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 nonlinearity. The nonlinearity is realized using electric-field-induced χ(2) (refs. 10–16), and the programmability is engineered by massively parallel control of the electric-field distribution within the device using a photoconductive layer and optical programming with a spatial light pattern. To showcase the versatility of our device, we demonstrate spectral, spatial and spatio-spectral engineering of second-harmonic generation by tailoring arbitrary quasi-phase-matching grating structures1 in two dimensions. The programmability of the device makes it possible to perform inverse design of grating structures in situ, as well as real-time feedback to compensate for fluctuations in operating and environmental conditions. Our work shows that we can break from the conventional one-device–one-function paradigm, potentially expanding the applications of nonlinear optics to situations in which fast device reconfigurability is desirable—such as in programmable optical quantum gates and quantum light sources7,17–19, all-optical signal processing20, optical computation21 and adaptive structured light for sensing22–24. An optical slab waveguide with highly programmable nonlinear functionality is described, enabling the demonstration of versatile control over broadband second-harmonic generation across the spectral, spatial and spatio-spectral domains.){kind=link}