Super-PON系统中SRS串扰的仿真分析

Simulation Analysis of SRS Crosstalk in Super-PON System

超无源光网络(Super-PON)凭借低成本、长距离传输、支持大量用户等优点逐渐成为研究热点。然而,在多波长长距离传输系统中,Super-PON上下行之间及Super-PON与以太网无源光网络(EPON)、10G以太网无源光网络(10G-EPON)系统共存时,皆面临着受激拉曼散射(SRS)串扰的挑战。因此,为了满足Super-PON系统的高链路预算需求,通过VPI仿真软件分别测量了在上述各种组合方式下系统所受到的SRS串扰。结果表明:将C波段作为下行并将L波段作为上行进行传输时,信号所受到的功率损伤最小,为0.43 dB(上下行单波长入射光功率分别为10 dBm和13 dBm),因此这是Super-PON系统的最佳波段分配方案。此外,当Super-PON与EPON上行、10G-EPON下行系统共存时,SRS效应给它们带来的影响很小,基本可以忽略不计。

Objective Super-passive optical network(Super-PON)has gradually become a hot topic due to its advantages of low cost,long-distance transmission,and supporting a large number of users.While in the multi-wavelength and longdistance transmission system,the upstream(US)and downstream(DS)of the Super-PON system which coexists with Ethernet passive optical network(EPON)and 10G-EPON systems are all confronted with the challenge of stimulated Raman scattering(SRS)effect.The SRS effect causes a transfer of energy from the shorter wavelengths(pump channels)to the longer wavelengths(Stokes channels)when multiple wavelengths are simultaneously transmitted in the standard single mode fiber(SSMF),which reduces the transmission performance of the system.Therefore,in order to satisfy the high power budget requirement of the Super-PON system,the VPI simulation software is adopted to measure the SRS crosstalk of systems under the above combinations.Methods Due to the high input power involved,the stimulated Brillouin scattering(SBS)effect can affect the transmission performance of the Super-PON system.Firstly,in order to accurately measure the power impairment of signals caused by the SRS effect,the threshold optical power of SBS is measured by an experiment,which is 13 dBm.Second,in the Super-PON system,the total number of wavelengths of US and DS is 32.Owing to the limitation of experimental conditions,the influence of SRS effect on 10 Gbit/s non-return-to-zero(NRZ)signals through a 50 km SSMF transmission system is investigated by simulation where the following two cases are considered.The one case is using C-band for US and L-band for DS,and the other case is using C-band for DS and L-band for US.In the Super-PON system,the significant difference between US and DS transmissions is that the DS signals are first amplified by an erbium-doped fiber amplifier(EDFA)and then transmitted through a 50 km SSMF,while the US signals are first transmitted through a 50 km SSMF and then amplified.Finally,when the Super-PON US and DS coexist with EPON US and 10G-EPON DS systems,the power penalty of Stokes channels induced by SRS is measured.Results and Discussions When using C-band for US and L-band for DS and setting the input optical powers of each US and DS channels to 4 dBm and 13 dBm,respectively,the maximum power impairment of US and DS signals caused by SRS is 2.94 dB and 0.73 dB,respectively(Fig.5).At the same time,the maximum power impairment of DS signals is 0.43 dB when using C-band for DS and L-band for US and setting the input optical powers of each US and DS channels to 10 dBm and 13 dBm,respectively(Fig.6).In addition,when the single wavelength optical power of US channel is set to 4 dBm,the sensitivity penalty of Ch-16 of DS transmission caused by SRS crosstalk is about 0.3 dB at a bit error rate(BER)of 1.0 × 10^(-2),and the received optical power achieves-28 dBm,which can satisfy the 41 dB power budget[Fig.7(a)].By comparison when C-band used as DS transmission and L-band used as US transmission,one can distinguish the optimal band-allocation scheme for the Super-PON system.When using C-band for DS and L-band for US in the Super-PON system,first we analyze the power impairment between Super-PON US and 10G-EPON DS,and it is obvious that the power impairment of 10G-EPON DS signals is very small.Even if the input optical power of each Super-PON US channel(Stokes channel)is increased to 13 dBm,the pump signals have the maximum power impairment of only 0.0098 dB[Fig.8(a)].Second,the maximum power impairment of EPON US signals is 0.0186 dB when EPON US and Super-PON US signals are together transmitted and the input power of each Super-PON US channel is set to 13 dBm[Fig.8(b)].Third,when the Super-PON DS and EPON US are transmitted through a 50 km SSMF and the input power of each Super-PON DS is configured as 13 dBm,the maximum power impairment of EPON US signals is 0.85 dB[Fig.9(a)].However,the transmission distance of the EPON system is generally 20 km.Therefore,in this combination,the power impairment caused by SRS crosstalk is reduced,which can be ignored.Finally,the maximum power impairment of the Super-PON DS signals induced by SRS is 0.31 dB when the Super-PON DS and 10G-EPON DS(the input power of each 10G-EPON DS channel is set to 13 dBm)are simultaneously transmitted in the optical fiber[Fig.9(b)].Conclusions In this paper,the influence of SRS crosstalk on the Super-PON system is investigated by simulation in which two cases are considered.The one case is using C-band for US and L-band for DS,and the other case is using C-band for DS and L-band for US.The simulation results show that when using C-band for DS and L-band for US,the power impairment of signals is the smallest,which is 0.43 dB(the single wavelength input optical powers of US and DS are 10 dBm and 13 dBm,respectively).Therefore,this combination mode is the best band-allocation scheme for the Super-PON system.Besides,we simulate the power impairment of signals caused by SRS when the Super-PON US and DS coexist with EPON US and 10G-EPON DS systems,and the results show that the SRS effect has little influence on them which can be basically ignored.