集成串联环型谐振光滤波器特性的数值分析

将串联结构的环型谐振滤波器类比为四端口网络,利用传输矩阵法推导出通路和下话路传输函数的通用公式。对表征串联双环谐振滤波器响应的特性参量:幅度平坦性、通带带宽、相位群时延进行了数值计算和优化设计。结果表明:尽管损耗将引起滤波响应幅度的轻微降低,但在目前改善了的制作工艺下,损耗对器件的影响可以忽略;滤波器的传输特性主要由环与环间耦合系数决定,通过优化使其从中间到两侧对称增加,可以在实现滤波响应最大平坦性的同时,改善通带带宽和过渡带的滚降特性。与单环结构相比,不仅幅度特性得到了明显的改善,而且消除了二阶群时延色散效应。     

Effect of ring spacing on spectral response of parallel-cascaded microring resonator arrays

In terms of the coupled mode theory and transfer matrix technique, novel formulas of the amplitude coupling ratio and transfer functions are presented for a parallel-cascaded microring resonator array (PCMRR). By using these formulas, effects of structural parameters, especially the ring spacing, on the spectral response are analyzed for this kind of polymer device. The box-like spectral response is successfully obtained due to the proper selection of the ring spacing, amplitude coupling ratio and the number of rings.     

Characteristic analysis of series-cascaded microring resonator arrays

In terms of the coupled mode theory, novel formulations of the transfer functions are presented for a series-cascaded microring resonator (MRR) array. Using these formulas, transmission characteristics are analyzed and some parameters are optimised for such a polymer device. Simulation results show that when several microrings are serially cascaded to form a MRR array, the passband becomes steep, and the nonresonant light and the crosstalk become weak.     

Characteristic Analysis of a Smooth Square Microring Resonant Wavelength Multiplexer

Novel formulas of amplitude coupling ratio and transmission functions are presented for a smooth square microring resonant (MRR) wavelength multiplexer. By using these formulas, transmission characteristics are analyzed and some parameters are optimized for such a 1 × 8 polymeric device around the central wavelength of 1550.92 nm with the wavelength spacing of 1.6 nm. In the design of the device, by using the smooth squares, a thicker coupling layer is obtained, and by resonating the light at different resonant orders in different filter elements, the ring radius increment is increased sufficiently, which is of benefit to the fabrication of the device. When the amplitude coupling ratio is 0.2, the 3-dB bandwidth of the spectral response is about 0.2 nm; the ratio between -1 dB and -10 dB bandwidths is about 0.2; the insertion loss is less than 1.33 dB; and the crosstalk is below -21 dB for every vertical output channel of the device.     

Design of full-bandwidth ROADM based on MMI and MRRs

In this paper, we propose a full-bandwidth reconfigurable optical add/drop multiplexer (ROADM) equipped with multiplexer/demultiplexer (MUX/DEMUX) and switch array. Based on the pairwise multimode interference (MMI) and side-ported MMI, the full-bandwidth MUX/DEMUX is achieved. The switch array based on microring resonators (MRRs) can achieve the function of the wavelength selective switches. By designing the second-order series-coupled MRR structure, using thermo-optic effect, the switch is able to get a switching ratio above 16 dB. The proposed ROADM system shows good performance for application in dynamic optical networks.     

Characteristics of vertical bent coupling between straight and curved rectangular optical waveguides

In terms of the coupled mode theory (CMT) and the transfer matrix method, we present a technique and relative formulas including the bent coupling coefficient, amplitude coupling ratio, amplitude transmission ratio and propagation power for analyzing the vertical bent coupling between a curved rectangular waveguide and a straight one. Investigations show that the bent coupling appears in an effective coupling region by both sides of the central coupling point. Beyond this effective coupling region, however, the bent coupling is very weak, and the propagation power in the waveguide is closer to a constant. As the bent radius increases, or the thickness of the coupling layer between these two waveguides decreases, this effective coupling region becomes wider, in which the coupling behavior becomes stronger.     

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。     

Electronic transport through a periodic array of quantum-dot rings

Using the tight-binding approximation and the transfer matrix method, this paper studies the electronic transport properties through a periodic array of quantum-dot (QD) rings threaded by a magnetic flux. It demonstrates that the even--odd parity of the QD number in a single ring and the number of the QD rings in the array play a crucial role in the electron transmission. For a single QD ring, the resonance and antiresonance transmission depend not only on the applied magnetic flux but also on the difference between the number of QDs on the two arms of the ring. For an array of QD rings, the transmission properties are related not only to the even--odd parity of the number $N_{0}$ of QDs in the single ring but also to the even--odd parity of the ring number $N$ in the array. When the incident electron energy is aligned with the site energy, for the array of $N$ rings with $N_{0}={\rm odd}$ the antiresonance transmission cannot occur but the resonance transmission may occur and the transmission spectrum has $N$ resonance peaks ($N-1$ resonance peaks) in a period for $N={\rm odd}$ (for $N={\rm even}$). For the array of $N$ rings with $N_{0}={\rm even}$ the transmission properties depend on the flux threading the ring and the QD number on one arm of the ring. These results may be helpful in designing QD devices.     

大气湍流对多抖动法相干合成技术中相位调制信号的影响

分析了大气湍流对采用多抖动法实现的相干合成阵列光束中相位调制信号的影响. 文章首先根据广义惠更斯-菲涅耳原理,采用折射率结构函数对大气湍流进行描述,推导了多抖动法相干合成中阵列光束通过大气湍流后相位调制信号的一般表达式. 在此基础上进行数值模拟,分析了传输距离、湍流强度、光束阵列占空比和光斑尺寸等因素对相位调制信号的影响. 研究发现随着传输距离的增大,相位调制信号强度会先增大后减小,存在一个极大值点;随着湍流强度的增强,相位调制信号强度极大值点的出现距离不断缩短;当光束阵列占空比一定时,随着光斑尺寸的增大 关键词： 大气湍流 相干合成 多抖动法 相位调制     

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。     

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.     

Magnetic flux and strain effects on electron transport in a linear array of nanoscopic rings

Electron transport through a linear array of nanoscopic rings with six quantum dot sites per ring is investigated in the presence of an external magnetic flux producing an Aharonov-Bohm phase shift effect. A tight-binding model is employed to analytically calculate the transmission as a function of electron energy, external flux, and inter-site coupling parameters. Current vs. voltage relationships of the ring system are computed using a standard scattering theory of transport and shown to modulate between semiconductor and ohmic characteristics. System parameters are adjusted in order to study the effects of a longitudinal strain on the transmission properties of the linear multiple-ring array. Longitudinal strain is modeled with a Slater-Koster type theory and is demonstrated to affect the transmission properties primarily by narrowing the transmission bands and opening up additional bandgaps in the band structure. In addition, a universal resonant transmission condition as a function of flux is extended to show that the application of strain causes the resonant transmission peaks to converge towards one-half of a flux quantum.     

串联双环光微谐振器的滤波特性

详细研究了串联双环光微谐振器的光带通滤波特性，给出了其通带带宽的公式，分析了出／入环光耦合系数和环间光耦合系数对通带特性的影响，计算并特别强调了滤波通带的结构特点，也分析了微环中存在的光损耗对串联双环光微谐振器的滤波特性的影响。     

Generalized analysis of multiple ring resonator filters: Modeling by using graphical approach

The filtering characteristics of multiple ring resonator (MRR) filters are modeled and investigated. The ring resonators of the MRR have identical perimeters and the coupling coefficients distribution provide passband characteristics with steeper roll-off, flatter top and greater stopband rejection than single ring resonator. The theoretical results are indicated that the optical loss in micro-rings has a strong influence on the characteristics of the MRR filters. A novel attempt has been made to employ a graphical approach in the analytical derivation of the optical transfer functions of MRR filters that can be represented in signal flow graph diagrams.     

Piecewise linear integrated optical device as an optical isolator using two-port nonlinear ring resonators

A nonlinear (piecewise linear) optical transfer function for optical applications generally and isolator especially is introduced and a realization method for the introduced block based on array of two-port nonlinear ring resonators is proposed. The effect of system parameters on the transfer function is studied. The characteristics of the introduced nonlinear device such as the threshold value and the slope of linear part can be controlled using the coupling coefficients and ring lengths. We show that using our proposed idea, easily more than 30-dB isolation well over 3 THz can be obtained only with similar two rings. Also, insertion loss less than 1 dB can be obtained using optical amplifier between rings. The proposed circuit is compact (0.2 mm²) and easily can be integrated with semiconductor lasers as well as other integrated devices and systems. Finally, the analytical result for approximation of the threshold and slope of linear part is presented.     

Performance analysis and improvement of semiconductor optical amplifier direct modulation with assistance of microring resonator notch filter

We demonstrate through numerical simulations that a passive single-bus microring resonator (MRR) employed as notch filter enables to directly modulate an ordinary semiconductor optical amplifier (SOA) at 10 Gb/s. This data rate constitutes a fourfold increase in the speed that it is possible to modulate the SOA due to its finite differential carrier lifetime. The theoretical analysis unveils how the MRR radius and detuning must be selected so that the MRR-based filtering scheme efficiently overcomes the pattern-dependent impairments incurred by the SOA narrow electrical bandwidth. Moreover, the small-signal analysis conducted to correlate the perturbations in power of the modulated optical signal inserted in the MRR with those at the MRR output confirms the enhancement in the electrical bandwidth of the SOA–MRR combination. Provided that the MRR response is tailored as suggested, which is technologically feasible, the MRR action permits the encoded signal to exhibit at extended data rate a pulse and eye diagram profile of acceptable quality, tolerable amplitude difference indices, an error probability below the forward error correction limit, and a sufficient system net gain for medium-haul transmission in standard single-mode fiber with dispersion compensation. These performance improvements can be beneficial for the direct modulation of standard SOAs. Together with SOAs inherent amplification capability, they can open new perspectives in using these active elements as external modulators in various target applications.     

An efficient method for solving spectral changes of microring resonator

Parameter optimization is performed, transmission characteristics are analyzed, and effects of fabrication errors are investigated for a lateral coupling microring resonator (MRR). Simulated results show that the fabrication errors result in the shift and shape change of the transmission spectrum compared with the designed case without errors. In order to reduce spectral changes, an efficient compensation method of fabrication errors is investigated.     

Amplifying Characteristics of Er3+/Yb3+ Co-Doped Parallel-Cascaded Double Microring Resonators

Abstract

In terms of the coupled mode theory, formulas of the transfer function and the output power gain are presented for an Er³⁺/Yb³⁺ co-doped parallel-cascaded double microring resonator. Around the pump wavelength of 0.98 μm and the central signal wavelength of 1.55 μm, analysis is performed for the dependence of the output power gain on the pump power, signal power, dopant concentration, amplitude coupling ratio, and ring spacing. The results show that the output power gain of this device is much larger than that of the Er³⁺/Yb³⁺ co-doped waveguide amplifier with identical waveguide lengths. In the case of the amplitude coupling ratio κ = 0.064, ring spacing L₂ = 10π R, pump power P_p0 = 8 mW, signal power P_s0 = 37.2 μW, Er³⁺ ion concentration N_Er = 1 × 26 m^?3, and Yb³⁺ ion concentration N_Yb = 3 × 27 m^?3, the device can produce higher signal power gain from 11.9 dB even up to 70 dB.     

Analytical and numerical study of quantum transport in an array of nanorings: A case study with double rings

We present an analytical method to obtain an expression for electron transmission through an array of disordered nanorings (ADNRs) sandwiched between two semi-infinite metallic leads in different lead-ring coupling strengths. Our approach is based on the nearest-neighbor tight-binding approximation and transfer matrix method. First, we derive an analytical formula for electron transmission across the system. Next, we apply our approach to study of the electron transport in a perfect double nanoring (PDNR) and design a NOR gate using the magnetic fluxes inputs. The conductance, current–voltage characteristics and threshold voltage of the system are calculated in the weak and strong coupling regimes.     

Template-directed synthesis of highly ordered nanoporous graphitic carbon nitride through polymerization of cyanamide

The fabrication of well-ordered nanoporous graphitic carbon nitride by condensation of cyanamide (CN-NH₂) as a molecular precursor using a colloidal silica crystalline array as a template is described. The resulting sample exhibited a three-dimensionally extended highly ordered pore array as shown by transmission electron microscopy, scanning electron microscopy and nitrogen isotherms. The carbon nitride structure revealed high graphitic nature with C₃N₄ stoichiometry. In particular, the C₃N₄ network structure consists of tri-s-triazine rings (C₆N₇) cross-linked by trigonal N atoms.