Eckhaus Instability in Laser Cavities with Harmonically Swept Filters

Feng Li, Dongmei Huang*, K. Nakkeeran, J. Nathan Kutz, Jinhui Yuan, Alex Wai

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

6 Citations (Scopus)


In this paper, we report the existence of Eckhaus instability in laser cavities with harmonically swept filters, of which Fourier Domain Mode Locked (FDML) laser is an important example. We show that such laser cavities can be modeled by a real Ginzburg Landau equation with a frequency shifting term arisen from the cavity dispersion. We analytically derived a solution of the governing equation and analyzed its stability. We found that the cavity dispersion introduces a continuous frequency shift to the laser signal such that it will be eventually pushed outside the stable region and trigger the Eckhaus instability. We show that the repeated triggering of the Eckhaus instability in the laser cavities is the dominant effect that leads to the high frequency fluctuations in FDML laser output, which is the unique feature of such laser cavities and intrinsically limits the signal quality of the FDML lasers with nonzero cavity dispersion.

Original languageEnglish
Pages (from-to)6531-6538
Number of pages8
JournalJournal of Lightwave Technology
Issue number20
Early online date11 Aug 2021
Publication statusPublished - 15 Oct 2021

Scopus Subject Areas

  • Atomic and Molecular Physics, and Optics

User-Defined Keywords

  • Eckhaus instability
  • real Ginzburg Landau equation
  • swept laser
  • Fourier domain mode locking


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