Novel optical sensor for temperature monitoring based on nematic liquid crystal (NLC) plasmonic structure

Herein, a theoretical investigation for a nanoscale thermosensor to measure living cells’ temperature has been suggested based on a coupling between nematic liquid crystal of E7 type with metal-insulator-metal plasmonic structure. The design is built from a square-shaped resonance cavity, coupled with air waveguides. The nanocavity has been filled by a nematic liquid crystal of E7 type. The index of refraction of E7 NLC varies with the ambient temperature. In addition, the resonance wavelength depends on the index of refraction of E7 NLC. As a result, the proposed sensor could be used to monitor the surrounding temperature. The optical transmittance, electric field distribution, and performance parameters have been studied and computed through the finite difference time domain (FDTD) method. Further, the optimization of geometrical dimensions considering the performance of the suggested sensor has been studied. The presented design has a sensitivity of 599.5 nm/RIU (≈ 1.44 nm/°C) for temperatures ranging from 15 to 55 °C. In addition, a quality factor of 24.42, a figure of merit of 14.21 RIU⁻¹ (≈ 0.034 °C⁻¹), and ultra-high linearity of 0.9999 may be accomplished. The suggested design with high performance parameters and compact size can make a great argument for in vitro thermotherapy and nano-thermometry applications.