Optical tuning of guided mode resonance in an azo-copolymer waveguide grating structure inscribed with a surface relief grating

摘要

Optical tuning of guided mode resonance (GMR) is demonstrated in a photosensitive azo-copolymer waveguide grating structure (WGS), consisted of a one-dimensional surface relief grating (SRG) inscribed on top of an azo-copolymer planar waveguide layer. The azo-copolymer WGS was designed and fabricated to have GMRs at visible wavelength range for transverse-electric (TE) polarization. The first-order GMR wavelength can be tuned to shorter wavelength by illuminating the WGS with a linear polarized light at 514?nm wavelength, which produces photoisomerization-induced refractive index change in the azo-copolymer waveguide layer. The photo-induced GMR wavelength shift increases with the pumping power, and its maximum shift is 25?nm. The WGS retains a memory for the optical pumping, and its GMR wavelength doesn't return to the original peak position after switching off the pumping beam. To make a full-recovery of the GMR peak position, the WGS has to be illuminated by a second pumping beam with a vertical polarization arrangement. Authors demonstrate the GMR peak position can be tuned back and forth reversibly by alternatively illuminating two cross-polarized laser beams in sequence. The results obtained in this work show the azo-copolymer WGS has the potential for the applications such as optical tunable GMR filter and optical modulation.