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.     

Reverse-symmetry waveguides: theory and fabrication

We present an extensive theoretical analysis of reverse-symmetry waveguides with special focus on their potential application as sensor components in aqueous media and demonstrate a novel method for fabrication of such waveguides. The principle of reverse symmetry is based on making the refractive index of the waveguide substrate less than the refractive index of the medium covering the waveguiding film (n_water=1.33). This is opposed to the conventional waveguide geometry, where the substrate is usually glass or polymers with refractive indices of ≈1.5. The reverse configuration has the advantage of deeper penetration of the evanescent electromagnetic field into the cover medium, theoretically permitting higher sensitivity to analytes compared to traditional waveguide designs. We present calculated sensitivities and probing depths of conventional and reverse-symmetry waveguides and describe schemes for easy implementation of reverse symmetry. Polymer waveguides are demonstrated to be candidates for cheap, mass-producible reverse-symmetry sensor modules. The grating-coupled waveguiding films of controlled thickness are produced by soft lithography. The resulting films are combined with air-grooved polymer supports to form freestanding single-material polymer waveguides of reverse symmetry capable of guiding light. Received: 20 December 2001 / Published online: 14 March 2002     

Vertical input optical ring resonator with differential operation for optical sensor

A novel waveguide ring resonator optical sensor with two resonant wavelength channels is proposed for a refractive index measurement of a test sample placed on the sensor substrate and its performance characteristics are investigated analytically and numerically. The waveguide device consists of a ring resonator, a split-ring-shaped loop waveguide, and a vertical input/output grating coupler, in which the loop waveguide acts as an additional resonator and provides another output wavelength channel of the sensor. The differential detection between the two wavelength channels enables the highly sensitive detection with temperature compensation. A numerical simulation based on a finite difference time domain (FDTD) method shows that a precise index change detection with a resolution of 10⁻⁶ can be achieved using of the proposed device.     

A novel Y-branch waveguide for power dividing and mode splitting

A novel Y-branch waveguide for variable-ratio power dividing and transverse electrical-transverse magnetic (TE-TM) mode splitting depending on the applied voltage is presented. The Y-branch waveguide is formed by two closely coupled waveguides tabricated by nickel indiffusion (NI) and by magnesium-oxide induced lithium outdiffusion (MILO) in a y-cut lithium niobate (LiNbO₃) substrate. The TE component of the randomly polarized light is tuned between these two waveguides, such that the device can be either a power divider or a mode splitter depending on the applied voltage. The measured TE mode extinction ratio is about 20 dB.     

光波导F-P干涉型电场和电压传感器

本文报道了 LiNbO₃质子交换光波导 F-P 干涉型电场和电压传感器的结构、制备、工作原理、实验装置与测量结果.用半导体激光器(780nm)作光源,测量了器件对频率在20Hz～1KHz 电场的响应特性,着重测量并得到工频(50Hz)交流电场(幅值为8.3～75V_zms/cm)和电压(20～180V_rms)与调制光输出电压之间的关系曲线.实验研究表明:该器件的线性度为1.4%,电场灵敏度为61.4mV_rms/V_rms/cm,电压灵敏度为25.6mV_rms/V_rms;且具有结构简单、制作容易、几何尺寸小、光传输插入损耗低等优点;稍加完善,可望制成实用化器件.     

衰减全反射型电压传感器的理论和实验研究

提出了一种新型反射型聚合物波导电压传感器理论,并且进行了实验研究。这种电压传感器采用棱镜波导耦合结构,在棱镜下底面依次镀有金属膜一聚合物一金属膜三层结构。通过两层金属膜对极化聚合物加电压,利用聚合物材料电光效应和导模共振吸收峰对聚合物折射率的敏感特性,通过反射光强的测量来确定作用电压的变化值。实验中的测试电压范围是从-140V至 140V,得到的线性度值为0．991,电压测量的分辨力为0．1V,电压测量灵敏度系数为0．0011V^-1。实验表明这种电压传感器具有良好的线性和较高的灵敏度。     

Synthesis of multi-walled carbon nanotubes for NH3 gas detection

It has been recently demonstrated that carbon nanotubes (CNTs) represent a new type of chemical sensor capable of detecting a small concentration of molecules such as CO, NO₂, NH₃.In this work, CNTs were synthesized by chemical vapor deposition (CVD) on the SiO₂/Si substrate by decomposition of acetylene (C₂H₂) on sputtered Ni catalyst nanoparticles. Their structural properties are studied by atomic force microscopy, high-resolution scanning electron microscopy (HRSEM) and Raman spectroscopy. The CNTs grown at 700 °C exhibit a low dispersion in size, are about 1 μm long and their average diameter varies in the range 25–60 nm as a function of the deposition time. We have shown that their diameter can be reduced either by annealing in oxygen environment or by growing at lower temperature (less than 600 °C).We developed a test device with interdigital Pt electrodes on an Al₂O₃ substrate in order to evaluate the CNTs-based gas sensor capabilities. We performed room temperature current–voltage measurements for various gas concentrations. The CNT films are found to exhibit a fast response and a high sensitivity to NH₃ gas.     

Universal SAW gas sensor

A new principle of designing a SAW gas sensor is described. This sensor, being essentially of sorption type, also offers properties of thermometric SAW sensors. The basic idea here is that heat fluxes propagate between the SAW substrate and the working surface of the temperature-regulating system with some delay. A sensor based on this principle can detect not only the vapors of volatile substances but also gases by their thermal properties, retaining high temperature stability and speed of response unlike conventional SAW thermometric sensors. The design of this sensor built around a LiNbO₃ SAW delay line is described, and experiments on detecting a household propane-butane mixture with this sensor are reported. In particular, the responses of the sensor are measured at different gas-flow rates, two different SAW substrate temperatures, and two propane-butane concentrations. Ways of improving the sensor’s performance are discussed.     

Supersensitive graphene-based gas sensor

Epitaxial graphene layers are produced with the aid of thermal destruction of the surface of a semi-insulating SiC substrate. Raman spectroscopy and atomic-force microscopy are employed in the study of the film homogeneity. A prototype of the gas sensor based on the films is fabricated. The device is sensitive to the NO₂ molecules at a level of 5 ppb (five particles per billion). A possibility of the industrial application of the sensor is discussed.     

Integrated optical proximity microsensor

This paper presents the design, simulation and experimental results of an integrated proximity sensor manufactured on silicon substrate. The sensor was designed for microrobotic applications like integration into a microgripper arm or detection of the position of gripper arms relative to an object. The structure is based on an SU8 polymeric optical waveguide splitted into three arms, integrated with a multielement photodetector on silicon substrate. Each element of the photodetector is a metal-semiconductor-metal (MSM) photodiode with Ti/Al Schottky interdigitated electrodes.The operation principle of this sensor consists in the light coupling in the central arm of the optical waveguide, interaction with the object (reflection) of the radiation which exits from this principal arm, the coupling of the “affected” radiation which comes back through the end of the waveguide and its splitting into three arms of the optical waveguide. From the optical waveguide, the light is coupled in photodiode and the photogenerated carriers are collected to the electrodes giving the electrical signal which is read and processed in real time.The optimal parameters of the waveguide (width, thicknesses of the core and the claddings) of the photodetector and the coupling between them were defined by simulation, using FDTD and BeamProp method (Opti FDTD software). Our microsensor can detect the position of an object in the range of 0-300 μm, as position sensor and with high precision in the range of zero to twice the wavelength, as proximity sensor.     

A Semiconductor Waveguide-Type Optical Frequency Shifter

A waveguide-type optical frequency shifter based on a rotating half-wave plate is proposed. The underlying principle can be used to realize a bit-rate-free and modulation-code-free optical frequency shifter. The waveguide was formed along the ≪1 1 1> direction on a GaAs (1 1 0) substrate by molecular beam epitaxy (MBE) and reactive ion beam etching (RIBE). A 10-MHz optical frequency shift with 16 V_p-p applied voltage and 22.5% shift efficiency is demonstrated.     

Design of a compact photonic crystal sensor

The development of technology in photonic crystal (PC) structures has seen rapid progress. Using PCs in biosensing area may open new venues to achieve single molecule detection, and high resolution scanning. A novel PC sensor with improved performances, in terms of size, compactness and sensitivity is presented in this paper. The sensing element consists of dielectric cylinders with varying radius introduced along <01> and <10> directions of the crystal. The results show that the peak wavelength shifts to the high frequency region when only six cylinders are filled with analytes. Also, the peaks show a larger shift compared to the structure obtained using the entire PC waveguide as sensing region. The proposed sensor shows a better sensitivity to water than other analytes, where the peak wavelength tends to shift towards the low frequency region.     

The fabrication of polymer-based evanescent optical waveguide for biosensing

A polymer waveguide was fabricated to amplify the evanescent optical field for biosensing. The structure of waveguide was designed to propagate a normal single mode at the input and output regions for low loss beam coupling and propagation. A sensing region was formed in the middle of the waveguide to activate the evanescent mode and to induce high birefringence by depositing a thin dielectric film with a high refractive index on a single mode waveguide. A polymer waveguide with the dimensions of 7 μm-width and 2.5 μm-thickness was fabricated by photolithography and dry-etching. The active region of the TiO₂ thin film was fabricated with the dimensions of 20 mm-length, 20 nm-thickness and 2 mm-tapered tail. A polarimetric interference technique was used to evaluate the evanescent waveguide biosensor, and biomaterial such as glycerol was tested. The sensitivity of the sensor increased with increasing TiO₂ film thickness. For the fabricated waveguide with a 20 nm-thick TiO₂ film, the measured index change to the lead phase variation of 2π was 1.8 × 10⁻⁴.     

The light-enhanced NO2 sensing properties of porous silicon gas sensors at room temperature

The NO2 gas sensing behavior of porous silicon（PS） is studied at room temperature with and without ultraviolet（UV） light radiation.The PS layer is fabricated by electrochemical etching in an HF-based solution on a p ＋-type silicon substrate.Then,Pt electrodes are deposited on the surface of the PS to obtain the PS gas sensor.The NO2 sensing properties of the PS with different porosities are investigated under UV light radiation at room temperature.The measurement results show that the PS gas sensor has a much higher response sensitivity and faster response-recovery characteristics than NO2 under the illumination.The sensitivity of the PS sample with the largest porosity to 1 ppm NO2 is 9.9 with UV light radiation,while it is 2.4 without UV light radiation.We find that the ability to absorb UV light is enhanced with the increase in porosity.The PS sample with the highest porosity has a larger change than the other samples.Therefore,the effect of UV radiation on the NO2 sensing properties of PS is closely related to the porosity.     

Highly integrated plasmonic sensor design for the simultaneous detection of multiple analytes

Herein, a highly integrated plasmonic sensor based on a multichannel metal-insulator-metal waveguide scheme for the simultaneous detection of multiple analytes is proposed. The numerical study is conducted via the finite element method based on commercially available software COMSOL. The sensor design is highly sensitive which can detect a minute change in the refractive index of the analyte. In this study, we have used the refractive index values of three different concentrations of ethanol and d-glucose solution to determine the sensor performance. It is observed that the device is highly sensitive as the operational wavelength lies in the deep shortwave infrared region. The numerically calculated sensitivity as high as 1948.67 nm/RIU is obtained for the cavity length of 325 nm which can be further improved by designing the device with large cavities. We believe that the proposed study is beneficial for the realization of the highly integrated plasmonic sensors for the lab-on-chip operations.     

Pulsed-laser deposition of a Nd:KGd(WO4)2 waveguide in Ar and O2 environments

Thin-film Nd-doped potassium gadolinium tungstate (Nd:KGW or KGd(WO₄)₂) waveguides are deposited on (1102)sapphire or (100)YAG substrates by KrF laser ablation of potassium-rich ceramic targets in Ar and O₂. The dependence of the stoichiometry, crystallinity and waveguide properties of the films on the environmental gas pressure and substrate temperature is studied. Highly textured crystalline (110) KGW films are grown. An optical waveguide loss as low as 3 dB/cm is obtained for the films grown in Ar. The as-grown films are optically active. Upon annealing at 900 °C in air, the crystallinity and the properties of the emission spectra are dramatically improved. PACS 81.15.Fg; 42.70.Hj; 78.20.Ek     

Integrated SU-8 photonic gas sensors based on PANI polymer devices: Comparison between metrological parameters

In this work, we have designed and developed three families of integrated photonic sensors for ammonia detection. These photonic sensors are integrated onto single-mode TE₀–TM₀ SU-8 polymer planar waveguides and based on a polyaniline (PANI) sensitive polymer material. The first family relies on the deposit of a PANI–polymethyl methacrylate (PMMA) composite sensitive layer on a given SU-8 waveguide. The second family relies on a PMMA passive layer deposited on the SU-8 waveguide before applying the PANI sensitive layer on the PMMA passive layer. The third family takes advantage of a PANI layer deposited by plasma technique directly onto the SU-8 waveguide. The working principle of such sensors is based on the optical intensity modulation induced within the single-mode waveguide owing to the interaction between the evanescent field and the sensitive layer. The sensing proprieties of these integrated photonic sensors to ammonia gas at room temperature were characterized and the comparison between these different families of photonic sensors is presented. Experimental results show that the sensor based on new plasma–PANI as sensitive layer has the better metrological parameters.     

声表面波生物传感器质量灵敏度的理论与实验验证

针对声表面波传感器在生物检测中的性能评价与优化,提出一种快捷验证适用于生物传感器的声表面波器件质量负载灵敏度的实时检测方法.首先基于二维近似假设和周期性边界条件,建立了以石英为压电基底材料、SiO2为波导层的Love波传感器的三维有限元分析模型,从理论上验证了波导层对Love波传感器灵敏度的影响.在实验上,通过MEMS...     

Design of an optical sensor array for hydrocarbon monitoring

Evanescent field optical sensors are accurately designed for hydrocarbon monitoring in water. Various kinds of waveguide sensors are optimized by considering a polydimethylsiloxane polymeric overlay as sensor region. The simulation results suggest that the selection of a suitable waveguide cross section can enhance the sensor performance. In particular, the hollow waveguide sensor exhibits very intriguing performance, the absorbance being quite linear with respect to the contaminant concentration. For the toluene pollution the absorbance exhibits a slope S_TE^A = 2.52 ×10^-2 ppm^-1{S_{\rm TE}^{A} =2.52 \times 10^{-2}\,{\rm ppm}^{-1}} for a waveguide reference length L = 1.18 mm. In order to simultaneously detect different pollutants in water such as toluene, benzene, chlorobenzene and ethilbenzene, an array of four miniaturized hollow waveguide sensors is designed.     

Intelligent sensor system for CO2 partial pressure measurements

Solid state electrochemical gas sensors allow the measurement of partial gas pressures with high accuracy. However, there are problems related to the response time, drift and cross sensitivity which should be solved to improve the performance of these sensors. An intelligent sensor system is presented which improves the sensor response time, compensates the drift and allows to calculate functional relationships between the electrical and the chemical energy of galvanic cell reactions. An electronic circuit for evaluating the measured cell voltage of a type III potentiometric CO₂ sensor is also presented.