Sub-carrier Multiplexed Optical Millimeter Wave Generation in Hybrid Communications Systems
Two frameworks are proposed for optimization of optical millimeter-wave (mm-wave) generation in communications systems based on tandem single side-band (TSSB) and single side-band (SSB) modulations. These frameworks are obtained based on mathematical analysis of optical mm-wave generating systems using cascaded Mach-Zehnder modulators (MZMs). The advantages of radio over fiber (RoF) systems are discussed and different optical modulators are analyzed. Based on the simulation results, the most appropriate modulator is considered for sub-carrier multiplexed RoF systems. In order to up-convert a signal's frequency to 60 GHz band, various methods can be utilized. However, optical frequency up-conversion is preferred due to system cost reduction and band-width efficiency. The optical transmission of high frequency signals over long distances of fiber faces significant chromatic dispersion effects. There are various techniques to overcome this fiber impairment. In this study, some of these methods are introduced and mathematically analyzed. Based on the mathematical analysis conducted in this research two specification tables are suggested for radio frequencies (RFs) applied to the MZMs. These tables are suggested for the case of two sub-carrier multiplexed mm-wave generation using optical tandem single side-band (OTSSB) or optical single side-band (OSSB) modulations. These analyses are verified through simulation. The mm-wave generation system is designed and tested for up to 1 Gb/s quadrature amplitude modulation (QAM) two sub-carrier multiplexed data transmission over 100 km of fiber. The fiber dispersion and attenuation are 17 ps/(nm.km) and 0.2 dB/km, respectively. If the RF channels' frequencies are chosen based on the suggested specification tables for OTSSB and OSSB modulations, then transmission can be done over up to 330 km of fiber when the fiber attenuation is mitigated. Furthermore, the mm-wave generation system is designed and tested for up to 7 Gb/s QAM data transmission over up to 250 km of fiber for one sub-carrier transmission. Moreover, the mm-wave generation system is designed and tested for up to 0.8 Gb/s QAM four sub-carrier multiplexed data transmission over 100 km of fiber over a dense wavelength division multiplexing (DWDM) network with 4 channels (4-DWDM). If the RF channels' frequencies are chosen based the suggested specification tables for OTSSB and OSSB modulations then the transmission can be done over up to 330 km of fiber if the fiber attenuation is compensated.
System performances using OSSB, OTSSB and ODSB modulation schemes are compared for two sub-carrier multiplexed data transmission. Also, comparison is done between OSSB and OTSSB modulation performances for four sub-carrier multiplexed data transmission over 4-DWDM network.