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.

Automated summary

Efficient and tunable electro-optic frequency shifters controlled by continuous and single-tone microwaves are achieved through engineering the coupling between optical modes in ultralow-loss waveguides and resonators in lithium niobate nanophotonics. The devices provide high frequency shifts up to 28 gigahertz with an on-chip conversion efficiency of approximately 90%, and can be reconfigured as tunable frequency-domain beam splitters.