  Intensity modulators are fundamental components for integrated photonics.
From near infrared to visible spectral ranges, they find applications in
optical communication and quantum technologies. In particular, they are
required for the control and manipulation of atomic systems such as atomic
clocks and quantum computers. Typical integrated electro-optic modulators
operating at these wavelengths show high bandwidth and low voltage operation,
but their extinction ratios are moderate. Here we present an integrated
thin-film lithium niobate electro-optic modulator operating in the C-band,
which uses a subsequent periodically poled waveguide to convert the modulated
signal from 1536 nm to 768 nm using second harmonic generation. We demonstrate
that the upconverted signal retains the characteristics of the modulated input
signal, reaching a measured high bandwidth of 40 GHz. Due to the nature of the
nonlinear process, it exhibits, with respect to the fundamental signal, a
doubled extinction ratio of 46 dB, which is the highest recorded for
near-infrared light on this platform.
