Brillouin Active Fiber Structural Sensor for Aging Aircraft

The temperature, strain, and doping sensitive back-scattered signal in an optical fiber of extremely narrow spectral width, generated by laser pumped stimulated Brillouin scattering (SBS) in an oscillator scheme is proposed for robust and fault tolerant ambient sensing. Practical implementation issues to be addressed center on lowest SBS threshold for shortest possible fiber sensor length, fiber coating for protection, compatibility in bonding to aircraft structural material, and possible SBS sensitivity enhancement. Thin film shape memory alloys are to be explored as coating candidates. Fibers are also chemically engineered to provide distinct, spectrally shifted SBS lines for multi-point sensing purposes. Observed ambient sensitive spectrum in a forward scattered signal by transverse acoustic eigenmodes or Guided Acoustic Wave Brillouin Scattering (GAWBS) is also studied for simultaneous sensing.