Mirror symmetric on-chip frequency circulation of light

TL;DR

This paper presents a mirror symmetric on-chip optical circulator using coupled resonators and RF modulation, achieving high isolation without magnetic materials, simplifying fabrication for integrated photonic systems.

Contribution

It introduces a mirror symmetric nonreciprocal device based on coupled lithium niobate resonators, enabling circulation without symmetry breaking or magnetic materials.

Findings

Nearly 40 dB of isolation achieved

Demonstrated nonreciprocal mode conversion and circulation

Operates with approximately 75 mW RF power near 1550 nm

Abstract

Integrated circulators and isolators are important for developing on-chip optical technologies, such as laser cavities, communication systems, and quantum information processors. These devices appear to inherently require mirror symmetry breaking to separate backwards from forwards propagation, so existing implementations rely upon magnetic materials, or interactions driven by propagating waves. In contrast to previous work, we demonstrate a mirror symmetric nonreciprocal device. Our device comprises three coupled photonic resonators implemented in thin-film lithium niobate. Applying radio frequency modulation, we drive conversion between the frequency eigenmodes of this system. We measure nearly 40 dB of isolation for approximately 75 mW of RF power near 1550 nm. We simultaneously generate nonreciprocal conversion between all of the eigenmodes in order to demonstrate circulation. Mirror symmetric circulation significantly simplifies the fabrication and operation of nonreciprocal integrated devices. Finally, we consider applications of such on-chip isolators and circulators, such as full-duplex isolation within a single waveguide.