What's Good About Optical Wiring On PCBs? See How Allegro PCB Editor Makes This Happen!

This week, I'm taking a brief break from the usual PCB solution/product technical discussions and focusing on a very interesting capability used with the Cadence Allegro PCB Editor product.

You can read all the details from this article - Integrated Optical & Electronic Interconnect PCB Manufacturing in a recent PCB007 update.

 Most of you know that my primary focus is the "front end" environment for the Cadence PCB products, so when I learn about PCB board intricacies, sometimes it's a bit more than I can comprehend. Nonetheless, there are key takeaways (that actually make sense to even me!) from the article:

• "In the highest speed computers, for communication between the central processor arrays, hard disc storage arrays, and through data routing switches, there is now considerable interest in incorporating high speed "optical wiring," by means of plastic light-guides, within large, metre-scale, electrical PCBs combining optical and electrical interconnections (OPCBs)."
• A three-year research project explored methods for the manufacture of optical waveguides within an optical layer laminated into the board and investigated their compatibility with techniques already in use in commercial PCB manufacturers.
• Four different polymer waveguide manufacturing techniques were investigated and compared: Photolithography, direct laser writing, laser ablation and inkjet printing.
• A large team of university and industrial collaborators worked to adapt existing PCB Design software (that would be Allegro PCB Editor folks!) to incorporate new rules suitable for designing optical waveguide layouts in OPCBs. You can read about all the team member contibutors in the article.
• "University College London (UCL), having established waveguide design rules from comprehensive waveguide measurements and modelling, collaborated with Cadence to use their PCB layout software to design complex waveguide interconnection patterns and test waveguide component structures, The waveguide design files were supplied directly or after fabrication of photomasks to all fabrication partners for waveguide fabrication."
• UCL was technical leader of the entire project and their research included the modification of Cadence Allegro/OrCAD to enable it to design the novel optically and electronically interconnected PCBs (OPCBs).
• "The waveguide design rules were used to design a novel complex optical backplane layout. The end user system industrial partners specified two main requirements for demonstration of a practically viable system: First, the line-cards had to be directly interchangeable (without rotation); so all optical interfaces were designed to face in the same direction and to be identical to each other; second, the line-cards were required to be closely spaced. An interconnection pattern was designed to allow each of several daughter cards to have bi-directional low loss communications to each of the others."
• "The optical interconnections were tested by UCL and Xyratex and it was demonstrated that 10 Gb/s Ethernet traffic could be passed error free through each of the waveguides, obtaining open eye-diagrams. This is, to our knowledge, the world's most highly-integrated demonstrator built to date, incorporating connectors to allow daughter cards to be attached and detached at right angles and to be interchanged."

As always, feel free to post your thoughts about OPCB technology.

Jerry "GenPart" Grzenia