Highly scalable and flexible on-chip all-silicon mode filter using backward mode conversion gratings

Area of Science:

• Photonics
• Optical Engineering
• Materials Science

Background:

• Mode filters are crucial for mode-division multiplexing (MDM) systems, enabling modal cross-talk reduction and routing.
• Existing silicon mode filters are limited to single-mode operation, requiring cascades for multi-mode filtering, which hinders integration.

Purpose of the Study:

• To propose a novel concept for compact, scalable, and flexible mode filters for MDM systems.
• To enable simultaneous filtering of one or multiple modes using a single device.

Main Methods:

• Development of mode filters based on backward mode conversion gratings embedded in multimode waveguides.
• Design and simulation of filters for various higher-order modes and a mode demultiplexer.
• Fabrication and experimental validation of two filter designs (TE1-pass and TE2-pass).

Main Results:

• Demonstrated a scalable method for higher-order-mode-pass or band-mode-pass filters of any order.
• Achieved excellent performance in fabricated filters: insertion loss <1.0dB/1.5dB and extinction ratio >29dB/28.5dB.
• Obtained a wide operational bandwidth of 51.2nm/48.3nm for the filters.

Conclusions:

• The proposed backward mode conversion grating offers a flexible and scalable solution for multi-mode filtering in MDM.
• The demonstrated filters achieve state-of-the-art performance, paving the way for highly integrated and efficient MDM systems.