Ultra-Broad-Band LiNbO_3 Electro-Optic Modulators with Novel Complex Electrode

1 IntroductionFOr LiNbO3 modulators, the bandwidth is mainly restricted by the microwaveattenuation of the travelling--wave electrode and the phase velocity ndsmatch betWeenmicrowave and optical wave in the devices. When the phase velocity matching issatisfied it is very i~rtant to decrease the microwave attenuation for expandingbandwidth. The thecrowave propagating lOSS is the main source Of the microwaveattenuation in the interactive region. The larger the cross-sectional area or the lOn…     

GaAs／GaAlAs定向耦合器型行波调制器：1.设计

从理论上重点分析和研究了器件行波电极的微波特性，在半绝缘ＧａＡｓ衬底上设计了具有ｎ＾＋重掺杂外延层和共平面电极的ＧａＡｓ／ＧａＡｌＡｓ定向耦合器型行波调制器，针对实验中发现的行波电极上微波的高传输损耗问题。分析了起因并提出了器件的改进设计方案，从而设计出可达到３５ＧＨｚ带宽的高速调制效应的光波导调制器。     

Characteristic of a broadband Ti:LiNbO3 optical modulator with buried electrodes and etched grooves in the buffer layer

Traveling wave Ti:LiNbO₃ Mach-Zehnder optical modulators with buried electrodes and etched grooves in the SiO₂ buffer layer are analyzed by the finite element method. The tradeoff between the bandwidth BW and the half-wave voltage Vπ is discussed. The value of BW/Vπ is used to weight the total performance of the modulator. Taking a thick buffer layer and etching deep grooves in the buffer layer are demonstrated as two effective methods to improve the performance of the modulator. A 3-dB optical bandwidth of 18 GHz with half-wave voltage 5V at a wavelength of 1.55 pm could be obtained even though the electrode is not very thick. When the requirement of half-wave voltage is not very critical, a bandwidth of more than 100 GHz can be obtained.     

新型结构超宽带LiNbO3电光调制器的优化设计

采用有限元软件对新型结构的铌酸锂电光调制器进行了优化设计.分析表明,采用脊波导和T型电极相结合的方式,能在保持高的特征阻抗的同时有效的实现相速匹配和有效降低电极损耗,从而较好的提高器件性能,是一种比较有潜力的调制器.利用优化结果,给出一种带宽达153 GHz,半波电压为8.55 V,特征阻抗为44 Ω的调制器的设计例子.     

超高速行波电吸收调制器的k值设计方法

介绍了一种用于超高速行波电吸收调制器(TW-EAM)设计的“k值带宽法”.该方法考虑了影响调制器带宽的阻抗失配、相速度失配、微波衰减等因素,说明一个优化设计的TW-EAM其带宽可达到140 GHz.     

15GHz马赫－陈德尔型Ti：LiNbO_3行波幅度电光调制器

比较了四种马赫－陈德尔调制器的结构特性，表明Ｚ切共面波导（ＣＰＷ）是最好的一种结构。用阶跃倒相电极设计了新型电光光波导幅度调制器，研制了包装式带尾光纤的有５段例相电极的马赫－陈德尔调制器。在１．５３２μｍ波长上，该器件调制带宽为１４．８ＧＨｚ，半波电压为１４Ｖ，消光比为２１．３ｄＢ，光纤－器件－光纤插入损耗７．６ｄＢ。     

高速光学模数转换器的分析

详细分析了由x切LiNbO3干涉式共面波导行波调制器阵列构成的模数(A/D)转换器，包括其研究进展。采用保角变换方法分析了梯形共面波导电极参数(包括电极厚度、缓冲层厚度与中心电极和接地电极的边沿倾角β1，βg)与转换器的带宽、损耗、特征阻抗和驱动功率的关系。β1=βg=10°，电极厚度为3μm时，4位A/D转换器的工作带宽为7.3GHz，所需驱动功率为6.7W。数值仿真结果表明，采用梯形共面波导调制器阵列设计分辨率适中的高速A/D转换器是可行的。     

应用HFSS和Designer对电光调制器的协同仿真

应用ANSYS公司的HFSS和Designer对一种内嵌共面波导电极结构的聚合物电光调制器进行了协同仿真,设计出了带宽为56 GHz的聚合物电光调制器.通过对光波有效折射率和微波有效折射率的优化,实现了速度匹配.同时利用协同仿真方法对电极进行了优化设计,实现了阻抗匹配并降低了微波损耗.结果表明应用协同仿真方法可以提高计...     

行波电吸收调制器中脊宽对频带宽度的影响

根据行波电吸收调制器（TW-EAM）的微波传输特性,提出了等效电路模型.制作了工作波长为850 nm的GaAs/GaAlAs材料的TW-EAM,并通过等效电路模型分析了特性阻抗Z0、微波传输常数γ和S21,得出脊宽对器件微波特性的影响.从理论上验证了较小脊宽可以降低微波和光波之间的速度失配、波导的传输损耗及传输线和终端及源端之间的阻抗失配.理论模拟得出：脊宽为2 μm时,器件提供的带宽为23.9 GHz.     

用于获取大调制度的驻波型电光调制器的设计与制作

设计并制作了一种采用微波驻波电极的电光调制器,该调制器被用于光谱展宽。通过非周期极性反转方法,在１６．２５ＧＨｚ的调制频率下实现了微波驻波与光波的相位匹配,从而获得了大调制度。实验中光谱展宽达到２．５ＴＨｚ。     

GaAs travelling-wave optical modulator using a coplanar slow-wave electrode with periodic overlays

A coplanar slow-wave electrode with periodic cross-tie overlays has been used to satisfy the essential phase velocity matching between the modulation and optical waves for wideband travelling-wave optical modulators. For an optimized modulator of 4 mm length at 1.3 m light wavelength, the calculated halfwave modulation voltage (23 V) is slightly higher than that (20 V) of conventional coplanar modulators but the 3 dB bandwidth (100 GHz) is much wider than the bandwidth limit (30 GHz) of walkoff-limited conventional coplanar modulators. The measured effective index (4.61) of the modulation wave is much higher than that (2.65) of conventional coplanar electrodes and agrees very well with the calculated one (4.25).     

Microwave Photonic Link with Carrier Suppression for Increased Dynamic Range

Theoretical analysis and experimental investigation of microwave photonic links with bias-shifted Mach-Zehnder modulators are presented. An optical amplifier is used to increase link gain and reduce noise figure. The combination of modulator bias shift away from quadrature and optical amplification reduces the link noise figure by more than 15 dB. For modulation frequencies from 2 to 18 GHz, the third-order limited spurious-free dynamic range (SFDR3) of these links is greater than 120 dB, normalized to a 1-Hz bandwidth. Conventional links based on Mach-Zehnder modulators are limited to SFDR3 values of approximately 110 dB, normalized to a 1-Hz bandwidth. This level of performance is achieved without electronic or optical linearization.     

Optimizing Design for the Traveling Wave Electrodes in Low-Drive High-Speed Electro-Optic Polymer Modulators

Electro-optic (EO) polymer modulators are very promising in the realization of cost-effective and high-performance optical transmissions. In this article, general strategies and specific designs of the traveling wave electrodes in EO polymer modulators were presented to reduce the modulator drive power while maintaining a broadband response. The optimum device parameters and corresponding conditions were estimated using finite element method based on electrode design. In calculating the results, the comprehensive characteristics of polymer modulator with 1.21 V half-wave voltage and 91 GHz bandwidth was demonstrated with electro-optic interaction length is 20 mm, electro-optic coefficient is 55 pm/V, and operation wavelength is 1.319 μm. These results agree with the 0.8 V half-wave voltage and 30 mm electro-optic interaction length reported in Science. In the five designs presented, a hybrid electrode structure combining CPW and microstrip lines were advanced. The characteristics of this structure are like that of microstrip lines with a single-arm electrode on one arm of the waveguide, but it solves the problem of microstrip to coaxial line transition and corona polarization.     

超宽带聚合物调制器的优化设计

设计了一种以聚合物作为材料的低损耗、宽带宽的Mach—Zehnder光波导调制器。分析了调制器的脊波导的模式特性,设计了脊波导的结构,并使用BPM软件模拟了脊形波导的光场分布;通过对光场分布的分析,优化了脊形波导的宽度Wg,脊高6,芯层高度H。同时对聚合物调制器的电极进行了优化,包括电极宽度W和电极间距D,使得调制器有较小的导体损耗以及较好的阻抗匹配。并结合了脊波导的结构参数和电极的优化参数,给出了优化结果,它能够使微波的有效折射率与光波的有效折射率达到匹配,从而使带宽达到177GHz,导体损耗为0．2569dB／cm·GHz1／2。     

Optimizing Design for the Traveling Wave Electrodes in Low-Drive High-Speed Electro-Optic Polymer Modulators

Electro-optic (EO) polymer modulators are very promising in the realization of cost-effective and high-performance optical transmissions. In this article, general strategies and specific designs of the traveling wave electrodes in EO polymer modulators were presented to reduce the modulator drive power while maintaining a broadband response. The optimum device parameters and corresponding conditions were estimated using finite element method based on electrode design. In calculating the results, the comprehensive characteristics of polymer modulator with 1.21 V half-wave voltage and 91 GHz bandwidth was demonstrated with electro-optic interaction length is 20 mm, electro-optic coefficient is 55 pm/V, and operation wavelength is 1.319 μm. These results agree with the 0.8 V half-wave voltage and 30 mm electro-optic interaction length reported in Science. In the five designs presented, a hybrid electrode structure combining CPW and microstrip lines were advanced. The characteristics of this structure are like that of microstrip lines with a single-arm electrode on one arm of the waveguide, but it solves the problem of microstrip to coaxial line transition and corona polarization.     

Operation of low driving voltage cascaded modulator over non-cascaded modulator for 4 dB extinction ratio at 100 giga bit per second (Gbps)

This paper describes improved results when comparing cascaded traveling wave electro absorption modulator (TWEAM) to non-cascaded TWEAM by simulation. Large signal modeling is used for both types of modulators to achieve 4 and 10 dB extinction ratios (ERs) with flat frequency response for applications in short distance as well as long distance optical fiber communication. To obtain 4 and 10 dB ERs with 110 GHz 3 dB bandwidth, a cascaded TWEAM requires 0.4 V peak to peak (V_P-P) and 1 V_P-P input driving voltages respectively. A non-cascaded TWEAM requires about two times the input driving voltage compared to the cascaded modulator to achieve the same values of ER and 3 dB bandwidth. Both modulators have been simulated with the same bias and also use the same circuit parameters except for the total active segment lengths (1 and 0.5 mm for cascaded and non-cascaded modulator respectively) and microstrip lengths to obtain the same ERs and 3 dB bandwidths.     

Wideband magneto-optic modulation in a bismuth-substituted yttrium iron garnet waveguide

We present a tunable wideband bismuth-substituted yttrium iron garnet (Bi-YIG) waveguide magneto-optic (MO) modulator. High-speed current transients are used to switch the in-plane magnetization of the film, which modulates an 800 nm optical beam. Large bandwidth optical modulation is achieved by driving the device in a non-resonant mode that is well below the ferromagnetic resonance frequency of the film. The MO modulator has the potential of operating at bandwidths higher than 1 GHz by tuning the applied static magnetic field.     

Broadband and low-driving-power LiNbO<Subscript>3</Subscript>electrooptic modulators

Microwave and optical properties of lithium niobate electrooptic modulators are investigated in this paper. The effect of simultaneous matching of optical and microwave velocities and impedance matching, conductor loss, dielectric loss on the optical bandwidth of an ultra-high-speed lithium niobate modulator are presented here. The metal electrode design, buffer thickness, ridge depth, and the gap between electrodes at different operating frequencies on device performance are thoroughly investigated by using the finite element method.     

Refined modeling of traveling-wave Ti:LiNbO3 channel waveguide modulator

A refined computation model for traveling-wave operation of external electro-optical phase modulators made of a single titanium in-diffused lithium niobate channel waveguide (Ti:LiNbO₃WG) is described. The modulator circuit model outlined as two traveling-wave coupled microstrips includes microwave losses and dispersion. In the optimization procedure, we consider different circuit load conditions. The influence of a dielectric overlay covering the electrodes is examined. The consolidated techniques of conformal mapping, multiple image, and finite element are used to investigate the microwave characteristics of the structure, and the refractive effective index method is used in calculating the characteristics of the diffused anisotropic optical channel. The performances of Y-cut and Z-cut substrate configurations are compared. We have verified that the Y-cut substrate modulator gives the best overall performance, and that the overlay presence causes significant improvements in the evaluated modulation efficiency and in the bandwidth. A model of the modulator that takes electrode thickness into account permits one to obtain a wider bandwidth.     

Polarization-independent terahertz wave modulator based on graphene-silicon hybrid structure

In this study, we propose and demonstrate a broadband polarization-independent terahertz modulator based on graphene/silicon hybrid structure through a combination of continuous wave optical illumination and electrical gating.Under a pump power of 400 mW and the voltages ranging from-1.8 V to 1.4 V, modulation depths in a range of-23%–62% are achieved in a frequency range from 0.25 THz to 0.65 THz. The modulator is also found to have a transition from unidirectional modulation to bidirectional modulation with the increase of pump power. Combining the Raman spectra and Schottky current–voltage characteristics of the device, it is found that the large amplitude modulation is ascribed to the electric-field controlled carrier concentration in silicon with assistance of the graphene electrode and Schottky junction.