Measurements of excess loss of the crossed waveguide using optical waveguide ring resonators

Crossed waveguide is widely used in optical devices, whose excess loss has a strong impact on multi-turn optical waveguide ring resonator and resonator integrated optic gyro. The resonance curve of the ring resonator is sharply dependent on the loss within the resonator. This paper presents how to get excess loss of the crossed waveguides nondestructively through the comparison of the resonance characteristics between one-turn and multi-turn optical waveguide ring resonators.     

Polarization-independent guided-mode resonance filter with cross-integrated waveguide resonators

A cavity-resonator-integrated guided-mode resonance filter (CRIGF) has been proposed and investigated in order to realize high-efficiency narrowband reflection with a small aperture. The CRIGF consists of a grating coupler integrated in a cavity resonator constructed by a pair of distributed Bragg reflectors on a thin-film waveguide. This time, orthogonally crossed integration of two CRIGFs was demonstrated in order to obtain polarization-independent reflection spectrum. An SiO₂-based device with 10?μm aperture was designed and fabricated for around 850?nm wavelength operation, and narrowband polarization-independent reflection was confirmed experimentally.     

Matching of quasioptical open resonators with waveguide feeders

We consider a semisymmetric open resonator (OR) included in a waveguide feeder, in which the first higher-order mode is excited. We show that a high efficiency of excitation of the mode can be achieved by appropriate choice of coupler dimensions due to the matching of structures of the exciting and operating fields. We analyze the behavior of the resonance reflection and transmission coefficients as well as the loaded Q-factor of an OR as functions of the parameters of one-dimensional E-polarized diffraction gratings located in a coupler aperture with dimensions of a few of wavelengths. Calculations are made with allowance for the resonance and excitation losses. The numerical results differ from the experimental data by no more than 13%, which allows one to construct open resonance systems with the required properties by changing the parameters of diffraction gratings in the coupler aperture. Institute of Radiophysics and Electronics, National Academy of Sciences of Ukraine, Kharkov, Ukraine Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 4, pp. 325–334, September, 2000.     

Ultra-compact terahertz switch with graphene ring resonators

We propose and numerically demonstrate a compact terahertz wave switch which is composed of two graphene waveguides and three graphene ring resonators. Changing the bias voltage of the Fermi level in the center graphene ring, the resonant mode can be tuned when the plasmon waves in the waveguides and rings are coupled. We theoretically explain their mechanisms as being due to bias voltage change induced carrier density of graphene modification and the coupling coefficients of graphene plasmon effect after carrier density change, respectively. The mechanism of such a terahertz wave switch is further theoretically analyzed and numerically investigated with the aid of the finite element method. With an appropriate design, the proposed device offers the opportunity to ‘tune' the terahertz wave ON–OFF with an ultra-fast, high extinction ratio and compact size. This structure has the potential applications in terahertz wave integrated circuits.     

光波导微环谐振器用于二进制格式变换研究

实验观测到了微环对入射二进制码的格式转换作用, 且这种转换作用对入射光波长具有强烈的依赖关系. 使用线性耦合模理论, 结合傅里叶变换以及电光马赫曾德强度调制作用, 理论再现了这一实验结果, 并通过使用简化的传递函数对此进行了解释. 理论分析还表明, 对于非临界耦合微环, 通过格式转换后波形的非对称性可以直观地判断微环的耦合状态, 即过耦合或欠耦合有不同的输出波形特点. 关键词： 微环谐振器 数据格式转换 耦合模方程 传递函数     

Superconducting tunable filter with constant bandwidth using coplanar waveguide resonators

In this paper we propose a two-pole varactor-tuned superconducting filter using coplanar waveguide(CPW) spiralin-spiral-out(SISO) resonators. Novel internal and external coupling structures are introduced to meet the requirements for a tunable filter with a constant absolute bandwidth. The fabricated device has a frequency tuning range of 14.4%at frequencies ranging from 274.1 MHz to 317.7 MHz, a 3-d B bandwidth of 5.14 ± 0.06 MHz, and an insertion loss of0.08 d B–0.70 d B. The simulated and measured results are in excellent agreement with each other.     

Cylindrical Gaussian-Hermite modes in rectangular waveguide resonators

Approximate solutions to the wave equation inside a rectangular metallic waveguide has been obtained in terms of cylindrical Gaussian-Hermite functions.E _mn ^π modes propagate with negligible straight guide losses in the far-infrared region. A new type of low-loss optical resonator suitable for FEL operation at long wavelengths is presented here.     

Microstubs resonators integrated to bent Y-branch waveguide

We report numerical simulations, based on a finite difference time domain (FDTD) method, of light propagation in two-dimensional semiconductor micro-optical waveguides coupled to one or several lateral stubs. It is shown that when the stub is covered with a perfectly metallic thin layer, the transmission spectrum contains several narrow dips. Such simulation of the metallic coating can be used in the far infrared frequency domain, far from the optical regime. We propose a selective filtering device based on the interaction between several stubs. Inserting an appropriate defect stub between a set of periodical stubs leads to a tunnelling transmission, with a narrow peak inside the gap. This filtering phenomenon is used to propose a demultiplexer based on a Y-shaped waveguide for separating signals with different frequencies. Finally, we show that the filtering effect of a stub can also be reproduced when the metal is described in the frame of a Drude model instead of being perfect, which makes plausible the realization of the above devices in the near optical regime.     

Theory of gyrotropic ring resonators with counterpropagating modes coupling

The Faraday effect in ring resonators leads to the resonance splitting of clockwise and counter-clockwise propagating modes. In this work we investigate how this resonance splitting influences the ring resonator's behavior if both modes are coupled by a sidewall corrugation of the resonator. Coupled mode theory is used to evaluate the transmission and reflection characteristics of a ring resonator coupled to a waveguide. Based on these evaluations, we characterize a novel ring resonator switch. The resonance of the corrugated gyrotropic resonator coupled to a waveguide can be switched off by the application of the external magnetic field. In this case, the resonance is not shifted, as what typically occurs at small perturbations, but suppressed.     

Cavity formation in split ring resonators

We report that it is possible to obtain a cavity structure by the deformation of a unit cell of an split ring resonator (SRR) structure. We presented the Q-factor of the cavity resonance as 192 for an SRR-based single cavity. Subsequently, we brought two and three cavities together with an intercavity distance of two metamaterial unit cells and investigated the transmission spectrum of SRR-based interacting 2-cavity and 3-cavity systems. The splitting of eigenmodes due to the interaction between the localized electromagnetic cavity modes was observed. Eventually, in taking full advantage of the effective medium theory, we modeled SRR-based cavities as 1D Fabry–Perot reflectors (FPRs) with a subwavelength cavity at the center. Finally, we observed that at the cavity resonance, the effective group velocity was reduced by a factor of 67 for an SRR-based single cavity compared to the electromagnetic waves propagating in free space.     

Resonance splitting in gyrotropic ring resonators

We present the theoretical concept of an optical isolator based on resonance splitting in a silicon ring resonator covered with a magneto-optical polymer cladding. For this task, a perturbation method is derived for the modes in the cylindrical coordinate system. A polymer magneto-optical cladding causing a 0.01 amplitude of the off-diagonal element of the dielectric tensor is assumed. It is shown that the derived resonance splitting of the clockwise and counterclockwise modes increases for smaller ring radii. For the ring with a radius of approximately 1.5μm, a 29GHz splitting is demonstrated. An integrated optical isolator with a 10μm geometrical footprint is proposed based on a critically coupled ring resonator.     

Optical-axis perturbation in nonplanar ring resonators

Several findings on the optical-axis perturbation of nonplanar ring resonators have been obtained identical by utilizing the augmented 5 × 5 matrix formulation and augmented 6 × 6 matrix formulation, respectively. It has been found out that in the whole region of 0 < L/R < 2, the longer the mirror radius, the higher the sensitivity of optical-axis decentration, while the total cavity length is L and the radius of the curvature mirrors is R. The sensitivity of optical-axis tilt in the region of 0 < L/R < 2 has been carried out too. The optical-axis decentration and optical-axis tilt inside the region of L/R > 2 have been discussed. The differences of the optical-axis perturbation between planar and nonplanar ring resonators have also been analyzed. These interesting findings are important to the cavity design of nonplanar ring resonators.     

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.     

Multistage dispersion compensator using ring resonators

A compact, multichannel dispersion-compensating filter is demonstrated with D=-4200ps/nm, a +/-5-ps group delay ripple, <3-dB loss, and a 4.5-GHz passband width out of a 12.5-GHz free spectral range. We show that multistage designs can achieve a substantial increase in passband width and peak dispersion for a given group-delay ripple compared with single-stage designs. The dispersion-compensation effectiveness was demonstrated in a 320-km, seven-channel nonlinear system simulation for OC48 signals.     

Novel high-quality Fano resonance based on metal-insulator-metal waveguide with L-shaped resonators

Developing a convenient method that can be routinely applied for ascertaining proportions of different vegetable oils employed in commercial blended edible oils remains a significant challenge. We address this issue by proposing a novel method for detecting volume fraction of different oils based on the fact that these oils are optically transparent and have slightly different indices of refraction at a given temperature and wavelength. Accordingly, we develop a highly sensitive sensor for measuring the index of refraction of oil blends based on Fano resonance spectra obtained using a metal-insulatormetal(MIM) waveguide structure comprising a gapped straight waveguide coupled with two L-shaped resonators. The index of refraction sensitivity and figure of merit of the structure are calculated based on modeling using the finite element method, and the waveguide structure is accordingly optimized by adjusting the different geometric parameters to achieve a high-quality Fano resonance spectrum. The optimized structure achieves an ultra-high refractive index sensitivity of 770 nm/RIU in terms of a refractive index unit(RIU) of 1. Moreover, a highly stable linear relationship is obtained between the refractive index of mixed edible oils and the resonance wavelength. Experimental results demonstrate that the proposed structure can detect slight changes in the volume fractions of the components in blended oils.     

一种大气微波环形波导等离子体设备

微波等离子体相对其它等离子体而言有很多的优点,具有极高的工业应用价值。但在大气条件下,大体积的微波等离子体较难获得。为达到产生该种微波等离子体并将之应用的目的,特设计了一台环形波导反应腔设备并从事了等离子体激发的相关研究。介绍了该设备的设计思路,给出了常用的非磁化微波等离子体工作气体的击穿曲线,通过软件仿真得到了反应腔内的电场分布,并陈述了微波等离子体反应的基本现象。结合试验的结果,证明了软件仿真的正确性和装置的有效性。目前,该装置可在大气压下顺利激发一定体积的氦、氩等离子体。     

无源空心波导谐振腔横模模式的竞争与转换

本文提出并采用非对角化的分析法研究无源空心波导谐振腔横模模式间的竞争与转换。从计算EH_(1m)类波导本征模在腔内的转换矩阵中发现:在模式的传输过程中,存在着横模模式间的相互转换,而且其互换的能量不相等。在一定的腔设计条件下,会出现高阶横模向低阶横模的能量净流动,这有利于谐振腔横模模式的选择和基模输出功率的提高。