Generation and distribution of UWB pulse signals by use of optical phase modulation and PM-IM conversions

Abstract

In this paper, we present two approaches to generating and distributing FCC-regulated UltraWideBand (UWB) pulse signals in the optical domain, based on optical phase modulation. In the first approach, an electrical Gaussian pulse train is applied to modulate the phase of an optical carrier using an electrooptic phase modulator. A 25-km single-mode fiber link is then used to realize PM-IM conversion which has a frequency response equivalent to a microwave bandpass filter. When the Gaussian pulse train is distributed over the 25-km fiber, the Gaussian pulses are then shaped into doublet pulses at the receiver front-end. Therefore, the UWB pulses are not generated but also distributed over optical fiber. In the second approach, instead of using an electrooptic phase modulator, optical phase modulation is implemented in the optical domain based on cross phase modulation in a nonlinear fiber. The PM-IM conversion is then achieved by use of a fiber Bragg grating that serves as a frequency discriminator. Electrical monocycle and doublet pulses are obtained at the output of the photodetector. Experimental results for both approaches are presented and discussed. The use of the second configuration to implement pulse on-off, polarity and shape modulation in the optical domain is also discussed.