Generation Of Ultra-wideband Signals By Directly Current-Modulating Distributed Feedback Laser Diode Subjected To Optical Feedback

Ultra-wideband(UWB) wireless communication system own high safety performance, high spectrum utilization percent and high processing gain, resistance to multipath fading ability, strong transmission ability, low power consumption, low cost and other advantages, which has been widely used in short distance wireless communication, secure communications, radar detection, intelligent transportation location and other commercial, civil and military fields.However, UWB technology also has to face the difficulties of development: It is difficult to generate UWB pulse signal with high rate and high spectrum utilization percent; UWB signal only transmit a relatively short space. UWB-Over-Fiber technology combine superiority of UWB technology with advantage of optical fiber transmission technology, which expand the application universality of UWB wireless communication system, make local UWB system, cable networks and other wireless network connect. UWB-Over-Fiber technology not only utilize huge bandwidth and low loss transmission of optical fiber, but also play the convenient advantages of ultra-wideband wireless communications technique, so UWB wireless communication system with UWB-Over-Fiber technology can avoid additional electrical to optical conversion and has a lot of advantages:low loss, high bandwidth, resistance to electromagnetic interference and so on. In the optical domain directly generating UWB microwave signal, which is the core technology of UWB-Over-Fiber.In this paper, the chaotic ultra-wideband(UWB) pulse signals are generated by directly modulating semiconductor laser subject to optical feedback. The main research works are summarized as follows:1.We elaborating the extant generation method of UWB signals. After analysis and comparison, we draw a conclusion:the generated UWB signal is the monocycle gaussian pulse and doublet pulse with shaping. The Spectrum bandwidth and center frequency of UWB signal are difficult to adjust, so which limits their range of applications in the complicate and different actual environment. In addition, the system don’t need additional a electroabsorption modulator so as to make the system simpleness and inexpensive2.We simulate the-10dB bandwidth and the central frequency of the RF spectrum of the chaotic UWB signals are influenced on by the bias current and feedback strength. The research results demonstrate the-10dB bandwidth of the RF spectrum of the UWB signals increases with increases of the bias current of the semiconductor laser and the feedback, the central frequency also increases with increases of the bias current and the feedback.3.Based on numerical simulation, in our experiments, chaotic Ultra-wideband (UWB) signals with steerable and flatted power spectrum were generated by directly modulating DFB-LD subject to optical feedback. The power spectrum of UWB signals is fully in compliant with the FCC indoor mask, while a large fractional bandwidth of133%and a central frequency of6.6GHz were achieved. The central frequency and-10dB bandwidth of the chaotic UWB signals is on a large scale tunable by adjusting the bias current and feedback power. In addition, the chaotic UWB signals were transmitted through a34.08-km single mode fiber(SMF) and the power spectrum do not have any discrete spectrum line. That means the generated chaotic UWB pulses have good tolerance to fiber dispersion and the system don’t need to optimize the modulation format.