Controllable in-line UV sensor using a side-polished fiber coupler with photofunctional polymer

A novel ultraviolet (UV) sensor using evanescent field coupling between singlemode-polished fiber and photochromic dye-dispersed polymer waveguide was demonstrated. It was found that resonance wavelength shifts occurred due to variations in the refractive index of the photochromic dye-dispersed polymer waveguide relative to UV intensities. A spiroxazine dye was chosen as the overlay material because of its photochromic isomerization induced by UV irradiation. The wavelength responses of these sensors by UV exposure power were measured 0.18 and 0.25 nm/mW when UV was exposed for 5 and 10 s, respectively. The recovery time for the sensor was independent of UV exposure power, and 80% recovery time was shown 90 s.