Micron scale directional coupler as a transducer for biochemical sensing

A microfabricated directional coupler (DC) was used for the detection of DNA conjugated with quantum dots. Output optical signals from DCs of a wide range of device lengths correspond well to theoretical and simulation results. Even 20 mu m-long DC devices could detect changes in the output optical intensity by monitoring the near-field pattern using a CCD camera. The signal was enhanced 60 x using a 1500 mu m-long DC device. For large cladding refractive-index changes between air and water, the normalized signal changed cyclically several times between 0 and 1. The results suggest that the DC can be the basis for miniaturized two-dimensionally integrated biochemical sensors. (C) 2015 Optical Society of America