Three-dimensional polymer optical waveguide interleaver with selectable channel spacing

A polymer optical waveguide interleaver with selectable channel spacing and adjustable flat top based on a three-dimensional structure is reported. This interleaver is made of two waveguides laid in two different but parallel layers. These two waveguides cross-over each other three times, with an electrode heater deposited on top of each crossing point to adjust the coupling ratio between the guides. This 3D structure has many advantages over the corresponding 2D counterpart such as the ease of fabrication and the adjustment of coupling ratio between the two waveguides. The channel spacing can be selected to be either 1.6 nm, 0.8 nm or 0.53 nm simply by changing the power supplied to each heater; also at the 1.6 nm channel spacing it is possible to create a flat-top spectral response (0.6 dB ripple over 0.5 nm), again by tuning the coupling ratios using the electrical heaters.     

InP阵列波导光栅的误差分析

在InP阵列波导光栅的制作过程中会引入不同的误差,从而影响器件的性能.为了最大限度地控制误差,提高半导体器件性能,本文采用传输函数法对InP基阵列波导光栅的系统误差和随机误差分别进行了分析.从系统误差的模拟结果中可以得到如下结论:深脊型波导的有效折射率n_c平均每偏移+0.000 1,中心波长偏移+0.05nm.相邻阵列波导长度差ΔL每偏移+0.01 μm,中心波长将偏移+0.44 nm.n_c和ΔL仅仅会影响到传输谱中心通道及其他各通道对应的波长,使得传输谱发生整体漂移,而信道间隔及串扰不会改变.罗兰圆半径R偏移不会影响器件的中心通道对应的波长,但会使其它通道对应的波长发生变化,最终使得信道间隔改变,R增加50 μm,信道间隔减小0.03 nm.从随机误差模拟结果中,得出:波导芯区折射率、上包层折射率、衬底折射率、波导宽度和波导芯层厚度的随机波动会对阵列波导光栅的串扰产生较大的影响.根据以上分析,可以通过控制不同参量来调节器件的中心波长以及信道间隔等来优化阵列波导光栅的光学性能.     

Simulation investigation on waveguide properties of terahertz wave through subwavelength semiconductor gap

The waveguide propagation properties of terahertz wave through subwavelength semiconductor trench have been simulationally investigated. The effects of gap width, temperature, doping concentration and dielectric filling materials on waveguide property have been given and discussed. The results show that as temperature and doping concentration increases, the skin depth and the propagation constant decreases. In addition, the effective index increases and the propagation length decreases as the dielectric constant of filling materials increases.     

High-performance unidirectional electrooptic modulator based on polymeric highly multi-mode waveguides

A unidirectional electrooptic modulator based on an asymmetrical highly multi-mode waveguide coupler is proposed. Firstly, the energy distributions of all the modes within two highly multi-mode waveguides are analyzed with eigenstate theory. Then, to achieve high switching performance in a guided-wave coupler, a dumping wall is placed on the larger waveguide of an asymmetric pair of waveguides, so that the larger waveguide has a dumping effect. This dumping effect makes the asymmetric highly multi-mode waveguide coupler possess a highly efficient unidirectional coupling process. Due to the large cross-section of the waveguide, a new modulation electrode structure is built. Based on this dumping effect, the unidirectional coupling process is theoretically modeled. Furthermore, in both scenarios, i.e., the unmodulated state and the electrooptically modulated state, the unidirectional coupling efficiencies are studied. As a result, not only can a high unidirectional coupling efficiency of 100% be achieved, but a high electrooptic modulation depth more than 90% can also be implemented in theory, and a high thermooptic modulation depth more than 90% under a low modulation voltage of 30 volts is also experimentally achieved. This device can be used for multi-mode optical interconnection systems such as data communication and fiber sensor networks.     

Buried ion-exchanged glass waveguides: burial-depth dependence on waveguide width

A detailed theoretical and experimental study of the depth dependence of buried ion-exchanged waveguides on waveguide width is reported. Modeling, which includes the effect of nonhomogeneous time-dependent electric field distribution, agrees well with our experiments showing that burial depth increases linearly with waveguide width. These results may be used in the proper design of integrated optical circuits that need waveguides of different widths at different sections, such as arrayed waveguide gratings.     

A wide-band polymeric electro-optic modulator array based on unidirectional coupling between multi-mode waveguide array and a vertical configured dumping planar waveguide

A polymeric wide-band electro-optic (EO) modulator array based on unidirectional mode-coupling between the guiding multi-mode waveguide array and a vertical configured planar dumping waveguide was developed. A low insertion loss of <1.7 dB was obtained due to asymmetrically designed guiding waveguide and the dumping waveguide. A modulation depth of 91% was achieved with the device length of 3.5 cm at a low driving voltage of 3.2 V. The employment of the dumping planar waveguide not only provides an efficient way to achieve the unidirectional coupling mechanism, but also effectively confines the light coupled from the guiding waveguides within the planar dumping waveguide. The combination of unidirectional coupling and light confinement effects ensures low cross talk of <22 dB between adjacent guiding waveguides. Since the proposed modulator is based on the unidirectional coupling mechanism, it is intrinsically wide-band. A wide-band operation from 1308 to 1324 nm was experimentally obtained. The unidirectional mode-coupling-based wide-band modulation principle can be readily applied to other wavelengths, such as 1330 and 1550 nm ranges.     

Compact tunable three-dimensional polymer optical waveguide comb filter

A compact channel spacing tunable polymeric three-dimensional (3D) comb filter has been designed and fabricated. This comb filter is made of three waveguides laid in two different but parallel layers: one is in the lower layer and the other two are in the upper layer. These two waveguides in upper layer do not cross each other but instead each twice cross over the waveguide in the lower layer. At each crossing point an electrode heater is deposited on the top surface to adjust the coupling ratio between these guides. By supplying power to each heater pair, respectively, the channel spacing can be selected to be either 1.6 nm or 0.8 nm; in addition a flat-top spectral response may be obtained at the 1.6 nm channel spacing if power is supplied to both the heater pairs simultaneously.     

Beam Steering Type of 1 : 4 Optical Switch Using Thermo-Optic Effect

We propose a beam steering type optical switch employing a phase shifter. It consists of collimating waveguide mirrors, an arrayed-waveguide which has deep trenches incorporating polymer materials, and input/output waveguides. The incident light is guided to the front mirror, where it is then collimated, and input to the arrayed waveguide. The number of trenches filled with polymer linearly increases in order. The refractive index of the polymer can be controlled with temperature, and the propagation direction of the output light from the arrayed waveguide can also be controlled. A switch with 15 waveguides in the array has been fabricated. The chip size is about 2:5 × 9:0 mm², the insertion loss is 10 dB, and the extinction ratio is about 10–13 dB.     

一种非矩形截面对浅刻蚀SOI脊形波导侧向泄漏损耗的影响

为了进一步探索用绝缘体上晶体硅制作的浅刻蚀脊形波导侧向泄漏损耗的规律,提出并研究了一种非矩形截面浅刻蚀绝缘体上晶体硅脊形波导.用光的干涉理论建立该波导的周期性损耗模型并推导出损耗周期公式,然后通过完美匹配层边界条件下的频域有限元法仿真观察该特殊波导类TM0模的侧向泄漏损耗周期的变化与最大损耗点的偏移现象.周期大小的仿真结果与理论计算符合度较高,其平均相对误差仅0.56%.此外,发现该类波导在某些沟槽宽度下可以通过改变截面来实现对类TM0模损耗从最大到最小的调节,而在另外一些沟槽宽度下,类TM0模损耗对截面变化不敏感.研究结果可以简化波导加工并提高制作容差,为该类型波导的设计与制作提供参考.     

小尺寸低折射率差硅基二氧化硅阵列波导光栅

随着AWG型器件在光通信系统中的大规模应用,对低成本AWG芯片的需求越来越多。在各种降成本方案中,减小AWG芯片的尺寸是最有效的方法之一。本文介绍了一种新型小尺寸低折射率差硅基二氧化硅阵列波导光栅（AWG）的设计。在该AWG中,输入波导/输出波导与平板波导连接的部分制作成两侧为空气槽的高折射率差波导,所以在与输出平板波导连接处的相邻输出波导间距较小,这样可以在设计上缩短平板波导的长度、减少阵列波导的数量,实现较小的AWG芯片尺寸。该AWG的其它部分,如输入/输出波导与光纤耦合的部分、阵列波导光栅等均采用常规的低折射率波导工艺,所以就同时具有与常规的低折射率波导AWG相同的优点：如低耦合损耗、较好的串扰以及光学特性等。根据这个原理,设计了一种40通道100 GHz频率间隔的低折射率差硅基二氧化硅AWG,其芯片尺寸只有23.88 mm?10.5 mm,是传统相同材料制作的AWG尺寸的1/6。     

Semi-Analytical Simulation of Titanium-Indiffused Lithium Niobate-Integrated Optic Directional Couplers Consisting of Curved Waveguides

Integrated optic directional couplers consisting of curved waveguides are simulated analytically by solving the Riccati equation. The coupling coefficient between the curved waveguides with a parabolically varying gap and the condition of total power transfer between the waveguides are derived. In order to compute the overall coupling coefficient and hence the power distribution along the waveguides for Ti:LiNbO₃ curved waveguide directional couplers, the coupling coefficient for straight waveguide couplers is computed for different gaps using the effective-index-based matrix method (EIMM). Finally, the power distribution in the curved waveguides along the length is computed. The method is mostly analytical except the effective-index method and is computationally simple.     

阵列波导光栅平坦化的研究

阵列波导光栅的平坦化在实际应用中有很重要的意义.本文系统地研究了阵列波导光栅的平坦化.在输入波导、输出波导、阵列波导输入端与输出端上分别引入了指数型锥形波导.通过改变锥形波导的形状和尺寸来实现平坦化的优化.本文首先从理论上论述了引入指数型锥形波导的输出光谱特性,给出了结构参量的关系表达式,阐明了输入波导处的锥形波导是影响输出光谱平坦化的主要因素,阵列波导和输出波导处的锥形波导对输出光谱的平坦化有一定的影响.其次采用数值模拟的方法模拟了输出光谱,优化了结构参量,总结出了指数型锥形波导对平坦化影响的趋势和规律.模拟结果显示,输出光谱1 dB带宽大于通道间隔的50%,插入损耗从5.2 dB减小到了4.0 dB,串扰小于-30 dB.最后,本文给出了实验结果,插入损耗减小了0.87 dB,串扰减小了3.67 dB,1 dB带宽增加0.1 nm,增加了54.7%.实验结果表明引入指数型锥形波导提高了阵列波导光栅器件的光谱性能.     

星形光波导耦合器的耦合特性分析

根据TE0模光波导的本征场分布、瑞利索末菲标量衍射积分公式和激励源与光波导耦合的匹配效率公式,给出光波导端面衍射和耦合的归一化发射系数和接收系数计算公式,推导出光波导端面非接触耦合的耦合效率计算公式。光波导模场分布采用高斯函数近似表达,给出简洁的计算光波导端面非接触耦合的耦合效率函数表达式。最后,基于星形光波导耦合器结构参量的特点,将累加运算采用积分运算近似表达,给出星形光波导耦合器接收光波导总的接收效率与耦合器基本参量的关系,阐明了星形光波导耦合器的耦合特性。     

基于时域有限差分法分析等离子波导和介质波导耦合

使用Rsoft软件中的时域有限差分模块Fullwave分析二维介质波导和等离子波导耦合特性,利用软件仿真耦合结构并自动计算出光在介质波导和等离子波导中传输的耦合效率,进而测绘耦合效率随波导尺寸和光波长的变化曲线图,发现MDM导波结构的缝隙宽度和光通信质量密切相关,在确定尺寸下,传输损耗随传输距离成指数衰减.根据分析得到的耦合效率变化规律发现介质波导和等离子波导间距最佳点都应设为15 nm,进而优化波导的几何结构参数后,可以将耦合效率提高到83%.     

Measurement of birefringence in thin-film waveguides by Rayleigh scattering

A method of measuring birefringence in slab and ridge waveguides based on the coherent superposition of Rayleigh light scattering from TE and TM polarized modes is described and demonstrated in silica-on-silicon waveguides. A measurement accuracy of approximately 10(-6) has been achieved. This method is used to determine the evolution of waveguide birefringence with annealing temperature in phosphorous-doped glass waveguides. The measured birefringence increases rapidly with annealing temperatures up to 800 degrees C but remains unchanged for higher-temperature anneals. We interpret this threshold as the temperature above which glass can flow.     

Negative index and indefinite media waveguide couplers

We study the coupling interaction between dielectric waveguides and coupling elements made from negative-refracting media. The coupling configuration consists of a length of dielectric waveguide, which terminates either directly into or near a planar layer composed of the negative-refracting medium, and is followed by a second waveguide. Radiation output from the first waveguide is refocused at the position of the second waveguide, so that the negative-refracting layer serves as a coupler between the waveguides. Because both isotropic negative-index layers and bilayers of indefinite media can recover the near-field, evanescent components of a source field distribution, the coupling between the input and output waveguides can be highly efficient – in principle providing perfect, lossless coupling. We present simulations and some initial experimental results illustrating the coupling effect, and speculate on the potential for optical fiber couplers and integrated modulators. PACS 42.79.Gn; 41.20.-q; 42.70.-a     

Variational analysis of Er:Ti:LiNbO3 waveguide lasers based on Gaussian/two-half Gaussian mode field distribution

Starting with two dimensional, scalar wave equation, a variational equation was established for the fundamental TE and TM modes guided in Ti:LiNbO₃ waveguides on the basis of assuming a symmetric Gaussian mode field function in the width direction and two-half Gaussian trial functions in the depth direction. The controllable waveguide fabrication parameters, including channel width, diffusion temperature, initial Ti-strip thickness and diffusion time, dependent of fundamental mode size, effective pump area, coupling efficiency between pump and laser modes, and the coupling loss between a Ti:LiNbO₃ waveguide and a fiber were numerically calculated for Z-cut Er:Ti:LiNbO₃ channel waveguide lasers at three possible emission wavelengths 1532,1563 and 1576 nm and two possible pump wavelengths 1480 and 980 nm. The calculated results were compared with those of Gaussian/Hermite–Gaussian mode field distribution in detail.     

Athermal waveguides for optical communication wavelengths

We report on the design, fabrication, and characterization of temperature insensitive strip silicon-on-insulator racetrack resonators. The influence of various parameters, such as waveguide width, waveguide height, ring radius, coupling length, ring gap, and operating wavelength, on temperature-dependent wavelength shift is examined. A resonant wavelength shift of 0.2 pm/K at a 1550 nm wavelength is measured for 335 nm × 220 nm waveguides. A significant reduction of waveguide propagation losses, improved ring Q value, and higher extinction ratio are obtained after overlaying the silicon waveguides with a polymer cladding.     

微细笔直写聚合物条形光波导的研究

提出一种采用微细笔直写技术直写聚合物光波导的简便方法，利用该技术成功直写出了氟化聚酰胺条形光波导，并着重研究了气体压力和直写速度对波导宽度的影响规律。实验结果表明：直写获得的条形波导的边缘整齐、表面光滑，而且不存在小孔等缺陷或杂质。当其他工艺参数不变的情况下，波导宽度随着气体压力的增加而增大，随着直写速度的增大而减小。微细笔直写获得的条形光波导成功地实现了通光，在波长为1550nm处的最小传输损耗为0.59dB/cm。     

温度测量范围加倍的单微环传感器

本文提出了一种基于U形波导耦合单微环结构的新型SOI(绝缘体上硅)温度传感器.温度变化引起感温部位有效折射率和长度变化,导致传感器的输出光谱发生漂移.根据传输矩阵法和耦合模理论,设计了新型传感器模型,并且分析了感温部位不同时系统输出光谱特性.结果表明:当U形波导耦合单微环整体结构感温时,输出光谱无伪模,消光比达到31 dB,可作为最佳感温元件.相比于传统的双直波导耦合单微环结构,当U形波导的两个耦合点间的距离为微环周长的整数倍数时,FSR(自由光谱范围)可加倍至56 nm,灵敏度提高到89.2 pm/?C,测量范围为298—720 K,实现了SOI微环谐振器的高温测量.