Coherent receivers are the optical darlings of the day, but Infinera Corp. (Nasdaq: INFN) is going to take its time getting to them. It will be two to three years before the company produces a coherent photonic integrated circuit (PIC) for 100-Gbit/s transport, a source tells Light Reading. In the meantime, the source says, Infinera plans to offer 100-Gbit/s channels by packing two wavelengths of 50 Gbit/s each -- the trick Nortel Networks Ltd. (now Ciena Corp. (NYSE: CIEN)) used for the first Verizon Communications Inc. (NYSE: VZ) 100-Gbit/s installation. (See Verizon Switches On 100G in Europe.)To clarify: We're talking about transport where each wavelength (or wavelength pair, in Infinera's case) carries 100 Gbit/s. That's different from the aggregate 100 Gbit/s that Infinera's PICs already do, by carrying 10 lanes of 10-Gbit/s traffic. That kind of density has served Infinera well. But operators do want to move to higher speeds, Heavy Reading analyst Sterling Perrin says. So, Infinera's apparent plan goes like this: First, the company will offer its 400-Gbit/s PIC, meaning 10 lanes carrying 40 Gbit/s apiece; this already went through tests last year. (See Infinera Touts 400G PIC.) The source says this will come with the bonus of 25GHz channel spacing, meaning Infinera will carry 160 40-Gbit/s wavelengths per fiber as opposed to the usual 80. After that would come 100-Gbit/s channels using the dual 50-Gbit/s trick. Each pair of 50-Gbit/s wavelengths would fit into one ITU grid slot, meaning Infinera would be able to carry these channels at 50GHz spacing (80 channels per fiber). Finally, the coherent 100-Gbit/s PIC would arrive in two to three years, the source says.

Other vendors are already demonstrating coherent receivers and announcing coherent 40-Gbit/s products. (See CoreOptics Does Coherent 40G, Fujitsu Intros 40G Coherent Optics, and NeoPhotonics Intros 40G/100G PIC.)

Fujitsu Network Communications Inc. , which is using a CoreOptics Inc. 40-Gbit/s coherent module, expects to come out with 100-Gbit/s offerings in 2011, and other vendors at last month's OFC/NFOEC said they expect to match that timeframe.Would Infinera be handicapped by lagging the coherent market? The source who shared Infinera's supposed timetable with Light Reading said no: "They were six years late to 10 Gbit/s, but it didn't matter."The dual 50-Gbit/s option is certainly viable, considering Verizon is using it. Glenn Wellbrock, the carrier's director of backbone network design, defended the technology during his talk at the The Optical Society (OSA) Executive Forum that preceded OFC/NFOEC, saying it works because the two wavelengths fit within one ITU slot."Spectral efficiency, going into one ITU 50GHz grid, is what mattered to us," he said. Heavy Reading's Perrin thinks Infinera intends to use a multi-wavelength technique for 40 Gbit/s as well.

The problem he sees is that competitors such as Alcatel-Lucent (NYSE: ALU), Huawei Technologies Co. Ltd. , and Opnext Inc. (Nasdaq: OPXT) are already testing out single-wavelength 100-Gbit/s transport, "so the momentum is definitely in that direction," he writes in an email to Light Reading."It is clear that 100G momentum is around coherent so any vendor will need this ability for long-haul applications. I don’t see a way around that requirement for long-haul DWDM," Perrin continues.Infinera isn't confirming or commenting on its future plans. But Rick Dodd, the company's vice president of marketing, makes it clear that coherent receivers are in Infinera's future. "We absolutely believe in coherent, this is in fact why we opened our design center in Ottawa and hired some of the best guys in the world there," Dodd writes in an email to Light Reading. Infinera considers coherent technology to be necessary only when carriers go beyond having 3.2 Tbit/s of traffic on one fiber, Dodd notes. That would equate to speeds exceeding 40 Gbit/s on an 80-wavelength grid.

Because Infinera's technology is based around the massive integration of components into PICs, Dodd says the company is looking forward to the era of coherent technology, which uses lots of components. — Craig Matsumoto, West Coast Editor, Light Reading