Speed-of-light effects in high-resolution long-cavity fiber Fabry–Perot scanning interferometers

High-resolution fiber Fabry–Perot scanning interferometers demonstrate bandwidths from 20 MHz to 4 kHz with corresponding cavity lengths from 26 mm to 500 m. Finite speed-of-light effects are observed for cavity lengths as short as 5 m. Analytical and experimental results show an inverse square-root dependence of bandwidth on cavity length in the speed-of-light-limited regime.