Wavelength-switchable ultra-narrow linewidth fiber laser enabled by a figure-8 compound-ring-cavity filter and a polarization-managed four-channel filter

TL;DR

This paper presents a novel four-wavelength fiber laser with ultra-narrow linewidth, tunable wavelength spacing, and stable single- and dual-wavelength operations enabled by a figure-8 compound-ring-cavity filter and polarization-managed filters.

Contribution

The work introduces a new fiber laser design combining a figure-8 compound-ring-cavity filter with polarization-managed filters, achieving high stability and tunability in multi-wavelength lasing.

Findings

Achieved stable single-wavelength lasing with linewidth <600 Hz.

Demonstrated dual-wavelength lasing with tunable spacing up to 23.10 GHz.

Realized fifteen lasing states including single, dual, triple, and quadruple wavelengths.

Abstract

We propose and demonstrate a high performance four-wavelength erbium-doped fiber laser (EDFL), enabled by a figure-8 compound-ring-cavity (F8-CRC) filter for single-longitudinal-mode (SLM) selection and a polarization-managed four-channel filter (PM-FCF) for defining four lasing wavelengths. We introduce a novel methodology utilizing signal-flow graph combined with Mason's rule to analyze a CRC filter in general and apply it to obtain the important design parameters for the F8-CRC filter used in this paper. By combining the functions of the F8-CRC filter and the PM-FCF filter assisted by the enhanced polarization hole-burning and polarization dependent loss, we achieve the EDFL with fifteen lasing states, including four single-, six dual-, four tri- and one quad-wavelength lasing operations. In particular, all the four single-wavelength operations are in stable SLM oscillation, typically with a linewidth of <600 Hz, a RIN of <=-154.58 dB/Hz@>=3 MHz and an output power fluctuation of <=+/-3.45%. In addition, all the six dual-wavelength operations have very similar performances, with the performance parameters close to those of the single-wavelength lasing operations. Finally, we achieve the wavelength spacing tuning of the dual-wavelength operations for the photonic generation of tunable microwave signals, and successfully obtain a signal at 23.10 GHz as a demonstration.