Wavelength dispersion of optical fibers directly measured by ''difference method'' in the 0.8-1.6 microm range

A novel technique to measure the wavelength dispersion of optical fibers in the 0.8-1.6 microm range, where germanium avalanche photodiodes possess adequate quantum efficiency, is described. Dispersion is defined as dtau/dlambda, which can safely be changed to the difference formula Deltatau/Deltalambda, when Deltalambda is small, where tau is the transit time of the wave and lambda is the light wavelength. A monochromatic light, whose amplitude is modulated by a sinusoidal baseband signal, is launched into the optical fiber. The phase of the sinusoidal baseband signal changes with the monochromatic light wavelength variation due to the dispersion of the fiber. The phase variation gives an accurate value of Deltatau. The wavelength dispersion is obtained directly from the values of both Deltatau and Deltalambda. Using this technique, the wavelength dispersion of a single mode optical fiber, for example, is measured in the single mode wavelength range from 0.92 to about 1.6 microm.