Active Intracavity Rotation Angle Sensor Based on a Simple Balloon-Shaped Fiber Ring

An intensity-modulated active intracavity rotation angle sensor was demonstrated based on a simple balloon-type fiber. The sensor leverages macrobending-induced loss, modulated by torsional deformation, where changes in the rotation angle are converted into variations in laser output power. Through geometric optimization, the passive structure achieves $7.34~\mu $ W/° sensitivity in a limited linear range (30°–120°). By integrating the sensor into a ring fiber laser cavity, the active configuration significantly suppresses high bending loss and enhances sensitivity to 0.4719 mW/° with a 50-dB signal-to-noise ratio (SNR) improvement. The linear measurement range expands to 40°–150° (full range: 0°–180°), outperforming passive designs by two orders of magnitude in sensitivity. This work presents a compact and cost-effective solution for high-dynamic-range angular sensing.