Wavelength demodulation Method using a tilted FBG and a PSD for a Fiber optic micro-displacement sensor

Micro-displacement is measured by the fiber Bragg grating (FBG) sensor based on a cantilever structure. The micro-displacement is generated by the piezoelectric transformer (PZT), which is placed under the free end of the cantilever. The FBG is attached at the center of the lower surface of the cantilever. When the PZT is expanded with the applied voltage, deflection at the free end of the cantilever will occur, resulting in the strain variation on the lower surface of the cantilever. This strain will act on the FBG sensor, whose reflected wavelength will shift. A tilted fiber Bragg grating (TFBG) is used to change the FBG's shifted wavelength to varied radiation angle from the TFBG, and a position sensitive device (PSD) is used to record the light spot position variation, which is corresponding to the varied radiation angle. Sensor structure and measurement principle are introduced. The feasibility is explained theoretically and results show that displacement measurement resolution of 62nm can be obtained.