Design, Implementation and Analysis of Real-Time Optical OFDM Transceivers

This thesis extensively explores, for the first time, the technical feasibility and performance of real-time end-to-end optical orthogonal frequency division multiplexing (OOFDM)transmission systems by implementing field programmable gate array (FPGA)-based OOFDM transceivers incorporating entirely self-developed digital signal processing (DSP)algorithms. Commercially available 4GS/s, 8 quantization-bit digital-to-analogue (DAC) and analogue-to-digital converters (ADC) are utilised in the transceivers and low-cost intensity modulation and direct detection (IMDD) transmission systems are also employed for all transmission systems as the research focuses on cost-sensitive access and inbuilding networks. A series of world–first and world-only, real-time, end-to-end OOFDM transmission systems were achieved. The initial DQPSK-based transceiver designs demonstrated first a 1.5Gb/s and subsequently a 3Gb/s net bit rate over 500m multi-mode fibres (MMFs). Thorough enhancement of the transceiver‟s DSP design, 16-quadrature amplitude modulation (16-QAM) with additional DSP features achieved a 6Gb/s net bit rate over 300m MMF, followed by an 11.25Gb/s line rate over 500m MMFs and 25km standard single-mode fibres (SSMFs) /MetroCore™ SMFs due to the utilisation of 64-QAM with more advanced DSP functions. The use of different intensity modulators, as alternatives to the initial DFB-based directly modulated laser (DML), was explored. A colourless OOFDM transceiver was demonstrated at 7.5Gb/s line rate over 25km SSMF using a 1GHz reflective semiconductor optical amplifier (RSOA) as an intensity modulator. To further reduce the transceiver cost, a low-cost VCSEL-based DML was successfully employed at 11.25Gb/s over 25km SSMF. To achieve a fully autonomous OOFDM receiver a synchronous clocking technique was proposed and experimentally demonstrated at 11.25Gb/s over 25km SSMF without degradation in system performance. Over the same IMDD systems, a versatile, highly accurate, performance penalty-free solution for automatic symbol synchronisation was also proposed and experimentally demonstrated using DC offset signalling. This research is a significant milestone in proving the technical feasibility of OOFDM for practical applications in future access and in-building networks