MultiPhy eyes 40 and 100 Gigabit direct-detect and coherent schemes

Visiting Israeli start-up MultiPhy at its office in Ness Ziona, near Rehovot, involves dancing around boxes. “We are about to move,” apologises Ronen Weinberg, director of product management at MultiPhy. But the company will not have to travel far. It is crossing buildings in the same Ness Ziona Science Park, moving in next to Finisar’s Israeli headquarters.

MultiPhy's Avi Shabtai (left) and Ronen Weinberg

MultiPhy is developing transceiver designs to boost the transmission performance of metro and long-haul 40 and 100 Gigabit-per-second (Gbps) links. The start-up is aiming its advanced digital signal processing (DSP) chips at direct detection and coherent-based modulation schemes.

“We are the only company, as far as we know, who is doing DSP-based semiconductors for the 40G and 100G direct-detect world,” says Avi Shabtai, CEO of Multiphy.

At 40Gbps the main direct-detection schemes are differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK), while at 100Gbps several direct-detect modulation schemes are being considered. “The fact that we are doing DSP at 40G and 100G enables us to achieve much better performance than regular hard-detection technology,” says Shabtai.

Established in 2007, the fabless semiconductor start-up raised US$7.2m in its latest funding round in May. MultiPhy is targeting its physical layer chips at module makers and system vendors. “While there is a clear ecosystem involving optical module companies and systems vendors, there is a lot of overlap,” says Shabtai. “You can find module companies that develop components; you can find system companies that skip the module companies, buying components to make their own line cards.”

MultiPhy’s CMOS chips include high-speed analogue-to-digital converters (ADC) and hardware to implement the maximum-likelihood sequence estimation (MLSE) algorithm. The company is operating the MLSE algorithm at “tens of gigasymbols-per-second”, says Shabtai. “We believe we are the only company implementing MLSE at these speeds.”

MultiPhy's office is alongside Finisar's Israeli headquartersMultiPhy will not disclose the exact sampling rate but says it is sampling at the symbol rate rather than at the Nyquist sampling theorem rate of double the symbol rate. Since commercial ADCs for 100Gbps have been announced that sample at 65Gsample/s, it suggests MultiPhy is sampling at up to half that rate.  

MLSE is used to compensate for the non-linear impairments of fibre transmission, to improve overall transmission performance. “We implement an anti-aliasing filter at the input to the ADC and we use the MLSE engine to compensate for impairments due to the low-bandwidth sampling,” says Shabtai.

“There is a good chance that 100Gbps will leapfrog 40Gbps coherent deployments”

Avi Shabtai, MultiPhy

MultiPhy benefits from using one-sample-per-symbol in terms of simplifying the chip design and its power consumption but the MLSE algorithm must counter the resulting distortion. Shabtai claims the result is a significant reduction in power consumption compared to the tradition two-samples-per-symbol approach: “Tens of percent – I won’t say the exact number but it is not 10 percent.”

Other chip companies implementing MLSE designs for optical transmission include CoreOptics, which was acquired by Cisco in May, and Clariphy. (See Oclaro and Clariphy)

Does using MLSE make sense for 40Gbps DPSK and DQPSK?

“If you use DSP for DQPSK at 40Gbps you can significantly improve polarisation mode dispersion tolerance, the limiting factor today of DQPSK transceivers,” says Shabtai.  MultiPhy expects the 40 Gigabit direct-detect market to shift towards DQPSK, accounting for the bulk of deployments in two years’ time.

Market applications

MultiPhy is delivering two solutions: for 40 and 100Gbps direct-detect, and 40 and 100Gbps coherent designs. The company has not said when it will deliver products but hinted that first it will address the direct-detect market and that chip samples will be available in 2011.

Not only will the samples enhance the reach of DQPSK-modulation based links but also allow the optical component specifications to be relaxed.  For example, cheaper 10Gbps optical components can be used which, says MultiPhy, will reduce total design cost by “tens of percent”. 

This is noteworthy, says Shabtai, as the direct-detect markets are increasingly cost-sensitive. “Coherent is being positioned as the high-end solution, and there will be pressure on the direct-detect market to show lower cost solutions,” he says.

MultiPhy is eyeing two 100Gbps spaces

MultiPhy’s view is that direct-detect modulation schemes will be deployed for quite some time due to their price and power advantage compared to coherent detection.

Another factor against 40Gbps coherent technology will be the price difference between 40Gbps and 100Gbps coherent schemes. “There is a good chance that 100Gbps will leapfrog 40Gbps coherent deployments,” he says. “The 40Gbps coherent modules will need to go a long way to get to the right price.”  MultiPhy says it is hearing about the expense of coherent modules from system vendors and module makers, as well as industry analysts.

Metro and long-haul

The company says it has received several requests for 40Gbps and 100Gbps direct-detect schemes for the metro due to its sensitivity to cost and power consumption. “We are getting to the point in optical communications where one solution does not fit all – that the same solution for long-haul will also suit metro,” says Shabtai.

He believes 100Gbps coherent will become a mainstream solution but will take time for the technology to mature and its costs to come down. It will thus take time before 100Gbps coherent expands beyond long-haul and into the metro. He also expects a different 100Gbps coherent solution to be used in the metro. “The requirements are different – in reach, in power constraints” he says. “The metro will increasingly become a segment, not only for direct-detect but also for coherent.”

Coherent: Already a crowded market

There are at least a dozen companies actively developing silicon for coherent transmission, while half-a-dozen leading system vendors developing designs in-house. In addition, no-one really knows when the 100Gbps market will take off. So how does MultiPhy expect to fare given the fierce competition and uncertain time-to-revenues?

“It is very hard to predict the exact ramp up to high volumes,” says Shabtai. “At the end of the day, 100Gbps will come instead of 10Gbps and when people look back in five and six years’ time, they will say: ‘Gee, who would have expected so much capacity would have been needed?’.”

The big question mark is when will coherent technology ramp and this explains why MultiPhy is also targeting next-generation direct-detect schemes with its technology. “We cannot come to market doing the same thing as everyone else,” says Shabtai. “Having a solution that addresses power consumption based on one-sample-per-symbol gives us a significant edge.”

MultiPhy admits it has received greater market interest following Cisco’s acquisition of CoreOptics. “While Cisco said it would fulfill all previous commitments, still it worried some of CoreOptics’ customers,” says Shabtai. The acquisition also says something else to Shabtai: 100Gbps coherent is a strategic technology. 

Did Cisco consider MultiPhy as a potential acquisition target? “First, I can’t comment, and I wasn’t at the company at the time,” says Shabtai.

As for design wins, Shabtai says MultiPhy is in “advanced discussion” with several leading module and system vendor companies concerning its 40Gbps and 100Gbps direct-detect and coherent technologies.



Further reading

See Opnext's multiplexer IC plays its part in 100Gbps trial