Spyrobenzopyran doped core PMMA fibers

Cylindrical PMMA fibers with core regions doped with spirobenzopyran molecules have been fabricated. Spirobenzopyran is a photochromic molecule with two forms: spiropyran and merocyanine. In the fibers, one state could be reverted to the other either by a photo-initiated reaction or by thermal excitation. The fluorescence from the merocyanine form could be generated by exciting the core with a 543nm laser. For spirobenzopyran, higher temperatures favor the reaction from spiropyran form to merocyanine form, hence as temperature increases the merocyanine form concentration in the core increase causing the fluorescence intensity to increase. It was observed that the fluorescence increased fairly linearly over a certain range and started rolling off as the temperature approached to 60°C. Refractive index and material dispersion characteristics of SP/PMMA was also measured. Fluorescence generation in the core by two-photon absorption from 40 ps pulses at 1064 nm has been demonstrated. The energy of the pulses was 1.8 uJ, which gave a peak intensity of 5GW/cm² in 33um core. A portion of the emitted fluorescence was guided to the end of the fiber and a portion of it escaped the cladding and radiated into the air.