Photonic modal circulator using temporal refractive-index modulation with spatial inversion symmetry

TL;DR

This paper introduces a simplified on-chip photonic modal circulator that achieves amplitude non-reciprocity using a single standing-wave modulator, preserving mirror symmetry and minimizing the number of modes involved.

Contribution

It demonstrates a novel modal circulator design that maintains spatial symmetry and requires only a single modulator, simplifying non-reciprocal photonic device implementation.

Findings

Achieves amplitude non-reciprocity through mode circulation.

Can be implemented with a single standing-wave modulator.

Represents the minimal mode configuration for symmetric non-reciprocal transport.

Abstract

It has been demonstrated that dynamic refractive index modulation, which breaks time-reversal symmetry, can be used to create on-chip non-reciprocal photonic devices. In order to achieve amplitude non-reciprocity, all such devices moreover require modulations that break spatial symmetries, which adds complexity in implementations. Here we introduce a modal circulator, which achieves amplitude non-reciprocity through a circulation motion among three modes. We show that such a circulator can be achieved in a dynamically-modulated structure that preserves mirror symmetry, and as a result can be implemented using only a single standing-wave modulator, which significantly simplifies the implementation of dynamically-modulated non-reciprocal device. We also prove that in terms of the number of modes involved in the transport process, the modal circulator represents the minimum configuration in which complete amplitude non-reciprocity can be achieved while preserving spatial symmetry.