Unconstrained splitting ratios in compact double-MMI couplers

Area of Science:

• Photonics and Waveguide Optics
• Integrated Optics
• Optical Devices

Background:

• Multimode Interference (MMI) devices are fundamental components in integrated photonics for beam splitting.
• Achieving precise and tunable optical power splitting ratios is crucial for various photonic applications.
• Existing solutions often face limitations in tunability and fabrication complexity.

Purpose of the Study:

• To introduce a novel guided-wave optical power coupler design.
• To demonstrate the tunability of splitting ratios by adjusting a phase shifter.
• To evaluate the performance and fabrication feasibility of the proposed coupler.

Main Methods:

• The proposed coupler integrates two 2x2 50/50 multimode interference splitters.
• Tapered waveguides are employed as tunable phase shifters between the MMI sections.
• Device simulations and experimental characterizations on silicon-on-insulator (SOI) wafers were performed.

Main Results:

• The double-MMI coupler design allows for arbitrary splitting ratios by tuning the phase shifter length.
• Simulations and experimental results show good agreement.
• Fabricated devices exhibited average losses of 0.4 ± 0.5 dB.
• Achieved splitting ratios ranged from 56/44 to 96/4.

Conclusions:

• The presented double-MMI coupler offers a flexible and tunable approach for optical power division.
• The design is compatible with standard silicon photonics fabrication processes.
• This solution provides a promising alternative for applications requiring adaptable optical splitting.