Finisar demonstrates its first silicon photonics transceiver
- Finisar unveiled its first silicon photonics-based product, a 400-gigabit QSFP-DD DR4 module, at the recent ECOC event.
- The company also showed transceiver technology that simplifies the setting up of dense wavelength-division multiplexing (DWDM) links.
- Two 200-gigabit QSFP56 client-side modules and an extended reach 30km 400-gigabit eLR8 were also demonstrated by Finisar.
- A 64-gigabaud integrated tunable transmitter and receiver assembly (ITTRA) was used to send a 400-gigabit coherent wavelength.
Finisar is bringing to market its first silicon photonics-based optical module.
Christian UrricarietThe 400GBASE-DR4 is an IEEE 500m-reach 400-gigabit parallel fibre standard based on four fibres, each carrying a 100-gigabit 4-level pulse amplitude modulation (PAM-4) signal. Finisar’s DR4 is integrated into a QSFP-DD module.
“The DR4 is the 400-gigabit interface that most of the hyperscale cloud players are interested in first,” says Christian Urricariet, senior director of global marketing at Finisar.
The company demonstrated the module at the recent European Conference on Optical Communication (ECOC), held in Rome.
Silicon photonics-based DR4
The DR4 is an integrated design, says Finisar, comprising modulators and photo-detectors as well as modulator drivers and the trans-impedance amplifiers (TIAs).
Finisar chose silicon photonics for the DR4 after undertaking an extensive technology study. Silicon photonics emerged as ‘a clear winner’ in terms of cost and performance for photonic designs made up of similar functions in parallel, such as the four-channel DR4. Silicon photonics manufacturing is also scalable, making it ideal for high-volume designs.
The DR4 is the 400-gigabit interface that most of the hyperscale cloud players are interested in first
The DR4 can also be used in a breakout mode to interface to four 100GBASE-DR modules. Also referred to as the DR1, the 100GBASE-DR fits within an SFP-DD or a QSFP28 module.
The DR4-DR1 combination can link four servers, each using a 100-gigabit link, to a 400-gigabit port on a top-of-rack or mid-row switch. The top-of-rack 400-gigabit DR4 can also connect to a leaf switch with multiple 100-gigabit ports. “The DR4 can be used ‘top-of-rack down’ [to servers] or ‘top-of-rack up’ [to leaf switches],” says Urricariet. “This is similar to what people are doing with the [100-gigabit parallel fibre] PSM4.”
400-gigabit eLR8
Finisar also showcased an extended reach version of the IEEE 400GBASE-LR8 standard.
Dubbed the eLR8, the QSFP-DD module is a technology demonstrator not a product that extends the reach of the LR8 from 10km to 30km.
Finisar already has an LR8 product in a CFP8 pluggable module and is moving the design to the smaller QSFP-DD. The LR8 is an eight-wavelength duplex interface where each wavelength carries a 50-gigabit PAM-4 signal.
“The 400GBASE-LR8 is a low-risk approach to achieving a 400-gigabit duplex single-mode link in the short term,” says Urricariet. “You don’t have to wait for 100-gigabit PAM-4 [ICs] to be manufactured in high volume.”
Urricariet says the IEEE is considering developing an extended LR8 standard with a 40km reach but such distances could also be addressed using inexpensive coherent technology.
Finisar’s design achieves the extended range using the same components as its LR8 module - directly modulated DFB lasers and PIN photodetectors. “There is plenty of margin with that [LR8 design],” says Urricariet. This suggests Finisar picked the best performing DFBs and PINs for the eLR8 design.
The QSFP-DD 10km LR8 design is sampling now, with general availability from the first half of 2019.
Flextune
Configuring DWDM links can be likened to two groups of people separated in a wood at night. Each individual has a flashlight and is tasked with finding a counterpart from the second group, a process repeated until everyone is paired.
Setting up DWDM links is comparable to telling each individual the exact path to take to find their counterpart. The Flextune technology that Finisar has developed can be viewed as giving each individual the confidence to stride out - sweeping their flashlights as they go - till they find a counterpart.
Currently, setting up a DWDM link requires coordination between a field engineer and network operations staff. Each tunable transceiver that is plugged into a port is told which wavelength to tune to. The system itself may tell the transceiver the wavelength to use or a field engineer programs each transceiver before it is plugged into the platform.
Equally, the transceiver output fibre must be connected to the right optical multiplexer and demultiplexer (mux-demux) port, as do the transceivers at the link’s other end.
The result is a time-consuming process that is prone to human error.
With Flextune, the tunable transceivers are plugged into the equipment’s ports and connected to the mux-demux’s ports. “It does not matter which port,” says Urricariet. “The transceivers search for each other and self-configure to the right wavelength.”
Each Flextune-enabled transceiver operates independently of the transceiver at the other end; there is no master-slave arrangement, says Urricariet, although a master-slave arrangement can be used if requested.
The mux-demux must also be a blocking architecture for Flextune to work. “If the mux-demux does not block the other wavelengths on each port, then you have a mess,” says Urricariet. With such a mux-demux, the channels scanned are blocked until the transceiver’s output is passed to the right channel. Once the link is established, the two transceivers set permanently to that wavelength.
“It [the process] happens at both ends simultaneously and on all the ports,” says Urricariet. “The basic technique can self-tune up to 96 [DWDM] channels in around five minutes.”
Being able to tune independently of the host equipment means that the Flextune-enabled transceivers can also be sold directly to operators and plugged into any of their equipment.
Urricariet says Flextune promises welcome operational savings given DWDM’s increasing adoption in the access network with developments such as 5G fronthaul.
The basic technique can self-tune up to 96 [DWDM] channels in around five minutes
Flextune will also be used for metro and data centre interconnect applications, as well as connecting Remote PHY nodes being deployed in cable networks. “The Remote PHY is also a big focus for this type of feature,” says Urricariet.
Finisar demonstrated Flextune with its 10-gigabit tunable SFP+ modules that are now sampling. Flextune will also be adopted for its 25-gigabit SFP+ that will sample ‘very soon’, followed by coherent modules.
“We do have a CFP2-ACO module in production and other coherent products on our roadmap,” says Urricariet. “We will be looking to implement Flextune technology in these products as well.”
Google has started deployments of 2x200GbE
200 Gigabit Ethernet: a growing interim solution
Finisar also demonstrated two 200-gigabit modules. The QSFP56 implements the 2km FR4 specification. The 200-gigabit FR4 uses four coarse WDM (CWDM) wavelengths, each carrying a 50-gigabit PAM-4 signal.
Finisar has previously said it will develop 200-gigabit modules for the large-scale data centres interested in the technology as an interim solution before 400-gigabit modules ramp. Such an intermediate market for “one hyperscaler and maybe two” is sufficient to justify making 200-gigabit modules, says Urricariet.
Market research firm LightCounting has increased its forecast for 200 Gigabit Ethernet (GbE) modules due to interest from Facebook.
A presentation by Facebook at ECOC suggested that 400 GbE is far from being ready, says Vladimir Kozlov, CEO of LightCounting. “It looks like 200GbE is being considered now, but Facebook may change its mind again,” says Kozlov. “In the meantime, Google has started deployments of 2x200GbE [in an OSFP module] as planned.”
As with the 400-gigabit eLR8, Finisar also demonstrated an extended reach version of the 200-gigabit FR4 to achieve a 10km reach. “This is not to be confused with the 10km 200-gigabit LR4 that is a LAN-WDM grid based design,” says Urricariet. “The extended FR4 uses a CWDM grid.”
ITTRA
At OFC 2018 in March, Finisar unveiled its 32-gigabaud (Gbaud) integrated tunable transmitter and receiver assembly (ITTRA) that combines the optics and electronics required for an analogue coherent optics interface.
The ITTRA comprises a tunable laser, an optical amplifier, modulators, modulator drivers, coherent mixers, a photo-detector array and the accompanying TIAs. All the components of the 32Gbaud ITTRA are integrated within a gold box that is 70 percent smaller than the size of a CFP2 module. The integrated assembly also has a power consumption below 7.5W.
At ECOC, the company demonstrated its second ITTRA design operating at 64Gbaud to transmit a 400-gigabit wavelength using 16-ary quadrature amplitude modulation (16-QAM). Finisar would not detail the power consumption of the 64Gbaud ITTRA.
“The doubling of the speed to 64Gbaud will enable 400-gigabit DCO modules as well as 400ZR,” says Urricariet. Digital coherent optics (DCO) refers to coherent modules that integrate the optics and the coherent digital signal processor (DSP).
Samples and production of the 64Gbaud ITTRA are due in 2019.
Intel targets 5G fronthaul with a 100G CWDM4 module
- Intel announced at ECOC that it is sampling a 10km extended temperature range 100-gigabit CWDM4 optical module for 5G fronthaul.
- Another announced pluggable module pursued by Intel is the 400 Gigabit Ethernet (GbE) parallel fibre DR4 standard.
- Intel, a backer of the CWDM8 MSA, says the 8-wavelength 400-gigabit module will not be in production before 2020.
Intel has expanded its portfolio of silicon photonics-based optical modules to address 5G mobile fronthaul and 400GbE.
Robert BlumAt the European Conference on Optical Communication (ECOC) being held in Rome this week, Intel announced it is sampling a 100-gigabit CWDM4 module in a QSFP form factor for wireless fronthaul applications.
The CWDM4 module has an extended temperature range, -20°C to +85°C, and a 10km reach.
“The final samples are available now and [the product] will go into production in the first quarter of 2019,” says Robert Blum, director of strategic marketing and business development at Intel’s silicon photonics product division.
Intel also announced it will support the 400GBASE-DR4, the IEEE’s 400 GbE standard that uses four parallel fibres for transmit and four for the receive path, each carrying a 100-gigabit 4-level pulse amplitude modulation (PAM-4) signal.
5G wireless
5G wireless will be used for a variety of applications. Already this year the first 5G fixed and mobile wireless services are expected to be launched. 5G will also support massive Internet of Things (IoT) deployments as well as ultra-low latency applications.
The next-generation wireless standard uses new spectrum that includes millimetre wave spectrum in the 24GHz to 40GHz region. Such higher frequency bands will drive small-cell deployments.
5G’s use of new spectrum, small cells and advanced air interface techniques such as multiple input, multiple output (MIMO) antenna technology is what will enable its greater data speeds and vastly expanded capacity compared to the current LTE cellular standard.
Source: Intel.
The 5G wireless standard will also drive greater fibre deployment at the network edge. And it is here where mobile fronthaul plays a role, linking the remote radio heads at the antennas with the centralised baseband controllers at the central office (see diagram). Such fronthaul links will use 25-gigabit and 100-gigabit links. “We have multiple customers that are excited about the 100-gigabit CWDM4 for these applications,” says Blum
Intel expects demand for 25-gigabit and 100-gigabit transceivers for mobile fronthaul to begin in 2019.
Intel is now producing over one million PSM4 and CWDM4 modules a year
Client-side modules
Intel entered the optical module market with its silicon photonics technology in 2016 with a 100-gigabit PSM4 module, quickly followed by a 100-gigabit CWDM4 module. Intel is now producing over one million PSM4 and CWDM4 modules a year.
Intel will provide customers with 400-gigabit DR4 samples in the final quarter of 2018 with production starting in the second half of 2019. This is when Intel says large-scale data centre operators will require 400 gigabits.
“The initial demand in hyperscale data centres for 400 gigabits will not be for duplex [fibre] but parallel fibre,” says Blum. “So we expect the DR4 to go to volume first and that is why we are announcing the product at ECOC.”
Intel says the advantages of its silicon photonics approach have already been demonstrated with its 100-gigabit PSM4 module. One is the optical performance resulting from the company’s heterogeneous integration technique combining indium-phosphide lasers with silicon photonics modulators on the one chip. Another advantage is scale using Intel’s 300mm wafer-scale manufacturing.
Intel says demand for the 500m-reach DR4 module to go hand-in-hand with that for the 100-gigabit single- wavelength DR1, given how the DR4 will also be used in breakout mode to interface with four DR1 modules.
“We don’t see the DR1 standard competing or replacing 100-gigabit CWDM4,” says Blum. “The 100-gigabit CWDM4 is now mature and at a very attractive price point.”
Intel is a leading proponent of the CWDM8 MSA, an optical module design based on eight wavelengths, each a 50 gigabit-per-second (Gbps) non-return-to-zero (NRZ) signal. The CWDM8 MSA was created to fast-track 400 gigabit interfaces by avoiding the wait for 100-gigabit PAM-4 silicon.
When the CWDM8 MSA was launched in 2017, the initial schedule was to deploy the module by the end of this year. Intel also demonstrated the module working at the OFC show held in March.
Now, Intel expects production of the CWDM8 in 2020 and, by then, other four-wavelength solutions using 100-gigabit PAM-4 silicon such as the 400G-FR4 MSA will be available.
“We just have to see what the use case will be and what the timing will be for the CWDM8’s deployment,” says Blum.
Business services and mobile revive WDM-PON interest
"WDM-PON is many things to many people" - Jon Baldry
It was in 2005 that Novera Optics, a pioneer of WDM-PON (wavelength-division multiplexing, passive optical networking), was working with Korea Telecom in a trial involving 50,000 residential lines. Yet, one decade later, WDM-PON remains an emerging technology. And when a WDM-PON deployment does occur, it is for business services and mobile backhaul rather than residential broadband.
WDM-PON delivers high-capacity, symmetrical links using a dedicated wavelength. The links are also secure, an important consideration for businesses, and in contrast to PON where data is shared between all the end points, each selecting its addressed data.
One issue hindering the uptake of WDM-PON is the lack of a common specification. "WDM-PON is many things to many people," says Jon Baldry, technical marketing director at Transmode.
One view of WDM-PON is as the ultimate broadband technology; this was Novera's vision. Other vendors, such as Transmode, emphasise the WDM component of the technology, seeing it as a way to push metro-style networking towards the network edge, to increase bandwidth and for operational simplicity.
WDM-PON's uptake for residential access has not yet happened because the high bandwidth it offers is still not needed, while the system economics do not match those of PON.
Gigabit PON (GPON) and Ethernet PON (EPON) are now deployed in the tens of millions worldwide. And operators can turn to 10G-EPON and XG-PON when the bandwidth of GPON and EPON are insufficient. Beyond that, TWDM-PON (Time and Wavelength Division Multiplexing PON) is an emerging approach, promoted by the likes of Alcatel-Lucent and Huawei. TWDM-PON uses wavelength-division multiplexing as a way to scale PON, effectively supporting multiple 10 Gigabit PONs, each riding on a wavelength.
Carriers like the reassurance a technology roadmap such as PON's provides, but their broadband priority is wireless rather than wireline. The bigger portion of their spending is on rolling out LTE since wireless is their revenue earner.
As for fixed broadband, operators are being creative.
G.fast is one fixed broadband example. G.fast is the latest DSL standard that supports gigabit speeds over telephone wire. Using G.fast, operators can combine fibre and DSL to achieve gigabit rates and avoid the expense of taking fibre all the way to the home. BT is one operator backing G.fast, with pilot schemes scheduled for the summer. And if the trials are successful, G.fast deployments could start next year.
Deutsche Telekom is promoting a hybrid router to customers that combines fixed and wireless broadband, with LTE broadband kicking in when the DSL line becomes loaded.
Meanwhile, vendors with a WDM background see WDM-PON as a promising way to deliver high-volume business services, while also benefiting from the operator's cellular push by supporting mobile backhaul and mobile fronthaul. They don't dismiss WDM-PON for residential broadband but accept that the technology must first mature.
Transmode announced recently its first public customer, US operator RST Global Communications, which is using the vendor's iWDM-PON platform for business services.
"Our primary focus is business and mobile backhaul, and we are pushing WDM deeper into access networks," says Baldry. "We don't want a closed network where we treat WDM-PON differently to the way we treat the rest of the network." This means using the C-band wavelength grid for metro and WDM-PON. This avoids having to use optical-electrical-optical translation, as required between PON and WDM networks, says Baldry.
The iWDM-PON system showing the seeder light source at the central office (CO) optical line terminal (OLT), and the multiplexer (MDU) that selects the individual light band for the end point customer premise equipment (CPE). Source: Transmode.
Transmode's iWDM-PON
Several schemes are being pursued to implement WDM-PON. One approach is seeded or self-tuning, where a broadband light source is transmitted down the fibre from the central office. An optical multiplexer is then used to pick off narrow bands of the light, each a seeder source to set the individual wavelength of each end point optical transceiver. An alternative approach is to use a tunable laser transceiver to set the upstream wavelength. A third scheme combines the broadband light source concept with coherent technology that picks off each transceiver's wavelength. The coherent approach promises extremely dense, 1,000 wavelength WDM-PONs.
Transmode has chosen the seeded scheme for the iWDM-PON platform. The system delivers 40, 1 Gigabit-per-second (Gbps) wavelengths spaced 50 GHz apart. The reach between the WDM-PON optical line terminal (OLT) and the optical network unit (ONU) end-points is 20 km without dispersion compensation fibre, or 30 km using such fibre. The platform uses WDM-PON SFP pluggable modules. The SFPs are MSA-compliant and use a fabry-perot laser and an avalanche photo-detector optimised for the injection-locked signal.
"We use the C-band and pluggable optics, so the choice of using WDM-PON optics or not is up to the customer," says Baldry. "It should not be a complicated decision, and the system should work seamlessly with everything else you do, enabling a mix of WDM-PON and regular higher speed or longer reach WDM over the same access network, as needed."
Baldry claims the approach has economic advantages as well as operational benefits. While there is a need for a broadband light source, the end point SFP WDM-PON transceivers are cheaper compared to fixed or tunable optics. Also setting the wavelengths is automated; the engineers do not need to set and lock the wavelength as they do using a tunable laser.
"The real advantage is operational simplicity," says Baldry, especially when an operator needs to scale optically connected end-points as they grow business and mobile backhaul services. "That is the intention of a PON-like network; if you are ramping up the end points then you have to think of the skill levels of the installation crews as you move to higher service volumes," he says.
RST Global Communications uses Transmode's Carrier Ethernet 2.0 as the service layer between the demarcation device (network interface device or NID) at the customer's premises, while using Transmode's packet-optical cards in the central office. WDM-PON provides the optical layer linking the two.
An early customer application for RST was upgrading a hotel's business connection from a few megabits to 1Gbps to carry Wi-Fi traffic in advance of a major conference it was hosting.
Overall, Transmode has a small number of operators deploying the iWDM-PON, with more testing or trialing it, says Baldry. The operators are interested in using the WDM-PON platform for mobile backhaul, mobile fronthaul and business services.
There are also operators that use installed access/ customer premise equipment from other vendors, exploring whether Transmode's WDM-PON platform can simplify the optical layer in their access networks.
Further developments
Transmode's iWDM-PON upgrade plans include moving the system from a two fibre design - one for the downstream traffic and one for the upstream traffic - to a single fibre one. To do this, the vendor will segment the C-band into two: half the C-band for the uplink and half for the downlink.
Another system requirement is to increase the data rate carried by each wavelength beyond a gigabit. Mobile fronthaul uses the Common Public Radio Interface (CPRI) standard to connect the remote radio head unit that typically resides on the antenna and the baseband unit.
CPRI data rates are multiples of the basic rate of 614.4 Mbps. As such 3 Gbps, 6 Gbps and rates over 10 Gbps are used. Baldry says the current iWDM-PON system can be extended beyond 1 Gbps to 2.5 Gbps and potentially 3 Gbps but because the system in noise-limited, the seeder light scheme will not stretch to 10 Gbps. A different optical scheme will be needed for 10 Gigabit. The iWDM-PON's passive infrastructure will allow for an in-service upgrade to 10 Gigabit WDM-PON technology once it becomes technically and economically viable.
Transmode has already conducted mobile fronthaul field trials in Russia and in Asia, and lab trials in Europe, using standard active and passive WDM and covering the necessary CPRI rates. "We are not mixing it with WDM-PON just yet; that is the next step," says Baldry.
Further information
WDM-PON Forum, click here
Lightwave Magazine: WDM-PON is a key component in next generation access