Photonic-crystal-based broadband graphene saturable absorber

The enhanced saturable absorption (SA) of a one-dimensional (1D) photonic crystal (PC) made from polymers and graphene composites by spin coating is observed. 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 β_eff for graphene nanoflakes embedded in the PC, when compared with the bulk graphene-polymer composite. The effect is studied in a wide range of laser intensities. Graphene inclusion into a 1D PC remarkably decreases the SA threshold and saturation intensity, providing a desired solution for an advanced all-optical laser mode-locking device.