Interrogation of an integrated optic modulator over a low-birefringence fiber using polarization tracking

The remote operations of an integrated optic Mach-Zehnder modulator via a low-birefringence fiber link using an input polarization control scheme is demonstrated. The polarization tracking scheme actively maintains the state of polarization arriving at the modulator in the state required for optimum operation of the device. As the feedback signal is determined by the overall optical throughput of the modulator, no modulation is itself required for the modulator to be set for optimum performance.<>     

A DC to multigigabit/s polarization-independent modulator based ona Sagnac interferometer

A broadband, electrically controlled polarization-independent intensity modulator (PLM) based on a Sagnac interferometer is presented. Influences from asymmetric modulation and traveling wave effects are analyzed and methods to eliminate these effects are proposed. Compared to Mach-Zehnder interferometer-based modulators, this modulator is independent of the input polarization state and less sensitive to ambient perturbations due to its reciprocity property. A prototype modulator operating at 1 and 2.488 Gb/s modulation rates is demonstrated     

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.     

Rapid direct fabrication of active electro-optic modulators in GaAs

We have developed several direct-write laser processing techniques to masklessly fabricate prototypes of waveguiding devices in GaAs/AlGaAs substrates. This flexible technology allows the rapid, successive fabrication and testing of devices such as modulators. Previously, we had reported use of this technology to fabricate low-loss single-mode passive waveguiding structures and devices. In this paper, we report the fabrication of active electro-optic modulators. These devices include an electro-optic polarization modulator, an integrated amplitude modulator consisting of a polarization modulator and an on-chip polarizer, and an integrated Mach-Zehnder interferometer     

Modulation and demodulation techniques in optical heterodyne PSKtransmission systems

Modulation and demodulation techniques are described for an optical PSK heterodyne transmission system operating at 560 Mb/s and 1.2 Gb/s. Performance limitations affecting the receiver sensitivity in a 1.2-Gb/s DPSK system, such as laser phase noise, phase modulation depth, IF center frequency deviation, and local laser power, are studied. High receiver sensitivities for PSK systems were achieved. The applicability of the Mach-Zehnder modulator as a phase modulator for 1.2-Gb/s DPSK is also demonstrated. A 1.2-Gb/s DPSK transmission of over 100 km, using polarization diversity with novel polarization-insensitive automatic frequency control in an attempt to overcome signal fading caused by polarization fluctuation in the transmitting fiber, is also described. A receiver sensitivity of less than -42.8 dBm and varying within 1.4 dB for all states of polarization was achieved. A multichannel high-definition TV (HDTV) transmission experiment using a DPSK polarization-diversity tunable receiver is described     

马赫曾德尔调制器偏压控制技术研究

介绍了马赫曾德尔调制器的工作原理及传输曲线随温度漂移引起偏置工作点改变的现象。理论推导出基于谐波分析的马赫曾德尔调制器偏压工作点稳定控制方法,同时通过导频信号来度量偏压工作点的漂移量。设计出基于FPAG的马赫曾德尔调制器偏压控制硬件模块,通过记录接入该模块前后PIN光电二极管电压及马赫曾德尔调制器输出光功率的变化情况,最终证实该偏压控制模块可以实现稳定马赫曾德尔调制器工作点的目的。     

Zn indiffusion waveguide polarizer on a Y-cut LiNbO3 at1.32-μm wavelength

A polarization-dependent loss measurement of Zn indiffusion (ZI) waveguide on a Y-cut LiNbO₃ substrate is firstly reported. The measured results show that the waveguides support either a single extraordinary polarization or both extraordinary and ordinary polarizations depending on the fabrication process parameters. For the single extraordinary polarization waveguide, the measured propagation loss at 1.32-μm wavelength is 0.9 dB/cm and the best measured polarization extinction ratio is 44 dB at a distance of 1.5 cm from the input end, which are quite good for being a waveguide polarizer. Moreover, the voltage-length product measured for the ZI Mach-Zehnder modulator shows that the substrate electrooptic coefficient is not degraded     

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.     

High Extinction Ratio Mach–Zehnder Modulator Applied to a Highly Stable Optical Signal Generator

Research into optical modulators has made remarkable progress in recent years. This paper discusses the possibility of applying the high extinction ratio optical modulator to a high-stability and high-frequency (over 100 GHz) optical reference signal generator. High-frequency reference signals are generated by a highly stable optical two-tone generator, which is used for high-rate communication and astronomical application. One method to generate two optical signals is producing them from a pair of laser sources using an optical phase-locked loop for feed back control; however, the optical phase-locked loop has a stability problem in its operation. A good alternative method to the optical phase-locked scheme is the LiNbO³ Mach-Zehnder (MZ) optical intensity modulator, which is capable of generating two highly stable optical signals (upper sideband and lower sideband components) by applying a sinusoidal microwave signal to an input laser signal. The two optical signals require phase stability better than 10^-13 in the Allan standard deviation, vibration robustness, and polarization maintaining capability. The signal coherence loss estimated from the phase stability of the two optical signals generated by the MZ modulator shows that the optical MZ modulator has the ability to generate highly stable optical signals.     

一种基于MZM的电信号任意倍频方法

文章提出一种使用马赫-曾德尔强度调制器(MZM)产生输入信号的任意倍频信号的方案,利用该方法不仅可以产生输入信号的偶数倍倍频信号,还可以产生输入信号的奇数倍信号.通过设置马赫-曾德尔强度调制器的直流偏置点在线性偏置点,产生了奇数倍信号,通过设置直流偏置点在特殊的非线性偏置点,产生了偶数倍信号.通过调节输入信号的幅度,可以得到想要的高阶倍频信号.理论分析和实验证实了该方案的可行性.     

Linearized microring-loaded Mach-Zehnder modulator with RF gain

A linearized modulator based on the Mach-Zehnder interferometer (MZI) loaded with a second-order allpass microring resonator is proposed and analyzed. The device is shown to exhibit much smaller intermodulation distortion than standard Mach-Zehnder modulators, thus greatly enhancing the device dynamic range. Gain effect associated with the microring resonance results in a modulator transfer function with high slope efficiency and large RF gain. Moreover, combined with the use of a highly electrooptic polymer, the high slope efficiency allows for the possibility of realizing modulators with subvolt drive voltage. The detrimental effect of loss in the microring resonators on device performance is also investigated and a design approach to mitigate its effect is presented. The proposed modulator can be linearized to any arbitrary nth order by loading the MZI with a higher order allpass microring resonator.     

一种60GHz毫米波全双工光纤无线通信系统

为了实现有线信号和无线信号的同时传输,采用将有线信号和无线信号分别在两个正交的偏振态中构造混合网络的方法,用非对称输入的双臂马赫-曾德尔调制器来产生无线信号中的毫米波;利用相位调制器实现差分相位键控调制格式,以便在上行链路中实现载波重用有线信号,分别将调制后两个正交偏振态信号耦合到同一光波长上经过光纤传输至基站。在基站处将两个正交偏振态的信号分离,携带无线信号光载波经光电检测放大后由天线传输出去,而携带有线信号光载波分为两路,一路经过平衡检测器检测得到有线信号,另外一路应用到上行链路中实现载波重用。通过OPTICSYSTEM软件进行了理论分析和实验验证,得到了10Gbit/s有线信号和60GHz无线信号通过光纤传输50km后的眼图。结果表明,该方案传输效果很好。     

Polarization-insensitive transition between sol-gel waveguide and electrooptic polymer and intensity modulation for all-optical networks

An intensity modulation using a hybrid electrooptic (EO) polymer/sol-gel straight channel waveguide, useful in the 1550-nm wavelength regime is demonstrated without using Mach-Zehnder interferometric waveguide. The sol-gel waveguide is selectively buried so that a vertical transition into and out of an EO polymer coated on the sol-gel waveguide is arranged. The throughput ratio for transverse electric (TE) and transverse magnetic (TM) modes of the light coupled out of the hybrid waveguide is improved up to 0.9 dB with the help of reduced birefringence of the EO polymer after corona poling. We show that the fabrication process of such hybrid-type waveguides enables production of a phase modulator operating at 1550-nm wavelength. The fabricated straight channel waveguide modulator exhibits stable- and high-intensity modulation efficiency (82%) using a simple cross-polarization setup after the polarization dependence is reduced. We demonstrate an all wet-etching process to fabricate polymeric EO modulators.     

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%.     

Improved electrooptic modulator with ridge structure in X-cut LiNbO3

A ridge-type Mach-Zehnder modulator on X-cut LiNbO₃ is fabricated by wet etching with proton-exchange pretreatment. Experimental results show that, with the assistance of the ridge structure, the drive voltage of the proposed modulator is reduced. The enhancement of overlap integral caused by ridge structure is also validated from numerical simulation. Moreover, an improved design to further reduce the drive voltage of the ridge-type Mach-Zehnder is proposed by a proper placement of waveguide relative to the electrode     

Optical clock recovery demonstration using periodic oscillations ofa hybrid electrooptic bistable system

Optical clock recovery using the periodic oscillations (also known as Ikeda oscillations) that arise from the astable behavior of a Ti:LiNbO₃ Mach-Zehnder modulator with delayed feedback at a frequency of 13.6 MHz is discussed. The jitter performance of the timing extraction scheme for several input patterns is presented. The circuit provides gain, and its speed can be improved by monolithic integration of the modulator and the feedback-loop components     

Polarization insensitive frequency converter with the capability ofchirp removal

We report on a new type of polarization insensitive frequency conversion technique using four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). In this technique the input signal is spectrally duplicated by a Mach-Zehnder type phase modulator. Then, the resulting two waves generate the frequency converted output signal by FWM with use of an additional pump wave. The converted output wavelength is independent of the wavelength of the input signal. In addition to the frequency conversion, the chirp of the input signal is removed by the FWM process bit-error-rate (BER)-measurements after transmission of the converted signal over standard communication fiber are reported     

Simultaneous Generation and Transmission of Downstream Multiband Signals and Upstream Data in a Bidirectional Radio-Over-Fiber System

We propose and experimentally demonstrate simultaneous generation and transmission of downstream multiband signals and upstream data in a bidirectional radio-over-fiber system. The scheme is based on a dual-parallel Mach-Zehnder modulator and a following single-drive Mach-Zehnder modulator. Multiband data including baseband, frequency-doubled, and frequency-quadrupled signals are generated through optical carrier suppression and frequency-shifting techniques. Upstream data transmission is realized by remodulation of the downstream differential phase-shift-keying signal without the need of additional light source and wavelength management at the base station.     

Analysis and design optimization of electrooptic interferometric modulators for microphotonics applications

Scaling the electrode layout (electrode gap, electrode length) down to microscale dimensions extends the application of electrooptic (EO) modulators to microphotonics. In this paper, design criteria are set up to minimize the switching voltage of microscale EO Mach-Zehnder interferometric modulators. Mach-Zehnder interferometric modulators under different directions of electric field with respect to the optic axis are analyzed. Three expressions of the intensity output characteristics are presented for various crystal classes and compared in terms of conditions of validity and design applications. The analysis in this paper suggests that the switching voltage is strongly related with the direction of the electric field relative to the optic axis. For the 4-mm BaTiO/sub 3/ (r/sub 33/=28 pm/V,r/sub 51/=820 pm/V) Mach-Zehnder modulators, r/sub 51/ is utilized when the electric field is applied normal to the optic axis. In this configuration, the thermal stability and polarization insensitivity improve but the extinction ratio becomes a function of the electrode length. The phase-retardation expression is useful to find a suitable modulator length and maximize the extinction ratio. Some of the discussions also apply to Fabry-Pe/spl acute/rot interferometric modulators.     

频率响应法测量光强度调制器啁啾参数

描述一种利用光纤频率响应法测量光强度调制器啁啾参数的方法 .通过利用网络分析仪测量光强度调制器(电吸收调制器和马赫 -曾德尔型铌酸锂调制器 )经过光纤后的频率响应特性 ,从而间接测量啁啾参数 .实验结果与理论相吻合 .