- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Inverse Photonic Design of Functional Elements That Focus Bloch Surface Waves
摘要： Bloch surface waves (BSWs) are surface states excited at the interface between a one-dimensional dielectric photonic crystal (1D-PC) and some ambient material. They are promising alternatives to propagating surface plasmon polaritons thanks to their much longer propagation lengths (up to thousand times the wavelength) that is not limited by absorption and the opportunity to excite them in both polarizations. They are currently considered for multiple applications in integrated optical systems or for sensing devices [1]. To control the propagation of BSWs, a structured functional layer is deposited on top of the 1D-PC. It consists of a thin dielectric layer with a desired shape that controls locally the dispersion relation of the BSW. This allows to implement, in general, optical elements with functions on demand. However, a severe limitation is the finite index contrast to be induced with the functional layer. For typical combinations of material and geometries, an index contrast only in the order of ~ 0.1 is achieved. This is insufficient to tightly focus a BSW with elements perceived by a rational design approach, e.g. with lens-like elements [2]. To solve this problem, we apply here methods developed in the context of computational photonic material design to perceive functional elements that focus BSWs highly efficiently [3]. We basically aim to solve the inverse problem. Computationally, we rely on a finite-difference frequency method as the Maxwell solver. To identify suitable structures, we discretize a finite spatial domain (typically in the order of 40μm x 10μm) where each pixel either is or is not covered by the functional layer. By systematically flipping each pixel, we can optimize structures that can focus the BSW into a predefined spatial domain. For a spatial domain directly behind the element, the BSW can be focused even below half its wavelength (a selected example is shown in Fig. 1a). To verify the findings, we fabricated the respective structures and measured the optical near-fields above them (a selected example is shown in Fig. 1b). The comparison between the simulation and the measurement shows an impressive agreement and allows to verify the ability to tightly focus the BSWs (Fig. 1c). This work introduces a new computational framework to design functional elements that can be used to control the propagation of BSWs and verifies it experimentally. Our approach is suitable for other material platforms where the limited index contrast is an obstacle to control the propagation of some waves. The elements we have studied can find immediate application in lab-on-chip systems where tightly focused BSWs interact with materials carried in fluidic channels to perform spectroscopic measurements.
关键词： functional elements,Bloch surface waves,photonic design,focusing,computational framework
更新于2025-09-23 15:19:57
-
[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Spectroscopic Evidence of Bloch Surface Waves in the Mid Infrared
摘要： Bloch Surface Waves are surface electromagnetic waves with very low intrinsic losses, existing in both in-plane and out-of plane polarizations, supported by a one-dimensional photonic crystal with an in-gap defect. We have developed thin-film deposition technology on CaF2 prisms suitable for biosensing applications of BSWs in the mid-infrared. Here we report spectroscopic evidence of BSWs, in perfect agreement with theory, in the wavelength range from 4 to 6 micrometers.
关键词： photonic crystal,spectroscopic evidence,mid-infrared,Bloch Surface Waves,biosensing
更新于2025-09-12 10:27:22
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Anisotropic Fluorescence Emission at the Surface of 1D-Photonic Crystal Biochips
摘要： Novel disposable optical biochips based on one-dimensional photonic crystals (1DPC) sustaining Bloch surface waves (BSW) are a desirable tool for the detection of several disease-related biomarkers. In particular, cancer biomarkers have gained considerable attention, due to the increasing demand for cancer treatment. Within this framework, the herein proposed optical biochips can quantify low concentration (sub ng/mL) of the ERBB2 breast cancer biomarker in biological complex matrices. To discriminate ERBB2 levels in several different cell lysate samples, we made use of a biosensing platform based on 1DPC biochips and on a reading instrument that can work in both a label-free and a fluorescence detection mode. Such combined configuration provides the advantage of complementary information and lower limit of detection (LoD) in the fluorescence mode [1]. In the label-free configuration the BSW excitation is achieved by a prism coupling system (Kretschmann-Raether configuration), like in the surface plasmon resonance (SPR) technique, resulting in a dip in the angular reflectance spectrum, shifting its position due to the refractive index changes [2]. The fluorescence mode is carried out by making use of dye labeled antibodies bound at the 1DPC surface. Coupling between the dye labels and a BSW results in strongly directional fluorescence emission. The advantages brought by the 1DPC, when compared to metal structures, are smaller energy dissipation and narrower resonances [3]. Presently, there is no study about photobleaching in experiments with BSW sustained by 1DPC, while it is evident that such phenomenon cannot be neglected in biosensing assays carried out close to the LoD, where quantitative and accurate information is needed. Here we report for the first time on cancer detection assays carried out with our platform, in which the trustworthiness of the output is put in doubt by photobleaching, which not only affects the overall emission intensity but also its polarization distribution via the TE and TM BSW modes provided by the 1DPC. The experimental data is interpreted by means of a theoretical model for the orientational distribution of dye labels over time, taking into account the density of the optical states of the 1DPC, photobleaching and rotational diffusion of surface bound emitters. The approach permits to model anisotropic fluorescence emission and to manage photobleaching effects in biosensing assays, leading to their correct interpretation.
关键词： one-dimensional photonic crystals,optical biochips,Bloch surface waves,cancer biomarkers,fluorescence emission,photobleaching
更新于2025-09-12 10:27:22
-
Design and Analysis of a Novel Phase-Shifted Bragg Grating for Bloch Surface Waves
摘要： A novel phase-shifted Bragg grating (PSBG) for Bloch surface waves (BSWs) propagating along the interface between a semiconductor thin layer and a multilayer stack is proposed. This structure is composed of a set of a special ridge fabricated on a multilayer stack supporting a Bloch surface wave. The multilayer stack is periodic, with the unit cell composed of two layers with different materials and thicknesses. The light con?nement capability and transmission properties of the proposed structure are investigated in the wavelength range of 1450–1650 nm by using the ?nite-element method and ?nite-difference time-domain method. Compared to existing PSBG structures based on surface plasmon polaritons waves, the proposed con?guration does not include any metal and the absorption losses upon propagation of the surface wave are negligibly small. Simulation results also indicate that the proposed structure exhibits outstanding transmission properties. The proposed PSBG for BSWs could be applied in narrow bandpass ?ltering, all optical computing, and enable on-chip integration photonic circuits.
关键词： resonance domain.,guided waves,Bloch surface waves,Phase-shifted Bragg grating
更新于2025-09-04 15:30:14
-
Inverse photonic design of functional elements that focus Bloch surface waves
摘要： Bloch surface waves (BSWs) are sustained at the interface of a suitably designed one-dimensional (1D) dielectric photonic crystal and an ambient material. The elements that control the propagation of BSWs are defined by a spatially structured device layer on top of the 1D photonic crystal that locally changes the effective index of the BSW. An example of such an element is a focusing device that squeezes an incident BSW into a tiny space. However, the ability to focus BSWs is limited since the index contrast achievable with the device layer is usually only on the order of Δn≈0.1 for practical reasons. Conventional elements, e.g., discs or triangles, which rely on a photonic nanojet to focus BSWs, operate insufficiently at such a low index contrast. To solve this problem, we utilize an inverse photonic design strategy to attain functional elements that focus BSWs efficiently into spatial domains slightly smaller than half the wavelength. Selected examples of such functional elements are fabricated. Their ability to focus BSWs is experimentally verified by measuring the field distributions with a scanning near-field optical microscope. Our focusing elements are promising ingredients for a future generation of integrated photonic devices that rely on BSWs, e.g., to carry information, or lab-on-chip devices for specific sensing applications.
关键词： focusing elements,scanning near-field optical microscope,integrated photonic devices,Bloch surface waves,photonic design
更新于2025-09-04 15:30:14