Narrow linewidth single-longitudinal-mode vortex fiber laser with switchable orbital angular momentum output.

Area of Science:

• Photonics
• Fiber Lasers
• Optical Engineering

Background:

• Single-longitudinal-mode (SLM) vortex fiber lasers offer dual-dimensional control over spectral and spatial properties.
• This spectral-spatial synergy is crucial for advanced photonic systems.

Purpose of the Study:

• To report a simple method for generating switchable orbital angular momentum (OAM) beams.
• To achieve narrow linewidth SLM lasing with tunable wavelengths and high OAM purity.

Main Methods:

• Incorporated a tunable bandpass filter, subring, and unpumped erbium-doped fiber into the laser cavity.
• Utilized a few-mode fiber Bragg grating (FBG) for selective transverse mode reflection.
• Tuned operating wavelength and adjusted polarization controllers for OAM switching.

Main Results:

• Achieved stable SLM lasing with Lorentz linewidths below 1.4 kHz and tunable wavelengths.
• Successfully generated switchable vortex modes with OAM values of 0, ±1ℏ, and ±2ℏ per photon.
• Demonstrated high purity of output OAM modes due to the self-coupling regime in the few-mode FBG and stable SLM lasing.

Conclusions:

• The proposed method provides a simple and effective way to generate switchable OAM beams from narrow linewidth SLM vortex fiber lasers.
• The combination of SLM lasing and few-mode FBG enables precise control and high purity of OAM modes.
• This work enhances the application potential of vortex fiber lasers in advanced photonic systems.