The High-speed Optical Transmission Research Based On Multimode Fiber

Recently, with the greatly increasing of bandwidth needs, Time-Frequency-Spatial and Polarization untied multi-dimensional-multi-level modulation technology becomes the trending of future optical communications.As a result, multimode fiber (MMF) which is rich in spatial mode resources with great potential capacities is attracting more and more interests. And many famous research institutes have taken many relative studies; however, the inherent serious inter-modal dispersion in MMF greatly limits its employment in long haul and high speed optical communications. So the key of high speed optical transmission over MMF is to efficiently overcome inter-modal dispersion, utilize its spatial resources and improve its bandwidth-length (BL) product as much as possible.In this paper we studied kinds of methods to improve the capacity of MMF. With the model stimulating and coupling theories in weak guide fibers, we analyzed the function and performance of standard MMF, few mode fiber, hollow fibers, special mode converters and multimode couplers and introduced some multimode devices in our experiments. Then we studied the Launching Optical Field Shaping combined with Feedback Equalization, which is proven to increase the capacity of MMF efficiently and make10Gbit/s signal transmit over1km MMF. We built a novel analytical model for an intensity-modulated-directly-detected (IMDD) MMF multi-input-multi-output (MIMO) system with offset transceivers and studied its performances including BER, training serials and so on. Moreover, based on the prototype of a commercial MMF product, we built a complete coherent optical MMF MIMO model with ring transceivers and it’s found out that2x2MIMO can at least double the BL product of MMF compared with single-input-single-output (SISO) systems with the same complexity. With this model we studied the DSP methods, advanced modulation and frequency domain pre-distortion for coherent MIMO systems and proposed a novel MIMO passive optical networks (PON) scheme. Finally we built a confirmatory experimental system of baseband optical orthogonal frequency division multiplexing (OFDM) over MMF. It’s proved that even without pilots and electronic equalization,5Gbit/s baseband OFDM signal can transmit over1km in OM2MMF.