Tunable liquid crystal optical microcavities

In this work we show that nematic liquid-crystal droplets can be used as low-loss and highly tunable whisperinggallery mode (WGM) optical microcavities. They are spontaneously formed by mixing the liquid crystal with an immiscible liquid. The optical modes can be tuned either by applying an electric field, changing the temperature or by mechanical deformation. The tuning range for the electric field is as high as 20 nm at 2.6 V/μm for a ~ 600 nm WGM in 17 μm diameter droplets. Tuning is fast and almost linear with the applied voltage. In the case of the temperature tuning, we can shift the modes by more than 15 nm at a temperature change of 30 K. Further, we can also apply mechanical deformation to a free standing film of PDMS polymer containing the liquid crystal droplets. At 15% strain the mode shift is more than 30 nm. In all the three cases the tuning exceeds the free spectral range of the resonators and is completely reversible.