Abstract
Various schemes based on electro-optic modulators have been reported to generate ultra-wideband (UWB) signals in the optical domain, but the availability of these methods always relies on small signal modulation. In this paper, the influence of large signal modulation on two typical schemes, representing two major categories of external-modulator-based photonic UWB generation schemes, is analytically and numerically studied. While the quasi single-sideband UWB (QSSB-UWB) pulse can maintain its shape, the Gaussian UWB (GUWB) generation scheme suffers serious modulation distortion when the phase modulation index is greater than π/6. The modulation distortion would have negative impact on the receiver sensitivity when the signal is sent to a correlation receiver.
Highlights
Ultra-wideband (UWB) is a promising technology to provide high data-rate, low cost and low power consumption connectivity for wireless personal area network [1,2]
According to the optical spectral properties of the generated UWB pulses, there are generally three types of UWB generation schemes based on electro-optic modulators [8]: 1) double-side band UWB (DSB-UWB) generation schemes, e.g. converting an electrical UWB pulse to the optical domain based on intensity modulation [3]; 2) quasi single-sideband UWB (QSSB-UWB) generation schemes, e.g. sending an electrical Gaussian pulse to a dual-drive Mach-Zehnder modulator (MZM) with the two paths delayed by tens of picoseconds [11], or phase modulation (PM) by an electrical pulse followed by a detuned optical bandpass filter [12,13,14,15]; 3) Gaussian UWB (GUWB) generation schemes, e.g. shaping an electrical pulse by a photonic microwave filter with one negative tap [16,17,18,19], or phase modulation (PM) by an electrical pulse followed by a dispersive element [2]
The generation of QSSB-UWB and GUWB signal has been extensively reported in the literature, most of them applied small signal modulation assumption
Summary
Ultra-wideband (UWB) is a promising technology to provide high data-rate, low cost and low power consumption connectivity for wireless personal area network [1,2]. The methods based on electro-optic modulation are promising for practical UWB over fiber system since electrooptic modulators are simple, reliable and cost effective, which have been widely deployed in the commercial optical communication networks. The generation of QSSB-UWB and GUWB signal has been extensively reported in the literature, most of them applied small signal modulation assumption. The small signal modulation can eliminate the nonlinear distortion introduced by electro-optic modulation, but it results in large optical to electrical conversion loss and low signal-to-noise ratio (SNR). We theoretically study the influence of large signal modulation on two typical external-modulator-based schemes for photonic generation of QSSB-UWB and GUWB signals, respectively. The study is aimed to provide the theoretical basis to construct an optical UWB transmitter with small optical to electrical conversion loss and small noise figure for UWB over fiber applications. The results can be extended to other UWB waveforms, such as Gaussian doublet, Gaussian triplet, and other more complicated waveforms
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