Emerging short-reach data center interconnect (typically in the range of tens of km) is a scenario wherein the capacity has to be maximized over point-to-point optical links without intermediate optical amplification, i.e. unrepeated links. For this application, cost and compactness of the optical transceiver form factor to fit the faceplate density requirement are essential to keep up with the bandwidth demand inside hyper-scale data centers. For the optical module to fit in the current dimensions of client routers without compromising the performance, both the electronics and the optics have to be efficiently designed. As far as the opto-electronic is concerned, photonic integrated circuits (PIC) have been discussed in the community so that all the photonic functionalities are performed accordingly with the physical dimensions, power budget and performance specifications. This paper addresses the basic building blocks of silicon photonics coherent optical transceivers, from the design to experimental validation. In addition to the silicon optical modulator, basic components such as polarization splitter-rotators (PSRs) and optical filters will be addressed.
Emerging short-reach data center interconnect is a scenario wherein the capacity has to be maximized over point- to-point optical links without intermediate optical amplification. Most of the transceiver solutions are based on 100G modules with direct detection modulation. Although these legacy solutions are cost-efficient in a short- term, they are not scalable in a long-term, when the capacity x distance product will become more and more stringent. This paper addresses coherent optical solutions for emerging data center interconnect, with optical transmission reach being limited to around unrepeated 100 km. The main advantage of coherent solutions, when compared to legacy direct detection technologies, is the inherently improved spectral efficiency (e.g. 400 Gb/s channels in a 50 GHz grid) and receiver sensitivity provided with high baudrate (>40 GBd) transceiver modules. In this paper, two technological options for single-carrier optical 400 Gb/s modules are exploited for high capacity links over short reach scenarios: 43 GBd polarization-division-multiplexed (PDM)-64QAM,
suitable for a 50-GHz grid; and 64 GBd PDM-16QAM, suitable for a 75-GHz grid. These two solutions are compared in terms of capacity allocated in C band (∼4 THz bandwidth), when considering 50 GHz (80 channels
at 400G, 32 Tb/s) and 75 GHz (53 channels with 21.2 Tb/s) grids and back-to-back requirements in terms of optoelectronics (digital-to-analog and analog-to-digital converters, modulators, receivers etc.).