Non-Hermitian Synthetic Phase Shifter: Topologically-Protected Phase Control via Tunable Losses

TL;DR

This paper introduces a novel loss-based synthetic phase shifter in photonics, leveraging non-Hermitian topological effects for robust, scalable phase control without changing the light amplitude.

Contribution

It presents a new approach to phase control using loss modulation and topological principles, enabling full-cycle phase tuning with constant amplitude.

Findings

Achieved full-cycle phase tunability with constant amplitude using loss modulation.

Developed a topological framework for robust phase control in photonics.

Demonstrated potential for scalable integrated photonic systems.

Abstract

Phase shifters are fundamental reconfigurable components in photonic circuits. In conjunction with passive elements, they control light flow and serve as foundational building blocks for diverse applications, including communication, sensing, analog signal processing, and quantum control. Conventional phase shifters achieve phase control by modulating the refractive index through various physical mechanisms such as thermo-optic or electro-optic effects. However, despite expectations that such index-based approaches would integrate seamlessly, they, in practice, restrict circuit size, bandwidth, and scalability and thus become bottlenecks to large-scale photonic integration. Here, we introduce an alternative phase-control approach based on optical loss modulation. We demonstrate a synthetic phase shifter that uses two independently controlled loss-modulation stages combined with multipath interference to achieve full-cycle phase tunability while maintaining constant amplitude. We develop a theoretical framework based on conserved topological charges to demonstrate how synthetic phase control can be achieved via non-Hermitian effects, enabling robust topologically-protected phase control. By shifting the paradigm from index control to loss modulation, the proposed synthetic phase shifter could pave the way for scalable integrated photonic systems that support applications from communications and sensing to photonic classical and quantum information processing.