Figure 8. Spectrum of modulated sinc pulses.

(a) Simulated spectrum resulting from modulating ideal sinc-shaped pulses with on-off keying (OOK) format, using an ideal rectangular modulating window. (b) Measured spectrum obtained from the OOK modulation of the generated sequence of sinc-shaped pulses using a pseudo-random binary sequence of length 2³¹−1. The measured spectrum (black straight line) is compared with the simulated one reported in a convolved with the finite spectral bandwidth (0.01 nm) of the OSA (red-dashed line). (c) Simulated spectrum resulting from modulating ideal sinc-shaped pulses with binary phase-shift keying (BPSK) format using an ideal rectangular modulating window. (d) Measured spectrum obtained from modulating the generated sequence of sinc-shaped pulses with BPSK. The measured spectrum (black straight line) is compared with the simulated one reported in c convolved with the filtering bandwidth of the OSA (red-dashed line). The dotted boxes in a and c show the rectangular spectrum of one single pulse and the dashed lines indicate the position of the two adjacent WDM channels, showing that although the spectrum is broadened by the modulation, no guard band between the channels is necessary.