Optical frequency combs are a series of phase-locked and equidistant laser lines in the spectral domain. In the time domain, they correspond to periodic pulse trains by the Fourier relation. The ability to shape optical combs and pulse trains is pivotal to many applications in optical communications and microwave photonics. For communication purposes, the information can be multiplexed in either time or frequency, by associating the data symbols to the comb lines or optical pulses. In particular, shaping optical pulses into sinc profile is of special interest, as it achieves high spectral efficiency when multiplexed. In regards to microwave photonics, frequency combs also have emerged as useful tools for processing radiofrequency (RF) signals in parallel. Comb-based RF photonic filter is one of the examples. Optical combs combined with dispersive propagation could construct filtering functions in the RF domain. Additionally, the shaping of comb spectra enables reconfiguration of the synthesized RF photonic filters.
The thesis presents results on various shaping techniques for the generation and applications of optical frequency combs. Both electro-optic combs and integrated microcombs are explored in the study, while their pulse shaping takes place either in the generation stage or externally. The first part of the thesis deals with optical sinc pulse shaping. A simple and flexible sinc pulse generator is demonstrated based on a single electro-optic modulator. Rectangular spectra of optical sinc pulses are harnessed to shape RF filters with sinc responses. Moreover, the method of sinc pulse shaping can fulfill the add-drop functionalities for superchannels multiplexed from sinc pulses.
In the second part, temporal Talbot shaping of frequency combs is addressed. The temporal Talbot effect multiplies the repetition-rates of optical pulse trains in time. A novel temporal Talbot multiplier is demonstrated in a conventional optical tapped delay line structure. Furthermore, such shaping concept is extended for the demonstration of azimuthal Talbot effect. When the orbital angular momentum modes are superimposed with Talbot phases, the light petal is self-imaged in the azimuthal angle.
Lastly, the third part exploits the internal shaping of soliton microcombs for the use in RF photonic filters. Versatile soliton states and thereby various microcomb spectra, are generated in a microresonator on demand. Such optical spectra could reconfigure their corresponding RF filters. Among others, perfect soliton crystals and two-soliton states are utilized, which respectively divide and translate their filter passband frequencies.