Comparison of round- and square-core fibers for sensing, imaging and spectroscopy

TL;DR

This paper compares square-core and round-core multimode fibers, showing that square-core fibers reduce focus aberrations and provide more uniform output, enhancing their potential for sensing, imaging, and spectroscopy.

Contribution

It introduces the use of square-core fibers for wavefront shaping, demonstrating advantages over traditional round-core fibers in focus quality and output uniformity.

Findings

Square-core fibers do not suffer from focus aberrations unlike round-core fibers.

Output intensity distribution in square-core fibers is more uniform and less correlated with input.

Interference pattern decorrelation in square-core fibers is largely independent of input frequency.

Abstract

Multimode fibers (MMFs) show great promise as miniature probes for sensing, imaging and spectroscopy applications. Different parameters of the fibers, such as numerical aperture, refractive index profile and length, have been already optimized for better performance. Here we investigate the role of the core shape, in particular for wavefront shaping applications where a focus is formed at the output of the MMF. We demonstrate that in contrast to a conventional round-core MMF, a square-core design doesn't suffer from focus aberrations. Moreover, we find that how the interference pattern behind a square-core fiber decorrelates with the input frequency is largely independent of the input light coupling. Finally, we demonstrate that a square core shape provides an on-average uniform distribution of the output intensity, free from the input-output correlations seen in round fibers, showing great promise for imaging and spectroscopy applications.