Infinera goes multi-terabit with its latest photonic IC
In his new book, The Great Acceleration, Robert Colvile discusses how things we do are speeding up.
In 1845 it took U.S. President James Polk six months to send a message to California. Just 15 years later Abraham Lincoln's inaugural address could travel the same distance in under eight days, using the Pony Express. But the use of ponies for transcontinental communications was shortlived once the electrical telegraph took hold. [1]
The relentless progress in information transfer, enabled by chip advances and Moore's law, is taken largely for granted. Less noticed is the progress being made in integrated photonic chips, most notably by Infinera.
In 2000, optical transport sent data over long-haul links at 10 gigabit-per-second (Gbps), with 80 such channels supported in a platform. Fifteen years later, Infinera demonstrated its latest-generation photonic integrated circuit (PIC) and FlexCoherent DSP-ASIC that can transmit data at 600Gbps over 12,000km, and up to 2.4 terabit-per-second (Tbps) - three times the data capacity of a state-of-the-art dense wavelength-division multiplexing (DWDM) platform back in 2000 - over 1,150km.
Infinite Capacity Engine
Infinera dubs its latest optoelectronic subsystem the Infinite Capacity Engine. The subsystem comprises a pair of indium-phosphide PICs - a transmitter and a receiver - and the FlexCoherent DSP-ASIC. The performance capabilities that the Infinite Capacity Engine enables were unveiled by Infinera in January with its Advanced Coherent Toolkit announcement. Now, to coincide with OFC 2016, Infinera has detailed the underlying chips that enable the toolkit. And company product announcements using the new hardware will be made later this year, says Pravin Mahajan, the company's director of product and corporate marketing.
The claimed advantages of the Infinite Capacity Engine include a 82 percent reduction in power consumption compared to a system using discrete optical components and a dozen 100-gigabit coherent DSP-ASICs, and a 53 percent reduction in total-cost-of-ownership compared to competing dense WDM platforms. The FlexCoherent chip also features line rate data encryption.
"The Infinite Capacity Engine is the industry's first multi-terabit it super-channel, says Mahajan. "It also delivers the industry's first multi-terabit layer one encryption."
Multi-terabit PIC
Infinera's first transmitter and receiver PIC pair, launched in 2005, supported 10, 10-gigabit channels and implemented non-coherent optical transmission.
In 2011 Infinera introduced a 500-gigabit super-channel coherent PIC pair used with Infinera's DTN-X platforms and also its Cloud Xpress data centre interconnect platform launched in 2014. The 500 Gigabit design implemented 10, 50 gigabit channels that implemented polarisation-multiplexed, quadrature phase-shift keying (PM-QPSK) modulation. The accompanying FlexCoherent DSP-ASIC was implemented using a 40nm CMOS process node and support a symbol rate of 16 gigabaud.
The PIC design has since been enhanced to also support additional modulation schemes such as as polarisation-multiplexed, binary phase-shift keying (PM-BPSK) and 3 quadrature amplitude modulation (PM-3QAM) that extend the DTN-X's ultra long-haul performance.
In 2015 Infinera also launched the oPIC-100, a 100-gigabit PIC for metro applications that enables Infinera to exploit the concept of sliceable bandwidth by pairing oPIC-100s with a 500 gigabit PIC. Here the full 500 gigabit super-channel capacity can be pre-deployed even if not all of the capacity is used. Using Infinera's time-based instant bandwidth feature, part of that 500 gigabit capacity can be added between nodes in a few hours based on a request for greater bandwidth.
Now, with the Infinite Capacity Engine PIC, the effective number of channels has been expanded to 12, each capable of supporting a range of modulation techniques (see table below) and data rates. In fact, Infinera uses multiple Nyquist sub-carriers spread across each of the 12 channels. By encoding the data across multiple sub-carriers a lower-baud rate can be used, increasing the tolerance to non-linear channel impairments during optical transmission.
Mahajan says the latest PIC has a power consumption similar to its current 500 Gigabit super-channel PIC but because the photonic design supports up to 2.4 terabit, the power consumption in gigabit-per-Watt is reduced by 70 percent.
FlexCoherent encryption
The latest FlexCoherent DSP-ASIC is Infinera's most complex yet. The 1.6 billion transistor 28nm CMOS IC can process two channels, and supports a 33 gigabaud symbol rate. As a result, six DSP-ASICs are used with the 12-channel PIC.
It is the DSP-ASIC that enables the various elements of the advanced coherent toolkit that includes improved soft-decision forward error correction. "The net coding gain is 11.9dB, up 0.9 dB, which improves the capacity-reach," says Mahajan. Infinera says the ultra long-haul performance has also been improved from 9,500km to over 12,000km.
Source: Infinera
The DSP also features layer one encryption implementing the 256-bit Advanced Encryption Standard (AES-256). Infinera says the request for encryption is being led by the Internet content providers but wholesale operators and co-location providers also want to secure transmissions between sites.
Infinera introduced layer two MACsec encryption with its Cloud Xpress platform. This encrypts the Ethernet payload but not the header. With layer one encryption, it is the OTN frames that are encoded. "When we get down to the OTN level, everything is encrypted," says Mahajan. An operator can choose to encrypt the entire super-channel or encrypt at the service level, down to the ODU0 (1.244 Gbps) level.
System benefits
Using the Infinite Capacity Engine, the transmission capacity over a fibre increases from 9.5 terabit to up to 26.4 terabit.
And with the newest PIC, Infinera can expand the sliceable transponder concept for metro-regional applications. The 2.4 terabits of capacity can be pre-deployed and new capacity turned up between nodes. "You can suddenly turn up 200 gigabit for a month or two, rent and then return it," says Mahajan. However, to support the full 2.4 terabits of capacity, the PIC at the other end of the link would also need to support 16-QAM.
Infinera does say there will be other Infinite Capacity Engine variants. "There will be specific engines for specific markets, and we would choose a subset of the modulations," says Mahajan.
One obvious platform that will benefit from the first Infinite Capacity Engine is the DTN-X. Another that will likely use an ICE variant is Infinera's Cloud Xpress. At present Infinera integrates its 500-gigabit PIC in a 2 rack-unit box for data centre interconnect applications. By using the new PIC and implementing PM-16QAM, the line-side capacity per rack unit of a second-generation Cloud Xpress would rise from 250 gigabit to 1.2 terabit. And with layer one encryption, the MACsec IC may no longer be needed.
Mahajan says the Infinite Capacity Engine has already been tested in the Telstra trial detailed in January. "We have already proven its viability but it is not deployed and carrying live traffic," he says.
Next-generation coherent adds sub-carriers to capabilities
Part 2: Infinera's coherent toolkit
Source: Infinera
Infinera has detailed coherent technology enhancements implemented using its latest-generation optical transmission technology. The system vendor is still to launch its newest photonic integrated circuit (PIC) and FlexCoherent DSP-ASIC but has detailed features the CMOS and indium phosphide ICs support.
The techniques highlight the increasing sophistication of coherent technology and an ever tighter coupling between electronics and photonics.
The company has demonstrated the technology, dubbed the Advanced Coherent Toolkit, on a Telstra 9,000km submarine link spanning the Pacific. In particular, the demonstration used matrix-enhanced polarisation-multiplexed, binary phased-shift keying (PM-BPSK) that enabled the 9,000km span without optical signal regeneration.
Using the ACT is expected to extend the capacity-reach product for links by the order of 60 percent. Indeed the latest coherent technology with transmitter-based digital signal processing delivers 25x the capacity-reach of 10-gigabit wavelengths using direct-detection, the company says.
Infinera’s latest PIC technology includes polarisation-multiplexed, 8-quadrature amplitude modulation (PM-8QAM) and PM-16QAM schemes. Its current 500-gigabit PIC supports PM-BPSK, PM-3QAM and PM-QPSK. The PIC is expected to support a 1.2-terabit super-channel and using PM-16QAM could deliver 2.4 terabit.
“This [the latest PIC] is beyond 500 gigabit,” confirms Pravin Mahajan, Infinera’s director of product and corporate marketing. “We are talking terabits now.”
Sterling Perrin, senior analyst at Heavy Reading, sees the Infinera announcement as less PIC related and more an indication of the expertise Infinera has been accumulating in areas such as digital signal processing.
Nyquist sub-carriers
Infinera is the first to announce the use of sub-carriers. Instead of modulating the data onto a single carrier, Infinera is using multiple Nyquist sub-carriers spread across a channel.
Using a flexible grid, the sub-carriers span a 37.5GHz-wide channel. In the example shown above, six are used although the number is variable depending on the link. The sub-carriers occupy 35GHz of the band while 2.5GHz is used as a guard band.
“Information you were carrying across one carrier can now be carried over multiple sub-carriers,” says Mahajan. “The benefit is that you can drive this as a lower-baud rate.”
Lowering the baud rate increases the tolerance to non-linear channel impairments experienced during optical transmission. “The electronic compensation is also much less than what you would be doing at a much higher baud rate,” says Abhijit Chitambar, Infinera’s principal product and technology marketing manager.
While the industry is looking to increase overall baud rate to increase capacity carried and reduce cost, the introduction of sub-carriers benefits overall link performance. “You end up with a better Q value,” says Mahajan. The ‘Q’ refers to the Quality Factor, a measure of the transmission’s performance. The Q Factor combines the optical signal-to-noise ratio (OSNR) and the optical bandwidth of the photo-detector, providing a more practical performance measure, says Infinera.
Infinera has not detailed how it implements the sub-carriers. But it appears to be a combination of the transmitter PIC and the digital-to-analogue converter of the coherent DSP-ASIC.
It is not clear what the hardware implications of adopting sub-carriers are and whether the overall DSP processing is reduced, lowering the ASIC’s power consumption. But using sub-carriers promotes parallel processing and that promises chip architectural benefits.
“Without this [sub-carrier] approach you are talking about upping baud rate,” says Mahajan. “We are not going to stop increasing the baud rate, it is more a question of how much you can squeeze with what is available today.“
SD-FEC enhancements
The FlexCoherent DSP also supports enhanced soft-decision forward-error correction (SD-FEC) including the processing of two channels that need not be contiguous.
SD-FEC delivers enhanced performance compared to conventional hard-decision FEC. Hard-decision FEC decides whether a received bit is a 1 or a 0; SD-FEC also uses a confidence measure as to the likelihood of the bit being a 1 or 0. This additional information results in a net coding gain of 2dB compared to hard-decision FEC, benefiting reach and extending the life of submarine links.
By pairing two channels, Infinera shares the FEC codes. By pairing a strong channel with a weak one and sharing the codes, some of the strength of the strong signal can be traded to bolster the weaker one, extending its reach or even allowing for a more advanced modulation scheme to be used.
The SD-FEC can also trade performance with latency. SD-FEC uses as much as a 35 percent overhead and this adds to latency. Trading the two supports those routes where low latency is a priority.
Matrix-enhanced PSK
Infinera has implemented a technique that enhances the performance of PM-BPSK used for the longest transmission distances such as sub-sea links. The matrix-enhancement uses a form of averaging that adds about a decibel of gain. “Any innovation that adds gain to a link, the margin that you give to operators is always welcome,” says Mahajan.
The toolkit also supports the fine-tuning of channel widths. This fine-tuning allows the channel spacing to be tailored for a given link as well as better accommodating the Nyquist sub-carriers.
Product launch
The company has not said when it will launch its terabit PIC and FlexCoherent DSP.
“Infinera is saying it is the first announcing Nyquist sub-carriers, which is true, but they don’t give a roadmap when the product is coming out,” says Heavy Reading’s Perrin. “I suspect that Nokia [Alcatel-Lucent], Ciena and Huawei are all innovating on the same lines.”
There could be a slew of announcements around the time of the OFC show in March, says Perrin: “So Infinera could be first to announce but not necessarily first to market.”