LAUSR

A simple capillary-based extrinsic Fabry–Perot structure is presented and fabricated, using the manual welding method with the strain sensing characteristics investigated in detail. Strain sensitivities of 4.2, 2.8, and 2.4  pm/μe are obtained experimentally with the interferometer length around 50 μm and the inner diameter of 75, 50, and 25 μm, respectively. The underlying physics of the strain sensitivity of this device is negatively correlated with the interferometer length and positively correlated with the capillary inner diameter, which provides two simple parameters to tailor the strain sensitivity.