MRV launches new transponders with wavelength and dispersion tunability

APRIL 9, 2007 By Meghan Fuller -- MRV Communications (search for MRV Communications) today announced the release of a pair of 10-Gbit/sec transponders that enable both wavelength tunability and per-wavelength dispersion compensation over the full C-band. Moreover, says the company, its TM-DXFP20T and TM-DXFP35T transponders support distances of up to 200 km and 350 km respectively over G652-compatible fiber.

"As you move around in frequency or wavelength in a transponder, the dispersion characteristics vary," explains Tim Smith, director of optical transport at MRV. "As you go up in frequency, your dispersion slope goes down, and as you go down in frequency, your dispersion slope goes up. You really have to strike a medium balance when you're doing a multi-color system," he says. "We have the ability to optimize the dispersion characteristics based on the given wavelength frequency that we program the transponder for."

MRV's new transponders use low-chirp lasers in lieu of external dispersion compensation modules (DCMs). "We can't change the fiber properties," says Smith, "so the cleaner the signal that you can launch into the fiber, the lesser the impact that dispersion has on it. By controlling the chirp characteristics of the laser, we can launch a more coherent beam out of that laser to overcome dispersion obstacles."

Smith says the tunable transponders were developed in response to both customer demand as well as the ongoing price sensitivity of the market, particularly when it comes to multi-colored systems. "The biggest problem we had in the past was the point of entry pricing on a DWDM network," he admits. "If a customer was going to build out a DWDM network and, say, only wanted to light four or five colors initially, his outlay cost for the dispersion compensators and the host transponder correction technologies was the same. He would pay [the same price] whether he was lighting five colors or 32 colors," says Smith.

With built-in tunable dispersion compensation, the TM-DXFP20T and TM-DXFP35T eliminate the need for external DCMs at the point of transmission and throughout the network. Given that a single DCM is typically priced at $20,000 or more, the new transponders enable significant capital expenditure savings, says Smith. In a long-haul network application, for example, the transponders reduce the need for downstream dispersion compensation from every 90 km to every 350 km, thereby reducing both the amount and overall cost of the equipment provided.

Moreover, says Smith, the more external or standalone DCMs you put in a network, the higher the attenuation. As a result, additional amplifiers are required to offset the increased attenuation caused by the dispersion compensators.

Both Lambda Driver TM-DXFP 10G transponders support STM64/OC-192 (9.955 Gbits/sec) and 10-Gigabit Ethernet (10-GbE) protocols for use in metro and long haul service provider networks. All Lambda Driver wavelength tunable transponders can be remotely set to any 50-GHz spacing DWDM waves on the ITU-T grid (G.694.1) in C-band, says the company. L-band option is possible per request.

Featuring full 3R support, the transponders offer both remote and local loop-back functionality. According to MRV, full power monitoring, XFP digital diagnostics, and link integrity notification (LIN) all come standard on the hot swappable devices. 

Looking ahead, Smith confirms that MRV is working on a 40-Gbit/sec tunable transponder with built-in dispersion compensation, though the company has not publicly announced a timeline for that project. The problems inherent at 10 Gbits/sec become even more acute at rates over 10 Gbits/sec, he says, and you can't change the fiber; it's in the ground to stay. "Really," he says, "the only way to combat that is to purify the emission so it is not impeded by the dispersion of the fiber itself. The cleaner you can launch the signal from the source side, the better off you are."

4-Gbit/sec Fibre Channel transponder

In a related announcement, the company also introduced a 4-Gbit/sec Fibre Channel DWDM transponder that targets the storage area networking (SAN) needs of the enterprise market. The TM-D4GSFP DWDM transponder can support distances up to 100 km over G652-compatible fiber without power or dispersion compensation. Longer distances are possible using amplifiers and DCMs.  

The TM-D4GSFP is a dual circuit SFP-based transponder, similar to the company's existing TM2-SFP product, which supports various protocols but offers a maximum bandwidth of 2.7 Gbits/sec. According to the company, use of SFPs on both the access and the WDM sides of a network result in the highest flexibility and lowest maintenance cost.

Smith notes that MRV has been working on the 4-Gbit/sec Fibre Channel transponder for "quite a while. We manufactured this card in such a way that it will allow customers to migrate from their existing, legacy 1-Gbit/sec Fibre Channel to 4-Gig over the same infrastructure without having to do a forklift upgrade."

Smith reports that both the 10-Gbit/sec tunable transponders and the 4-Gbit/sec Fibre Channel transponders exemplify MRV's top-level mandate that its customers' existing infrastructure should be able to accommodate new technology without a folklift upgrade. "That is the intended, continued evolution of MRV's products," he says. "Whatever you buy today, we're going to support going forward."

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