Directional coupler design for orbital angular momentum mode-based photonic integrated circuits.

Area of Science:

• Photonics
• Optical Engineering
• Integrated Optics

Background:

• Orbital Angular Momentum (OAM) modes offer unique properties for optical communication.
• On-chip integration of OAM modes requires specialized waveguide structures.
• Directional couplers are fundamental components in photonic integrated circuits.

Purpose of the Study:

• To propose and demonstrate a novel on-chip directional coupler for OAM modes.
• To address the challenge of equalizing coupling strengths for degenerate OAM modes (l=±1).
• To enable efficient optical power transfer for OAM-based photonic integrated circuits.

Main Methods:

• Utilizing coupled mode theory for analysis.
• Designing a modified cross-shaped waveguide structure.
• Performing numerical simulations to validate performance.

Main Results:

• A functional on-chip OAM mode directional coupler was designed.
• The device exhibits a coupling length of 670 µm.
• Numerical simulations confirmed negligible OAM mode purity degradation during power transfer.

Conclusions:

• The proposed cross-shaped waveguide structure effectively solves the coupling strength equalization problem for OAM modes.
• This work presents the first on-chip OAM mode directional coupler.
• The design approach is applicable to various OAM-based photonic integrated circuit devices.