Reduction of differential modal gain in a two-mode amplifier using a void-inscribed EDF

Area of Science:

• Optical Fiber Technology
• Laser-Induced Material Modification
• Photonics and Waveguide Devices

Background:

• Differential modal gain (DMG) in two-mode erbium-doped fibers (2M-EDFs) is a critical parameter affecting optical amplifier performance.
• Managing DMG is essential for achieving high-quality signal amplification in advanced fiber systems.

Purpose of the Study:

• To propose and demonstrate a novel technique for reducing DMG in 2M-EDFs.
• To investigate the impact of femtosecond laser-inscribed voids on modal gain and loss characteristics.
• To optimize void parameters for effective DMG control and acceptable gain/noise performance.

Main Methods:

• Inscribing voids at the core center of a 2M-EDF using a femtosecond laser.
• Selectively attenuating the linearly polarized (LP01) mode while minimizing loss for the LP11 mode.
• Investigating the influence of void diameter and longitudinal position on DMG, gain, and noise figure (NF).

Main Results:

• Demonstrated selective attenuation of the LP01 mode by an empty core-center void.
• Showcased DMG control through precise adjustment of void diameter.
• Achieved a sufficiently low DMG (< 0.5 dB) across the full C-band.
• Confirmed acceptable gain and noise figure characteristics.

Conclusions:

• Femtosecond laser-inscribed core voids offer an effective method for reducing DMG in 2M-EDFs.
• Void diameter is a key parameter for controlling DMG.
• The proposed technique enables low-loss, high-performance 2M-EDF amplifiers.