Femtosecond direct-written integrated mode couplers

Area of Science:

• Photonics and Optical Engineering
• Materials Science

Background:

• Optical fiber capacity is limited by single-mode transmission.
• Mode-division multiplexing (MDM) offers a path to increase fiber capacity by utilizing multiple spatial modes.
• Developing efficient integrated devices for mode manipulation is crucial for practical MDM systems.

Purpose of the Study:

• To design and fabricate three-dimensional (3D) integrated mode couplers.
• To demonstrate multiplexing of multiple spatial modes (LP01, LP11a, LP11b) in optical fibers.
• To assess the performance of these couplers in terms of mode extinction ratio and insertion loss.

Main Methods:

• Fabrication of mode couplers using the femtosecond laser direct-write technique on boro-aluminosilicate photonic chips.
• Design of two-core and three-core integrated mode couplers.
• Characterization of coupler performance, including mode extinction ratios and coupling efficiency across the C-band (1500-1580 nm).

Main Results:

• Achieved excellent mode extinction ratios (25-37+ dB) and low insertion loss (~1 dB) for horizontally and vertically written two-core couplers.
• Demonstrated near 100% coupling ratios with optimized fabrication parameters.
• Successfully multiplexed LP01, LP11a, and LP11b modes using sequential or single 3D three-core couplers.

Conclusions:

• 3D integrated mode couplers fabricated via femtosecond laser direct-write are effective for mode multiplexing.
• These devices offer a compact, versatile, and potentially cost-effective solution for increasing optical fiber capacity.
• The technology shows significant potential for advanced mode-division multiplexing systems.