Although the market for 40 Gbit/s components has been slow to get started, speakers at the conference left us in no doubt that it is finally here. That’s due in part to the industry working out where the market opportunities for 40 Gbit/s can be found. The initial driver appears to be coming from the enterprise, with real momentum starting when Cisco introduced 40 Gbit/s interfaces for its CRS-1 core router, but carriers are also now showing an interest in using 40 Gbit/s in long haul networks.
“Last year the key question was: is 40G going to get superseded by 100G before 40G really gets going? But this year the industry seems to have resolved the problem by treating 40G and 100G as a single entity,” said Karen Liu, vice president, components for research firm Ovum RHK, speaking at the 2008 Executive Forum on Monday.
According to Liu, the market for 40 Gbit/s optical modules is forecasted to be worth $900 million by 2012, and this assumes only 10% penetration against 10 Gbit/s.
Another important contributor to the rise of 40 Gbit/s is the fact that the industry has made significant progress in developing the technologies required. Here’s our pick of 40 Gbit/s product announcements from the show:
40G tunables
NeoPhotonics unveiled a widely-tunable integrable tunable laser assembly (ITLA) that delivers 40 mW, which the vendor claims is twice the power of modules available from competitors like Emcore (Intel) and Santur.
An ITLA is a subassembly with an industry standard interface for the electrical functions, so that transponder manufacturers can build it into a module without having to worry about the underlying technology. The subassembly is a continuous wave device that requires an external modulator to add data to the signal.
Having a high-power tunable is important for 40 Gbit/s, says Ferris Lipscomb, VP of marketing for NeoPhotonics . “Higher bit rates means fewer photons per bit, but you still need the same number of photons to distinguish a bit,” he explains. In addition, the advanced modulation schemes used at 40 Gbit/s need to split the signal and detect it on multiple photodetectors.
The ITLA is based upon technology that NeoPhotonics acquired from start-up Paxera, which uses an acousto-optic wave in a piezo-electric crystal as a tunable grating, although Lipscomb points out that the high power version has been developed since the acquisition.
“The next thing that’s coming along at 40G is the ITTA, or integrable tunable transmitter subassembly — an assembly that has the modulator on board — but it will be a couple more years before that capability is built in,” says Lipscomb.
Mini modulators
Bookham unveiled an ultrasmall modulator chip designed to process 40 Gbit/s optical signals using differential quadrature phase shift keying (DQPSK) coding schemes. At just 5 mm long, Bookham's device is a lot smaller than traditional modulators made out of lithium niobate, which are typically around 48 mm in size.
Really Bookham's device is a demodulator because its purpose is to convert phase-modulated signals into amplitude-modulated signals, so they can be detected with ordinary photodetectors. Bookham’s chip integrates three Mach-Zehnder (MZ) modulators made out of indium phosphide; two are needed for non-return-to-zero DQPSK, while return-to-zero DQPSK requires three.
“The InP MZ platform has the flexibility to implement a range of modulation schemes at 40G, but it is our vision that DQPSK, in which we have significant intellectual property, is the modulation format to allow the correct price positioning at 40G, and the scalability to 100G,” says Adam Price, Bookham’s product line manager for active optical components and subsystems.
According to Price, there’s a lot of interest in making 40 Gbit/s modulators small enough to be put into pluggable module formats. “Our vision is to copackage the modulator with a tunable laser in something the size of an iTLA,” he told fibresystems.org.