Creating performant communication channels between different parts of digital processing units is more then ever the limiting factor to further digital processing development. The confluence of increased performance of computing chips, huge off-chip interconnectivity requirements, and increasingly high channel speeds together with a looming issue of thermal and power management make that current galvanic links are without any doubt under high strain. It is indeed not unusual for the multigigabyte galvanic board links to require compensation on the high-frequency absorption for as much as 30 to 45 dB of attenuation, while crosstalk, dispersion, and timing issues become more severe with each newly introduced complementary metal oxide semiconductor (CMOS) technology node.
Optical interconnects have therefore been often cited as a possible route to alleviate the current technology conundrum. Indeed, the use of photons for communication has some clear advantages from a physical point of view compared to its galvanic contenders and is already now the default interconnect choice for link lengths above a few hundred meters. At a shorter distance, optics have also demonstrated their ability to enable high data transmission at a very high bitrate per channel and massive parallelism with single dependent electromagnetic interference (EMI). This has lead to an enormous and successful development in optoelectronic devices and hybridization technologies. Yet, optical interconnect at such length scales have thus far failed to become a mainstream commercial reality mostly because of cost, uncertainties in reliability, and unsatisfying packaging solutions.
The incumbent technology, the printed circuit board (PCBs), has moreover relentlessly continued to become a cheaper and more mature technology, aided by the development in signal processing chips and new packaging technologies. Nevertheless, it is unclear with this technology where the future performance increases can be found without trading off too much in cost and complexity.
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