II-VI expands its 400G and 800G transceiver portfolio
II-VI has showcased its latest high-speed optics. The need for such client-side modules is being driven by the emergence of next-generation Ethernet switches in the data centre.
The demonstrations, part of the OFC virtual conference and exhibition held last month, featured two 800-gigabit and two 400-gigabit optical transceivers.
“We have seen the mushrooming of a lot of datacom transceiver companies, primarily from China, and some have grown pretty big,” says Sanjai Parthasarathi, chief marketing officer at II-VI.
But a key enabler for next-generation modules is the laser. “Very few companies have these leading laser platforms – whether indium phosphide or gallium arsenide, we have all of that,” says Parthasarathi.
During OFC, II-VI also announced the sampling of a 100-gigabit directly modulated laser (DML) and detailed an optical channel monitoring platform.
“We have combined the optical channel monitoring – the channel presence monitoring, the channel performance monitoring – and the OTDR into a single integrated subsystem, essentially a disaggregated monitoring system,” says Parthasarathi.
An optical time-domain reflectometer (OTDR) is used to characterise fibre.
High-speed client-side transceivers
II-VI demonstrated two 800-gigabit datacom products.
One is an OSFP form factor implementing 800-gigabit DR8 (800G-DR8) and the other is a QSFP-DD800 module with dual 400-gigabit FR4s (2x400G-FR4). The DR8 uses eight fibres in each direction, each carrying a 100-gigabit signal. The QSFP-DD800 supports two FR4s, each carrying four, 100-gigabit wavelengths over single-mode fibre.
“These are standard IEEE-compliant reaches: 500m for the DR8 and 2km for the dual FR4 talking to individual FR4s,” says Vipul Bhatt, senior strategic marketing director, datacom at II-VI.
The 800G-DR8 module can be used as an 800-gigabit link or, when broken out, as two 400-gigabit DR4s or eight individual 100-gigabit DR optics.
II-VI chose to implement these two 800-gigabit interfaces based on the large-scale data centre players’ requirements. The latest switches use 25.6-terabit Ethernet chips that have 100-gigabit electrical interfaces while next-generation 51.2-terabit ICs are not far off. “Our optics is just keeping in phase with that rollout,” says Bhatt.
During OFC, II-VI also showcased two 400-gigabit QSFP112 modules: a 400-gigabit FR4 (400G-FR4) and a multi-mode 400-gigabit SR4 (400G-SR4).
The SR4 consumes less power, is more cost-effective but has a shorter reach. “Not all large volume deployments of data centres are necessarily in huge campuses,” says Bhatt.
II-VI demonstrated its 800-gigabit dual FR4 module talking to two of its QSFP112 400-gigabit FR4s.
Bhatt says the IEEE 802.3db standard has two 400G-SR4 variants, one with a 50m reach and the second, a 100m reach. “We chose to demonstrate 100m because it is inclusive of the 50m capability,” says Bhatt.
II-VI stresses its breadth in supporting multi-mode, short-reach single-mode and medium-reach single-mode technologies.
The company says it was the electrical interface rather than the optics that was more challenging in developing its latest 400- and 800-gigabit modules.
The company has 100-gigabit multi-mode VCSELs, single-mode lasers, and optical assembly and packaging. “It was the maturity of the electrical interface [that was the challenge], for which we depend on other sources,” says Bhatt.
100-gigabit PAM-4 DML
II-VI revealed it is sampling a 100-gigabit PAM-4 directly modulated laser (DML).
Traditionally, client-side modules for the data centre come to market using a higher performance indium phosphide externally-modulated laser (EML). The EML may even undergo a design iteration before a same-speed indium phosphide DML emerges. The DML has simpler drive and control circuitry, is cheaper and has a lower power consumption.
“But as we go to higher speeds, I suspect we are going to see both [laser types] coexist, depending on the customer’s choice of worst-case dispersion and power tolerance,” says Bhatt. It is too early to say how the DML will rank with the various worst-case test specifications.
Parthasarathi adds that II-VI is developing 100-gigabit and 200-gigabit-per-lane laser designs. Indeed, the company had an OFC post-deadline paper detailing work on a 200-gigabit PAM-4 DML.
Optical monitoring system
Optical channel monitoring is commonly embedded in systems while coherent transceivers also provide performance metrics on the status of the optical network. So why has II-VI developed a standalone optical monitoring platform?
What optical channel monitors and coherent modules don’t reveal is when a connector is going bad or fibre is getting bent, says Parthasarathi: “The health and the integrity of the fibre plant, there are so many things that affect a transmission.”
Operators may have monitoring infrastructure in place but not necessarily the monitoring of the signal integrity or the physical infrastructure. “If you have an existing network, this is a very easy way to add a monitoring capability,” says Parthasarathi.
“As we can control all the parts – the optical channel monitoring and the OTDR – we can configure it [the platform] to meet the application,” adds Sara Gabba, manager, analysis, intelligence & strategic marcom at II-VI. “Coherent indeed provides a lot of information, but this kind of unit is also suitable for access network applications.”
The optical monitoring system features an optical switch so it can cycle and monitor up to 48 ports.
With operators adopting disaggregated designs, each element in the optical network is required to have more intelligence and more autonomy.
“If you can provide this kind of intelligent monitoring and provide information about a specific link, you create the possibility to be more flexible,” says Gabba.
Using the monitoring platform, intelligence can be more widely distributed in the optical network complementing systems operators may have already deployed, she adds.
Macom readies its silicon photonics platform for 400G
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Macom has announced a laser-integrated photonic integrated circuit (L-PIC) for the 400G-FR4 standard
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The company is also working with GlobalFoundries to use the semiconductor foundry’s 300mm wafer silicon photonics process
Vivek Rajgarhia (centre) being interviewed at OFC. Source: Macom.
Macom has detailed its latest silicon photonics chip to meet the upcoming demand for 400-gigabit interfaces within the data centre.
The chip, a laser-integrated photonic integrated circuit (L-PIC), was unveiled at the OFC show held last month in San Diego. The L-PIC implements the transmitter circuitry for the 400G FR4 2km interface standard.
Backing silicon photonics
“Five to six years ago, we saw that silicon photonics would have a key role to play in photonics and optical interconnect,” says Vivek Rajgarhia, senior vice president and general manager, lightwave at Macom.
Macom acquired several companies to gain the capabilities needed to become a silicon photonics player.
In 2014 the company paid $230 million for BinOptics which provided Macom with etched facet laser technology that plays a key role in how its L-PIC platform is assembled. Also acquired was the silicon photonics design company, Photonic Controls. In 2015 Macom added FiBest, a packaging specialist, for $60 million.
“We also have the electronics expertise to go alongside [the photonics] to provide chipset solutions,” says Rajgarhia.
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“Today, as a photonics company, if you don’t have a play in silicon photonics, you are legacy ”
Laser-integrated PIC
The biggest challenge in silicon photonics is integrating the laser, says Rajgarhia. Coupling and aligning the laser, especially when developing optical interfaces for the high-volume data centre market, needs to be done in a cost-effective and scalable way, he says.
The L-PIC, a coarse wavelength division multiplexing (CWDM) design, tackles this by having four cavities for the lasers. “Each laser is flip-chipped and inserted into a cavity without any lens or isolator, and without active alignment,” says Rajgarhia.
The self-alignment is possible by using the etched-facet laser technology from BinOptics. “When you cleave the laser facet, the dimensional control has a lot of play - the tolerance is very high - but with an etched facet, you lithographically define the mechanical dimensions,” he says. “We create a cavity in the silicon that matches the laser’s dimensions.” Macom has also incorporated multiple alignment structures as part of its L-PIC platform to enable the self-alignment.
Macom has already developed the L-PIC for the 100-gigabit CWDM4 standard. “We started with the CWDM4 because it had four wavelengths,” says Rajgarhia. “The CWDM4 is a more challenging design [than the 100-gigabit PSM4 interface] because it requires multiplexing.”
The L-PIC has now been extended to support 100-gigabit channels, to address the DR single channel and the four-channel 400-gigabit FR4 standards. The modulator bandwidth had to be extended and the laser power is different but the approach - the platform - remains the same, says Rajgarhia.
Macom refers to the L-PIC as a smart device. The electro-absorptive modulated lasers (EMLs) used for the FR4 are uncooled. The L-PIC includes ‘structures’ in the silicon such as heaters for tuning the optical elements and photo-detectors that monitor the optical performance. Macom has developed an accompanying micro-controller that sets and controls the device using such structures.
“We have developed software which we give to customers,” says Rajgarhia. “You can type in what extinction ratio you want, what power you want and it sets that up.”
The company has also started the FR4 receiver development that will also be an integrated design with a demultiplexer and four optical receiver channels.
Macom is not saying when the L-PIC will be available. However, the company says 'meaningful demand' for 400-gigabit interfaces will start from 2021.
GlobalFoundries
Macom also announced at OFC that it is working with GlobalFoundries to use the chip maker’s 90nm silicon-on-insulator 300mm wafer processing line.
“Today, as a photonics company, if you don’t have a play in silicon photonics, you are legacy,” says Rajgarhia, adding that in order to make money, what is needed is a working solution that can scale.
“When we started developing [silicon photonics devices], we and others used research foundries to get our products ready,” says Rajgarhia. “Now, what we have announced is that we are scaling this up at GlobalFoundries.”
Macom has started the development at GlobalFoundaries’ East Fishkill fab, the former IBM Microelectronics site that has undertaken a lot of research in silicon photonics, says Rajgarhia.
GlobalFoundries recently created a process development kit (PDK) for its silicon photonics line. Now Macom is an early user of the PDK.
Last year, silicon photonics start-up, Ayar Labs, entered into a strategic agreement with GlobalFoundries, providing the foundry with its optical input-output (I/O) technology while gaining access to its 45nm silicon photonics process.
Inphi adds a laser driver to its 100-gigabit PAM-4 DSP
Inphi has detailed its second-generation Porrima chip family for 100-gigabit single-wavelength optical module designs.
Source: Inphi
The Porrima family of devices is targeted at the 400G DR4 and 400G FR4 specifications as well as 100-gigabit module designs that use 100-gigabit 4-level pulse-amplitude modulation (PAM-4). Indeed, the two module types can be combined when a 400-gigabit pluggable such as a QSFP-DD or an OSFP is used in breakout mode to feed four 100-gigabit modules using such form factors as the QSFP, uQSFP or SFP-DD.
The Gen2 family has been launched a year after the company first announced the Porrima. The original 400-gigabit and 100-gigabit Porrima designs each have three ICs: a PAM-4 digital signal processor (DSP), a trans-impedance amplifier (TIA) and a laser-driver.
“With Gen2, the DSP and laser driver are integrated into a single monolithic CMOS chip, and there is a separate amplifier chip,” says Siddharth Sheth, senior vice president, networking interconnect at Inphi. The benefit of integrating the laser driver with the DSP is lower cost, says Sheth, as well as a power consumption saving.
The second-generation Porrima family is now sampling with general availability expected in mid-2019.
PAM-4 families
Inphi has three families of PAM-4 ICs targeting 400-gigabit interfaces: the Polaris, Vega and Porrima.
The Polaris, Inphi’s first product family, uses a 200-gigabit die and two are used within the same package for 400-gigabit module designs. As well as the PAM-4 DSP, the Polaris family also comprises two companion chips: a laser driver and an amplifier.
Inphi’s second family is the Vega, a 8x50-gigabit PAM-4 400-gigabit DSP chip that sits on a platform’s line card.
“The chip is used to drive backplanes and copper cables and can be used as a retimer chip,” says Sheth.
Siddharth Sheth
“For the Porrima family, you have a variant that does 4x100-gigabit and a variant that does 1x100-gigabit,” says Sheth. The Porrima can interface to a switch chip that uses either 4x25-gigabit non-return-to-zero (NRZ) or 2x50-gigabit PAM-4 electrical signals.
Why come out with a Gen2 design only a year after the first Porrima? Sheth says there was already demand for 400-gigabit PAM-4 chips when the Porrima first became available in March 2018. Optical module makers needed such chips to come to market with 400-gigabit modules to meet the demand of an early hyperscale data centre operator.
“Now, the Gen2 solution is for the second wave of customers,” says Sheth. “There are going to be two or three hyperscalers coming online in 2020 but maybe not as aggressively as the first hyperscaler.” These hyperscalers will be assessing the next generation of 400-gigabit PAM-4 silicon available, he says.
The latest design, like the first generation Porrima, is implemented using 16nm CMOS. The DSP itself has not been modified; what has been added is the laser-driver circuitry. Accordingly, it is the transmitter side that has been changed, not the receiver path where Inphi does the bulk of the signal processing. “We did not want to change a whole lot because that would require a change to the software,” he says.
A 400-gigabit optical module design using the first generation Porrima consumes under 10W but only 9W using the Gen2. The power saving is due to the CMOS-based laser driver consuming 400mW only compared to a gallium arsenide or silicon germanium-based driver IC that consumes between 1.6W to 2W, says Inphi.
The internal driver can achieve transmission distances of 500m while a standalone driver will still be needed for longer 2km spans.
Sheth says that the advent of mature low-swing-voltage lasers will mean that the DSP’s internal driver will also support 2km links.
PAM-4 DSP
The aim of the DSP chip is to recover the transmitted PAM-4 signal. Sheth says PAM-4 chip companies differ in how much signal processing they undertake at the transmitter and how much is performed at the receiver.
“It comes down to a tradeoff, we believe that we are better off putting the heavier signal processing on the receive side,” says Sheth.
Inphi performs some signal processing on the transit side where transmit equalisation circuits are used in the digital domain, prior to the digital-to-analogue converter.
The goal of the transmitter is to emit a signal with the right amplitude, pre-emphasis, and having a symmetrical rise and fall. But even generating such a signal, the PAM-4 signal recovered at the receiver may look nothing like the signal sent due to degradations introduced by the channel. “So we have to do all kind of tricks,” he says.
Inphi uses a hybrid approach at the receiver where some of the signal processing is performed in the analogue domain and the rest digitally. A variable-gain amplifier is used up front to make sure the received signal is at the right amplitude and then feed-forward equalisation is performed. After the analogue-to-digital stage, post equalisation is performed digitally.
Sheth says that depending on the state of the received signal - the distortion, jitter and loss characteristics it has - different functions of the DSP may be employed.
One such DSP function is a reflection canceller that is turned on, depending on how much signal reflection and crosstalk occur. Another functional block that can be employed is a maximum likelihood sequence estimator (MLSE) used to recover a signal sent over longer distances. In addition, forward-error correction blocks can also be used to achieve longer spans.
“We have all sorts of knobs built into the chip to get an error-free link with really good performance,” says Sheth. “At the end of the day, it is about closing the optical link with plenty of margin.”
What next?
Sheth says the next-generation PAM-4 design will likely use an improved DSP implemented using a more advanced CMOS process.
“We will take the learning from Gen1 and Gen2 and roll it into a ‘Gen3’,” says Sheth.
Such a design will also be implemented using a 7nm CMOS process. “We are now done with 16nm CMOS,” concludes Sheth.
NeoPhotonics ups the baud rate for line and client optics
- Neophotonics’ 64 gigabaud optical components are now being designed into optical transmission systems. The components enable up to 600 gigabits per wavelength and 1.2 terabits using a dual-wavelength transponder.
- The company’s high-end transponder that uses Ciena’s WaveLogic Ai coherent digital signal processor (DSP) is now shipping.
- NeoPhotonic is also showcasing its 53 gigabaud components for client-side pluggable optics capable of 100-gigabit wavelengths at the current European Conference on Optical Communication (ECOC) show being held in Rome.
NeoPhotonics says its family of 64 gigabaud (Gbaud) optical components are being incorporated within next-generation optical transmission platforms.
Ferris LipscombThe 64Gbaud components include a micro intradyne coherent receiver (micro-ICR), a micro integrable tunable laser assembly (micro-ITLA) and a coherent driver modulator (CDM).
The micro-ICR and micro-ITLA are the Optical Internetworking Forum’s (OIF) specification, while the CDM is currently being specified.
“Three major customers have selected to use all three [64Gbaud components] and several others are using a subset of those,” says Ferris Lipscomb, vice president of marketing at NeoPhotonics.
NeoPhotonics also unveiled and demonstrated two smaller 64Gbaud component designs at the OFC show held in March. The devices - a coherent optical sub-assembly (COSA) and a nano-ITLA - are aimed at 400-gigabit coherent pluggable modules as well as compact line-card designs.
“These [two compact components] continue to be developed as well,” says Lipscomb.
Baud rate and modulation
The current 100-gigabit coherent transmission uses polarisation-multiplexing, quadrature phase-shift keying (PM-QPSK) modulation operating at 32 gigabaud. The 100 gigabits-per-second (Gbps) data rate is achieved using four bits per symbol and a symbol rate of 32Gbaud.
Optical designers use two approaches to increase the wavelength’s data rate beyond 100Gbps. One approach is to increase the modulation scheme beyond QPSK using 16-ary quadrature amplitude modulation (16-QAM) or 64-QAM, the other is to increase the baud rate.
“The baud rate is the on-off rate as opposed to the bit rate. That is because you are packing more bits in there than the on-off supports,” says Lipscomb. “But if you double the on-off rate, you double the number of bits.”
Doubling the baud rate from 32Gbaud to 64Gbaud achieves just while using 64-QAM trebles the data sent per symbol compared to 100-gigabit PM-QSPK. Combining the two - 64Gbaud and 64-QAM - creates the 600 gigabits per wavelength.
A higher baud rate also has a reach advantage, says Lipscomb, with its lower noise. “For longer distances, increasing the baud rate is better.”
But doubling the baud rate requires more capable DSPs to interpret things at twice the rate. “And such DSPs now exist, operating at 64Gbaud and 64-QAM,” he says.
Three major customers have selected to use all three [64Gbaud components] and several others are using a subset of those
Coherent components
NeoPhotonics’ 64Gbaud optical components are suitable for line cards, fixed-packaged transponders, 1-rack-unit modular platforms used for data centre interconnect and the CFP2 pluggable form factor.
For data centre interconnect using 600-gigabits-per-wavelength transmissions, the distance achieved is up to 100km. For longer distances, the 64Gbaud components achieve metro-regional reaches at 400Gbps, and 2,000km for long-haul at 200Gbps.
But to fit within the most demanding pluggable form factors such as the OSFP and QSFP-DD, smaller componentry is required. This is what the coherent optical sub-assembly (COSA) and nano-ITLA are designed to address. The COSA combines the coherent modular driver and the ICR in a single gold-box package that is no larger than the individual 64Gbaud micro-ICR and CDM packages.
Source: Gazettabyte
“There is a lot of interest in 400-gigabit applications for a CFP2, and in that form factor you can use the separate components,” says Lipscomb. “But for data centre interconnect, you want to increase the density as much as possible so going to the smaller OSPF or QSFP-DD requires another generation of [component] shrinking.”
NeoPhotonics says there are two main approaches. One, and what NeoPhotonics has done with the nano-ITLA and COSA, is to separate the laser from the remaining circuitry such that two components are needed overall. A benefit of a separate laser is also lower noise. “But the ultimate approach would be to put all three in one gold box,” says Lipscomb.
For data centre interconnect, you want to increase the density as much as possible so going to the smaller OSPF or QSFP-DD requires another generation of [component] shrinking
Both approaches are accommodated as part of the OIF’s Integrated Coherent Transmitter-Receiver Optical Sub-Assembly (IC-TROSA) project.
Another challenge to achieving coherent designs such as the emerging 400ZR standard using the OSFP or QSFP-DD is accommodating the DSP with the optics while meeting the modules’ demanding power constraints. This requires a 7nm CMOS DSP and first samples are expected by year-end with limited production occurring towards the end of 2019. Volume production of coherent OSFP and QSFP-DD modules are expected in 2020 or even 2021, says Lipscomb.
100G client-side wavelengths
NeoPhotonics also used the OFC show last March to detail its 53Gbaud components for client-side pluggables that are 100-gigabit single-wavelength and four-wavelength 400-gigabit designs. Samples of these have now been delivered to customers and are part of demonstrations at ECOC this week.
The components include an electro-absorption modulated laser (EML) and driver for the transmitter, and photodetectors and trans-impedance amplifiers for the receiver path. The 53Gbaud EML can operate uncooled, is non-hermetic and is aimed for use with OSFP and QSFP-DD modules.
To achieve a 100-gigabit wavelength, 4-level pulse-amplitude modulation (PAM-4) is used and that requires an advanced DSP. Such PAM-4 DSPs will only be available early next year, says NeoPhotonics.
The first 400-gigabit modules using 100-gigabit wavelengths will gain momentum by the end of 2019 with volume production in 2020, says Lipscomb.
The various 8-wavelength implementations such as the IEEE-defined 2km 400GBASE-FR8 and 10km 400GBASE-LR8 are used when data centre operators must have 400-gigabit client interfaces.
The adoption of 100-gigabit single-wavelength implementations of 400 gigabits, in contrast, will be adopted when it becomes cheaper on a cost-per-bit basis, says Lipscomb: “It [100-gigabit single-wavelength-based modules] will be a general replacement rather than a breaking of bottlenecks.”
NeoPhotonics is also making available its DFB laser technology for silicon-photonics-based modules such as the 2km 400G-FR4, as well as the 100-gigabit single-wavelength DR1 and the parallel-fibre 400-gigabit DR4 standards.
WaveLogic AI transponder
NeoPhotonics has revealed it is shipping its first module using Ciena’s WaveLogic Ai coherent DSP. “We are shipping in modest volumes right now,” says Lipscomb.
The company is one of three module makers, the others being Lumentum and Oclaro, that signed an agreement with Ciena to use of its flagship WaveLogic Ai DSP for their coherent module designs.
Lipscomb describes the market for the module as a niche given its high-end optical performance, what he describes as a fully capable, multi-haul transponder. “It has lots of features and a lot of expense too,” he says. “It is applied to specific cases where long distance is needed; it can go 12,000km if you need it to.”
The agreement with Ciena also includes the option to use future Ciena DSPs. “Nothing is announced yet and so we will have to see how that all plays out.”
Oclaro makes available its EMLs and backs 400G-FR4
Lumentum’s plan to acquire Oclaro for $1.8 billion may have dominated the news at last month’s OFC show held in San Diego, but it was business as usual for Oclaro with its product and strategy announcements.
Adam Carter, chief commercial officer (pictured), positions Oclaro’s announcements in terms of general industry trends.
“On the line side, everywhere there are 100-gigabit and 200-gigabit wavelengths, you will see that transition to 400 gigabit and 600 gigabit,” he says. “And on the client side, you have 100 gigabit going to 400 gigabit.”
400G-FR
Oclaro announced it will offer the QSFP56-DD module implementing 400-FR4, the four-wavelength 400-gigabit 2km client-side interface. The 400G-FR4 is a design developed by the 100G Lambda MSA.
“This [QSFP-DD FR4] will enable our customers, particularly network equipment manufacturers, to drive 400 gigabit up to 36 ports in a one-rack-unit [platform],” says Carter.
Oclaro has had the required optical components - its 53-gigabaud lasers and high-end photo-detectors - for a while. What Oclaro has lacked is the accompanying 4-level pulse amplitude modulation (PAM-4) gearbox chip to take the 8x50 gigabits-per-second electrical signals and encode them into four 50-gigabaud ones.
The chips have now arrived for testing and if the silicon meets the specs, Oclaro will deliver the first modules to customers later this year.
Oclaro chose the QSFP-DD first as it expects the form factor to sell in higher volumes but it will offer the 400G-FR4 in the OSFP module.
Certain customers prefer the OSFP, in part because of its greater power-handling capabilities. “Some people believe that the OSFP’s power envelope gives you a little bit more freedom,” he says. “There is still a debate in the industry whether the QSFP-DD will be able to do long-reach [80km data centre interconnect] types of products.”
Oclaro says its transmit and receive optical sub-assemblies (TOSAs and ROSAs) are designed to fit within the more demanding QSFP-DD such they will also suit the OSFP.
If people want to buy the [EML] chips and do next-generation designs, they can come to Oclaro
EMLs for sale
Oclaro has decided to sell its electro-absorption modulated lasers (EMLs), capable of 25, 50 and 100-gigabit speeds.
“If people want to buy the chips and do next-generation designs, they can come to Oclaro for some top-end single-mode chipsets that we have developed for our own use,” says Carter.
Oclaro's EMLs are used for both coarse wavelength-division multiplexing (CWDM) and the tighter LAN-WDM wavelength grid based client-side interfaces and are available in uncooled and cooled packages.
Until now the company only sold its 25-gigabit directly modulated lasers (DMLs). “We have been selling [EMLs] strategically to one very large customer who consigns them to a manufacturer,” says Carter.
The EMLs are being made generally available due to demand. “There are not many manufacturers of this chip in the world,” says Carter, adding that the decision also reflects an evolving climate for business models.
5G and cable
Oclaro claims it is selling the industry’s first 10-gigabit tunable SFP+ operating over industrial temperature (I-temp) ranges: -40 to 85oC. There are two tunable variants spanning 40km and 80km, both supporting up to 96 dense WDM (DWDM) channels on a fibre. The module was first announced at OFC 2017.
Oclaro says cable networks and 5G wireless will require the I-temp tunable SFP+.
The cable industry’s adoption of a distributed access architecture (DAA) brings fibre closer to the network’s edge and splits part of the functionality of the cable modem termination system (CMTS) - the remote PHY - closer to the residential units. This helps cable operators cope with continual traffic growth and their facilities becoming increasingly congested with equipment. Comcast, for example, says it is seeing an annual growth in downstream traffic (to the home) of 40-50 percent.
The use of tunable SFP+ modules boost the capacity that can be sent over a fibre, says Carter. But the tunable SFP+ modules are now located at the remote PHY, an uncontrolled temperature environment.
For 5G, the 10Gbps tunables will carry antenna traffic to centralised base stations. Carter points out that the 40km and 80km reach of the tunable SFP+ will not be needed in all geographies but in China, for example, the goal is to limit the number of central offices such that the distances are greater.
Oclaro also offers an I-temp fixed-wavelength 25-gigabit SFP28 LR module. “It is lower cost than the tunable SFP+ so if you need 10km [for mobile fronthaul], you would tend to go for this transceiver,” says Carter.
Also unveiled is an optical chip combining a 1310nm distributed feedback laser (DFB) laser and a Mach-Zehnder modulator. “The 1310nm device will be used in certain applications inside the data centre,” says Carter. “There are customers that are looking at using PAM-4 interfaces for short-reach connections between leaf and spine switches.” The device will support 50-gigabit and 100-gigabit PAM-4 wavelengths.
Line-side optics
Oclaro announced it is extending its integrated coherent transmitter and integrated coherent receiver to operate in the L-band. The coherent optical devices support a symbol rate of up to 64 gigabaud to enable 400-gigabit and 600-gigabit wavelengths.
Telcos want to use the L-band alongside the C-band to effectively double the capacity of a fibre.
Also announced by Oclaro at OFC was a high-bandwidth co-packaged modulator driver, an indium phosphide-based Mach-Zehnder modulator.
Oclaro was part of the main news story at last year’s OFC when Ciena announced it would share its 400-gigabit WaveLogic Ai coherent digital signal processor (DSP) with three module makers: Oclaro, Lumentum and NeoPhotonics. Yet there was no Oclaro announcement at this year’s OFC regarding the transponder.
Carter says the WaveLogic Ai transponder is sampling and that it has been demonstrated to customers and used in several field trials: “It is still early right now with regard volume deployments so there is nothing to announce yet."
New MSA to enable four-lambda 400-gigabit modules
A new 100-gigabit single-wavelength multi-source agreement (MSA) has been created to provide the industry with 2km and 10km 100-gigabit and 400-gigabit four-wavelength interfaces.
Mark NowellThe MSA is backed by 22 founding companies including Microsoft, Alibaba and Cisco Systems.
The initiative started work two months ago and a draft specification is expected before the year end.
“Twenty-two companies is a very large MSA at this stage, which shows the strong interest in this technology,” says Mark Nowell, distinguished engineer, data centre switching at Cisco Systems and co-chair of the 100G Lambda MSA. “It is clear this is going to be the workhorse technology for the industry for quite a while.”
Phased approach
The 100G Lambda MSA is a phased project. In the first phase, three single-mode fibre optical interfaces will be specified: a 100-gigabit 2km link (100G-FR), a 100-gigabit 10km link (100G-LR), and a 2km 400-gigabit coarse wavelength-division multiplexed (CWDM) design, known as the 400G-FR4. A 10km version of the 400-gigabit CWDM design (400G-LR4) will be developed in the second phase.
For the specifications, the MSA will use work already done by the IEEE that has defined two 100-gigabit-per-wavelength specifications. The IEEE 802.3bs 400 Gigabit Ethernet Task Force has defined a 400-gigabit parallel fibre interface over 500m, referred to as DR4 (400GBASE-DR4). The second, the work of the IEEE 802.3cd 50, 100 and 200 Gigabit Ethernet Task Force, defines the DR (100GBASE-DR), a 100-gigabit single lane specification for 500m.
Twenty-two companies is a very large MSA at this stage, which shows the strong interest in this technology
“The data rate is known, the type of forward-error correction is the same, and we have a starting point with the DR specs - we know what their transmit levels and receive levels are,” says Nowell. The new MSA will need to contend with the extra signal loss to extend the link distances to 2km and 10km.
With the 2km 400G-FR4 specification, not only does the design involve longer distances but also loss introduced using an optical multiplexer and demultiplexer to combine and separate the four wavelengths transmitted over the single-mode fibre.
“It is really a technical problem, one of partitioning the specifications to account for the extra loss of the link channel,” says Nowell.
One way to address the additional loss is to increase the transmitter’s laser power but that raises the design’s overall power consumption. And since the industry continually improves receiver performance - its sensitivity - over time, any decision to raise the transmitter power needs careful consideration. “There is always a trade off,” says Nowell. “You don't want to put too much power on the transmitter because you can’t change that specification.”
The MSA will need to decide whether the transmitter power is increased or is kept the same and then the focus will turn to the receiver technology. “This is where a lot of the hard work occurs,” he says.
Origins
The MSA came about after the IEEE 802.3bs 400 Gigabit Ethernet Task Force defined 2km (400GBASE-FR8) and 10km (400GBASE-LR8 interfaces based on eight 50 gigabit-per-second wavelengths. “There was concern or skepticism that some of the IEEE specification for 2km and 10km at 400 gigabits were going to be the lowest cost,” says Nowell. Issues include fitting eight wavelengths within the modules as well as the cost of eight lasers. Many of the large cloud players wanted a four-wavelength solution and they wanted it specified.
The debate then turned to whether to get the work done within the IEEE or to create an MSA. Given the urgency that the industry wanted such a specification, there was a concern that it might take too long to get the project started and completed using an IEEE framework, so the decision was made to create the MSA.
“The aim is to write these specifications as quickly as we can but with the assumption that the IEEE will pick up the challenge of taking on the same scope,” says Nowell. “So the specs are planned to be written following IEEE methodology.” That way, when the IEEE does address this, it will have work it can reference.
“We are not saying that the MSA spec will go into the IEEE,” says Nowell. “We are just making it so that the IEEE, if they chose, can quickly and easily have a very good starting point.”
Form factors
The MSA specification does not dictate the modules to be used when implementing the 100-gigabit-based wavelength designs. An obvious candidate for the single-wavelength 2km and 10km designs is the SFP-DD. And Nowell says the OSFP and the QSFP-DD pluggable optical modules as well as COBO, the embedded optics specification, will be used to implement 400G-FR4. “From Cisco’s point of view, we believe the QSFP-DD is where it is going to get most of its traction,” says Nowell, who is also co-chair of the QSFP-DD MSA.
Nowell points out that the industry knows how to build systems using the QSFP form factors: how the systems are cooled and how the high-speed tracks are laid down. The development of the QSFP-DD enables the industry to reuse this experience to build new high-density systems.
“And the backward compatibility of the QSFP-DD is massively important,” he says. A QSFP-DD port also supports the QSFP28 and QSFP modules. Nowell says there are customers that buy the latest 100-gigabit switches but use lower-speed 40-gigabit QSFP modules until their network needs 100 gigabits. “We have customers that say they want to do the same thing with 100 and 400 gigabits,” says Nowell. “That is what motivated us to solve that backward-compatibility problem.”
Roadmap
A draft specification of the phase one work will be published by the 22 founding companies this year. Once published, other companies - ‘contributors’ - will join and add their comments and requirements. Further refinement will then be needed before the final MSA specification, expected by mid-2018. Meanwhile, the development of the 10km 400G-LR4 interface will start during the first half of 2018.
The MSA work is focussed on developing the 100-gigabit and 400-gigabit specifications. But Nowell says the work will help set up what comes next after 400 gigabits, whether that is 800 gigabits, one terabit or whatever.
“Once a technology gets widely adopted, you get a lot of maturity around it,” he says. “A lot of knowledge about where and how it can be extended.”
There are now optical module makers building eight-wavelength optical solutions while in the IEEE there are developments to start 100-gigabit electrical interfaces, he says: “There are a lot of pieces out there that are lining up.”
The 22 founding members of the 100G Lambda MSA Group are: Alibaba, Arista Networks, Broadcom, Ciena, Cisco, Finisar, Foxconn Interconnect Technology, Inphi, Intel, Juniper Networks, Lumentum, Luxtera, MACOM, MaxLinear, Microsoft, Molex, NeoPhotonics, Nokia, Oclaro, Semtech, Source Photonics and Sumitomo Electric.