ROME Switches

ROME Fabric



Optical Backplane

Author: David Wang   Publication Date: September 23, 2016

What does the electrical backplane mean to the optical backplane?


The electrical backplane comes from the concept of switches or networking equipment. In order for the user interface to get connected to a networking equipment, like a Cisco switch, you would connect to a line card. How does the line card work and interconnect to each other and function as a full switch? You will have a backplane. This is a physical plane that is a printed circuit board or electronic buss, meaning cross electronic signal and its connections to transfer data, that’s how an electrical backplane works.


Adding optical backplane is a new concept. When you build the switches you will have different line cards and their interconnections are electronic connections and their speed is dependent on the capability of that electrical backplane. Speed, size and capacity may change, but is it still fundamentally the same electronic base backplane.


Currently, there is a lack of defining this concept of optical backplane. It’s an evolving concept and because of the optical interconnects, the nature of optical interconnects, the optical backplane is potentially different from the electrical backplane. I think there is a definition to be made and that definition is an evolving effort.


So what drives an optical backplane? Silicon Photonics, the much larger density and volume of optical inter-connectivity in a switch is the revolutionary technology that is driving the need for the optical backplane. Meaning; your switching capability and computing capability is now built in a chip and the chip is integrated with an optical interface. In certain cases, we are talking about 3-ml by a 3-ml surface, with more than a hundred fiber optical connections, with individualized fibers that latch onto the chip. So you can see the box is not the box it used to be. Which is electronic components and PCB boards which will require an electronic connection. Now the chip is coming out with direct optical interface.


A lot of that optical interface and the line cards will get interconnected to each other to form an entire equipment. That equipment can be switching, computing or storage. So the interaction will rely on the physical optical connection, that’s where the so called optical backplane comes into play. We are in the leading edge in terms of connectivity right off the chip, so we are helping the industry define what an optical backplane should look like, based on the equipment or the application.


Optical backplane offers much more flexibility from an optical connectivity standpoint. You can transmit the signal beyond the box. One of the features of ROME is it can be part of the automated connectivity platform. Not only can we interconnect between line card to line card inside of one box, but we are able to interconnect directly with another chip sitting at the end of the data center.


So we are talking about another scale, a leap in technology. When optical connectivity is directly from chip to chip, then the data center will be based on the optical connectivity. Optical backplane came from the electrical backplane concept, but is yet to be defined. Optical backplane does not have to be part of the box anymore. It is simply a facilitation of optical connectivity and that optical connectivity, from a data center standpoint, does not have to be part of the box. This offers many evolutional form factors and benefits that include space; power consumption; cooling requirements; and performance efficiencies.