Adam Carter, Oclaro’s chief commercial officer, discusses the company’s 400-gigabit and higher-speed coherent optical transmission plans and the 400-gigabit client-side pluggable opportunity.    

Oclaro showcased its first coherent module that uses Ciena’s WaveLogic Ai digital signal processor at the ECOC show held recently in Gothenburg.

Adam CarterOclaro is one of three optical module makers, the others being Lumentum and NeoPhotonics, that signed an agreement with Ciena earlier this year to use the system vendor’s DSP technology and know-how to bring coherent modules to market. The first product resulting from the collaboration is the Waveserver 4Ai, a 5x7-inch board-mounted module that supports 400-gigabits on a single-wavelength.   

First Waveserver 4Ai modules are already being tested at several of Oclaro’s customers’ labs. “They [the module samples] are very preliminary,” says Adam Carter, the chief commercial officer at Oclaro. “The really important timeframe is when we get towards the new year because then we will have beta samples.”

DSP developments

The Waveserver 4Ai module is a Ciena design and Carter admits there isn’t going to be much differentiation between the three module makers’ products.

“We have some of the key components that sit inside that module and the idea is, over time, we would design in the rest of the componentry that we make that isn’t already in there,” says Carter. “But it is still going to be the same spec between the three suppliers.” 

The collaboration with the module makers helps Ciena promote its coherent DSP to a wider market and in particular China, a market where its systems are not deployed. 

Over time, the scope for differentiation between the three module makers will grow. “It [the deal] gives us access to another DSP chip for potential future applications,” says Carter.

Here, Oclaro will be the design authority, procuring the DSP chip for Ciena before adding its own optics. “So, for example, for the [OIF’s] 400G ZR, we would ask Ciena to develop a chip to a certain spec and then put our optical sub-assemblies around it,” says Carter. “This is where we do believe we can differentiate.” 

Oclaro also unveiled at ECOC an integrated coherent transmitter and an intradyne coherent receiver optical sub-assemblies using its indium phosphide technology that operate at up to 64 gigabaud (Gbaud).

We expect to see 64Gbaud optical systems being trialed in 2018 with production systems following at the end of next year

A 64Gbaud symbol rate enables a 400-gigabit wavelength using 16-ary quadrature amplitude modulation (16-QAM) and a 600-gigabit wavelength using 64-QAM.

Certain customers want such optical sub-assemblies for their line card designs and Oclaro will also use the building blocks for its own modules. The devices will be available this quarter. “We expect to see 64Gbaud optical systems being trialed in 2018 with production systems following at the end of next year and the beginning of 2019,” says Carter.

Oclaro also announced that its lithium niobate modulator supporting 400-gigabit single wavelengths is now in volume production. “Certain customers do have their preferences when it comes to first designs and particularly for long-reach systems,” says Carter. “Lithium niobate seems to be the one people go with.”

400-gigabit form factors

Oclaro did not make any announcements regarding 400-gigabit client-side modules at ECOC. At the OFC show held earlier this year, it detailed two CFP8-based 400-gigabit designs based on eight wavelengths with reaches of 10km and 40km.

“We are sampling the 400-gigabit 10km product right now,” says Carter. “The product is being tested at the system level and will go through various qualification runs.” 

The 40km CFP8 product is further out. There are customers interested in such a module as they have requirements to link IP routers that are more than 10km apart.

Carter describes the CFP8 400-gigabit modules as first-generation products. The CFP8 is similar in size to the CFP2 pluggable module and that is too large for the large-scale data centre players. They want higher aggregate bandwidth and greater front panel densities for their switches and are looking such form factors as the double-density QSFP (QSFP-DD) and the Octal Small Form Factor pluggable (OSFP).

The OSFP is a fresh design, has a larger power envelope - some 15W compared to the 12W of the QSFP-DD - and has a roadmap that supports 800-gigabit data rates. In contrast, the QSFP-DD is backward compatible with the QSFP, an attractive feature for many vendors.

But it is not only a module’s power envelope that is an issue for 400-gigabit designs but also whether a one-rack-unit box can be sufficiently cooled when fully populated to avoid thermal runaway. Some 36 QSFP-DDs can fit on the front panel compared to 32 OSFPs.

Carter stresses both form factors can’t be dismissed for 400-gigabit: “Everyone is pursuing designs that are suitable for both.” Oclaro is not an advocate of either form factor given it provides optical sub-assemblies suitable for both.

The industry really wants four-channels. When you use more lasers, you are adding more cost.

Optical formats

Oclaro’s core technology is indium phosphide and, as such, its focusses on single-mode fibre designs.

The single mode options for 400 gigabits are split between eight-wavelength designs such as the IEEE 802.3bs 2km 400GBASE-FR8 and 10km 400GBASE-LR8 and the newly announced CWDM8 MSA, and four-wavelength specifications - the 500m IEEE 802.3bs parallel fibre 400GBASE-DR4 and the 2km 100G Lambda MSA 400G-FR4 that is under development. Oclaro is a founding member of the 100 Gigabit Lambda MSA but has not joined the CWDM8 MSA. 

"The industry really wants four channels," says Carter. "When you use more lasers, you are adding more cost." It is also not trivial fitting eight lasers into a CFP8 never mind into the smaller QSFP-DD and OSFP modules. 

“There might be some that have the technology to do the eight-channel part and there might be customers that will use that,” says Carter. “But most of the discussions we’ve been having are around four channels.”

Challenges

The industry’s goal is to have 400-gigabit QSFP-DD and OSFP module in production by the end of next year and into 2019. “There is still some risk but everybody is driving to meet that schedule,” says Carter.

Oclaro says first samples of 100-gigabit PAM-4 chips needed for 100-gigabit single wavelengths are now in the labs. Module makers can thus add their optical sub-assemblies to the chips and start testing system performance. Four-channel PAM-4 chips will be needed for the 400-gigabit module products.

Carter also acknowledges that any further delay in four-wavelength designs could open the door for other 400-gigabit solutions and even interim 200-gigabit designs.

“As a transceiver supplier and an optical component supplier you are always aware of that,” he says. “You have to have backup plans if that comes off.”  

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