Study On The Theory And Technology Of Single-Sideband Modulation Based On ROF

In the radio-over-fiber (ROF) system, the fiber chromatic dispersion will cause severe RF power penalty in the traditional double-sideband (DSB) modulation scheme. In order to overcome the power penalty, some optical single-sideband (SSB) modulation techniques have been introduced. However, those schemes have some drawbacks such as costliness or high complexity.Considering that Chirped Fiber Bragg Grating (CFBG) has many advantages such as all-fiber geometry, fiber compatibility, low insertion loss, potential low cost and it can provide dispersion pre-compensation for optical signal within the band-pass, CFBG as a band-pass filter to implement SSB modulation has been proposed to solve those problems.The principle of the generation of double-sideband signal by sub-carrier modulation based on Mach-Zehnder modulator is introduced. Then quasi-analytical expression of optic double sideband signal is given. The mechanism of power penalty of optic double-sideband signal in the receiver due to dispersion during its transmission in the fiber is also analyzed.Then the fundamental theory of FBG is introduced in detail, and the reflection spectrum as well as the delay characteristics of some kinds of FBGs are analyzed. The principle of the SSB filter and the time-domain and frequency-domain response characteristics of the FBG are theoretically discussed. Taking Gaussian optic signal as an example, the propagation of optical double-sideband signal in 60GHz ROF is simulated. The results demonstrate that sideband suppression ratio can obtain 22dB and pre-compensation distance can be prolonged to 88Km.By means of the optical communication software, the experiment of filtering system operating on 60GHz is designed. The simulation results show that the SSB modulation with the sideband suppression ratio over 40dB can be easily realized, which can significantly reduce the power penalty caused by the chromatic dispersion. Moreover, compared with conventional FBG filter, CFBG filter can largely reduce the bit error rate in the communication system.