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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup><mml:mrow><mml:mi>μ</mml:mi></mml:mrow> <mml:mrow><mml:mi>o</mml:mi></mml:mrow> </mml:msup> <mml:mi>C</mml:mi> <mml:mo>/</mml:mo> <mml:msqrt><mml:mrow><mml:mi>H</mml:mi> <mml:mi>z</mml:mi></mml:mrow> </mml:msqrt> </mml:mrow> </mml:math> and 80.6 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>p</mml:mi> <mml:mi>ε</mml:mi> <mml:mo>/</mml:mo> <mml:msqrt><mml:mrow><mml:mi>H</mml:mi> <mml:mi>z</mml:mi></mml:mrow> </mml:msqrt> </mml:mrow> </mml:math> 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.