Research On The Key Technologies Of Optical Microwave Singal Generation Based Intensity Modulators

With the emergence of microwave photonics,optical microwave singal generation technology has become the research focus because of its low loss,large bandwidth,wide tuning range,and the advantages of resistance to electromagnetic interference,and the external modulation frequency multiplication method with system simplicity and low cost to generate tunable,high quality,low phase noise microwave signal has got more attention.This thesis is based on using Direct Digital Synthesizer AD9914 to generate linear frequency modulation singal with output frequency from 4 to 12 GHz and phase noise less than-110 d Bc/Hz@10kHz.This thesis researches high frequency multiplication factor above eight based on external modulation method.The main content and results are as follows:(1)This thesis proposed a novel scheme based five MZMs to generate frequency 10-tupling microwave signal with modulation index from 2.5 to 8.7 to ensure the radio frequency spurious suppression ratio(RFSSR)better than 20 dB,the best RFSSR was 68 dB.This thesis made the mathematical derivation and used Optisystem to simulate the whole structure.Simultaneously,risk points including extinction ratios of MZMs,transmission point drifts of MZMs,electrical phase of RF inputs,unbalance of RF amplitude were analyzed in simulation.When the ultralow half-wave voltage MZM ensured the large modulation index,this structure could achieve frequency 30-tupling.Through changing transmission point to full point,frequency 20-tupling is achieved.(2)This thesis proposed two novel schemes based six MZMs,the first scheme to generate frequency 12-tupling microwave signal with modulation index from 3.3 to 9.8 to ensure the RFSSR better than 20 dB,the best RFSSR was 68 dB.the other scheme to generate frequency 12-tupling microwave signal with lower modulation index from 1.8 to 4.9,the best RFSSR was 50 d B.This thesis made the mathematical derivation and used Optisystem to simulate the two structures.Simultaneously,risk points including extinction ratios of MZMs,transmission point drifts of MZMs,electrical phase of RF inputs,unbalance of RF amplitude were analyzed in simulation.When the large modulation index was satisfied,the both structures could achieve frequency 36-tupling.Through removing the optical phase shift of the first structure,frequency 24-tupling was achieved.(3)This thesis designed a 16-tupling structure based on two frenquency quadrupling systems cascaded,analyzing the feasibility of three kinds of frenquency quadrupling system in simulation and experiment.This thesis verified the performance indexs of 16-tupling structure experimentally,the RFSSR was more than 30 dB and the deterioration of phase noise was 24.18 dB with the frequency offset 10 kHz and 26.25 dB with the frequency offset 1 MHz.