Phsae Stabilization Technology Of Microwave Signal Transmission Over Optical Fiber

It is highly required to transmit the microwave signal or reference signal from local node to remote node or receiving end with a high precision and a minimal phase jitter in many applications,such as radio astronomy,radar systems,satellite navigation and deep space exploration.It is well known that optical fiber has the advantages of wide bandwidth,low loss,light weight and immunity to electromagnetic interference etc.Therefore,microwave signal transmission over the optical fiber has become a hot topic in recent years.Owing to the influence of the external environment such as temperature and stress,the phase jitter of microwave signal is introduced when the microwave signal is transmitted through the optical fiber,such that the quality of received microwave signal would be distorted.Therefore,it is necessary to compensate for the phase jitter caused by the transmission of the microwave signal over the optical fiber in real time,and to provide stabilized phase of the received microwave signal at the remote nodes.In this dissertation,the research background and advances concerning microwave signal transmission over optical fiber are introduced firstly.The main factors contributing to the phase jitter in optical fiber are analyzed,including the stability of laser,temperature and mechanical stress.Further,the transmission theory of microwave signal with a stable phase over the optical fiber is studied,and the characterization of the stability of microwave signal is given in the time and frequency domain.In traditional approaches,the phase-locked loop has been used to pre-compensate for the phase jitter,but the frequency range of the phase identification module is limited(such as the highest frequency of AD8302 is-2.7 GHz).To overcome this limitation,a compensation method in the electrical filed has been proposed for microwave signal transmission system over optical fiber with stable phase with multiple bands(S/C-band).The frequencies of the local and returned microwave signal are divided,and they are sent to a phase discriminator with the frequency-divided original microwave signal.The feedback voltage of the phase discriminator is used to control a phase shifter and the generated phase jitter from the optical transmission is compensated in the real time,thus the transmission of multi-band microwave signal with a stable phase is realized along with the simplification of traditional algorithm.In the experiment,two microwave signals at 2.4-GHz(S-band)and 4.2-GHz(C-band)have been tested over a 50-km fiber link at time duration of 2000 s.The peak-to-peak phase jitter of the root mean square(RMS)is 1.7ps and 2ps,and the phase noise is measured as-102dBc/Hz @1kHz,-98 dBc/Hz @ 1kHz,respectively.Furthermore,in order to realize faster response,wider frequency compensation range and less system complexities,stable phase transfer approach for microwave signals based on phase co-cancellation is proposed.By mixing the triple-frequency one-path microwave signal with the triple-path microwave signal,the phase jitter caused by fiber link is reduced and stable phase transfer from local node to remote node is realized.In the experiment,stable phase transfer for 2.4-GHz microwave signal over 50-km single mode fiber is tested.The experimental results show that the RMS phase jitter is 4ps over a measurement period of 1800s,while the phase noise is-112dBc/Hz @ 1kHz.