Microfluidic droplet grating for reconfigurable optical diffraction

This Letter presents a reconfigurable optical diffraction grating using multiphase droplets on a microfluidic chip. The uniform and evenly spaced circular droplets are generated by continuously dispersing two immiscible liquids into a T junction to produce plugs, which are then transformed into a circular shape at a sudden expansion of the microchannel. In experiments, the droplet grating shows a detection limit of ∼6.3 × 10-5 when used as an optofluidic refractometer and produces different colors as a color filter. Such a grating has the advantages of high stability and wide tunability in droplet size, grating period, and refractive index, making it promising for biochemical and bio- material applications.