EXPERIMENTAL INVESTIGATION OF GROWTH DYNAMICS OF HIGHER ORDER BRAGG GRATINGS IN POLYMER FIBERS

摘要

A possibility of fabrication of Bragg gratings in polymer fibers with multiple reflection peaks using a 325 nm UV beam and a standard phase mask is demonstrated. Growth dynamics of higher order reflection peaks was studied experimentally in two types of polymer fibers. The first was a microstructured polymer fiber made of pure PMMA and the second a PMMA fiber with a core made of PMMA/PS copolymer, in the diffraction spectrum of the phase mask with a period Λ=1.052 μm. A complex interference pattern arising behind the phase mask thanks to the existence of 0th, ±1st, ±2nd, ±3rd diffraction orders is transferred into longitudinal modulation of the refractive index containing different spatial frequencies. As a result, good quality higher order Bragg peaks placed at λ_B/2=782 nm and 2λ_B/3=1040 nm for the grating with the primary peak at λ_B=1555 nm were observed in the microstructured fiber. For the grating in the PMMA/PS fiber, additional peaks at λ_B/3=525 nm 2λ_B/5=628nm were present in the reflection spectrum. We highlight the differences in the growth dynamics as well as temporal and temperature stability of the gratings fabricated in the two fibers.