Theoretical study on slow light in different structures of optical microfiber knot resonators (OMKRs)

Based on the light propagation theory of the single-ring optical microfiber knot resonator (OMKR), we further establish the similar theory for OMKRs with a parallel connection structure and that with a serial connection structure, respectively. The relationships of the output and the input light fields in different OMKRs are analyzed. Numerical simulations of the slow-light performances of the OMKRs with single ring, multi-parallel rings and multi-serial rings at the communication wavelength around 1550 nm are given and discussed. Compared with the single-ring OMKR, it is found that a large group time delay with very narrow bandwidth can be obtained in OMKRs with n-ring parallel connection structure, while a broadband group time delay can be achieved in OMKRs with n-ring serial connection structure.     

High efficiency and low threshold diode-end-pumped blue-ray laser at 457 nm wavelength with straight type cavity

Based on the analysis of laser threshold of quasi-three-level laser system and the parameters optimization of resonant cavity, a compact setup of 457 nm blue-ray laser system is designed, and the laser operation at 914 nm and its second harmonic at 457 nm was obtained by intracavity frequency doubling with LBO nonlinear crystal. At an incident pump power of 24.3 W, the maximum output power at 457 nm is 2.34 W the optical-to-optical conversion efficiency is greater than 9.74%, and the fluctuation of the blue output power is less than 3.01%, besides, laser threshold of this laser system is 3.7 W which is the lowest at present.     

Optical delay lines using coupled slab waveguides and ring resonator with a negative refractive index core

Total delay time of a structure composed of a slab waveguide coupled with a ring resonator where negative refractive index material is replaced in the core of the structure is investigated in this work. In this paper, a two-port ring resonator (TPRR) which is made of a core with negative refractive index has been used to generate a time delay for a Gaussian-shaped pulse with 1 GHz bandwidth. It is shown that the creation of the ring how causes more n_g of a straight waveguide and results are compared with positive refractive index core TPRR. We have used metamaterial to make an n < 0 media and have used two cascaded metamaterial rings to increase the bandwidth.     

Development of two-port surface acoustic wave resonator with Al/Au electrodes for gas sensing

Simple and efficient surface acoustic wave(SAW)two-port resonators with low insertion loss and high Q-values on ST-X quartz substrate using a corrosion-proof A1/Au-stripe electrode structure are developed for gas sensing.It was composed of two shorted grating reflectors and adjacent intedigital transducers(IDT),and an active metal film in the cavity between the IDTs for the sensitive film coating.The devices are expected to provide good protection towards metal electrode for gas sensors application in chemically reactive environments.Excellent device performance as low insertion loss,high Q factor and single-mode are achieved by carefully selecting the metallic electrode thickness,cavity length and acoustic aperture.Prior to fabrication,the coupling of modes(COM)model was performed for device simulation to determine the optimal design parameters.The fabricated single-mode SAW resonator at operation frequency of 300 MHz range exhibits matched insertion loss of~6.5 dB and loaded Q factor in the 3000 range.Using the fabricated resonator as the feedback element,a dualresonator-oscillator with excellent frequency stability(0.1 ppm)was developed and evaluated experimentally,and it is significant for performance improvement of SAW gas sensor.     

Modified model for four-wave mixing-based wavelength conversion in silicon micro-ring resonators

A modified model for wavelength conversion based on the four-wave mixing (FWM) in a silicon micro-ring resonator is presented. Unlike previous contributions, the nonlinear phase shifts caused by self-phase modulation and cross-phase modulation are also taken into account in the present theoretical analysis besides the linear propagation loss and the nonlinear losses caused by two-photon absorption and free-carrier absorption. Analysis shows that the nonlinear phase shifts will cause different red shifts for the pump and signal (or converted) resonant wavelengths, and consequently an additional wavelength difference between the signal transmission dip and the efficiency peak, which will increase/decrease the conversion efficiency of the signal channel far from/near the pump. The conversion efficiency and the conversion peak width of each signal channel are both affected by the micro-ring radius and coupling coefficient. A broader conversion peak width can be obtained by using a micro-ring resonator with a smaller Q factor.     

Characterization and improvement of absorption and scattering by profiled architectural surfaces without specialized test facilities

A turntable apparatus and measurement procedure, based on ISO 17497-1, were developed for measuring the random-incidence absorption and scattering of surfaces, without specialized facilities. While not highly accurate, they proved adequate for determining the general characteristics of surfaces. Two original profiled wooden architectural surfaces, and a hard, flat reference surface, were characterized, and found to have low absorption and scattering. They were then modified for increased absorption by creating Helmholtz-resonator configurations, obtaining good performance at low- and mid-frequencies. They were also modified for increased scattering, in one case by creating a Schroeder diffuser. In the other case, the surface was integrated into a novel frame-array configuration, which scattered sound very well above 500 Hz.     

Generalised ABCD matrix treatment for laser resonators and beam propagation

A generalised ABCD matrix treatment for laser resonators and beam propagation is developed for computer programming. In this treatment, imaginary parts are introduced into the matrixes for all optical elements, and the beam quality factor M² and the index of the medium are also taken into account. When the imaginary parts of the complex matrix are zero and the beam quality factor M² and medium index are unity, the stated method is transformed back into the more classic ABCD matrix format in which the fundamental-mode Gaussian beam transmits through real elements in the vacuum. Based on this method, laser resonator software is realised by the VB programme language. The software can be used to analyse and design stable/unstable standing/travelling cavities, phase-conjugate cavities and beam transformations.     

Fano resonance and spectral compression in a ring resonator drop filter with feedback

We propose a ring resonator drop filter with feedback loop which can form the other ring cavity to produce an asymmetric Fano-resonance line shape and mode compression. By properly adjusting the feedback loop, the asymmetric line shapes of the transmission spectra can be controlled and selectively mode compression of the circuiting intensity in the feedback loop is achieved. Such characteristics are useful for applications in ring resonator-based photonic devices such as all-optical switches, sensors and intracavity frequency selection single-mode laser.     

基于二维质点振动模型的半球谐振陀螺谐振子进动分析

半球谐振陀螺是基于固体波的进动效应进行角速度检测的一种全固态陀螺。为分析半球谐振子中固体波的进动效应,基于虚功原理,建立了理想条件下半球谐振陀螺谐振子中固体波进动的动力学模型。针对进动波的动力学模型过于复杂、难于分析的缺陷,提出采用相似系统的分析方法,将该动力学模型等效为二维空间质点的简谐振动模型;采用快变量与慢变量分离的方法,对等效模型进行了参数分析,通过与实际的半球谐振陀螺信号处理系统采集的李沙育图形进行对比,验证了等效简谐振动模型的有效性和正确性。     

基于人工复合材料的太赫兹波双波段滤波

本文分别从实验和理论模拟两方面详细的讨论了金属双环和反双环两种亚波长阵列结构在太赫兹波段的双频率响应特性. 这两种双环结构都可以实现双频率调制,金属双环结构表现为两个明显的吸收峰,反双环结构则表现出明显的透过峰. 这两种结构不仅在物理结构上互补,在太赫兹波段的响应也表现为吸收和透过互补的特性. 其中高频响应来源于内环电子振荡,低频影响则来源于外环电子振荡,并且这种结构在太赫兹波段的响应与周期无关. 关键词： 太赫兹 滤波器 亚波长阵列 FDTD