TTM Shines a Light on Optical Interconnect

I-Connect007 | 04-20-2017

Are embedded optics on PCBs set to make a breakthrough in the upcoming years? According to Dr. Craig Davidson, VP of Corporate Technology at TTM, it might be closer than you’d expect. In a recent interview with the I-Connect007 team, Craig outlines TTM’s current pursuit of high-volume manufacturing lines able to deliver embedded optical interconnect, what that would mean for the PCB industry, and why he thinks there will be manufacturing production capability by 2020.

Barry Matties: Craig, for context, tell us a little bit about the optical side of TTM and what you guys are doing there.

Craig Davidson: Sure. We’re engaged already with the optical groups of many large customers. As you probably know, there are optical products today that do not include onboard optical interconnect or inboard optical interconnect, but rather optical cables to the edge of the board. These include fiber connectors and transceivers embedded in connectors. TTM certainly supports networking companies with these kinds of products formally classified as optical.

What we’re really taking about here is the future as we bring optical signals on board, onto the printed circuit board directly embedded in the board for optical packages, line cards or backplanes.

Matties: Yes.

Davidson: The basic capability has been around for decades. I first got involved in it back in the year 2000 when there was a big push for onboard optical interconnect and just about every printed circuit board fabricator at the time was doing something around embedding fibers into boards. Many PCB fabricators have these kinds of processes. It’s relatively simple to do but it’s not a very happy solution.

You still have problems with 90° bends, for example, and the z-axis in the board, and you certainly have continuing difficulties associated with connectorizing the fibers. Also, importantly, is registration—making sure the fibers actually end up where they need to be. That’s a very difficult task. So those types of problems haven›t really been solved for a long time. The TTM team in Europe has been working on this for a long time now.

And you interviewed Marika Immonen on our team back in 2015, I believe. TTM now has technology we can offer that will allow embedded waveguides in boards. This includes polymer waveguides either buried inside a board or built-up on the board surface and with in-plane or 90° connectors. We›re working jointly with several consortia and individual companies to demonstrate this technology.

So that’s a brief history of where we have been and at least a little preview of what we can offer. TTM has a long experience of fabricating multimode waveguides for short-reach datacom applications. Now as silicon photonics at OEMs is pushing through, we are scaling technology to support their single-mode roadmaps.  There we pursue both polymer- and glassbased waveguides. Polymers are very versatile, low cost and easy to fabricate, whereas glass provides low loss at the longer wavelengths and optical   compliance with fibers. Single mode waveguides are looked at to provide complex routing between chips or to serve as “bridges” between sub-micron silicon waveguide and 9-micron fiber. In single mode, accuracy and registration both in waveguide fabrication and termination is critical.

To read the full version of this interview which appeared in the April 2017 issue of The PCB Magazine, click here.