Data-carried optical ultra-wideband monocycle pulses generation using two DGD modules

Abstract

ABSTRACT A novel method to generate ultra-wideband (UWB) signals based on two differential group delay modules and one Mach-Zehnder Modulator is proposed. Both simulation and experiments verified that the method could generate two kinds of UWB monocycles using low bit-rate non-return-to-zero data source (1Gbps). The monocycles have a fractional bandwidth of 127% at centre frequency 5.5GHz. Keywords: Ultra wideband (UWB), radio-over-fiber (RoF), differential group delay (DGD) 1. INTRODUCTION Ultra-wideband (UWB) is a fast emerging technology for short-range broadband wireless communication such as wireless personal area network and sensor network, etc. The UWB signal occupies wide bandwidth and has low power density, and it has immunity to multi-path fading [1]. As a carrier-free modulation scheme, direct-sequence impulse radio is more cost-effective and simpler compared with multi-band orthogonal frequency scheme. Since UWB is a room-scaled short range wireless communication technique, the wireless networks can operate mainly in indoor environment in standa lone mode. Considering the integration of UWB access networks and fixed wired networks, the combination of UWB-over-fiber technology and fiber-to-the-home (FTTH) technology is a competitive candidate for future wideband access networks [2]. So many all-optical schemes that fit for UWB-over-fiber technology to generate and distribute UWB impulses have been reported recently. Zeng et al. proposed two approaches to generate UWB impulses using one phase modulator (PM), and 25-km single mode fiber (SMF) or FBG to convert phase-modulated light to UWB pulses [3, 4]. Wang and Dong proposed UWB signal generation using cross-gain modulation or cross-phase modulation in semiconductor optical amplifier [5, 6], which requires two laser sources and may increase the system complexity. Chen proposed a scheme based on optical polarization time delay [7]. It is a simple method, but the elect rical signal source needs at least twice bit-rate compared to the carried data. Most of the schemes n eed an electrical Gaussian pulse source, which is comm only composed of a high-speed pulse pattern generator (PPG). This is an expensive construction, for which the PPG should work at least 10 Gbps. Furthermore, if data are carried on the UWB pulses, another modulator should be added to the systems, which increase the system cost and complexity. In this paper, we proposed and experimentally demonstrated a simple method to generate data-carried UWB monocycle pulses based on two differential group delay (DGD) modules and one Mach-Zehnder modulator (MZM). Instead of the data pattern “1000 0000 ”, which has one “1” followed by several “0”s to form the UWB signal, we use electrical non-return-to-zero (NRZ) data. The NRZ data modulate the optical signal in MZM to get an optical binary phase shift keying (BPSK) signal, which is then fed into two cascade DGD module s while the polarization of the light is carefully adjusted