Launching condition dependence of bandwidth in graded-index multimode fibers fabricated by MCVD or VAD method

Baseband frequency response of a single or concatenated MCVD and VAD fibers measured by two representative launching conditions-equilibrium mode distribution (EMD) and overfill mode distribution (OMD)-is studied. From computations based on the WKB approximation method and from experiments, it is found that the OMD exciter on the average results in a greater 6-dB bandwidth than the EMD exciter for a single MCVD fiber, but is does a smaller bandwidth for a single VAD fiber. On the other hand, in concatenated fibers, the EMD exciter results in a greater bandwidth of about 10 percent in comparison with the OMD exciter. The concatenation factors for MCVD fiber and VAD fiber are different for EMD excitation, while they are nearly identical with each other for OMD excitation.