Hybrid configuration of Sagnac and modal interferometer with high extinction ratio

A hybrid configuration of Sagnac and modal interferometer is proposed to obtain high extinction ratio (ER). Firstly, a modal interferometer based on core-offset splicing of three sections of single mode fiber is obtained through manually controlling the fusion parameters. Then the modal interferometer is inscribed into a Sagnac loop, which can obtain a higher ER by carefully adjusting the polarization controller (PC). There is about 10 dB extinction ratio higher than the modal interferometer. The higher the extinction ratio is, the sharper the bottom of waveform will be, so the wavelength shifts can be measured more accurately when sensing temperature, pressure or other parameters. The measured sensitivity of temperature is 48.67 pm/°C in the band of 1550 nm. It also can be applied in strain measurement, vibration measurement and so on.