The Basic Research Of Waveform Generation Based On Recirculating Frequency Shifter

Due to the extensive application of microwave photonics technology in radar,wireless communication and microwave signal processing,photonics-assisted arbitrary waveform generation has become a hot topic in recent years.The traditional electrical method for the generation of microwave waveforms has disadvantages such as high timing jitter,big loss,large size,low frequency and narrow bandwidth,while the microwave photonics method utilizes the electro-optic effect to modulate the electrical signal onto the optical wave,which can effectively have a breakthrough on the electronic bottleneck and has the characteristic of anti-electromagnetic interference.In this thesis,the recirculating frequency shifting loop is used to shift the optical signal frequency,which can be used for microwave waveform generation and microwave signal conversion.This thesis mainly consists of the following parts:A method for synthesizing optical microwave waveforms based on electro-optic modulation is proposed.Multiple microwave waveforms can be generated by controlling three bias points of the dual-parallel Mach-Zehnder modulator and setting the modulation coefficient reasonably.Firstly,three conditions to suppress even order harmonics are obtained through theoretical analysis,and then the modulation coefficients of triangular and rectangular waveforms are calculated respectively.In the experiment,sinusoidal modulating signals of 1GHz,2GHz and 3GHz were used to generate triangular,rectangular,sawtooth and reverse sawtooth microwave waveforms successfully.An optical microwave waveform generation method based on recirculating frequency shifter is presented.By combining the frequency-shifted feedback characteristics of the recirculating frequency shifting cavity with the polarization characteristics of the polarization rotator,microwave waveforms are synthesized eventually.The recirculating frequency shifting cavity can output an optical comb spectrum with equal frequency interval,while the 45°polarization rotator can make the polarization directions of two spectral lines whose frequency interval are double of the shift-frequency perpendicular with each other,which can effectively suppress the even order harmonics after beating frequency.The feasibility of the scheme was verified through theoretical analysis and simulation.Rectangular and triangular microwave waveforms of 5GHz and 20 GHz were successfully generated.An optical microwave signal conversion scheme based on recirculating frequency shifter is proposed.The high frequency signal to be processed and the local oscillator signal are applied to two radio frequency input ports of dual-parallel Mach-Zehnder modulator.With the help of the two-way frequency shifting characteristics of the recirculating frequency shifter,down conversion of large dynamic range microwave signal with a low-frequency local oscillator signal is realized,and the feasibility of the scheme was theoretically analyzed and experimentally demonstrated.