APPLICATION OF A FIBER FOURIER-TRANSFORM SPECTROMETER TO THE DETECTION OF WAVELENGTH-ENCODED SIGNALS FROM BRAGG GRATING SENSORS

We describe an all-fiber Fourier transform spectrometer for decoding t he wavelength shifts from a series of Bragg grating sensors. The syste m described uses an optical fiber Michelson interferometer with one ar m wrapped on a piezoelectric driven stretcher capable of inducing a si milar to 10 cm fiber length change. Passive polarization compensation is utilized which eliminates the possibility of random polarization fa ding in the interferometer causing apodization of the interferogram. T his permits an all-fiber design without the need for specialty optical fiber or external polarization adjustments. A reference Nd:YAG laser is used to stabilize the interferometric scan in a phase-locked loop c onfiguration by way of slow and fast feedback correction elements. A s pectral resolution of <0.07 cm(-1) was obtained, which corresponds to a Bragg wavelength shift of similar to 0.015 nm in the 1.55 mu m regio n, The simultaneous wavelength determination capacity of the device al so permits it to be used in a variety of other applications for analys is of optical spectra.