基于Franz-Keldysh效应的倏逝波锗硅电吸收调制器设计

本文设计了一种基于Franz-Keldysh (FK) 效应的GeSi电吸收调制器. 调制器集成了脊形硅单模波导. 光由脊形硅波导以倏逝波形式耦合进锗硅吸收层. 在硅基锗二极管FK效应实验测试的基础上, 有源区调制层锗硅中的硅组分设计为1.19%, 从而使得器件工作在C (1528–1560 nm) 波段. 模拟结果显示该调制器的3 dB带宽可达64 GHz, 消光比为8.8 dB, 而插损仅为2.7 dB. 关键词： 锗硅 调制器 电光集成     

Selective polarization mode excitation in InGaAs/GaAs microtubes

We report on selective polarization mode excitation in InGaAs/GaAs rolled-up microtubes. The microtubes are fabricated by selectively releasing a coherently strained InGaAs/GaAs quantum dot layer from its host GaAs substrate. An optical fiber abrupt taper is used to pick up the microtube, while an adiabatically tapered optical fiber is used to couple light into the resonant optical modes of the microtube. By varying the polarization of the light in the adiabatically tapered fiber both transverse electric and transverse magnetic modes are observed in the microtube. We also show that the microtube can be used as a red (0.6?μm) to infrared light (1.5?μm) optical-optical modulator taking advantage of the thermal-optical effect.     

Low voltage electro-optic polymer light modulator using attenuated total internal reflection

An improved electro-optic (EO) polymer light modulator based on attenuated-total-internal-reflection (ATR) is demonstrated. The modulator consists of a prism–metal–EO-polymer–metal multilayer structure. An applied electric field across the EO polymer layer electrically modulates the energy coupling efficiency of incoming light into guided wave resonance at fixed angles. Compared with conventional ATR modulators based on surface plasmon resonance, the driving voltage for this modulator has been greatly reduced because of the newly chosen working interior angle. It also offers advantages in terms of insertion loss and aperture size over other techniques for the amplitude modulation of a collimated light beam.     

新型电光强度调制器的研究

在全硅和GeSi电光强度调制器研究的基础上，提出了一种新型的电光强度调制器结构，目的在于减小调制电流和提高调制频率。     

10 Gbit/s Silicon modulator and germanium detector chip-to-chip optical link

Experimental results of a high-speed silicon optical modulator based on carrier depletion in a pipin diode and Germanium photodetectors are presented. 10 Gbit/s data transmission is obtained for both optoelectronic devices, with for the optical modulator an extinction ratio (ER) higher than 8 dB and insertion loss (IL) lower than 6 dB and for Ge photodetector, a zero-bias operating at 10 Gbit/s. Finally, a 10 Gbit/s optical link combining Si modulator and Ge photodetector is demonstrated.     

Fabrication of an electro-absorption modulated distributed feedback laser by quantum well intermixing with etching ion-implantation buffer layer

We report the fabrication details of a monolithically integrated electro-absorption modulated distributed feedback laser(EML) based on the ion-implantation induced quantum well intermixing(QWI) technique.To well-preserve material quality in the laser region, thermal-oxide Si O2 is deposited before implantation and the ion-implantation buffer layer is etched before annealing. Thirteen pairs quantum well and barrier are employed to compensate deterioration of the modulator's extinction ratio(ER) caused by the QWI process.The fabricated EML exhibits an 18 d B static ER at 5 V reverse bias. The 3 d B small signal modulation bandwidth of modulator is over 13.5 GHz indicating that this EML is a suitable light source for over 16 Gb/s optical transmission links.     

光子晶体平面波导与脊波导高效耦合技术的研究

利用一维变周期谐振腔阵列和非线性缓变边界，可以实现光波从脊波导到光子晶体平面波导 （PCW）的高效耦合.基于平面波展开法（PWE）和时域有限差分法（FDTD），深入分析和讨 论了普通脊波导、2D-PCW结构和本征模以及工作模式、缓变边界形状等对耦合效率的影响， 从而得出光波从脊波导到2D-PCW、再返回脊波导的统一图景.指出考虑模式转换和采用缓变 边界条件可以极大提高PCW与脊波导间的耦合效率.对PC-PW边界采用线性和非线性缓变结构 进行了仿真，讨论了边界缓变程度对耦合效率的影响.结果表明，采用模式耦合和PC-PW余弦 缓变边界时的耦合效率在较宽的带宽内超过了95%. 关键词： 光子晶体波导 脊波导 PWE FDTD 耦合边界     

The measurement of sucrose concentration by two-tapered all-fiber Mach–Zehnder interferometer employing different coupling structures and manufacture processes

The sucrose concentration measurement and characteristics of light coupling taper structure on sensitivity with various fabrication processes of taper structure for all-fiber Mach–Zehnder interferometer (AFMZI) are presented. Using fusion splicer with electrical discharge, the standard single-mode fiber is employed to be fabricated as conical coupling/decoupling taper structure. The basic two fabrication processes are designed as single fusion-stretching (SFS), multiple fusions without stretching (MF). The third advanced process is composed of SFS and multiple fusions without stretching processes, and called multiple fusions with single stretching (MFSS). Various types of coupling/decoupling taper structures were fabricated based on the three kinds of fabrication processes. The effects of geometry shape including taper waist, taper angle, and sensing length on sensing sensitivity of AFMZIs are estimated. The modifications of fiber core and cladding induced by thermal effect affect the refractive index distributions and shapes of taper structure. The effects of refractive index changes of fiber core and cladding on sensing sensitivity are also discussed. The AFMZI was tested by measuring aqueous sucrose solution of refractive index unit (RIU) from 1.333 to 1.420 RIU. The optical spectrums are measured by a spectrometer. The spectrum dip shifts and sensing sensitivity was measured and calculated, respectively. As shown in results, sensing sensitivities of AFMZIs of taper structure fabricated by MFSS and multiple fusions without stretching processing are generally higher than SFS. The reasons could be aimed on materials modification through thermal effect on blurring fiber core-cladding interface and proper taper angle of taper structure. The more homogeneous refractive index distribution on fiber core-cladding interface, the more detecting light power decoupled through core-cladding interface to interact with exterior environment and enhance the sensing sensitivity. Similarly, an appropriate taper angle also provides a better coupling/decoupling performance. The optimal sensitivities relative to low refractive index, high refractive index, and full refractive index range are 87.62, 133.55, and 104.20 nm/RIU, respectively, and the corresponding sensing length are 30, 50, and 30 mm, respectively, with taper angle of 25° and taper waist of 40 μm.     

High efficiency fiber coupling to silicon sandwiched slot waveguides

The design of a fiber coupler for high efficiency light coupling to silicon sandwiched slot waveguides is reported. The proposed fiber coupler is based on the inverted taper approach. Parameters have been optimized to maximize coupling efficiency for λ = 1550 nm and TM polarization. Maximum coupling efficiencies of 93% for a inverted taper length of 150 μm and a inverted taper tip width of 40 nm have been obtained by means of the overlap integral and 3D beam propagation method (BPM) simulations.     

纤维光锥有效透过率的理论分析

光锥的有效透过率不仅影响光锥与CCD的耦合效率,而且会影响到耦合器件的信噪比.本文主要从理论上讨论了影响光锥有效透过率性能的因素,从纤维光学元件的实际内部结构推导出了其实际有效填充率,从光线在光锥中的传输特征推导出了光线在光锥中传播时产生的衰减损耗,最后提出了提高光锥有效透过率的方法和途径.     

Photonic crystal tapers for ultracompact mode conversion

We have studied the coupling of a classic ridge waveguide with a two-dimensional photonic crystal (PC) waveguide, using finite-difference time-domain calculations. The ridge waveguide exhibits only a weak refractive-index confinement of light, as it is commonly used in buried-heterostructure or ridge-waveguide lasers. The light is coupled to a PC waveguide that consists of one missing row along the ?K direction in a triangular lattice of air cylinders in AlGaAs. We compare various designs for PC tapers with that of a classic taper and for butt coupling. The calculation yields high coupling efficiency that exceeds 80% for a 2.5-microm-long PC taper. In addition, the dependence of the efficiency on the PC air-fill factor and on alignment tolerances is analyzed.     

扫描近场光学显微镜光纤锥中导波反射特性

利用局部模耦合模型理论上分析了扫描近场光学显微镜光纤的光场性质,给出光纤维中存在的正,反向传播的基模场微分方程,以及基模反向耦合系数的数值计算结果,其最高反射系数达１％左右。这种反射光可起着光纤维激光器谐振腔输出端镜的作用。     

A novel scheme of hyperbolic-end microlens using the arc technology

This study proposes a new scheme of the tapered hyperbolic-end fiber (THEF) by etching the fiber end in a hydrofluoride (HF) solution with a thin layer of oil floating on top of the HF. This study makes it possible to fabricate the hyperbolic microlenses using unique etching and fusion techniques. Compared with previous hemispherical microlenses, the study shows that a THEF with a smaller taper angle and longer taper length fabricated by lower oil density exhibits a smaller radius of curvature, thus resulting in a better coupling efficiency. The THEF microlens results in a more than 2 dB improvement in coupling efficiency when compared with the currently available hemispherical microlenses. The calculation of the effect of oil density in HF etching solution on taper angle and taper length based on an empirical model is in agreement with the measured results. The THEFs have demonstrated up to 86% coupling efficiency for a laser with an aspect ratio of 1:1.5 at a wavelength of 1550 nm.     

Forming Dislocation Pairs in the Ge/GeSi/Si(001) Heterostructure

Physics of the Solid State - In the Ge/LTGe/GeSi/Si(001) heterostructures, the GeSi buffer layer remains pseudomorphic in a certain range of the heterostructure parameters and growth regimes, while...     

Specific features of plastic relaxation of a metastable Ge x Si1 − x layer buried between a silicon substrate and a relaxed germanium layer

Heterostructures Ge/Ge _x Si_{1 ? x} /Si(001) grown by molecular beam epitaxy have been investigated using atomic scale high-resolution electron microscopy. A germanium film (with a thickness of 0.5–1.0 μm) grown at a temperature of 500°C is completely relaxed. An intermediate Ge_0.5Si_0.5 layer remains in a strained metastable state, even though its thickness is 2–4 times larger than the critical value for the introduction of 60° misfit dislocations. It is assumed that the Ge/GeSi interface is a barrier for the penetration of dislocations from a relaxed Ge layer into the GeSi layer. This barrier is overcome during annealing of the heterostructures for 30 min at a temperature of 700°C, after which dislocation networks having different degrees of ordering and consisting predominantly of edge misfit dislocations are observed in the Ge/GeSi and GeSi/Si(001) heteroboundaries.     

Temperature-dependent photoluminescence and Raman spectra from porous GeSi/Si heterostructures

Porous GeSi/Si heterostructures were fabricated by laterally anodization in HF-based solutions. Photoluminescence spectra have been investigated as a function of temperature (77–300 K), showing that porous GeSi has a quite different temperature dependence from that of porous silicon. Raman spectra indicated that the sample structure changed after anodization. Phonon participation and direct recombination of excitons are proposed to be responsible in the light emission processes of porous GeSi and Si, respectively.     

硅衬底上锗硅合金光波导设计及工艺的优化考虑

报道用射频加热化学气相沉积法制备Ｓｉ／ＧｅＳｉ／Ｓｉ大断面单模脊形光波导中设计和工艺的进一步完善，ＧｅＳｉ合金层中Ｇｅ的含量Ｘ要满足脊形光波导是单模，光波导的数值，孔径接近单模光纤值，脊高小于临界厚度值等，计算表明兼顾上述三项要求应取ｘ＝１～３％，脊的高与宽受大断面及单模的制约。Ｓｉ的晶体结构使脊的二个腐蚀侧壁是斜坡，为此起始脊宽取５～６μｍ为宜；腐蚀液，抛光液的选取人保证脊则壁及波导面端的优良镜     

电光聚合物波导中的锥形结构

提出并设计了一种基于电光聚合物的锥形波导,可用于单模光纤与电光聚合物波导器件之间的连接.锥形波导中采用了宽度锥形和折射率锥形结构.宽度锥形采用劈形形状,通过宽度和折射率的缓慢变化实现模场转换.劈形形状的宽度锥形具有较小的损耗且易于制作,折射率锥形可采用灰度掩膜光刻技术制作.研究了锥形波导的传输损耗与锥形波导的长度、波导宽度和厚度、材料吸收损耗等参数的关系及其优化,分析了锥形波导中的功率传输、模场分布与模式转换效率.结果显示锥形波导的传输损耗小于0.37 dB,光纤-波导-光纤的连接损耗优于1.62 dB,对插入损耗的改善达到8.78 dB,模场转换效率达到了83.7%.     

Ge0.05Si0.95/Si异质结单模共面布拉格反射波导光栅的设计与分析

GeSi/Si异质结布拉格反射光栅是硅基光电集成领域一种重要的集成光学器件,分析GeSi/Si异质结的传光特性和布拉格条件,通过求解布拉格光栅方程,得出耦合系数和耦合效率。利用上述原理设计出入射角为66°,波导层的厚度为2μm,光栅长度为4252μm,槽深为0.05μm,光栅周期为0.456μm,滤波带宽为0.214nm,耦合效率为84.1%的1.3μm Ge_0.05Si_0.95/Si异质结单模共面布拉格反射光栅,并用数值模拟了入射光波电场和反射光波电场的分布。     

X-ray spherical wave scattering patterns of the epitaxial Si/GeSi/Si (001) heterosystem

The interference effects of x-ray diffraction topography in the Si/GeSi/Si (001) heterosystem have been investigated. This heterosystem is a film interferometer in which the GeSi solid solution layer of variable thickness serves as a separating gap. A topograph obtained for a 004 reflection (CuK _α radiation) using a spherically bent monochromator demonstrates both maxima of the pendulum solution observed for the case of a thin crystal (1) and interference fringes due to the variable thickness of the separation layer (2). The correlation of effects (1) and (2) with the successive extinction effect of interference maxima on the slope of the diffraction reflection curve is shown by the calculated topographs obtained for the different ranges of the angle of radiation incidence θ (200 and 1400″). The possibility of precisely determining the thickness of the crystal separation layer of an interferometer based on the indicated effect is demonstrated.