Compound lasing fiber optic ring resonators for sensing

In this work, we present a new method for increasing simultaneously the sensitivity and interrogation stability of fiberoptic intensity sensors. The configuration is based on a double-coupler ring resonator. On one side, the attenuation sensitivity of the sensor is enhanced by placing it inside a ring resonator. On the other side, the stability of the interrogation method is rendered close to perfect by creating an external lasing ring resonator with matched spectral response. The resulting lasers allow the stable interrogation of the sensors with an impressive sensitivity enhancement. In our experiments, the dynamic range of the intensity sensor (and consequently its sensitivity) is increased 15 dB by using this laser-based interrogation system. Simultaneously, the instability of the system is reduced to ±0.05 dB. In comparison with systems based on external interrogation, our method is >100 times more stable and also simpler, as no wavelength tunable elements are required.