Switching the Nonparametric Optical Nonlinearity of Tungsten Oxide by Electrical Modulation

Abstract 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.