Jieun Yim

Spatiotemporal modulation approaches have been often employed as alternatives for producing optical nonreciprocity without magneto‐optic materials. Unidirectional inter‐modal scattering, enabled by either acousto‐optic or electro‐optic (EO) modulation, is a promising method in this category as it can directly modify optical dispersions and even enables linear nonreciprocal photonic devices in the strong coupling limit. Although EO approaches are often preferred for their practicality, it is challenging to generate the large spatiotemporal momentum required for inter‐modal phase matching without EO drive schemes involving multiple drive stimuli. Here, we demonstrate highly selective nonreciprocal inter‐modal EO scattering enabled by a single high‐index radiofrequency (RF) traveling wave stimulus. Our experimental demonstration is performed on a thin‐film lithium niobate‐integrated photonics platform in which we engineer a slow‐wave radiofrequency (SWRF) transmission line with an effective RF index that natively generates the required RF momentum while simultaneously maintaining strong RF‐optical mode overlap. By additionally engineering the interaction length, we achieve a directional dB nonreciprocal scattering contrast. The SWRF architecture provides a scalable route to magnetic‐free nonreciprocity and establishes momentum‐engineered RF waves as a powerful tool for next‐generation, fully integrated nonreciprocal photonic systems.

In the quest for manipulating sound propagation, innovative approaches in acoustics, inspired by quantum phenomena, have yielded remarkable functionalities. Despite these advances in acoustics, the potential of supersymmetry, a powerful tool for shaping a system's Hamiltonian, remains untapped. In this Letter, we demonstrate the application of supersymmetric transformations in acoustics through the creation of supersymmetric isophase acoustic potentials. Our theoretical exploration centers on isospectral supersymmetric transformations within an acoustic wave equation framework, enabling the generation of isophase acoustic potentials that preserve both transmission and reflection characteristics. Experimentally, we have developed a reconfigurable acoustic metamaterial platform to validate isophase scattering characteristics facilitated by the principles of supersymmetry. This design strategy offers a general method to create a family of continuously variable acoustic structures that remain indistinguishable under broadband acoustic wave probing, holding great promise for the future of sonar technology.

Asymmetric energy exchange interactions, also known as Hatano-Nelson type couplings, enable the study of non-Hermitian physics and associated phenomena like the non-Hermitian skin effect and exceptional points (EPs). Since these interactions are by definition nonreciprocal, there have been very few options for implementations in integrated photonics. In this work, we show that asymmetric couplings are readily achievable in integrated photonic systems through time-domain dynamic modulation. We experimentally study this concept using a two-resonator photonic molecule produced in a lithium niobate on insulator platform that is electro-optically modulated by rf stimuli. We demonstrate the dynamic tuning of the Hatano-Nelson coupling between the resonators, surpassing the asymmetry that has been achieved in previous work, to reach an EP for the first time. We are additionally able to flip the relative sign of the couplings for opposite directions by going past the EP. Using this capability, we show that the through-chain transport can be configured to exhibit both giant (∼60 dB) optical contrast as well as photonic gyration or nonreciprocal π phase contrast.

To achieve single fundamental supermode operation in coupled arrays, a two-dimensional supersymmetry formalism for mode control is developed and experimentally demonstrated with microring laser arrays.

Supersymmetric switch-on: A common route to enhancing the output light from a laser system is to couple multiple lasers to form an array. However, crosstalk and interference between different modes of the individual lasers are generally detrimental to performance, leading to instabilities, and could ultimately be damaging to the laser cavities. Qiao et al. worked with the mathematical framework of supersymmetry, a theory developed in high-energy physics to attempt to describe the makeup and properties of particles, to design a stable two-dimensional laser array. Based on symmetry arguments, the method is scalable and could prove to be a practical platform with which to design and develop complex photonic systems. Science , this issue p. 403