Recirculating frequency shifter(RFS)can generate stable multi-carrier,but the carrier-to-noise-ratio(CNR)is limited because noise is accumulated round by round in the recirculation loop structure.A modified RFS with a delay interferometer(DI)is proposed in this paper.The DI can suppress the accumulated noise,and enhance the CNR of multi-carrier.The principle of the generation of high quality multi-carrier based on an RFS with DI is analyzed theoretically.50 stable carriers with spacing of 10.7 GHz are successfully generated.The flatness of 50 stable carriers is 3 dB,and the CNR is 43 dB which is increased by 3 dB compared with the structure without DI.
An optical bandpass filter(OBF) is an important element whose properties considerably influence the output performance of a single side band multicarrier source based on a re-circulating frequency shifter.The influence of the OBF in the loop on the output spectrum is theoretically analyzed.Numerical simulations and experiments are also carried out.Results show that the steepness and deepness of a nonflat-top filter influence the stability of the spectrum of an output multicarrier.To obtain multicarrier output with tone to noise ratio(TNR) >26 dB and error vector magnitude(EVM) <0.25,the steepness ratio of the filter should be greater than 0.75 and deepness should be larger than 0.99.
The laser source is an important element whose properties have influence on the output performance of single sideband(SSB) optical comb based on recirculating frequency shifter(RFS).The theoretical and experimental results show that the tone-to-noise ratio(TNR),flatness,and stability of optical comb improve using laser source with narrower linewidth.In order to obtain the optical comb with TNR larger than 42 dB and degree of stability(DOS) smaller than-6.7 dB,external cavity laser(ECL) with linewidth from 100 kHz to 1 MHz is a trade-off choice.
IMS(IP Multimedia Subsystem)作为下一代网络的核心网的标准架构,在IP多媒体应业务的开发方面,受到了越来越多的关注。本文在IMS呈现的基础上,实现了基于IMS呈现的社交网络管理系统(Social Network Management System based on the IMS Presence),它丰富了传统电信IMS呈现的业务能力,将手机地址本扩展为社交网络,丰富了好友间互操作,扩展了群组聊天。本文从业务角度出发,分析了IMS呈现的可扩展性,设计了基于IMS呈现的社交管理系统的架构和功能实体,详细阐述了系统功能实现的关键点,并实现了系统与媒体的接口,最后以单个用户操作、一对一好友操作和群组操作为例,具体实现了相应的功能。
