The Power of Silicon Photonics

Created September 16, 2021
Guest Blog

Silicon photonics has transformed coherent transmission by continually delivering significant reductions in the power, size, and cost of optical modules. An increasing number of optics vendors today are leveraging this technology for their pluggable coherent solutions. However, this was not always the case. Only nine years ago, many companies were challenging whether silicon photonics was even going to work at 100G coherent optics.

Below are a few reasons that silicon photonics has emerged as a key technology for existing and future optics solutions.

  • Leverages CMOS Processes to benefit from higher yields and lower cost associated with CMOS.
  • Enables Package Level Integration that can better optimize high-speed interfaces and accelerate the realization of higher data rates at lower power. In addition, silicon photonics is temperature tolerant and thus is not affected by the heat-generating DSP.
  • Ensures High Reliability by reducing the number of component interconnects, eliminating the need for hermetic gold boxes, and enabling testing at the wafer level.
  • Simplifies Deployment and Management through pluggable modules with industry standard interfaces.

Higher baud rate designs

As the gap to Shannon’s Limit narrows, it is becoming more difficult to increase channel capacity by increasing the modulation order while keeping the same transmission distance. This leaves higher baud rates as a preferred method to increase capacity and decrease cost per bit. Silicon photonics and advances in packaging technology enabled by silicon photonics are key for enabling higher baud rate designs.

 Component Stacking

In component stacking, electrical impairments are reduced due to very short electrical connections between key RF components, creating a robust signal path for extremely high frequency/baud rate operation. The gold-box packaging is eliminated, the DSP and PIC are tightly co-packaged on the same substrate, and the high-speed modulator driver and TIA components are stacked on the PIC.  Stacked design has a higher frequency response than the traditional gold-box design. Advanced stacking designs can further reduce interconnect impairments, resulting in even higher frequency response.

Illustration of example electrical interconnect frequency response comparing traditional gold-box and stacking integration shows that stacking provides a path to >100Gbaud.

One of the first pioneers of this technology was Acacia, now part of Cisco, when in 2012 it was the first coherent module vendor to envision silicon as the platform for the integration of multiple discreet photonic functions while increasing the density and reducing cost of optical interconnect products.

Leveraging advancements in silicon photonics, Acacia has delivered generations of high-volume silicon photonics-based products that continually enabled higher transmission data rates, lower power, and higher performance than the generation before it. As evidenced by today’s deployments of Acacia’s 1.2T multi-haul AC1200 coherent optical module in well over a hundred customer networks which include subsea, long-haul, regional, metro and DCI applications, silicon photonics can achieve industry leading performance.

Acacia’s silicon photonics leadership timeline for coherent transmission.

New, Innovative Architectures and Future Innovations

Silicon photonics has the potential to unlock new architectures needed to keep up with rising demand.  An example is pluggable coherent transceivers that can be plugged directly into switches and routers offering the same density for both coherent DWDM and client optics in the same chassis.  It can also drive future generations of optics design that push the envelope on performance, cost, complexity, and size.

The industry is now turning to silicon to produce a wide variety of devices, using mainstream silicon manufacturing process technologies that have matured over many years.  As optical transceivers need to support higher data-rate, driven by the demand for higher speed networks that can handle the rising bandwidth demand, silicon photonics can once again allow the capacity to grow without significantly increasing the size and cost of the devices needed for the future.

Learn more about silicon photonics solutions from Acacia.