Long dispersion-compensating grating reduces dispersion in fiberoptic networks

Long dispersion-compensating grating reduces dispersion in fiberoptic networks

Scientists at the Harlow, England, research and development facility of Northern Telecom (Nortel; Paignton, England) have developed a 2.4-m dispersion-compensating grating (DCG) for fiber optic networks; Nortel claims this is the longest in the world. The grating offers an alternative to tens of kilometers of dispersion-compensating fiber (DCF), which is a more-expensive specialty fiber. In addition to consisting of a shorter optical fiber, the DCG is also a lower-loss device than the DCF--it has a reflective grating structure written into its core using ultraviolet laser holography.

With the recent increases in data-transmission rates and the realization of optical amplification, the limitation on information throughput is now dispersion rather than loss, according to Nortel. And the DCG provides an economical method of compensating for dispersion in installed single-mode fiber. The significance of increasing the grating length to 2.4 m is that it allows more dense wavelength-division-multiplexed channels to be transmitted on the same fiber.