Optical Interconnects Finally Seeing the Light in Silicon Photonics: Past the Hype

Abstract

Electrical interconnects are becoming a bottleneck in the way towards meeting future performance requirements of integrated circuits. Moore’s law, which observes the doubling of the number of transistors in integrated circuits every couple of years, can no longer be maintained due to reaching a physical barrier for scaling down the transistor’s size lower than 5 nm. Heading towards multi-core and many-core chips, to mitigate such a barrier and maintain Moore’s law in the future, is the solution being pursued today. However, such distributed nature requires a large interconnect network that is found to consume more than 80% of the microprocessor power. Optical interconnects represent one of the viable future alternatives that can resolve many of the challenges faced by electrical interconnects. However, reaching a maturity level in optical interconnects that would allow for the transition from electrical to optical interconnects for intra-chip and inter-chip communication is still facing several challenges. A review study is required to compare the recent developments in the optical interconnects with the performance requirements needed to reach the required maturity level for the transition to happen. This review paper dissects the optical interconnect system into its components and explains the foundational concepts behind the various passive and active components along with the performance metrics. The performance of different types of on-chip lasers, grating and edge couplers, modulators, and photodetectors are compared. The potential of a slot waveguide is investigated as a new foundation since it allows for guiding and confining light into low index regions of a few tens of nanometers in cross-section. Additionally, it can be tuned to optimize transmissions over 90° bends. Hence, high-density opto-electronic integrated circuits with optical interconnects reaching the dimensions of their electrical counterparts are becoming a possibility. The latest complete optical interconnect systems realized so far are reviewed as well.

Scalability of Large-Scale Photonic Integrated Circuits

“…Optical interconnects have dominated long-haul signal transmission for decades in optical fiber communications . Recently, with the exponential scaling of the bandwidth for interconnect networks, conventional copper lines are experiencing capacity crunch in short-reach scenarios, especially for on-board applications . PICs have been introduced to solve the bandwidth bottleneck faced by current interconnect networks.…”

ReSiPI: A Reconfigurable Silicon-Photonic 2.5D Chiplet Network with PCMs for Energy-Efficient Interposer Communication

“…Therefore, the interposer network should be able to handle a high volume of traffic among chiplets. Moreover, the interposer is large and metal interconnects impose a high delay for long-distance communication [12]. To this end, silicon-photonic interposers have been proposed to improve the latency and bandwidth compared to conventional electronic interposer networks [8,16,25].…”

Lossless High-speed Silicon Photonic MZI switch with a Micro-Transfer-Printed III-V amplifier

“…Thanks to the high refractive index contrast and the availability of a variety of high performance passive and active monolithic building blocks (doped Si and Si/Ge components), complex PICs with compact footprint can be realized for applications in a wide range of fields, e.g. optical interconnects [1], optical computing [2], optical sensors [3], bio-medical instruments [4], LiDARs [5], etc. However, the increase in complexity is always accompanied by additional optical losses, which becomes a significant obstacle in scaling the size and complexity of PICs.…”