Active Vibration-induced PM Noise Control in Optical Fibers: Preliminary Studies

Vibration causes mechanical distortions in fiberoptic transmission lines that induce time (phase) fluctuations. RF systems are increasingly using optical fibers in various ways and must occasionally operate in environments with acoustic and structure-born vibration. A scheme is described which enables electronic suppression and cancellation of vibration-induced spurious phase noise in an optical fiber wound on a spool. The scheme is applied to an opto-electronic oscillator (OEO). Close-to-carrier spectral lines often occur due to mechanical vibration of state-of-the-art oscillators. Passive vibration-suppression schemes (shock mounts, isolation chambers, etc.) do not always adequately reduce discrete line spectra that originate from vibration effects. However, vibration can be readily detected and measured by use of accelerometers. One can correct for these low-frequency vibration artifacts by subtracting a digitally-generated version of the artifacts based on their detection. This approach is generically referred to as "active noise control" and is used for selective noise-cancellation, room acoustic and vibration isolation, vibration suppression in video recording, active magnetic shielding, and other situations that require external noise cancellation or suppression. Active noise control can be applied to virtually all systems and applications that are subject to vibration-induced PM noise. We present simulation results in several cases representing typical vibrating oscillator scenarios. We report progress and experiences with operational hardware.