Linearization Techniques of Electroabsorption Modulators for Lightwave Narrowcast Hybrid Fiber Coax Systems

• Main Authors: Yu Shau-Lun, 于紹倫
• Other Authors: Winston I. Way
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/94874048984557463007

碩士 === 國立交通大學 === 電信工程系 === 88 === A predistortion circuit with adjustable amount of third-and fifth-order predistortions is studied both theoretically and experimentally. The circuit is used to cancel the third- and fifth-order intermodulations distortion of a 1.55μm integrated electroabsorption modulator/DFB laser. The CSO obtained is -61 dBc and the CTB is reduced by 22 dB to -65 dBc. This performance is maintained after fiber amplification and propagation through 47 km of standard fiber due to the modulator’s low chirp. Dithering of the DFB laser’s injection current is employed to increase the stimulated Brillouin scattering (SBS) threshold to + 12 dBm. Also, an experiment with a AM-VSB broadcast channel and one QAM-format narrowcast channel is performed to confirm the performance of 1550-nm narrowcast transmission systems using EML (Electroabsorption Modulator integrated Laser ) over 70km of standard fiber, through two cascaded Erbium-Doped Fiber Amplifiers with sufficiently low distortion performance and 3 dB dynamic range of received power. We find that dispersion-induced distortion of the MQW—EA modulator is smaller than that of the direct-modulated laser. Carrier-to-noise ratios (CNR’s) of 35 dB for channel 116 (the worst channel) are measured after 70 km transmission. It is found that the deterioration of the broadcast CNR is mainly caused by the cascaded erbium doped fiber amplifiers (EDFA’s), RIN noise and NLD from EML; the narrowcast CNR deterioration is mainly due to the EDFA intensity noise from high received power of broadcast channel. It shows that the output power of the modulator should be higher to improve CNR.