An Ultra-Narrow Tunable Optical Bandpass Filter

Ultra-narrow bandpass tunable filters in the visible and infrared spectral regions are needed for the remote sensing industry and NASA in particular. Such filters are applicable in high-resolution spectroscopy, tunable lasers, and multi-spectral and hyperspectral imaging. During Phase I, we performed a feasibility study of an innovative ultra-narrow bandpass filter based on unique features of a photonic crystal interferometer (PCI), and did a meticulous and extensive analysis and modeling of its characteristics. We then assembled and tested a PCI breadboard and demonstrated its tunability over a 1 nm spectral range with a bandpass close to 0.02 nm and an acceptance angle close to 1o. The acquired data demonstrated conclusively that an approach based on the PCI concept provides an optimal solution for designing and constructing an ultra-narrow tunable optical bandpass filter. During Phase II we will design, build, deliver to NASA, and perform field testing of a compact and robust prototype module of a 1? diameter PCI filter with a tunability range of 1 nm and a bandpass range of 0.01 nm at 50% transmittance range. The Phase II design should allow for retrofitting the PCI to existing instruments and provide a stable performance in harsh operating environments.