Corning: Raman amplification key for 40-Gbit transmission
By Stephen Hardy
Like many companies in the fiber-optic component and subsystem field, Corning Inc. (Corning, NY) has turned its attention to anticipating future requirements for 40-Gbit/sec transmission speeds. The company, which has bolstered its bedrock fiber-production business with an increasing investment in component and subsystem technologies, is attacking the issue on several fronts. Its investigations in the amplifier space have led researchers to conclude that the Raman amplification that provides the luxury of extended distance between repeaters for traffic at speeds up to 10 Gbits/sec will be mandatory for more "standard" repeater spacings at 40 Gbits/sec.
According to George Wilde man, Corning's product-line manager for optical amplifiers, the dispersion compensation and nonlinearity issues present in amplification at 10 Gbits/sec are even more pronounced at 40 Gbits/sec. In particular, center-stage loss issues such as signal shaping, polarization mode dispersion (PMD), and gain equalization must be addressed. Such factors place new, more stringent tolerance requirements on am p lifier components. While technology for erbium-doped fiber amplifiers (EDFAs) continues to advance, Wilde man predicts that Raman amplification will prove necessary to overcome the present loss/noise hurdles and make 40-Gbit/sec transmission a reality. He foresees 40-Gbit/sec systems reaching the field by 2002. Toward that end, Corning may have Raman amplifiers for these applications ready for examination as early as the end of this year.
Meanwhile, the company is working on ways to address these compensation dilemmas. Joe Antos, director of fiber development at Corning, says that dispersion compensation modules will have to accommodate slope as well as dispersion (for more on this notion, see the special report "Full-band chromatic-dispersion management" on page 66). He also predicts that tunable compensation will be come mandatory as data rates increase to 40 Gbits/sec and beyond. Dynamic gain equalization also will become a requirement for high-speed, high-channel-count networks.
Corning also is working on fiber that may prove useful in tomorrow's high-speed networks. A slope-compensated fiber solution that contains segments of both positive and negative dispersion characteristics may prove beneficial for such applications, says Antos. The small effective area typical of slope-compensated fiber works particularly well with Raman amplification, he says; such fiber could lower overall Raman pump power requirements.
A product road map for a fiber with both positive and negative dispersion remains unclear at this point; a single fiber solution may prove adequate for some carriers' needs.