Herein, we designed a novel D-type symmetric two-core photonic crystal fiber surface plasmon resonance refractive index sensor. A significant dual resonance peak phenomenon occurred in the visible and near-infrared bands when the surface plasmon resonance effect generated at the interface between two-core and metal-sensing layer in this structure is combined with different metal-sensing layers. The mutual independence of the dual resonance peaks was analyzed using the finite element method. Moreover, the effects of the spacing and diameter of air holes, the thickness of metal-sensing layers, and the radius and spacing of nanometer columns in the structure on the dual peaks were examined. Results demonstrate that after the structural parameters are optimized, double peak resonance facilitates the good sensing performance of the sensor. In the refractive index range of 1.32-1.43, the respective average sensitivities corresponding to the double resonance peaks are up to 6209.09 nm/RIU and 8390.91 nm/RIU, and the figures of merit are greater than 19.64 RIU-1 and 27.06 RIU-1. These results provide a theoretical reference for the design of a photonic crystal fiber surface plasmon biosensor.

提出了一种新型的方形腔耦合金属波导结构,该结构由两个相互平行的矩形金属波导和一个内嵌可连通的方形谐振腔构成.利用方形谐振腔局域表面等离子体实现带阻滤波特性,并通过多路复用实现双端口全光等离子体开关.采用时域有限差分方法(FDTD)研究了方形腔的边长、折射率和谐振距离对强透射特性的影响.结果 表明,基于方形腔耦合金属波导结构的光开关在工作中具有较好的阻带特性和透射特性,其最大透射率可达92％,最小阻带透射率达0.2％,工作波长范围为607～785 nm.

Herein, a metal-insulator-metal asymmetric circular structure comprising two circular cavities, a transmission waveguide, and two coupled waveguides is proposed. The coupling effect of surface plasmon polaritons is strengthened through the local effect of resonant cavities, and a good extraordinary transmission is obtained. The effects of the radii and number of circular resonant cavities and that of the inter-circle distance on such an extraordinary transmission arc investigated via the finite difference time domain method. The results show that in the case that the radius of the circular resonant cavity resonator and the inter-circle distance arc 100 nm and 200 nm, respectively, the structure exhibits a very good extraordinary transmission. The optimization of these main parameters could allow an average stopband width of 1000 nm and increase the working range up to 2500 nm. Key words integrated optics; surface plasmon polaritons; metal-insulator-metal; finite difference time domain method; circular resonant cavity; stopband width

提出了一种基于光纤端面金属正六边形晶格圆孔阵列-二氧化硅结构,该结构的表面等离激元耦合作用受到其法布里-珀罗腔的加强,获得了较好的光谱传输特性.采用时域有限差分法对该结构进行数值仿真,研究了正六边形晶格圆孔阵列结构中圆孔直径和阵列周期等参数对反射光谱的影响,并分析了基于该现象的折射率传感特性.仿真结果表明:当金属厚度、圆孔直径和阵列周期分别为100 nm、200 nm和530 nm时,该结构展现出较好的反射特性.并在此基础上优化结构参数,获得486+4 nm/RIU的折射率灵敏度,能为应用在环境监测、食品安全等传感领域提供一个新的技术支持.

提出了一种基于H形金属狭缝阵列的新型结构.利用该结构形成的法布里-珀罗腔(Fabry-Perot,F-P)来加强表面等离激元的耦合作用,以获得一种双共振反射现象;同时研究了基于该现象的折射率传感特性.采用时域有限差分法研究了该结构中狭缝长度、宽度、金膜厚度等参数对双共振反射现象的影响.研究发现,双共振谷波长可由以上主要参数有效调控,当竖直狭缝长度为150 nm、水平狭缝长度为200 nm、狭缝宽度为50 nm、金膜厚度为300 nm时,该结构具有较好的双共振反射现象,其灵敏度分别为590和1 199 nm/RIU.该发现为新一代高性能表面等离子共振传感器设计提供了理论参考.

A sawtooth resonant-cavity-coupled metal-waveguide structure is proposed. It is found that adding a sawtooth resonator improves the signal output frequency of the waveguide structure. In addition, the output signal frequency of the logic-gate light source can be controlled by adjusting the length and width of the sawtooth resonator. Moreover, the increase of logic signal output ports by increasing the number of output waveguides can help to realize the two- and three-channel signal outputs. This logic gate output light source, constructed by coupling a sawtooth resonator with a metal waveguide structure, has a broad working bandwidth and a high transmission efficiency. With a suitable adjustment of the length and width of the sawtooth resonator one can get a transmission efficiency of 60% and an average working range of 1000 nm.

In this study, we design a plasma refractive index sensor with a cross tic-shaped graphene array structure. Further, the double-resonance transmission phenomenon in the mid -infrared band can be obtained by using the surface plasmon effect produced by the interface between the graphene and dielectric, and the dynamic regulation of the transmission spectrum can be realized by combining the electrically adjustable characteristics of graphenes. Subsequently, the effects of the chemical potential, number of layers, and geometric parameters of graphenes on the double-resonance transmission phenomenon in the structure arc studied using the finite-difference time-domain method. The results denote that the resonance position can be tuned by changing the chemical potential and the number of layers of the graphene. Compared with a traditional sensor, this structure exhibits better sensing performance and double-resonance transmission phenomenon after the structural parameter optimization. The sensitivities of two resonance valleys arc as high as (1280 +/- 21) and (2800 +/- 19) nm/RIU with quality factors of 17.1 and 12.3 RIU-1, respectively. These results provide a theoretical basis for the graphene plasma biosensor design.

A new kind of tunable multi-channel wavelength demultiplexer (WDM) based on metal-insulator-metal (MIM) plasmonic nanodisk resonators with a metal block is proposed. The transmission properties of such structure are simulated by the Finite-Difference Time-Domain (FDTD) method, and the eignwavelengths of the disc resonator are calculated theoretically. It is found that the transmission characteristics of the filter can be easily adjusted by changing the geometrical parameters of the metal block of the nanodisk. The multichannel WDM structure consisting of a plasmonic waveguide and several nanodisk resonators with metal block, by changing the parameter of metal block of nanodisk resonators, the filter shows the resonant mode filter function. Basing on this characteristic, a three-port wavelength demultiplexer is designed, which can separate resonant modes inside the nanodisk with high transmission up to 60%. It can find important potential applications in highly integrated optical circuits.

This study aims to propose a nanodisk structure embedding a rectangular metal block. The Fabry-Perot cavity formed by this structure is used to enhance the coupling effect of the surface plasmons. The structure has a narrow bandwidth, high quality factor, and high filtering performance. Herein, a multi-channel wavelength-division multiplexer is constructed by multiple cavities coupling. The influence of the horizontal and vertical widths of the rectangular metal block and the coupling distances between the embedded disk and rectangular metal block on the transmission characteristics of the device is described with the time-domain finite-difference method, for which a device without embedded rectangular metal block is used as the control group. A multi-channel wavelength division multiplexer is realized according to its transmission characteristics. The filter shows strong transmission characteristics when the disk resonance filter is embedded in the rectangular metal block; its full width at half maximum is significantly reduced and the quality factor is increased. By coupling a number of inlinc rectangular-metal-block/disk resonators, we construct the filter. Such plasmon multi-channel wavelength-division multiplexers can provide two- and three-channel demultiplexing functions. The resonant wavelength of each channel can be adjusted by selection of the parameters of the embedded metal block in the resonator, the transmission efficiency can reach up to 70%, and the minimum insertion loss is 1.519 dB. The average operating range is 189 nm, and there is no adjacent-channel crosstalk. We demonstrate that the proposed structure has good de-multiplexing frequency characteristics.

A surface plasmon resonance (SPR) sensor on an optical fiber endface with metallic rectangular slit array structure is presented. The finite-difference time-domain (FDTD) method was utilized to study the influence of structural parameters on the transmission spectrum and the refractive index (RI) sensing characteristic based on the two transmission peaks. The proposed sensor is compact and has the potential to be used in biomedical applications, having two transmission peaks with a sensitivity of 1209 and 500 nm per refractive index unit (RIU) respectively.