Optical Interconnects - Definitions and principles

Being connected anywhere and anytime has become a way of life. As information flows continue to grow and networks multiply, the speed and quality of data transfer have become paramount. The advent of artificial intelligence has caused a surge in demand for data transmission, to the point where the introduction of optical solutions between processors—or even within processors—is being considered for data transmission. To meet this need, optical fiber is ubiquitous, whether, for example, in very high-speed long-distance telecommunications, in very short-range sensor networks, or in signal processing. Optical interconnection techniques offer intrinsic advantages (attenuation, coherence, parallelism, integration, etc.) which, combined with their widespread use in long-distance communications networks, make them an ideal candidate for interconnections between components.

Wherever we go, we have the ability to connect with others and exchange information, photos, or videos in real time. All of this is now possible thanks to the increased processing capabilities of processors and other electronic components, which are capable of performing several million—or even billions—of operations per second. The Internet, with nearly 17.5 billion connected devices by the end of 2025 (source: Internet World Stats), and the deployment of high-speed mobile networks (5G and beyond) require infrastructure capable of meeting the resulting demand. The number of inputs/outputs, which correlates with data throughput, is currently the bottleneck and the limiting factor for these infrastructures. Electrical links are no longer capable of transmitting the required data rates (exceeding 100 Gbit/s), so optical transmission has become the only viable option.

This article introduces optical interconnect technologies, along with their advantages and disadvantages compared to traditional interconnects. Following a brief review of the concepts of guided propagation, the reader will be introduced to the components suitable for optical interconnects and the fundamentals of optoelectronic interface design, enabling them to understand the various technologies implemented within optoelectronic modules. This article describes the impact of optical interconnects on the physical and software architecture of processing and communication systems. The various passive and active technologies are detailed, leading to the development of integrated modules and their characterization in a real-world environment.