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 3− x ). The sign and magnitude of the effective nonlinear absorption coefficient (β eff ) can be modulated via application of an external bias. With laser excitation at 1030 nm, WO 3− x shows a relatively large saturable absorption (SA) under an applied voltage ( V A ) of − 2.5 V, with β eff being as large as −632 cm GW −1 , while reverse saturable absorption (RSA) is found for V A 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 3− x occur during V A variation, with SA resulting mainly from the electrochemical doping (the intercalation of H + into the lattice of WO 3− x ). The wavelength‐dependent NLO performance of pristine WO 3− x is attributed to competition between one‐photon absorption and two‐photon absorption, while the V A ‐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.