The invention pertains to optical fiber transmission systems, and is particularly relevant to transmission of large volumes of data over long distances at high rates. An improved apparatus and method for measuring dispersion in a fiber span is disclosed. In particular, the invention teaches a highly accurate technique for measuring the fiber dispersion at a single wavelength. Transmitter and receiver structure and data processing algorithms are disclosed. An improved apparatus and method for measuring dispersion in a fiber span. In particular, the invention teaches a highly accurate technique for measuring the fiber dispersion at a single wavelength. Transmitter and receiver structure and data processing algorithms are disclosed.