Modal noise prediction in fibre-spectroscopy I: Visibility and the coherent model

TL;DR

This paper develops a predictive model for fibre modal noise in high-resolution spectrographs, linking noise visibility to measurable parameters to improve instrument performance.

Contribution

It introduces a coherent model that relates modal noise visibility to experimental data, enabling accurate noise prediction in fibre-spectrograph systems.

Findings

Modal noise can be predicted by measuring pattern visibility.

Visibility depends on key system parameters.

The model aligns theory with experimental results.

Abstract

Fibre modal noise occurs in high spectral resolution, high signal-to-noise applications. It imposes fundamental limits on the photometric accuracy of state-of-the-art fibre-spectrograph systems. In order to maximize the performance of current and future instruments it is therefore essential to predict fibre modal noise. To attain a predictive model we are using a dual approach, bringing theoretical assumptions in line with the experimental data obtained using a test-bench spectrograph. We show that the task of noise prediction can be reduced to determining the visibility of the modal pattern which can be measured at the detector plane. Subsequently, the visibility-dependence of essential parameters is presented. This work will soon provide a basis for prediction of modal noise limitations in fibre-coupled spectrograph designs.