Research On UEB Pulse Generation Based On Electro-optic Modulator

UWB-over-fiber is a technique transmitting UWB signal on optical fiber, which combines the advantage of wide bandwidth, low loss and immune to EMI of the optical communications and the advantages of low power, carrier free and high data rate of the UWB communication, and enlarges the transmission range of UWB signal. UWB signals generated in the optical domain, without the need for extra optical-electrical and electro-optical conversions, has become the hot topic in UWB-over-fiber technique.In this paper, firstly, we introduce the feature and appliance of the UWB signal, then simply analyze UWB pulse should be Gaussian monocycle and doublet pulses and the main modulation scheme of UWB pulse. Next, we analyze UWB pulse generation based on optical phase modulator, mainly based on PM-IM conversion. Optical band-pass filter be used as a phase discriminator. When the optical phase modulated signal locates at the left or right slope of the filer, Gaussian monocycle can be generated. UWB doublet can be generated based on Chromatic dispersion while the signal performance will be influenced by the length of the fiber. UWB monocycle can be generated based on AMZI which is equivalent to a first-order differentiator for the production of Gaussian UWB monocycle. In the AMZI, firstly, the phase modulated signal is split into two parts with vertical polarization direction and one of the signals undergoes a small delay, then the two parts signal are coupled together via a coupler and a polarizer is used before PD. Finally, we analyze the scheme to generate UWB pulses based on MZ modulator. UWB monocycle can be generated when the modulator work in the liner point and then detected by a BPD or a small delay is introduced between two arms of the modulator and the DC bias is1/2of the half wave voltage. UWB doublet can be generated when the modulation signal is large enough and the DC bias is near the minimal or maximum point. Based on the generation of UWB doublet, UWB triplet can be generated when there are two MZ modulators generating polarity reversed UWB doublets and the two pulses are coupled together after one of the pulses undergoes a small delay. Based this structure, UWB PSM and PAM can be realized easily.