A high-sensitivity photonic crystal fiber (PCF) based on the surface plasmon resonance (SPR) biosensor for detection of density alteration in non-physiological cells (DANCE)

A highly sensitive photonic crystal fiber based on the surface plasmon resonance (PCF-SPR) biosensor for the detection of the density alteration in non-physiological cells (DANCE) is described. Human acute leukemia cells are determined by the discontinuous sucrose gradient centrifugation (DSGC) in which the cells are separated into several bands. The separated cells with different intracellular densities and refractive indexes (RI) ranging from 1.3342 to 1.3344 are distinguished in situ by means of the differential transmission spectrum. The biosensor shows a maximum amplitude sensitivity of 2000?nm/RIU and resolution as high as 5?×?10^?5?RIU. According to the wavelength interrogation method, a maximum spectral sensitivity of 9000?nm/RIU in the sensing range between 1.33 and 1.53 is achieved, corresponding to a resolution as high as 1.11?×?10^?5?RIU for the biosensor. The proposed PCF-SPR biosensor has promising application in biological and biochemical detection.     

Highly sensitive photonic crystal fiber biosensor based on titanium nitride

A highly sensitive surface plasmon resonance photonic crystal fiber (PCF) biosensor based on Titanium Nitride (TiN) as a new alternative plasmonic material is proposed and analyzed. The TiN has high stability, high conductivity, and corrosion resistance which make it an ideal material for nanofabrication. The suggested biosensor is analyzed by full vectorial finite element method with perfectly matched layer as boundary conditions. In this paper, the biosensor geometrical parameters are studied to achieve high sensitivity for both polarized modes. A refractive index sensitivity of 7700 and 3600 nm/RIU for quasi-transverse electric and quasi transverse magnetic modes, respectively, are obtained. Additionally, the reported biosensor could be used for detecting an unknown analyte refractive index ranging from 1.32 to 1.34 with a high linearity. Further, the proposed biosensor structure is easy for fabrication using standard PCF fabrication current technologies.     

Sensitivity enhancement of graphene coated surface plasmon resonance biosensor

In this paper, a highly sensitive surface plasmon resonance biosensor is presented using angular interrogation. Due to low sensitivity of conventional biosensor, graphene/two-dimensional transition metal are used in surface plasmon resonance biosensor to improve the sensitivity. Here, we propose a seven layer model of biosensor which shows by incorporating silicon layer in addition of transition metal dichalcogenides MoS₂ and graphene, the sensitivity of the proposed SPR biosensor can be greatly enhanced than the conventional gold film SPR sensors. It is observed that the highest sensitivity can be obtained by optimizing the structure with 8 nm thickness of silicon layer, one layer of MoS₂ and one layer of graphene. The highest sensitivity of our proposed sensor is 210°/RIU.     

Photonic crystal fiber sensor based on hybrid mechanisms: Plasmonic and directional resonance coupling

We propose a special refractive index sensor design based on a photonic crystal fiber. Two analyte channels are introduced, with one analyte channel coated with gold layer and the other one without gold layer. A hybrid resonance method is used in the sensor to achieve a large dynamic index range, where surface plasmon resonance occurs when the analyte index is lower than that of the fiber material, while the core mode couples with the resonant mode of the adjacent analyte-filled cylinder when the analyte index is larger than the fiber material. When considering fluorinated polymer fibers, a broad index range of analyte refractive index from 1.25 to 1.45 with high sensitivity can be achieved. The maximal sensitivities reach 1.4 × 10⁴ nm/RIU and 2.7 × 10⁴ nm/RIU respectively when refractive index is in the range of 1.25 to 1.383 and 1.383 to 1.45. The sensor characteristics, make this simple sensor very interesting for detecting a wide range of fluid's refractive index or chemical agent concentration.     

Integrated Si‐based nanoplasmonic sensor with phase‐sensitive angular interrogation

This work is related to the development of an integrated Surface Plasmon Resonance (SPR) sensor on silicon platform. The optical properties of metallic nanogratings fabricated on the semiconductor structure allow direct plasmonic detection in transmission mode. Specially designed angular interrogation method provides a periodic signal with phase dependent on the conditions of surface plasmon excitation. Proposed technique leads to sensitivity better than 10^?6 RIU for conventional SPR Kretschmann configuration and was tested on the integrated Si‐based nanoplasmonic chip. Developed concept is promising for low‐cost mono and multi ‐sensing applications by portable or stationary platforms.     

Design and optimization of nano-column array based surface plasmon resonance sensor

In this paper, a surface plasmon resonance fiber sensor based on gold nano-column array instead of gold film is designed and optimized. The finite element method is used to optimize the diameter of the nano-gold column under the consideration of figure of merit, which relates to the sensitivity, resonance wavelength and resonance intensity. The optimized sensor has 70 nm gold nano-column coated on a side polished single mode fiber. The results show that the average sensitivity reaches 5318 nm/RIU when the environmental refractive index changing from 1.33 to 1.39 RIU, which is much higher than those in the conventional surface plasmon resonance structure. The optimizes design will serve a vital foundation to the fabrication of high performance fiber optic surface plasmon resonance sensors based on nano metallic structure.     

内置调制层型光纤表面等离子体波共振传感器研究

研究了一种基于内置调制层结构的光纤表面等离子体波共振(SPR)传感器。通过在金膜与纤芯的内侧增覆具有不同厚度和属性的光学透明薄膜作为内调制层,构成了性能独特的光电复合薄膜,起到调节倏逝波矢量和金膜表面等离子体振荡波矢量的双重作用,进而控制共振效应,为调节灵敏度提供依据。采用时域有限差分方法对内置调制层结构光纤SPR共振激励模型属性进行数值仿真。在此基础上,研制了用于液体折射率测量的内置调制层型光纤SPR传感探针。实验结果表明,该传感器在1.335～1.392折射率范围内,随着待测液体折射率的增大,SPR共振光谱向长波方向偏移,且灵敏度达到2263.1nm/RIU,与基于纤芯-金膜-环境介质三层结构的常规光纤SPR传感器相比提高一倍,能够更好地满足环境折射率检测的需求。     

Silicon nano crystal filled ellipse core based quasi photonic crystal fiber with birefringence and very high nonlinearity

In this paper, we have proposed a new type of quasi photonic crystal fiber (PCF) with a silicon nano crystal core. This structure can be used to sense aqueous analysis over a wavelength range of 1.00?µm to 3.00?µm. The properties of this structure are simulated using the vector-finite element method (VFEM) employing a boundary condition. The proposed model provides a significant effect of birefringence and a very high nonlinear coefficient for two different fundamental modes, which are obtained by adjusting the size of the silicon nano crystal filled ellipse core. This provides a high nonlinearity of 4.2?×?10⁵ W^?1Km^?1 and a birefringence of ? 3.2?×?10^?1 at the wavelengths 1.00?µm and 3.00?µm, respectively. Some others properties, such as the effective area, scattering loss, confinement loss, numerical aperture (NA)and power fraction are also analyzed to measure the performance of this structure. The proposed model is useful for sensing and biomedical imaging applications. The proposed structure may also find extensive applications in optical communication and sensor systems.     

Simultaneous Measurement of Refractive Index and Temperature Using a Hybrid Fiber Bragg Grating/Long-Period Fiber Grating Configuration

Abstract

A fiber optic sensing system for simultaneous measurement of refractive index and temperature, based on a hybrid fiber Bragg grating/long-period grating arrangement is described. The experimental results show that this setup has a good performance in terms of linearity and sensitivity, the ratiometric output changes 4%/0.001 RIU and 3.6%/°C, respectively. The sensor resolution for the refractive index is ≈2 × 10^?5 RIU. The simultaneous measurement of the refractive index and temperature was demonstrated. The sensing configuration has the ability to be read-out in reflection and works in the telecommunications window.     

Refractive index sensors based on Ag-metalized nanolayer in microstructured optical fibers

We propose refractive index sensors based on Ag-metalized nanolayer in microstructured optical fibers. The surface plasmon resonance modes and the sensing properties are theoretically analyzed using finite element method (FEM). In the calculation, Drude–Lorentz model is used to describe the Metal Dielectric constant. The calculation results show that the sensitivity of Ag-metalized SPR sensor can reach 1500 nm/RIU corresponding to a resolution of 6.67 × 10^?5 RIU. Comparing with conventional detecting material-Au under the same structure, the sensitivity and 3 dB bandwidth of our device are better.     

Optical fiber SPR biosensor with sandwich assay for the detection of prostate specific antigen

We present a new, sensitive, few mode fiber (FMF) surface plasmon resonance (SPR) biosensor with a sandwich assay for the detection of PSA. The side-polished FMF biosensor does not need a polarizer and a thin high-index overlayer. The optical sensitivity of the SPR sensor was determined as 2.5 × 10⁻⁶ RIU. In the SPR PSA sensor, the SPR signals were amplified by a factor of 6 in average over no secondary antibody, using the sandwich assay. The proposed FMF SPR biosensor has great potential for real-time analysis of immune reaction between biomolecules and the advantages of high-sensitivity and label-free detection.     

U-shaped optical fiber sensor based on multiple total internal reflections in heterodyne interferometry

In this paper, an optical fiber sensor based on multiple total internal reflections (MTIRs) in heterodyne interferometry is proposed. With the optical fiber sensor the phase shift difference due to the multiple total internal reflections effect between the p- and s-polarizations is measured by using heterodyne interferometry. Substituting the phase shift difference into Fresnel's equations, the refractive index for the tested medium can be calculated. The resolution of the sensor can reach 1.6×10^?6 refractive index unit (RIU). The optical fiber sensor could be valuable for chemical, biological and biochemical sensing. It has some merits, such as, high resolution and stability, high sensitivity, high resolution and real-time measurement.     

High sensitivity plasmonic temperature sensor based on a side-polished photonic crystal fiber

A high sensitivity plasmonic temperature sensor based on a side-polished photonic crystal fiber is proposed in this work.In order to achieve high sensitivity and high stability,the gold layer is coated on the side-polished photonic crystal fiber to support surface plasmon resonance.The mixture of ethanol and chloroform is used as the thermosensitive liquid.The performances of the proposed temperature sensor were investigated by the finite element method(FEM).Simulation results indicate that the sensitivity of the temperature sensor is as high as 7.82 nm/℃.It has good linearity(R;=0.99803),the resolution of 1.1×10;℃,and the amplitude sensitivity of 0.1008℃;.In addition,the sizes of the small air hole and polishing depth have little influence on the sensitivity.Therefore,the proposed sensor shows a high structure tolerance.The excellent performance and high structure tolerance of the sensor make it an appropriate choice for temperature measurement.     

A theoretical study of a plasmonic sensor comprising a gold nano-disk array on gold film with a SiO_2 spacer

A plasmonic refractive index(RI) sensor with high RI sensitivity based on a gold composite structure is proposed.This composite structure is constructed from a perfect gold nano-disk square array on a gold film, with a SiO_2 spacer. The reflection spectra of the composite structure, with analyte RI in the range of 1.30 to 1.40, are theoretically studied using the finite-difference time-domain method. The incident light beam is partly coupled to the localized surface plasmons(LSP) of the single nano-disks and partly transferred to the propagating surface plasmons(PSP) by grating coupling. The reflectivity is nearly zero at the valley of the reflection spectrum because of the strong coupling between LSP and PSP. Also, the full width at half maximum(FWHM) of one of the surface plasmon polaritons(SPPs) modes is very narrow, which is helpful for RI sensing. An RI sensitivity as high as 853 nm/RIU is obtained. The influence of the structure parameters on the RI sensitivity and the sensor figure of merit(FOM) are investigated in detail. We find that the sensor maintains high RI sensitivity over a large range of periods and nano-disk diameters. Results of the theoretical simulation of the composite structure as a plasmonic sensor are promising. Thus, this composite structure could be extensively applied in the fields of biology and chemistry.     

Design of a highly sensitive photonic crystal waveguide platform for refractive index based biosensing

In this paper, a photonic crystal waveguide platform on silicon-on-insulator substrate is proposed in order to realize a highly sensitive refractive index based biosensor. Following the design, the analysis of the sensor structure are made by using the three dimensional Finite Difference Time Domain method. The principle of sensing is based on the change in refractive index, which in turn changes the output spectrum of the waveguide. Results show that the sensitivity of the sensor depends mainly on the geometrical properties of the defect region of the photonic crystal structure. The phenomenon is verified for various samples having refractive index ranging from 1 (air) to 1.57 (Bovine serum albumin). Further, the structure is compared with few other conventional photonic crystal waveguide designs to analyze the sensing performance. The estimated value of sensitivity of the sensor is found to be 260 nm/RIU with a detection limit of 0.001 RIU. This high sensitivity can enhance the performance of low-concentration analytes detection.     

Tapered Mach–Zehnder interferometer based on two mechanically induced long-period fiber gratings as refractive index sensor

A Mach–Zehnder interferometer formed in single mode fiber is implemented. The interferometer is built by two mechanically-induced long-period gratings. In addition, a fiber taper in the middle section is inserted. The spectral properties of the whole system are analyzed. Visibility of the interference fringes up to 0.80 (the higher ever reported using mechanically-induced long-period gratings) with fringe spacing in the 4.1 to 0.86 nm range are experimentally demonstrated. The proposed device allows reducing the fiber diameter of the section between gratings with a minimal effect in the interference fringe spacing. The sensitivity of the interferometer to external refractive index changes was also studied. It is experimentally shown that, due to the nature of the cladding mode excited, it is necessary to taper the fiber to improve the system sensitivity to external refractive index. Fiber tapers with different diameter, inserted between the long-period gratings pair were fabricated and tested for measuring external refractive index changes. A maximum resolution of 2.3×10^?4 RIU in a refractive index range from 1.36 to 1.402 is achieved.     

High-<Emphasis Type="Italic">Q</Emphasis> surface modes in photonic crystal/iron garnet film heterostructures for sensor applications

A novel type of a plasmonic sensor based on a magnetophotonic plasmonic heterostructure with an ultrahigh-Q resonance is considered. A magnetoplasmonic resonance with an angular width of 0.06°, which corresponds to a Q factor of 700 and is a record value for magnetoplasmonic sensors, is experimentally demonstrated. It is shown that, owing to the excitation of long-propagation-range plasmons, the transverse magneto-optical Kerr effect is considerably enhanced and, thus, the sensitivity of the magnetoplasmonic sensor to variations in the refractive index increases to 18 RIU^–1, where RIU is the refractive index unit. Numerical calculations indicate that the parameters of the magnetoplasmonic structure can be further optimized to attain sensitivities up to 5 × 10³ RIU^–1.     

Plasmonic refractive index sensor based on the combination of rectangular and circular resonators including baffles

We numerically designed a plasmonic refractive index sensor with high sensitivity and tunable optical feature based on two metal-insulator-metal bus waveguides connecting with the central-coupled rectangular and circular ring resonators, including silver (Ag) baffles. In the design process, Ag baffles' influence on transmittance spectrum, magnetic and electric field distributions, surface power flow intensity, energy streamlines, and sensor performance are investigated using the finite element method. The proposed structure can use as a high precision plasmonic refractive index sensor for refractive index in the increment range of 0.01. The maximum sensitivity can reach 3400 nm/RIU (RIU is a refractive index unit), which remarkably increases the sensitivity of 1.36 times compared to the case without Ag baffles. Besides, the figure of merit and quality factor can achieve 36.00 and 42.28, respectively. The sensitivity and figure of merit can be increased by adding the Ag baffles in the proposed plasmonic sensor system, generating an additional gap plasmon resonance mode that cannot find in a typical case.     

Surface plasmonic resonance sensor by metal strip pair arrays

We present a surface plasmonic resonance sensor composed of Ag strip pairs array embedded in the background material. The calculated results demonstrate that one of the transmission dips of the structure is very sensitive to the background materials. Meanwhile, the structure could achieve the sensitivity (nm/RIU) about 700 nm/RIU, when the slits width of Ag strip pairs is 10 nm.     

Mid-infrared high birefringence bow-tie-type Ge20Sb15Se65 based PCF with large nonlinearity by using hexagonal elliptical air hole

A high birefringence Ge₂₀Sb₁₅Se₆₅ based photonic crystal fiber (PCF) is proposed. It consists of a central defect core surrounded by two kinds of elliptical air holes with different size. The Finite Difference Time Domain method (FDTD) is used to simulate the guided modes of the designed PCF. The properties of this PCF are investigated including the birefringence, nonlinearity, and polarization mode dispersion in the mid-infrared range. The results show that for the optimized structure parameters, the highest birefringence of 0.1176 is obtained. The maximum nonlinearity coefficients of 38390 w^?1km^?1 and 49760 w^?1km^?1 for x- and y-polarization modes are achieved.