The Investigation Of Fiber-Optic Fabry-Perot Strain Sensor

Strain measurement is becoming more and more important in industry and civil structure monitoring. In this paper, the working principle of Fabry-Perot fiber optical sensors is investigated in detail. The significance of self-calibrated interferometric-intensity-based optical fiber F-P sensors for strain measurements is analyzed.In fiber optical strain sensor system, the extrinsic fiber Fabry-Perot interferometric (EFPI) cavity fabricated in our laboratory is used as the sensing unit and a self-calibrated interferometric-intensity-based (SCIIB) demodulation method is employed to demodulate the strain signal. The central wavelength of the light-emitting diode (LED) light source is 1310nm. A coarse Wavelength Division Multiplexer (CWDM) separates to split the reflected lights, coming from the F-P cavity, into two branches, which contain a narrowband spectrum and a broadband spectrum. The ratio of the two branch signals can eliminate the influence of the fluctuation of both the light source output power and fiber loss. The sensor system is able to measure both static and dynamic strain. Experimental results show that in static strain measurements the full scale of 200 ^με and the minimum resolution of 0.5 ^με can be reached. In dynamic strain measurements the accurate frequency of the cantilever can be obtained. The experimental results also show that the SCIIB sensing system is suitable for strain measurements and especially for dynamic strain measurements. It is more steady because it combines the advantages of the interferometry and intensity modulation mechanism.