Optical amplification of the cutoff mode in planar asymmetric polymer waveguides

Modes with low threshold for optical gain were observed at wavelengths close to the cutoff in experiments probing the amplified spontaneous emission of light-emitting polymer thin films. The polymer was the semiconductor layer in a multilayer semiconductor-insulator-metal structure that simulates the one-dimensional waveguide characteristics in the channel of a field-effect transistor. The "cutoff" mode propagates at the polymer/gate-insulator interface, has an optical gain threshold of approximately 10 kW/cm(2), and is not influenced by absorption of the gate electrode. The wavelength of the amplified emission tracks the cutoff wavelength of the asymmetric double-waveguide structure and the cutoff mode is, therefore, tunable in wavelength. Our results suggest that the light-emitting field-effect transistor architecture is a promising route for the construction of an injection laser. (C) 2003 American Institute of Physics.