On-chip mode-selective manipulation based on the modal-field redistribution assisted with subwavelength grating...

Area of Science:

• Photonics and Optical Engineering
• Integrated Optics
• Nanophotonics

Background:

• Scalable and flexible mode-division multiplexing (MDM) systems require efficient mode-selective manipulation.
• Existing methods face challenges in precisely controlling individual optical modes within multimode waveguides.

Purpose of the Study:

• To propose and demonstrate a novel scheme for mode-selective manipulation in multimode photonics.
• To enable independent and free add/drop functionality for fundamental and higher-order modes.
• To enhance the performance of mode-division multiplexing systems.

Main Methods:

• Utilizing subwavelength grating (SWG) structures to engineer refractive-index profiles.
• Redistributing modal field distributions in multimode bus waveguides for mode localization.
• Manipulating coupling coefficients (κ) and their ratios (δ/κ) for distinct mode channels.

Main Results:

• Demonstrated a three-channel mode-selective add-drop coupler on silicon.
• Achieved low excess losses (0.1–1.9 dB) over a 70 nm wavelength range.
• Reported inter-mode crosstalk below -19.4 dB (1525–1600 nm) and port crosstalk suppressed to -18 to -30 dB.

Conclusions:

• The proposed SWG-assisted scheme effectively enables flexible, mode-selective manipulation.
• This approach significantly suppresses undesired mode coupling while enhancing desired coupling.
• The concept paves the way for advanced silicon photonic devices for MDM systems.