System Experiments with Multimode Waveguides and Fibers for Applications in Computer Interconnects

Future optical computer interconnects are likely to employ short lengths of multimode waveguides somewhere in the optical path. In computer interconnects where the bit-error-ratio must be smaller than 10−15 and where mode selective losses may be large it is of extreme importance to minimize any traces of modal noise. We investigate the effect on the modal noise induced bit-error-rate floor when passing light through short lengths (0.5 → 70 mm) of large core epoxy ridge wave-guides and multimode fibers. It is demonstrated that the bit-error-rate floor declines rapidly with the waveguide transmission distance, whereas for the multimode fiber the floor is independent on the length. The behavior is caused by a rapid mode fill taking place in the epoxy guide, and lack hereof in the fiber. This makes the epoxy waveguide an attractive candidate for short distance on-board and backplane interconnects and as a guiding interface between the multimode fiber and the laser and photodetector in main frame links. © 1991 IEEE