60-second interview with .... Sterling Perrin
Heavy Reading has published a report Photonic Integration, Super Channels & the March to Terabit Networks. In this 60-second interview, Sterling Perrin, senior analyst at the market research company, talks about the report's findings and the technology's importance for telecom and datacom.
"PICs will be an important part of an ensemble cast, but will not have the starring role. Some may dismiss PICs for this reason, but that would be a mistake – we still need them."
Sterling Perrin, Heavy Reading
Heavy Reading's previous report on optical integration was published in 2008. What has changed?
The biggest change has been the rise of coherent detection, bringing electronics to prominence in the world of optics. This is a big shift - and it has taken some of the burden off photonic integration. Simply put, electronics has taken some of the job away from optics.
How important is optical Integration, for optical component players and for system vendors?
Until now, photonic integration has not been a ‘must have’ item for systems suppliers. For the most part, there have been other ways to get at lower costs and footprint reductions.
I think we are starting to see photonic integration move into the must-have category for systems suppliers, in certain applications, which means that it becomes a must-have item for the components companies that supply them.
How should one view silicon photonics and what importance does Heavy Reading attach to Cisco System's acquisition of silicon photonics' startup, Lightwire?
When we published the last [2008] report, silicon photonics was definitely within the hype cycle. We’ve seen the hype fade quite a bit – it’s now understood that just because a component is made with silicon, it’s not automatically going to be cheaper. Also, few in the industry continue to talk about a Moore’s Law for optics today. That said, there are applications for silicon photonics, particularly in data centre and short-reach applications, and the technology has moved forward.
Cisco’s acquisition of Lightwire is a good testament for how far the technology has come. This is a strategic acquisition, aimed at long-term differentiation, and Cisco believes that silicon photonics will help them get there.
"It will be interesting to watch what other [optical integration] M&A activity occurs, and how this activity affects the components players"
What are the main optical integration market opportunities?
In long haul, we already see applications for photonic integrated circuits (PICs). Certainly, Infinera’s PIC-based DTN and DTN-X systems stand out. But also, the OIF has specified photonic integration in its 100 Gigabit long haul, DWDM (dense wavelength division multiplexing) MSA (multi-source agreement) – it was needed to get the necessary size reduction.
Moving forward, there is opportunity for PICs in client-side modules as PICs are the best way to reduce module sizes and improve system density. Then, beyond 100G, to super-channel-based long-haul systems, PICs will play a big role here, as parallel photonic integration will be used to build these super-channels.
Were you surprised by any of the report's findings?
When I start researching a report, I am always hopefully for big black and white kinds of findings – this is the biggest thing for the industry or this is a dud. With photonic integration, we found such a wide array of opinions and viewpoints that, in the end, we had to place photonic integration somewhere in the middle.
It’s clear that system vendors are going to need PICs but it’s also clear that PICs alone won’t solve all the industry’s challenges. PICs will be an important part of an ensemble cast, but will not have the starring role. Some may dismiss PICs for this reason, but that would be a mistake – we still need them.
What optical integration trends/ developments should be watched over the next two years?
The year started with two major system suppliers buying PIC companies: Cisco and Lightwire and Huawei and CIP Technologies. With Alcatel-Lucent having in-house abilities, and, of course, Infinera, this should put pressure on other optical suppliers to have a PIC strategy.
It will be interesting to watch what other M&A activity occurs, and how this activity affects the components players.
The editor of Gazettabyte worked with Heavy Reading in researching photonic integration for the report.
Huawei boosts its optical roadmap with CIP acquisition
Huawei has acquired UK photonic integration specialist, CIP Technologies, from the East of England Development Agency (EEDA) for an undisclosed fee. The acquisition gives the Chinese system vendor a wealth of optical component expertise and access to advanced European Union R&D projects.
"By acquiring CIP and integrating the company’s R&D team into Huawei’s own research team, Huawei’s optic R&D capabilities can be significantly enhanced," says Peter Wharton, CEO at the Centre for Integrated Photonics (CIP). CIP Technologies is the trading name of the Centre for Integrated Photonics.
Huawei now has six European R&D centres with the acquisition of CIP.
CIP Technologies has indium phosphide as well as planar lightwave circuit (PLC) technology which it uses as the basis for its HyBoard hybrid integration technology. HyBoard allows actives to be added to a silica-on-silicon motherboard to create complex integrated optical systems.
CIP has been using its photonic integration expertise to develop compact, more cost-competitive WDM-PON optical line terminal (OLT) and optical network unit (ONU) designs, including the development of an integrated transmitter array.
The company employs 50 staff, with 70% of its work coming from the telecom and datacom sectors. About a third of its revenues are from advanced products and two thirds from technical services.
The CEO of CIP says all current projects for its customers will be carried out as planned but CIP’s main research and development service will be focused on Huawei’s business priorities. “We expect all contracted projects to be completed and current customers are being assisted to find alternate sources of supply," says Wharton.
CIP is also part of several EU Seventh Framework programme R&D projects. These include BIANCHO, a project to reduce significantly the power consumption of optical components and systems, and 3CPO, which is developing colourless and coolerless optical components for low-power optical networks.
Huawei's acquisition will not affect CIP's continuing participation in such projects. "For EU framework and other collaborative R&D projects, the ultimate share ownership does not matter so long as it is a research organisation based in Europe, which CIP will continue to be," says Wharton.
CIP said it had interest from several potential acquirers but that the company favoured Huawei.
What this means
CIP has a rich heritage. It started as BT's fibre optics group. But during the optical boom of 1999-2000, BT shed its unit, a move also adopted by such system vendors as Nortel and Lucent.
The unit was acquired by Corning in 2000 but the acquisition did not prove a success and in 2002 the group faced closure before being rescued by the East of England Development Agency (EEDA).
CIP has always been an R&D organisation in character rather than a start-up. Now with Huawei's ambition, focus and deep pockets coupled with CIP's R&D prowess, the combination could prove highly successful if the acquisition is managed well.
Huawei's acquisition looks shrewd. Optical integration has been discussed for years but its time is finally arriving. The technologies of 40 Gigabit and 100 Gigabit is based on designs with optical functions in parallel; at 400 Gigabit the number of channels only increases.
Optical access will also benefit from photonic integration - from board optical sub-assemblies for GPON and EPON to WDM-PON to ultra dense WDM-PON. China is also the biggest fibre-to-the-x (FTTx) market by far.
A BT executive talking about the operator's 21CN mentioned how system vendors used to ask him repeatedly about Huawei. Huawei, in contrast, used to ask him about Infinera.
Huawei, like all the other systems vendors, has much to do to match Infinera's photonic integrated circuit expertise and experience. But the Chinese vendor's optical roadmap just got a whole lot stronger with the acquisition of CIP.
Further reading:
Reflecting light to save power, click here
Bringing WDM-PON to market
"We see just one way to bring down the cost, form-factor and energy consumption of the OLT’s multiple transceivers: high integration of transceiver arrays"
Klaus Grobe, ADVA Optical Networking
Considerable engineering effort will be needed to make next-generation optical access schemes using multiple wavelengths competitive with existing passive optical networks (PONs).
Such a multi-wavelength access scheme, known as a wavelength division multiplexing-passive optical network (WDM-PON), will need to embrace new architectures based on laser arrays and reflective optics, and use advanced photonic integration to meet the required size, power consumption and cost targets.
Current PON technology uses a single wavelength to deliver downstream traffic to end users. A separate wavelength is used for upstream data, with each user having an assigned time slot to transmit.
Gigabit PON (GPON) delivers 2.5 Gigabit-per-second (Gbps) to between 32 or 64 users, while the next development, XG-PON, will extend GPON’s downstream data rate to 10 Gbps. The alternative PON scheme, Ethernet PON (EPON), already has a 10 Gbps variant. Vendors are also extending PON’s reach from 20km to 80km or more using signal amplification.
But the industry view is that after 10 Gigabit PON, the next step will be to introduce multiple wavelengths to extend the capacity beyond what a time-sharing approach can support. Extending the access network's reach to 100km will also be straightforward using WDM transport technology.
The advent of WDM-PON is also an opportunity for new entrants, traditional WDM optical transport vendors, to enter the access market. ADVA Optical Networking is one firm that has been vocal about its plans to develop next-generation access systems.
“We are seriously investigating and developing a next-generation access system and it is very likely that it will be a flavour of WDM-PON,” says Klaus Grobe, senior principal engineer at ADVA Optical Networking. “It [next-generation access] must be based on WDM simply because of bandwidth requirements.”
The system vendor views WDM-PON as addressing three main applications: wireless backhaul, enterprise connectivity and residential broadband. But despite WDM-PON’s potential to reduce operating costs significantly, the challenge facing vendors is reducing the cost of WDM-PON hardware. Indeed it is the expense of WDM-PON systems that so far has assigned the technology to specialist applications only.
A non-reflective tunable laser-based WDM-PON ONU. Source: ADVA Optical NetworkingAccording to Grobe, cost reduction is needed at both ends of the WDM-PON: the client receiver equipment known as the optical networking unit (ONU) and the optical line terminal (OLT) housed within an operator’s central office.
ADVA Optical Networking plans to use low-cost tunable lasers rather than a broadband light source and reflective optics for the ONU transceivers. “For the OLT, we see just one way to bring down the cost, form-factor and energy consumption of the OLT’s multiple transceivers: high integration of transceiver arrays,” says Grobe.
This is a considerable photonic integration challenge: a 40- or 80-wavelength WDM-PON uses 40 or 80 transceiver bi-directional clients, equating to 80 and 160 wavelengths. If 80 SFPs optical modules were used at the OLT, the resulting cost, size and power consumption would be prohibitive, says Grobe.
ADVA Optical Networking is working with several firms, one being CIP Technologies, to develop integrated transceiver arrays. ADVA Optical Networking and CIP Technologies are part of the EU-funded project, C-3PO, that includes the development of integrated transceiver arrays for WDM-PON.
Splitters versus filters
One issue with WDM-PON is that there is no industry-accepted definition. ADVA Optical Networking views WDM-PON as an architecture based on optical filters rather than splitters. Two consequences result once that choice is made, says Grobe.
One is insertion loss. Choosing filters implies arrayed waveguide gratings (AWGs), says Grobe. “No other filter technology is seriously considered for WDM-PON if filters are used,” he says.
With an AWG, the insertion loss is independent of the number of wavelengths supported. This differs from using a splitter-based architecture where every 1x2 device introduces a 3dB loss - “closer to 3.5dB”, he says. Using a 1x64 splitter, the insertion loss is 14 or 15dB whereas for a 40-channel AWG the loss can be as low as 4dB. “I just saw specs of a first 96-channel AWG, even that one isn’t much higher [than 4dB],” says Grobe. Thus using filters rather than splitters, the insertion loss is much lower for a comparable number of client ONUs.
There is also a cost benefit associated with a low insertion loss. To limit the cost of next-generation PON, the transceiver design must be constrained to a 25dB power budget associated with existing PON transceivers. “This is necessary to keep these things cheap, possibly dirt cheap,” says Grobe.
The alternative, using XG-PON’s sophisticated 10 Gbps burst-mode transceiver with its associated 35dB power budget, achieving low cost is simply not possible, he says. To live with transceivers with a 25dB power budget, the insertion loss of the passive distribution network must be minimised, explaining why filters are favoured.
The other main benefit of using filters is security. With a filter-based PON, wavelength point-to-point connections result. “You are not doing broadcast,” says Grobe. “You immediately get rid of almost all security aspects.” This is an issue with PON where traffic is shared.
Low power
Achieving a low-power WDM-PON system is another key design consideration. “In next-gen access, it is absolutely vital,” says Grobe. “If the technology is deployed on a broad scale - that is millions of user lines – every single watt counts, otherwise you end up with differences in the approaches that go into the megawatts and even gigawatts.”
There is also a benchmarking issue, says Grobe: the WDM-PON OLT will be compared to XG-PON’s even if the two schemes differ. Since XG-PON uses time-division multiplexing, there will be only one transceiver at the OLT. But this is what a 40- or 80-channel WDM-PON OLT will be compared with, even if the comparison is apples to pears, says Grobe.
WDM-PON workings
There are two approaches to WDM-PON.
In a fully reflective architecture, the OLT array and the ONUs are seeded using multi-wavelength laser arrays; both ends use the lasers arrays in combination with reflective optics for optical transmission.
ADVA Optical Networking is interested in using a reflective approach at the OLT but for the ONU it will use tunable lasers due to technical advantages. For example, using the same wavelength for the incoming and modulated streams in a reflective approach, Rayleigh crosstalk is an issue when the ONUs are 100km from the OLT. In contrast, Rayleigh crosstalk at the OLT is avoided because the multi-wavelength laser array is located only a few metres from the reflective electro-absorption modulators (REAMs).
REAMs are used rather than semiconductor optical amplifiers (SOAs) to modulate data at the OLT because they support higher bandwidth 10 Gbps wavelengths. Indeed the C-3PO project is likely to use a monolithically integrated SOA-REAM for this task. “The reflective SOA is narrower in bandwidth but has inherent gain while the REAM has loss rather than gain – it is just a modulator,” says Grobe. “The combination of the two is the ideal: giving high modulation bandwidth and high transmit power.”
The integrated WDM-PON OLT. In practice the transmit array uses a reflective architecture based on SOA-REAMs and is fed with a multi-wavelength laser source. Source: ADVA Optical Networking
For the OLT, a multi-wavelength laser is fed via an AWG into an array of SOA-REAMs which modulate the wavelengths and return them through the AWG where they are multiplexed and transmitted to the ONUs via a demultiplexing AWG. An added benefit of this approach, says Grobe, is that the same multi-wavelength laser source can be use to feed several WDM-PON OLTs, further decreasing system cost.
For the upstream path, each ONU’s wavelength is separated by the OLT’s AWG and fed to the receiver array. In a WDM-PON system, the OLT transmit wavelengths and receive wavelengths (from the ONUs) operate in separate optical bands.
Grobe expects its resulting WDM-PON system to use 40 or 80 channels. And to best meet size, power and cost constraints, the OLT design will likely implemented as a photonic integrated circuit. “We are after a single PIC solution,” he says. “It is clear that with the OLT, integration is the only way to meet requirements.” A photonically-integrated OLT design is one of the products expected from the C-3PO project, using CIP Technologies' hybrid integration technology.
ADVA Optical Networking has already said that its WDM-PON OLT will be implemented using its FSP 3000 platform.
- To see some WDM-PON architecture slides, click here.
Reflecting light to save power
System vendors will be held increasingly responsible for the power consumption of their telecom and datacom platforms. That’s because for each watt the equipment generates, up to six watts is required for cooling. It is a burden that will only get heavier given the relentless growth in network traffic.
"Enterprises are looking for huge capacity at low cost and are increasingly concerned about the overall impact on power consumption"
David Smith, CIP Technologies
No surprise, then, that the European 7th Framework Programme has kicked-off a research project to tackle power consumption. The Colorless and Coolerless Components for Low-Power Optical Networks (C-3PO) project involves six partners that include component specialist CIP Technologies and system vendors ADVA Optical Networking.
CIP is the project’s sole opto-electronics provider while ADVA Optical Networking's role is as system integrator.
“It’s not the power consumption of the optics alone,” says David Smith, CTO of CIP Technologies. “The project is looking at component technology and architectural issues which can reduce overall power consumption.”
The data centre is an obvious culprit, requiring up to 5 megawatts. Power is consumed by IT and networking equipment within the data centre – not a C-3PO project focus – and by optical networking equipment that links the data centre to other sites. “Large enterprises have to transport huge amounts of capacity between data centres, and requirements are growing exponentially,” says Smith. “They [enterprises] are looking for huge capacity at low cost and are increasingly concerned about the overall impact on power consumption.”
One C-3PO goal is to explore how to scale traffic without impacting the data centre’s overall power consumption. Conventional dense wavelength division multiplexing (DWDM) equipment isn’t necessarily the most power-efficient given that DWDM tunable lasers requires their own cooling. “There is the power that goes into cooling the transponder, and to get the heat away you need to multiply again by the power needed for air conditioning,” says Smith.
Another idea gaining attention is operating data centres at higher ambient temperatures to reduce the air conditioning needed. This idea works with chips that have a wide operating temperature but the performance of optics - indium phosphide-based actives - degrade with temperature such that extra cooling is required. As such, power consumption could even be worse, says Smith
A more controversial optical transport idea is changing how line-side transport is done. Adding transceivers directly to IP core routers saves on the overall DWDM equipment deployed. This is not a new idea, says Smith, and an argument against this is it places tunable lasers and their cooling on an IP router which operates at a relatively high ambient temperature. The power reduction sought may not be achieved.
But by adopting a new transceiver design, using coolerless and colourless (reflective) components, operating at a wider temperature range without needing significant cooling is possible. “It is speculative but there is a good commercial argument that this could be effective,” says Smith.
C-3PO will also exploit material systems to extend devices’ temperature range - 75oC to 85oC - to eliminate as much cooling as possible. Such material systems expertise is the result of CIP’s involvement in other collaborative projects.
"If the [WDM-PON] technology is deployed on a broad scale - that is millions of user lines – every single watt counts"
Klaus Grobe, ADVA Optical Networking
Indeed a companion project, to be announced soon, will run alongside C-3PO based on what Smith describes as ‘revolutionary new material systems’. These systems will greatly improve the temperature performance of opto-electronics. “C-3PO is not dependent on this [project] but may benefit from it,” he says.
Colourless and coolerless
CIP’s role in the project will be to integrate modulators and arrays of lasers and detectors to make coolerless and colourless optical transmission technology. CIP has its own hybrid optical integration technology called HyBoard.
“Coolerless is something that will always be aspirational,” says Smith. C-3PO will develop technology to reduce and even eliminate cooling where possible to reduce overall power consumption. “Whether you can get all parts coolerless, that is something to be strived for,” he says.
Colourless implies wavelength independence. For light sources, one way to achieve colourless operation is by using tunable lasers, another is to use reflective optics.
CIP Technologies has been working on reflective optics as part of its work on wavelength division multiplexing, passive optical networks (WDM-PON). Given such reflective optics work for distances up to 100km for optical access, CIP has considered using the technology for metro and enterprise networking applications.
Smith expects the technology to work over 200-300km, at data rates from 10 to 28 Gigabit-per-second (Gbps) per channel. Four 28Gbps channels would enable low-cost 100Gbps DWDM interfaces.
Reflective transmission
CIP’s building-block components used for colourless transmission include a multi-wavelength laser, an arrayed waveguide grating (AWG), reflective modulators and receivers (see diagram).
Reflective DWDM architecture. Source: CIP Technologies
Smith describes the multi-wavelength laser as an integrated component, effectively an array of sources. This is more efficient for longer distances than using a broadband source that is sliced to create particular wavelengths. “Each line is very narrow, pure and controlled,” says Smith.
The laser source is passed through the AWG which feds individual wavelengths to the reflective modulators where they are modulated and passed back through the AWG. The benefit of using a reflective modulator rather than a pass-through one is a simpler system. If the light source is passed through the modulator, a second AWG is needed to combine all the sources, as well as a second fibre. Single-ended fibre is also simpler to package.
For data rates of 1 or 2Gbps, the reflective modulator used can be a reflective semiconductor optical amplifier (RSOA). At speeds of 10Gbps and above, the complementary SOA-REAM (reflective electro-absorption modulator) is used; the REAM offers a broader bandwidth while the SOA offers gain.
The benefit of a reflective scheme is that the laser source, made athermal and coolerless, consumes far less power than tunable lasers. “It has to be at least half the cost and we think that is achievable,” says Smith.
Using the example of the IP router, the colourless SFP transceiver – made up of a modulator and detector - would be placed on each line card. And the multi-wavelength laser source would be fed to each card’s module.
Another part of the project is looking at using arrays of REAMs for WDM-PON. Such an modulator array would be used at the central office optical line terminal (OLT). “Here there are real space and cost savings using arrays of reflective electro-absorption modulators given their low power requirements,” says Smith. “If we can do this with little or no cooling required there will be significant savings compared to a tunable laser solution.”
ADVA Optical Networking points out that with an 80-channel WDM-PON system, there will be a total of 160 wavelengths (see the business case for WDM-PON). “If you consider 80 clients at the OLT being terminated with 80 SFPs, there will be a cost, energy consumption and form-factor overkill,” says Klaus Grobe, senior principal engineer at ADVA Optical Networking. “The only known solution for this is high integration of the transceiver arrays and that is exactly what C-3PO is about.”
The low-power aspect of C-3PO for WDM-PON is also key. “In next-gen access, it is absolutely vital,” says Grobe. “If the technology is deployed on a broad scale - that is millions of user lines – every single watt counts, otherwise you end up with differences in the approaches that go into the megawatts and even gigawatts.”
There is also a benchmarking issue: the WDM-PON OLT will be compared to the XG-PON standard, the next-generation 10Gbps Gigabit passive optical network (GPON) scheme. Since XG-PON will use time-division multiplexing, there will be only one transceiver at the OLT. But this is what a 40- or 80-channel WDM-PON OLT will be compared with.
CIP will also be working closely with 3-CPO partner, IMEC, as part of the design of the low-power ICs to drive the modulators.
Project timescales
The C-3PO project started in June 2010 and will last three years. The total funding of the project is €2.6 million with the European Union contributing €1.99 million.
The project will start by defining system requirements for the WDM-PON and optical transmission designs.
At CIP the project will employ the equivalent of two full-time staff for the project’s duration though Smith estimates that 15 CIP staff will be involved overall.
ADVA Optical Networking plans to use the results of the project – the WDM-PON and possibly the high-speed transmission interfaces - as part of its FSP 3000 WDM platform.
CIP expects that the technology developed as part of 3-CPO will be part of its advanced product offerings.