Ultra-small fiber taper Fabry-Perot modal interferometer

We present an ultra-small fiber taper based Fabry-Perot modal interferometer (FPMI). Our FPMI is made of a microcavity (~ 4.4 μm in length) directly fabricated into a fiber taper with its diameter less than 10 μm. Its working head is a miniaturized single-mode-multi-mode fiber configuration without splicing. The underlying mechanism of FPMI is the interference among reflected fundamental mode and excited high-order modes at the end-faces. This kind of interferometer takes up little space because of its unique geometry and ultra-small size. The new device is attractive for sensing applications such as in high-temperature harsh environments with the advantages of fast response and high sensitivity.