Beating of two FDML lasers in real time

Christin Grill, Simon Lotz, Torben Blömker, Dominic Kastner, Tom Pfeiffer, Sebastian Karpf, Mark Schmidt, Wolfgang Draxinger, Christian Jirauschek, Robert Huber


Fourier domain mode locking (FDML) is a recently developed technique for lasers to generate ultra-rapid wavelength sweeps, equivalent to a train of extremely chirped pulses. FDML lasers are the light sources of choice for fastest megahertz optical coherence tomography (MHz-OCT). Measuring the coherence properties of FDML lasers is of particular importance for the image quality in OCT but it is also crucial to develop a better understanding of this unconventional mode locking mechanism. Usually, experiments to analyze the phase stability of FDML lasers use interferometers to generate interference of a single laser by delaying a part of the output to generate a beat signal. Here, for the first time, we present real time beat signal measurements between two independent FDML lasers over the entire sweep range of ∼5 THz width for more than 80 roundtrips (∼200 μs), evaluate their phase stability and explain the consequence for our understanding of the FDML mechanism. Beat signal measurements allow direct access to the phase difference between the FDML lasers and therefore the difference in timing of the circulating sweeps as well as their instantaneous frequency.

Original languageEnglish
Title of host publicationFiber Lasers XVII: Technology and Systems
EditorsLiang Dong
Number of pages7
Publication date21.02.2020
Article number1126014
ISBN (Print)978-151063283-7
Publication statusPublished - 21.02.2020
EventFiber Lasers XVII: Technology and Systems 2020 - San Francisco, United States
Duration: 03.02.202006.02.2020
Conference number: 159211

Research Areas and Centers

  • Academic Focus: Biomedical Engineering

DFG Research Classification Scheme

  • 205-32 Medical Physics, Biomedical Engineering


Dive into the research topics of 'Beating of two FDML lasers in real time'. Together they form a unique fingerprint.

Cite this