Opto-Mechanical Interactions in Multi-Core Optical Fibers and Their Applications

TL;DR

This paper explores how acoustic waves in multi-core optical fibers cause cross-phase modulation between cores, enabling new applications like opto-electronic oscillators and liquid sensing outside the fiber cladding.

Contribution

It reveals the mechanism of opto-mechanical coupling in multi-core fibers and demonstrates novel applications leveraging this effect.

Findings

Acoustic modes induce inter-core cross-phase modulation.

Resonance peaks can be narrow or quasi-continuous.

Effect magnitude is comparable to Kerr nonlinearity.

Abstract

Optical fibers containing multiple cores are being developed towards capacity enhancement in space-division multiplexed optical communication networks. In many cases, the fibers are designed for negligible direct coupling of optical power among the cores. The cores remain, however, embedded in a single, mechanically-unified cladding. Elastic (or acoustic) modes supported by the fiber cladding geometry are in overlap with multiple cores. Acoustic waves may be stimulated by light in any core through electrostriction. Once excited, the acoustic waves may induce photo-elastic perturbations to optical waves in other cores as well. Such opto-mechanical coupling gives rise to inter-core cross-phase modulation effects, even when direct optical crosstalk is very weak. The cross-phase modulation spectrum reaches hundreds of megahertz frequencies. It may consist of discrete and narrow peaks, or may become quasi-continuous, depending on the geometric layout. The magnitude of the effect at the resonance frequencies is comparable with that of intra-core cross-phase modulation due to Kerr nonlinearity. Two potential applications are demonstrated: single-frequency opto-electronic oscillators that do not require radio-frequency electrical filters, and point-sensing of liquids outside the cladding of multi-core fibers, where light cannot reach.