Surface Wave Sensor Research Articles

Design and optimization of Bloch surface wave sensor with high sensitivity and quality factor using LiNbO3

Design and optimization of Bloch surface wave sensor with high sensitivity and quality factor using LiNbO3

Theoretical investigation of transition metal dichalcogenides based Bloch surface wave sensors with mono and double absentee layers

In this paper, the performance of a transition metal dichalcogenides based Bloch surface wave (BSW) sensor with mono or double absentee layers is investigated. By adding mono absentee layer with high refractive index at some particular locations, the linewidth (FWHM) and the figure of merit (FOM) of the BSW sensor are improved. The BSW sensor with double absentee layers is also studied and the results indicate that FOM is further improved by using double absentee layers. In particular, the FOM of the BSW sensor with double GaAs absentee layers is up to 766.43 RIU−1, which is 5.83% higher than the one of a traditional BSW sensor without absentee layer. It is believed that the usage of absentee layers in a BSW sensor can improve its FOM, which is useful for the development of high-performance optical sensors.

Refractometric sensitivity of Bloch surface waves: perturbation theory calculation and experimental validation.

The sensitivity of one-dimensional Bloch surface wave (BSW) sensors to external refractive index variations using Kretschmann's configuration is calculated analytically by employing first-order perturbation theory for both TE and TM modes. This approach is then validated by comparison with both transfer matrix method simulations and experimental results for a chosen photonic crystal structure. Experimental sensitivities of (8.4±0.2)×102 and (8.4±0.4)×102 nm/RIU were obtained for the TE and TM BSW modes, corresponding to errors of 0.02% and 4%, respectively, when comparing with the perturbation theory approach. These results provide interesting insights into photonic crystal design for Bloch surface wave sensing by casting light into the important parameters related with sensor performance.

The High-Sensitivity Phase Interrogation of Bloch Surface Wave Sensor Based on 1-D Photonic Crystal

The Bloch surface wave (BSW) is excited in a 1-D photonic crystal and supports a rather steep resonance dip, much sharper than that of traditional surface plasmon resonance (SPR). A highly sensitive sensor based on BSW was fabricated by electron beam evaporation, the structure was characterized by scanning electron microscopy (SEM) and ellipsometry spectrometer, and the sensitivity in wavelength and phase interrogation was achieved experimentally by an optical system based on a Mach–Zehnder interferometer. The wavelength sensitivity and the phase sensitivity can reach 219 nm/RIU and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.16\times10$ </tex-math></inline-formula> 4 deg/RIU, respectively. After comparison, we demonstrate that the phase interrogation has a higher sensitivity than the wavelength interrogation and is more suitable for BSW sensors. Experimental results show that the detection limit of the sensor is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8.62\times10$ </tex-math></inline-formula> −7 RIU in phase interrogation, which proves that the sensor could become a valuable and promising tool to replace traditional SPR sensors for the application of ultralow concentration detection. This sensor, only composed of TiO2 and SiO2 materials, has the advantages of mechanical and chemical stability, easy fabrication, and low cost, which can be used as an alternative to traditional SPR sensors in the fields of biomedicine, chemical analysis, and environmental monitoring.

Constrained optimization of transition metal dichalcogenide-based Bloch surface wave sensor using improved genetic algorithm

Constrained optimization of transition metal dichalcogenide-based Bloch surface wave sensor using improved genetic algorithm

Fiber optics - A new route to surface wave sensors with ultra-wide refractive index sensing range and ultra-high figure of merit

Fiber optics - A new route to surface wave sensors with ultra-wide refractive index sensing range and ultra-high figure of merit

High-sensitivity Bloch surface wave sensor with Fano resonance in grating-coupled multilayer structures

A new type of device consisting of a lithium niobate film coupled with a distributed Bragg reflector (DBR) was theoretically proposed to explore and release Bloch surface waves for applications in sensing and detection. The film and grating made of lithium niobate (LiNbO3) were placed on both sides of the DBR and a concentrated electromagnetic field was formed at the film layer. By adjusting the spatial incidence angle of the incident light, two detection and analysis modes were obtained, including surface diffraction detection and guided Bloch detection. Surface diffraction detection was used to detect the gas molecule concentrations, while guided Bloch detection was applied for the concentration detection of biomolecule-modulated biological solutions. According to the drift of the Fano curve, the average sensor sensitivities from the analysis of the two modes were 1560 °/RIU and 1161 °/RIU, and the maximum detection sensitivity reached 2320 °/RIU and 2200 °/RIU, respectively. This study revealed the potential application of LiNbO3 as a tunable material when combined with DBR to construct a new type of biosensor, which offered broad application prospects in Bloch surface wave biosensors.

One-Dimensional Photonic Crystal Inner Coated Hollow Fiber Sensor Based on Bloch Surface Wave With Ultra-High Figure of Merit

A high-performance Bloch surface wave (BSW) sensor based on the hollow fiber (HF) inner coated with the one-dimensional photonic crystal (1DPC) consisting of TiO2 and SiO2 bilayers is proposed. Performances including sensitivity and figure of merit (FOM) of the sensor are investigated theoretically with the ray transmission model. Several structure parameters such as the center wavelength of 1DPC, the thickness of the cap layer and the bilayer period are optimized to obtain a best performance of the sensor. The results show that the proposed sensor has an ultra-high FOM over 1100 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , which is approximately two and one orders of magnitude higher than that of the HF surface plasmon resonance (SPR) sensor and HF long-range SPR sensor, respectively. Moreover, the proposed sensor has a much broader practical RI detection range, which makes it more useful in sensing applications. The performance of the proposed sensor applicated in temperature sensing is also estimated to prove its application potential.

Effect of a Magnetic Field on the Propagation of Waves in a Homogeneous Isotropic Thermoelastic Half-Space

The prime objective of the present paper is to analyze the propagation of thermoelastic waves in a homogeneous isotropic elastic semi-infinite space that is exposed to a magnetic field at initial temperature T0 and whose boundary surface is subjected to the moving heat source and load moving with finite velocity. Temperature and stress distribution occurring due to heating or cooling have been determined using certain boundary conditions. Numerical results indicate that the effect of the magnetic field is very pronounced. Comparison is made with the results predicted by the theory of thermoelasticity in the absence of a magnetic field. Apart from geophysical applications, the consequences of the present study offer a better platform to design a surface wave sensor by means of its established results. The obtained results may be also used for acquiring a better performance in surface acoustic wave devices and waveguides.

Surface Wave Enhanced Sensing in the Terahertz Spectral Range: Modalities, Materials, and Perspectives.

The terahertz spectral range (frequencies of 0.1–10 THz) has recently emerged as the next frontier in non-destructive imaging and sensing. Here, we review amplitude-based and phase-based sensing modalities in the context of the surface wave enhanced sensing in the terahertz frequency band. A variety of surface waves are considered including surface plasmon polaritons on metals, semiconductors, and zero gap materials, surface phonon polaritons on polaritonic materials, Zenneck waves on high-k dielectrics, as well as spoof surface plasmons and spoof Zenneck waves on structured interfaces. Special attention is paid to the trade-off between surface wave localization and sensor sensitivity. Furthermore, a detailed theoretical analysis of the surface wave optical properties as well as the sensitivity of sensors based on such waves is supplemented with many examples related to naturally occurring and artificial materials. We believe our review can be of interest to scientists pursuing research in novel high-performance sensor designs operating at frequencies beyond the visible/IR band.

Ultra-Sensitive Refractive Index Sensors Based on Bloch Surface Waves With Transition Metal Dichalcogenides

Bloch surface wave (BSW) sensors are considered to be a great candidate to replace the conventional surface plasmon resonance (SPR) sensors. In this paper, a high performance refractive index sensor based on BSW resonance in the truncated one-dimensional photonic crystal (1DPC) has been theoretically confirmed using transition metal dichalcogenides (TMDCs). The impact of four different two-dimensional TMDCs nanosheets on the sensors are studied, with which the state of art sensitivity of wavelength-interrogation has been achieved. Specifically, with MoSe2, WSe2, MoS2, and WS2 nanosheets, the measured figure of merit (FOM) are 732.1/RIU, 733.0/RIU, 730.5/RIU, and 700.7/RIU, respectively. To our knowledge, this is the best performance achieved so far compared to the existing BSW and SPR sensors. Besides, the impact of the 1DPC period and the number of TMDCs layers were discussed in detail. In addition, at the interface of TiO2 and TMDCs, it is found that the electric intensity is enhanced by nearly 7 times compared to the initial intensity, which also results in an increased evanescent depth in the sensing medium. The high sensitivity sensors proposed in this paper can be applied in the field of biological and chemical sensing.

Optimization of sensors based on surface waves in flat-layered structures

A method for increasing the sensitivity of surface-wave sensors in multifilm structures is proposed based on the results of a theoretical study of the reflection of a plane electromagnetic wave from a flat-layered structure containing homogeneous films. A method for optimizing the parameters of the films forming the surface structure is developed and tested. The devices proposed are characterized by high field amplification in a surface layer of multifilm structure and a higher sensitivity to variations in the optical properties of the thin near-surface layer. Application of the proposed multifilm structures is expected to increase significantly the sensitivity of the existing sensors based on surface-plasmon polaritons, which are applied in modern optical multichannel biological, chemical, and physical sensor systems.

Effect of thickness disorder on the performance of photonic crystal surface wave sensors.

We investigated experimentally and numerically the robustness of optical sensors based on Bloch waves at the surface of periodic one-dimensional photonic crystals. The distributions of sensor characteristics caused by the fabrication uncertainties in dielectric layer thicknesses have been analyzed and robustness criteria have been set forth and discussed. We show that the performance of the surface wave sensors is sufficiently robust with respect to the changes of the photonic crystal layer thicknesses. Layer thickness optimization of the photonic crystal, carried out to achieve low limit of detection, leads to an improvement of the robustness of the surface wave sensors that is attributed to Bloch states lying deeper in the photonic band gap.

Plasmonic Photonic-Crystal Slabs: Visualization of the Bloch Surface Wave Resonance for an Ultrasensitive, Robust and Reusable Optical Biosensor

A one-dimensional photonic crystal (PhC) with termination by a metal film—a plasmonic photonic-crystal slab—has been theoretically analyzed for its optical response at a variation of the dielectric permittivity of an analyte and at a condition simulating the molecular binding event. Visualization of the Bloch surface wave resonance (SWR) was done with the aid of plasmon absorption in a dielectric/metal/dielectric sandwich terminating a PhC. An SWR peak in spectra of such a plasmonic photonic crystal (PPhC) slab comprising a noble or base metal layer was shown to be sensitive to a negligible variation of refractive index of a medium adjoining to the slab. As a consequence, the considered PPhC-based optical sensors exhibited an enhanced sensitivity and a good robustness in comparison with the conventional surface-plasmon and Bloch surface wave sensors. The PPhC biosensors can be of practical importance because the metal layer is protected by a capping dielectric layer from contact with analytes and, consequently, from deterioration.

P-polarized surface waves in a slab waveguide with left-handed material for sensing applications

Abstract In this paper, surface waves excited at the interface between left-handed and right-handed materials are employed for sensing applications. The propagation of p-polarized (TM) surface waves in a three-layer slab waveguide structure with air core layer as an analyte and anisotropic left-handed materials as claddings is investigated for detection of any changes in the refractive index of the analyte. The dispersion equations and the sensitivity of the effective refractive index to any change in the air layer index are derived, plotted, and discussed in details. The field profile is also explored. It is found that the sensitivity of the proposed surface wave sensor is almost independent of the wavelength of the propagating wave. A considerable sensitivity improvement can be obtained with the increase of transverse components of the left-handed material permittivity.

Optimization of angularly resolved Bloch surface wave biosensors.

Bloch surface wave (BSW) sensors to be used in biochemical analytics are discussed in angularly resolved detection mode and are compared to surface plasmon resonance (SPR) sensors. BSW supported at the surface of a dielectric thin film stack feature many degrees of design freedom that enable tuning of resonance properties. In order to obtain a figure of merit for such optimization, the measurement uncertainty depending on resonance width and depth is deduced from different numerical models. This yields a limit of detection which depends on the sensor's free measurement range and which is compared to a figure of merit derived previously. Stack design is illustrated for a BSW supporting thin film stack and is compared to the performance of a gold thin film for SPR sensing. Maximum sensitivity is obtained for a variety of stacks with the resonance positioned slightly above the TIR critical angle. Very narrow resonance widths of BSW sensors require sufficient sampling but are also associated with long surface wave propagation lengths as the limiting parameter for the performance of this kind of sensors.

Phase-sensitive Bloch surface wave sensor based on variable angle spectroscopic ellipsometry.

In this paper, we propose a phase-sensitive Bloch surface wave sensor based on the variable angle spectroscopic ellipsometry and numerically simulate the phase behavior of the sensor. The simulation results show that the dependence of resonant phase is step-like when BSWs are excited. In contrast to the reflectance behavior, even though losses of the dielectric layers are very small, the resonance dip in the reflectivity will be shallow while the step-like change of the reflection phase of the BSW still be remarkable. This means that phase detection is an alternative to reflectivity intensity detection for the sensing applications of the BSWs in this case. Our experimental results indicate that phase detection for the BSW sensors has the potential to achieve the higher sensitivity and the lower limit of detection.

High-sensitivity sensing based on intensity-interrogated Bloch surface wave sensors

A high-sensitivity sensing scheme based on Bloch surface wave is presented with the simple intensity interrogation configuration. The p-polarized electromagnetic surface wave is designed to be excited in a one-dimensional photonic crystal band-gap structure, and support a rather steep resonance dip, much sharper than that of the well-known surface plasmon resonance (SPR). Although the angular shift of this Bloch-surface-wave-based sensor is not as sensitive, the intensity measurement proves to be a more suitable scheme for Bloch surface wave based sensors, thanks to the sharpness of their resonance. Through detection of glycerol in water solution for different concentrations, the intensity sensitivity of our Bloch-surface-wave-based sensor significantly surpasses that of the conventional SPR-based sensors. Experimental results show that the sensor could achieve a detection limit as low as 7.5×10−7 refractive index units in a simple lab setup, which is much simpler than many of the much more complicated SPR-based platforms.

Efficiency of optical sensing by a plasmonic photonic-crystal slab

A one-dimensional photonic crystal with termination by a noble metal film—a plasmonic photonic-crystal slab—is theoretically analysed for its optical response at the variation of the dielectric permittivity of an analyte. A sharp attenuation peak associated with a ‘noble metal-visualized’ Bloch surface wave is observed due to plasmon absorption in the metal. We investigate the sensing performance of the slab and show that it is tolerant to the variation of probing conditions and the slab's structural parameters. As a consequence, the considered sensor exhibits an enhanced sensitivity and good robustness in comparison with conventional surface-plasmon and Bloch surface wave sensors.

Design and Application of Surface Wave Sensors for Nonintrusive Power Line Fault Detection

This paper describes a novel conformal surface wave (CSW) launcher that can excite electromagnetic surface waves along unshielded power line cables nonintrusively. This CSW launcher can detect open circuit faults on power cables. Unlike conventional horn-type launchers, this CSW launcher is small, lightweight, and cost effective, and can be placed easily on a power cable. For a nonintrusive open fault detection, the error is <; 5% when the cable length is <; 10 m, which is comparable with other direct-connect fault-finding techniques. For a cable length of 15.14 m, 7.6% error is noted. Besides cable fault detection, the potential applications of the proposed launcher include broadband power line communication and high-frequency power transmission.