Research On The Key Technologies Of High Frequency Spectrally Efficiency Optical Transmission Networks

In recent years,with the unprecedented development of Internet business,the bandwidth demand for mobile data traffic has been explosively growing.Improving the spectral efficiency of the transmission system is considered to be the preferred solution for solving the huge traffic demands.Two popular multiplexing technologies,which are coherent optical orthogonal frequency division multiplexing?CO-OFDM?and Nyquist wavelength division multiplexing?Nyquist-WDM?technology,have attracted a lot of attentions because of the high spectrally efficiency and the strong ability to resist the carrier crosstalk.This thesis focuses on the study and research on the key technologies for high-spectral-efficiency optical transmission networks.The main contents and corresponding innovations are as follows:1.A modulation technique based on discrete Fourier transform spread?DFT-Spread? has been studied,which utilized to solve the problem of high peak to average of power ratio?PAPR?in OFDM system.The optical OFDM system by using this modulation technique is named DFT-Spread OFDM technology.Firstly,the principle of reducing PAPR in DFT-Spread OFDM system is analyzed in detail.The results of PAPR based on different mapping modes and modulation formats are simulated,the results show as follows:interleaved mapping and low-order modulation format with the lowest PAPR.Furthermore,we compared the computational complexity of the technique that we proposed to the traditional OFDM and selective mapping method?SLM?.The comparison results show that the proposed scheme not only can effectively reduce the system PAPR,but also slightly increase the system's computational complexity.Finally,the corresponding simulation experiments are set up to verify the theoretical derivation,and the results match well with the theoretical analysis.2.A hybrid 10G/100G Nyquist-WDM-PON system based on independent sideband modulation method?ISB?has been proposed and demonstrated.In traditional optical modulation,the bandwidth utilization efficiency for double-sideband and single-sideband is 50%.In this thesis,the proposed ISB modulation format which can realize100%bandwidth utilization efficiency is proposed and studied.The principle is as follows:Nyquist pulse architecture makes use of the full?100%?bandwidth around a carrier by delivering independent information over upper and lower sideband.In order to develop the advantages of the system,we combine the coherent detection with high reception sensitivity and polarization division multiplexing?PDM?in the WDM-PON system.The design experimental setup is as follows:at the transmitter,the lower sidebands carry 4×10Gbit/s PM-QPSK signals;and upper sideband carries1×100Gbit/s PM-16QAM signal.3.The ROF system has become the research hotpot to address the growing bandwidth requirements,and how to produce high quality and low cost millimeter wave?mm-wave?is always research focus.In this thesis,we have proposed a novel and simple scheme for photonic frequency eightfold mm-wave generation with optical carrier suppression?OCS?based on only one single-drive Mach-Zehnder modulator?MZM?.According to the theoretical analysis,two fourth-order sidebands with suppressed optical central carrier and other sideband can be realized?frequency eightfold?by appropriately adjusting the direct current bias voltage and driving voltage of MZM.In the experiment,the 9GHz electrical RF signal is eightfold to optical mm-wave of 72GHz.The 3.5Gbit/s downlink signal is tested at the ROF user end after 20km SMF transmission.The experimental results show that the received optical power only consumes 0.9dB penalty compared to the back-to-back case at the BER of 10^-9.The eye diagram for the received signal is still very clear.The scheme can realize the frequency eightfold optical mm-wave with carrier suppressed by using only one single-drive MZM,which not only greatly reduces the cost of the system,but also makes the system more flexible and simple.