Advanced Modulation and Multiplexing Techniques for Direct Detection Optical Transmission Systems

• Main Authors: Wei-Ren Peng, 彭煒仁
• Other Authors: Sien Chi
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/67750625112703119875

博士 === 國立交通大學 === 光電工程系所 === 96 === In this dissertation, we review and propose several new approaches for orthogonal frequency division multiplexing (OFDM), advanced modulation formats, and code division multiplexing (OCDM) techniques in optical transmission systems. For OFDM, we propose an RF-tone assisted OFDM and virtual single-sideband OFDM (VSSB-OFDM) systems for direct detected optical transmission. With an RF tone inserted at the edge of the signal band, the sensitivity and CD tolerance are both improved compared to the previous power modulated SSB-OFDM. Besides, our approach also relaxes the bandwidth requirement for digital to analog converter (DAC) which would be very critical in a high speed transmission with a data rate of ≥ 10 Gbps. In addition, we firstly propose a 2x2 matrix equalization technique to jointly compensate the distortions resulted from both the transmission and the imbalances of the optical modulator. Moreover, we successfully transmit a 4-QAM, 10-Gbps signal through 1600 km uncompensated standard single mode fiber (SSMF) with only ~ 3 dB penalty, which is smaller than any other proposed direct-detected transmission systems. For advanced modulation formats, we numerically evaluate and experimentally demonstrate the generation of complex modulation formats by using one dual-drive Mach-Zehnder modulator (DD-MZM). We also analyze the performance bound, i.e. quantum limit, of 4ASK format. We further propose a phase modulated 4ASK (PM4ASK) format which shows a better CD, PMD and filtering tolerances compared to conventional 4ASK format. For CDMA, we propose a simple and cost-effective fast frequency hopping CDMA (FFH-CDMA) light source which uses a self-injected Fabry Perot laser and one string of fiber Bragg grating array (FBGA). By tuning the stress of each individual grating, we can encode the transmitted data by the destination codeword. Aimed to eliminate the inherent multiple access interference (MAI) in optical FFH-CDMA, we propose a frequency-interleaved multi-group approach which fully uses the frequency gap between the gratings to reduce the spectrum overlapping among different users, and design the new codeword searched by computers which is suitable for this proposed technique. Finally we versify this technique by some simulation results.