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 the wavelength shifts from a series of Bragg grating sensors. The system described uses an optical fiber Michelson interferometer with one arm wrapped on a piezoelectric driven stretcher capable of inducing a similar to 10 cm fiber length change. Passive polarization compensation is utilized which eliminates the possibility of random polarization fading in the interferometer causing apodization of the interferogram. This 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 configuration by way of slow and fast feedback correction elements. A spectral 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 region, The simultaneous wavelength determination capacity of the device also permits it to be used in a variety of other applications for analysis of optical spectra.