  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.
