed and numerically analysed for the broadband and highly coherent supercontinuum sources in the mid-IR region. The structural parameters of the designed W-type optical fiber are optimized to obtain small absolute group velocity dispersion in broad spectral range in the mid-IR region. The proposed W-type fiber structure possesses a flat dispersion profile with the flatness of the dispersion of ±2.45 ps/nm/km in the spectral range of 4.9 – 12.6 μm. The broadband and coherent mid-IR supercontinuum spectrum extending from 2.28 μm to 15.52 μm at -40 dB level is obtained using a 4 cm long chalcogenide W-type fiber pumped by 200 fs laser pulse of peak power of 10 kW at 7 μm. The average coherence property of the supercontinuum spectrum is almost unity in the full spectral range for the chalcogenide W-type fiber. Such broad and highly coherent mid-IR supercontinuum spectrum is very important because most of the biological tissue possesses their molecular fingerprints within this spectral range. Therefore, this region of electromagnetic spectrum is extremely useful to determine a tissue spectral map which provides very important information concerning the existence of the critical diseases such as cancer. The W-type chalcogenide fiber structure reported in this paper is a promising candidate for the development of the coherent broadband mid-IR supercontinuum sources which have potential applications in early cancer diagnostic, food quality control, gas sensing, and imaging.