Key Technologies Research On Optical Undersampling Links

Microwave photonic link is the link for microwave/millimeter-wave signal transmission and processing which uses photon as the carrier.Compared with the traditional electronic technology,microwave photonic link has a wide range of applications in new radar system,electronic countermeasures,broadband wireless access etc.by the reason of many advantages such as low loss,light weight,high bandwidth,resistance of electromagnetic interference,large dynamic range,etc.Based on microwave fiber link,the down-conversion of RF signals is realized by applying the under-sampling technology,avoiding the nonlinear loss of mixer effectively and reducing the system noise obviously,more conducive to long distance transmission,therefore has a bright prospect.The main works of the thesis are listed as follows:1.Model and simulation of microwave photonic link based on CW laserThe mathematical model is established to analyze the main evaluation indexes of microwave fiber link based on CW laser,including gain,noise figure,nonlinear distortion and spurious-free dynamic range(SFDR).At the same time,simulation analysis is obtained to show the influences of the optical detection current and the modulator half-wave voltage.In conclusion,to improve microwave factors needs considering every index performance.2.The study on optical under-sampling link based on ultrashort pulsesTo solve the problem of limited bandwidth at the receiving end,optical under-sampling link based on ultrashort pulses is proposed.The key technologies such as signal down-conversion based on optical under-sampling,passively mode-locked fiber laser and photoelectric detection are studied.What's more,the different performance between the short pulse laser and CW laser at the receiving end are compared.3.The influence of dispersion control broadening optical pulse on conversion efficiencyFor optical under-sampling link based on ultrashort pulses,a programmable optical processor(WaveShaper)is used to control dispersion of laser pulse,which produced by mode-locked lasers(MLL)with the repetition frequency of 12.2 MHz,pulse width of about 760 fs,more than 13 times of pulse broadening is achieved.What's more,the change of received power after detection is theoretically analyzed,and the effect of photoelectric conversion efficiency on account of pulse broadening is discussed.