Flexible gauge length intrinsic fiber-opticstrain sensor using broadband interferometry

Monitoring strain is important in precision engineering applications that require maintaining the precise alignments of structures over time, such as those found in machine tools and metrology frames. We present a fiber-optic strain measurement technique based upon broadband interferometry that is variously configurable in terms of gauge length and sensitivity. This is achieved by the use of an unbalanced interrogation interferometer configuration that alleviates the cavity length limit imposed by the temporal coherence of the system. We also demonstrate that dispersion in fiber sensors based on intrinsic Fabry–Perot interferometers must be considered to optimize performance. The possibility of multisensor interrogation using the same optical system is also reported.