High-Performance ROF Links Based On Balanced Detector

Radio Over Fiber(ROF) combines fiber communication and radio communication, which has the characteristics of low loss, high bandwidth and easy to access. In recent years, with the increasing demand of communication network capacity, ROF will be an important tendency in the future communication network. The nonlinearity of photoelectric devices in ROF system severely affect the system's performance, which has attracted attention of many researchers all over the world, who have come up with kinds of linear methods in order to restrain the nonlinearity of the system.This paper mainly studies the linear system based on balanced detector. The balanced detector is used to receive the signal which has been specially processed at the transmitter and receiving end before. In this case, noise and distortion can be reduced without the loss of the useful signal. Firstly, the components of ROF system are introduced, such as LD, MZM, PD, and polarizing devices involved in the present paper, etc. Then, DSB intensity modulation link is introduced as a model of ROF system, with its parameters such as NF, Gain and SFDR analyzed. At last, two linear optimization schemes based on balanced detector are proposed.Sagnac loop and polarization technique are used in the linear optimization scheme based on BD and Sagnac loop. On this condition, two signals that meet requirements of BD to suppress noise and distortion are generated on the use of only one phase modulator. Upon introducing the structure and mathematical principles in detail, VPItransmissionmaker 8.5, one of optical simulation softwares, is used to simulate and verify the scheme. Results indicate that SFDR is more than 2/3116.8dB×Hz, improved by 6 dB in comparison to the link based on IM-DD. In addition, noise and even harmonics are effectively suppressed, and noise figure is also reduced by 9dB.The optimized linear ROF link based on BD and DP-DPMZM takes the advantage of polarization technique to make two child DPMZMs work separately on different polarization states. Next, the DC offset of the modulator is adjusted to obtain two signals which meet requirements of BD to suppress noise and distortion. On the condition of suppressing IMD3 with single DPMZM, balance detection technology is used to reduce noise and IMD2, which leads to the obvious improvement of SFDR. Simulation result shows that SFDR is improved by 9dB in comparison to the scheme based on single DPMZM, reaching 2/3132.1dB×Hz. In the meantime, noise is reduced and even harmonics are almost completely restrained. What's more, noise figure is decreased about 11 dB.