Interrogation of fiber Bragg-grating resonators by polarization-spectroscopy laser-frequencyLocking

We report on an optically-based technique that provides an
efficient way to track static and dynamic strain by locking the frequency of
a diode laser to a fiber Bragg-grating Fabry-Pérot cavity. For this purpose, a
suitable optical frequency discriminator is generated exploiting the fiber
natural birefringence and that resulting from the gratings inscription
process. In our scheme, a polarization analyzer detects dispersive-shaped
signals centered on the cavity resonances without need for additional optical
elements in the resonator or any laser-modulation technique. This method
prevents degradation of the resonator quality and maintains the
configuration relatively simple, demonstrating static and dynamic
mechanical sensing below the picostrain level.