High-gain and wide-band optical amplifications induced by a coupled excited state of organic dye molecules co-doped in polymer waveguide

We investigated optical gain and lasing characteristics of a polymer thin film co-doped with Rhodamine 6G and 4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran dye molecules. By the co-doping of these dyes, the optical gain coefficient and its spectral range were enhanced and widened, respectively. These results cannot be accounted for by the linear combination of the optical gain properties of single-doped films. Owing to this high-gain and wide-band optical amplification property, a distributed feedback lasing with a low threshold of 70 μJ/cm as well as a widely tunable wavelength range of 587-613 nm was achieved. We attribute this amplification property of the co-doped film, which cannot be achieved with the single-doped films, to the appearance of a coupled excited state between the two molecules.