Light-induced spectral shifting generated from azo-dye doped holographic 2D gratings

[[abstract]]Optically tunable two-dimensional (2D) gratings were holographically fabricated in azobenzene-doped polymer-dispersed liquid crystals (LCs) using a single diffractive element. Our experiments showed that the diffraction efficiency of the gratings could be switched reversibly upon light irradiation. More importantly, we demonstrated for the first time that the diffractive spectrum from the holographic 2D gratings could be optically tuned by about 24 nm, which might be useful for optically switchable filters and spectroscopic applications. The dynamic switching is attributed to the changes of refractive index modulation between LC-rich and polymer-rich areas due to the trans-cis-isomerization-triggered nematic-isotropic phase transition of liquid crystals. In addition, our 2D holographic gratings have polarization-insensitive optical properties for normally incident light. The all-optical tuning behavior is highly reversible and reproducible, making this kind of grating promising in active photonic elements.[[note]]SC