Influence of nanometer-size interface roughness on light transmission in polyfluorene waveguides studied by amplified spontaneous emission measurements

Amplified spontaneous emission from optically pumped thin-film waveguides of poly(9,9-dioctylfluorene) (F8) has been measured to study the influence of interface roughness on transmission loss within F8 waveguides. It is found that the transmission loss coefficient at the emission wavelength is reduced with increasing thickness of the waveguides. A theoretical model is employed to explain the relationship between the transmission loss of F8 waveguides and their thickness. The model explains the relationship found experimentally. A major source of loss is shown to be due to nanometer-size interface roughness of F8 waveguides. Such information is valuable for the design of organic solid-state lasers.