Piezo drive tunable optic filter
thesisposted on 23.05.2021, 16:32 by Wen Zu
Tunable fiber optic filter has extensive applications in telecommunications, spectroscopy, and fiber optic sensing. Many research attempts have been devoted to develop a filter with a wide tuning range, a fast tuning speed, a fine tuning resolution, and high reliability. Despite of the progress made so far, a tunable fiber optic filter that combines all these qualities is still a subject of intensive research. This thesis describes the design, fabrication and test results of a high performance tunable fiber optic filter. The filter is piezo-driven using a flexural hinge structure for displacement magnification and an axial strain of a fiber Bragg grating. Finite element analysis was used to design the mechanical structure to achieve the required displacement magnification and reaction force for grating compression. A passive thermal compensation design was implemented with two spacers of different coefficients of thermal expansion to compensate the thermal-induced wavelength drift. A feedback control system with a linear variable differential transformer was employed to control the displacement and to achieve the designed tuning accuracy. A tuning range of 13.7 nm, a maximum closed loop switching time of 17.3 ms, and a wavelength drift of 1.4 pm/C were achieved. The flexural-hinge structure, that offers noise-free motion, no need of lubricants and no wear, ensures its long-term reliability.