Startup pushes long-reach alternative to external modulation

March 12, 2004 Wilmington, MA -- Azna LLC, an emerging company based in Wilmington, MA, believes it has found a cost-effective alternative to the use of external modulation for long-haul links and metro overlays. Chairman, founder, and CEO Parviz Tayebati says the company's Chirp Managed Directly Modulated (CMDM) laser technology can create a TOSA-sized transmitter capable of 200 km without dispersion compensation.

March 12, 2004 Wilmington, MA -- Azna LLC, an emerging company based in Wilmington, MA, believes it has found a cost-effective alternative to the use of external modulation for long-haul links and metro overlays. Chairman, founder, and CEO Parviz Tayebati says the company's Chirp Managed Directly Modulated (CMDM) laser technology can create a TOSA-sized transmitter capable of 200 km without dispersion compensation.

Tayebati -- who founded tunable-laser startup CoreTek, then sold it to Nortel in 2000 � says that his company has developed a device it calls an Optical Spectral Reshaper. The device manipulates the chirp of a DFB laser to create a directly modulated transmitter that has demonstrated transmission reaches of 200 km. The reshaper is small enough to fit with the DFB into a TOSA package, thus saving significant footprint over externally modulated devices, particularly those using lithium niobate modulators.

The CMDM laser offers better performance and lower power consumption than directly modulated approaches, Tayebati asserts. For example, Azna claims a CMDM transmitter will offer 7 to 8 dBm of output power, while EMLs "barely give you 0 to 2 dBm of power" Tayebati says. Also, while lithium niobate modulators require a 5.5-V power supply, the OSR pulls only 150 mW -- and then only when it is being used as a wavelength locker. For fixed-wavelength applications, Tayebati says that power requirements should be similar to standard DFB and direct modulator combinations.

The CMDM lasers will work with standard laser drivers and do not require special receive electronics, Tayebati asserts. While temperature stabilization is a requirement when the wavelength-locker function is evoked, it is not necessary in "standard" use.

Wavelength locking is important in tunable applications, and Tayebati says that the reshaper's spectral performance is periodic in line with the 50-GHz ITU grid. Thus, the reshaper can be used in tunable applications. "We are right now specifying the product as an eight-channel system," Tayebati says. "But we are also looking at some widely tunable systems, and we think it can be done."

Tayebati says the device should find use in a pair of applications initially. The 200-km reach makes it an obvious candidate for long-haul applications. However, Tayebati believes the device will also prove attractive in applications where carriers want to upgrade 120- to 220-km networks from 2.5 to 10 Gbits/sec, but don't want to add dispersion compensation. Along these lines, Azna has spoken to several XFP transceiver vendors; Tayebati says that samples of XFP modules using the CMDM technology could appear within the next 9 months.

In addition to the XFP community, system houses also have expressed interest in the device, Tayebati says. Azna has delivered samples to "selected" Tier-1 vendors, he says. Additional samples should be available in the near future.

While Azna touts its technology's ability to save costs, Tayebati isn't ready to talk numbers yet. "The cost is something we're still trying to work out with our perspective customers," he offers. The price may end up somewhere between a lithium niobate approach and EMLs, he implied.

-- S. Hardy

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