EE Seminar: Distributed and Dynamic Fiber-Optic Sensing

You are cordially invited to attend a lecture on

by

Arik Bergman

Ph.D. student of

Professor Moshe Tur of Electrical Engineering, Physical Electronics Department

Following the immense impact they had on telecommunications, optical fibers have finally established their advantageous value also in the field of sensing. These sensors, owing to their light weight and small diameter, have the potential to revolutionize the current field of Structural Health Monitoring (SHM) as they are easily embedded into composite structures and inherently sensitive to critical deformation parameters. The vast majority of distributed fiber-optic sensing technologies rely on one or more of the Rayleigh, Raman and Brillouin scattering effects. The sensing information is extracted by using an appropriate interrogator, which transmits optical radiation into the fiber and then collects the scattered radiation. Dedicated processing is then used to infer the relevant measurand at every resolution cell along the fiber. The significance of the presented work lies in the innovative results achieved in the field of fiber-optic sensors, extending their operating envelope and enhancing reliability.

The first part of the research deals with in-fiber Rayleigh scattering, a linear process in which electromagnetic radiation is scattered by random refractive index fluctuations in the amorphous silica. Existing interrogators (e.g., Optical Frequency-Domain Reflectometry – OFDR) employ this weak reflection to evaluate the longitudinal strain distribution along the fiber with millimeter-order spatial resolution. We have developed an amplifying module which increases by a factor of 10 the measurement dynamic range of the OFDR technique which helps to overcome the unavoidable loss in many embedded applications or faulty installations. Also to be presented – benchmark studies on several critical SHM applications of fiber-optic sensors in composite-made aircraft structures: wing load monitoring, detection of impact-induced damage and bond strength evaluation of composite repairs.

The second part of the research deals with nonlinear fiber optics. Methods for increasing the speed, precision and accuracy of sensors based on Brillouin Dynamic Gratings (BDGs) will be presented: (i) Extending the BDGs sensing technique to the dynamic regime; (ii) Resolving the trade-off between the spatial resolution and measurand estimation error, through the application of optical codes. (iii) Finally, a novel interrogation technique based on the measurement of Brillouin phase-shift in BDGs, with largely increased tolerance to laser power fluctuations and fiber bend losses will be presented.