Programmable All-Fiber Optical Pulse Shaping

Abstract

Techniques for the precise synthesis and control of the temporal shape of optical pulses with durations in the picosecond and sub-picosecond regimes have become increasingly important for a wide range of applications in such diverse fields as ultrahigh-bit-rate optical communications (Parmigiani et al., 2006; Petropoulos et al., 2001; Oxenlowe et al., 2007; Otani et al., 2000), nonlinear optics (Parmigiani et al., 2006 b), coherent control of atomic and molecular processes (Weiner, 1995) and generation of ultra-wideband RF signals (Lin & Weiner, 2007). To give a few examples, (sub-)picosecond flat-top optical pulses are highly desired for nonlinear optical switching (e.g. for improving the timing-jitter tolerance in ultrahigh-speed optical time domain de-multiplexing (Parmigiani et al., 2006; Petropoulos et al., 2001; Oxenlowe et al., 2007)) as well as for a range of wavelength conversion applications (Otani et al., 2000); high-quality picosecond parabolic pulse shapes are also of great interest, e.g. to achieve ultra-flat self-phase modulation (SPM)-induced spectral broadening in super-continuum generation experiments (Parmigiani et al., 2006 b). For all these applications, the shape of the synthesized pulse needs to be accurately controlled for achieving a minimum intensity error over the temporal region of interest. The most commonly used technique for arbitrary optical pulse shaping is based on spectral amplitude and/or phase linear filtering of the original pulse in the spatial domain; this technique is usually referred to as ‘Fourier-domain pulse shaping’ and has allowed the programmable synthesis of arbitrary waveforms with resolutions better than 100fs (Weiner, 1995). Though extremely powerful and flexible, the inherent experimental complexity of this implementation, which requires the use of very high-quality bulk-optics components (high-quality diffraction gratings, high-resolution spatial light modulators etc.), has motivated research on alternate, simpler solutions for optical pulse shaping. This includes the use of integrated arrayed waveguide gratings (AWGs) (Kurokawa et al., 1997), and fiber gratings (e.g. fiber Bragg gratings (Petropoulos et al., 2001), or long period fiber gratings (Park et al. 2006)). However, AWG-based pulse shapers (Kurokawa et al., 1997) are typically limited to time resolutions above 10ps. The main drawback of the fiber grating approach (Petropoulos et al., 2001; Park et al. 2006) is the lack of programmability: a grating device is designed to realize a single pulse shaping operation over a specific input pulse (of prescribed wavelength and bandwidth) and once