Distributed Ultraviolet Sensor Based on Brillouin Optical Correlation-Domain Analysis Using An Azobenzene Polymer-Coated Optical Fiber

A distributed ultraviolet sensor based on Brillouin scattering in an azobenzene polymer-coated optical fiber is experimentally demonstrated. A Brillouin optical correlation domain analysis applying injection locking and a differential measurement scheme is utilized for the characterization of the extra coating of azobenzene polymer on a single-mode optical fiber with various types of inner coatings. The saturation and relaxation properties of the coated sensor probe are analyzed according to the time and UV intensity. It is demonstrated that the azobenzene coatings on bare and polyimide-coated fiber provide a change in the Brillouin frequency above 70 MHz under UV irradiation of ∼25 mW/cm
²
at a wavelength of 365 nm, and the saturation level and saturation time depend on the material of the inner coating and the thickness of the azobenzene coating.