文中提出了一种高效、多功能的超表面极化转换器,该转换器由双分裂环谐振器周期阵列构成并置于F4B-2介电基板上.通过双分裂环谐振器的耦合效应可以有效拓展工作带宽.采用有限积分法对其极化特性进行分析.仿真结果表明:在5.5～8.55 GHz的频带(相对带宽为43.4％),实现了线极化到圆极化的转换,其能量转换效率优于99.5％;在10.31～15.31 GHz的频带(相对带宽为39％),实现了线极化到其交叉极化的转换,其极化转换比大于0.99.实验上,制备了样品并测试了其极化转换特性,实验结果与仿真结果基本吻合,验证了该转换器设计的合理性和有效性.所提出的超表面具有高效率、大工作带宽、多功能的特点,可应用于无线通信和极化操控设备.

Surface Plasmon Resonance (SPR) is a physical phenomenon,when the frequency and wave number of incident light coincide with the frequency of free electrons vibrating on the metal surface,then the electrons (i.e.,plasma) on the metal surface absorb light energy and resonate,and its resonance wavelength changes with the refractive index of the precious metal surface,so SPR has a wide range of application needs in medical detection,environmental monitoring and other fields. Based on the principle of SPR, this work investigates the refractive index sensing characteristics of D-type highly birefringent photonic crystal fibers in detail. The current reports on PCF SPR sensors are mainly based on the establishment of theoretical models and numerical simulations. It is difficult to experimentally prepare PCF SPR sensors. According to the high birefringence photonic crystal fiber used in the experiment, the photonic crystal fiber of the simulation model is composed of five layers of air holes. The first layer of the cladding contains 2.2 mu m, the diameter of the large air hole is 4.5 mu m, and the polishing depth is represented by h, that is, the distance from the core of the photonic crystal fiber to the polishing surface, and the angle between the slow axis of the high birefringence photonic crystal fiber and the polishing surface is defined as the polishing direction theta. The gold film is coated on the flat polishing surface of the optical fiber to facilitate contact with the object to be measured. According to previous theoretical and experimental research,we set the thickness (t) of the gold film to 45 nm. The refractive index of the photonic crystal fiber background material and the refractive index of gold used in the simulation are given by the experimental data of linear interpolation. In order to obtain the waveguide mode of the side-polished high-birefringent photonic crystal fiber, this paper uses the finite element method commercial software COMSOL Multiphysics and sets the boundary conditions of the perfect matching layer for simulation. The refractive index of the analyte is set in the range of 1.330 to 1.400. Through finite element method modeling and simulation,the influence of polishing angle on the sensitivity of birefringence and refractive index sensing are studied in this paper. The simulation results show that when the height of the polishing surface from the fiber core is less than 1.5 times the duty cycle,the closer the polishing surface is to the core,the smaller the birefringence. As the polishing angle increases, the birefringence first increases and then decreases,and the refractive index sensing sensitivity decreases accordingly. When the polishing angle is 0 degrees and the refractive index ranges from 1.330 to 1.400,the average refractive index sensitivity of the device is as high as 3 457.14 nm/RIU. In addition,we have prepared a D-type high birefringence photonic crystal fiber SPR sensor. There is a big difference between the theoretical and experimental sensitivity values. The main reasons are:1) The polishing surface is uneven (defects caused by air holes),which makes it difficult to completely remove the debris generated during the polishing process,which will affect the sensing performance. Performance;2) After preparing the D-type fiber sample,the fiber is not coated in time. The D-type fiber is exposed to the air for a long time,and the dust in the air will further affect the performance of the device;3)Although every time Before the test,the sensor will be cleaned repeatedly with ethanol,but it is difficult to completely remove the refractive index matching liquid left in the PCF air hole,which will affect the accuracy of the subsequent measurement results. For example,we tested the refractive index of 1.33 for the first time and cleaned it with alcohol. Drop 1.34 optical fiber matching liquid,because the previous liquid remains,the real value is difficult to achieve 1.34,and the calculation is still calculated according to 1.34; 4) The theoretical maximum value is under the condition that the polishing plane is parallel to the connection line of the two large air holes. The D-type high birefringence photonic crystal fiber SPR sensor was further used to test the concentration of glucose dissolved. The concentration of glucose solution increases from 0 g/dL to 10 g/dL in steps of 2 g/dL. As the glucose concentration increases, the D-type high birefringence photonic crystal fiber SPR sensor The peak wavelength of the pit of the transmission spectrum will be red-shifted. In the 0 g/dL glucose solution,the SPR resonance wavelength appeared at 578.96 nm,and when the glucose solution concentration was 10 g/ dL, the SPR resonance wavelength drifted to 587.49 nm. According to the relationship between the glucose concentration and the peak wavelength of the pit of the transmission spectrum,the average sensitivity is 1.89 nm/(g/dL). The research results show that the D-shaped photonic crystal fiber SPR sensor can be applied to the fields of biology,chemistry and environmental monitoring.

We propose and numerically investigate a multi-parameter integrated sensor based on a selectively filled D-shaped photonic crystal fiber (PCF). The simple structure can be used to comprehensively detect refractive index, magnetic field, temperature, and voltage. According to the surface plasmon resonance and directional coupling effect, the PCF is coated with a gold nano-film to detect the refractive index of the external environment. In addition, magnetic fluid (water-based Fe3O4), toluene, and nematic liquid crystal (NLC E7) are selectively filled into different cladding air holes of the D-shaped PCF to realize the different sensing of the magnetic field, temperature, and voltage. The measurement of refractive index, magnetic field, temperature, and voltage are independent of each other, so these four parameters can be measured simultaneously. The sensing characteristics of the proposed structure are investigated systematically by the finite element method. The results show that the sensitivities of refractive index, magnetic field, temperature, and voltage are 4600 nm/RIU, 1.375 nm/Oe, 15.143 nm/°C, and 0.971 nm/V, respectively. The presented design based on materials selectively filled with D-shaped PCF might enable promising application in multi-parameter optical sensing.

Full width at half maximum (FWHM) is an important factor affecting the performance of the sensor. In order to improve the quality factor of the surface plasmon resonance sensor, a grating-assisted ultra-narrow band multispectral plasmon resonance sensor structure is proposed in this paper. The structure is composed of periodically alternating SiO2 and Au rectangular nanorods and is placed on the SiO2/Al2O3 thin film layer. The full vector finite element method is used to simulate the optical transmission and sensing characteristics, and the effects of structural parameters and polarization state of incident light on FWHM and sensing characteristics are analyzed. The simulation results show that in the wavelength range of 800-1100 nm, there are two dips formed by plasma resonance and dielectric grating in the transmission spectrum of the structure. The corresponding FWHM can reach 0. 35 nm and 0. 59 nm, respectively. The refractive index sensitivity is 525. 7 nm /RIU and 475. 7 nm /RIU, respectively. The figure of merit is 1502. 00 RIU-1 and 806. 27 RIU-1, respectively, which had potential applications in biological detection, drug screening, membrane biology and other fields.

We propose a graphene plasmonic structure by applying two graphene layers mingled with a thin gold layer in a silicon grating. By utilizing the finite-difference time-domain (FDTD) method, we investigate the optical response of the system, and observe that the design achieves dual tunable electromagnetically induced transparency (EIT)-like effect at terahertz frequencies. The EIT-like effect arises from the destructive interference between the grapheme-layer bright modes and the gold-layer dark mode. The EIT-like phenomenon can be adjusted by the Fermi level, which is related to the applied voltage. The results show that the group delay of the present structure reaches 0.62 ps in the terahertz band, the group refractive index exceeds 1200, the maximum delay-bandwidth product is 0.972, and the EIT-like peak frequency transmittance is up to 0.89. This indicates that the device has good slow light performance. The proposed structure might enable promising applications in slow-light devices.

In this study we demonstrate a high-performance polarization rotator (PR) based on flat-shaped photonic crystal fiber. The flat surfaces of the fiber are plated on gold films as electrodes, and the core of the structure is filled with liquid crystal. The polarization rotation characteristics of the flat-shaped fiber can be effectively adjusted by applying external voltage. The optical properties are analyzed using the finite element method (FEM). The results show that the magnitude of the modulation voltage is closely related to the thickness of the flat fiber. When the fiber thickness is 20 μm, only 100 V is required to achieve the highest PR performance. In the wavelength of the 1.55 μm band (~200 nm bandwidth), the conversion length of the PR is only 3.99 μm, the conversion efficiency is close to 100%, and the minimum crosstalk value is −26.2 dB. The presented PR, with its excellent performance, might enable promising applications in the communication system and the photonic integrated circuits.

Beam splitters play important roles in several optical systems. Due to the growing demand for the miniaturization of optical systems, it is necessary to design beam splitters with nanoscale dimensions to miniaturize the essential components for integrated optical circuits. In this work, we propose and numerically demonstrate a broadband, high efficient, and four-channel beam splitter based on a fishnet-shaped metasurface. The proposed structure is constructed of cruciform AlSb nanoantennas on the PDMS substrate. The simple design can split a beam of light into four beams with equal intensity, it achieves a conversion efficiency above 83%, and an anomalous transmission intensity exceeding 0.8 for the wavelength range of 761-835 nm. In this wavelength range, the beam splitting angle changes from 46.45° to 53.68°. Moreover, the four-channel beam splitter is tunable when the metasurface is designed as a discrete structure. At the wavelength of 874 nm, the beam splitting angle can be adjusted from 56.34° to 46.39° as the period increases from 1050 nm to 1207 nm by stretching the substrate. The presented metasurface might enable promising applications in integrated optical devices, owing to its advantages of multi-channel, wide broadband, high efficiency, and large beam split angle.

We report a quasi-continuous beam splitter with highly efficient equal-power beam splitting in a wide spectral range. It consists of rhombic aluminum antimonide nanorods standing on a silica substrate. Firstly, a beam splitter based on discrete structures is designed, and the structures are optimized to obtain the quasi-continuous beam splitter. The beam splitter achieves a splitting efficiency of over 80% within the region of 675-786 nm (bandwidth = 111 nm), where the splitting angle can vary in the range of 97.2°-121.8°. In particular, the splitting efficiency reaches 93.4% when the wavelength is 690 nm. Overall, the proposed beam splitter potentially paves the way for realizing broadband metasurfaces and high-performance quasi-continuous metasurface-based devices.

To reduce the saturation voltage of fiber filter and improve the sensitivity of voltage sensing, we propose and numerically demonstrate a multifunctional optoelectronic device with a flat-plate photonic crystal fiber structure in this paper. One of the air holes is selectively filled with liquid crystal, and the upper and lower planes of the fiber are plated with gold films to form electrodes. Based on the applied voltage, the coupling wavelength of the core fundamental mode and filling mode is adjusted. This structure can realize the functions of tunable filtering and external voltage sensing. In addition, the metal film is close enough to the fiber core to enable coupling between the core waveguide mode and the surface plasmon resonance mode. Thus, the external RI can be measured. The measurements of the voltage and refractive index of the device are independent of each other, thus realizing a simultaneous measurement of the two parameters. We used the finite element method to investigate its photoelectric characteristics systematically. When the thickness of the plate fiber is 18 mu m, as a fiber filter, the applied saturation voltage decreases from 2900 V (photonic crystal fiber with a conventional structure) to 650 V, and the threshold voltage decreases from 45 to 8 V. When used as a voltage sensor, the voltage sensitivity is improved from 0.025 to 0.117 nm/V. As a dual-parameter sensor for simultaneously measuring the voltage and RI, the RI sensitivity is 2700 nm/RIU. Evidently, the superior performance of the proposed structure renders it a high application value in the fields of optical fiber sensing and communication.

Beam splitters are vital components in several optical systems. It is highly desirable, and compact beam splitters with ultra-broadband performances, high efficiencies, and large split angles are still being sought. In this paper, we demonstrate and numerically investigate an ultra-broadband and highly efficient optical beam splitter based on a quasi-continuous metasurface. The proposed design is constructed of quasi-continuous triangle-shaped gallium phosphide nanoantennas on a silica substrate. The simple structure can achieve a conversion efficiency and an anomalous transmission intensity above 90% and 0.8 covering the wavelength range of 1537–1826 nm, respectively. The maximum beam split angle in the operating bandwidth reaches 131.84° at the wavelength of 1826 nm. Particularly, the operating bandwidth is still as high as 125 nm with the anomalous transmission intensity above 0.92 and the conversion efficiency exceeding 99%. Moreover, the results show that the performance of the metasurface-based optical beam splitter can be further enhanced by optimizing structural parameters. We also demonstrate the adjustability of the beam splitter by adding refractive index (RI) materials on the surface of the device. The results show that the incident plane wave can be divided into three beams with intensity adjustability. The presented metasurface is very promising in the fields of multiplexers, interferometers, and optical communications, owing to its advantages of ultra-broadband, highly efficient, and large split angle simultaneously.

All-dielectric Huygens’ metasurfaces have been widely used in wavefront manipulation through multipole interactions. Huygens’ metasurfaces utilize the superposition between an electric dipole and a magnetic dipole resonance to realize transmission enhancement and an accumulated 2π phase change. Benefiting from this unique property, we design and numerically investigate an all-dielectric Huygens’ metasurface exhibiting high-efficiency anomalous refraction. To suppress the substrate effect, the metasurface structure is submerged in a dielectric plate. We strategically placed two elements in four short periods to form a unit cell and adjusted the spacing between the two elements to effectively inhibit the interaction between elements. At the operating wavelength of 692 nm, the obtained anomalous transmission efficiency is over 90.7% with a diffraction angle of 30.84°. The performance of the proposed structure is far superior to most of the existing phase-gradient metasurface structures in the visible region, which paves the way for designing efficient beam deflection devices.

针对现阶段表面等离子体激元(SPP)传感器存在灵敏度低、结构制造复杂等问题,提出了一种由金属-绝缘体-金属波导和嵌入银纳米棒的谐振腔构成的高灵敏度、可调谐的SPP传感器.采用时域有限差分法对所设计传感器的光传输特性及传感特性进行了理论研究.仿真结果表明:当谐振腔引入或者不引入银纳米棒时,传输谱在500～3500 nm波长范围会呈现4个或者2个谐振峰;该结构的折射率灵敏度高达2116.72 nm/RIU,品质因数为27.503;通过对谐振腔填充乙醇,该结构可实现对环境温度的测量,温度灵敏度可达0.982 nm/℃.

We propose and numerically demonstrate a phase-gradient metasurface with high anomalous transmission efficiency and a large anomalous refraction angle that consists of discontinuous regular hexagonal nanorods supported by a silica substrate. The metasurface achieves high anomalous transmission efficiency and a full 2[Formula: see text] phase shift for the wavelength range of 1400-1600 nm. At a central wavelength of approximately 1529 nm, the total transmission efficiency reaches 96.5%, and the desired anomalous transmission efficiency reaches 96.2%, with an anomalous refraction angle as large as 30.64. With the adjustment of the period and the number of nanorods per periodic interval, the anomalous transmission efficiency exceeds 69.6% for a large anomalous refraction angle of 68.58. The superior performance of the proposed design may pave the way for its application in optical wavefront control devices.

This paper proposes a broad-band linear-to-circular polarization converter based on a multi-layer stripline metasurface. The structure is constructed of three stripline metallic layers stacked with two dielectric plates, and it has different electromagnetic response characteristics in two orthogonal directions. Based on this, the amplitude of the two orthogonal components of the transmitted wave is equal, and the phase difference is 90°. To better understand the working principle of the proposed converter, a detailed equivalent circuit model is presented. The simulation results indicate that the converter can convert linearly polarized incident waves into circularly polarized transmitted waves in the frequency range of 4.96–12.44 GHz. For an increased incident angle of 50°, the device can still maintain an axial ratio bandwidth of 53.7% in the x-z and y-z planes. Because of its broadband, small size, and wide-angle, the proposed converter can be integrated into a linearly polarized antenna system to generate circularly polarized waves without significantly affecting antenna performance.

We numerically demonstrate an ultra-broadband plasmonic absorber by applying chromium and titanium in a 3D metamaterial structure. One unit cell of the proposed absorber consists of continuous Cr/SiO2 multi-layers covered by two Ti nanodisks for exciting multiple magnetic dipole resonances and localized surface plasmon resonance. The optical simulation results show that the average absorption of the plasmonic structure exceeds 98.4% in the wavelength range of 400- % in the wavelength range of 400−4000 nm. The broadband and high absorption benefits from impedance matching between the nanodisks array and the free space in the wavelength range. Through thermal simulation, we also investigated the photothermal heating generation in the plasmonic metamaterial structure. The temperature rise in the proposed structure is approximately 447 K with an incident wavelength of 618 nm and a light flux of 100 W/cm2. Due to the ultra-broadband absorbing performance, the presented design has possibilities in the fields of photodetector applications, solar energy harvesting, thermal emitters, and infrared cloaking.

We propose and experimentally demonstrate a Sagnac interferometer for strain measurements in side-polished birefringent fibers. The interferometer is fabricated by welding a section of side-polished panda fiber to a 3 dB coupler. Experimental results show birefringence decreased as the polish depth increased, and strain sensitivity linearly increased with increasing the polish length. We find that the use of polishing birefringent fibers is a very effective method for improving strain sensitivity. A relatively small polishing length (40 mm) could effectively increase strain sensitivity from $19.66\ \ \text{pm}/\mu\varepsilon$ to $37.12\ \text{pm}/\mu\varepsilon$ in the first type of sample. In addition, a thin-film gold coating is applied to the polished fiber surface to produce a biochemical sensor utilizing surface plasmon resonance (SPR). Experimental results indicate that the SPR absorption and the figure of merit (FOM) are different in the two types of samples. With the analyte refractive index (RI) varying from 1.32 to 1.40, the sensitivity increases from 800 nm/RIU to 3500 nm/RIU and the FOM increases from 14.8 to 52.2 in the first type of sample. These values of the FOM are approximately twice as high as that of an SPR fiber sensor based on a D-shaped single mode fiber in the same RI environment. These results suggest a D-shaped panda fiber could develop promising fiber devices for the internet of things sensing technology.