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We demonstrate efficient coupling to the optical whispering gallery modes (WGMs) of nematic liquid crystal (NLC) microdroplets immersed in an immiscible aqueous environment. An individual NLC microdroplet, confined at the tip of a microcapillary, was coupled via a tapered optical fiber waveguide positioned correctly within its vicinity. Critical coupling of the taper-microdroplet system was facilitated by adjusting the gap between the taper and the microdroplet to change the overlap of the evanescent electromagnetic fields; efficient and controlled power transfer from the taper waveguide to the NLC microdroplet is indeed possible via the proposed technique. We also found that NLC microdroplets can function as highly sensitive thermal sensors: A maximum temperature sensitivity of 267.6 pm/°C and resolution of 7.5 × 10^-2 °C were achieved in a 78-μm-diameter NLC microdroplet.

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This paper reports the observation of optically pumped whispering gallery mode (WGM) lasing emission from dye-doped emulsion microdroplets of cholesteric liquid crystals (CLCs) suspended in an immiscible aqueous environment. The higher index contrast between the immersion liquid and CLC microdroplet contributes to the generation of WGM resonance so that lasing emission can be realized in the CLC microdroplet via total internal reflection. The WGM lasing nature is verified by numerical simulations as well as experiment of size-dependent lasing action. The lasing wavelength depends on the refractive index of the CLC microdroplet and can be tuned by varying the temperature. A tuning range of 9.1 nm within 6 °C temperature interval is realized in a 20-μm-diameter microdroplet. Such a temperature tunable microlaser is promising for applications of flexible photothermic devices.

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