Traceable instruments for encircled angular flux measurements

TL;DR

This paper presents the development and validation of two traceable instruments for measuring Encircled Angular Flux (EAF) using optical fiber outputs, achieving high accuracy and establishing measurement traceability.

Contribution

It introduces two independent EAF measurement instruments based on far-field intensity analysis and validates their accuracy and traceability through inter-comparisons.

Findings

Achieved measurement uncertainty at the 10^-3 level.

Demonstrated excellent agreement between two independent systems.

Validated traceability of EAF measurements.

Abstract

We report on the development of an instrument for the measurement of the Encircled Angular Flux (EAF) and on establishing its metrological traceability at the required level of uncertainty. We designed and built for that purpose two independent EAF measuring instruments, both based on the analysis of the two-dimensional far field intensity profile observed at the output of an optical fibre, using either CMOS or CCD cameras. An in depth evaluation of the factors influencing the accuracy of the measurements was performed and allowed determining an uncertainty budget for EAF measurements, which was validated by a first series of inter-comparisons. Theses comparisons were performed between the two independent EAF measuring systems, using a 850 nm LED coupled into a gradient index fibre as a test object. We demonstrated a very good equivalence between the two systems, well within the absolute measurement uncertainties that were estimated at the 10-3 level. Further inter-comparisons using light sources coupled to step-index, large core and small core multimode fibres are still ongoing, with the aim to confirm the performances of the instrument under various illuminating conditions.