PhD defence by Jakob Milo Hauge

Title: Coherence-induced instabilities in single-frequency fiber amplifiers

Supervisors:
Principal supervisor: Associate Professor, Jesper Lægsgaard, DTU Electro
Co-supervisor: R&D Manager Jens Engholm Pedersen, NKT Photonics, Denmark
Co-supervisor: Research Engineer Magalie Bondu, NKT Photonics, Denmark

Evaluation Board:
Professor Ole Bang, DTU Electro
Examiner: Associate Professor, Morten Ibsen, University of Southampton, UK
Examiner: Jan Hald, Danmarks Nationale Metrologiinstitut, Denmark

Master of the Ceremony:
Professor Peter Uhd Jepsen, DTU Electro

Abstract:
In the last couple of decades, fiber lasers and amplifiers have been applied within a wide range of fields in both academia and industry due to several properties that enable the generation of a high-power light beam of excellent quality. The demand for ever higher performance continues to drive the development of this technology. A sub-class of fiber lasers called single-frequency fiber lasers (SFFLs) have an extremely well-defined wavelength, which make them attractive for applications where ultra-low noise properties are required. A potential limitation to power scaling for SFFL systems is a power instability induced when the light frequency-modulated as required for some applications. The instability is detrimental for the system performance and can ultimately lead to component damage and system failure.

The purpose of the research carried out in this PhD project is to gain an understanding of this instability. This should benefit future work on mitigation strategies. The instability was characterized experimentally, and some of the observed features were used to inform the development of a theoretical model that provides a simplified description of the underlying physics. It was shown that the model could explain most of the features observed experimentally.