Design of a nonlinear metastructure for temperature detection and biosensing based on the second harmonic generation in theory.

When the second harmonic generation (SHG) occurs in temperature-controlled ferroelectric crystals, it serves as an effective method for detecting temperature and changes in the refractive index (RI). A one-dimensional nonlinear metastructure (NM) composed of periodically poled lithium niobate crystals is designed precisely to exhibit significant SHG enhancement in the visible to near-infrared spectral range. When a tunable fundamental electromagnetic wave is incident at a frequency () near 241.067 THz, the NM achieves frequency conversion and enables wide-range temperature detection (25-105 °C) at the second harmonic wave (SHW) scale 2 with a sensitivity of = 0.32% per °C. By altering the filling material of the sample layer, it is possible to distinguish between three types of healthy or cancerous liver tissues using RI biosensing with a fundamental wave around 273 THz. The sensing range is from 1.3463 to 1.3655, with an value of 14.75 THz per RIU. The proposed NM integrates the SHW effect with optical detection and sensing, offering new insights for SHW applications and biomedical fields.