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ECOC: the 40G supply chain

A few more things I saw at ECOC are worth noting, albeit belatedly, and a bunch of them were about 40 Gbit/s components.

In his market focus presentation, Kim Papakos from Tellabs highlighted single source components as a real problem for systems vendors wanting to build 40 and 100 Gbit/s networking gear. Ideally companies like Tellabs would like at least three sources on the market, so that if one supplier goes belly up, there are still multiple sources available. That requirement is passed down to them from their operator customers.

The lack of suitable off-the-shelf parts for 40 Gbit/s has often been cited as one of the factors that delayed the adoption of 40 Gbit/s networking. Nevertheless, it surprised me to find that there are still quite a lot of 40 Gbit/s components that are only made by one company, and some that simply aren’t available at all.

A case in point, Inphi and Sierra Monolithics joined forces to create the industry’s first reference design for 40 Gbit/s DQPSK (differential quadrature phase-shift keying) modulation. The booth demo showed interoperability of Inphi’s 40 Gbit/s modulator driver with Sierra Monolithics’ SerDes multiplexer/clock multiplier unit.

As I understand it, Inphi is the sole supplier of DQPSK modulator drivers, while Sierra Monolithics is currently the sole supplier of 40 Gbit/s SerDes. That’s because high-speed, high-voltage chips are difficult to make in silicon, so vendors have to resort to other materials systems.

Inphi’s DQPSK modulator driver for example, which has to output two streams of 20 Gbit/s at an amplitude of 8 V, is made out of gallium arsenide. (For comparison, networking chips in other roles typically require 1 V.) Meanwhile Sierra Monolithics makes its present generation of chips out of silicon germanium using IBM’s 7HP process.

The supply situation will improve over time of course — CoreOptics announced a 40 Gbit/s SerDes chip earlier this year, and AMCC is possible also working on one. But right now the components supply chain isn’t complete at 40 Gbit/s, let alone 100 Gbit/s.

In fact, Loi Nguyen, co-founder and vice president of technology for Inphi, told me: “Nobody has a TIA [transimpedance amplifier] for 40 Gbit/s DP-QPSK [dual-polarisation quadrature phase-shift keying].” The TIA sits on the recieve side in the equivalent position to the modulator driver on the transmit side, and amplifies the weak electrical signal coming in from an optical detector before passing it to the SerDes.

DP-QPSK is the modulation format selected by the Optical Internetworking Forum (OIF) for 100 Gbit/s components, which is supposed to hit the market in 2010, and yet it’s still not possible to get standard parts for the previous speed incarnation. Clearly components vendors have a lot of work to do.

Posted by Pauline Rigby on October 16, 2008 7:54 PM | Permalink