微环耦合谐振光波导中的色散控制模型与数值仿真

本文利用传输矩阵法得到了微环耦合谐振光波导的色散关系,讨论了耦合损耗、传输损耗及耦合系数对微环耦合谐振光波导色散的影响,改变耦合损耗、传输损耗及耦合系数可控制其色散曲线的形状、位置、以及带宽,色散曲线的变化及控制对微环耦合谐振光波导在滤波、光信号延迟及缓存等方面的应用有重要意义. 关键词： 光波导 微环光波导 传输矩阵法     

Transmission and group delay of microring coupled-resonator optical waveguides

We measured the transmission and group delay of microring coupled-resonator optical waveguides (CROWs). The CROWs consisted of 12 weakly coupled, microring resonators fabricated in optical polymers (PMMA on Cytop). The intrinsic quality factor of the resonators was 18,000 and the interresonator coupling was 1%, resulting in a delay of 110-140 ps and a slowing factor of 23-29 over a 17 GHz bandwidth.     

Optical soliton with group delay in microring coupled-resonator optical waveguides

This paper derives the dispersion relation of microring coupled-resonator optical waveguides (CROWs) without any approximation by using the transfer matrix method. Based on the established dispersion relation of CROWs it obtains the slow group velocity and dispersion coefficient. It finds that the effect of dispersion on optical pulses can be adjusted to balance the effect of nonlinearity by changing coupling coefficient or loss, so optical soliton with group delay can be obtained in microring CROWs. The optical soliton with group delay is of great significance for applications of microring CROWs in delay lines and optical buffers of future all-optical communication systems.     

光脉冲在微环耦合谐振光波导中传输线性特性的数值仿真

利用传输矩阵法得到了微环耦合谐振光波导色散关系的一般表达式,并由色散关系出发讨论了光脉冲在微环耦合谐振光波导中传输时的线性特性,包括带宽、群速度、色散和线性相位变化,这些特性对微环耦合谐振光波导在光通信和光传感领域的应用有重要意义. 关键词： 微环光波导 光脉冲线性特性 传输矩阵法 数值仿真     

Polarization-independent optical directional coupler based on slot waveguides

A polarization-independent optical directional coupler based on slot waveguides is proposed and analyzed by using rigorous full-vectorial analysis methods based on a finite-element scheme. Properly choosing materials and structural parameters makes the coupling length for quasi-TE modes become equal to that for quasi-TM modes. Tolerances to operating wavelength and structural parameters are also discussed. The proposed coupler can be used for highly integrated optical circuits without polarization diversity schemes.     

Waveguide modes in coupled-resonator optical waveguides

Coupling between cavities within coupled-resonator optical waveguides (CROWs) affects transmission properties. Our results show that, in addition to the number of the waveguide modes, the group velocity of electromagnetic waves transmitted in the CROWs can be controlled by changing the stiffness of coupling between cavities. This is significant for the applications.     

Dispersion characteristics of coupled-resonator optical waveguides

A tight-binding optical waveguide formed by proximity coupling of nearest-neighbor resonators, e.g., a coupled-resonator optical waveguide (CROW), has distinct wave and pulse propagation characteristics compared with a conventional waveguide, and several applications in photonic devices have been proposed recently. But analysis of the dispersion, and in particular the group-velocity dispersion, in such a waveguide requires particular attention: the waveguide displays two distinct regimes of operation, depending on the position of the wave packet in the dispersion relationship.     

Mach-Zehnder interferometer employing coupled-resonator optical waveguides

A simple theoretical model of a Mach-Zehnder interferometer (MZI) consisting of two coupled-resonator optical waveguides with different lengths is proposed and experimentally demonstrated at microwave frequencies. Good agreement between theoretical and experimental results is observed. MZIs in planar photonic crystals may become key building blocks in the development of microscale optical integrated devices such as filters, demultiplexers, switches, and modulators.     

Low-power continuous-wave four-wave mixing in silicon coupled-resonator optical waveguides

We demonstrate four-wave mixing in silicon-on-insulator coupled-resonator optical waveguides consisting of 35 and 65 microring resonators, using a cw pump with coupled power below 20 mW and observed parametric conversion across more than 10 THz. The conversion efficiency is enhanced by +16 dB relative to a silicon straight waveguide of equivalent length, due to the slowing factor of the coupled-resonator structure.     

Continuously tunable 1 byte delay in coupled-resonator optical waveguides

A reconfigurable coupled-resonator optical waveguide made of a few directly coupled ring resonators is employed to control the delay of data streams modulated at tens of gigabits per second. A delay of 8 bit lengths (1 optical byte) with a small pulse broadening and 1 dB/bit fractional loss is achieved by using only eight rings. The limiting role of waveguide loss and spurious backreflections is experimentally investigated. The high storage efficiency (1 bit/ring) of the device enables an easy, reliable, hitless, and relatively low-power-consuming management of the delay. A higher storage efficiency is demonstrated to be associated to an unavoidable higher pulse distortion.     

The characteristics of a nonlinear directional coupler with nonparallel waveguides

The nonlinear coupling characteristics of the nonparallel coupler due to photorefraction is investigated using coupled mode theory with a step-like refractive index profile. The calculated results show no significant degradation of the performance of the device when less than 3×10⁴ W cm^-2 optical intensity is coupled into the waveguide. The optically induced drift effects depend on the structural geometry and the initial light intensity. Means of reducing the crosstalk induced by the photorefractive damage are also presented. Numerical results are given to illustrate the nonlinear coupling characteristics of various structures and to establish useful guidelines for the design of nonparallel directional couplers.     

Systematic design of single-mode coupled-resonator optical waveguides in photonic crystals

By establishing a direct relation between the dispersion and the field profile of a coupled-resonator optical waveguide (CROW) and those of its constituent cavities, we present a systematic method for the design of a single-mode CROW and for control of its dispersion. The procedure includes the design of a single-mode cavity and control of its frequency by engineering its structure. Then, by chaining these cavities in the proper direction and at an appropriate distance, we achieve the desired dispersion for the CROW.     

Surface plasmon polaritons based optical directional coupler

As a basic optical device, the optical directional coupler (ODC) is basically used as optical splitters, optic switches and so on. A novel ODC employing surface plasmon polaritons (SPPs) is proposed for high integration. The finite difference time domain (FDTD) method is adopted to simulate and analyze its properties. Results show that the ODC proposed here follows the general regulations of a conventional dielectric ODC, but its transverse size is of nanoscale, which improves the optical integration greatly. For 1550 nm and 1310 nm input wavelengths, when the coupling region length (L) equals half of its coupling length, the Excess Loss is respectively 0.57 dB and 0.56 dB, which is practical in applications. So the research on the present ODC is of some practical importance.     

All-optical logic gates using semiconductor-based three-coupled waveguides nonlinear directional coupler

All-optical logic gates with nonlinear optical (NLO) properties of three-coupled identical waveguides have been proposed and designed theoretically in a unique semiconductor-based symmetric structure. The model uses the NLO interactions of the coupled waveguides, like Kerr effect and Two Photon Absorption (TPA). Unlike the previous studies, we take into account higher order NLO effects of semiconductors such as Free Carriers (FC) and loss to control the switching operation. These NLO phenomena lead to high functionality in a simple unique structure. Therefore, in this work, by setting the input intensity of the waveguides, the logic AND, OR, NAND, and NOR gates are designed in a unique structure with different lengths. Our analysis deals with continuous waves (CW) region and the results are valid for the ranges of short optical pulses with time duration longer than FC life time.     

Study of ultra-fast optical pulse propagation in a nonlinear directional coupler

We showed that the application of a soliton in a nonlinear coupler does not show a better switching performance than a Gaussian pulse, unlike what the existing theory expected. Like the Gaussian pulse, a soliton could also suffer distortion, broadening, or narrowing in a nonlinear directional coupler. In addition, by using a new normalized format the linearly coupled nonlinear Schrödinger equations were investigated. For the first time, we found that both the coupling behavior and the switching performance of pulses in a nonlinear coupler depend on the product of the coupling coefficient and the dispersion length. We also showed that for a given nonlinear coupler with a Gaussian-like or soliton-like pulse input, switching performance and whether a pulse breaks up or not mainly depend on the input pulse width, not the pulse shape. PACS 42.65.Tg; 42.65.Wi; 42.81.Qb     

光子晶体耦合腔波导的色散特性

理论研究表明，在基于光子晶体的耦合腔波导中，杂质带的色散性质取决于相邻缺陷间局域电磁场的特性，而非缺陷间距离的大小.在第一布里渊区中出现的杂质带的反常色散实际上是能带折叠的结果.通过计算结构的有效折射率，证实了杂质带色散是正常色散. 关键词： 光子晶体 反常色散 耦合腔 杂质带     

Analysis of adiabatic coupling between photonic crystal single-line-defect and coupled-resonator optical waveguides

A detailed analysis of adiabatic coupling between conventional photonic crystal single-line-defect and coupled-resonator optical waveguides is reported. Adiabatic coupling by progressive variation of the radii of the spacing defects between cavities is investigated. Flat transmission spectra with coupling efficiencies greater than 90% are achieved in a broad frequency range with short coupling lengths. Moreover, we find that flat transmission at low frequencies requires longer coupling lengths partly because the requirements imposed for adiabatic transmission in photonic crystals are violated.     

Efficient coupler between chip-level and board-level optical waveguides

We propose an efficient optical coupler between a submicrometer-sized silicon waveguide on a silicon photonic chip and a multi-micrometer wide polymer waveguide on an optical printed circuit board for interchip optical networks. We show low coupling loss <0.4 dB with high lateral and angular tolerance to misalignment so that coupling can be done by automatic pick-and-place equipments with high throughput and low cost. The coupler has a wide optical bandwidth from 1470 to 1650 nm.     

Periodic spectral filter with integrated optical directional coupler

The direction of light propagation in integrated optical circuits can be inverted at the substrate edges by halved directional couplers with mirror planes at the substrate end facets. Thus the output and input of a directional coupler can be fed back on to the substrate forming a periodic spectral filter with extremely high frequency sensitivity. The filter characteristic is analysed with respect to frequency, feedback efficiency, parameters of the directional coupler and temperature. The filter pass and stop bands can be controlled electrically.