At last week's SuperComm, Yafo Networks showed what the company claims to be the first PMD compensation solution for a 40 Gigabit per second (Gbps) return-to-zero (RZ) signal. The demonstration came just three months after the company successfully demonstrated a solution for a 40 Gbps NRZ signal.
PMD is the tendency for the optical signal to become difficult to receive accurately when the two planes of light travel at different speeds. PMD occurs when the optical fiber is not perfectly circular and is a significant problem at data speeds of 10 Gbps and above. PMD is an unpredictable effect that varies with time, temperature, and wavelength, making it one of the most difficult problems to detect and correct.
Return-to-zero, or RZ signal format, refers to an optical signal where each bit is shaped in short, sharp pulses, and offers greater resistance to dispersion and other problems caused by imperfect fiber than conventional NRZ, or non-return-to-zero, pulses. RZ signals will still require PMD compensation in 40 Gbps networks, because pulses will still spread with only tiny imperfections in fiber, but tolerances will be greater than in NRZ format. Optical systems makers are now actively developing both RZ and NRZ format systems for 40 Gbps networks.
The first 40 Gbps networks are likely to be NRZ format, due to the limited availability of 40 Gigabit electronics and components, but RZ's robustness with respect to PMD may well make it a better solution, particularly for ultra-long-haul networks.
Yafo's 40 Gbps solutions will be available next year. The Yafo10, a commercially-available PMD compensation solution for 10 Gbps networks, will be available this year.
About Yafo Networks:
Yafo Networks provides adaptive optical subsystems for the Internet. For more information, visit www.yafonet.com.