Sensing based on Bloch surface wave and self-referenced guided mode resonances employing a one-dimensional photonic crystal

Direct competitive assay for HER2 detection in human plasma using Bloch surface wave-based biosensors

The overexpression and/or amplification of the HER2/neu oncogene has been proposed as a prognostic marker in breast cancer. The detection of the related peptide HER2 remains a grand challenge in cancer diagnosis and for therapeutic decision-making. Here, we used a biosensing device based on Bloch Surface Waves excited on a one-dimensional photonic crystal (1DPC) as valid alternative to standard techniques. The 1DPC was optimized to operate in the visible spectrum and the biosensor optics has been designed to combine label-free and fluorescence operation modes. This feature enables a real-time monitoring of a direct competitive assay using detection mAbs conjugated with quantum dots for an accurate discrimination in fluorescence mode between HER2-positive/negative human plasma samples. Such a competitive assay was implemented using patterned alternating areas where HER2-Fc chimera and reference molecules were bio-conjugated and monitored in a multiplexed way. By combining Label-Free and fluorescence detection analysis, we were able to tune the parameters of the assay and provide an HER2 detection in human plasma in less than 20 min, allowing for a cost-effective assay and rapid turnaround time. The proposed approach offers a promising technique capable of performing combined label-free and fluorescence detection for both diagnosis and therapeutic monitoring of diseases.

From Bloch surface waves to cavity-mode resonances reaching an ultrahigh sensitivity and a figure of merit

We report on a new sensing concept based on resonances supported by a one-dimensional photonic crystal (1DPhC) microcavity resonator in the Kretschmann configuration. For a 1DPhC comprising six bilayers of TiO2/SiO2 with a termination layer of TiO2 employed to form a microcavity, we show that when the angle of incidence is changed, the Bloch surface waves (BSWs) can be transformed into cavity-mode resonances exhibiting an ultrahigh sensitivity and a figure of merit. Using wavelength interrogation, we demonstrate that Bloch surface TE wave excitation shows up as a sharp dip in the reflectance spectrum with a sensitivity and a figure of merit (FOM) of 70 nm per refractive index unit (RIU) and 19.5 RIU-1, respectively. When the angle of incidence decreases, cavity-mode resonances for both TE and TM waves are resolved for RI in a range of 1.0001-1.0005. The sensitivity and FOM can reach 52,300 nm/RIU and 402,300 RIU-1 for the TE wave, and 14,000 nm/RIU and 2154 RIU-1 for the TM wave, respectively. In addition, resonances are confirmed experimentally for a humid air with a sensitivity of 0.073 nm per percent of the relative humidity (%RH) for BSW resonance and is enhanced to 1.367 nm/%RH for the TM cavity-mode resonance. This research, to the best of the authors' knowledge, is the first demonstration of a new BSW-like response that can be utilized in a simple sensing of a wide range of gaseous analytes.

Anomalous polarization-sensitive Fabry-Perot resonance in a one-dimensional photonic crystal containing an all-dielectric metamaterial defect

Owing to polarization-independent property of propagating phases inside isotropic dielectric layers, Fabry-Perot resonances in metal-dielectric-metal sandwich structures and one-dimensional (1-D) photonic crystals (PhCs) with isotropic dielectric defects are polarization-insensitive. Herein, we introduce an all-dielectric elliptical metamaterial (EMM) defect into a 1-D PhC to realize an anomalous polarization-sensitive Fabry-Perot resonance empowered by the polarization-sensitive property of the propagating phase inside the all-dielectric EMM layer. The wavelength difference of the Fabry-Perot resonance between transverse magnetic and transverse electric polarizations is larger than 100 nm at the incident angle of 45 degrees. Enabled by the polarization-sensitive property of the Fabry-Perot resonance, high-performance polarization selectivity can be achieved in a broad angle range. Our work offers a viable recipe, well within the reach of current fabrication technique, to explore polarization-dependent physical phenomena and devices.

Spin-dependent and tunable perfect absorption in a Fabry-Perot cavity containing a multi-Weyl semimetal

Spin-dependent absorption has been widely studied in metamaterials and metasurfaces with chirality since it develops significant applications in multiplexed holograms, photodection, and filtering. Here, the one-dimensional photonic crystal Fabry-Perot (FP) cavity containing a multi-Weyl semimetal (mWSM) defect is proposed to investigate the spin-dependent perfect absorption. Results denote that the distinct refractive indices of right hand circularly polarized (RCP) and left hand circularly polarized (LCP) waves are present due to the nonzero off-diagonal term of mWSM, thus supporting the perfect absorption of RCP and LCP waves at distinct resonant wavelengths. The different perfect absorption wavelengths of RCP and LCP waves reveal the spin-dependent perfect absorption. By altering the Fermi energy, tilt degree of Weyl cones, Weyl nodes separation, topological charge, and thickness of the mWSM layer, the perfect absorption wavelength of RCP and LCP waves can be regulated conveniently. Particularly, the linear tunable perfect absorption wavelength with thickness of the mWSM layer supports the accurate determination of perfect absorption wavelength at distinct mWSM thicknesses. Our studies develop simple and effective approaches to acquire the spin-dependent and adjustable perfect absorption without the external magnetic field, and can find practical applications in spin-dependent photonic devices.

Ultra-large near-infrared omnidirectional photonic bandgaps in cascaded one-dimensional photonic crystals containing all-dielectric metamaterials

In conventional one-dimensional (1-D) photonic crystals (PCs) consisting of isotropic dielectrics, photonic bandgaps (PBGs) substantially shift toward shorter wavelengths as incident angle increases. This strong blueshift characteristic of PBGs significantly reduces the widths of near-infrared omnidirectional photonic bandgaps (OPBGs). Recently, researchers achieved a kind of special PBG called angle-insensitive PBGs in 1-D PCs containing all-dielectric elliptical metamaterials (EMMs). The emergence of angle-insensitive PBGs provides us a possibility to achieve ultra-large near-infrared OPBGs. Herein, we design two 1-D PCs containing all-dielectric EMMs with near-infrared angle-insensitive PBGs in different wavelength ranges. By cascading two 1-D PCs containing all-dielectric EMMs together, we achieve an ultra-large near-infrared OPBG with a width up to 1.004 µm (relative bandwidth of 63.9%). In addition, the width of the near-infrared OPBG demonstrates robustness against the layer thickness. Our work not only provides a feasible route to achieving ultra-large near-infrared OPBGs, but also facilitates the design of broadband omnidirectional mirrors.

Bloch Surface Waves in Open Fabry-Perot Microcavities

Thanks to the increasing availability of technologies for thin film deposition, all-dielectric structures are becoming more and more attractive for integrated photonics. As light-matter interactions are involved, Bloch Surface Waves (BSWs) may represent a viable alternative to plasmonic platforms, allowing easy wavelength and polarization manipulation and reduced absorption losses. However, plasmon-based devices operating at an optical and near-infrared frequency have been demonstrated to reach extraordinary field confinement capabilities, with localized mode volumes of down to a few nanometers. Although such levels of energy localization are substantially unattainable with dielectrics, it is possible to operate subwavelength field confinement by employing high-refractive index materials with proper patterning such as, e.g., photonic crystals and metasurfaces. Here, we propose a computational study on the transverse localization of BSWs by means of quasi-flat Fabry-Perot microcavities, which have the advantage of being fully exposed toward the outer environment. These structures are constituted by defected periodic corrugations of a dielectric multilayer top surface. The dispersion and spatial distribution of BSWs' cavity mode are presented. In addition, the hybridization of BSWs with an A exciton in a 2D flake of tungsten disulfide (WS₂) is also addressed. We show evidence of strong coupling involving not only propagating BSWs but also localized BSWs, namely, band-edge and cavity modes.

Wide-angle high-efficiency absorption of graphene empowered by an angle-insensitive Tamm plasmon polariton

In recent years, researchers utilized Tamm plasmon polaritons (TPPs) in conventional heterostructures composed of a metal layer, a dielectric spacer layer and an all-dielectric one-dimensional (1-D) photonic crystal (PhC) to achieve high-efficiency absorption of graphene. According to the Bragg scattering theory, photonic bandgaps (PBGs) in all-dielectric 1-D PhC strongly shift toward shorter wavelengths (i.e., blueshift) as the incident angle increases. Therefore, TPPs in conventional heterostructures also show strongly blueshift property. Such strongly blueshift property of TPPs greatly limits the operating angle range of the high-efficiency absorption of graphene. Herein, we realize an angle-insensitive TPP in a heterostructure composed of a metal layer, a dielectric spacer layer and a 1-D PhC containing hyperbolic metamaterial layers. Empowered by the angle-insensitive property of the TPP, we achieve wide-angle high-efficiency absorption of graphene. The operating angle range (A > 80%) reaches 41.8 degrees, which is much larger than those in the reported works based on TPPs and defect modes. Our work provides a viable route to designing cloaking devices and photodetectors.

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.

Guided-mode resonance sensors with ultrahigh bulk sensitivity and figure of merit assisted by a metallic layer and structural symmetry-breaking

We propose a refractive index sensor with both high bulk sensitivity and figure of merit (FOM) that engages the guided-mode resonance (GMR) effect with the assistance of a metallic layer and structural symmetry-breaking in the grating layer. Owing to the existence of the metallic layer, the electric field at resonance can be reflected to the sensing environment, and enhanced bulk sensitivity is realized. Meanwhile, the full width at half maximum of the GMR mode can be decreased by increasing the asymmetrical degree of the grating, thus obtaining a high FOM which benefits the sensing resolution. A bulk refractive index sensitivity of 1076.7 nm/RIU and an FOM up to 35889 RIU^-1 are achieved simultaneously. Other structural parameters such as the refractive index and fill factor of the grating are systematically discussed to optimize the sensing performance. The proposed GMR sensor with both high bulk sensitivity and FOM value has potential uses in applications with more stringent sensing requirements.

Polarization-independent and ultra-sensitive biosensor with a one-dimensional topological photonic crystal

Optical biosensor, which perceptively captures the variety of refractive index (RI) of the surrounding environment, has great potential applications in detecting property changes and types of analytes. However, the disequilibrium of light-matter interaction in different polarizations lead to the polarization-dependence and low sensitivity. Here, we propose a polarization-independent and ultrasensitive biosensor by introducing a one-dimensional topological photonic crystal (1D TPhC), where two N-period 1D photonic crystals (PhC1 and PhC2) with different topological invariants are designed for compressing the interaction region of the optical fields, and enhancing the interaction between the light and analyte. Since the strong light-matter interaction caused by the band-inversion is polarization-independent, the biosensor can obtain superior sensing performance both for TE and TM polarization modes. The sensitivity and Figure of Merit (FOM) of the designed biosensor are 1.5677×10⁶ RIU^-1 (1.3497 × 10⁶ RIU^-1) and 7.8387×10¹⁰ RIU^-1deg^-1 (4.4990×10¹⁰ RIU^-1deg^-1) for TM (TE) polarization mode, which performs two orders of magnitude enhancement compared with the reported biosensors. With the protection of the topological edge state, this biosensor has high tolerance to the thickness deviations and refractive index (RI) variations of the component materials, which can reduce the requirements on fabrication and working environment. It is anticipated that the proposed biosensor possesses excellent sensing performances, may have great potentials in environmental monitoring, medical detection, etc.

Dynamic moist air monitor in a micro area with extremely high figure-of-merit

In the rapidly changing moisture air, conventional relative humidity (RH) sensors are often difficult to respond in time and accurately due to the limitation of flow rate and non-uniform airflow distribution. In this study, we numerically demonstrate that humidity changes on micro-zones can be monitored in real time using a Bloch surface wave (BSW) ubiquitous in one-dimensional photonic crystals (1DPC). This phenomenon can be observed by leakage radiation microscope (LRM). After theoretically deriving the angular resolution limit of LRM, we obtained the minimum BSW angular change on a practical scheme that can be observed in the momentum space to complete the detection, and realized the dynamic real-time monitoring of small-scale humidity change in experiment for the first time. This monitoring method has extremely high figure of merit (FOM) without hysteresis, which can be used in humidity sensing and refractive index sensing as well as the research on turbulence.

Optical fractal resonances in Cantor-like photonic crystals

We theoretically investigate the optical fractal effect in one-dimensional quasiperiodic photonic crystals (PCs). Dielectric multilayers arrayed alternately submit to the Cantor-like sequence rule. The optical fractal phenomenon is induced by modulating the generation number of the dielectric sequence. The optical fractal effect corresponds to a series of resonant modes, and the Cantor-like PCs approve more resonance modes than those in the Cantor PCs with the same order number. The transmission channels of resonances exponentially increase with the increase in the sequence generation number. Furthermore, the central waves of the transmission channels can be regulated by the incident angle flexibly. We expect this paper may pave a new way for the development of wavelength division multiplexers.

Ultra-sensitive refractive index sensing enabled by a dramatic ellipsometric phase change at the band edge in a one-dimensional photonic crystal

Surface plasmon polaritons (SPPs) and Bloch surface waves (BSWs) have been widely utilized to design sensitive refractive index sensors. However, SPP- and BSW-based refractive index sensors require additional coupling component (prism) or coupling structure (grating or fiber), which increases the difficulty to observe ultra-sensitive refractive index sensing in experiments. Herein, we realize dramatic ellipsometric phase change at the band edges in an all-dielectric one-dimensional photonic crystal for oblique incidence. By virtue of the dramatic ellipsometric phase change at the long-wavelength band edge, we design an ultra-sensitive refractive index sensor at near-infrared wavelengths. The minimal resolution of the designed sensor reaches 9.28×10^-8 RIU. Compared with SPP- and BSW-based refractive index sensors, the designed ultra-sensitive refractive index sensor does not require any additional coupling component or coupling structure. Such ultra-sensitive refractive index sensor would possess applications in monitoring temperature, humidity, pressure, and concentration of biological analytes.

Excitation of Hybrid Waveguide-Bloch Surface States with Bi2Se3 Plasmonic Material in the Near-Infrared Range

Bloch surface waves (BSWs) with Bi₂Se₃ in a composite structure consisting of a coupling prism, distributed Bragg reflector (DBR) and cavity layer have been demonstrated. The design relies on the confinement of surface waves that originates from the coupling between the defective layer of plasmonic material (Bi₂Se₃) and DBR. The presence of the cavity layer modifies the local effective refractive index, enabling direct manipulation of the BSWs. The transfer matrix method (TMM) is used to evaluate the reflectance and absorptance responses in the spectral domain for various angles of incidence, demonstrating the presence of sharp resonances associated with the BSW. With an optimal thickness of DBR bilayers, the energy of an evanescent wave can be transferred into the periodic stack resulting in the excitation of waveguide modes (WGMs). It is believed that the proposed design possesses the advantage in terms of easy fabrication to develop integrated photonic systems, especially for biological and chemical sensing.

Distributed Bragg Reflectors Employed in Sensors and Filters Based on Cavity-Mode Spectral-Domain Resonances

Spectral-domain resonances for cavities formed by two distributed Bragg reflectors (DBRs) were analyzed theoretically and experimentally. We model the reflectance and transmittance spectra of the cavity at the normal incidence of light when DBRs are represented by a one-dimensional photonic crystal (1DPhC) comprising six bilayers of TiO2/SiO2 with a termination layer of TiO2. Using a new approach based on the reference reflectance, we model the reflectance ratio as a function of both the cavity thickness and its refractive index (RI) and show that narrow dips within the 1DPhC band gap can easily be resolved. We revealed that the sensitivity and figure of merit (FOM) are as high as 610 nm/RIU and 938 RIU−1, respectively. The transmittance spectra include narrow peaks within the 1DPhC band gap and their amplitude and spacing depend on the cavity’s thickness. We experimentally demonstrated the sensitivity to variations of relative humidity (RH) of moist air and FOM as high as 0.156 nm/%RH and 0.047 %RH−1, respectively. In addition, we show that, due to the transmittance spectra, the DBRs with air cavity can be employed as spectral filters, and this is demonstrated for two LED sources for which their spectra are filtered at wavelengths 680 nm and 780 nm, respectively, to widths as narrow as 2.3 nm. The DBR-based resonators, thus, represent an effective alternative to both sensors and optical filters, with advantages including the normal incidence of light and narrow-spectral-width resonances.

Thermal Stability Analysis of Surface Wave Assisted Bio-Photonic Sensor

In this paper, the thermal stability of a Bloch Surface Wave (BSW) assisted bio-photonic sensor is investigated. The structural analysis is carried out using the transfer matrix method (TMM). The design comprises a truncated one-dimensional photonic crystal (1D-PhC) structure along with a defective top layer. The structural parameters are optimized to excite a BSW at the top interface for an operating wavelength of 632.8 nm. The mode confinement is confirmed by using wavelength interrogation, angular interrogation and surface electric field profile. Further, the effect of thermal variation on BSW excitation angle and sensitivity is carried out. The analysis shows the average variations in excitation angle and sensitivity of about −0.00096 degree/°C and 0.01046 (degree/RIU)/°C, respectively. Additionally, the analysis is also extended towards different lower wavelengths of 400 nm and 550 nm, which provides average variations in the excitation angles of about −0.0027 degree/°C, and 0.0016 degree/°C. This shows that the structural sensitivity response is more thermally stable at the lower wavelength range. Thus, showing its potential applications in designing thermally stable bio-photonic sensors.

Theoretical Model for a Highly Sensitive Near Infrared Biosensor Based on Bloch Surface Wave with Dirac Semimetal

In this work, we present a theoretical model of a near-infrared sensitive refractive index biosensor based on the truncate 1D photonic crystal (1D PC) structure with Dirac semimetal. This highly sensitive near-infrared biosensor originates from the sharp reflectance peak caused by the excitation of Bloch surface wave (BSW) at the interface between the Dirac semimetal and 1D PC. The sensitivity of the biosensor model is sensitive to the Fermi energy of Dirac semimetal, the thickness of the truncate layer and the refractive index of the sensing medium. By optimizing the structural parameters, the maximum refractive index sensitivity of the biosensor model can surpass 17.4 × 103/RIU, which achieves a certain competitiveness compared to conventional surface plasmon resonance (SPR) or BSW sensors. Considering that bulk materials are easier to handle than two-dimensional materials in manufacturing facilities, we judge that 3D Dirac semimetal and its related devices will provide a strong competitor and alternative to graphene-based devices.

Efficient Optical Sensing Based on Phase Shift of Waves Supported by a One-Dimensional Photonic Crystal

Interferometric methods of optical sensing based on the phase shift of the Bloch surface waves (BSWs) and guided waves (GWs) supported by a one-dimensional photonic crystal are presented. The photonic crystal, composed of six SiO₂/TiO₂ bilayers with a termination layer of TiO₂, is employed in the Kretschmann configuration. Under resonance condition, an abrupt phase change is revealed, and the corresponding phase shift is measured by interferometric techniques applied in both the spectral and spatial domains. The spectral interferometric technique employing a birefringent quartz crystal is used to obtain interference of projections of p- and s-polarized light waves reflected from the photonic crystal. The phase shifts are retrieved by processing the spectral interferograms recorded for various values of relative humidity (RH) of air, giving the sensitivity to the RH as high as 0.029 rad/%RH and 0.012 rad/%RH for the BSW and GW, respectively. The spatial interferometric technique employs a Wollaston prism and an analyzer to generate an interference pattern, which is processed to retrieve the phase difference, and results are in good agreement with those obtained by sensing the phase shift in the spectral domain. In addition, from the derivative of the spectral phase shifts, the peak positions are obtained, and their changes with the RH give the sensitivities of 0.094 nm/%RH and 0.061 nm/%RH for the BSW and GW, respectively. These experimental results demonstrate an efficient optical sensing with a lot of applications in various research areas.

Novel Photonic Bio-Chip Sensor Based on Strained Graphene Sheets for Blood Cell Sorting

A photonic biochip with a tunable response in the visible range is suggested for blood cell sorting applications. Multi-layers of ZnS and Ge slabs (as the main building blocks), hosting a cell in which bio-sample could be injected, are considered as the core of the sensor. In order to increase the sensitivity of the chip, the bio-cell is capsulated inside air slabs, and its walls are coated with graphene sheets. Paying special attention to white and red blood components, the optimum values for structural parameters are extracted first. Tunability of the sensor detectivity is then explored by finding the role of the probe light incident angle, as well as its polarization. The strain of the graphene layer and angle in which it is applied are also suggested to further improve the performance tunability. Results reflect that the biochip can effectively identify selected components through their induced different optical features, besides of the different figure of merit and sensitivity amounts that are recorded for them by the sensor.