IS THE 3-dB BANDWIDTH OF OPTICAL FIBERS REPRESENTATIVE OF THEIR TRANSMISSION CAPACITY?

The transmission bandwidth of optical fibers is usually described by their 3-dB bandwidth. This is however problematic if the fiber is operated close to the wavelength lambda //0 where its dispersion becomes zero and its bandwidth maximum. It is shown that in this case (or more precisely: if lambda //0 is within the spectrum of the optical source) the useful bandwidth is well below the 3-dB bandwidth, and that the so-called 1/5 sigma -bandwidth, which is related to the rms width sigma of the fiber's impulse response, is both a more realistic and a more convenient figure for characterizing fiber performance at any wavelength.