Teradvance: A New Take on 40 Gig

Startup says it's conquered some of the challenges of next generation transmission systems

September 14, 2001

5 Min Read
Teradvance: A New Take on 40 Gig

Earlier this year, Light Reading published a report that identified some of the challenges facing developers of 40 Gbit/s transmission systems (see 40-Gig Forecast).

They include the scarcity, cost and unproven performance of 40-gig components, big problems with dispersion and nonlinear effects and difficulties in using this technology over legacy fiber. Another challenge is also implicit in the report’s long list of companies developing systems in this field. The competition is extremely tough.

Enter Teradvance Communications, Inc., a startup that’s aiming to demonstrate that it’s got a couple of winning differences in this field.

First, it isn’t competing head-to-head with system vendors. It’s raised a relatively small amount of angel funding - $2 million – and is limiting its goals to developing 40-gig and 80-gig transmission technology and then selling it to a systems vendor. "A few people" have already shown some interest, the company says.

Teradvance is actually working on two versions of its technology – a pair of boxes (transmit and receive) for use in ultra-long haul, long haul and marine applications, and a much lower cost pair of chips for use in metro networks. The metro chips don't have the snazzy stuff needed for long distance transmissions.

The company expects to demonstrate a 40-gig proof-of-concept version of its technology later this month, and have a 80-gig prototype ready by November.

The second winning difference is that Teradvance believes that it's conquered many of the technical challenges facing 40-gig systems.

In particular, it’s found a way of splitting transmissions into four wavelengths each carrying 10 Gbit/s while using a single laser for all four wavelengths. This means that it can make use of well-proven, low-cost 10 Gbit/s components while avoiding the need for four expensive lasers, one for each wavelength, as would normally be the case.

That’s just for starters. Teradvance says its technology achieves a 4 decibel signal to noise (SNR) advantage over the normal return-to-zero modulation schemes used by other developers of 40-gig systems. This also minimizes the impact of non-linearities, polarization mode dispersion and chromatic dispersion, it adds.

The bottom line is that Teradvance's pair of boxes can carry as many as 80 40-gig channels in the C band over “any type of fiber”, and can do this over distances of up to 2,000 km, according to the company.

This eliminates requirements for forward error correction (FEC) or Raman amplication when using non-zero-dispersion-shifted-fiber (NZ-DSF). It also eliminates requirements for separate dispersion compensators, the company says.

In addition, Teradvance's SNR performance means that carriers aren’t faced with having to upgrade amplifiers and shorten their spacing, as they might well have to with alternative 40-gig technologies, according to the company.

Teradvance says that its closest competitor is probably OptiMight Communications Inc., which also makes a big thing out of achieving long transmission distances without resorting to Raman amplification (see Raman Risks Emerge and OptiMight Details Long-Haul Box).

In order to get an expert’s opinion on Teradvance’s technology, Light Reading invited Stuart Barnes, now with Atlas Venture, a venture capital company, to comment on a technology overview from the startup.

Until recently, Barnes was director of engineering at Ilotron, a startup that was developing, among other things, transmission systems before it ran into funding problems earlier this year (see Ilotron Hits Hard Times). Prior to that, Barnes worked for Alcatel SA (NYSE: ALA; Paris: CGEP:PA), developing transmission systems.

Barnes says that Teradvance’s spectral efficiency (how much carrying capacity can be squeezed out of fiber) looks better than Optimight’s. However, Alcatel, Tyco International Ltd. (NYSE: TYC) and “the Japanese” (probably NEC Corp.) (Nasdaq: NIPNY)) have even better spectral efficiency figures than Teradvance, according to Barnes. Another couple of un-named U.S. startups might also have comparable performance, he adds.

Barnes’ comments on Teradvance’s technology follow, together with responses from the startup’s technical team:

  • Barnes: Modulation scheme looks key to long reach. Other than polarisation multiplexing (to get in extra channels). They remain silent on the details here. Presumably this is key IP.
    Teradvance: We fully agree. The modulation scheme is key to our IP.

  • Barnes: PMD compensation is a must at 40G (but everyone’s in this space). Still if they have the chip sets in hand they are on the leading edge.
    Teradvance: We do not need chipsets that we do not have - so we are indeed on the leading edge. We do not require the same PMD compensation equipment that other systems need. This is a tremendous advantage for us since the compensation equipment required by other systems is not yet available or not yet cost effective.

  • Barnes: The 4dB Noise Figure claimed for amplifiers is complete tosh (English colloquialism for baloney) for a legacy system. NF's here are typically 6.
    Teradvance: We agree. However, our reach using amplifiers with a noise figure of 6dB is still well over 1,500 km on SMF. Regardless of the noise figure used, our system is always better than other systems by the same amount. That is, the performance delta is always the same.

  • Barnes: Have they tested the solution over the whole C band? Generally the greatest problems come with the external channels. If it just simulation, have they reconciled with some experimental data.
    Teradvance: The only effects that would kick in at the external channels are dispersion slope effects, which we can handle due to the higher tolerance to residual dispersion. We have indeed reconciled simulations and experiments.

    — Peter Heywood, Founding Editor, Light Reading

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