Forward fiber Fourier transform spectrometer modeling and design with PZT phase modulation real-time compensation.

Piezoelectric ceramic transducers (PZTs) are often applied in all-fiber Fourier transform spectrometers (FFTSs) to realize phase modulation. Combining a PZT and optical fiber features, a theoretical FFTS modeling is established. We systematically deduced the main causes of spectral errors and the factors of the instrumental resolution, then designed a new FFTS system and provided real-time compensation methods for spectral errors. We creatively employed two Mach-Zehnder interferometers by winding the sensing arms of the two on the same PZT cylinder to realize the dual optical path experiencing the same and simultaneous phase modulation. A processing circuit is designed to achieve selective sampling of the test interferogram, avoiding the spectral artifacts generated by the PZT phase discontinuities. The narrow line width of the reference spectrum is obtained at the same time for real-time calibration of spectral shift resulting from dispersion and other phase errors. By the comparison of the original interferogram and spectrum with those after compensation, the experiments validated that the system design could effectively compensate for the spectral errors caused by PZT and optical fiber physical limitations. Finally, the improved ideas are discussed if the FFTS prototype is to be applied to test a real-time gas spectrum.