High Resolution Millihertz Fibre-Optic Strain Sensor Based on Time Delay Interferometry

The frequency drift of lasers is one of the most significant source of phase noise in fiber-optic sensing systems. Time delay interferometry (TDI) in gravitational wave detection mission can effectively suppress the frequency noise of laser. We applied TDI to fiber-optic sensing systems and achieved 80 dB noise floor suppression at 10 mHz and the strain resolution reached 2.39
$p\varepsilon/\sqrt{Hz}{@}> 10mHz$
on a 100 km ultra-long SMF link. The signal to noise ratio was improved by 10 dB and 25 dB at 500 mHz and 2 Hz respectively. The proposed method has the potential to significantly improve the low-frequency response of fiber optic sensing systems such as DAS and OFDR.