Experimental Demonstration of Direct-Detection Optical Fast-OFDM using Memory Polynomials

Fast-OFDM has been used extensively in optical and wireless systems, with its advantages of simple implementation and spectral efficiency making it a good candidate for optical access networks. This work proposes a new time domain equalization method for Fast-OFDM optical access networks, which deals with ameliorating the effects of linear and nonlinear behavior of system components and optical channel. The proposed equalization technique simplifies system implementation and shows excellent results when used in conjunction with training signals designed for the purpose of minimization of least square error and hence equalization of the channel. The work reports details of the design approach and then implementation of the algorithm in an experimental test bed with an direct-detection optical link and a 10 km single mode fibre. Experimental results, obtained for transmission of 7.5 Gbit/s 4PAM signals, demonstrate error rate/transmission power advantages for the new equalization technique, relative to traditional system implementation. Results are shown for various system implementation and parameters and are based on real time signal transmission and off line receiver processing. The reported results are the first demonstration of such a system.