Rayleigh scattering in an optical nanofiber as a probe of higher-order mode propagation

TL;DR

This paper demonstrates a nondestructive optical method using Rayleigh scattering to visualize and analyze higher-order mode propagation in optical nanofibers, enabling precise control and measurement of modal content and fiber geometry.

Contribution

It introduces a rapid, in situ optical diagnostic technique for visualizing and controlling higher-order modes in nanofibers through Rayleigh scattering imaging.

Findings

Visualized mode propagation and interference in nanofibers

Measured fiber waist variations below 3 nm

Controlled modal superposition via input adjustments

Abstract

Optical nanofibers provide a rich platform for exploring atomic and optical phenomena even when they support only a single spatial mode. Nanofibers supporting higher-order modes provide additional degrees of freedom to enable complex evanescent field profiles for interaction with the surrounding medium, but local control of these profiles requires nondestructive evaluation of the propagating fields. Here, we use Rayleigh scattering for rapid measurement of the propagation of light in few-mode optical nanofibers. Imaging the Rayleigh scattered light provides direct visualization of the spatial evolution of propagating fields throughout the entire fiber, including the transition from core-cladding guidance to cladding-air guidance. We resolve the interference between higher-order modes to determine local beat lengths and modal content along the fiber, and show that the modal superposition in the waist can be systematically controlled by adjusting the input superposition. With this diagnostic we can measure variations in the radius of the fiber waist to below 3 nm in situ using purely optical means. This nondestructive technique also provides useful insight into light propagation in optical nanofibers.