ECOC 2015 Review - Part 1
- Several companies announced components for 400 gigabit optical transmission
- NEL announced a 200 gigabit coherent DSP-ASIC
- Lumentum ramps production of its ROADM blades while extending the operating temperature of its tunable SFP+
400 gigabit
Oclaro, Teraxion and NeoPhotonics detailed their latest optical components for 400 gigabit optical transmission using coherent detection.
Oclaro and Teraxion announced 400 gigabit modulators for line-side transmission; Oclaro’s based on lithium niobate and Teraxion’s an indium phosphide one.
NeoPhotonics outlined other components that will be required for higher-speed transmission: indium phosphide-based waveguide photo-detectors for coherent receivers, and ultra-narrow line-width lasers suited for higher order modulation schemes such as dual-polarisation 16-quadrature amplitude modulation (DP-16-QAM) and DP-64-QAM.
There are two common approaches to achieve higher line rates: higher-order modulation schemes such as 16-QAM and 64-QAM, and optics capable of operating at higher signalling rates.
Using 16-QAM doubles the data rate compared to quadrature phase-shift keying (QPSK) modulation that is used at 100 Gig, while 64-QAM doubles the data rate again to 400 gigabit.
Higher-order modulation can use 100 gigabit optics but requires additional signal processing to recover the received data that is inherently closer together. “What this translates to is shorter reaches,” says Ferris Lipscomb, vice president of marketing at NeoPhotonics.
These shorter distances can serve data centre interconnect and metro applications where distances range from sub-100 kilometers to several hundred kilometers. But such schemes do not work for long haul where sensitivity to noise is too great, says Lipscomb.
What we are seeing from our customers and from carriers looking at next-generation wavelength-division multiplexing systems for long haul is that they are starting to design their systems and are getting ready for 400 Gig
Lipscomb highlights the company’s dual integrable tunable laser assembly (iTLAs) with its 50kHz narrow line-width. “That becomes very important for higher-order modulation because the different states are closer together; any phase noise can really hurt the optical signal-to-noise ratio,” he says
The second approach to boost transmission speed is to increase the signalling rate. “Instead of each stream at 32 gigabaud, the next phase will be 42 or 64 gigabaud and we have receivers that can handle those speeds,” says Lipscomb. The use of 42 gigabaud can be seen as an intermediate step to a higher line rate - 300 gigabit – while being less demanding on the optics and electronics than a doubling to 64 gigabaud.
Oclaro’s lithium niobate modulator supports 64 gigabaud. “We have increased the bandwidth beyond 35 GHz with a good spectral response – we don’t have ripples – and we have increased the modulator’s extinction ratio which is important at 16-QAM,” says Robert Blum, Oclaro’s director of strategic marketing.
We have already demonstrated a 400 Gig single-wavelength transmission over 500km using DP-16-QAM and 56 gigabaud
Indium phosphide is now coming to market and will eventually replace lithium niobate because of the advantages of cost and size, says Blum, but lithium niobate continues to lead the way for highest speed, long-reach applications. Oclaro has been delivering its lithium niobate modulator since the third quarter of the year.
Teraxion offers an indium phosphide modulator suited to 400 gigabit. “One of the key differentiators of our modulator is that we have a very high bandwidth such that single-wavelength transmission at 400 Gig is possible,” says Martin Guy, CTO and strategic marketing at Teraxion. “We have already demonstrated a 400 Gig single-wavelength transmission over 500km using DP-16-QAM and 56 gigabaud.”
“What we are seeing from our customers and from carriers looking at next-generation wavelength-division multiplexing systems for long haul is that they are starting to design their systems and are getting ready for 400 Gig,” says Blum.
Teraxion says it is seeing a lot of activity regarding single-wavelength 400 Gig transmission. “We have sampled product to many customers,” says Guy.
NeoPhotonics says the move to higher baud rates is still some way off with regard systems shipments, but that is what people are pursuing for long haul and metro regional.
200 Gig DSP-ASIC
Another key component that will be needed for systems operating at higher transmission speeds is more powerful coherent digital signal processors (DSPs). NTT Electronics (NEL) announced at ECOC that it is now shipping samples of its 200 gigabit DSP-ASIC, implemented using a 20nm CMOS process.
Dubbed the NLD0660, the DSP features a new core that uses soft-decision forward error correction (SD-FEC) that achieves a 12dB net coding gain. Improving the coding gain allows greater spans before optical regeneration or longer overall reach, says NEL. The DSP-ASIC supports several modulation formats: DP-QPSK, DP-8-QAM and DP-16-QAM, for 100 Gig, 150 Gig and 200 Gig rates, respectively. Using two NLD0660s, 400 gigabit coherent transmission is achieved.
NEL announced its first 20nm DSP-ASIC, the lower-power 100 gigabit NLD0640 at OFC 2015 in March. At the same event, ClariPhy demonstrated its own merchant 200 gigabit DSP-ASIC.
Reconfigurable optical add/ drop multiplexers
Lumentum gave an update on its TrueFlex route & select architecture Super Transport Blade, saying it has now been qualified, with custom versions of the line card being manufactured for equipment makers. The Super Transport Blades will be used in next-generation ROADMs for 100 gigabit metro deployments. The Super Transport Blade supports flexible grid, colourless, directionless and contentionless ROADM designs.
“This is the release of the full ROADM degree for next-generation networks, all in a one-slot line card,” says Brandon Collings, CTO of Lumentum. “It is a pretty big milestone; we have been talking about it for years.”
Collings says that the cards are customised to meet an equipment maker’s particular requirements. “But they are generally similar in their core configuration; they all use twin wavelength-selective switches (WSSes), those sort of building blocks.”
This is the release of the full ROADM degree for next-generation networks, all in a one-slot line card. It is a pretty big milestone; we have been talking about it for years
Lumentum also announced 4x4 and 6x6 integrated isolator arrays. “If you look at those ROADMs, there is a huge number of connections inside,” says Collings. The WSSes can be 1x20 and two can be used - a large number of fibres - and at certain points isolators are required. “Using discrete isolators and needing a large number, it becomes quite cumbersome and costly, so we developed a way to connect four or six isolators in a single package,” he says.
A 6x6 isolator array is a six-lane device with six hardwired input/ output pairs, with each input/ output pair having an isolator between them. “It sounds trivial but when you get to that scale, it is truly enabling,” says Collings.
Isolators are needed to keep light from going in the wrong direction. “These things can start to accumulate and can be disruptive just because of the sheer volume of connections that are present,” says Collings.
Tunable transceivers
Lumentum offers a tunable SFP+ module that consumes less than 1.5W while operating over a temperature range of -5C to +70C. At ECOC, the company announced that in early 2016 it will release a tunable SFP+ with an extended temperature range of -5C to +85C.
Further information
Heading off the capacity crunch, click here
For the ECOC Review, Part 1, click here
Finisar adds silicon photonics to its technology toolkit
- Finisar revealed its in-house silicon photonics design capability at ECOC
- The company also showed its latest ROADM technologies: a dual wavelength-selective switch and a high-resolution optical channel monitor.
- Also shown was an optical amplifier that spans 400km fibre links
These two complementary technologies [VCSELs and silicon photonics] work well together as we think about the next-generation Ethernet applications.
Rafik Ward
Finisar demonstrated at ECOC its first optical design implemented using silicon photonics. The photonic integrated circuit (PIC) uses a silicon photonics modulator and receiver and was shown operating at 50 Gigabit-per-second.
The light source used with the PIC was a continuous wave distributed feedback (DFB) laser. One Finisar ECOC demonstration showed the eye diagram of the 50 Gig transmitter using non-return-to-zero (NRZ) signalling. Separately, a 40 Gig link using this technology was shown operating error-free over 12km of single mode fibre.
"Finisar, and its fab partner STMicroelectronics, surprised the market with the 50 Gig silicon photonics demonstration,” says Daryl Inniss, practice leader of components at Ovum.
"This, to our knowledge, was the first public demonstration of silicon photonics running at such a high speed," says Rafik Ward, vice president of marketing at Finisar. However, the demonstrations were solely to show the technology's potential. "We are not announcing any new products," he says.
Potential applications for the PIC include the future 50 Gig IEEE Ethernet standard, as well as a possible 40 Gig serial Ethernet standard. "Also next-generation 400 Gig Ethernet and 100 Gig Ethernet using 50 Gig lanes," says Ward. "All these things are being discussed within the IEEE."
Jerry Rawls, co-founder and chairman of Finisar, said in an interview a year ago that the company had not developed any silicon photonics-based products as the technology had not shown any compelling advantage compared to its existing optical technologies.
Now Finisar has decided to reveal its in-house design capability as the technology is at a suitable stage of development to show to the industry. It is also timely, says Ward, given the many topics and applications being discussed in the standards work.
The company sees silicon photonics as part of its technology toolkit available to its engineers as they tackle next-generation module designs.
Finisar unveiled a vertical-cavity surface-emitting laser (VCSEL) operating at 40 Gig at the OFC show held in March. The 40 Gig VCSEL demonstration also used NRZ signalling. IBM has also published a technical paper that used Finisar's VCSEL technology operating at 50 Gbps.
"What we are trying to do is come up with solutions where we can enable a common architecture between the short wave and the long wave optical modules," says Ward. "These two complementary technologies [VCSELs and silicon photonics] work well together as we think about the next-generation Ethernet applications."
Cisco Systems, also a silicon photonics proponent, was quoted in the accompanying Finisar ECOC press release as being 'excited' to see Finisar advancing the development of silicon photonics technology. "Cisco is our biggest customer," says Ward. "We see this as a significant endorsement from a very large user of optical modules." Cisco acquired silicon photonics start-up Lightwire for $271 million in March 2012.
ROADM technologies
Finisar also demonstrated two products for reconfigurable optical add/ drop multiplexers (ROADM): a dual configuration wavelength-selective switch (WSS) and an optical channel monitor (OCM).
The dual-configuration WSS is suited to route-and-select ROADM architectures.
Two architectures are used for ROADMs: broadcast-and-select and route-and-select. With broadcast-and-select, incoming channels are routed in the various directions using a passive splitter that in effect makes copies of the incoming signal. To route signals in the outgoing direction, a 1xN WSS is used. However, due to the optical losses of the splitters, such an architecture is used for low node-degree applications. For higher-degree nodes, the optical loss becomes a barrier, such that a WSS is also used for the incoming signals, resulting in the route-and-select architecture. A dual-configuration WSS thus benefits a route-and-select ROADM design.
Finisar's WSS module is sufficiently slim that it occupies a single-chassis slot, unlike existing designs that require two. "It enables system designers to free up slots for other applications such as transponder line cards inside their chassis," says Ward.
The dual WSS modules support flexible grid and come in 2x1x20, 2x1x9 and 2x8x12 configurations. "There are some architectures being discussed for add/ drop that would utilise the WSS in that [2x8x12] configuration," says Ward.
The ECOC demonstrations included different traffic patterns passing through the WSS, as well as attenuation control and the management of super-channels.
Finisar also showed an accompanying high-resolution OCM that also occupies a single-chassis slot. The OCM can resolve the spectral power of channels as narrow as 6.25GHz. The OCM, a single-channel device, can scan a fibre's C-band in 200ms.
A rule of thumb is that an OCM is used for each WSS. A customer often monitors channels on a single fibre, says Ward, and must pick which fibres to monitor. The OCM is typically connected to each fibre or to an optical switch to scan multiple fibres.
"People are looking to use the spectrum in a fibre in a much more optimised way," says Ward. The advent of flexible grid and super-channels requires a much tighter packing of channels. "So, being able to see and identify all of the key elements of these channels and manage them is going to become more and more difficult," he says, with the issue growing in importance as operators move to line speeds greater than 100 Gig.
Finisar also used the ECOC show to demonstrate repeater-less transmission using an amplifier that can span 400km of fibre. Such an amplifier is used in harsh environments where it is difficult to build amplifier huts. The amplifier can also be used for certain submarine applications known as 'festooning' where the cable follows a coastline and returns to land each time amplification is required. Using such a long-span amplifier reduces the overall hops back to the coast.