A photonic crystal-based broadband graphene saturable absorber

Abstract: The enhanced nonlinear optical response of a one-dimensional (1D) photonic crystal (PC) made from polymers and graphene composites is observed. The graphene PC was fabricated by spin-coating. It shows obvious bandgaps at two wavelengths in transmittance. Femtosecond Z-scan measurement at 515 nm and 1030 nm reveals a distinct enhancement in the effective nonlinear absorption coefficient Beff (and imaginary part of third-order dielectric susceptibility ImX(3)) for graphene nanoflakes embedded in the PC, when compared with the bulk graphene-polymer dispersion. The effect is studied in a wide range of laser intensities. The inclusion of graphene into a 1D-PC remarkably decreases the saturable absorption threshold and saturation intensity, providing a desired solution for an advanced all-optical laser mode-locking device.