Recent advances in integrated electro-optic modulators (EOM) target small footprint and low power consumption with various physical effects such as plasma dispersion in silicon photonics, electro-absorption and the linear electro-optic/Pockels effect of organic polymers and ferroelectric materials. EOMs operate primarily in the C-band, suited for telecommunication, and devices operating in the visible or near-infrared ranges have been far less investigated. Here, we aim to develop integrated EOM with operating wavelengths around 780 nm and shorter to be used in quantum optics to address trapped-ions, atoms, or color center experiments. The lithium niobate on insulator (LNOI) platform seems ideal to achieve single-mode operation down to the visible range due to the high transparency of the material (down to 330 nm wavelength [Reig Escalé et al., APL Photonics 5, 121301, 2020]) and its availability as thin films (from 300 to 700 nm). Besides the fabrication challenge, the photorefractive damage becomes a limiting factor at shorter wavelengths that we will study on the LNOI platform, especially at >10 mW optical powers. Preliminary work carried out at ETH Zurich with Mach-Zehnder EOM at 780 nm shows that the voltage-length product is <1.8 V·cm, in contrast to standard LNOI EOM at 1550 nm with >2.2 V·cm due to the accumulated phase-shift at longer wavelengths. In terms of optical response, the optical extinction ratio of the 780 nm-EOM can be maximized by optimizing the splitting of the waveguides. We will explore Y-splitters and multimode interferometric (MMI) couplers at 780 nm and below. Besides ions trapping, pulse generation and picking applications may benefit from developments and advances in this area.
