Signal Up-conversion for Radio-over-Fiber Transport System Using Twice Optical Carrier Suppression Technique

• Main Authors: Yu-Peng Chang, 張鈺蓬
• Other Authors: Wen-Jeng Ho
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/y34564

碩士 === 國立臺北科技大學 === 光電工程系研究所 === 101 === In this thesis, signal up-conversion for Radio-over-Fiber (RoF) transport system using twice optical carrier suppression (OCS) is proposed. The proposed scheme can produce four times frequency of the RF signals for downstream optical signal by using phase characteristics of the intensity modulated spread spectrum and with using simple electrical components processing. As a result, the optical filter can be completely removed from the use of the transmission system. First, we employ cascade two single drive intensity modulators to generate frequency quadrupling optical microwave. The two modulators were biased at the minimum transmission point to form the optical carrier suppression (OCS). We measured the spectrum at different points of transmission system by optical spectrum analyzer (OSA) and electrical spectrum analyzer (ESA), respectively. Here, the most optimum optical carrier suppression ratio of 40.4 dB was obtained when using an electrical phase shifter to adjust the time delay. Second, two modulated methods, direct modulation and external modulation, to up-convert the baseband signals are demonstrated. The up-converted signals were formed through the frequency quadrupling technique mechanism. 622 Mbps and 1.25 Gbps Pseudo Random Bit Sequence (PRBS) downlink signals are transmitted and characterized through 10 km and 20 km of single-mode fiber (SMF), respectively, which the optimum optical carrier suppression ratio of these modulation methods are compared. After 10 km and 20 km of signals transmission, bit error rate (BER) of 10-9 can be achieved and the clear eye diagrams are obtained. Nevertheless, the power penalties are still maintained at less than 1 dB.