(CIU Journal, 2020-12-01) M R Karim1, Nayem Al Kayed2, Md. Rabiul Hossain3, Golap Kanti Dey4
Varying dispersion and nonlinearity by tapering the thickness of a planar waveguide along the pulse propagation direction instead of keeping it uniform, create an opportunity to extend the supercontinuum spectral coverage further into the mid-infrared region. In this work, we numerically proposed a 5-mm-long group-velocity dispersion tailored silicon-rich nitride tapered waveguide for wideband supercontinuum coverage in the mid-infrared. Applying 50 fs FWHM sech pulses at the center of 1.55 µm wavelength with a relatively low input power of 50 W, it was possible to achieve supercontinuum coverage from 0.8 µm to 9 µm by our proposed design. Besides, the results obtained using our proposed waveguide show that tapering the geometry enhances the supercontinuum coverage approximately 90% compared to a uniform waveguide of the same length. To the best of our knowledge, this would be the widest spectrum demonstrated ever using the tapered waveguide structure proposed so far. It may enable some spectacular mid-infrared region applications such as spectroscopic measurement, biomedical imaging, optical coherence tomography as well as sensing applications, etc.
