Research On Microwave Signal Generation Based On Microwave Photonics

Microwave photonics is a new technology to accomplish the generation, transmission and processing of microwave signal by optical method. Cmpared with the traditional electronic technology, microwave photonics technology has the advantages of low-loss, high-bandwidth, small in size, light in weight and anti-electromagnetic. Techniques to generate microwave signals in the optical domain is a very important research content in microwave photonics. In this thesis, we focus on two aspects: 1, frequency doubling based on microwave photonics; 2, generation of triangular wave based on microwave photonics.Firstly, this thesis introduces several common electro-optic modulators, and the structure and working principle are analyzed in theory. On the basis of the introduction of MZM, we make a simulation analysis for DSB, SSB and OCS-DSB modulation methods using the VPI simulation software. Then, this thesis gives the definitions of the OSSR, RFSSR and phase noise.Secondly, this thesis discuss a new scheme of octave millimeter signal generation based on DP-QPSK modulator, which is analyzed by simulation and verified by experiment. The experiment results show that the optical sideband suppression radio(OSSR) is 10.28 dB; and the radio frequency spurious suppression radio(RFSSR) is 12.68 dB; The phase noise deteriorates 18 dB compared with the LO signal, which meets the phase noise deterioration theory. With no optical or electrical filter used, this scheme is simple, easy to handle, and highly adjustable which is most important. During the experiment, we use 3 GHz,4.5 GHz, 5 GHz and 6 GHz LO signals to complish the experiment, and relatively ideal spectrums are abtained.At the same time, this thesis discuss a new scheme to generate triangular waveforms based on a PM modulator and a FBG. A simulation is conducted to verify this method. In the simulation, a 3 GHz LO signal is applied to drive the PM. When the optical carrier and the +1st order sideband are both suppressed by 6 dB using the FBG and the modulation index is set as 0.68, the second-order harmonic is suppressed and the third-order harmonic is 19.12 dB lower than the fundamental term(corresponding to the amplitude ratio of 1/9), so a triangular waveform with a repetition rate of 3 GHz can be generated. When the optical carrier and the +1st order sideband are both suppressed by 4 dB using the FBG and the modulation index is set as 0.75, the second-order harmonic is suppressed and the third-order harmonic is 19.06 dB lower than the fundamental term(corresponding to the amplitude ratio of 1/9), so a triangular waveform with a repetition rate of 3 GHz can be generated.