Optical Fiber Sensor Based On Inner Air Cavity

Optical Fabry-Perot interferometer sensors based on inner air-cavity is featured with compact size,good robustness and high strain sensitivity,especially when an ultra-thin air-cavity is adopted.The typical shape of Fabry-Perot inner air-cavity with reflection mode of operation is elliptic,with minor axis along with and major axis perpendicular to the fiber length.The first reflection surface is diverging whereas the second one is converging.To increase the visibility of the output interference pattern,the length of major axis should be large for a given cavity length.However,the largest value of the major axis is limited by the optical fiber diameter.If the major axis length reaches the fiber diameter,the robustness of the Fabry-Perot cavity device would be decreased,we mainly completed the following work:1.The background of Optical Fabry-Perot interferometer sensors and the classifications of Optical Fabry-Perot interferometer sensors were introduced.The advantages and disadvantages for each type of Optical Fabry-Perot interferometer sensors were briefly commented.2.we demonstrate an ultra-thin crescent shaped Fabry-Perot cavity for strain sensing with ultra-high sensitivity and low temperature cross-sensitivity.The crescent-shape cavity consists of two converging reflection surfaces,which provide the advantages of enhanced strain sensitivity when compared with elliptic or D-shaped FP cavity.The device is fabricated by fusion splicing an etched multimode fiber with a single mode fiber,and hence is simple in structure and economic in cost.3.We demonstrate a Fabry-Perot interferometer with inner air-cavity for ultra-sensitive strain measurement.The device is fabricated by fusion splicing of two sections of etched multimode fiber with offset.By selecting the appropriate value of the offset,the strain sensitivity can be greatly increased.In the case of introducing two dimension offset,the strain sensitivity can be increased by more than 4.5 pm/??.The device is simple in fabrication,robust in structure,economic in cost and convenient in operation and has high potential in many strain sensing applications.