Fiber bandwidth-spectrum studies.

This paper presents some thoughts on how to improve the bandwidth spectrum of multimode optical fibers. We consider the signal bandwidth of germanium- and phosphorus-doped fibers with ideal power law refractive index profiles and investigate how the bandwidth as a function of wavelength (bandwidth spectrum) is changed as the ideal index profile is distorted. We also study what happens if two fibers with different undistorted power law profiles are used in cascade. Examples are also given of bandwidth calculations of fibers made with a mixture of germanium and phosphorus dopants. It is shown that such fibers are capable of realizing a bandwidth which exceeds 5 GHz.km over a wavelength range from 0.8 microm to 1.45 microm. Finally, bandwidth vs wavelength curves are computed for several real fibers whose refractive index profiles were measured.