Planar-Waveguide Fourier-Transform Spectrometers for Space Exploration

Optical spectroscopy is a powerful, fundamental analytical technique that is deployed across many domains of scientific research. Due to the widespread use of this technique, the development of novel methods and instruments for collecting and analyzing spectral data provides new foundations and bridges by which the frontier of human inquiry may be explored. Miniature spectrometers, in particular, lead to advancements in space exploration by enabling advanced analytical techniques to be deployed on small rovers and satellites. One promising platform for realizing miniature spectrometers with high resolving power are integrated optical circuits consisting of many hundreds of discrete optical components implemented via planar-waveguides printed lithographically on wafers.

This dissertation presents the design, fabrication, and characterization of two miniature spectrometers based on planar-waveguide technology. The miniature spectrometers are based on a spatial-heterodyne Fourier-transform spectrometer architecture that results in very high spectral resolution over a limited spectral range.

The first device presents an advanced method for mitigating temperature sensitivity of the device|an enabling step towards deployment of the sensor in harsh environments. The device is also used to demonstrate, for the first time, the retrieval of a complex spectrum consisting of multiple gas absorption features using on-chip Fourier-transform spectroscopy. The second device advances the state of the art by deploying novel spectral retrieval techniques from the field of compressive sensing in order to substantially increase the spectral range of the instrument while maintaining high spectral resolution. This dissertation motivates planar-waveguide Fourier-transform spectrometers as the ideal vehicle for the adoption of this technique, which ultimately results in a significant increase in capability for the spectrometer. Ultimately, a four-fold increase in spectral range over conventional systems is achieved for the compressive-sensing instrument, and spectral retrieval of complex spectra is achieved despite significant under-sampling with respect to a conventional instrument architecture. The invention and successful demonstration of this novel instrument architecture, and the development of techniques for fabricating such devices, creates an avenue through which high-performing on-chip spectrometers may be deployed to advance scientific inquiry across a multitude of fields including space applications.