64-CHANNEL FIBER OPTIC SPECTROMETER FOR A DUAL-WAVELENGTH INTERFEROMETRIC PRESSURE SENSOR ARRAY

As part of a fiber optic, interferometric pressure sensing array system for hypersonic wind tunnel studies, a 64 channel spectrometer has been developed to separate the return signals by both position and wavelength. The spectrometer is designed to optically separate the quadrature signals from the interferometer. A ribbon of single-mode fibers carrying the dual wavelengths (811.7 and 813.3 nm) from the sensing surface array forms the entrance slit to the spectrometer. This spectrometer uses a unique optical layout consisting of a 32 element microlens array, narrow passband interference filter and concave mirror to separate and focus the optical signals onto the photosensitive surface of a 1×64 photodiode array. The microlens array collimates the emerging beams from the single-mode fibers to minimize cross talk between channels. The detector array and its control electronics are an integral part of the spectrometer and are mounted on the same baseplate as the other optical components. Fast scanning and digitizing electronics produce an effective data rate of 160 kHz for 64 channels. Details of the construction and results of the calibration are presented. © 1995 American Institute of Physics.