瑞利布里渊光时域分析系统中电光调制器的理论模型与实验研究

瑞利布里渊光时域分析系统能够以非破坏性方式实现单光源、单端工作,利用强度型电光调制器同时调制脉冲基底和脉冲信号是获得该系统所需连续光和脉冲光的关键技术.本文理论分析、仿真和实验研究了一种将脉冲信号输入到电光调制器偏置端、微波信号输入到电光调制器射频端同时调制脉冲基底和脉冲信号的新调制方法,探讨了电光调制器用于瑞利布里渊光时域分析系统时的最佳工作点问题.结果表明,当调制脉冲基底和脉冲时分别将电光调制器偏置在传输曲线的谷点和峰点,并根据实际系统的组成和性能指标要求选择合适的微波调制信号幅度,可获得满足瑞利布里渊光时域分析系统要求的连续光和脉冲光.本文的研究结果为瑞利布里渊光时域分析系统的最佳化设计提供了理论依据.     

瑞利布里渊光时域分析系统中电光调制器的理论模型与实验研究

瑞利布里渊光时域分析系统能够以非破坏性方式实现单光源、单端工作,利用强度型电光调制器同时调制脉冲基底和脉冲信号是获得该系统所需连续光和脉冲光的关键技术.本文理论分析、仿真和实验研究了一种将脉冲信号输入到电光调制器偏置端、微波信号输入到电光调制器射频端同时调制脉冲基底和脉冲信号的新调制方法,探讨了电光调制器用于瑞利布里渊光时域分析系统时的最佳工作点问题.结果表明,当调制脉冲基底和脉冲时分别将电光调制器偏置在传输曲线的谷点和峰点,并根据实际系统的组成和性能指标要求选择合适的微波调制信号幅度,可获得满足瑞利布里渊光时域分析系统要求的连续光和脉冲光.本文的研究结果为瑞利布里渊光时域分析系统的最佳化设计提供了理论依据.     

偏置M-Z调制器构建2-bits电光模数转换相位编码方法的分析与模拟

为了降低电光相位编码器功率消耗和解决内部M Z调制器一致性要求高的问题,利用2个偏置M Z调制器构成了用于电光模数转换的2 bits电光相位编码器。理论分析了偏置M Z调制器实现2 bits电光相位编码的方法、特点和性能。仿真结果验证了采用偏置M Z调制器构成的2 bits相位编码方法可行性,并实现了对1 GHz模拟电信号的采样速率12 GSa/s模数转换。分析和仿真结果表明,采用该方法对调制器一致性要求低,对输入信号功率要求低于0.32 W。分析结果表明,调制器直流漂移不影响最低位量化结果,引起最高位量化结果的判决模糊低于3.8%。     

幅度调制器对宽带低相干光时频特性的影响

通过改变马赫-曾德干涉型幅度调制器的射频系数和偏置电压,调制光脉冲的强度。研究了幅度调制器对宽带低相干光时频特性影响的规律,分析调制后的光脉冲时域波形分布、光谱和复相干度模值曲线,结果表明,射频系数对光脉冲的光谱成分和时间相干性无明显的调制,射频系数存在最佳工作区间使得输出光脉冲的波形保真度最佳。当偏置电压处于半波电压时,光脉冲的时域波形保真度最好,时间相干性最低,但光谱成分会缺失。理论仿真了调制器的臂长差、偏置电压对宽带低相干光频域特性的影响,与由实测光谱计算出调制器的臂长差,实验结果进行了对比,结果基本符合。由于实际的电光重叠积分因子随加载电压值变化,因而模拟与实测结果存在误差,但研究得出的规律将为低相干脉冲精密整形系统提供更为明确的方向。     

基于电吸收调制器的解复用器窗口特性分析及优化

数值模拟了基于电吸收调制器 (Electro absorptionmodulator,EAM)解复用器的开关窗口特性 ,在考虑邻道串扰和强度抖动 (由同步偏离和时间抖动导致 )的光时分复用数值模型中对解复用信号的误码率进行分析。数值模拟结果表明 ,电吸收调制器的窗口特性 (消光比和窗口宽度 )满足 4× 10Gb/s的光时分复用通信系统中解复用器的要求 ;在小的偏置电压下 ,邻道串扰和解复用器的透过率特性必须仔细考虑以达到最小的误码率 ;在大的偏置电压下 ,较大的射频幅度将会使解复用信号误码率最小     

双音调制下星上微波光子系统的交调失真分析

马赫-曾德尔调制器的非线性会严重恶化星上微波光子系统的性能。建立了包括光源、马赫-曾德尔调制器和光电探测器的双音调制理论模型,利用傅里叶级数展开、傅里叶变换和Gegenbauer加法定理,推导出了调制器非线性失真的严格通用解析解。根据该解析解,可精确地预计不同调制方式下星上微波光子系统的非线性失真,优化系统性能。分析结果表明,双边带和单边带调制条件下,将调制器输出信号保留至二次谐波能较好地近似计算三阶交调失真比和三阶交调截点,三阶交调失真比随调制系数的增大先增大后减小。当调制系数小于1.4674时,单边带调制三阶交调失真比至少比双边带调制小6dB,适合于星上微波光子系统的应用。     

一种倍频因子及输出相位连续可调的微波光子移相系统

提出一种倍频因子连续可调,且相位连续变化的微波光子移相系统.系统主要由两个集成双偏振双平行马赫增德尔调制器组成,在不使用光滤波器的情况下,调节双平行马赫曾德尔调制器及相位调制器的射频驱动和直流偏置电压,生成二倍频,三倍频,…,六倍频微波信号,同时实现输出微波信号相位0～360°连续可调.仿真结果表明,当射频信号频率为10GHz时,可分别产生频率为20、30、40、50、60GHz的微波信号.调节相位调制器的直流偏置电压与半波电压比值从-1到1变化时,对应微波信号的相位从-180°到180°变化.此外,分析了调制器消光比对输出微波信号光载波抑制比和电杂散抑制比的影响,以及90°电桥相位平衡对微波信号相位漂移和幅度波动的影响.     

同相正交硅基光调制器的自动偏置电压控制技术

描述了基于同相正交硅基光调制器的自动偏置电压控制算法理论及实现方案。首先比较了硅基光调制器与传统铌酸锂调制器的调制特性,结合同相正交硅基光调制器模型推导出了调制器输出光信号与电场信号的函数关系式,根据此关系式提出了一种基于正弦dither信号注入调制器偏置工作点并解析调制器内置低带宽监控光电二极管反馈信号频域参数的控制方案,并通过数值仿真验证方案的可行性;然后搭建自动偏置电压控制算法的测试平台,通过测试平台得出不同偏置电压条件下I(in-phase)路、Q(quadrature-phase)路与Phase(outer-phase)路调制器内置监控光电二极管的反馈信号波形,并将测试结果与仿真数据进行对比,对比结果验证了本研究假定的同相正交硅基光调制器光电传递函数模型的准确性;最后测试了128 Gb/s双偏振正交相移键控调制格式下偏置电压控制算法的精度,并通过矢量幅度误差指标得到算法所引入的光信噪比代价。     

基于Volterra滤波器的参量阵扬声器互调失真补偿研究

针对单边带调制方法预处理的参量阵扬声器系统在复杂信号输入情况下存在明显互调失真的问题,引入Volterra滤波器模型和简化的一维Volterra滤波器模拟了其互调失真。设计了相应的逆滤波器,并对其抑制系统互调失真的性能进行了实验对比。结果表明,所设计的逆滤波器都能有效降低系统的互调失真,而后者具有较低的计算复杂度。     

两路输入前置光放大星间微波光子链路优化

考虑到星间微波光子链路传输损耗大且多路微波信号之间交调干扰严重,利用前置光放大来提高链路的信号噪声失真比RSNDR。建立了两路输入前置光放大星间微波光子链路模型,推导出了RSNDR的解析表达式。通过优化马赫-曾德尔调制器的直流偏置相移,使得在给定输入射频信号功率条件下RSNDR最大,并进一步分析了前置光放大器参数对最优直流偏置相移和RSNDR的影响。仿真结果表明,前置光放大改变了影响RSNDR的主要因素,使信号放大的倍数大于噪声和三阶交调(IM3)放大的倍数,从而提高了链路的RSNDR。当前置光放大器增益为20dB、噪声系数为3dB时,最优的RSNDR比不加前置光放大器时提高24dB。前置光放大器增益和噪声系数对最优的RSNDR影响很大,而对最优的直流偏置相移几乎无影响。     

Analog Performance of Multiple-quantum-well Electroabsorption Modulator

Linearity is an important property of optical devices in analog communication systems. In this paper, we study the 3rd-order intermodulation distortion (IMD3) of an InP/InGaAsP multiple-quantum-well (MQW) traveling-wave type electroabsorption modulator (TW-EAM). We observe that dips in the measured IMD3 results are different from those by general transfer curve of electroabsorption modulators (EAMs). In order to verify it, we analyse the phenomena by using the absorption coefficients according to a wavelength and a bias voltage. Thus, we can see that the dips result from the quantum-confined Stark effect (QCSE). We propose the method to enhance linearity of MQW-EAMs by using this effect in addition to the E/O response     

无滤波高倍频光载毫米波生成技术

提出了一种无滤波的高倍频光载毫米波生成方案.该方案未使用相关的光/电滤波器就可16倍频的毫米波信号.整个系统采用三平行的马赫-曾德尔调制器结构和单个马赫-曾德尔调制器级联,通过调整系统的参数可以很好地抑制所有冗余光边带,只留下高质量的8阶光边带,无需任何光/电滤波器就能够得到16倍频的高质量毫米波信号.另外,详细分析了系统的工作原理,并通过仿真验证了调制深度、消光比、移相器偏移以及调制器偏压对系统的影响.研究结果表明将2 Gbit/s的非归零码型数据与10 GHz的射频信号混频后作为马赫-曾德尔调制器的驱动信号,系统经过50 km光纤传输后的链路功率代价为1.0 dB,具有良好的传输性能.该方案对于无滤波的高倍频毫米波生成有一定的参考价值.     

Simulation of Third-Order Intermodulation Distortion Suppression Incorporating Dual-Parallel Mach–Zehnder Modulator in a CR-SSB Modulation

A novel scheme is proposed to enlarge the spurious free dynamic range (SFDR) of microwave photonic (MWP) link by using dual-parallel Mach–Zehnder modulator, which modifies the single sideband signal and replaces the optical carrier with an unmodulated one to remove the optical main sources of third-order intermodulation distortion (IMD3). Simulation results show that the IMD3 and fifth-order intermodulation distortion can be suppressed greatly even when the modulation depth increases to a high value, and the link is limited by seventh-order intermodulation distortion and the SFDR is improved by 34.2 dB Hz in a 1-Hz bandwidth. The error vector magnitude of the MWP link with the proposed scheme is improved significantly for the transmitted 1-Gbit/s 16- quadrature amplitude modulation (QAM) signal.     

Generation of linearized optical single sideband signal for broadband radio over fiber systems

We propose a new scheme to generate broadband linearized optical single-sideband （OSSB） signal for radio over fiber systems. By using an unbalanced dual parallel Mach-zehnder modulator （DPMZM） followed by optical filtering, a linearized OSSB signal is obtained. With coherent detection, radio frequency （RF） signal can be recovered with simultaneously suppressed second-order distortion and third-order intermodulation. This scheme can be used to realize broadband systems with wide dynamic range.     

Switchable down-, up- and dual-chirped microwave waveform generation with improved time-bandwidth product based on polarization modulation and phase encoding

A switchable down-, up- and dual-chirped microwave waveform generation technique with improved time-bandwidth product (TBWP) is proposed and demonstrated based on a dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM) cascaded with a polarization modulator (PolM). By properly controlling the phase shifts of the radio frequency signals applied to the DP-DPMZM, switchable down-, up- and dual-chirped waveforms with simultaneous frequency and bandwidth doubling can be generated. To enlarge the TBWP further, splitting parabolic signal and phase-encoding splitting parabolic signal are used to drive the PolM for the enhancement of bandwidth and time duration. Numerical results demonstrate the generation of down-, up- and dual-chirped microwave waveform with TBWP of 8, 160 and 10240. The proposed method may find applications in future multifunction radar systems due to the high performance and flexibility.     

Postcompensation for nonlinearity of Mach-Zehnder modulator in radio-over-fiber system based on second-order optical sideband processing

A postcompensation technique for nonlinearity of a Mach-Zehnder modulator in a radio-over-fiber (ROF) system is proposed and experimentally demonstrated based on second-order optical sideband processing and optical carrier band attenuation. The phase of the second-order optical sideband is shifted to suppress the third-order intermodulation distortion (IMD3) in a direct detection ROF link. The optical carrier band is attenuated to make two kinds of origins of IMD3 have equal intensity and cancel each other out. A spurious-free dynamic range of 124.8 dB·Hz(2/3) is achieved, which is about 25 dB more than that without compensation.     

Modeling the pressure dependence of DC bias voltage in asymmetric,capacitive RF sheaths

A semianalytical model for capacitively coupled radio frequency (RF) sheaths of asymmetric (unequal electrode area) systems has been developed. It can be applied in the high-frequency (ω > ω _pi) regime at different pressures. An analytical approximation to the pressure-dependent ion density profile is used. The time-varying electric field and potential within the sheath are obtained by solving Poisson's equation. The current balance and zero net DC current conditions are applied to solve for the RF sheath parameters and DC bias voltage. The DC voltage ratio between the powered and grounded electrode sheaths increases as the pressure decreases, which results in a larger DC bias voltage at lower pressures     

A Low-Cost 16 Quadrature Amplitude Modulation Direct-Detection–Orthogonal Frequency-Division Multiplexing Radio-over-Fiber System Using Low-Cost Direct-Modulation Laser to Generate Optical mm-Wave

Abstract

This article demonstrates a novel scheme to generate 16 quadrature amplitude modulation orthogonal frequency-division multiplexing signals for radio-over-fiber systems using a low-cost direct-modulation laser to generate an optical millimeter-wave. Mathematical analysis of that system is also investigated. The fiber Bragg grating is employed because the repetitive frequency of the radio frequency source and the bandwidth of the optical modulator are largely reduced, and the architecture of the radio-over-fiber system is simpler. Because no expensive broadband external modulator is used, the overall system is considered a low-cost solution. The simple structure and low cost of the radio-over-fiber system is attractive for the future cost-effective systems.