On-chip electro-optic frequency shifters and beam splitters

Efficient frequency shifting and beam splitting are important for a wide range of applications, including atomic physics 1 , 2 , microwave photonics 3 – 6 , optical communication 7 , 8 and photonic quantum computing 9 – 14 . However, realizing gigahertz-scale frequency shifts with high efficiency, low loss and tunability—in particular using a miniature and scalable device—is challenging because it requires efficient and controllable nonlinear processes. Existing approaches based on acousto-optics 6 , 15 – 17 , all-optical wave mixing 10 , 13 , 18 – 22 and electro-optics 23 – 27 are either limited to low efficiencies or frequencies, or are bulky. Furthermore, most approaches are not bi-directional, which renders them unsuitable for frequency beam splitters. Here we demonstrate electro-optic frequency shifters that are controlled using only continuous and single-tone microwaves. This is accomplished by engineering the density of states of, and coupling between, optical modes in ultralow-loss waveguides and resonators in lithium niobate nanophotonics 28 . Our devices, consisting of two coupled ring-resonators, provide frequency shifts as high as 28 gigahertz with an on-chip conversion efficiency of approximately 90 per cent. Importantly, the devices can be reconfigured as tunable frequency-domain beam splitters. We also demonstrate a non-blocking and efficient swap of information between two frequency channels with one of the devices. Finally, we propose and demonstrate a scheme for cascaded frequency shifting that allows shifts of 119.2 gigahertz using a 29.8 gigahertz continuous and single-tone microwave signal. Our devices could become building blocks for future high-speed and large-scale classical information processors 7 , 29 as well as emerging frequency-domain photonic quantum computers 9 , 11 , 14 . Engineering of the coupling between optical modes in a lithium niobate chip enables the realization of tunable, bi-directional and low-loss electro-optic frequency shifters controlled using only continuous and single-tone microwaves.