Background
Spectrally pure microwaves are essential for many applications ranging from wireless communication to radar, clocks, and high-speed electronics. Soliton microcombs—phase-locked Kerr frequency combs produced on a monolithic chip—have recently come to light as a promising technique for synthesizing microwaves owing to their exceptional coherence properties. However, since the fixed physical size of the monolithic comb resonator fundamentally determines its repetition rate, development of these soliton microcombs tuned to microwave frequencies must rely on off-chip laser modulation that is relatively slow or off-chip comb modulation whose efficiency is fairly limited.
Technology Overview
We have demonstrated the first microwave-rate soliton microcomb whose repetition rate can be tuned at a high speed. By integrating electro-optic tuning/modulation elements directly into the lithium niobate comb microresonator, we are able to achieve a frequency modulation speed of up to 75 MHz, orders of magnitude faster than other soliton comb devices reported to date, as well as a frequency modulation rate faster than state-of-the-art electronic microwave frequency modulation technology.
Benefits
Soliton microcombs as devices exhibit superior coherence compared with alternative microwave production techniques such as optoelectronic oscillators, dual frequency lasers, Brillouin lasers, etc. Our device additionally offers a significant bandwidth of up to tens of gigahertz for locking of the repetition rate to an external microwave reference, enabling both direct injection locking and feedback locking to the comb resonator itself without involving external modulation. Consequently, the demonstrated fully integrated electro-optically reconfigurable soliton microcomb opens up an avenue toward high-speed dynamic control and processing of microwaves.
Applications
Microwave photonics