Studies On Mixing And Phase Shifting Technology Based On Electro-optic External Modulation

Microwave photonics combines the advantages of traditional microwave communication and modern optical fiber communication,and exhibits the advantages of large bandwidth,immunity to electromagnetic interference and small transmission loss.On the basis of previous studies,three kinds of the local oscillator frequency doubled mixers with phase shift function based on microwave photonic electro-optic external modulation technology are proposed.The technique of up/down frequency conversion is studied and the method of image rejection in down frequency conversion is proposed.The main research work in this paper is as follows:(1)An up-converter system with local oscillator frequency doubled is proposed by cascading dual-parallel polarization modulator(DP-POLM)and dual-polarization dual parallel Mach-Zehnder modulator(DP-DPMZM).The phase and amplitude of the system are also controllable.The results show that the proposed scheme can achieve 360°phase shift and the phase imbalance is less than 3° within the bandwidth of the 16 to 36 GHz.Because of the CS-SSB modulation method,the up-converted signal is relatively pure and the spurs suppression ratio is 24.66 d B.(2)To solve the problem that the down-conversion system is susceptible to image signal interference,an IRM based on a microwave photonic phase shifter is proposed.The I/Q channel is constructed by setting the bias voltage of the polarization division multiplexing dual-parallel Mach-Zehnder modulator(PDM-DPMZM).The phase in the orthogonal state between the two IF signals are stable within 10 to 40 GHz,and the image rejection can be achieved after combining an intermediate frequency quadrature hybrid coupler.The results show that the image rejection ratio is more than 46 d B,the phase imbalance is less than 2°,and the spurs suppression ratio is greater than 69 d B.(3)Aiming at the problems of DC offset and even-order distortion in IRM,a scheme to optimize IRM by using balance detection technology is proposed.The system builds the I/Q channel by adjusting the polarization controller(PC)and polarization beam splitter(PBS).The results show that the proposed scheme not only has the advantage of large bandwidth as the previous scheme,but also has an image rejection ratio greater than 47 d B.The spur suppression ratio is 11 d B larger than that of the previous scheme,and the phase imbalance is less than 1°.At the same time,by adjusting the angle with the PC,the continuous 360°phase shifting of the IF signal can be realized.