A comparison of the performance of LiNbO3, and LiTaO3, traveling-wave phase modulators

Abstract

A comparison of the phase modulators made by Ti:LiNbO₃ and Ti:LiTaO₃ optical waveguides is presented. Of particular interest is their halfwave voltages at the wavelength 0.6328 μm and the frequency responses for the same electrode structure. For the Ti:LiNbO₃ phase modulator, a halfwave voltage of 6.6 V and a band-width of 13 GHz are obtained. Whereas, the Ti:LiTaO₃, a 6.8 V halfwave voltage and 12 GHz bandwidth are obtained.     

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.     

Fully packaged high-speed Ti:LiNbO3, waveguide mach-zehnder intensity modulator

A fully packaged high-speed Ti:LiNbO₃, Mach-Zehnder intensity modulator at a 1.5μm wavelength has been designed and fabricated. The design has been considered with respect to optical insertion loss, switching voltage, and modulation bandwidth. Re fiber-pigtailed device has a 6.7 dB fiber-to-fiber loss and an optical modulation bandwidth of 8 GHz. The voltage required to switch the device from the on to off state is measured to be 7.3 V, with an on-off extinction ratio of 21 dB.     

LiNbO3和LiTaO3晶体Er3+/Yb3+掺杂水热外延层室温吸收光谱分析

本文引入与浓度和厚度有关的k_NL待定参数, 在J-O理论基础上, 对Er³⁺/Yb³⁺掺杂的LiNbO₃和LiTaO₃单晶衬底上 的多晶水热外延样品进行了基于吸收光谱的拟合计算. LiNbO₃:Ω₂=2.34× 10^-20 cm², Ω₄=0.77× 10^-20 cm², Ω₆=0.31×10^-20 cm², k_NL=4.32× 10^-2 mol·m^-2. LiTaO₃:Ω₂=1.68×10^-20 cm², Ω₄=0.84×10^-20 cm², Ω₆=0.45×10^-20 cm², k_NL=9.17×10^-3 mol· m^-2. 该方法可尝试推广到粉体或胶体等难以直接获得浓度和厚度数据的体系. 经上转换发光测试及光谱参数计分析认为Er³⁺/Yb³⁺离子的掺杂浓度比为1:1的情况下, 样品呈现绿色上转换发光光谱; 可尝试以降低基质声子能量的方法提高⁴I_13/2能级 对²H_11/2和⁴S_3/2能级的量子剪裁效率.     

伸缩-剪切模式自偏置铌酸锂基复合材料的磁电性能和高频谐振响应

选用多种切型铌酸锂(LiNbO_3)单晶,研究了铁基非晶合金(Metglas)/LiNbO_3叠层复合材料基于伸缩-剪切模式的磁电耦合性能,揭示了铌酸锂单晶压电系数与复合材料剪切磁电耦合系数的对应关系,在使用铌酸锂xzt/30~?切型时得到了最优化剪切磁电系数.通过SrFe12O19薄磁带提供偏置磁场,Metglas/LiNbO_3磁电复合材料可在没有外加直流磁场时实现剪切磁电响应,并在0.991 MHz和3.51 MHz频率时分别测出了谐振磁电系数,有望将铌酸锂基剪切磁电复合材料用于高频磁场探测.     

Secondary ion mass spectrometry and optical characterization of Ti:LiNbO3 optical waveguides

Secondary ion mass spectrometry (SIMS) and m-lines spectroscopy have been applied to study Ti:LiNbO₃ slab optical waveguides with high titanium surface concentration. By combining the two techniques, a saturation in the dependence of the refractive index change on the dopant concentration has been found. By the use of SIMS in image mode, the lateral diffusion of titanium in Ti:LiNbO₃ channel waveguides has been observed and analyzed.     

Structure and optical damage resistance of near-stoichiometric Zn:Fe:LiNbO3 crystals

A series of near-stoichiometric Zn:Fe:LiNbO₃ crystals were grown by the high-temperature top-seed solution growth (HTTSSG) method from stoichiometric melts doped with 6 mol% K₂O. Infrared (IR) transmission spectra were measured and discussed in terms of the defect structure of the near-stoichiometric Zn:Fe:LiNbO₃ crystals. The results of the transmitted beam pattern distortion method show that the optical damage resistance of the near-stoichiometric Zn:Fe:LiNbO₃ crystals increases rapidly when the ZnO concentration exceeds a threshold value. The threshold value concentration of ZnO of the near-stoichiometric Zn:Fe:LiNbO₃ crystals is much lower than that of the congruent LiNbO₃ crystals. The dependence of the optical damage resistance on the defect structure of the near-stoichiometric Zn:Fe:LiNbO₃ crystals are discussed, and the holographic recording properties of the near-stoichiometric Zn:Fe:LiNbO₃ crystals are investigated.     

Phase relationships in an Al3 (Ti,V) based in-situ composite

The phases and the crystallographic relationships between phases observed in an Al₇₀Ti₁₀V₂₀ alloy following chill casting and post-solidification heat treatment have been characterized using analytical transmission electron microscopy and electron diffraction. The chill-cast microstructure comprised a mixture of primary dendrites of δ-Al₃ (Ti,V) and interdendritic eutectic zones in which the continuous phase was δ-Al₃ (Ti,V) and the rode-like discontinuous phase was ζ-Al₈V₅. Following isothermal heat treatments in the temperature range 1073–1273 K, a uniform distribution of rod-like particles was observed to develop throughout the δ matrix and a phase transformation was detected within the dispersed particles, as the intermetallic ζ phase was replaced by b.c.c.β-(Ti,V) metallic solid solution. This transformation was typically complete within 100 hr at 1073 K, leading to the formation of an in-situ composite consisting of a uniform dispersion of metallic β-phase in a brittle Al₃(Ti,V) intermetallic matrix. The orientation relationship between the discontinuous β-(Ti,V) particles and the DO₂₂δ-Al₃(Ti,V) matrix involved parallelism of the closest-packed planes and close-packed directions in those planes, i.e. (110)_β//(112)_δ(DO22) and [ 11]_β//[ 10]_δ(DO22).     

Cu,Fe掺杂LiNbO_3晶体电子结构和光学性质的第一性原理研究

利用基于密度泛函理论的第一性原理对Cu,Fe单掺及共掺LiNbO_3晶体的电子结构和光学性质进行了计算.结果显示:Cu,Fe单掺杂LiNbO_3晶体禁带内均产生了杂质能级,主要由Cu3d,Fe3d轨道及O 2p轨道贡献;共掺LiNbO_3晶体禁带内出现了双能级结构,深能级由Cu3d和O2p轨道贡献,浅能级由Fe3d和O2p轨道贡献.Cu,Fe单掺和共掺LiNbO_3晶体带隙依次缩小,在可见光区的光吸收明显增强.共掺LiNbO_3在445和630nm左右分别表现出一个宽吸收峰,比单掺LiNbO_3晶体表现出更好的光吸收性质.研究表明,Fe占Nb位比Fe占Li位的双掺样品在双光存储应用中更有优势;同时,浓度比[Fe2+]/[Fe3+]值的适当降低有助于这种优势的形成.     

Analysis of Ti:LiNbO3 zero-gap directional coupler for wavelength division multiplexer/demultiplexer

For the purpose of multichannel integrated-optical wavelength division MUX/DEMUX design, the wavelength tuning method of Ti:LiNbO₃ zero-gap directional coupler is analysed by effective-index based matrix method (EIMM). In this method, first, the 2D refractive index profile of the Ti:LiNbO₃ zero-gap directional coupler is transformed into lateral 1D effective-index profile by WKB method. Finally, matrix method is applied to this effective-index profile and the propagation constants are computed from the resonance peaks of the excitation efficiency versus propagation constant characteristics. It has been shown that the channel wavelength tuning can be achieved by varying the Y-branching angle at the input and output of the device or by a slight variation of two-mode-section length. The method of electro-optic fine tuning of the channel wavelength and channel separation of the device has also been investigated. A cascaded structure with proper parameters for four-channel application is also simulated and the results are presented.     

Carbon multi-walled nanotubes grown by HWCVD on a pyroelectric detector

Carbon multi-wall nanotubes (MWNTs) were grown on a lithium niobate (LiNbO₃) pyroelectric detector with a nickel film as the catalyst by hot-wire chemical vapor deposition (HWCVD). Two detectors are documented, each with slightly different deposition conditions. The absolute spectral responsivity of each device was measured from 600 nm to 1800 nm and indicates that the MWNT-coating absorptance is spectrally uniform, with variations of only a few percent. We also discuss growth of MWNTs on LiTaO₃ by CVD and the limitations presented by the Curie temperature of the pyroelectric material.     

Information capacity and resolution in three-dimensional imaging

In this paper we report experimental studies of nonvolatilephotorefractive holographic recording in doping In(3mol%), which exceed the so-called threshold, in Ce:Cu:LiNbO₃ crystals. The In:Ce:Cu:LiNbO₃ crystal was grown by the Czochralski method and oxidized. The OH⁻ absorption band of In:Ce:Cu:LiNbO₃ crystal is 3507cm⁻¹. The nonvolatile holographic recording in In:Ce:Cu:LiNbO₃crystal is realized by two-photon fixed method. From the experiment, we found that the recording time of In:Ce:Cu:LiNbO₃ crystal is lower than that of Ce:Cu:LiNbO₃ crystal and there are a little lose of nonvolatile diffraction efficiencies between In:Ce:Cu:LiNbO₃ and Ce:Cu:LiNbO₃ crystals. In this paper, the mechanism of OH⁻ absorption band shifting and two-photon fixed was discussed, too.     

Co,Zn共掺铌酸锂电子结构和吸收光谱的第一性原理研究

利用基于密度泛函的第一性原理的计算方法,研究了Co单掺及Co和Zn共掺LiNbO_3晶体的电子结构和吸收光谱.研究显示,各掺杂体系铌酸锂晶体的带隙均较纯铌酸锂晶体变窄. Co:LiNbO_3晶体禁带宽度为3.32 eV; Co:Zn:LiNbO_3晶体, Zn的浓度低于阈值或达到阈值时,禁带宽度分别为2.87或2.75 eV. Co:LiNbO_3晶体在可见-近红外光波段2.40, 1.58, 1.10 eV处形成吸收峰,这些峰归结于Co 3d分裂轨道的跃迁;加入抗光折变离子Zn~(2+),在1.58, 1.10 eV处的吸收峰增强,可以认为Zn~(2+)与Co~(2+)之间存在电荷转移,使e_g轨道电子减少,但并不影响t_(2g)轨道电子.结果表明,晶体中的Co离子在不同共掺离子下可充当深能级中心(2.40 eV),或可充当浅能级中心(1.58 eV),两种情况下,掺入近阈值的Zn离子均有助于实现优化存储.     

Design of the spot size for single-mode Ti/Mg:LiNbO3, channel waveguide for optimum coupling with fibers

To improve the coupling effciency between fibers and conventional Ti:LiNbO₃ diffused channel waveguides, it is feasible that the elliptical mode pattern of the channel waveguide can be modified by the Ti/Mg double diffusion method. By means of the three-dimensional beam propagation method, we successfully show that the mode size of the waveguide fabricated by this method is well matched to that of the fiber for TE and TM polarizations separately.     

SrNb2O6-NaNbO3-LiNbO3赝三元系相图的研究

本文用X射线衍射、热处理及差热分析等方法测定了SrNb₂O₆-NaNbO₃-LiNbO₃赝三元系的室温截面及相应的SrNb₂O₆-NaNbO₃,SrNb₂O₆-LiNbO₃和NaNbO₃-LiNbO₃等三个赝二元系相图;粗略地研究了Sr_0.42Na_0.16NbO₃-LiNbO₃系的纵截面;含5mol％LiNbO₃及10mol％LiNbO₃的SrNb₂O₆-NaNbO₃的纵截面。确定了室温Sr₂Na(NbO₃)₅(以下略为S₂N)相为四方钨青铜结构。其点阵常数为a=12.36?,c=3.906?.LiNbO₃在S₂N相内的溶解度可达～10mol％,当LiNbO₃含量超过5mol％时,S₂N相畸变为S₂N′相。S₂N′相为正交晶系。实验确定室温S₂N(S₂N′)相系亚稳相。在900-1100℃长时间退火即分解为SrNb₂O₆和以NaNbO₃为基的固溶体的混合物。 关键词：     

第一原理研究Mn掺杂LiNbO3晶体的磁性和光吸收性质

采用基于密度泛函理论和局域密度近似的第一性原理分析了Mn掺杂LiNbO₃晶体的结构, 磁性, 电子特性和光吸收特性. 文中计算了Mn占据Li位和Nb位体系的形成焓, 对应的形成焓分别为-8.340 eV/atom和-8.0062 eV/atom, 也就意味着Mn 原子优先占据Li位. 这也就意味着Mn原子占据Li位的掺杂LiNbO₃晶体结构更稳定. 磁性分析的结果显示, 其对应磁矩也比占据Nb位的高. 进一步分析磁性的来源, 自旋态密度结果显示: Mn掺杂LiNbO₃晶体的磁性主要源于掺杂原子Mn, Mn原子携带的磁矩高达 4.3 μ_B, 显示出高自旋结构. 由于Mn-3d与近邻O-2p及次近邻Nb-4d 轨道的杂化作用, 计算表明: 诱导近邻O原子及次近邻Nb原子产生的磁矩对总磁矩的贡献较小. 通过光学吸收谱的分析, 得出在可见光区Li位被Mn原子替代以后显示出更好的光吸收响应相比于Nb位. 本文还分析了O空位对于LiNbO₃晶体磁性与电子性质的影响, 结果显示O空位的存在可以增加Mn掺杂LiNbO₃体系的磁性.     

低能离子轰击后铌酸锂晶体表面层的性质

从实验中观察到,低能离子轰击后的铌酸锂晶体表面层在3500—6500?之间出现至少两个光吸收峰,表面的相对暗电导率增加两个数量级。这表明离子轰击后的铌酸锂中产生了附加的光吸收和电导激活中心。在离子轰击过程中,由于某些原子基团和原子的优先溅射,在表面层中造成相当大的化学计量比偏离,它直接影响晶体的光学和电学性质。XPS(X射线电子能谱)测试结果证实,这一表面层的构成符合铌酸锂缺陷结构的空位模型。讨论了附加激活中心的成因,并据此解释了Ar⁺/O⁺混合离子轰击铌酸锂晶体所得到的结果。 关键词：     

Fe:Mg:LiNbO3晶体电子结构和吸收光谱的第一性原理研究

基于密度泛函理论的第一性原理, 研究了LiNbO₃晶体以及不同Mg浓度的Fe:Mg:LiNbO₃晶体的电子结构和吸收光谱. 研究结果显示: 掺铁铌酸锂晶体的杂质能级由Fe 的3d轨道和O的2p轨道贡献, 禁带宽度为2.845 eV; 对于Mg, Fe共掺样品, Mg的浓度小于或等于阈值时, 禁带宽度分别为2.901 和2.805 eV; 掺铁铌酸锂晶体的吸收谱在2.3和2.6 eV处分别存在一个吸收峰, 其强度因Mg的浓度不同而发生变化. 研究结果还表明, 不同浓度的Mg对晶体内Fe²⁺和Fe³⁺的浓度以及占位产生了不同的影响. 还提出了光电子的形成不应单独考虑铁的轨道电子态, 而应同时考虑与铁成键的氧的轨道电子态的观点.     

Design and demonstration of interferometric integrated-optic sensors in Ti:LiNbO3 waveguides

The design of an integrated optic Michelson interferometer sensor for stress, temperature, and microdisplacement measurements consisting of a semi-asymmetric X-junction made by Ti in-diffused LiNbO₃ waveguides is reported. The possibility of performing simultaneous measurements of strain and temperature is investigated, and different calibration schemes are proposed. Experimental results of displacement-only measurements show a 64% intensity modulation with 33-dB optical loss.     

一种电光可调的铌酸锂/钠基表面等离子体定向耦合器

为了满足日益增加的集成光子器件设计的需求,本文研究了一种铌酸锂/钠表面等离子体波导(Li Nb O3/Na surface plasmonic waveguide, LNSPW),并利用LNSPW构成电光可调的定向耦合器(directional coupling,DC).利用有限元方法 (finite element method, FEM)对波导的模式特性和耦合器的耦合特性进行了分析.结果表明,随着波导尺寸的增大,传播长度可达约200μm,归一化有效模场面积小于0.4.通过调节耦合间距(W_gap)、耦合长度(L_C)和工作波长(λ)等参数,铌酸锂钠表面等离子体波导构建的定向耦合结构可实现3 d B耦合.当W_gap=100 nm和L_C=17μm时, DC在V₀=53 V时可实现3 d B耦合,且具有较好的方向性和隔离度.LNSPW的研究为实现可调的DC提供了一种可行的方案,在集成电光可调器件研究领域有潜在的应用前景.除此之外, LNSPW还可广泛应用于非线性光学、光信号处理及光全...