Photonic generation and processing of microwave arbitrary waveforms based on advanced fiber Bragg gratings

Photonic generation and processing of microwave arbitrary waveforms has been a topic of interest recently. Compared with the electronic techniques, photonics techniques provide the capabilities of generating and processing high-frequency and large-bandwidth microwave waveforms which cannot be fulfilled by the electronic techniques. In this thesis, techniques to generate and process microwave arbitrary waveforms in the optical domain using advanced fiber Bragg gratings (FBGs) are investigated, with an emphasis on the system architectures in which FBGs are employed as spectral shapers and dispersive elements.

The thesis consists of two main parts. In the first part, we investigate the generation of a microwave arbitrary waveform using advanced FBGs. Two techniques to generating microwave arbitrary waveforms based on coherent optical pulse shaping are investigated. The first technique is based on optical spectral shaping and frequency-to-time mapping. The use of an FBG as an optical filter to achieve spectral shaping, as a dispersive element to achieve frequency-to-time mapping, and as a multifunctional device to perform both optical spectral shaping and frequency-to-time mapping is investigated. In the second technique, the photonic microwave arbitrary waveform generation is realized based on Fourier-transform pulse shaping. Time-domain Fourier-transform pulse shaping is first studied, where a pair of linearly chirped FBGs is employed as dispersive elements to temporally stretch and compress the input optical pulse. Fourier-transform pulse shaping is also implemented in the frequency domain, where a linearly chirped FBG functioning as both an optical spectral shaper and a conjugate dispersive element pair to perform pulse stretching and pulse compression is employed.

In the second part, we investigate the photonic processing of a microwave arbitrary waveform using advanced FBGs. A photonic microwave filter is usually used to process microwave signals in the optical domain. Two different photonic microwave filters are explored. The first filter is a nonuniformly spaced photonic microwave multi-tap delay-line filter, which is designed to have a quadratic phase response to achieve matched filtering of a frequency-chirped microwave waveform. A spatially-discrete chirped fiber Bragg grating (SD-CFBG), which can be designed to arbitrarily control the tap coefficients and the time delays, is utilized in the multi-tap delay-line filter to achieve the desired microwave filter response. The second photonic microwave filter is implemented based on optical filter response to microwave filter response conversion in which an FBG with the desired magnitude and phase response is employed as the optical filter. The employment of the photonic microwave filter for matched filtering of a frequency-chirped microwave waveform is demonstrated.