Slow-Light-Enhanced Spectral Interferometers

We proposoe a research program aimed at developing spectral interferometers with dramatically enhanced performance. A key aspect of our approach is to place a highly dispersive (slow-light) material into one arm of a two-path, Mach Zehnder interferometer (MZI). Theoretical analysis shows that the spectral resolution under these circumstances can be enhanced by a factor as large as the group index of the slow-light material being used. Slow-light interferometers can produce dramatic increases in the resolution or a spectrometer or they can permit much smaller physical dimensions than standard spectrometers without any degradation of resolution. In the present program, we will undertake to develop spectrometers that can be employed under practical conditions and especially those of interest to NASA. We propose three related approaches to the design of enhanced spectrometers and will perform conceptual to quantify the relative merits of these approaches. This will allow future work to further develop the most promising design(s). The three approaches: 1.) A hybrid interferometer: a Fabry-Perot (FP) interferometer will be placed within a MZ interferometer. The transfer characteristics of the FP mimic those of a slow-light material. This design can achieve the same sort of enhancement of sensitivity as that of a true slow-light medium placed inside the MZI. 2.) Our second approach makes use of a similar analogy, but on a much smaller distance scale. This approach entails the fabrication of wavelength-scale defect resonators in an otherwise perfect photonic crystal (PhC). The design employs a sequence of such resonators each with a slightly different resonance wavelength. 3.) Our third approach is to fabricate mm-scale interferometers using nano fabrication on silicon. The slow light medium is a PhC waveguide formed by a line defect in a silicon PhC structure. We will couple these structures to waveguides in an interferometer configuration.

The compact and robust enhanced spectral interferometers developed in this program will enable expansion of NASA's astrophysical and Earth science observation capability. The dramatic reduction is size without a reduction in sensitivity can allow spectral sensing technology to expanded platforms such as autonomous vehicles that can more rapidly collect data on species such as green house gases.

The compact sensors enabled by this program could enhance military detection of toxic or explosive chemicals on autonomous aerial platforms or on ground based measurements. These sensors could greatly expand the spectral sensor use in production facilities for quality control and product purity verification.

This is early/mid-stage (TRL 5) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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