Imec demos 32-channel silicon-based wavelength filter

The research institution, renowned for its contributions to nanoelectronics and digital technologies, unveiled a compact 32-channel silicon-based wavelength filter. This development marks a first in achieving low loss and high tuning efficiency, facilitating a fourfold increase in the capacity of transmitted and received wavelength channels in comparison with current commercial transceivers. This advancement promises to enhance the bandwidth density and power efficiency of future silicon-photonics-based transceivers, catering to the demands of short-reach optical interconnects in high-performance AI/ML compute clusters.

The ongoing evolution of optical interconnects is pivotal for advancing performance and efficiency in AI/ML compute environments. Silicon photonics stands as a crucial technological foundation for the cost-effective amalgamation of Tbps-scale transceivers. However, the stringent requirements for bandwidth density, power efficiency, and latency in AI/ML system interconnects call for significant enhancements at the process, device, and circuit levels. Historically, augmenting link bandwidth through the addition of more wavelength channels has been hindered by considerable optical losses and excessive tuning power in silicon-integrated components.

Leveraging Imec’s state-of-the-art Si patterning capabilities within its 300mm Silicon Photonics platform (iSiPP300), along with innovative and optimally designed Si ring resonator and interleaver components, Imec has successfully addressed these challenges. It achieved a WDM filter encompassing 32 wavelengths with 100GHz channel spacing in the O-band, aligning with the specifications of the CW-WDM multi-source agreement (MSA). Thanks to meticulous design optimisation, the filter maintains low optical insertion losses of approximately 2dB and crosstalk levels superior to 16dB, even with such a high channel count. By employing Imec’s local Si substrate undercut process and refined heater designs, the filter's thermo-optic tuning efficiency is reported among the highest at 290GHz/mW.

Joris Van Campenhout, a Fellow and R&D Programme Director at Imec, commented on the development: "Imec’s optical I/O R&D programme is geared towards the disruptive scaling of bandwidth density and power consumption in silicon-integrated optical interconnects, which are often seen as conflicting objectives. Our novel 32-channel WDM filter enables Tbps-scale aggregate bandwidth per optical fibre with individual lane rates of only 32Gbps, ensuring error-free link operation without the need for energy-intensive digital signal processing. With its compact size, low optical losses, and superior wavelength tuning efficiency, the new WDM filter paves the way for Tbps/mm-scale optical interconnects with unparalleled power efficiency of just 1pJ/bit."