Optimizing graded-index few-mode fiber for space division multiplexing.

Area of Science:

• Optical Communications
• Photonics
• Fiber Optics

Background:

• Mode-division multiplexing (MDM) is crucial for increasing fiber optic communication capacity.
• Few-mode fibers (FMFs) are essential for MDM, but controlling mode properties like differential mode delay (DMD) is challenging.
• Graded-index FMFs (GI-FMFs) offer a promising approach to manage multiple spatial modes.

Purpose of the Study:

• To optimize GI-FMF parameters for achieving a 4-LP-mode fiber suitable for MDM.
• To investigate the trade-offs between effective index difference (Δn_eff) and DMD in GI-FMFs.
• To demonstrate the feasibility of GI-FMFs for both weakly-coupled (WC-FMF) and strongly-coupled (SC-FMF) regimes.

Main Methods:

• Utilized numerical simulations to optimize GI-FMF parameters including profile parameter (α), core radius (a), and refractive index difference (n_co-n_clad).
• Analyzed effective index differences (Δn_eff), differential mode delay (DMD), effective mode area (A_eff), and bending loss (BL).
• Investigated narrow air trench-assisted GI-FMF structures to further reduce DMD.

Main Results:

• Optimized WC-GI-FMF achieved Δn_eff = 0.6 × 10^-3, low |DMD| = 5.4 ns/km, and minimal bending loss.
• Optimized SC-GI-FMF achieved Δn_eff = 0.1 × 10^-3, lowest |DMD| = 0.9 ns/km, and acceptable bending loss.
• Reported the lowest reported DMD of 5.4 ns/km for a weakly-coupled 4-LP-mode FMF.
• Achieved a record low DMD of 16 ps/km for a 4-LP-mode GI-FMF using a narrow air trench-assisted design.

Conclusions:

• GI-FMFs are highly suitable for 4-LP-mode MDM transmission by adjusting design parameters.
• The study presents record-low DMD values for both WC- and SC-FMF regimes, enabling higher capacity optical networks.
• Air trench-assisted GI-FMFs offer a pathway to further minimize DMD, pushing the boundaries of fiber optic communication.