FBG/DFB-induced chaotic self-mixing analysis and sensing applications

• Self-mixing noise induced in high-feedback DFB/FBG fiber optic systems is analyzed.
• Noise covariance matrix is decomposed in its eigenvalues, finding a robust strain dependency.
• Applications in static and dynamic interrogation systems are discussed.

Optical feedback induced by a highly reflective fiber Bragg grating (FBG) onto a distributed feedback (DFB) laser is investigated. In static strain conditions, the covariance matrix of the chaotic noise generated by DFB/FBG self-mixing interference is decomposed into its eigenvalues. Then, by observing the eigenvalue pattern, it is possible to detect the strain applied to FBG independently from source power and electrical noise level. Furthermore, by employing a Capon spectral estimator, and splitting and filtering out the self-mixing eigenvalues, it is possible to dynamically detect acoustic signals in harsh signal-to-noise conditions. This technique provides dual static and dynamic FBG interrogation independent on optical power and fiber link losses variations.