LADYBIRD - high-resolution, high-speed laser dynamics based optical fiber sensing for crack detection

The backbone of our communication system is composed of an increasingly dense network of optical
fibers carrying light signals. Optical fibers can however also be exploited as sensors to measure
strain and temperature. In this case, a small section of the fiber is altered so that it reflects a certain
wavelength range. The latter will vary in direct relation with the applied measurands. Sending a wellspecified light signal – either from a broadband light source or a tunable laser – allows to precisely
measure which wavelengths are reflected and thus recover the sensor information.
Lasers, on the other hand, are very sensitive to feedback, i.e. when light is reflected back to the
laser cavity. In these conditions, the laser can exhibit an incredible range of dynamical behavior:
from simple oscillations to pulses and even chaos. The interesting point is that the resulting behavior
strongly depends on many parameters including the feedback strength, delay, laser current, and so
on. As a result, small changes of the reflector can lead to large changes of the dynamics.
Combining these aspects, we propose to monitor the laser’s dynamics subject to optical feedback
from fiber sensors to retrieve sensor signals. We will harness the hypersensitivity of the laser to
feedback for achieving ultra-high-resolution sensing at high read-out frequencies and demonstrate its
relevance for crack detection and structural health monitoring for civil engineering and aerospace
applications