A mode-locked fibre laser temperature independent strain sensor based on intracavity pulse interference

High resolution, accurate strain sensors find vital applications in civil, aerospace, and mechanical engineering. Photonic solutions, especially fibre Bragg gratings, despite being promising platforms for strain sensing in harsh environments, and achieving microstrain resolution, suffer from strong sensitivity to temperature fluctuations and require expensive optical detection methods. To tackle these challenges, in this work we present a mode-locked fibre laser strain sensor based on intracavity pulse interference. Our all-fibre sensor, using an intracavity Mach-Zehnder interferometer architecture achieves 20 microstrain resolution with linear response over a 4 millistrain range. Our proposed sensor does not require external locking, and it is environmentally stable, decoupling temperature and strain effects. Furthermore, through a full electronic read-out in radio-frequency domain, our solution can bypass expensive and bulky optical detection. These features pave the way for low-cost and robust photonic strain sensors technology with disruptive real world impact.