Fourier-transform on-chip microspectrometers

We present some of the latest developments in silicon-based Fourier-transform microspectrometers for the near and mid-infrared. The devices comprise waveguide arrays of Mach-Zehnder interferometers with linearly increasing optical path differences, enabling scan-less spectral retrieval with large radiant throughput. Resolutions down to 40pm are experimentally demonstrated. Spatial heterodyne Fourier-transform (SHFT) spectrometry is an interferometric technique which circumvents the need of moving elements and provides an increased \u3b5\u301tendue. The SHFT scheme can be implemented with a waveguide array of Mach-Zehnder interferometers (MZI) with linearly increasing optical path differences. The high refractive index contrast of the SOI platform and the waveguide bend radius of ~ 5 \u3bcm readily allow achieving high resolutions in a reduced footprint. We report three alternative implementations of the SHFT principle in SOI waveguides. Firstly, a SHFT chip with Si-wire microphotonic spirals, reaching a resolution of 40 pm at a central wavelength near 1.5 \u3bcm. Secondly, a SHFT micro-spectrometer with subwavelength gratings for refractive index engineering of the optical delay lines. Finally, an extension of the SHFT scheme to the mid-infrared, addressing specific challenges of this spectral region such as efficient coupling and power splitting structures, and robust performance over a substantially broader free spectral range. SHFT spectrometers are promising for a wide range of applications, including chemical and biological sensing, astronomy, communications, hand-held spectroscopy, and sensing from satellites or planetary rowers. Furthermore, the resolution of these devices can be readily scaled up to very long optical delays, opening a new pathway toward possibly overcoming current resolution limits of state-of-the-art spectroscopic instruments.Peer reviewed: YesNRC publication: Ye