Random optical parametric oscillator fibre sensor

Fibre laser-sensors have emerged as a promising solution for long-distance sensing, offering high SNR and fine spatial resolution. However, their adoption is constrained by fundamental limitations: they typically require a fixed mirror at the sensing location or access to both fibre ends for electronic selection of the sensing location. This work introduces a random optical parametric oscillator (R-OPO) fibre sensor that addresses these challenges. Similar to a laser-sensor but exploiting modulation instability and continuous weak reflections, the R-OPO sensor enables long-distance access ( > 25 km) sensing by arbitrarily addressing 1 m-long fibre sections over a long sensing range ( > 1 km). It supports both backward and forward sensing, but unlike most forward sensors, the sensing location information is readily available at both fibre ends. Most importantly, it eliminates the need for a fixed mirror at the sensing location, offering electronically tunable sensing locations. The proposed detection scheme enables straightforward quantitative measurement of dynamic perturbations, requiring only a single fast Fourier transform, thus enabling real-time monitoring. Temperature and strain noise-limited sensitivities of 10.73 ${\mu }^{o}C/\sqrt{Hz}$ and 80.6 $p\epsilon /\sqrt{Hz}$ were obtained. Taking advantage of four-wave-mixing by-products inherent to R-OPOs, the sensitivity to external perturbations could be enhanced by a factor of two compared to conventional Rayleigh-based sensors. A simple frequency-unwrapping algorithm is proposed to extend the dynamic measurement range, and the continuous monitoring of a 2 °C temperature increase was accurately measured. This first demonstration of a R-OPO fibre sensor establishes the foundations for parametric fibre sensors.