Silica distributed-feedback fiber laser beyond 2.1 µm

Area of Science:

• Optics and Photonics
• Fiber Lasers
• Laser Spectroscopy

Background:

• High-performance lasers operating in the 2.1-2.2 µm atmospheric window are crucial for remote sensing.
• Applications in biological sciences require lasers for detecting C-H bond signatures.
• Silica-based distributed feedback (DFB) fiber lasers have not previously operated beyond 2.1 µm.

Purpose of the Study:

• To report the first silica-based DFB fiber laser operating beyond 2.1 µm.
• To demonstrate a gain-switched nanosecond pulsed laser output at 2112 nm.
• To characterize the laser's performance, including wavelength, power, efficiency, and polarization.

Main Methods:

• Fabrication of an ultra-short cavity DFB fiber Bragg gratings (FBGs) in a thulium-doped fiber (TDF) using femtosecond laser inscription.
• Utilizing a 1.55 µm nanosecond-pulsed fiber laser as the pump source with an inband resonant pumping scheme.
• Confirmation of single longitudinal mode operation using a scanning Fabry-Perot interferometer (SFPI).

Main Results:

• Achieved a laser output at 2112 nm, the longest wavelength reported for a silica-based DFB fiber laser.
• Obtained a maximum average power of 22.5 mW and a slope efficiency of 4.2% at an absorbed pump power of 650 mW.
• Measured a polarization extinction ratio (PER) of >18 dB from the non-PM-TDF-based DFB laser.
• Deduced pulse energy of 450 nJ and peak power of 29.5 W with a pulse width of 15.2 ns.

Conclusions:

• The developed silica-based DFB fiber laser successfully operates beyond 2.1 µm, marking a significant advancement.
• The laser exhibits single longitudinal mode operation and good polarization characteristics.
• Future work suggests potential for higher peak power (>100 W) and shorter pulse durations (<20 ns) with optimized pumping and FBGs.