Wavelength dispersion of optical fibers directly measured by ’’difference method’’ in the 0.8–1.6 μm range

A novel technique to measure the wavelength dispersion of optical fibers in the 0.8–1.6 μm range, where germanium avalanche photodiodes possess adequate quantum efficiency, is described. Dispersion is defined as dτ/dλ, which can safely be changed to the difference formula Δτ/Δλ, when Δλ is small, where τ is the transit time of the wave and λ 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 Δτ. The wavelength dispersion is obtained directly from the values of both Δτ and Δλ. 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 μm.