Generation of almost-ideally, sinc-shaped Nyquist pulse sequences with arbitrary bandwidth and repetition ratec

Abstract:
Due to the rectangular spectrum of sinc-shaped Nyquist pulses, data modulated with such pulse shapes can be transmitted in optical fibers with the maximum baud rate. Recently, a method for the generation of sinc-shaped Nyquist-pulse sequences was presented. Although very simple, the method can produce almost ideally sinc-shaped Nyquist-pulse sequences with a rectangular spectrum. Much more important, it was shown that these sequences possess the same properties for optical transmission systems as the single pulses. However in complete contrast to single pulses, which are noncausal and therefore just a theoretical construct, these pulse sequences can be generated by a frequency comb produced by one or two cascaded intensity modulators. Unfortunately, due to the limited bandwidth of the modulators, the minimum time duration of the generated pulses is restricted and for low repetition rates, the setup can become quite complicated. Here we present a method for the generation of almost ideally sinc-shaped Nyquist pulse sequences with arbitrary bandwidth and repetition rate. The method is based on the extraction of single lines from a mode-locked laser or a comb generator and a subsequent multiplication of these lines by modulation. The bandwidth of the generated pulses is in principle just restricted by the bandwidth of the comb generator and can be in the THz-range. The repetition rate can be adjusted and tuned by the subsequent modulation.