All-optical ultrawideband monocycle and doublet generation using cascaded PPLN waveguides

Abstract

Ultrawideband (UWB) is an attractive technology for short-range high-capacity wireless communication systems. A novel all-optical method for generating UWB pulses is proposed and theoretically analyzed using cascaded periodically poled LiNbO 3 (PPLN) waveguides. The operation principle relies on the sum-frequency generation (SFG) in the first PPLN and the cascaded second-harmonic generation and difference-frequency generation (SHG+DFG) in the second PPLN. We simulate the proposed PPLN-based UWB pulses generation using the well-known coupled-mode equations describing the SFG and SHG+DFG processes. A pair of polarity-reversed UWB monocycle pulses is generated with a central frequency of 5 GHz and a 10 dB bandwidth of 8.75 GHz. Thus the fractional bandwidth is 175%. Moreover, a pair of polarity-reversed UWB doublet pulses is also obtained. One has a central frequency of 5 GHz, a 10 dB bandwidth of 7.5 GHz, and a fractional bandwidth of 150%, and the other has a central frequency of 5 GHz, a 10 dB bandwidth of 3.75 GHz, and a fractional bandwidth of 75%. It is found that all generated pairs of polarity-reversed UWB monocycle and doublet pulses match well with the UWB definition of Federal Communications Commission (FCC).