Research Of Distribution Of Highly Stablized Microwave Signals Over Optical Fiber Link

Since the turn of the century,the rapid development of distributed measurement technology is a revolution in measurement technology.The key technology of distributed measurement is the distribution of highly stable microwave references over each measurement devices to achieve the synchronization and coherence between each site.Benefitting from the advantages of low loss,wide band width and anti-electromagnetic interference,the optical fiber attracts great interest in disseminating frequency reference over long distance with high stability.And this becomes a research focus in recent decades in the field of frequency transmission technology.However,the transmission delay variations of the fiber link would be introduced owing to the fact that the environmental perturbations like temperature and mechanical stress on the fiber links is changing,which would degrade the phase stability（or frequency instability）of the signals after transmission.This issue becomes the major problem of dissemination of the highly stable frequency reference over optical fiber.To address this problem,the thesis carries out the research work aiming at the stable distribution of radio frequency signals over the optical fiber.The innovative approaches are proposed to solve the key issues about the phase detection and control of the optical microwave signals.The highly stable distribution of the microwave signals over long distance optical fiber for different application requirements are demonstrated.Furthermore,the performance and noise evolution of the transmission system is analyzed theoretically,and the optimization of the multi-frequency distribution system is figured out.The main research work and innovations in the thesis are shown in the following words:1.A highly stabilized millimeter-wave signal distribution over optical fiber based on phase control of the optical frequency comb.In this thesis,a mm-wave distribution scheme over optical fiber is proposed based on phase control of the optical frequency comb（OFC）.By employing a photonic generated mm-wave voltage-controlled oscillator（VCO）which is realized by pre-filtering and re-modulating the optical spectral lines of an optical frequency comb,the phase between the optical spectral lines extracted from the OFC can be adjusted accurately.Thus,the phase error of the transmitted optical mm-wave signal can be compensated precisely.During the process,the two optical spectral lines which carry the mm-wave signal stay in the same optical path,preventing the incoherent phase noise induced by the separate loose optical links from being imported into the transmitted signal.Thus,a highly phase-stabilized mm-wave signal distribution can be achieved over long transmission distance compared to the acousto-optic-frequency-shifter-based（AOFS-based）system which our research group proposed before.By employing the above method,a 100.02 GHz optical mm-wave signal distribution system over a 160-km standard single-mode fiber（SSMF）link is demonstrated.The long-term fractional frequency instability of 4.1×10^-17 at 10000 s averaging time is achieved.Comparing with the AOFS-based system under the same testing environment,the distribution system shows a capability of higher phase stability over the long term.2.A highly stabilized multi-frequency microwaves distribution over optical fiber based on dual-heterodyne phase error transfer mixing of the optical frequency comb.It is necessary to distribute highly-stable and phase-locked multi-frequency microwaves over long distance in the multi-band distributed microwave measurement system,while the traditional transmission methods of single-frequency microwave signal are difficult to support these applications.Facing this urgent requirement,the phase-stabilized multi-frequency microwave distribution over optical fiber is proposed based on dual-heterodyne mixing of the OFCs.The multi-frequency microwave signals are generated with the OFC.By applying the dual OFC structure of a transmitted OFC and a reference OFC,the phase variations of the multi-frequency microwave signals are extracted using the dual-heterodyne phase error transfer mixing scheme.And the phase noise of the optical multi-frequency microwave signals is compensated by adjusting the frequency/phase of the repetition signal of the transmitted OFC.Based on the above scheme,the OFC-based multi-frequency microwave dissemination is demonstrated over a 100 km standard single-mode fiber.The fractional frequency instability of the 10.015 GHz signal is achieved at 1.4×10^-16 at 10000 s averaging time.3.Theoretical analysis and optimization of the multi-frequency distribution system.By conducting a simulation model of the multi-frequency microwave signals transmission system which is mentioned above,the performance,noise sources and evolution process of the system is analyzed carefully.The effect of the phase detection signal frequency and the dividing ratio of the phase locked loop（PLL）in the distribution system is studied with the simulation.It is shown in the simulation results that the stability of the transmission system can be improved effectively by detecting the phase error of higher harmonics with larger frequency intervals and reducing the frequency division ratio in the PLL.Based on the theoretical analysis,the optimization of the multi-frequency microwaves distributions system is conducted.By using higher detection frequency and lower division ratio of the PLL,the system noise floor can be reduced.By properly adjusting the experimental setup,the phase fluctuation is detected with the 10th harmonic frequency（100 GHz）and the frequency division ratio of the PLL can be reduced to 2.Thus,on one hand the signal-to-noise ratio（SNR）of the time delay fluctuation detection can be improved.And on the other hand the noise floor of the transmission system is reduced.The residual phase noise of the received 100 GHz signal in the 100 km phase-locked simulation system with 100 GHz detection frequency is reduced by 20 d B within the loop bandwidth compared to the simulation system with the repetition frequency（10 GHz）detection signal.And the fractional frequency instability of the received signal（100 GHz）is reduced by more than an order of magnitude to 7.5×10^-18 at 10000 s averaging time compared with the 10 GHz detection frequency.