Measurements and simulation of multipath interference for 1.7-Gb/s lightwave transmission systems using single- and multifrequency lasers

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Abstract
Power penalties due to multipath interference (MPI) have been measured for 1.7-Gb/s lightwave systems that use single-frequency (SF) or multifrequency (MF) lasers. Systems that use SF lasers potentially exhibit worse degradation than those using MF lasers. Bit-error-rate (BER) floors occur only under the worse-case conditions of poor receiver margin and large multiple reflections. The use of optical isolation to reduce laser feedback is ineffective in reducing multipath interference, and in many cases may worsen the penalty. It is shown that for a typical transmission system, these degradations are reduced if optical interconnection reflections are maintained below -20.5 dB. The experimental study is in good agreement with theoretical predictions using an analytic expression of the MPI noise power spectral density and with computer simulations using multimode laser rate equations.