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Optical pulse shaping is a widely adopted technique in which intensity and phase manipulation of optical spectral components allow synthesis of user-specified ultrashort pulse fields according to a Fourier transform relationship. Furthermore, mode-locked lasers producing combs of frequency-stabilized spectral lines have resulted in revolutionary advances in frequency metrology. However, until recently pulse shapers addressed spectral lines in groups at low spectral resolution. Line-by-line pulse shaping, in which spectral lines are resolved and manipulated individually, leads to a fundamentally new regime for optical arbitrary waveform generation (O-AWG) in which the advantages of pulse shaping and of frequency combs are exploited simultaneously.
Bringing pulse shaping and frequency combs together allows O-AWG with both a controllable ultrafast time structure and long-term coherence. Intuitively, full control of individual frequency comb lines require (1) frequency-stabilized sources to generate stable spectral lines and (2) high-resolution pulse shapers to resolve and control individual spectral lines. O-AWG promises a broad impact both in optical science, allowing for example coherent control generalizations of comb-based time-frequency spectroscopies, and in technology, enabling new truly coherent multiwavelength processing concepts for spread spectrum light wave communications and lidar.
This chapter is organized as follows. The significance of spectral line-by-line shaping will be first compared to conventional pulse shaping. Shaper setup will be explained. Line-by-line shaping examples using an actively mode-locked fiber laser will be presented in the second section. Impact of frequency comb frequency instabilities over line-by-line shaped waveforms are explored in the third section. In the fourth section, shaping examples using alternative comb sources are given.
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