Study On Waveform Synthesis Method Based On Optical Pulse Shaping Technique

Broadband microwave signals have great application value in long-range radar,RF optical transmission,test and measurement,and broadband wireless communication.The available spectrum resources at the low-end of the wireless spectrum are decreasing gradually,and extending to the high-end could effectively alleviate the problem of the shortage of low-end spectrum resources.Limited by factors such as noise and electron transition time,conventional electronic techniques have entered a bottleneck period in broadband microwave signal synthesis.Since the advent of the laser,great progress has been made in optics and photonics,which makes the synthesis of broadband microwave signals using photonics techniques a reality.Starting from the basic principle of photonassisted waveform synthesis,this thesis studies the similarities and differences in optical pulse shaping and frequency-to-time mapping when using active and passive light sources for waveform synthesis,as well as corresponding reasons.Firstly,the research status of photon-assisted waveform synthesis was briefly introduced,and the characteristics of different optical pulse shaping techniques were analyzed and compared.An experimental system composed of an optical pulse source,optical pulse shaper,and frequency-to-time mapping was designed,and the basic principle was described.Erbium-doped fiber mode-locked laser(passive)and electro-optical frequency comb generator(active)were designed and built.The main theory and working principle of the erbium-doped fiber mode-locked laser were introduced in detail,and an erbium-doped fiber mode-locked laser with a repetition frequency of 100 MHz was designed and built.The electro-optic effect and the performance characteristics of the electro-optic modulator were theoretically studied in detail,and a 1 GHz electro-optic frequency comb generator with a cascaded structure was designed and built.The basic principle of fiber Bragg grating and the tunability of the free spectral range were studied.On this basis,two optical pulse shapers suitable for active and passive light sources were designed and built.The optical delay line changes the free spectral range and enhances the tenability of frequency response.When the light sources are active and passive,the relative problems that need to be considered when using dispersion compensation fiber for frequency-to-time mapping were studied,and the specific method to determine the parameters of dispersion compensation fiber was given.Finally,the envelopes of the active and passive optical pulses were shaped by the designed system,and the microwave signal outputs with a time-bandwidth product of 8and 72 were obtained,respectively.The pulse widths are 1 ns and 4 ns,and the bandwidths are 8 GHz and 18 GHz,respectively.The final conclusions are as follows: the active optical pulses are sensitive to the dispersion of the optical pulse shaper due to its large pulse width and narrow spectrum,and the pulse envelopes are easy to shape,requiring a large amount of dispersion to complete the frequency-to-time mapping;the passive optical pulses are not sensitive to the dispersion of the optical pulse shaper,the pulse envelopes are difficult to shape,and the frequency-to-time mapping can be completed with only a small amount of dispersion.The research work of this thesis lays a basis for the compactification and practicalization of photonic waveform synthesizers.