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Stable four-wavelength switchable ultra-narrow linewidth thulium-holmium co-doped fiber laser by self-injection
Optics Express
|March 18, 2026
Summary
This study presents a novel four-wavelength switchable fiber laser with an ultra-narrow linewidth, ideal for optical communication and sensing. Self-injection locking significantly reduces linewidth to sub-kHz levels for enhanced performance.
Area of Science:
- Photonics and Laser Technology
- Optical Engineering
- Materials Science
Background:
- Demand for multi-wavelength, ultra-narrow linewidth laser sources is increasing for applications like high-speed coherent optical communication and high-precision sensing.
- Existing laser technologies face challenges in achieving stable, switchable, and narrow-linewidth operation in the 2 µm band.
Purpose of the Study:
- To propose and experimentally demonstrate a stabilized four-wavelength switchable ultra-narrow linewidth thulium-holmium co-doped fiber laser.
- To achieve wavelength switching and linewidth reduction using self-injection locking (SIL) and nonlinear polarization rotation.
Main Methods:
- Utilized superimposed polarization-maintaining fiber Bragg gratings for wavelength selection.
- Incorporated a triple-coupler quadruple-ring compound cavity filter for single-longitudinal-mode operation.
- Employed nonlinear polarization rotation for intracavity loss control and wavelength switching, coupled with SIL feedback via a 100 m delay fiber.
Main Results:
- Successfully demonstrated stable switching among four wavelengths (1940.20, 1940.60, 1941.86, 1942.31 nm).
- Achieved an optical signal-to-noise ratio exceeding 72.91 dB for all wavelengths.
- Reduced linewidth from ~7 kHz to sub-kHz levels (optimal 0.21 kHz) via SIL, with relative intensity noise below -135.35 dB/Hz.
- Demonstrated excellent stability with <0.007 nm wavelength drift and <0.27 dB peak power fluctuation over 60 minutes.
Conclusions:
- The developed thulium-holmium co-doped fiber laser offers a high-performance, multi-wavelength switchable, narrow-linewidth light source in the 2 µm band.
- The integration of SIL and nonlinear polarization rotation provides an effective method for achieving desired laser characteristics.
- This laser technology holds significant potential for advancing optical communication and precision sensing applications.
