A few-layer InSe-based sensitivity-enhanced photothermal fiber sensor

Two-dimensional (2D) InSe has recently attracted increasing attention due to its outstanding electrical transport property, excellent photo-response, and direct band gap characteristics. In this contribution, few-layer InSe was successfully fabricated via a facile liquid phase exfoliation (LPE) method. Compared with other 2D materials, the photothermal response measurements demonstrate that InSe has excellent photothermal conversion efficacy. A novel Vernier-cascaded photothermal fiber sensor with high sensitivity that takes advantage of the photothermal effect of few-layer InSe has been proposed and demonstrated for the first time. The experimental results have shown that the photothermal optical sensitivity and spectral shifts of the MZI (Mach-Zehnder interferometer)-MKR (microfiber knot ring) Vernier sensor and the Vernier part are 0.126 nm mW^-1, 12.22 nm and 0.0047 nm mW^-1, 0.49 nm, respectively. A maximum sensitivity amplification factor of ∼26.8 is realized. Our present work can provide more possibilities of 2D materials that can be utilized towards cascade sensors.