Bifurcated overtones of one-way localized Fabry-Pérot resonances in parity-time symmetric optical lattices

Since the first observation of parity-time(PT) symmetry in optics, varied interesting phenomena have been discovered in both theories and experiments, such as PT phase transition and unidirectional invisibility, which turns PT-symmetric optics into a hotspot in research. Here, we report on the one-way localized Fabry-Pérot(FP) resonance, where a welldesigned PT optical resonator may operate at exceptional points with bidirectional transparency but unidirectional field localization. Overtones of such one-way localized FP resonance can be classified into a blue shifted branch and a red shifted branch. Therefore, the fundamental resonant frequency is not the lowest one. We find that the spatial field distributions of the overtones at the same absolute order are almost the same, even though their frequencies are quite different.     

Analysis of the blackbody-radiation shift in an ytterbium optical lattice clock

We accurately evaluate the blackbody-radiation shift in a171 Yb optical lattice clock by utilizing temperature measurement and numerical simulation. In this work. three main radiation sources are considered for the blackbody-radiation shift, including the heated atomic oven, the warm vacuum chamber, and the room-temperature vacuum windows. The temperatures on the outer surface of the vacuum chamber are measured during the clock operation period by utilizing seven calibrated temperature sensors. Then we infer the temperature distribution inside the vacuum chamber by numerical simulation according to the measured temperatures. Furthermore, we simulate the temperature variation around the cold atoms while the environmental temperature is fluctuating. Finally, we obtain that the total blackbody-radiation shift is -1.289(7)Hz with an uncertainty of 1.25×10~(-17) for our ~(171)Yb optical lattice clock. The presented method is quite suitable for accurately evaluating the blackbody-radiation shift of the optical lattice clock in the case of lacking the sensors inside the vacuum chamber.     

适用于高阶QAM解调的载波恢复算法及其实现验证

高阶正交幅度调制（QAM）系统中,随着QAM信号阶数的提高,频偏和相偏对系统解调性能的影响越敏感,其对同步性能的要求也越来越高。因此,必须在接收端对系统中的频偏和相偏进行更精确的补偿,使得接收端与发送端的载波信号达到同频同相,来提高解调系统的性能。本文首先简单介绍了两种常用两种面向判决的载波相位恢复算法,并利用MATLAB／Simulink为该算法搭建了系统仿真模型进行分析,然后给出了具体的实现方法并对其性能进行了分析。仿真结果表明,面向判决的载波恢复算法实现简单,稳态时抖动较小,非常适用于高阶QAM解调系统。     

高阶QAM载波恢复的FPGA设计实现

本文介绍了适用于高阶QAM载波恢复的极性判决算法。该算法利用极性判决器捕获大概频偏,再利用DD算法跟踪并进一步纠正频偏,减小抖动误差,从而相较传统算法具有更好的频偏捕获能力和健壮性。同时,该算法能对两种算法模式进行自动切换以达到精确的频偏纠正目的。本文采用实用有效的MSE方法对这两种算法模式进行自动转换控制,并以128QAM为例对该算法进行MATLAB仿真分析。最后在FPGA平台上实现了128QAM的载波恢复算法,并且效果理想,有很好的移植性。     

400Gbit/s光模块的技术浅析

随着IEEE 802.3ba标准的制定完成,100Gbit/s以太网技术已经得到验证并标准化。400Gbit/s以太网和OTN(光传输网)标准成为了下一步人们关注的焦点。文章基于现行100Gbit/s标准,讨论了双载波偏振复用的16QAM(正交幅度调制)、阵列相干探测等以太网和OTN的400Gbit/s光网络模块相关技术。     

基于Bigband平台数字电视增值业务系统架设初探

简要分析了数字电视后整转时代增值业务的现状和困惑,提出了一种基于Bigband平台新一代数字电视增值业务体系,重点阐述了系统建设方案,并给出了系统的经典应用和升级意见。     

有线模数混合传输信号的测量

在模拟信号和数字信号混合传输的情况下,通过对两种信号的原理及测量方法进行分析,熟悉并掌握信号测量的各项指标,通过实例分析网络中出现故障的原因及排除的方法,熟练掌握网络参数与仪器的使用技能,以进一步提高维护水平,保证电视安全播出。     

ADS在16QAM通信系统中的应用

介绍了16QAM通信系统的概念、工作原理以及利用ADS软件建立通信系统模型的方法,并进行了系统分析。在ADS中,对调制信号的表示方法、脉冲形成、通道滤波、频谱分析——数值频谱和频率频谱、客户化调制等技术进行了仿真,实现了通信系统的模拟。     

光OFDM系统中削波噪声的建模与研究

针对光正交频分复用(OFDM)系统中峰值平均功率比(PAPR)较高的缺点,研究了削波法降低PAPR的原理;根据这一原理,通过大量数据分析计算,建立了基于MQAM调制下光OFDM系统中的削波噪声模型;由所建立的模型,直接计算得出不同调制下光OFDM系统削波后的误符率。仿真结果表明,每种进制调制下,根据本文建立的削波噪声模型与OFDM具体系统模型仿真所得到的两条曲线基本吻合,并且这两条曲线在不同削波比下的最大均方误差(MSE)不超过1.26×10-2。这充分论证了所建立的削波噪声模型的可行性与适用性。     

16‐QAM‐Based Highly Spectral‐Efficient E‐band Communication System with Bit Rate up to 10 Gbps

This paper presents a novel 16‐quadrature‐amplitude‐modulation (QAM) E‐band communication system. The system can deliver 10 Gbps through eight channels with a bandwidth of 5 GHz (71‐76 GHz/81‐86 GHz). Each channel occupies 390 MHz and delivers 1.25 Gbps using a 16‐QAM. Thus, this system can achieve a bandwidth efficiency of 3.2 bit/s/Hz. To implement the system, a driver amplifier and an RF up‐/down‐conversion mixer are implemented using a 0.1 µm gallium arsenide pseudomorphic high‐electron‐mobility transistor (GaAs pHEMT) process. A single‐IF architecture is chosen for the RF receiver. In the digital modem, 24 square root raised cosine filters and four (255, 239) Reed‐Solomon forward error correction codecs are used in parallel. The modem can compensate for a carrier‐frequency offset of up to 50 ppm and a symbol rate offset of up to 1 ppm. Experiment results show that the system can achieve a bit error rate of 10^?5 at a signal‐to‐noise ratio of about 21.5 dB.