Low loss side-polished pumping coupler for high order OAM modes amplification

Area of Science:

• Optical Engineering
• Telecommunications
• Photonics

Background:

• Orbital Angular Momentum (OAM) multiplexing offers potential for increased fiber optic communication capacity.
• Efficiently amplifying OAM modes within an all-fiber format remains a significant challenge.

Purpose of the Study:

• To develop and demonstrate an all-fiber coupler for efficient pumping and amplification of OAM modes.
• To enable high-capacity modal-division multiplexing (MDM) fiber communication systems.

Main Methods:

• Fabrication of a coupler by side-polishing and bonding a ring-core erbium-doped fiber (RC-EDF) and a single-mode fiber (SMF).
• Optimization of phase-matching conditions for efficient 976 nm pump coupling.
• Characterization of insertion loss for 1st to 3rd-order OAM modes over a broadband wavelength range.

Main Results:

• Achieved high pump coupling efficiency (>90%) into the RC-EDF.
• Demonstrated low insertion loss (<0.58 dB) for OAM signal modes (1st-3rd order) across 1530-1565 nm.
• The coupler operates as a wavelength division multiplexing device.

Conclusions:

• The proposed side-polished pumping coupler technique effectively amplifies high-order OAM modes.
• This all-fiber approach is a key enabler for future high-capacity MDM fiber communication systems.