DFB FL Sensor Cross-Coupling Reduction

The effect of weak external reflections on distributed feedback (DFB) fiber laser (FL) sensor frequency noise has been studied. For multiplexed DFB FL arrays, it was demonstrated that out-of-band reflections from DFB FL raise the noise level of adjacent lasers by up to 50 dB. It was further demonstrated that by incorporating a complex phase- and amplitude-apodized FL grating design with high sidelobe suppression, cross coupling due to out-of-band reflections can be reduced to negligible levels, and Rayleigh backscatter limited noise performance can be achieved. Practical limitations to acoustic sensitivity of DFB FL sensors due to increased laser frequency noise are discussed, and ways to reduce DFB FL sensitivity to external reflections are proposed