Fiber-optic spectrum analyzer

A fiber-optic spectrum analyzer of the Michelson echelon type was investigated. Sections of a fiber-optic waveguide served as analogs of the plates of a classical Michelson echelon. The lengths of the waveguide sections were successively increased by a given amount. By virtue of the exceptionally low losses in fiber-optic waveguides, the resolving power of a fiber-optic spectrum analyzer can exceed greatly that of classical Michelson echelons. A prototype fiber-optic spectrum analyzer was built to demonstrate the resolution of longitudinal modes of a helium–neon laser with a 0.8-pm intermode separation.