Mode-selective coupler pair for mode-group demultiplexing over graded-index few-mode fiber

Area of Science:

• Optical Engineering
• Telecommunications
• Photonics

Background:

• Few-mode fibers (FMF) offer increased bandwidth but require effective mode demultiplexing.
• Degenerate mode groups in graded-index FMF (GI FMF) pose challenges for selective signal extraction.
• Existing mode-selective couplers have limitations in handling multiple degenerate mode groups.

Purpose of the Study:

• To propose and analyze a novel mode-selective coupler pair (MSCP) for demultiplexing degenerate mode groups in GI FMF.
• To design and evaluate MSCPs for the third and fourth mode groups.
• To construct and assess a complete four-mode-group demultiplexer by cascading MSCPs with a degenerate mode-selective coupler (DSMC).

Main Methods:

• Mode coupling analysis comparing MSCP with conventional couplers.
• Design of MSCPs targeting specific mode groups (3rd and 4th).
• Cascading MSCPs with a DSMC to create a four-mode-group demultiplexer.
• Performance evaluation through simulations: demultiplexing efficiency, modal crosstalk, and C-band bandwidth.

Main Results:

• The proposed MSCP effectively demultiplexes spatial modes within the third and fourth mode groups.
• Simulations demonstrate high demultiplexing efficiency and low modal crosstalk for individual MSCPs and the cascaded demultiplexer.
• The MSCP-based demultiplexer exhibits favorable bandwidth characteristics across the C-band.

Conclusions:

• The MSCP is a viable solution for demultiplexing degenerate mode groups in GI FMF.
• The cascaded MSCP-DSMC demultiplexer enables MIMO-free mode-group-division multiplexing transmission.
• This approach simplifies optical systems, reducing the need for complex digital signal processing and enhancing compatibility with direct-detection transceivers.