Characterizing octagonal and rectangular fibers for MAROON-X

TL;DR

This paper evaluates the scrambling performance and focal-ratio-degradation of various octagonal and rectangular fibers for MAROON-X, highlighting the impact of cladding thickness and stress, and introducing a new metric for non-linear scrambling performance.

Contribution

It introduces a new metric for assessing non-linear scrambling in non-circular fibers and provides detailed analysis of how cladding and stress affect fiber performance.

Findings

Thick, round cladding reduces FRD in fibers.

Stress at connectors increases FRD.

Non-circular fibers exhibit complex scrambling behavior.

Abstract

We report on the scrambling performance and focal-ratio-degradation (FRD) of various octagonal and rectangular fibers considered for MAROON-X. Our measurements demonstrate the detrimental effect of thin claddings on the FRD of octagonal and rectangular fibers and that stress induced at the connectors can further increase the FRD. We find that fibers with a thick, round cladding show low FRD. We further demonstrate that the scrambling behavior of non-circular fibers is often complex and introduce a new metric to fully capture non-linear scrambling performance, leading to much lower scrambling gain values than are typically reported in the literature (<1000 compared to 10,000 or more). We find that scrambling gain measurements for small-core, non-circular fibers are often speckle dominated if the fiber is not agitated.