Highly sensitive optical temperature sensor based on a SiN micro-ring resonator with liquid crystal cladding

This work develops a sensitivity-enhanced optical temperature sensor that is based on a silicon nitride (SiN) micro-ring resonator that incorporates nematic liquid crystal (NLC) cladding. As the ambient temperature changes, the refractive index of the NLCs, which have a large thermal-optical coefficient, dramatically varies. The change in the refractive index of the NLC cladding that is caused by the temperature shift can alter the effective refractive index of the micro-ring resonator and make the resonance wavelength very sensitive to the ambient temperature. The temperature-sensitivity of the device with 5CB cladding for TM-polarized light was measured to be as high as 1nm/°C between 25 and 33 °C and over 2nm/°C at temperatures close to clearing temperature of the 5CB cladding. The temperature-sensitivity of the proposed device is at least 55 times that of the micro-ring resonator with air cladding, whose temperature-dependent wavelength shift for TM-polarized light is 18pm/ °C.