Studying focal ratio degradation of optical fibers for Subaru Prime Focus Spectrograph

TL;DR

This paper presents a precise measurement system for focal ratio degradation (FRD) in optical fibers, crucial for optimizing spectrograph performance in the Subaru Prime Focus Spectrograph project.

Contribution

It introduces a new metrology system for accurate FRD measurement and provides detailed fiber characterization for the Subaru PFS project.

Findings

FRD measurements for specific fibers show low and similar degradation levels

The system accurately measures fiber throughput and angular distribution changes

Fiber characteristics are essential for spectrograph design optimization

Abstract

Focal Ration Degradation (FRD) is a change in light angular distribution caused by fiber optics. FRD is important to fiber-fed, spectroscopic astronomical systems because it can cause loss of signal, degradation in spectral resolution, or increased complexity in spectrograph design. Laborat\'orio Nacional de Astrof\'isica (LNA) has developed a system that can accurately and precisely measures FRD, using an absolute method that can also measure fiber throughput. This paper describes the metrology system and shows measurements of Polymicro fiber FBP129168190, FBP127165190 and Fujikura fiber 128170190. Although the FRD of the two fibers are low and similar to one another, it is very important to know the exact characteristics of these fibers since both will be used in the construction of FOCCoS (Fiber Optical Cable and Connectors System) for PFS (Prime Focus Spectrograph) to be installed at the Subaru telescope.