MetroLaser proposes to design and develop an innovative narrowband tunable IR filter based on the properties of a one-dimensional photonic crystal structure with a resonant cavity. Such structure would exhibit an ultra-narrow, high-throughput band in the middle of a wide, low-transmission stop-band. During Phase I, through an extensive and detailed analysis, we performed a feasibility study to establish the operational characteristics and performance of the proposed tunable filter. Following this, we assembled and tested a breadboard and demonstrated filter tunability over 4 cm 1 with bandpass close to 0.25 cm-1, rejection level better than 23 dB, and acceptance angle of about 1 degree at 10.6 microns. The acquired data demonstrated our optimal approach 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 narrowband filter with a tunability range of 10 cm-1, a bandpass range of 0.1 cm-1, background rejection of 30 dB, and transmittance better than 50%. A rugged and monolithic filter design will allow this instrument to be incorporated in air- or space-based platforms providing stable performance in harsh operating environments.