Switching the Nonparametric Optical Nonlinearity of Tungsten Oxide by Electrical Modulation

This work shows the electrical switching of the nonparametric optical nonlinearity of tungsten oxide (WO ). The sign and magnitude of the effective nonlinear absorption coefficient (β ) can be modulated via application of an external bias. With laser excitation at 1030 nm, WO shows a relatively large saturable absorption (SA) under an applied voltage (V ) of −2.5 V, with β being as large as −632 cm GW , while reverse saturable absorption (RSA) is found for V larger than −1.5 V. The electrical switching of the nonlinear optical (NLO) response is reproducible and durable. Both electrostatic and electrochemical dopings of WO occur during V variation, with SA resulting mainly from the electrochemical doping (the intercalation of H into the lattice of WO ). The wavelength-dependent NLO performance of pristine WO is attributed to competition between one-photon absorption and two-photon absorption, while the V -derived NLO response is correlated with variation in the band structure and its population. These results suggest a promising approach for the postsynthesis modulation of the NLO response and a potential device configuration for further optoelectric applications.H.L. and R.H. contributed equally to this work. This research was financially supported by the National Natural Science Foundation of China (Grant Nos. 51772214, 51432006, and 51701170), the Ministry of Science and Technology of China (Grant No. 2011DFG52970), the Ministry of Education of China (Grant No. IRT14R23), 111 Project (B13025), the Innovation Program of Shanghai Municipal Education Commission, the National Youth Talent Support Program (W03070073), and the Project of Science and Technology Plan of Fujian Province (Grant No. 2018J01520). M.G.H. and C.Z. thank the Australian Research Council for support (DP170100411