Tuesday, September 23, 2014

New fiber connector is nifty

Corning has recently teamed up with Intel in introducing some new optical equipment. Corning's contribution (fibers, connectors) likely mean there will be some unfamiliar looking optical infrastructure in your data center soon.

The fiber is a new 1310nm singlemode variety that Corning touts as "bend-insensitive". The minimum allowable bend radius of this fiber is 7.5mm. This is impressive, but expected under ITU-T G.657.B.

More interesting is the MXC connector. This is a push-on connector with a locking tab like the 8P8C connectors used for twisted pair Ethernet. It supports up to 64 fiber strands, each running at 25Gb/s.
MXC connector. Image from Corning-Intel Whitepaper.

The only place I've seen this fiber or connector in use is on a prototype 100G CLR4 transceiver shot by Greg Ferro at the Intel Developer Forum a couple of weeks ago.
Greg's shot of CLR4 transceivers with MXC connectors.
The CLR4 alliance explains that their approach puts four channels running at 25Gb/s each onto a single pair of single mode fiber, and specifically calls for LC connectors on the transceiver, so I'm a little confused about why these transceivers are sporting MXC connectors.

It seems the MXC connector will be used not directly on the transceivers, but for rapid deployment of many strands of structured fiber between racks. There will probably be a fan-out cassette of some sort to turn each MXC-terminated bundle into 32 LC connectors.

Anyway, none of that is the most interesting part of the connector. The most interesting bit is the termination of the optical fibers in the MXC connector. Did you notice that you can actually see the 64 strands (maybe even count them) in that first picture? Consider the following photo of an MPO connector for comparison:
MPO connector from Wikipedia
Most folks don't even notice the individual fiber strands on an MPO connector because they're distracted by the holes for the alignment pins. But you can actually see the 64 ends on the MXC connector. What's going on here?

Still from Intel-Corning video on youtube
The MXC connector includes tiny lenses which expand the light beam at the point where connectors meet. The beam expansion mitigates alignment and contamination issues common to traditional connectors which align fibers face-to-face.

It's pretty neat, though I'm a bit confused about some of the claims made in the various Intel and Corning announcements. The video linked above compares these new fibers to fibers in legacy connectors which have "50um fiber face" and claims that the 180um lens expands the diameter of the mating surface "almost four times"

Clearly they're not talking about single-mode when making these comparisons, but Intel is pushing single-mode based CLR4 transceivers.

Meh. I'm sure this will all become clear when products start shipping. For now I just thought it was interesting to note that these new high density connectors have baked-in lenses.

1 comment:

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