Research On Linearization Of Coherent Microwave Photonic Link

Owing to the characteristics of linear modulation,bias-free,and high receiving sensitivity,the coherent microwave photonic links possess important application potential and research value in the fields of deep space detection,radar,electronic warfare,and ubiquitous network.Aiming at the challenges of limited transmission distance,serious broadband nonlinear distortion,and high-frequency image interference of linearized coherent microwave photonic links,this paper studies the long-distance dynamic range improvement,multi-octave linearization,and highfrequency high fidelity reception in the coherent microwave photonic links.The main innovative achievements are summarized as follows:Aiming at the limited transmission distance of linearized coherent microwave photonic link,a long-distance dynamic range enhancement technology based on homodyne optical phase-locking and geneticalgorithm(GA)assisted digital demodulation is proposed in this paper,which realizes the transmission and reception of 500 kHz～100 MHz signals over a long distance(100.8 km)without relay amplifier under the wide temperature(-40℃～70℃),and the RF gain of the link reaches-12 dB.After the digital demodulation,the suppression ratio of the output third-order intermodulation distortion(IMD3)reaches 30.5 dB,and finally,the spurious-free dynamic range(SFDR)of the wide temperature and longdistance coherent microwave photonic link reaches more than 122 dB·Hz2/3.Aiming at the serious broadband nonlinear distortion of linearized coherent microwave photonic link,a high redundancy multi-octave linearization technology based on the direct-current residual(DCR)demodulation algorithm is proposed in this paper,which improves the suppression ratios of second and third-order distortion in 2 MHz～100 MHz multi-octave coherent microwave photonic link to 60 dB,and the SFDR2 and SFDR3 of the link reach 103.74 dB·Hz1/2 and 116.31 dB·Hz2/3 respectively.When there are 5%DC and amplitude errors at the receiving end of the link,compared with the traditional I/Q digital demodulation,the DCR algorithm further suppresses the IMD3 and IMD2 by 8.1 dB and 17.7 dB,effectively improving the redundancy of broadband nonlinear distortions to the digital processing error(not less than 5%)in the coherent microwave photonic link.Aiming at the high-frequency image interference of linearized coherent microwave photonic link,an all-optical mixing high fidelity receiving technology based on digital image-interference suppression and nonlinear-distortions compensation is proposed,which realizes the 47-dB image suppression ratio of Ku band coherent microwave photonic link.In addition,the MMD and IMD3 suppression ratio near the target intermediate frequency in the image suppression coherent microwave photonic link reach 18.1 dB and 10.9 dB.Finally,the gain and SFDR of the image-suppressed Ku-band coherent microwave photonic link reach21.9 dB and 108.8 dB·Hz2/3.