传输矩阵法分析微环谐振器阵列传输特性

微环谐振器可用作未来高密度、超大规模集成光路的基本构件,其重要发展方向之一是多环化、阵列化,微环谐振器阵列近来成为研究的热点。基于定向耦合器、环形谐振腔、直波导腔的基本单元传输矩阵,建立了用于分析微环谐振器阵列传输特性的传输矩阵模型。讨论了列间距对传输特性的影响,并数值模拟了不同尺度的奇数行和偶数行情况下谐振器阵列的传输特性。结合此传输矩阵模型,讨论了通过改变微环谐振器阵列的尺度以及耦合系数以实现滤波特性改善的方案。最后数值研究了最小尺度微环谐振器阵列传输特性与腔间耦合系数的关系。     

Filter synthesis for periodically coupled microring resonators

The theory of filter synthesis using periodically coupled microring resonators is developed as a means to overcome the fabrication sensitivities inherent in conventional higher-order filters, while still achieving desirable spectral characteristics. Each resonator in the array can compensate for deficiencies in any of the others. These filters exhibit a boxlike shape and very high extinction ratios.     

Single-photon all-optical switching using coupled microring resonators

We study the nonlinear phase response of a microring resonator coupled to a bus waveguide and the use of this nonlinear phase shift to store information in the microring resonator and enhance the switching characteristics of a Mach-Zehnder interferometer (MZI). By introducing coupling between adjacent microring resonators, the switching characteristics of the MZI can be exponentially enhanced as a function of the number of microring resonators, when compared to the linear enhancement for uncoupled resonators. With only a few moderate-finesse microring resonators, the switching power can be reduced to attowatt level, allowing for photonic switching devices that operate at single-photon level in ordinary optical waveguides.      

Performance Investigation of Photonic Crystal-Based Microring Resonator for Optical Signal Processing

Abstract

A detailed theoretical analysis is presented to characterize wave propagation at 1,550 nm inside a glass (SiO₂) microring resonator implemented using photonic crystal technology. A photonic crystal reflection is used at each microring resonator corner to enhance the bending efficiency. The characteristics of both photonic crystal beam splitter and microring resonator bending losses are analyzed and investigated using both effective refractive index and finite difference time domain methods. Analytical expressions are also derived to describe the field enhancement inside the microring resonator, the transfer function of the microring resonator, and the main parameters characterizing the resonator such as resonator band width and quality factor. The analysis is also extended to characterize a drop filter implemented using photonic crystal-based microring resonator. The results indicate clearly that the effective refractive index method can give accurate results if one starts the calculations with finite difference time domain-estimated beam splitter parameters. Further, bending efficiency as high as 99% can be obtained using a ten-post layer photonic crystal mirror at each microring resonator corner.     

Electro-optically tunable microring resonators on lithium niobate

Electro-optical tuning of a microring resonator fabricated on lithium niobate (LiNbO3) is presented. The device structure, including microring resonator and couplers, is designed in detail and is produced by titanium diffusion on the wet-etched LiNbO3 ridge surface. The resonance wavelengths for TM and TE polarizations can be tuned by electro-optic effect. The output characteristics of through port and drop port in the microring resonators are measured, and the effect of applied voltage on the shift of resonant wavelength is discussed. The presented microring resonators have the features of fast tuning speed, high material stability, bidirection wavelength shift, and no heating interference. Realization of such a microring resonator on LiNbO3 makes the utilization of electro-optic tuning and nonlinear effects in the versatile photonic applications of microring resonators achievable.     

Generalized fast and slow lights using multi-state microring resonators for optical wireless links

We propose an interesting result on fast and slow light generation using nonlinear microring resonators. When a soliton pulse is generated within the first ring resonator, the specific signals can be generated using the chaotic filter characteristics of light pulses travelling within the microring devices. We have demonstrated that two different frequency bands can be generated and they are suitable for use in optical wireless links. The other application of fast and slow lights is also presented, whereas signal security can be formed using the add/drop device to retrieve the original signal from the chaotic noisy signals. The key advantage is that the original signal can be kept in secret without any tapping due to the problem of fast light pulses and noisy signals, which are difficult to intercept.     

基于超材料结构的小型化可调滤波器

为了提高频谱资源的利用率,解决传统滤波器组体积大的问题,利用开口环结构的超材料具有高集成度的特性,设计了一款整体尺寸仅为15mm×20mm的滤波器.基于时域有限积分法分析了开口环结构滤波器的反射系数曲线与电磁参数之间的响应特性,通过在开口环缝隙处加载可调谐的二极管器件,实现了超材料滤波器在X波段(10.9~12GHz)的连续可调,扩展了滤波器的工作频带.该可调谐超材料滤波器的工作带宽达11.0%,通带内回波损耗最小值为32dB,插入损耗最大值为0.38dB,具有高集成度、宽频带、通带内选频特性良好的特点.     

基于微环谐振器阵列与马赫-曾德尔干涉仪的反射型滤波器性能分析

理论分析了一种将微环谐振器阵列与马赫-曾德尔干涉仪(MZI)相结合实现的反射型滤波器结构。将此结构类比为两类四端口网络级联模型,利用传输矩阵法推导出其通用函数形式,并给出单环及三环结构下的能量反射系数具体公式。通过传输函数矩阵模拟计算了取不同耦合系数值情况下的反射谱形变化,给出了原因分析及讨论。并模拟了引入传输损耗对三环结构谐振峰反射率的影响。数值结果表明:适当选取直波导与微型环以及微型环间耦合系数幅值时,此结构能够作为反射型滤波器件应用于密集波分复用(DWDM)系统,也可实现激光器反射镜面的功能;由于传输损耗增加而引起的谐振峰反射率下降程度依赖于所选取的耦合系数值。     

Modeling of coupling loss in ultra-compact SOI microring resonators

Ultra-compact microring resonators, made of high index contrast (HIC)-silicon on insulator (SOI) materials, have become key optical devices in integrated photonics systems. Both computer simulations and actual experiments have showed that coupling loss was a significant contributor to the total losses in ultra-compact microring resonators. In this paper, a computable model derived from step approximation method was present to theoretically determine the coupling loss. Excellent matching results between the model and literatures were achieved. The proposed model can be applied to evaluate the coupling loss for microring resonators with various geometries and guide the design of low loss optical devices based on ultra-compact microring resonators.     

Predistortion techniques for synthesizing coupled microring filters with loss

A general method based on the predistortion technique is presented for determining the optimum coupling parameters of multiple-coupled microring filters in the presence of known uniform resonator loss. The technique involves predistorting the filter transfer function by shifting its poles and zeros to compensate for loss in the microring resonators due to material absorption, surface roughness scattering, coupling loss and bending loss. It is shown that by sacrificing some in-band insertion loss, both the amplitude and group delay responses of the filter can be recovered when loss is present. Application of the method to synthesizing lossy microring filters in both the digital z-domain and analog s-domain will be presented. The proposed technique is general in that it can be applied to both amplitude and phase filters constructed of coupled microresonators in the most general two-dimensional coupling topology.     

Analysis of scattering from a finite array of circular cylinders using a model of layered cylindrical arrays

A semi-analytical approach for a periodic planar array formed by a finite number of circular cylinders is presented using a model of layered cylindrical arrays. The method consists in extracting the reflection and transmission matrices of a cylindrically periodic array of circular cylinders and then obtaining the characteristics of layered structures by using a recursive formula.     

Simultaneous fast and slow light in microring resonators

Two orthogonal light polarizations in a waveguide overcoupled to microring resonators can propagate as fast and slow light. Which polarization is fast (slow) is determined by input polarization and the number of resonators.     

Broadband locally resonant beams containing multiple periodic arrays of attached resonators

The plane wave expansion method is extended to study the flexural wave propagation in locally resonant beams with multiple periodic arrays of attached spring-mass resonators. Complex Bloch wave vectors are calculated to quantify the wave attenuation performance of band gaps. It is shown that a locally resonant beam with multiple arrays of damped resonators can achieve much broader band gaps, at frequencies both below and around the Bragg condition, than a locally resonant beam with only a single array of resonators, although the two systems have the same total resonator masses.     

Experimental investigation on submicron rib waveguide microring/racetrack resonators in silicon-on-insulator

In experiment, characteristics of silicon microring/racetrack resonators in submicron rib waveguides have been systematically investigated. It is demonstrated that only a transverse-electric mode is guided for a ratio of slab height to rib height h/H = 0.5. Thus, these microring/racetrack resonators can only function for quasi-transverse-electric mode, while they get rid of transverse-magnetic polarization. Electron beam lithography and inductively coupled plasma etching were employed and improved to reduce sidewall roughness for low propagation loss and high performance resonators. Then, the effects of waveguide dimensions, coupling region design, waveguide roughness, and oxide cladding for the resonators have been considered and analyzed.     

Box-like spectral response of 2-D microring resonator arrays

In terms of the coupled mode theory and the transfer matrix technique, novel formulas of the transfer functions are presented for a 2-D microring resonator array. By using these formulas, transmission characteristics are analyzed for this kind of Si based polymer device. Simulation shows that by means of parallel-cascading multiple microrings in every filter element, the passband can be flattened, and the box-like spectral response can be formed; in terms of series-cascading such several filter elements, the passband becomes precipitous, and the non-resonant light and the crosstalk become weak.     

Resonance and band filtration on the basis of two-phase crystal-like structures

Two-phase crystal-like structures for the resonance and band filtration of signals are proposed. It is shown that the selectivity of a two-phase resonator is higher than that of a traditional half-wave one. Implementation of band filtration by coupled resonators is considered. Experimental and calculated characteristics of a band filter on the basis of a two-phase electromagnetic crystal are presented.     

Propagation in a directional coupler of parallel microring coupled-resonator optical waveguides

The fundamental concept of coupled-resonator optical waveguides (CROWs) is for the first time taken a step farther to propose the more complicated case of coupled-resonator directional couplers, by analyzing the phenomenon of propagation in two parallel chains of microring resonators. Using the method of transfer matrices it is shown that the infinite coupler supports even and odd supermodes that satisfy frequency-shifted replicas of the familiar CROW dispersion equation as well as modified periodic Floquet conditions. Depending on the relative coupling strengths between neighboring resonators in the same chain and between the two chains, the frequency bands of the supermodes can overlap or be completely separated, resulting, in the latter case, to a complete bandgap around the central resonance frequency of the microrings. Three frequency windows, corresponding to totally different properties of directional coupling, are defined through this band-overlap mechanism along the increased total bandwidth of the coupler. These predictions are fully confirmed in the response of the realistic finite-length version of the considered coupler which is also analyzed.     

Embedded ring resonators for microphotonic applications

We propose a new type of optical resonator that consists of embedded ring resonators (ERRs). The resonators exhibit unique amplitude and phase characteristics and allow designing compact filters, modulators, and delay elements. A basic configuration of the ERRs with two rings coupled in a point-to-point manner is discussed under two operating conditions. An ERR-based microring modulator shows a high operation speed up to 30 GHz. ERRs with distributed coupling are briefly described as well.     

Enhanced linear and nonlinear optical phase response of AlGaAs microring resonators

We have constructed and characterized several optical microring resonators with scale sizes of the order of 10 microm. These devices are intended to serve as building blocks for engineerable linear and nonlinear photonic media. Light is guided vertically by an epitaxially grown structure and transversely by deeply etched air-clad sidewalls. We report on the spectral phase transfer characteristics of such resonators. We also report the observation of a pi-rad Kerr nonlinear phase shift accumulated in a single compact ring resonator evidenced by all-optical switching between output ports of a resonator-enhanced Mach-Zehnder interferometer.