ECOC 2015 Review - Final Part

The second and final part of the survey of developments at the ECOC 2015 show held recently in Valencia.  

Part 2 - Client-side component and module developments   

• The first SWDM Alliance module shown
• More companies detail CWDM4, CLR4 and PSM4 mid-reach modules
• 400 Gig datacom technologies showcased
• The CFP8 MSA for 400 Gigabit Ethernet unveiled

The CFP MSA modules including the newest CFP8. Source: Finisar

• Lumentum and Kaiam use silicon photonics for mid-reach modules
• Finisar demonstrates a 10 km 25 Gig SFP28, and low-latency 25 Gig and 100 Gig SR4 interfaces 

Shortwave wavelength-division multiplexing

Finisar demonstrated the first 100 gigabit shortwave wavelength-division multiplexing (SWDM) module at ECOC. Dubbed the SWDM4, the 100 gigabit interface supports WDM over multi-mode fibre. Finisar showed a 40 version at OFC earlier this year. “This product [the SWDM4] provides the next step in that upgrade path,” says Rafik Ward, vice president of marketing at Finisar. 

The SWDM Alliance was formed in September to exploit the large amount of multi-mode fibre used by enterprises. The goal of the SWDM Alliance is to extend the use of multi-mode fibre by enabling link speeds beyond 10 gigabit.

“We believe if you can do something with multi-mode fibre, you can achieve cost points that are not achievable with single-mode fibre,” says Ward. “SWDM4 allows us to have not only low-cost optics on either end, but allows customers to reuse their installed fibre.”

The SWDM4 interface uses four 25 gigabit VCSELs operating at wavelengths sufficiently apart that cooling is not required. “By having this [wavelength] gap, you can keep to relatively low-cost components like for multiplexing and de-multiplexing,” says Ward.

The 100 Gig SWDM4 achieves 70 meters over OM3 fibre and 100 meters over OM4 fibre. SWDM can scale beyond 100 gigabit, says Ward, but the challenge with multi-mode fibre remains the tradeoff between speed and distance.

Finisar is already shipping SWDM4 alpha samples to customers.

The SWDM Alliance founding members include CommScope, Corning, Dell, Finisar, H3C, Huawei, Juniper Networks, Lumentum, and OFS.

CWDM4, CLR4 and PSM4

Oclaro detailed a 100 gigabit mid-reach QSFP28 module that supports both the CWDM4 multi-source agreement (MSA) and the CLR4 MSA. “We can support either depending on whether, on the host card, there is forward-error correction or not,” says Robert Blum, director of strategic marketing at Oclaro.

Both MSAs have a 2 km reach and use four 25 gigabit channels. However, the CWDM4 uses a more relaxed optical specification as its overall performance is complemented with forward-error correction (FEC) on the host card. The CLR4, in contrast, does not use FEC and therefore requires a more demanding optical specification.

“The requirements are significantly harder to meet for the CLR4 specification,” says Blum. By avoiding FEC, the CLR4 module benefits low-latency applications such as financial trading.

Oclaro showed its dual-MSA module achieving a 10 km reach at ECOC even though the two specifications call for 2 km only. “We have very large margins for the module compared to the specification,” says Blum, adding that customers now need to only qualify one module to meet their CWDM4 or CLR4 line card needs.

Other optical module vendors that announced support for CWDM4 in a QSFP28 module include Source Photonics, whose module is also CLR4-compliant. Kaiam is making CWDM4 and CLR4 modules using silicon photonics as part of its designs.

Lumentum also detailed its CWDM4 and the PSM4, a QSFP28 that uses a single-mode ribbon cable to deliver 100 Gig over 500 meters. Lumentum says its CWDM4 and PSM4 QSFP28 products will be available this quarter. “These 100 gigabit modules are what the hyper-scale data centre operators are clamouring for,” says Brandon Collings, CTO of Lumentum.

The question is who can ramp and support the 100 Gig deployments that are going to happen next year

Lumentum says it is using silicon photonics technology for one of its designs but has not said which. “We have both technologies [indium phosphide and silicon photonics], we use both technologies, and silicon photonics is involved with one of these [modules],” says Collings.

There is demand for both the PSM4 and CWDM4, says Lumentum. Which type a particular data centre operator chooses depends on such factors as what fibre they have or plan to deploy, whether they favour single-mode fibre pairs or ribbon cable, and if their reach requirements are beyond 500 meters.

Quite a few module companies have already sampled [100 Gig] products, says Oclaro’s Blum: “The question is who can ramp and support the 100 Gig deployments that are going to happen next year.”

Technologies for 400 gigabit

Several companies demonstrated technologies that will be needed for 400 gigabit client-side interfaces.

NeoPhotonics and chip company InPhi partnered to demonstrate the use of PAM-4 modulation to achieve 100 gigabit. “To do PAM-4, you need not only the optics but a special PAM-4 DSP,” says Ferris Lipscomb, vice president of marketing at NeoPhotonics.

The 400 Gigabit Ethernet standard under development by the IEEE 802.3bs supports several configurations using PAM-4 including a four-channel parallel single-mode fibre configuration, each at 100 gigabit that will have a 500m reach, and two 8 x 50 gigabit, for 2 km and 10 km links.    

The company showcased its 4x28 Gig transmitter optical sub-assembly (TOSA) that uses a photonic integrated circuit comprising electro-absorptive modulated lasers (EMLs). Combined with InPhi’s PAM-4 chip, two channels were combined to achieve 100 gigabit. NeoPhotonics says its EMLs are also capable of supporting 56 gigabaud rates which, coupled with PAM-4, would achieve 100 gigabit single channels. 

Lipscomb points out that not only are there several interfaces under development but also various optical form factors. “For 100 Gig and 400 Gig client-side data centre links, there are several competing MSA groups,” says Lipscomb. “The final winning approach has not yet emerged and NeoPhotonics wants its solution to be generic enough so that it supports this winning approach once it emerges.” 

Meanwhile, Teraxion announced its silicon photonics-based modulator technology for 100 gigabit (4 x 25 Gig) and 400 gigabit datacom interfaces. “People we talk to are interested in WDM applications for short-reach links,” says Martin Guy, Teraxion’s CTO and strategic marketing.

Teraxion says a challenge using silicon photonics for WDM is supporting a broad band of wavelengths. “People use surface gratings to couple light into the silicon photonics,” says Guy. “But surface gratings have a strong wavelength-dependency over the C-band.”

Teraxion has developed an edge coupler instead which is on the same plane as the propagating light. This compares to a surface grating where light is coupled vertical to the plane.

You hear a lot about the cost of silicon photonics but one of the key advantages is the density you can achieve on the chip itself. Having many modulators in a very small footprint has value for the platform; you can make smaller and smaller transceivers. 

“We can couple light efficiently with large-tolerance alignment and our approach can be used for WDM applications,” says Guy. Teraxion’s modulator array can be used for CWDM4 and CLR4 MSAs as well as optical engines for future 400 gigabit datacom systems. 

“You hear a lot about the cost of silicon photonics but one of the key advantages is the density you can achieve on the chip itself,” says Guy. “Having many modulators in a very small footprint has value for the platform; you can make smaller and smaller transceivers.” 

CFP8 MSA

Finisar demonstrated a 400 gigabit link that included a mock-up of the CFP8 form factor, the latest CFP MSA member being developed to support emerging standards such as 400 Gigabit Ethernet.

The 400 gigabit demonstration implemented the 400GE-SR16 multi-mode standard. A Xilinx FPGA was used to implement an Ethernet MAC and generated 16, 25 Gig channels that were fed to four CFP4 modules, each implementing a 100GBASE-SR4 but collectively acting as the equivalent of the 400GE-SR16. The 16 fibre outputs were then fed to the CFP8 prototype which performed an optical loop-back function, sending the signals back to the CFP4s and FPGA.

The CFP8 will be able to support 6.4 terabit of switching on a 1U card when used in a 2 row by 8 module configuration. The CFP8 has a similar size and power consumption profile of the CFP2. “There is still a lot of work putting an MSA together for 400 gigabit,” says Ward, adding that there is still no timeframe as to when the CFP8 MSA will be completed.

25 Gig SFP28

Finisar also announced at ECOC a 1310nm SFP28 supporting 25 gigabit Ethernet over 10 km, complementing the 850nm SFP28 short reach module it announced at OFC 2015.

Ethernet vendors are designing their next-generation series of switches that use the SFP28, says Finisar, while the IEEE is completing standardising 25 Gigabit Rthernet over copper and multi-mode fibre options.

“There hasn’t yet been a motion to standardise a long-wave interface,” says Ward. “With the demo at ECOC, we have come out with a 25 Gig long-wave interface in advance of a standard.”       

Ward points out that the large-scale data centres several years ago only had 40 gigabit as a higher speed option beyond 10 gigabit. Now enterprises will also have a 25 gigabit option.

Ward points out that 25 gigabit compared to 40 Gig delivers an attractive cost-performance. Forty gigabit short-reach and long-reach interfaces are based on four channels at 10 gigabit, whereas 25 gigabit uses one laser and one photo-detector that fit in an SFP28. This compares to a QSFP for 40 Gig.

“25 Gigabit Ethernet is a very interesting interface for the next set of customers after the Web 2.0 players that are looking to migrate beyond 10 gigabit,” said Ward.     

Low-latency 25 Gig SR and 100 Gig Ethernet SR4 modules

Also announced by Finisar are 25 Gigabit Ethernet SFP28 SR and 100GE QSFP28 SR4 transceivers that can operate without accompanying FEC on the host board. The transceivers achieve a 30 meter reach on OM3 fibre and 40 meters using OM4 fibre.

“Using FEC simplifies the optical link,” says Ward. “It can take the cost out of the optics by having FEC which gives you additional gain.”  But some customers have requested the parts for use without FEC to reduce link latency, similar to those that choose the CLR4 MSA for mid-reach 100 Gig.

Finisar has not redesigned its modules but offering modules that have its higher performing VCSELs and photo-detectors. “Think of it as a simple screen,” says Ward.

Click here for the ECOC 2015 Review - Part 1.