Mid-Infrared Integrated Wideband Dual-Polarization Fourier-Transform Spectrometer

Due to their unique vibrational/rotational frequencies in the mid infrared (MIR) fingerprint region, which scans from 500 to 1500 cm(-1), molecules can be assuredly identified and quantified. Thus, integrated on-chip mid infrared spectroscopic systems, with low power consumption and high performance, would show great value for numerous applications, such as medical diagnosis, astronomy, chemical and biological sensing or security. Different solutions can be envisioned, such as Fourier-Transform spectrometers, echelle gratings, or arrayed waveguide gratings (AWG). The integrated spatial heterodyne Fourier-Transform spectrometer (SHFTS) shows relaxed fabrication tolerances while applying a phase and amplitude correction algorithm. Meanwhile, it provides high optical throughput and high spectral resolution compared with AWG or echelle gratings. However, up to now in the literature, most of the reported integrated Fourier-Transform based spectrometer is based on silicon-on-insulator operating in the near infrared typically at 1.55 mu m wavelength. Thereby the development of integrated Fourier-Transform spectrometers operating in the MIR covering the wide fingerprint region is highly desirable. In this work, we experimentally demonstrate the first duel polarization SHFTS operating in the mid infrared beyond 5 mu m wavelength. The fabricated FTS, which is based on the graded-index Ge-rich SiGe platform, contains 19 Mach-Zehnder interferometers with a linearly increasing path difference. A spectral resolution better than 15 cm(-1) has been demonstrated within an unprecedented spectral range of 800 cm(-1) (from 5 to 8.5 mu m wavelength).