An integrated tunable interferometer controlled by liquid diffusion in polydimethylsiloxane.

We demonstrated an integrated tunable interferometer in Polydimethylsiloxane (PDMS). In contrast to most on-chip interferometers which require complex fabrication, our design is realized by conventional soft lithography fabrication. The optical path difference occurs during propagation across a fluid-fluid interface. The diffusion level of the two miscible liquids which is controlled by liquid flow rates provides tunability. Different ratio of two liquid flow rates result in the interference spectral shift. Interference peak numbers are varied with flow rate ratio of two liquids. Mutual diffusion between two liquids changes the profile of the refractive index across the fluidic channel. The two arms structure of our design provides convenience for sensing and detection in biology system. This device not only offers the convenience for microfluidic networks but also paves the way for sensing in chemical microreactors.