Cold weather has proven troublesome for fiber optic cable performance, often changing the internal geometry of the fiber. Scientists from Bellcore in San Diego have monitored the problem during the past several years, subjecting fiber optic cable to simulated seasonal cycles. Their findings reveal that minor problems have cropped up with equipment that carried light at 1310 nm. However, temperature-induced cable loss is much more severe with dense wavelength division multiplexing (WDM) transmission at 1550 nm. Proposed dense WDM systems set for 1625 nm would be even more susceptible to cold weather problems, they said. As a solution, the Bellcore scientists suggest individual assessments for different products. They also are writing a list of generic requirements for dense WDM equipment and fiber optic cable.