Research On High-Performance Radio-over-Fiber Communication System Based On Photonic Signal Processing Technology

High-performance radio-over-fiber communication system,is a communication system that employs optical fiber for microwave/millimeter-wave signal transmission,and achieves significant improvement in performance indicators(such as gain,carrier-to-interference ratio,spurious-free dynamic range and so on)by employing signal processing technology.The high-performance radio-over-fiber communication system effectively solves the problems of deep coverage,high-frequency networking,flexible deployment of base stations and explosive growth of traffic in LTE network.Furthermore,it plays a key role in the fourth-generation and next-generation mobile communications.At present,based on the approaches implemented in the physical layer,high-performance radio-over-fiber communication systems can be divided into the radio-over-fiber communication system based on digital signal processing technology and the radio-over-fiber communication system based on photonic signal processing technology.Compared with the system based on digital signal processing technology,the system based on photonic signal processing technology,where the bandwidth and syetem performance does not limited by the electronic bottleneck effect,it does not require upconversion/downconversion and analog-to-digital conversion.Moreover,it can processes microwave/millimeter-wave signals in optical domain directly,which has superior advantages such as low noise,high gain,ultra wideband,and high speed.However,photonic signal processing technnology(such as Class-AB technology,optical sideband processing technology and hybird photonic signal processing technology),which were reported and frequently used in radio-over-fiber communication systems,have their disadvantages and problems.In this dissertation,to solve the above problem,we propose some improved proposals.Moreover,they are applied to achieve the proposed systems with better performance.The details are depicted as below.1.Class-AB technology is a long-estalished photonic signal processing technology.It introduces a secondary link in the primary link,by manipulating the bias,the system transfer functions of the primary and secondary links can be controlled simultaneously,and the system indicators can be improved.However,Class-AB technology has the disadvantages of a complex system structure and being susceptible to bias drift.Moreover,Class-AB technology was only reported and used in intensity-modulated/polarized-modulated radio-over-fiber communication systems,and the phase-modulated Class-AB technology has not been reported.To solve above problems,we propose a phase-modulated Class-AB technology in this dissertation.In principle,an optical attenuator and an electric attenuator are added to the main and auxiliary links of the proposed system respectively.Studies have shown that when the attenuation powers of the optical attenuator and the electric attenuator has a specific relationship,it can replace the bias control function in intensity-modulated systems and thus the phase-modulated Class-AB technology which does not affected by bias drift is achieved.We apply the proposed technology to the radio-over-fiber communication system.It is theoretically and experimentally demonstrated that the proposed system can effectively suppress the third-order intermodulation distortion,and improve the linearity as well as the spurious-free dynamic range(SFDR>120 dB · Hz4/5).2.Optical sideband phase shift technology based on optical processor is a new research hotspot in the field of photonic signal processing.It only use the phase resources of the optical processor,and is capable of reducing the performance requirements of the optical processor while preserving the flexible controllability of the optical sideband processing technology.However,the reported optical sideband processing technology can only improve one system indicator in the radio-over-fiber communication system.Moreover,the reported high linear system based on optical sideband phase shift technology is unsuitable to be used for medium-haul and long-haul transmission due to dispersion.To solve above problems,we propose a new optical sideband phase shift technology.The technology can precisely control the phase of the optical sideband without increasing the performance requirements of the optical processor and the complexity of the system,thereby realizing the improvement of various system performances.We apply the proposed technology to the radio-over-fiber communication system.It is theoretically and experimentally demonstrated that in the proposed system with fiber transmission,third-order intermodulation distortion can be suppressed(SFDR?115 dB · Hz4/5)and dispersion is completely compensated.3.The optical sideband processing technology based on Bragg grating has the advantages of small insertion loss,easy integration and high commercial value.It can control the optical sideband power ratio of the signal by using a Bragg grating to filter specific sidebands of the optical signal.However,at present,the reported optical sideband processing technology based on Bragg grating can only improve one system indicator.Furthermore,if the filtered sideband contains the first-order sideband,using this technology will reduce the system gain.To solve above problems,we propose a phase-modulated full spectrum optical sideband processing technology.In principle,we use two tunable optical Bragg gratings and a circulator in a phase-modulated radio-over-fiber communication system to achieve full spectrum sideband power manipulation,optical single-sideband modulation,and reflection spectrum reuse.We apply the proposed technology to the traditional radio-over-fiber communication system.It is theoretically and experimentally demonstrated that the proposed system can simultaneously eliminate the third-order intermodulation distortion(SFDR>120 dB· Hz4/5),suppress the dispersion-induced power fading,solve the problem of bias drift,and significantly increase the gain(?15.5 dB).4.At present,the reported broadband high-performance radio-over-fiber communication systems are based on hybird photonic signal processing technology.And the hybird photonic signal processing technology is the technology that uses two or more photonic signal processing technologies simultaneously.However,the reported hybird photonic signal processing technologies have only been used in intensity-modulated/polarized-modulated radio-over-fiber communication systems,and the phase-modulated hybird photonic signal processing technology have not been reported.Furthermore,the reported hybrid photonic signal processing technologies cannot simultaneously solve the nonlinear distortion and dispersion problems in broadband systems.To solve above problems,we propose a novel phase-modulated hybird photonic signal processing technology.In principle,we use polarization-dependent modulation and optical sideband processing technology in the phase-modulated radio-over-fiber communication system to achieve the elimination of all the intermodulation and harmonic distortions(IMD2,IMD3,and SHD),and solve the problem of dispersion-induced power fading in broad bandwidth(>20 GHz).