This SBIR Phase I project will research and develop multimode step-profile fiber resonators for internal reflectance spectrometric applications, both for absorption and luminescence. Attenuated total reflection spectroscopy is used to measure the constitutive optical constants of a dielectric, or metal, analyte cladding layer replacing lengths of the primary optical cladding. In conventional applications, optical fiber excitation is single-pass, coupled in one end and propagated out the other fiber endface. Alternatively, with the proposed development, forms of fiber-optic resonators would store optical power increasing the spectral sensitivity for small absorption indices by enhancing the analyte cladding interaction. One particular resonator type is a continuous fiber ring, i.e., no endfaces. The practicable purpose of the proposed SBIR Phase I is to develop the fabrication techniques for the fiber optical coupler component appropriate for such a resonator. A unique fiber coupler is described. This type optical coupler will, by design, couple modal power into the resonator selectively, predominately either TE/TM or EH/HE with low or high orders depending on the optimal modal distribution associated with the fiber sensor application.
