Optical Waveguide Sensor Research Articles

Sensitivity of tapered optical fiber surface plasmon resonance sensors

The sensitivity of surface plasmon resonance based tapered optical waveguide sensors having various profile is analyzed and compared. Using ray approach the change of resonance wavelength with taper ratio is obtained and hence the variations of sensitivity with taper ratio for each considered tapered profile are presented. It is observed that as the taper ratio decreases the sensitivity of proposed sensor for each profile increases up to certain taper ratio where the plasmonic condition is satisfied. Also, the effect of profiles on the sensitivity is significant for lower taper ratio. In all considered cases the maximum sensitivity is obtained for sinusoidal tapered profile.

Optimization of transverse electric peak-type metal-clad waveguide sensor using double-negative materials

In a very recent work, a transverse electric peak-type metal-clad waveguide optical sensor was proposed in which a double-negative material (DNM) was used as a guiding layer. The sensor was found to exhibit a considerable angular shift of the reflectance peak for small changes in the refractive index of the analyte, due to the DNM layer. In this work, the optimization of the structure parameters is investigated to find out the most appropriate metal and its optimal thickness. Moreover, the optimal DNM layer parameters corresponding to the highest sensitivity are explored. Our calculations reveal that metals with high absolute value of the real part of the permittivity correspond to sharper peaks. Moreover, as the absolute value of the real part of both e and μ of the DNM increases, the reflectance peak becomes sharper and the dip following the peak becomes deeper.

Flexible multilayer substrate based optical waveguides: Applications to optical sensing

The performance of flexible waveguides based microsystems such as optical waveguide sensors or a lab-on-a-chip platform is closely related to the parameters of the waveguides and substrates. In order to achieve enhanced performance of microsystems, we proposed a concept of flexible multilayer substrate based waveguides. We show that the mechanism properties of the flexible substrates and waveguides including the Young's modulus and the structural thickness can be well engineered and regulated by ranging the configuration of the multilayers with different materials. The multilayer substrate itself can also serve as a thin-film optical waveguide. The experimental results show that this structure is suitable for developing optical sensor chips like double-ring resonator based accelerometers. As an example, the theoretical analysis based on the tunable Young's modulus and thickness of the waveguides also provides an approach to achieve manufacturing error insensitive or accelerometer chips with different sensitivities between 10 per g and 53 per g. The sensitivity will be tenfold if propagation loss of the waveguides is reduced from 1.9dB/cm to 0.3dB/cm. This tunable structure promises to meet the requirements of various sensors and lab-on-a-chip systems for displacement, chemistry or biology measurements.

Determination of trace chromium (VI) using a hollow-core metal-cladding optical waveguide sensor

A biosensor capable of highly sensitive detection of trace chromium (VI) with a simple hollow-core metal-cladding waveguide (HCMW) structure is theoretically modeled and experimentally demonstrated. Owing to the high sensitivity of the excited ultrahigh-order modes in the waveguide, a tiny variation of the extinction coefficients in the waveguide guiding layer where the chromate ions reacts with the diphenylcarbazide (DPC) can lead to a significant change of light intensity in the reflection spectrum. The experimental results indicate that using the proposed method, the chromium (VI) sensitivity detection limit can be as low as 1.2 nM, which represents a 16-fold improvement compared to the surface plasmon field-enhanced resonance light scattering (SP-RLS) method, and a 4-fold improvement compared to the flame atomic absorption spectrometry and fluorimetry spectroscopy, respectively.

Surface plasmon resonance based silicon carbide optical waveguide sensor

In this paper, we investigated a new surface plasmon resonance (SPR) based optical waveguide sensor formed on a wide bandgap semiconductor material – silicon carbide (SiC). The wide bandgap energy of SiC (Eg=2.2eV of 3C-SiC polytype) enables the waveguide to operate in the visible and near-infrared wavelength range. Assessment of the potential sensing properties was performed by investigating the confinement factor in fundamental transverse magnetic mode (TM0) using the effective index method (EIM). The results show that at the incident light of 633nm, a confinement factor of 0.95 can be achieved at the refractive index of n=1.45. Comparing to reported non-SPR structure, the confinement factor of SiC SPR sensor was clearly improved over the refractive index range of n=1.3–1.5, and by more than 3.3 times at n=1.35. The improved sensing property by SPR structure combined with the superior chemical/biological inertness of SiC material and compatibility between SiC and Si device manufacturing makes the proposed SiC SPR sensor very promising for chemical sensing and bio-sensing.

Transverse magnetic peak type metal-clad optical waveguide sensor

Transverse magnetic (TM) waves in a four-layer slab waveguide structure are studied for optical sensing applications. The structure consists of a semi-infinite substrate, a thin metal layer, a medium with negative permittivity and permeability as a guiding layer, and a semi-infinite layer as a cover. The proposed sensor is operated in reflection mode in which the angular position of the reflectance peak is used to detect small changes in the refractive index of the cover medium. The optimal structure parameters that correspond to the sharpest and highest peak are presented. The results reveal that for aluminum metal layer, a thickness of about 9nm represents the optimum metal thickness. Moreover, the thickness, negative permittivity, and negative permeability of the guiding layer are found to have great impacts on the performance of the proposed optical waveguide sensor.

Novel Compact Waveguide Optical Chemical Sensor for Control of Gaseous Ammonia Concentration

The operation principle and construction of the waveguide optical chemical sensor control of absorbing type is considered. Characteristics of a sensor element on the basis of the waveguide structure generated on a Y-cutoff of lithium niobate for control of level of gaseous substances, in particular ammonia are experimentally researched. Potential possibilities of data application of instruments in different industries, ecology and telecommunication technologies are considered.

Transverse magnetic peak type metal-clad optical waveguide sensor

Transverse magnetic (TM) waves in a four-layer slab waveguide structure are studied for optical sensing applications. The structure consists of a semi-infinite substrate, a thin metal layer, a medium with negative permittivity and permeability as a guiding layer, and a semi-infinite layer as a cover. The proposed sensor is operated in reflection mode in which the angular position of the reflectance peak is used to detect small changes in the refractive index of the cover medium. The optimal structure parameters that correspond to the sharpest and highest peak are presented. The results reveal that for aluminum metal layer, a thickness of about 9nm represents the optimum metal thickness. Moreover, the thickness, negative permittivity, and negative permeability of the guiding layer are found to have great impacts on the performance of the proposed optical waveguide sensor.

Integrated Phase-Interrogation LN Optical Waveguide Sensor

We develop a phase interrogation optical waveguide sensor by integrating a phase modulator and a sensing transducer fabricated with the same Zn-indiffused lithium niobate substrate. The proposed sensing chip effectively reduces the footprint of the measurement setup and has the potential to provide a compact module for a portable metrology system. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1821–1823, 2013

Metal-clad optical waveguide sensor with anisotropic metamaterial

We propose a metal-clad optical waveguide (MCOW) sensor based on a four-layered structure with anisotropic metamaterial. The expressions of reflectance of the four-layered system are given and the properties of MCOW sensor are also analyzed by simulation results. The anisotropy of metamaterial brings lots of different properties compared with isotropic one. It can be found that six different parameters of the proposed MCOW sensor have different influence on the reflectance dips which provide more flexibility in designing this kind of sensors.

PCB-Integrated Optical Waveguide Sensors: An Ammonia Gas Sensor

This paper presents a novel platform for the formation of cost-effective PCB-integrated optical waveguide sensors. The sensor design relies on the use of multimode polymer waveguides that can be formed directly on standard PCBs and commercially-available chemical dyes, enabling the integration of all essential sensor components (electronic, photonic, chemical) on low-cost substrates. Moreover, it enables the detection of multiple analytes from a single device by employing waveguide arrays functionalised with different chemical dyes. The devices can be manufactured with conventional methods of the PCB industry, such as solder-reflow processes and pick-and-place assembly techniques. As a proof of principle, a PCB-integrated ammonia gas sensor is fabricated on a FR4 substrate. The sensor operation relies on the change of the optical transmission characteristics of chemically functionalised optical waveguides in the presence of ammonia molecules. The fabrication and assembly of the sensor unit, as well as fundamental simulation and characterisation studies, are presented. The device achieves a sensitivity of approximately 30 ppm and a linear response up to 600 ppm at room temperature. Finally, the potential to detect multiple analytes from a single device is demonstrated using principal-component analysis.

光波导传感器在气体检测中的应用进展

有效检测易燃、易爆、有毒、有害气体及时掌握污染发生和发展实况，并对污染进行有效控制，需要高灵敏度检测方法。气体传感器是气体检测系统的核心，作为传感技术的一个重要分支光波导传感器以独特的优势同样受到了广泛重视。本论文介绍了光波导传感器在检测有毒气体中的原理和制作方法，并且对利用光波导传感器方法来检测有害气体的最新研究成果进行综述。 In order to determine flammable, explosive, toxic and harmful gases, and to grasp the occurrence of pollution and its development and control effectively, there is a need for highly sensitive detecting method. The gas sensor is a core of the gas detecting system. The optical waveguide (OWG) sensor is an important branch of the sensor technology, and attracts considerable attention with its unique qualities. This paper introduces the principle and making method of optical waveguide sensor in the detection of toxic gases, and latest research results of the optical waveguide sensor that detecting harmful gases are reviewed.

Design and Fabrication of Silicon Oxynitride Based Evanescent Optical Waveguide Sensor for Rapid Detection of Adulteration in Petrol

In this paper we report on the design and fabrication of an Evanescent Optical Waveguide Sensor (EOWS) using silicon oxynitride (SiON) as the core layer on silica-silicon wafer and its implementation for rapid detection of adulterant traces in pure petrol incorporating composite planar waveguide geometry. The embedded waveguide of length ∼ 10,000μm and core width ∼ 50μm was fabricated using standard Plasma Enhanced Chemical Vapour Deposition (PECVD) technologies and Reactive Ion Etching (RIE) technique. The main aim of this work is to encompass an abrupt choice to the time-consuming existing adulteration detection methods which generally requires some time to give the consequence. Using Simple Effective Index Method (SEIM), the theoretical predictions and experimental results at wavelength 632.8nm are analyzed and presented, which demonstrated that the sensitivity of the proposed EOWS is ∼40 times more than that of the existing planar waveguide sensors and also 20 times more than that of asymmetric waveguide structure thereby allowing rapid detection of adulterant traces in pure petrol without involving the use of chemicals. It is found that the sensor structure is polarization independent and advantages include high sensitivity, easy fabrication and more importantly, requirement of very minimal amount of sample volume for detecting adulteration.

Optical Waveguide BTX Gas Sensor Based on Yttrium-Doped Lithium Iron Phosphate Thin Film

Yttrium-doped LiFePO4 powder was synthesized using the hydrothermal method in one step and was used as a sensing material. An optical waveguide (OWG) sensor based on Yttrium-doped LiFePO4 has been developed by spin coating a thin film of LiFe0.99Y0.01PO4 onto a single-mode Tin-diffused glass optical waveguide. Light was coupled into and out of glass OWG employed by a pair of prisms. The guided wave transmits in waveguide layer and passes through the film as an evanescent wave. The sensing film is stable in air, but when exposed to target gas at room temperature, its optical properties such as transmittance (T) and refractive index (nf) were changed; thus, the transmitted light intensity was changed. The LiFe0.99Y0.01PO4 thin film OWG exhibits reversible response to xylene gas in the range of 0.1–1000 ppm. When the concentration of BTX gases was lower than 1ppm, other substances caused a little interference with the detection of xylene vapor. Compared to pure LiFePO4 thin film OWG, this sensor exhibited higher sensitivity to BTXs.

Formaldehyde gas sensor based on silver-and-yttrium-co doped-lithium iron phosphate thin film optical waveguide

Abstract Several formaldehyde gas sensors were fabricated using silver-and-yttrium-co doped-lithium iron phosphate (LiFe 1−0.01 x Y 0.005 x Ag 0.005 x PO 4 )-thin-film-based optical waveguides (OWGs). LiFe 1−0.01 x Y 0.005 x Ag 0.005 x PO 4 powders with different concentrations of the dopants Ag and Y were prepared in high purity via a one-step hydrothermal method, and characterized using their X-ray diffraction patterns and energy dispersion spectra. The obtained powders were subsequently utilized in a spin-coating procedure for the fabrication of LiFe 1−0.01 x Y 0.005 x Ag 0.005 x PO 4 thin films. The obtained thin films were characterized by refractive index, thickness, attenuation, and sensing properties to formaldehyde at room temperature. The response of LiFe 1−0.01 x Y 0.005 x Ag 0.005 x PO 4 -thin-film/tin-diffused-glass-based optical waveguide sensors to formaldehyde was higher than their responses to other VOCs. For a set of formaldehyde concentrations ranging from 1 ppb to 1000 ppm, the sensitivity of the sensors increased with a decrease in the dopant concentrations. Moreover, the ability to be used repeatability as well as the selectivity of the sensors was tested using lower gas concentrations; at the lower concentrations (below 250 ppm), the sensor only responsive to formaldehyde gas.

PH-indicators doped polysaccharide LbL coatings for hazardous gases optical sensing

Sensitive layer-by-layer (LbL) coatings for optical detection of gaseous NH3 and HCl were prepared by self-assembly of oppositely charged polysaccharides (chitosan and λ-carrageenan) followed by doping LbLs with pH-sensitive dyes – bromothymol blue (BTB) and Congo red (CR). It has been shown that CR, being an amphoteric dye, diffuses into LbL films regardless of the charge of the outermost polyelectrolyte layer, and the dye loading increases linearly with the LbL film thickness, whereas BTB diffuses into LbL films only when the outermost layer is positively charged, and linearity between dye loading and film thickness holds only up to 8–12 double layers (DLs) deposited. Formation of dye-doped LbL coatings at the surface of K+/Na+ ion-exchanged glass has allowed fabrication of composite optical waveguide (OWG) gas sensor for detection of ammonia and hydrochloric acid vapors. The response time of BTB-doped composite OWG for ammonia detection was below 1s, and the detection limit was below 1ppm. CR-doped OWG sensors have shown high sensitivity to HCl vapor but slow relaxation time (up to several hours for 12DL LbL films).

Analysis of Wavelength and Intensity Interrogation Methods in Cascaded Double-Ring Sensors

Optical waveguide sensors based on cascaded double-ring resonators are analyzed theoretically and experimentally, for both wavelength interrogation and intensity interrogation methods. It is shown that for the wavelength interrogation, the sensitivity can be increased by over three orders of magnitude by combining the intensity ratio detection of two central peaks, compared with the simple digital operation mode of the central peak wavelength shift detection of the transmission spectrum. While the detection limit of the wavelength interrogation method is several times smaller than that of intensity interrogation method, the latter has advantages of simplicity and low cost which can outweigh the sensitivity reduction for many practical applications. Experimental results showed good agreements with the theoretical analysis.

Optical properties and sensing applications of lithium iron phosphate thin films

A composite optical waveguide sensor, consisting of lithium iron phosphate (LiFePO4, LFP) as the sensing material, was constructed and utilized for the detection of volatile organic compound gases. Nano-LFP powder was prepared via the hydrothermal method and was subsequently utilized in a dip-coating procedure for the fabrication of LFP thin films. The effect of heat treating temperature on the refractive index of the thin films was studied. A glass optical waveguide gas sensor was fabricated by coating an LFP thin film on the surface of single-mode tin-diffused glass optical waveguide. The sensor was found to exhibit a linear response to xylene in the range of 50–1000ppm, with response times of less than 5s.

Graphene-Based Waveguides: Novel Method for Detecting Biological Activity

We demonstrate the fabrication of a biosensor based on graphene coupled with polydimethylsiloxane (PDMS) waveguide. Biosensors work on the principle of local evanescent graphene-coupled wave sensor. It is observed that the evanescent field shifts in the presence of chemical or biological species as evanescent waves are extremely sensitive to a change in refractive index. This method helps to monitor the target analyte by attaching the selective receptor molecules to the surface of the PDMS optical waveguide resulting in its optical intensity distribution shift. We monitor the electrical properties of graphene in the dark and under illumination of PDMS waveguide. The changes in photocurrent through the graphene film were monitored for blue, green, and red light. We observed that the fabricated graphene-coupled PDMS optical waveguide sensor is sensitive to visible light for the used bioanalytes.

Surface Loading Sensitivity Characterization of a Resonant Planar Optical Waveguide Stack

Detuning of a coupled planar waveguide pair through surface loading of the top waveguide that is in contact with the analyte serves as a transducer for a Stacked Planar Affinity-Regulated Resonant Optical Waveguide (SPARROW) sensor. Here we investigate the surface loading detection sensitivity of a SPARROW transducer composed of a stack of two planar alumina waveguides grown using ion beam assisted e-beam deposition. Using a sucrose analyte solution introduced to the stack surface in a poly-di-methyl-siloxane (PDMS) microfluidic channel, the change in optical output power through the coupled waveguide pair as a function of sucrose analyte solution concentration was experimentally determined. Based on the analyte in the evanescent field penetration depth volume, the effective minimum detectable surface loading of the stack was determined to be 20 with a bulk index sensitivity of 5.6 refractive index units (RIU) for this stack configuration and experimental setup.