Bragg grating evanescent field sensor made in biconical tapered fiber with femtosecond IR radiation

Retro-reflective Bragg gratings were made with a phase mask and femtosecond radiation from a Ti : sapphire infrared laser into the core and cladding region of a tapered single-mode fiber. The evanescent field in the taper interacts with the ambient environment and the intensity of the reflected signal is used to measure the refractive index changes of the ambient environment as low as 2.5×10^-5. By controlling the immersion depth of the grating taper, use of the taper as a single port point sensor for measuring fluid levels is also demonstrated.