The sensor consists of two concave-lens-like long-period fiber gratings and is engraved by the high frequency ${{\rm CO}_2}$CO2 laser. 
CO2 laser
Temperature self-compensation strain sensor based on cascaded concave-lens-like long-period fiber gratings.A robust, novel, to the best of our knowledge, fiber Mach-Zehnder interferometer strain sensor is designed and experimentally implemented. 
Mach-Zehnder interferometer