Measuring Thermal Load in Fiber Amplifiers in the Presence of Transversal Mode Instabilities

TL;DR

This paper presents in-situ temperature measurements and simulations to analyze thermal load and mode instability thresholds in high power fiber amplifiers, showing photodarkening's negligible impact.

Contribution

It provides the first detailed in-situ thermal load measurements in a high power fiber amplifier and compares them with simulations to assess factors affecting TMI thresholds.

Findings

Thermal load measurements match simulations closely.

Photodarkening has negligible impact on TMI threshold.

Thermal load varies with seed wavelength.

Abstract

We report on detailed in-situ distributed temperature measurements inside a high power fiber amplifier. The deducted thermal load and the TMI-threshold of a commercial LMA fiber with 25 micron core and 400 micron cladding was measured at various seed wavelengths. By matching these results with detailed simulations we show that photodarkening has a negligible impact on the thermal load and, therefore, on the TMI threshold in this fiber.