High repetition rate fiber and integrated waveguide femtosecond lasers

Abstract

Femtosecond lasers and the development of frequency combs have revolutionized multiple fields like metrology, spectroscopy, medical diagnostics and optical communications. However, to enable wider adoption of the technology and new applications like photonic sampling, optical arbitrary waveform generation or the calibration of astronomical spectrographs, multi-GHz repetition rate femtosecond lasers with robust performance metrics, low cost, and a compact footprint are highly desirable. In this thesis, different approaches to develop GHz mode-locked laser systems at telecommunication wavelengths are discussed and current achievements presented. Design aspects for constructing a long-term stable and compact fiber laser with 187 fs short pulses at a repetition rate of 1 GHz are covered. In order to scale the repetition rate into the multi- GHz regime, coherent pulse interleaving in novel thermally tunable waveguide interleavers is demonstrated at 10 GHz. A femtosecond erbium-doped waveguide laser is developed at GHz repetition rates and important design guidelines are provided. As saturable Bragg reflectors are crucial in all of the described systems to enable mode-locking, saturable absorber optimization is discussed and their optical performance compared. Thus, this research paves the way for compact, affordable high repetition rate fiber lasers and monolithically integrated femtosecond laser sources which can be combined on-chip with additional functionalities to develop novel photonic systems with impact on spectroscopy, sensing, telecommunications and biomedical applications.