Tunable nonlinear absorption properties of Ti3C2Tx MXene for all-optical bipolar modulation applications.

The demand for ultrafast and multifunctional all-optical modulators based on two-dimensional nonlinear optical materials is continuously growing in the era of big data and artificial intelligence. Herein, we report the experimental realization of the first, to the best of our knowledge, all-optical bipolar modulator that is based on pump intensity-dependent nonlinear absorption of Ti₃C₂T_x MXene. This tunable nonlinear absorption with a conversion threshold of approximately 65 GW/cm² is characterized and analyzed by the Z-scan technology, and Ti₃C₂T_x MXene shows a stronger nonlinear absorption coefficient of 10²cm/GW than most of two-dimensional materials. According to the proposed four-energy-level model, the numerical simulation results suggest that the tunable nonlinear absorption transition is from the interplay between the absorption cross section ratios of the first and second excited states relative to the ground state. Inspired by this, the all-optical bipolar modulation with a nanosecond-level response time is demonstrated by changing the pump intensity. This work opens up exciting possibilities for the design of innovative multifunctional all-optical modulation devices based on two-dimensional nonlinear media.