September 2, 2004 Fremont, CA, and Berlin, Germany -- Avanex Corp. and SHF Communication Technologies AG today announced the joint development of a 40-Gbit/sec duobinary modulator-driver assembly, which they claim is a significant milestone toward field-applicable 40-Gbit/sec transmission.
The new 40-Gbit/sec duobinary transmitter sub-assembly combines an optimized SHF driver amplifier (SHF 825F) and the Avanex PowerBit 40-Gbit/sec Intensity Modulator to enable at least five times longer transmission distances compared to the traditional intensity-modulated NRZ approach--and without dispersion compensation. According to the companies, it reduces the bandwidth requirements of electronics and modulators because of its higher spectral efficiency.
In addition to improved performance, the subassembly approach will simplify the manufacturing of line cards to reduce overall cost of ownership because manufacturers will not need to go through the costly process of matching the driver and modulator to obtain the required performance. Because of the less stringent technological demands on the electronics and modulator, the transmitter subassembly also can be manufactured with larger specification margins.
"This new duobinary modulator-driver assembly is a major breakthrough to support 40 Gbit/sec transmission rates," asserts Dr. Giovanni Barbarossa, chief technology officer and vice president, product development, at Avanex. "It permits the 40-Gbit/sec optical signal to pass beyond 10 km, exponentially multiplying the transmission reach without dispersion compensation. It also enables 400-Gbit/sec transmission in the 50-GHz ITU grid by using the existing 10-Gbit/sec optical infrastructure. This highly attractive modulation format outperforms the common 40- Gbit/sec NRZ transmission and illustrates Avanex's leadership in developing integrated solutions for next-generation networks," he adds.
At 10 Gbits/sec, the well-known duobinary modulation format enables uncompensated transmission distances of 200 km or more (over SMF fiber), corresponding to about 12 km at 40 Gbits/sec. By combining the specifically designed components, Avanex and SHF have succeeded in creating a building block that overcomes the electrical and optical challenges of 40-Gbit/sec duobinary signal generation. This assembly allows for more than 12-km uncompensated transmission.
The Avanex-SHF solution also addresses the tendency of duobinary transmission to be particularly jitter sensitive. By integrating a low pass Bessel filter into the driver amplifier, Avanex and SHF say they have succeed in reducing the number of electrical transitions that could contribute to jitter generation, resulting in significantly improved optical signal quality.
The low modulator drive voltage (Vpi) of less than 4 V and the specifically designed driver amplifier enable the "two-Vpi" modulator operation required to convert the duobinary electrical signal into a binary optical signal. The overall electro-optic bandwidth of approximately 13 GHz is sufficient to realize 42.8-Gbits/sec transmission. The spectral width of the optical signal is only about 13 GHz at -3 dB, and 30 GHz at -10 dB respectively, and the 50-GHz bandwidth is below -40 dB. The unique characteristics of this assembly lead to a Q-factor penalty of only 1 dB after 150-ps/nm total dispersion (at 42.8 Gbits/sec), with 3-dB FEC margin or potentially 300-ps/nm dispersion tolerance.