An Ultra-Narrow Tunable Optical Bandpass Filter

MetroLaser proposes to design and develop an innovative ultra-narrow tunable optical bandpass filter (UNTOBF) based on the properties of a dielectric photonic crystal structure with a resonant cavity. Such a structure can exhibit an ultra-narrow high-transmission band in the middle of a wide low-transmission stop-band. During Phase I, we will demonstrate experimentally the proof-of-concept for an UNTOBF with sub-angstrom bandpass and a tuning range of at least 2 nm in both visible and infrared (IR) regions. We will also develop a complete model of the functional characteristics, based on specific features of photonic crystal structures with a resonant cavity, and develop a strategy for building a prototype of the instrument. Fine-tuning of the filter will be accomplished by varying the optical cavity length. The proposed filter is expected to have an acceptance angle of at least 1? and an aperture of about 2 inches. During Phase II the compact UNBTOF prototype module will be demonstrated with an expected tunability range of 10 nm and a bandpass range of 0.01 nm. A compact, low-weight, single-assembly design of the filter will allow it to be retrofitted to existing instruments and provide a stable performance in harsh operating environments.