Photonics Generation, Modulation And Transmission Research Of Ultra-wideband Impulse Radio Signals

Ultrawideband (UWB) impulse radio is regarded as a promising solution for short-range, high-capacity wireless communication systems and broadband sensor networks owing to the distinct advantages of high immunity to multipath fading, lower power consumption and enhanced capability. In the past few years, many approaches for UWB signal generation have been realized by using electronic circuits in electrical domain. However the restriction of the maximum transmission power spectral density limits their operating range to a few hundreds of meters. To overcome the UWB short-range wireless transmission limitation, UWB-over-fiber technology has emerged to increase the propagation distance of wireless signal. Therefore photonic operation of UWB signals is extraordinary attractive since it can be directly incorporated into the fiber link and eventually radiate at the receiver front-end. Our research achievements and contributions are summarized as follows:(1) Filter-free UWB doublet pulse generation is experimentally demonstrated in the optical domain based on cross-gain modulation (XGM) in semiconductor optical amplifier (SOA) and dispersion-induced pulse broadening effect in single-mode fiber (SMF). The scheme is simple and robust since a single SOA and a span of fiber is required. The UWB signals can be flexibly adjusted and easily optimized.(2) We experimentally demonstrate a wavelength division multiplexing (WDM) transmission system supporting converged transport of multi-wavelength UWB signals. Optical signals of8x10Gb/s are successfully transmitted through a25km SMF. This paper mainly studies the influence and change of the waveforms and spectra of the optical signals during the co-propagation process.(3) A simple and flexible photonic code UWB sequence generator containing a phase modulator and a DI-based frequency discriminator is successfully demonstrated. The polarity-reversed monocycle and doublet pulses can be generated. Moreover, the generation of UWB pulse shape modulation (PSM) is the advantage of our scheme. It has the ability to propagate the UWB sequence through a length of75km fiber with neglectable distortion. In addition, the pulse position modulation (PPM) and on-off keying (OOK) can also be obtained, which can easily find applications in the future UWB-over-fiber access work.(4) A UWB monocycle and doublet pulses generator consisting of a DI-based frequency discriminator and SOA-based gain saturation is proposed and experimentally demonstrated. The polarity-reversed monocycle can be generated by adjusting the voltage of DI. Afterwards, the doublet pulse can be generated at the output of SOA. In addition, the UWB generator has the ability to propagate the UWB doublet OOK code pattern through a length of60km fiber with negligible distortion in a dispersion-compensation-free transmission, presenting that the generated UWB pulses have a good tolerance to dispersion over fiber and application in photonic integrated circuit technology.(5) A simple and flexible photonic code UWB sequence generator using a phase modulator and two optical bandpass filter (OBFs) served as frequency discriminators are successfully demonstrated. The polarity-reversed monocycle and doublet pulses can be achieved, and PSM consisting of positive or negative monocycle and doublet or zero pulses is discussed by adjusting the predefined data sequence and optical path difference, which can expressly find applications in future UWB over fiber access work.