Spectral broadening of frequency combs via pulse apodization prior to nonlinear propagation

This thesis focuses on specific methods for spectrally broadening large repetition rate frequency combs using the idea that tailoring the shape of the seed pulse prior to nonlinear propagation will result in a spectrally flatter comb. A spectrally flat comb is desired for applications in optical communications, arbitrary waveform generation, and microwave photonic filtering. Three experimental setups using Fourier transform pulse shapers, Dispersion Decreasing Fiber (DDF) or Highly Nonlinear Fiber (HNLF) as the nonlinear propagation media were performed. Simulations employing the Split Step Fourier Method to solve the Nonlinear Schrodinger Equation were performed to analyze the experimental results. The first experiments employed DDF to produce a compressed pulse via Adiabatic Soliton Compression. This pulse was launched into the second stage and HNLF broadened the comb spectrum via Self Phase Modulation. A promising 130nm broadened comb spectrum was returned. The next experiments showed that, by apodizing the pulse produced by the optoelectronic frequency comb generator prior to propagation in HNLF, a flatter broadened comb spectrum was returned. These results were extended to a two-stage setup. The setup used two stages of HNLF. Sech apodization in the first stage and parabolic apodization in the second stage led to promising simulation results. With the insight gained by the simulations, experiments were performed and a flat broadened frequency comb led to applications in RF photonic filtering. An RF photonic phase filter was implemented with the comb generated as the source, and pulse compression experiments were performed.