Latest coherent ASICs set the bar for the optical industry

Feature: Beyond 100G - Part 3

Alcatel-Lucent has detailed its next-generation coherent ASIC that supports multiple modulation schemes and allow signals to scale to 400 Gigabit-per-second (Gbps). 

The announcement follows Ciena's WaveLogic 3 coherent chipset that also trades capacity and reach by changing the modulation scheme.

"They [Ciena and Alcatel-Lucent] have set the bar for the rest of the industry," says Ron Kline, principal analyst for Ovum’s network infrastructure group.

 "We will employ [the PSE] for all new solutions on 100 Gigabit"

Kevin Drury, Alcatel-Lucent

Photonic service engine

Dubbed the photonic service engine (PSE), Alcatel-Lucent's latest ASIC will be used in 100Gbps line cards that will come to market in the second half of 2012.

The PSE compromises coherent transmitter and receiver digital signal processors (DSPs) as well as soft-decision forward error correction (SD-FEC). The transmit DSP generates the various modulation schemes, and can perform waveform shaping to improve spectral efficiency. The coherent receiver DSP is used to compensate for fibre distortions and for signal recover.

The PSE follows Alcatel-Lucent's extended reach (XR) line card announced in December 2011 that extends its 100Gbps reach from 1,500 to 2,000km. "This [PSE] will be the chipset we will employ for all new solutions on 100 Gigabit," says Kevin Drury, director of optical marketing at Alcatel-Lucent. The PSE will extend 100Gbps reach to over 3,000km.

Ciena's WaveLogic 3 is a two-device chipset. Alcatel-Lucent has crammed the functionality onto a single device. But while the device is referred to as the 400 Gigabit PSE, two PSE ASICs are needed to implement a 400Gbps signal.  

"They [Ciena and Alcatel-Lucent] have set the bar for the rest of the industry"

Ron Kline, Ovum

"There are customers that are curious and interested in trialling 400Gbps but we see equal, if not higher, importance in pushing 100Gbps limits," says Manish Gulyani, vice president, product marketing for Alcatel-Lucent's networks group.

In particular, the equipment maker has improved 100Gbps system density with a card that requires two slots instead of three, and extends reach by 1.5x using the PSE.

Performance

Alcatel-Lucent makes several claims about the performance enhancements using the PSE: 

• Reach: The reach is extended by 1.5x. 

• Line card density: At 100Gbps the improvement is 1.5x. The current 100Gbps muxponder (10x10Gbps client input) and transponder (100Gbps client) line card designs occupy three slots whereas the PSE design will occupy two slots only. Density will be improved by 4x by adopting a 400Gbps muxponder that occupies three slots.

• Power consumption: By going to a more advanced CMOS process and by enhancing the design of the chip architecture, the PSE consumes a third less power per Gigabit of transport: from 650mW/Gbps to 425mW/Gbps. Alcatel-Lucent is not saying what CMOS process technology is used for the PSE. The company's current 100Gbps silicon uses a 65nm process and analysts believe the PSE uses a 40nm process. 

• System capacity: The channel width occupied by the signal can be reduced by a third. A 50GHz 100Gbps wavelength can be compressed to occupy a 37.5GHz. This would improve overall 100Gbps system capacity from 8.8 Terabit-per-second (Tbps) to 11.7Tbps. Overall capacity can be improved from 88, 100Gbps ports to 44, 400Gbps interfaces. That doubles system capacity to 17.6Tbps. Using waveform shaping, this is improved by a further third, to greater than 23Tbps.

"We are not saying we are breaking the 50GHz channel spacing today and going to a flexible grid, super-channel-type construct," says Drury. "But this chip is capable of doing just that." Alcatel-Lucent will at least double network capacity when its system adopts 44 wavelengths, each at 400Gbps. 

400 Gigabit

To implement a 400Gbps signal, a dual-carrier, dual-polarisation 16-QAM coherent wavelength is used that occupies 100GHz (two 50GHz channels). Alcatel-Lucent says that should it commercialise 400Gbps using waveform shaping, the channel spacing would reduce to 75GHz. But this more efficient grid spacing only works alongside a flexible grid colourless, directionless and contentionless (CDC) ROADM architecture.

A 400Gbps PSE card showing four 100 Gigabit Ethernet client signals going out as a 400Gbps wavelength. The three-slot card is comprised of three daughter boards. Source: Alcatel-Lucent.

Alcatel-Lucent is not ready to disclose the reach performance it can achieve with the PSE using the various modulation schemes. But it does say the PSE supports dual-polarisation bipolar phase-shift keying (DP-BPSK) for longest reach spans, as well as quadrature phase-shift keying (DP-QPSK) and 16-QAM (quadrature amplitude modulation).

"[This ability] to go distances or to sacrifice reach to increase bandwidth, to go from 400km metro to trans-Pacific by tuning software, that is a big advantage," says Ovum's Kline. "You don't then need as many line cards and that reduces inventory."

Market status

Alcatel-Lucent says that it has 55 customers that have deployed over 1,450 100Gbps transponders.

A software release later this year for Alcatel-Lucent's 1830 Photonic Service Switch will enable the platform to support 100Gbps PSE cards.

A 400Gbps card will also be available this year for operators to trial.