Bloch Surface Wave Resonance Research Articles

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.

Nonlinear Excitation and Self-Action of Bloch Surface Waves Governed by Gradient Optical Forces

Self-action of light is among the most important nonlinear optical effects with a plethora of present and potential applications. Suspensions of subwavelength particles are characterized by high artificial optical nonlinearity induced by gradient optical forces. Here, we report on an experimental study of self-action of the Bloch surface wave (BSW) excited at the interface between a one-dimensional photonic crystal and a water suspension of dielectric nanoparticles by a continuous-wave diode laser. We demonstrate the modification of the BSW resonance with increasing optical power and, for the first time to our knowledge, experimentally show self-focusing of BSWs. A plane-wave model is used to describe the mechanism of the observed resonance modification. Our results demonstrate the great potential of guided waves in multilayer structures for optical signal processing and open up new possibilities for the light-controlled operation of BSWs.

Bloch Surface Wave‐Assisted Ultrafast All‐Optical Switching in Graphene

AbstractGraphene has ultrafast charge carrier dynamic and shows strong light–matter interaction allowing the use in photovoltaic devices, fast photodetectors, saturable absorbers, and electro‐optical modulators. However, despite the high nonlinear optical susceptibilities, the small amount of material significantly limits the use of graphene for nonlinear optical applications. In this work, Bloch surface waves (BSWs) are employed, enhancing the graphene–light interaction, for all‐optical switching realization. By placing a graphene monolayer on top of a 1D photonic crystal, it is shown that for the wavelength corresponding to the BSW resonance, the reflection coefficient is modulated on the sub‐picosecond time scale by an order of magnitude larger than that for bare graphene. The magnitude of the reflection change reaches 0.3% at the fluence of 40 µJ cm−2. The reported results are proof of priciple possibility of BSW‐assisted enhancing the reflection modulation of any 2D materials and transparent thin films while maintaining their inherent ultrafast dynamics, which is useful for the further development of all‐optical switches.

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

Sensing abilities of a one-dimensional photonic crystal (1DPhC) represented by a multilayer dielectric structure are analyzed theoretically and experimentally, using a new wavelength interrogation interference method. The structure comprising a glass substrate and six bilayers of TiO2/SiO2 with a termination layer of TiO2 is employed in both gas sensing based on the Bloch surface wave (BSW) resonance and liquid analyte sensing based on a self-referenced guide-mode resonance (GMR). We model the spectral interference reflectance responses in the Kretschmann configuration with a coupling prism made of BK7 glass and show that a sharp dip with maximum depth associated with the BSW excitation is red-shifted as the refractive index (RI) changes in a range of 1-1.005. Thus, a sensitivity of 1456 nm per RI unit (RIU) and figure of merit (FOM) of 91 RIU-1 are reached. Similarly, we model the responses for aqueous solutions of ethanol to show that dips of maximum depth are associated with the GMRs, and the highest sensitivity and FOM reached are 751 nm/RIU and 25 RIU-1, respectively. Moreover, we show that one of the dips is with the smallest shift as the RI changes, and hence it can be used as a reference. The theoretical results are confirmed by the experimental ones when the BSW resonance is used in sensing of humid air with a sensitivity of 0.027 nm/%relative humidity (RH) and FOM of 1.4×10-3 %RH-1. Similarly, the GMR is used in sensing of aqueous solutions of ethanol, and the highest sensitivity and FOM reached 682 nm/RIU and 23 RIU-1, respectively. The reference dip is also resolved and this self-reference makes the measurement more accurate and repeatable, and less sensitive to optomechanical drifts.

Guided Bloch surface wave resonance for multispectral enhancement of absorption in mono-layer grapheme

A multispectral absorber based on Bloch surface wave (BSW) resonance with distributed Bragg reflectors (DBRs) coated with monolayer graphene is proposed. The guided Bloch surface wave resonance (GBSWR) is realized by coupling the diffraction of a subwavelength grating with the BSW at the interface between a 1D-PhC and graphene layer. Strong absorption phenomenon occurs induced by the coupling of the incident light and GBSWR. The highly efficient absorption and spectral selectivity with designing structural parameters in the visible range are verified through the rigorous coupled-wave analysis (RCWA) method. It is found that the number of absorption peaks is strongly related with the stacked period number of two dielectric materials in DBR. Compared with previous studies, not only the complete absorption of single-atomic-layer graphene can be achieved, but also the above 90 % absorption for all of resonance positions is maintained. These characteristics open up new methods of enhancing the light-graphene interaction, which may find potential application in high-performance modulators and sensors.

Fluorophore Coupling to Internal Modes of Bragg Gratings

Multilayer structures with two dielectrics having different optical constants and no structural features in the x-y plane can display photonic band gaps (PBGs) and are called one-dimensional photonic crystals (1DPCs). If the top layer thickness is carefully selected, the electromagnetic energy can be trapped at the top surface. These highly enhanced fields are called Bloch surface waves (BSWs). The BSW resonance angles are sensitive to the dielectric constant above the top dielectric layer. As a result, BSW structures have been used for surface plasmon resonance-like measurements without the use of a metal film. However, the emphasis on surface-localized BSWs has resulted in limited interest in fluorophore interactions with other optical modes of 1DPCs or Bragg gratings without the different thickness top layer. Herein, three different fluorescent probes were used to cover the short, center, and long wavelengths of the PBG. We demonstrate efficient coupling of fluorophores to both the BSW and internal modes (IMs) of a 1DPC. Coupling to the IM is expected to be low because of the micron-scale distances between the fluorophores and IM, which exists inside the Bragg gratings. At different wavelengths or observation angles, the IM-coupled emission (IMCE) can occur with the first three modes of the multilayer. This coupling is not dependent on a BSW mode. IMCE was also observed for a monolayer of fluorophore-labeled protein. IMCE enables sensitive detection of surface-bound fluorophores. Applications are anticipated in high sensitivity detection and super-resolution imaging.

Bloch Surface Wave Resonance Based Sensors as an Alternative to Surface Plasmon Resonance Sensors.

We report on a highly sensitive measurement of the relative humidity (RH) of moist air using both the surface plasmon resonance (SPR) and Bloch surface wave resonance (BSWR). Both resonances are resolved in the Kretschmann configuration when the wavelength interrogation method is utilized. The SPR is revealed for a multilayer plasmonic structure of SF10/Cr/Au, while the BSWR is resolved for a multilayer dielectric structure (MDS) comprising four bilayers of TiO/SiO with a rough termination layer of TiO. The SPR effect is manifested by a dip in the reflectance of a p-polarized wave, and a shift of the dip with the change in the RH, or equivalently with the change in the refractive index of moist air is revealed, giving a sensitivity in a range of 0.042–0.072 nm/%RH. The BSWR effect is manifested by a dip in the reflectance of the spectral interference of s- and p-polarized waves, which represents an effective approach in resolving the resonance with maximum depth. For the MDS under study, the BSWRs were resolved within two band gaps, and for moist air we obtained sensitivities of 0.021–0.038 nm/%RH and 0.046–0.065 nm/%RH, respectively. We also revealed that the SPR based RH measurement is with the figure of merit (FOM) up to 4.7 × 10−4 %RH, while BSWR based measurements have FOMs as high as 3.0 × 10 %RH and 1.1 × 10−3 %RH, respectively. The obtained spectral interferometry based results demonstrate that the BSWR based sensor employing the available MDS has a similar sensitivity as the SPR based sensor, but outperforms it in the FOM. BSW based sensors employing dielectrics thus represent an effective alternative with a number of advantages, including better mechanical and chemical stability than metal films used in SPR sensing.

Design and characterization of an ultra-low-cost 3D-printed optical sensor based on Bloch surface wave resonance

This paper demonstrates the design, construction, and testing of an optical sensor based on Bloch surface wave resonance. The single target, flow-cell sensor makes use of simple, inexpensive optical components and mechanical parts largely created using 3D printing. We demonstrate that this simple instrument is capable of high resolution refractive index measurements and affinity binding experiments of the type used to probe reaction kinetics.

Azimuthal illumination enabled ultra-high polar angle sensitivity by a Bloch surface wave resonance refractive index sensor

The scheme of a polar angle space refractive index (RI) sensor based on grating-coupled Bloch surface wave (BSW) resonance excited by azimuthal illuminations is studied. It is shown that, for any polar angle, one can always find a case of BSW resonance with the tangential wave vector of the BSW mode perpendicular to that of the incident electromagnetic wave. When the sensor is designed to work around this BSW resonance, ultra-high polar angle sensitivity can be expected. The numerical simulated polar angle sensitivity reaches as large as 1786 degrees per RI unit (Deg/RIU), which is almost one order higher than that found in the literature.

Highly Sensitive THz Gas-Sensor Based on the Guided Bloch Surface Wave Resonance in Polymeric Photonic Crystals

THz waves have interesting applications in refractive index sensing. A THz gas sensor based on the guided Bloch surface wave resonance (GBSWR) in a one-dimensional photonic crystal (1DPhC), which consists of periodic polycarbonate (PC) layers and polyvinylidene fluoride (PVDF) layers, has been proposed. Numerical results based on finite element method (FEM) show that the photonic band gap that confines Bloch surface waves (BSWs) lies in the regime of 11.54 to 21.43 THz, in which THz wave can transmit in both PC and PVDF with the ignored absorption. The calculated sensitivity of hazardous gas HCN in angle is found to be 118.6°/RIU (and the corresponding figure of merit (FOM) is 227) and the sensitivity in frequency is 4.7 THz/RIU (the corresponding FOM is 301.3). The proposed structure may also be used for monitoring hazardous gases which show absorption to the incident THz wave. Further results show that for N2O gas, the maximum sensitivity goes up to 644 (transmittance unit/ one unit of the imaginary part of the refractive index). The proposed design may find applications in the detection of dangerous gases.

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.

Bloch surface wave resonance in photonic crystal fibers: towards ultra-wide range refractive index sensors.

In this work, a new approach based on the use of a one-dimensional photonic crystal (1DPC) made of dielectric layers with alternating refractive indexes deposited inside a photonic crystal fiber (PCF) is proposed as a suitable platform for the excitation of Bloch surface waves (BSWs). The presence of an additional dielectric layer on the 1DPC modifies the local effective refractive index, enabling a direct manipulation of the BSWs. In particular, we investigate BSW resonance conditions in a 1DPC of alternating layers of TiO2 and SiO2 deposited inside a three-hole suspended-core PCF to design an ultra-wide range refractive index sensor in the near infrared. The obtained simulation results indicate that BSW sensors based on PCF could be an alternative to surface plasmon resonance (SPR) sensors, with a ultrahigh sensing figure-of-merit, which might facilitate applications in high-resolution refractive index sensing.

Sensing performance optimization of the Bloch surface wave biosensor based on the Bloch impedance-matching method.

We propose a novel strategy to optimize sensing performance of the Bloch surface wave (BSW) biosensor. First of all, a one-dimensional photonic crystal with an omnidirectional photonic bandgap is designed. Except for sustaining the BSW, the omnidirectional photonic bandgap guarantees a tiny full width at half maximum (FWHM=0.84 nm) for the reflection dip induced by BSW resonance. Then, the specific dependence of wavelength sensitivity on incident angle is obtained by the Bloch impedance-matching method. Study shows that wavelength sensitivity increases with the decreases in incident angle (larger than the critical angle). At the same time, when the incident angle approaches the critical angle (θ=67.5 deg), wavelength sensitivity increases rapidly (Sλ=1570 nm/RIU). Moreover, theoretical research reveals that biosensor sensitivity can also be further enhanced by other system parameters. Combining the tiny FWHM of the reflection dip and large wavelength sensitivity, the figure of merit of the optimized biosensor can reach as high as 1869 RIU-1. These results enable the design of biosensors with high performance in a predictable manner.

Guided Bloch surface wave resonance by near normal and near in-plane illuminations: the hyper azimuthal sensitivity.

Refractive index sensors based on the interrogation of guided Bloch surface wave resonance (GBR) in the azimuthal angle domain are studied both theoretically and numerically. The azimuthal sensitivity of the sensors is shown to be inversely proportional to the sines of both the azimuthal angle and the polar angle of the detecting electromagnetic signals. Extremely large azimuthal sensitivity is then achieved when the GBR sensor is designed to work near a small azimuthal angle and the polar angle is also fixed to a small one (For the azimuthal angle domain near φ = 5° and a fixed polar angle of θ = 5°, the azimuthal sensitivity gets larger than 5000 degrees per refractive index unit (Deg/RIU)).

Confinement of Bloch surface waves in a graphene-based one-dimensional photonic crystal and sensing applications**Project supported by the National Natural Science Foundation of China (Grant Nos. 61203211 and 41675154), the Six Major Talent Peak Expert of Jiangsu Province, China (Grant No. 2015-XXRJ-014), and the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20141483).

Bloch surface waves (BSWs) are excited in one-dimensional photonic crystals (PhCs) terminated by a graphene monolayer under the Kretschmann configuration. The field distribution and reflectance spectra are numerically calculated by the transverse magnetic method under transfer-matrix polarization, while the sensitivity is analyzed and compared with those of the surface plasmon resonance sensing method. It is found that the intensity of magnetic field is considerably enhanced in the region of the terminated layer of the multilayer stacks, and that BSW resonance appears only in the interface of the graphene and solution. Influences of the graphene layers and the thickness of a unit cell in PhCs on the reflectance are studied as well. In particular, by analyzing the performance of BSW sensors with the graphene monolayer, the wavelength sensitivity of the proposed sensor is 1040 nm/RIU whereas the angular sensitivity is 25.1°/RIU. In addition, the maximum of figure of merit can reach as high as 3000 RIU−1. Thus, by integrating graphene in a simple Kretschmann structure, one can obtain an enhancement of the light–graphene interaction, which is prospective for creating label-free, low-cost and high-sensitivity optical biosensors.

Refractive index sensor based on graphene-coated photonic surface-wave resonance.

We propose a graphene-coated photonic system with the excitation of Bloch surface waves (BSWs) for refractive index sensing. Through manipulation of the BSW resonance in the truncated photonic crystal under a Kretschmann configuration, the absorption in a graphene monolayer is significantly enhanced, assisted by the strong electromagnetic confinement of BSWs. The sharp and low reflectivity dip and the strong wave-environment interaction enable highly sensitive optical sensing. First-order perturbation theory and transfer-matrix calculation indicate that the system sensitivity is strongly related to the ratio of the electric field energy in the detection area, operation wavelength, and incident angle. Study shows that the wavelength sensitivity and figure of merit of the optimized system can reach 7023 nm/RIU and 196.44, respectively. More generalized BSW system configurations, e.g.,aperiodic BSW design, are proposed for refractive index sensing application.

Design of guided Bloch surface wave resonance bio-sensors with high sensitivity

The sensing performance of bio-sensors based on guided Bloch surface wave (BSW) resonance (GBR) is studied. GBR is realized by coupling the propagating electromagnetic wave with BSW on one side of a one-dimensional photonic crystal slab via the grating on the other side. The sensitivity of the designed bio-sensors is proportional to the grating constant when the wavelength spectrum is analyzed, and inversely proportional to the normal wave vector of the incident electromagnetic wave when the angular spectrum is resolved. For a GBR bio-sensor designed to operate near 70° angle of incidence from air, the angular sensitivity is very high, reaching 128degRIU−1. The sensitivity can be substantially increased by designing bio-sensors for operating at larger angles of incidence.

Sub-nanometer linewidth perfect absorption in visible band induced by Bloch surface wave

We demonstrate the unity absorption of visible light with an ultra-narrow 0.1 nm linewidth. It arises from the Bloch surface wave resonance in alternating TiO2/SiO2 multilayers. The total absorption and narrow linewidth are explained from the radiative and absorptive damping, which are quantitatively determined by the temporal coupled mode theory. When a silver film with proper thickness is added to the absorber, the perfect absorption is achieved with only 3 structural bilayers, in contrast with 8 bilayers required without Ag. Furthermore, significant field enhancement and an ultrahigh 2600/RIU sensing figure-of-merit are simultaneously obtained at resonance, which might facilitate applications in nonlinear optical devices and high resolution refractive index sensing.

Guided Bloch surface wave resonance for biosensor designs.

A guided Bloch surface wave resonance (GBR) configuration is introduced for label-free biosensing. The GBR is realized by coupling the first-order diffraction of a subwavelength grating with the Bloch surface wave at the interface between a 1D photonic crystal slab and bio-solution. In addition to sustaining the Bloch surface mode, the photonic crystal provides the design freedom of simultaneously increasing the quality and decreasing the sideband transmissions of the resonance spectrum. The low sideband and high-quality features along with the large sensitivity rising from the strong overlap between the Bloch surface mode and the bio-solution make the GBR suitable for the design of biosensors. Biosensors with a high figure of merit are realized by the compact configurations.

Magneto-optical switching of Bloch surface waves in magnetophotonic crystals

Bloch-surface-wave (BSW) excitation controlled by Faraday rotation in one-dimensional magnetophotonic crystals is presented. Dispersion curves of the Bloch surface wave and waveguide modes of magnetophotonic crystals consisting of silicon dioxide and bismuth-substituted yttrium-iron-garnet (Bi:YIG) quarter-wavelength-thick layers are calculated using Berreman's 4×4 transfer matrix method. Enhanced Faraday rotation observed in the magnetophotonic crystals in the spectral vicinity of the BSW resonance enables the magneto-optical switching of BSWs. The excitation of the BSWs at the magnetophotonic crystal surface for p-polarized incident light is induced by magneto-optical activity in the Bi:YIG layers.