Elenion's coherent and fibre-to-the-server plans
- Elenion’s coherent chip - an integrated modulator-receiver assembly - is now generally available.
- The company has a silicon photonics design library that includes over 1,000 elements.
- Elenion is also developing an optical engine for client-side interfaces.
Elenion Technologies has given an update on its activities and strategy after announcing itself eight months ago. The silicon photonics-based specialist is backed by private equity firm, Marlin Equity Partners, which also owns systems vendor, Coriant. Elenion had already been active for two and a half years and shipping product when it emerged from its state of secrecy last December.
Larry SchwerinElenion has since announced it is selling its telecom product, a coherent transceiver PIC, to Coriant and now other companies.
It has also progressed its optical engine design for the data centre that will soon be a product. Elenion has been working with Ethernet switch chip maker, Cavium, and data centre player, Microsoft, as part of its datacom work.
“We have moved forward,” says Larry Schwerin, the CEO of Elenion.
Coherent PIC
Elenion’s integrated modulator-receiver assembly is being used by Coriant for two CFP2 Analogue Coherent Optics (CFP2-ACO) modules as part of its Groove G30 platform.
The first is a short-reach CFP2-ACO for point-to-point 200-gigabit links that has a reach of at least 80km. The second is a high-performance CFP2-ACO that has a reach of up to 4,000km at 100 gigabits and 650km at 200 gigabits.
Schwerin says the company is now selling the coherent PIC to “a lot of people”. In addition to the CFP2-ACO, there is the Digital Coherent Optics (DCO) pluggable market where the PIC and the coherent digital signal processor (DSP) are integrated within the module. Examples include the CFP-DCO and the smaller CFP2-DCO which is now being designed into new systems. ADVA Optical Networking is using the CFP2-DCO for its Teraflex, as is its acquisition target MRV with its 200-gigabit coherent muxponder. Infinera’s latest XTM II platforms also use the CFP2-DCO.
We have got a library that has well over 1,000 elements
Using silicon photonics benefits the cost and performance of the coherent design, says Schwerin. The cost benefit is a result of optical integration. “You can look at it as a highly simplified supply chain,” says Schwerin. Coupling the electronics close to the optics also optimises overall performance.
Elenion is also targeting the line-card market for its coherent PIC. “This is one of the reasons why I wanted to stay out of the pluggable business,” says Schwerin. “There are a lot more customers out there if you stay out of pluggables because now you are selling an [optical] engine.”
The company is also developing a coherent PIC design that will support higher data rates such as 400- and 600-gigabit per lambda. “Without being too specific because we do remain stealthy, we have plans to support these applications,” says Schwerin.
Schwerin stresses that the real strength of the company is its design library used to develop its silicon photonics circuits. Elenion emerged out of a silicon photonics design-for-service company. “We have got a library that has well over 1,000 elements,” he says. Elenion says it can address custom design requests of companies using its design library.
Datacom
Elenion announced at the OFC show held in Los Angeles in March that it is working with Jabil AOC Technologies, a subsidiary of the manufacturing firm, Jabil Circuits. Elenion chose the contract manufacturer due to its ability to address both line-card and pluggable designs, the markets for its optical engines.
The two firms have also been working at the chip level on such issues as fibre attach, coupling the laser and adding the associated electronics. “We are trying to make the interface as elegant and streamlined as possible,” says Schwerin. “We have got initiatives underway so that you don't need these complex arrangements.”
Schwerin highlights the disparity between the unit volumes needed for the telecom and datacom markets. According to forecasts from market research firms, the overall coherent market is expected to grow to 800,000 and 1 million units a year by 2020. In contrast, the interfaces used inside one large-scale data centre can be up to 2 million. “To achieve rapid manufacturing and yield, you have got to simplify the process,” he says.
This is what Elenion is tackling. If 1,000 die can be made on a single silicon wafer, and knowing the interface volumes required and the yields, the total number of wafer runs can be determined. And it is the overall time taken from starting a wafer to the finished transceiver PIC output that Elenion is looking to shorten, says the CEO.
We ran that demo from 7 AM to 2 AM every day of the show
At OFC, Elenion hired a hotel suite near the convention centre to demonstrate its technologies to interested companies. One demonstration used its 25Gbps optical engine directly mounted on a Cavium QLogic network interface card (NIC) connecting a server to a high-capacity Cavium Xpliant Ethernet switch chip. The demo showed how 16 NICs could be connected to the switch chip for a total capacity of 400 gigabits. “No more direct-attached cables or active optical cables, literally fibre-to-the-server,” says Schwerin. “We ran that demo from 7 AM to 2 AM every day of the show.”
Elenion’s on-board optics design was based on the emerging Consortium of On-Board Optics (COBO) standard. “The Microsoft folks, we work with them closely, so obviously what we are doing follows their intent,” says Schwerin.
The optical engine will also support 56Gbps links when used with four-level pulse-amplitude modulation (PAM-4) and the company is even eyeing 100Gbps interfaces. For now, Elenion’s datacom optical engine remains a technical platform but a product will soon follow.
The company’s datacom work is also benefiting its telecom designs. “The platform technology that we use for datacom has now found its way into the coherent programme, especially around the packaging,” says Schwerin.
* The article was changed on July 25th to mention that Elenion's PIC is being used in two Coriant CFP-ACOs.
Meeting the many needs of data centre interconnect
High capacity. Density. Power efficiency. Client-side optical interface choices. Coherent transmission. Direct detection. Open line system. Just some of the requirements vendors must offer to compete in the data centre interconnect market.
“A key lesson learned from all our interactions over the years is that there is no one-size-fits-all solution,” says Jörg-Peter Elbers, senior vice president of advanced technology, standards and IPR at ADVA Optical Networking. “What is important is that you have a portfolio to give customers what they need.”
Jörg-Peter Elbers
Teraflex
ADVA Optical Networking detailed its Teraflex, the latest addition to its CloudConnect family of data centre interconnect products, at the OFC show held in Los Angeles in March (see video).
The platform is designed to meet the demanding needs of the large-scale data centre operators that want high-capacity, compact platforms that are also power efficient.
A key lesson learned from all our interactions over the years is that there is no one-size-fits-all solution
Teraflex is a one-rack-unit (1RU) stackable chassis that supports three hot-pluggable 1.2-terabit modules or ‘sleds’. A sled supports two line-side wavelengths, each capable of coherent transmission at up to 600 gigabits-per-second (Gbps). Each sled’s front panel supports various client-side interface module options: 12 x 100-gigabit QSFPs, 3 x 400-gigabit QSFP-DDs and lower speed 10-gigabit and 40-gigabit modules using ADVA Optical Networking’s MicroMux technology.
“Building a product optimised only for 400-gigabit would not hit the market with the right feature set,” says Elbers. “We need to give customers the possibility to address all the different scenarios in one competitive platform.”
The Teraflex achieves 600Gbps wavelengths using a 64-gigabaud symbol rate and 64-ary quadrature-amplitude modulation (64-QAM). ADVA Optical Networking is using Acacia’s Communications latest Pico dual-core coherent digital signal processor (DSP) to implement the 600-gigabit wavelengths. ADVA Optical Networking would not confirm Acacia is its supplier but Acacia decided to detail the Pico DSP at OFC because it wanted to end speculation as to the source of the coherent DSP for the Teraflex. That said, ADVA Optical Networking points out that Teraflex’s modular nature means coherent DSPs from various suppliers can be used.
The 1 rack unit Teraflex
The line-side optics supports a variety of line speeds – from 600Gbps to 100Gbps, the lower the speed, the longer the reach.
The resulting 3-sled 1RU Teraflex platform thus supports up to 3.6 terabits-per-second (Tbps) of duplex communications. This compares to a maximum 800Gbps per rack unit using the current densest CloudConnect 0.5RU Quadflex card.
Markets
The data centre interconnect market is commonly split into metro and long haul.
The metro data centre interconnect market requires high-capacity, short-haul, point-to-point links up to 80km. Large-scale data centre operators may have several sites spread across a city, given they must pick locations where they can find them. Sites are typically no further apart than 80km to ensure a low-enough latency such that, collectively, they appear as one large logical data centre.
“You are extending the fabric inside the data centre across the data-centre boundary, which means the whole bandwidth you have on the fabric needs to be fed across the fibre link,” says Elbers. “If not, then there are bottlenecks and you are restricted in the flexibility you have.”
Large enterprises also use metro data centre interconnect. The enterprises’ businesses involve processing customer data - airline bookings, for example - and they cannot afford disruption. As a result, they may use twin data centres to ensure business continuity.
Here, too, latency is an issue especially if synchronous mirroring of data using Fibre Channel takes place between sites. The storage protocol requires acknowledgement between the end points such that the round-trip time over the fibre is critical. “The average distance of these connections is 40km, and no one wants to go beyond 80 or 100km,” says Elbers, who stresses that this is not an application for Teraflex given it is aimed at massive Ethernet transport. Customers using Fibre Channel typically need lower capacities and use more tailored solutions for the application.
The second data centre interconnect market - long haul - has different requirements. The links are long distance and the data sent between sites is limited to what is needed. Data centres are distributed to ensure continual business operation and for quality-of-experience by delivering services closer to customers.
Hundreds of gigabits and even terabits are sent over the long-distance links between data centres sites but commonly it is about a tenth of the data sent for metro data centre interconnect, says Elbers.
Direct Detection
Given the variety of customer requirements, ADVA Optical Networking is pursuing direct-detection line-side interfaces as well as coherent-based transmission.
At OFC, the system vendor detailed work with two proponents of line-side direct-detection technology - Inphi and Ranovus - as well as its coherent-based Teraflex announcement.
Working with Microsoft, Arista and Inphi, ADVA detailed a metro data centre interconnect demonstration that involved sending 4Tbps of data over an 80km link. The link comprised 40 Inphi ColorZ QSFP modules. A ColorZ module uses two wavelengths, each carrying 56Gbps using PAM-4 signalling. This is where having an open line system is important.
Microsoft wanted to use QSFPs directly in their switches rather than deploy additional transponders, says Elbers. But this still requires line amplification while the data centre operators want the same straightforward provisioning they expect with coherent technology. To this aim, ADVA demonstrated its SmartAmp technology that not only sets up the power levels of the wavelengths and provides optical amplification but also automatically measures and compensates for chromatic dispersion experienced over a link.
ADVA also detailed a 400Gbps metro transponder card based on PAM-4 implemented using two 200Gbps transmitter optical subassemblies (TOSAs) and two 200Gbps receiver optical subassemblies (ROSAs) from Ranovus.
Clearly there is also space for a direct-detection solution but that space will narrow down over time
Choices
The decision to use coherent or direct detection line-side optics boils down to a link’s requirements and the cost an end user is willing to pay, says Elbers.
As coherent-based optics has matured, it has migrated from long-haul to metro and now data centre interconnect. One way to cost-reduce coherent further is to cram more bits per transmission. “Teraflex is adding chunks of 1.2Tbps per sled which is great for people with very high capacities,” says Elbers, but small enterprises, for example, may only need a 100-gigabit link.
“For scenarios where you don’t need to have the highest spectral efficiency and the highest fibre capacity, you can get more cost-effective solutions,” says Elbers, explaining the system vendor’s interest in direct detection.
“We are seeing coherent penetrating more and more markets but still cost and power consumption are issues,” says Elbers. “Clearly there is also space for a direct-detection solution but that space will narrow down over time.”
Developments in silicon photonics that promise to reduce the cost of optics through greater integration and the adoption of packaging techniques from the CMOS industry will all help. “We are not there yet; this will require a couple of technology iterations,” says Elbers.
Until then, ADVA’s goal is for direct detection to cost half that of coherent.
“We want to have two technologies for the different areas; there needs to be a business justification [for using direct detection],” he says. “Having differentiated pricing between the two - coherent and direct detection - is clearly one element here.”
600-gigabit channels on a fibre by 2017
NeoPhotonics has announced an integrated coherent receiver that will enable 600-gigabit optical transmission using a single wavelength. A transmission capacity of 48 terabits over the fibre’s C-band is then possible using 80 such channels.
NeoPhotonics’ micro integrated coherent receiver operates at 64 gigabaud, twice the symbol rate of deployed 100-gigabit optical transport systems and was detailed at the recent ECOC show.
Current 100 gigabit-per-second (Gbps) coherent systems use polarisation-multiplexing, quadrature phase-shift keying (PM-QPSK) modulation operating at 32 gigabaud. “That is how you get four bits [per symbol],” says Ferris Lipscomb, vice president of marketing at NeoPhotonics.
Optical designers have two approaches to increase the data transmitted on a wavelength: they can use increasingly complex modulation schemes - such as 16 quadrature amplitude modulation (16-QAM) or 64-QAM - and they can increase the baud rate. “You double the baud rate, you double the transmission capacity,” says Lipscomb. “And using 64-QAM and 64 gigabaud, you can go to 600 gigabit per channel; of course when you do that, you reduce the reach.”
The move to the higher 64 gigabaud symbol rate will help Internet content providers increase capacity between their large-scale data centres. Typical transmission distances between sites are relatively short, up to 100km.
Telcos too will benefit from the higher baud rate as it will enable them to use software-defined networking to adapt, on-the-fly, a line card’s data rate and reach depending on the link. Such a flexible rate coherent line card would allow 600Gbps on a single channel over 80km, 400 gigabit (16-QAM) over 400km, or 100 gigabit over thousands of kilometers.
Status
NeoPhotonics says it is now sampling its 64 gigabaud coherent receiver. It is still premature to discuss when the high-speed coherent receiver will be generally available, the company says, as it depends on the availability of other vendors’ components working at 64 gigabaud. These include the modulator, the trans-impedance amplifier and the coherent digital signal processor ASIC (DSP-ASIC).
Lipscomb says that a 64-gigabaud modulator in lithium niobate already exists but not in indium phosphide. The lithium niobate modulator is relatively large and will fit within a CFP module but the smaller CFP2 module will require a 64-gigabaud indium phosphide modulator.
“General availability will be timed based on when our customers are ready to go into production,” says Lipscomb. “Trials will happen in the first half of 2017 with volume shipments only happening in the second half of next year.”
Using 64-QAM and 64 gigabaud, you can go to 600 gigabit per channel
Challenges
A micro integrated coherent receiver has two inputs - the received optical signal and the local oscillator - and four balanced receiver outputs. Also included are two polarisation beam splitters and two 90-degree hybrid mixers.
Lipscomb says Neophotonics worked for over a year to develop its coherent receiver: “It is a complete design from the ground up.”
The slowest element sets the speed at which the receiver can operator such that the design not only involves the detector and trans-impedance amplifier but other elements such as the wirebonds and the packaging. “Everything has to be upgraded,” says Lipscomb. “It is not just a case of plopping in a faster detector and everything works.”
Nano-ICR and the CFP2-DCO
The industry is now working on a successor, smaller coherent detector dubbed the nano integrated coherent receiver (nano-ICR). “It has not all gelled yet but the nano-ICR would be suitable for the CFP2-DCO.”
The CFP2-DCO is a CFP2 Digital Coherent Optics pluggable module that integrates the coherent DSP-ASIC. In contrast, the CFP2 Analog Coherent Optics (CFP2-ACO) modules holds the optics and the DSP-ASIC resides on the line card.
“As the new DSPs come out using the next CMOS [process] nodes, they will be lower power and will be accommodated in the CFP2 form factor,” says Lipscomb. “Then the optics has to shrink yet again to make room for the DSP.”
Lipscomb sees the CFP2-ACO being used by system vendors that have already developed their own DSP-ASICs and will offer differentiated, higher-transmission performance. The CFP2-DCO will be favoured for more standard deployments and by end-customers that do not want to be locked into a single vendor and a proprietary DSP.
There is also the CFP2-DCO’s ease of deployment. In China, currently undertaking large-scale 100-gigabit optical transport deployments, operators want a module that can be deployed in the field by a relatively unskilled technician. “The ACOs with the analogue interface tend to require a lot of calibration,” says Lipscomb. “You can’t just plug it in and it works; you have to run it in, calibrate it and bring it up to get it to work properly.”
The CFP2-DCO module is expected in 2018 as the DSP-ASICs will require an advanced 12nm or even 7nm CMOS process.
Ranovus developing DWDM links for the data centre
Ranovus has raised US $11 million in funding to develop Terabit capacity links for the data centre. The Ottawa-based start-up plans to use dense wavelength-division multiplexing (DWDM) technology to create huge data pipes that reduce significantly the power consumption, and cost, per bit.
The company says that it is not a silicon photonics start-up but rather a user of the technology to make its interface. Ranovus will use a foundry to make its optical chips.
Ranovus includes former staff of the coherent transmission and DSP specialist, CoreOptics, acquired by Cisco Systems in 2010. "Electronics, as we learnt from our previous endeavour, can impact in a big way the cost-performance of links," says Aramideh. "It doesn't have to be expensive equaliser technology we developed in the past, but there are ways of using similar technology in CMOS ICs to solve some of the network problems."
This suggests that DSP will be used to help cram the multiple channels in the fibre as well as achieve several hundred kilometers of reach. But the DSP will use simpler algorithms than those for long-distance coherent transmission.
Aramideh says its Terabit interface is inevitably a proprietary design. "[Industry] standards are important and you need to have dual sourcing, but people value having disruptive technologies," he says. "The challenge the industry has is that there hasn't been a lot of innovation going into technologies specifically for the data centre."
The start-up's technology is being validated with several lead customers. "It is early proof of technology and the platform in terms of configurations that the customers will be using," he says.
The $11m funding raised will be used to commercialise the technology and make the first products for lead customers. "We are very advanced in our plans with respect to delivery of our product," says Aramideh. Ranovus expects to provide first details of its product at OFC 2014.