High spatial resolution fiber-optic Fizeau interferometric strain sensor based on an in-fiber spherical microcavity

We present a fiber-optic Fizeau interferometric strain sensor consisting of an in-fiber spherical microcavity of $39\mu \mathrm{m}$ in diameter. The spherical microcavity was formed by splicing a normal single-mode fiber with a hollow-core photonic crystal fiber. We demonstrate that strain sensing can be realized by using the interference between the light signals reflected by the front and rear surfaces of the sphere. Experiments have shown that the strain sensor has a strain sensitivity of $3.36\mathrm{pm}∕\mu \epsilon$ and a temperature sensitivity of $1.35\mathrm{pm}∕°\mathrm{C}$ .