Air-cladded mode-group selective photonic lanterns for mode-division multiplexing

Area of Science:

• Photonics
• Optical Fiber Communications
• Waveguide Engineering

Background:

• Mode group (de)multiplexing is crucial for increasing optical fiber capacity.
• Traditional methods often involve complex structures like capillary tubes for cladding.
• Efficient mode conversion requires adiabatic guiding principles.

Purpose of the Study:

• To fabricate and characterize an air-cladded mode-group selective photonic lantern.
• To investigate the use of air as a cladding material for photonic lanterns.
• To analyze the impact of structural features, like airholes, on mode conversion.

Main Methods:

• Fabrication of an air-cladded photonic lantern taper.
• Characterization of multiplexing and de-multiplexing crosstalk.
• Microscopic imaging of the taper cross-section.
• Numerical investigation using an eigenmode expansion method and a full-vectorial mode solver.

Main Results:

• Achieved multiplexing crosstalk between -20 dB and -12 dB.
• Obtained de-multiplexing crosstalk around -12 dB for the fundamental mode and slightly higher for the LP11 mode.
• Identified an uncollapsed airhole in the taper structure.
• Demonstrated numerically that the airhole aids adiabatic mode conversion.

Conclusions:

• An effective air-cladded photonic lantern was successfully fabricated.
• Air as cladding offers a simple and efficient solution for mode (de)multiplexing.
• The presence of an airhole is beneficial for adiabatic mode conversion in the taper.