Broadband Optical Amplification of Waveguide Cut-Off Mode in Polymer Waveguide Doped with Graphene Quantum Dots

Graphene quantum dots (GQDs) showing a wide-range tunability in their emission wavelength are promising materials for next-generation optoelectronic applications. However, there are few studies on optical amplification functionalities for broadband emission of GQDs. Here, the authors demonstrate a broadband optical amplification of GQDs mixed with a polymer matrix. The GQD particles prepared by microwave-assisted hydrothermal method show a large variation in their dimension and a broadband emission with a large Stokes shift. In a form of polymeric thin film, the GQDs exhibit amplified spontaneous emission (ASE) signal showing the broadband gain of approximate to 370-650 nm and the gain coefficient up to approximate to 4 cm(-1). Cut-off mode propagation is the origin of ASE signal generation. The optical amplification performance is found to be associated to the photoluminescence quantum yield, which is improved by the GQDs passivation with the polymer matrix. These results demonstrate that the GQDs are a promising active material as a wideband optical amplification medium.