We review recent work on all-fiber (long-period fiber grating) devices for optical pulse shaping, particularly flat-top pulse generation, down to the subpicosecond range and their application for nonlinear switching (demultiplexing) of optical time-division multiplexed (OTDM) data signals in fiber-optic telecommunication links operating up to 640？Gbit/s. Experiments are presented demonstrating error-free 640-to-10？Gbit/s demultiplexing of the 64 tributary channels using the generated flat-top pulses for temporal gating in a Kerr-effect-based nonlinear optical loop mirror. The use of flat-top pulses has critical benefits in the demultiplexing process, including a significantly increased timing-jitter tolerance (up to ~500？fs, i.e., 30% of the bit period) and the associated improvement in the bit-error-rate performance (e.g., with a sensitivity increase of up to ~13？dB as compared with the use of Gaussian-like gating pulses). Long-period fiber grating pulse shapers with reduced polarization dependence are fabricated and successfully used for polarization-independent 640-to-10？Gbit/s demultiplexing experiments. 1. Introduction Techniques for the precise synthesis and control of the temporal shape of optical pulses with durations in the picosecond and subpicosecond regimes [1] are of fundamental importance for a wide range of applications in ultrahigh-bit-rate optical communications, particularly to enhance the performance of a range of nonlinear optics-based data-processing operations [1–10]. As a very relevant example, (sub)picosecond flat-top (rectangular-like) optical pulses are highly desired in applications requiring the use of a well-defined temporal gating window, for example, for nonlinear time-domain switching of optical telecommunication data. The use of flat-top optical pulses as control/gating pulses in nonlinear time-domain optical switches translates into important advantages as compared with the (more conventional) use of Gaussian-like optical control pulses. Figure 1 illustrates the concept of nonlinear optical switching for temporal demultiplexing of serial optical time-division multiplexed (OTDM) data. For optimum performance, the gating pulse has to be shorter than the one-bit time window and at the same time it should have constant intensity over a time interval as long as possible. Both of these requirements can be fulfilled when using flat-top pulses. Indeed, as illustrated in Figure 1, flat-top optical control pulses increase the tolerance to timing jitter in the system, thus improving the overall performance of the nonlinear
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