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

An all-fiber fiber coupler was demonstrated for pumping orbital angular momentum (OAM) modes amplification, which was fabricated by side-polishing and bonding a ring-core erbium-doped fiber (RC-EDF) and a pre-tapered side-polished single-mode fiber (SMF). With the selected phase-matching condition at 976 nm, the pumping laser was coupled into the RC-EDF from the SMF with optimized high efficiency, whereas the 1st to 3rd-order OAM mode signals were transmitted with the low insertion loss in the RC-EDF over a broadband wavelength range from 1530 to 1565 nm. This all-fiber wavelength division multiplexing coupler was optimized by the polished length and depth of the two coupled fibers. The insertion loss for the OAM signal modes was obtained lower than 0.58 dB with the pump power coupling ratio of above 90%. The proposed side-polished pumping coupler technique can ensure high-order OAM modes amplification, paving the way for the all-fiber optical amplifier in high-capacity modal-division multiplexing fiber communication systems.

Automated summary

An all-fiber fiber coupler was developed for amplification of orbital angular momentum (OAM) modes by side-polishing and bonding a ring-core erbium-doped fiber (RC-EDF) and a pre-tapered side-polished single-mode fiber (SMF). The pumping laser was efficiently coupled into the RC-EDF from the SMF for the selected phase-matching condition at 976 nm, and the 1st to 3rd-order OAM mode signals were transmitted with low insertion loss in the RC-EDF over a wide wavelength range. The proposed side-polished pumping coupler technique enables high-order OAM mode amplification, making it promising for all-fiber optical amplifiers in high-capacity modal-division multiplexing fiber communication systems.