Photonic Generation And Modulation Research For Ultra-wideband Signals

Ultra-wideband (UWB) technologies for short-range high-speed wireless communications, sensor networks and high-precision radar systems have received extensive attention owing to some distinct advantages, such as immunity to multipath fading, wide bandwidth and low-power spectral density. Due to low-power spectral density, UWB communication distance is limited to a few meters to tens of meters range. To increase the area of coverage, UWB-over-fiber technologies have been investigated, which takes advantages of broad bandwidth, low loss and cost of optical fiber, combining the optical fiber wired communication and UWB wireless communication to construct a fiber-wireless (FiWi) system.Photonic generation for UWB signals is a key technique of UWB-over-fiber communication and high-precision radar system applications. In this paper, a novel all-optical method for UWB monocycle pulse generation based on cross polarization modulation (CPM) effect in small-core highly nonlinear photonic crystal fiber (HNPCF) is proposed. Due to the CPM effect between the probe light and the pump pulse, a pair of polarity reversed Gaussian pulses is produced. After the proper differential delay and photodetection, an UWB monocycle pulse with time duration of 84ps, a -10dB bandwidth occupying the frequency range from 2.5 to 18.9 GHz and a fractional bandwidth of 153% is generated.Achieving UWB system applications, another key technique is to encode and modulate with a specific code representing some information. The feasibility of directly utilizing photonic generation approaches of UWB signal to complement pulse modulation is investigated in this paper. Based on the nonlinear effect of HNPCF and precode for the input electrical signals, UWB pulse bipolar modulation (PBM) is experimentally realized, with the redundancy 2/3 as the worst situation and 0 as the best situation. To eliminate the redundancy of UWB pulse modulation, a novel and simple architecture to achieve UWB PBM and pulse shape modulation (PSM) is demonstrated in simulation and experiment. The proposed scheme is based on a symmetric phase modulation to intensity modulation (PM-IM) conversion architecture consisted of two phase modulators to achieve phase modulation and a band-pass filter as a frequency discriminator. The PBM with the fixed and arbitrary chip length and PSM without the limit of pulse shape are simulated. In experiment, UWB monocycle and doublet PBM are obtained at a high speed with a bit rate of 4.0Gbits/s and 2.6Gbit/s respectively. The feasibility of this scheme is verified by the results of simulation and experiment.