Ge-rich SiGe based wideband polarization insensitive photonic platform for mid-infrared free-space communications

摘要

The recent advances in the development of quantum cascade laser with room temperature operation in the mid infraredpaved the way for the realization of wideband communication systems. Particularly, two mid-infrared atmospheretransparency windows lying between 3-5 μm and between 8-14 μm exhibit great potential for further implementation ofwideband free space communications. Additionally this wide unregulated spectral region shows reduced backgroundnoise and low Mie and Rayleigh scattering. Despite the development of a plethora of photonic components in midinfrared such as sources, detectors, passive structures, less efforts have been dedicated to investigate polarizationmanagement for information transport. In this work, the potential of Ge-rich SiGe waveguides is exploited to build apolarization insensitive platform in the mid-infrared. The gradual index evolution in SiGe alloys and geometricparameter optimization are used to obtain waveguides with birefringence below 2×10-4 and an unprecedented bandwidthin both atmosphere transparency windows i.e. near 3.5 μm and 9 μm. Following waveguide birefringence optimizationan ultra-wideband and polarization insensitive multimode interference coupler was designed. The optimized structureshows a 4.5 μm wide bandwidth in transverse electric and transverse magnetic polarization at 9 μm wavelength. Thedeveloped ultra-wideband polarization insensitive photonic building blocks presented in this work pave the way forfurther implementation of free space communication systems in the mid infrared spectral region.