A chromatic dispersion compensation system for an optical transmission system incorporates circuitry which determines the length of an optical fiber extending between an output amplifier and an input amplifier. A purge ring having specific major and minor exhaust to inlet area ratios may be partially made of flame polished quartz to improve flow dynamics. The heat sink is oriented between the axial fan and the hot electronic device such that the hot electronic device, the heat sink, and the axial fan are axially oriented, wherein cool air is forced onto the heat sink by one impeller in the axial fan, and wherein heated air from the heat sink is removed by an other impeller in the axial fan.