A novel auto-bias control scheme for stabilizing lithium niobate Mach-Zehnder modulator at any operating point

In this paper,we propose and experimentally demonstrate an auto-bias control scheme for stabilizing a lithium niobate（LN）Mach-Zehnder modulator（MZM）at any operating point along the power transmission curve.It is based on that the bias drift would change the operating point and result in varying the output optical average power of the Mach-Zehnder modulator and its first and second derivatives.The ratio of the first to the second derivative of the output optical average power is used in the proposed scheme as the key parameter.The experimental results show that the output optical average power of the LN MZM hardly changes at the desired operating point,and the maximum deviation of output optical average power is less than±4%.     

Simple model for a distributed feedback laser integrated with a Mach-Zehnder modulator

Presents a time-domain traveling-wave algorithm for the modeling of the large-signal dynamic response of a distributed feedback laser integrated with a Mach-Zehnder (MZ) modulator. The influence of residual optical feedback from the output of the modulator facet on the dynamic frequency chirp is studied. It is found that the difference in frequency chirp between the turn-on and -off states (i.e., adiabatic chirp) of a /spl pi//2-shifted 2 /spl times/2 MZ modulator is minimal and is independent of-the residual optical feedback. In addition, it can be shown that the presence of chirped frequency spikes (i.e., transient chirp), due to the change in refractive index as a result of the rapid variation of the bias voltage, can broaden the linewidth and distort the spectrum of the modulated optical signal. Furthermore, the possibility of doubling the modulation frequency of MZ modulators using a dual-arm dual-signal modulation format is investigated.     

Electrical and optical interactions between integrated InGaAsP/InPDFB lasers and electroabsorption modulators

Electrical and optical interactions occurring in InGaAsP/InP integrated light sources composed of DFB lasers and electroabsorption modulators have been studied. Static measurements indicated that an isolation resistance between the laser and the modulator should be as large as 100 kΩ or more in order to reduce a lasing wavelength shift associated with biasing the modulator. The useful guided light out of the modulator was about 1-2 percent of the laser output. At high frequency modulation, asymmetric sidebands were observed in dynamic spectra measured at the modulator facet, which were caused by additional modulation of the laser part. Such additional modulation was relatively large at the relaxation oscillation frequency of the laser, but it was reduced by connecting an RF bypass condenser in parallel to the laser diode and by depositing an antireflection coating at the modulator facet. After eliminating the additional modulation, an integrated device showed a high frequency response of 5.7-GHz 3-dB bandwidth and a small linewidth enhancement factor of α=0.8     

High-frequency characterization of high-speed modulators and photodetectors in a link with low-speed photonic sampling

We propose a low-speed photonic sampling for independent high-frequency characterization of a Mach–Zehnder modulator(MZM)and a photodetector(PD)in an optical link.A low-speed mode-locked laser diode(MLLD)provides an ultrawideband optical stimulus with scalable frequency range,working as the photonic sampling source of the link.The uneven spectrum lines of the MLLD are firstly characterized with symmetric modulation within the interesting frequency range.Then,the electro-optic modulated signals are down-converted to the first Nyquist frequency range,yielding the self-referenced extraction of modulation depth and half-wave voltage of the MZM without correcting the responsivity fluctuation of the PD in the link.Finally,the frequency responsivity of the PD is self-referenced measured under null modulation of the MZM.As frequency responses of the MZM and the PD can be independently obtained,our method allows self-referenced high-frequency measurement for a high-speed optical link.In the proof-of-concept experiment,a 96.9 MS/s MLLD is used for measuring a MZM and a PD within the frequency range up to 50 GHz.The consistency between our method and the conventional method verifies that the ultra-wideband and self-referenced high-frequency characterization of high-speed MZMs and PDs.     

Synthesis of photonic microwave filters based on external opticalmodulators and wide-band chirped fiber gratings

The synthesis of photonic microwave filters employing optical sources with modulation side-bands, as multimode optical sources, and chirped fiber gratings is addressed. A single wavelength laser externally modulated using electrooptical Mach-Zehnder modulators and electroabsorption modulators have been proved as optical sources with modulation sidebands. Microwave filter features such as wide range tunability, compactness, readily reconfigurable frequency responses and flexibility have been achieved and demonstrated for the proposed structure. Experimental results using both a dual-electrode Mach-Zehnder electrooptical modulator and an electroabsorption modulator as optical sources with modulation sidebands are provided to demonstrate the feasibility of this technique     

Y波导调制器残余强度调制的测量

为了便于分析Y波导调制器残余强度调制的产生机理,提出一种Y波导调制器残余强度调制的测试方法.系统采用Spartan-6系列的FPGA作为主控芯片,控制模数转换芯片ADS5560对经光电转换后的调制光信号进行采集,将采集到的数据打包后通过UART通信模式发送至PC机,获取Y波导调制器残余强度调制大小及波形信息.根据残余强度调制大小和波形信息分析模场改变引起的线性和杂散光与输出光的干涉两种机理产生的残余强度调制所占比例.测试结果表明,系统稳定性良好,对于Y波导调制器的开发有重要意义.     

A linearized optical modulator for reducing third-orderintermodulation distortion

A novel linearized optical modulator circuit with cascaded dual Mach-Zehnder interferometers has been theoretically analyzed. In this scheme, the electrical RF modulation power requirement and the modulated optical power output can be optimized at the same time. A greater than 20 dB reduction of third-order intermodulation distortion has been achieved in experiments     

Theoretical Model and Experimental Verification of 2 × 1 Mach–Zehnder EOM With Dispersive Optical Fiber Link Propagation

In this paper, we present a complete and closed theoretical model and its subsequent practical verification for a special type of Mach-Zehnder electrooptical modulator with a 2times1 optical ports configuration (two optical inputs/one output). This device present special modulation features due to its own optical structure. Its employment for modulation of millimeter and microwave signals and their further transmission through dispersive fiber is addressed, showing interesting and particular features respect to the carrier suppression effect or dispersion fading.     

Optical phase-locked loop for coherent detection optical receiver

A novel subcarrier-based optical phase-locked loop (SC-OPLL/sup /spl reg//), with off-the-shelf optical components, is presented and demonstrated. The method, based on a continuous-wave laser and optical subcarrier modulation using a standard LiNbO/sub 3/ Mach-Zehnder modulator, allows easier practical implementation than the previously proposed OPLL circuits based on laser direct modulation.     

Optimizing the bias and modulation voltages of MQW Mach-Zehndermodulators for 10 Gb/s transmission on nondispersion shifted fiber

The chirp and optical extinction ratio of a multiple quantum-well (MQW) Mach-Zehnder modulator depend on the device design and on the voltage waveforms applied to the arm electrodes. For 10 Gb/s transmission over nondispersion shifted fiber, joint optimization of the bias and modulation voltages is considered for a conventional modulator and a π-phase-shift modulator. Measured attenuation and phase constants for an optical signal propagating in the modulator waveguide are used to accurately model the Mach-Zehnder modulators. The influence of asymmetric Y-branch waveguides in the modulators is examined taking into consideration group velocity dispersion and self-phase modulation arising from the Kerr nonlinearity. When the modulators are operated with maximum optical extinction ratio, the dispersion limited transmission distance depends on the device design (phase-shift and Y-branch splitting ratio) and modulation format (dual drive or single drive). Optimization of the bias and modulation voltages reduces this dependence significantly, while also increasing the dispersion limited transmission distance     

A Photonic UWB Generator Reconfigurable for Multiple Modulation Formats

In this letter, we propose and demonstrate a simple and flexible optical ultra-wideband (UWB) pulse generator that can be reconfigured for pulse-position modulation, biphase modulation, and pulse-shape modulation. The system is implemented using a dual-drive Mach-Zehnder modulator and an electrically reconfigurable asymmetric Mach-Zehnder interferometer (AMZI). The AMZI consists of a polarization modulator (PolM), a polarization controller (PC), a section of polarization-maintaining fiber, and an optical polarizer. By adjusting the PC and the drive voltage to the PolM, the system is reconfigured to generate UWB signals with different modulation formats. An experiment is performed, which verifies the proposed technique.     

Influence of facet reflection on the performance of a DFB laserintegrated with an optical amplifier/modulator

The influence of output facet reflection on characteristics of a monolithically integrated optical device consisting of a distributed feedback (DFB) laser and an optical amplifier/modulator is analyzed. Basic equations used for the analysis are the characteristic equation for a DFB laser and the rate equations. As a result, it is known that static and dynamic properties of such optical integrated devices are seriously degraded by the optical feedback from the output facet. It is concluded that the power reflectivity of the output facet should be reduced to at least less than 0.1% for the integrated region to work as an optical amplifier and less than 0.01% as an intensity modulator     

Comparison of the propagation performance over standard dispersive fiber between InP-based /spl pi/-phase-shifted and symmetrical Mach-Zehnder modulators

We estimated and experimentally verified the output phase and intensity characteristics versus the applied voltage of an InP-based Mach-Zehnder modulator from the measured data of refractive index and loss variations specific to the phase section material (Fabry-Perot method). We have then simulated the propagation performance of a Mach-Zehnder modulator taking into account the possible phase-shift between both arm of the interferometer. In total agreement with experimental results, we show that the simple single-arm modulation scheme does not require high voltages and that the /spl pi/-phase-shifted Mach-Zehnder modulator is far more convenient for a 10-Gb/s propagation over standard dispersive fiber than a symmetrical modulator.     

基于双平行相位调制器的OFDM–ROF系统仿真

建立一种基于双平行相位调制器的OFDM-ROF实验仿真系统.在中心站采用双平行相位调制器产生双边带光载毫米波,利用光交错复用器将信号进行上边带和下边带分离,将OFDM信号通过马赫曾德尔调制器调制到一个边带上进行传输.OFDM的调制和解调部分使用MATLAB软件编写,OFDM-ROF系统实验仿真平台基于软件Optisystem进行搭建,并给出了光载OFDM信号的产生模型和系统仿真结果.实验表明,OFDM-ROF系统经过色散补偿后大幅度提高了系统的传输距离.     

利用相位和强度调制器产生高消光比超短光脉冲

提出了一种产生高消光比超短光脉冲的新方法.利用相位调制器调制连续光生成啾啁光,而后利用M-Z强度调制器的倍频调制抑制对压缩不利的啁啾部分的影响,再通过等效啁啾光纤光栅进行压缩产生光脉冲.理论和仿真结果表明,该方法可以很好地消除光脉冲的基底及减小旁辦,产生消光比大于30 dB、波形理想的光脉冲,具有很强的可实现性.最后利用实际制作的色散系数为-380 ps/nm的等效啁啾光纤光栅对该方法进行了实验验证,结果表明,在重复频率为2.5 GHz、相位调制系数为9时,可产生脉宽小于18 ps的高质量光脉冲.     

Design of mm-RoF system based on OFM technique with optimized OFDM modulation

We present the design of a novel bi-directional millimeter-wave radio-over-fiber (mm-RoF) system based on the millimeter-wave generation by optical frequency multiplication (OFM). A dual-drive Mach-Zehnder modulator is used to generate high-order optical side-modes which beat in the photo-detector, producing a 40-GHz carrier. Over 100-Mb/s orthogonal frequency division multiplexing (OFDM) modulation scheme is employed. The emphasis is on developing a mathematical model for optimizing optical modulation index to the Mach-Zehnder intensity modulator (IM) for OFDM signal with high peak-to-average power ratio which imposes a limitation on the system bit error rate (BER) performance due to the non-linearity of IM. The theoretical analysis on composite carrier to composite triple beat ratio is performed based on which extension to the system BER formula for quadrature phase shift keying/ multiple quadrature amplitude modulation (QPSK/MQAM) format is presented. The experimental proof is given in a 40-GHz RoF system at a bit rate of up to 280 Mb/s in 100-MHz bandwidth.     

电光调制器自适应偏振控制系统设计与实现

为了保持电光调制器(EOM)输入光偏振方向始终与其内部可传播模式偏振方向一致,使EOM获得良好的调制效果,提出了一种基于比例-积分-微分(PID)算法的EOM自适应偏振控制方法,理论分析并实验验证了该方法的可行性。实验结果表明,基于该方法设计的控制系统不仅能实时监测EOM输出光功率,而且能保持其输出光功率最大;与激光器和EOM输入端直接用保偏光纤连接时相比,PID偏振控制下EOM输出平均功率提高了3.08 dB,PD输出电压标准差由0.121 4降至1.237 510-4,稳定控制状态下偏振态矫正时间在ms量级。     

Frequency-modulated laser beam with highly efficient intensity stabilisation

The limitation of the amplitude modulation rejection due to the spatial modulation of the output beam of an acousto-optic modulator, which is used in an active laser beam stabilisation system when a frequency modulation of a few megahertz is applied to this modulator, is analysed. It is shown how to overcome this problem, using a single-mode optical fibre at the output of the modulator. A residual amplitude modulation of 10/sup -5/ is achieved.     

低波长漂移的电吸收调制DFB激光器

采用端面有效反射率法,从理论上计算了单片集成电吸收调制DFB激光器（Electroabsorption Modulated DFB Laser,EML）的腔面反射率、耦合强度（κL）对其波长漂移的影响.同时在实验中通过改变腔面的反射率来验证计算结果.理论与实验的结果表明：为提高EML的模式稳定性,必须减小调制器一端的反射率,同时增加DFB激光器的κL.最终我们采用选择区域生长（Selective Area Growth,SAG）的方法,制作了低光反馈出光面的单脊条形EML,在2.5Gb/s的非归零(NRZ)码调制下,经过280km的标准光纤传输后,没有发现色散代价.     

基于双平行马赫曾德尔调制器和受激布里渊散射效应的十倍频毫米波信号生成

提出了一种基于双平行马赫-曾德尔调制器(DPMZ M)和受激布里渊散射(SBS)效应的10倍频mm 波信号生成方案,具有覆盖频段高和频谱纯度高等优点。在本文方案中,低频率的射频(RF )信号通过DPMZM 对激光器发出的光波进行调制,调节直流偏置电压,使DPMZM的主调制器和两个子调制器均 工作在最小传 输点(MITP),抑制光载波和偶数边带,进一步调节两个子调制器的调制深度和移相器的相 移,抑制一阶和 七阶边带,留下三阶和五阶边带,然后利用SBS效应进行布里渊边带滤波滤除三阶边带,仅 保留五阶边带, 再经光电探测器(PD)拍频即可获得10倍频mm波信号。通过仿真实验,以10 GHz的R F信号为驱 动信号,得到了100GHz的mm波信号,验证了方案的可行性。