Optical generation of binary-phase-coded, direct-sequence ultra-wideband signals by polarization modulation and FBG-based multi-channel frequency discriminator.

In this paper a novel optical generation approach for binary-phase-coded, direct-sequence ultra-wideband (UWB) signals is experimentally demonstrated. Our system consists of a laser array, a polarization modulator (PolM), a fiber Bragg grating (FBG), a length of single mode fiber, and a photo detector (PD). The FBG, designed based on the superimposed, chirped grating, is used as the multi-channel frequency discriminator. The input electronic Gaussian pulse is modulated on the optical carrier by the PolM and then converted into UWB monocycle or doublet pulses sequence by the multi-channel frequency discriminator. The PolM is used so that the desired binary phase code pattern could be simply selected by adjusting the polarization state of each laser, rather than tuning the laser wavelengths. The desired UWB shape, monocycle or doublet, could be selected by tuning the FBG. Based on our proposed approach, four-chip, binary-phase-coded, DS-UWB sequences with different pulse shapes and code patterns are experimentally demonstrated. The impact of the fiber dispersion on the generated UWB pulses is also discussed in our paper.