Coupling light from an organic light emitting diode (OLED) into a single-mode waveguide: Toward monolithically integrated optical sensors

Evanescent coupling is used to couple light from a polymer light emitting diode (PLED) into a planar single-mode waveguide. The PLED is monolithically integrated on top of the waveguide in a stacked configuration. Due to the waveguide's proximity, the emission zone of the PLED and the waveguide modes overlap substantially, so that the PLED can directly excite the modes. An additional spacer layer between PLED and waveguide is shown to improve the coupling efficiency by about a factor of 5. For iridium-based diodes PLED-to-waveguide coupling efficiencies of as high as 3.2% have been obtained.