Research On Key Technologies Of Large Capacity Optical Interconnection For Data Centers

With the rapid development of mobile Internet,cloud computing,metaverse and other applications,data centers are facing explosive traffic growth,and the improvement of transmission capacity in short-distance scenarios is the key research direction of researchers.Cost and power consumption are the main factors that limit the transmission capacity of short-distance optical transmission systems in data centers,so the intensity-modulated direct detection(IMDD)scheme has been mainly used.Discrete Multitone Modulation(DMT)technology,as a direct detection scheme,has the advantages of high spectral efficiency and channel adaptation,but it also faces high peak-to-average power ratio(PAPR)and device non-linear when used in data centers.The combination of space division multiplexing(SDM)technology based on multi-core fiber(MCF)and DMT can multiply the port density and transmission capacity,but in practical applications,it faces random fluctuation and monitoring problems of inter-core crosstalk(ICXT),it is urgent to develop an ICXT monitoring technology within transmission system.With the increase in traffic demand and the limitation of device bandwidth,the IMDD solution is difficult to meet the transmission rate of more than 200Gb/s on a single wave,thus the coherent optical transmission technology with high sensitivity and high spectral efficiency sinks into the data center short-distance interconnection scenario has receiver extensive attention,but how to significantly reduce the complexity of digital signal processing(DSP)on the basis of maintaining the spectral efficiency of coherent optical communication faces a huge challenge.In response to the above challenges,the thesis conducts research on optical interconnection transmission technology for short-distance high-capacity data centers.The main research contents and innovative achievements include:(1)The complete theoretical model of DMT transmission system is introduced as the research basis for the follow-up work.Several schemes of peak-to-average power ratio reduction(PAPR)are compared and analyzed,and a scheme for power optimization of DMT signal training sequence is proposed for the scenario where the signal power of IMDD system is limited.The experimental results of 20 GBaud 16-quadrature amplitude modulation(QAM)signal transmitted 25.2km standard single mode fiber(SSMF)show that up to 0.8 d B receiver sensitivity improvement is achieved.(2)The influence of the precoding matrix on the DMT frequency domain symbols is studied,and we discovered that precoding induces high correlation between time domain signal and frequency domain symbols of DMT,so that the recovered frequency domain symbols reflect the nonlinear effects on the time domain signals.The noise relative strength ratio(NRR)and symbol error rate(SER)are introduced to evaluate the nonlinear noise distribution degree of the precoding DMT system due to the nonlinear influence of the modulator.Probabilistic constellation shaping(PCS)and geometric shaping(GS)are introduced into the precoded DMT system.Through simulation and experimental verification,compared with the DMT system without the constellation shaping scheme,it achieves 2～4 d B and 0.8～0.9 d B ROP sensitivity improvement,respectively.(3)For the inter-core crosstalk(ICXT)that are difficult to monitor in multi-core optical fiber transmission systems,a MCF crosstalk monitoring scheme based on precoded DMT is proposed.Monitoring the ICXT distributed within the signal bandwidth at the microsecond level while the signal is being transmitted is realized.In addition,the corresponding relationship between the monitoring crosstalk value and the system bit error rate(BER)is analyzed,and a system performance evaluation scheme based on the monitored inter-core crosstalk is proposed,which helps warning the system failure according to the monitored ICXT.(4)Aiming at the problem of LO power and polarization fading in the self-homodyne coherent detection system,an injection-locked self-homodyne coherent detection architecture is proposed.At the receiving end,the excellent local oscillator light with stable power,determinate polarization state,and frequency and phase consistent with the signal optical carrier is recovered.The self-homodyne coherent detection can be carried out with the recoverd local oscillator light.While no frequency offset recovery(FOE)and expensive narrow linewidth lasers are used,it is verified by experiments that 50 G baud polarization division multiplexing 16-QAM can be realized with ROP of-27 d Bm at optical back to back condition.