Figure 4.

Schematic of Ring-Up Spectroscopy Sensing Mechanism

Sharply rising detuned probe pulses (left inset) lead to the build-up of a cavity field. As this weak field leaks back into the fiber, it interferes with the probe, resulting in a beating signal at the output (right inset). The resonance width, 2κ, the detuning, δ, and the splitting of the resonance, 2g, can be derived from the ring-up signal.