A linear chirp fiber Bragg grating with tunable bandwidth enabled by MXene's photothermal effect

An efficient method for tunable spectra of the fiber Bragg grating (FBG) using a gradient temperature field is proposed theoretically and experimentally. The temperature field modulation in the core region of the FBG is achieved by utilizing the photothermal conversion properties of MXene Ti₃C₂T_x, which guarantees a flexible adjustment of temperature gradients in the FBG axis. The spectra of FBG under different gradients of temperature fields are simulated by the transfer matrix method. The simulation results show that the gradient temperature distribution in the FBG axis can induce spectral chirps of FBG. The increase in the bandwidth of the spectrum and the decrease in the reflection intensity are caused by the rise of the temperature gradient. In the experiments, Ti₃C₂T_x films are coated onto the sidewall of FBG, and the non-uniform temperature gradient field in the FBG axis is formed and tuned by varying the intensity and spatial distribution of the pump laser on the Ti₃C₂T_x film. The spectral bandwidth measured at 10 dB can be broadened by 4.6 times from 0.57 to 2.63 nm with excellent linear tunability as a function of the pump power. This method provides an effective scheme for the spectral tuning of linear chirp FBGs in all-optical control.