Vibration-Temperature Separation Using Few-Mode Forward Transmission Distributed Fiber-Optic Sensor

Long-distance distributed fiber-optic sensing can be achieved using forward transmission distributed sensing technology. However, current forward transmission methods struggle to distinguish between vibrations and temperature changes when their frequencies are similar, which poses a significant limitation for practical applications. We present and experimentally demonstrate a dual-parameter distributed sensing system based on forward transmission in a few-mode graded-index fiber, in-phase/quadrature demodulation and phase-spectrum time delay methods to resolve the amplitude, frequency and position of vibrations. Simultaneous distributed sensing of vibration and temperature is demonstrated over 1 km of few-mode fiber, with vibration and temperature limit of detection as low as 26.1 pϵ/Hz<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> and 0.397°C. The positioning results over sensing range of 2 km (without inline amplification) revealed that the positioning error can be as small as 0.2 m when employing bidirectional optical transmission (forward transmission). The vibration frequency range tested is between 100–600 Hz, limited by the piezoelectric transducer.