Can cheaper lasers handle short distances?

Summary

Optical technology is well established for long-haul communications, but the distances it serves are shrinking — especially in the data center. Vertical-cavity surface-emitting lasers (VCSELs) already drive short fiber links. But efforts are underway to further scale them down to provide more connections through waveguides than fiber can provide. “We have seen the transition from long haul to metro-to-local area networks and then into the data center,” said Suresh Jayaraman, senior director for package development at Amkor Technology. “Fiber has moved from the edge of the card to on-board, and more recently onto the package.” Much research is underway to move optics closer to servers in the data center. Today, the technology typically is employed for rack-to-rack communication, while most intra-rack wires are copper. Replacing the copper with fiber remains a development opportunity. Integrating lasers with silicon Of particular interest is where the fibers will attach to processors. Standard pluggable formats may give way to linear pluggable optics (LPO) and co-packaged optics (CPO). But those are still in development. Three laser attributes dominate concerns over how to integrate optical communications — reliability, temperature sensitivity, and energy consumption. Reliability has been a top concern, and although it’s improved, developers are still concerned about soldering a laser onto a board in case it goes bad and must be replaced. This is the central motivator for pluggable formats. “The good news is that the lasers are getting pretty robust, pretty reliable now compared to what they were in the past,” said Mitch Heins, senior product manager at Synopsys. But designers remain wary. Lasers are notoriously sensitive to changes in temperature, and that can be challenging when precise wavelengths are necessary. (Note that in electronics we typically define speed in terms of frequency, or Hz, whereas in optics we tend to speak of the wavelength, typically in nm.) F...