Optical Isolation Can Occur in Linear and Passive Silicon Photonic Structures

TL;DR

This paper demonstrates that optical isolation can occur in linear and passive silicon photonic structures due to modal conversion and information dissipation, challenging the notion that nonreciprocity requires nonlinearity or magnetism.

Contribution

It provides a detailed analysis showing that effective optical isolation is achievable in linear, passive silicon photonic structures without violating reciprocity principles.

Findings

Round-trip reflectivity is much smaller than forward transmissivity.

Optical isolation arises from modal conversion and information dissipation.

No conflict with reciprocal principle in observed isolation.

Abstract

On-chip optical isolators play a key role in optical communications and computing based on silicon integrated photonic structures. Recently there have raised great attentions and hot controversies upon isolation of light via linear and passive photonic structures. Here we analyze the optical isolation properties of a silicon photonic crystal slab heterojunction diode by comparing the forward transmissivity and round-trip reflectivity of in-plane infrared light across the structure. The round-trip reflectivity is much smaller than the forward transmissivity, justifying good isolation. The considerable effective nonreciprocal transport of in-plane signal light in the linear and passive silicon optical diode is attributed to the information dissipation and selective modal conversion in the multiple-channel structure and has no conflict with reciprocal principle.