Compact and scalable mode (de)multiplexer using inverse-designed subwavelength gratings

Area of Science:

• Photonics
• Integrated Optics
• Nanophotonics

Background:

• Mode division multiplexing (MDM) is crucial for increasing on-chip optical communication capacity.
• Existing mode (de)multiplexers often suffer from large footprints and complex structures.
• Subwavelength gratings offer precise control over waveguide properties, and inverse design optimizes complex structures.

Purpose of the Study:

• To propose and experimentally demonstrate a compact mode (de)multiplexer utilizing inverse-designed subwavelength gratings.
• To achieve high-performance mode (de)multiplexing with a significantly reduced device length.
• To showcase the scalability and flexibility of the proposed design for dual-polarization applications.

Main Methods:

• Utilized inverse design algorithms to optimize subwavelength grating structures for mode (de)multiplexing.
• Fabricated a six-channel mode (de)multiplexer with ultra-short coupling lengths and no adiabatic tapers.
• Designed and demonstrated a dual-polarization, eight-channel device as a proof-of-concept.

Main Results:

• Achieved a compact device length of only 76 µm for the six-channel multiplexer.
• Measured peak insertion losses below 0.77 dB for all channels across a 100 nm bandwidth.
• Exhibited crosstalk levels below -15 dB for all channels.
• Successfully demonstrated a dual-polarization, eight-channel device.

Conclusions:

• The inverse-designed subwavelength grating approach enables highly compact and efficient mode (de)multiplexers.
• This technology offers a promising solution for large-scale, dense integration in on-chip polarization and mode division multiplexing systems.
• The demonstrated flexibility paves the way for advanced optical interconnects.