Tunable self-imaging effect using hybrid optofluidic waveguides.

Multimode interference (MMI) is a typical self-imaging phenomenon and has been widely exploited for optical devices like couplers and splitters. Usually, it utilizes solid waveguides only and thus has very limited tunability in self-imaging properties. This paper reports our original work on tunable MMI using a hybrid optofluidic waveguide. It is generated by the diffusion between miscible flows in a microchannel and consists of two parts: gradient-index liquid-liquid waveguide for light modulation and step-index liquid-solid waveguide for image formation. Simulation and experiments have shown successful realization of the real-time tuning of self-imaging properties. For detail, the image point (focal spot) width could be modulated from 7 μm to 16 μm, and the self-imaging period changes in the range of 500 μm by varying the fluid properties. It is foreseeable that such a hybrid optofluidic waveguide may find wider applications in lab-on-a-chip systems and optical devices.