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In this paper, the performances of a wavelength interrogation-based optical fiber surface plasmon resonance sensor for hemoglobin (Hb) concentration is investigated by theoretical simulation. The proposed configuration incorporates optical fiber, 70 nm silver, 18 nm barium titanate (BaTiO3), and 2 nm zinc oxide. Simulation results show the sensor exhibits refractive index sensitivity of 4023 nm/RIU and concentration sensitivity of 10.0873 nm/(gꞏdL), along with Hb concentration varying from 0 to 14 g/dL. This paper especially focuses on the influence of BaTiO3 on the performances of the proposed sensor with light wavelength ranging from 350 to 1000 nm. Comparison analysis indicates sandwiching 18 nm BaTiO3 between sensing layers not only enhances the concentration sensitivity by 30.14% but also decreases the nonlinear error of the sensor from 0.68% to 0.63%. For a wavelength accuracy of 0.1 nm, the proposed sensor can provide a resolution of 0.0099 g/dL for Hb concentration detection. [ABSTRACT FROM AUTHOR]

[Display omitted] • Early detection of melamine using an SPR-based optical fiber sensor. • Ag and MoTe 2 layers optimized for maximum sensitivity and FoM. • Analyzed sensor performance for various milk fat concentrations. • Achieved maximum sensitivity of 11532.6 nm/RIU for 40 % milk fat. • Detailed fabrication procedure and experimental feasibility. • Significant advancement over existing sensor technologies. Melamine is a type of plastic, which is harmful to humans due to its potential to cause severe kidney damage and other urinary system issues. Acute and chronic exposure can lead to significant health problems, necessitating stringent regulatory oversight and preventive measures to protect public health. Therefore, this paper explores the early detection of the melamine with help of optical fiber-based surface plasmon resonance (SPR) sensor by employing the silver (Ag) and molybdenum ditelluride (MoTe 2). Ag is employed to excite the surface plasmons, whereas MoTe 2 is used for the protection of Ag and for enhancing the sensing capacity. For this study, sensor's performances are analyzed by employing the wavelength and angular interrogation methods simultaneously. The angular and wavelength interrogation methods include monitoring the changes in the angle and wavelength of incidence or reflection of light within an optical sensor. Four different concentrations of milk's fat, such as 0, 20, 30, and 40 % are considered for the detection process. Firstly, the optimization of Ag and MoTe 2 is shown by measuring the performance of sensitivity and figure of merit (FoM). Secondly, performance analysis for the detection of melamine is shown, resulting in the maximum achieved sensitivity and FoM are 11532.6 nm. RIU - 1 and 80.647 RIU - 1 for fat concentration of 40 %, respectively. Thirdly, the fabrication procedure and experimental feasibility of the proposed sensor are well discussed. Finally, the comparative study between the proposed work and existing work is discussed. Overall, the proposed optical fiber-based SPR sensor has a high potential for early detection of melamine residue in food products. [ABSTRACT FROM AUTHOR]

The Bloch surface wave (BSW) is excited in a 1-D photonic crystal and supports a rather steep resonance dip, much sharper than that of traditional surface plasmon resonance (SPR). A highly sensitive sensor based on BSW was fabricated by electron beam evaporation, the structure was characterized by scanning electron microscopy (SEM) and ellipsometry spectrometer, and the sensitivity in wavelength and phase interrogation was achieved experimentally by an optical system based on a Mach–Zehnder interferometer. The wavelength sensitivity and the phase sensitivity can reach 219 nm/RIU and $1.16\times10$ 4 deg/RIU, respectively. After comparison, we demonstrate that the phase interrogation has a higher sensitivity than the wavelength interrogation and is more suitable for BSW sensors. Experimental results show that the detection limit of the sensor is $8.62\times10$ −7 RIU in phase interrogation, which proves that the sensor could become a valuable and promising tool to replace traditional SPR sensors for the application of ultralow concentration detection. This sensor, only composed of TiO2 and SiO2 materials, has the advantages of mechanical and chemical stability, easy fabrication, and low cost, which can be used as an alternative to traditional SPR sensors in the fields of biomedicine, chemical analysis, and environmental monitoring. [ABSTRACT FROM AUTHOR]

Surface plasmons (SP) can be effectively tuned in the entire UV–visible–near-infrared (NIR) spectrum, bringing together a variety of optical sensors to monitor the surrounding conditions at the metal–analyte interface. To initiate such a plasmonic phenomenon, aluminum (Al) as a plasmonic metal has gained much industry-related relevance, being relatively low-cost and widely available, and furthermore is compatible with CMOS technology. In the present work, we have employed Al-based 2D plasmonic nanostructures with different periodicity in the x and y directions, placed over a thin Al film, to observe transmission peaks at SP resonances. Modulating different geometric parameters including the height, width, and thickness of the Al film deposited below the nanostructures yielded an optimized design. As a result, when light is incident normally, the 2D periodic nanostructures produce a transmission peak corresponding to SP resonance for a period (PX) = 1000 nm (along the x-direction) in the NIR region, while for PY = 500 nm (along the y-direction), a transmission peak is produced in the visible region. Structures with different periods in different directions, exhibiting multiple SP resonances, could find potential applications in optical sensors, wherein characteristics of analytes coated on the nanostructures at different wavelengths could be extracted in a single experiment. In short, the proposed engineered plasmonic nanostructures open a new door for biosensing applications in both the visible and NIR regions with the same plasmonic substrate. [ABSTRACT FROM AUTHOR]

In an optical fiber based SPR sensor, a segment of metal clad silica fiber is used as the sensing element and resonant coupling occurs to the surface plasmon mode excited at the interface of the metal and ambient which surrounds the sensing element. When polychromatic light is transmitted through the sensing element, the spectrum of light detected at the other end shows minima at a resonance wavelength. In wavelength interrogation, the shift in the resonance wavelength is a measure of change in the refractive index of the ambient. Alternatively, intensity interrogation can be used in which the change in transmitted power at a given wavelength is a measure of change in refractive index of the ambient. The sensitivity and detection accuracy of the sensor depend on the numerical aperture (NA) of the multimode optical fiber used to fabricate the sensor. In the present work, we have carried out a study of the dependence of the sensitivity and detection accuracy on numerical aperture to obtain the optimal value for a multimode optical fiber which is used to fabricate the sensing element under both wavelength and intensity interrogation. For a gold clad sensing element with l/a = 33.33 for the refractive index of the ambient in the range 1.33 to 1.38, the optimized numerical aperture is obtained as NA = 0.2 for spectral interrogation mode. At this optimal value, the sensitivity is estimated to be 4040 nm/RIU and detection accuracy lies between 20 and 48 μm−1. In single wavelength intensity interrogation, at the He–Ne laser wavelength (633 nm), the optimized numerical aperture is obtained as NA = 0.42. Experimental results on a sensing element fabricated with gold coating on the core of a plastic clad silica fiber are also reported. [ABSTRACT FROM AUTHOR]

Silicon-based optical biosensors have garnered significant interest since their inception. They are, however, susceptible to temperature fluctuations in a controlled environment. In order to address this issue, we provide a solution including the utilization of a silicon-on-insulator (SOI) cascaded micro-ring resonators (CMRR) biosensor that is designed to be insensitive to temperature changes. It consists of two ring resonators exposed to the reference solution and analyte, respectively, their radius and waveguide width are designed to meet the temperature - insensitivity criterion of the CMRR sensor. The results of experiments indicate that by real-time monitoring of the envelope peak drift in the transmission spectrum of the sensor, the bulk refractive index (RI) sensitivity is 2940.71 nm/RIU, the limit of detection (LOD) is 3.1×10−5 RIU, and the temperature sensitivity is less than 40 pm/℃. Furthermore, the sensor was applied for HSA detection, with a calculated LOD of 18.09 ng/mL. The effect of temperature on HSA detection is much smaller than that of a CMRR sensor without athermal design. The sensor demonstrates high sensitivity and temperature insensitivity, and the absence of negative thermo-optic coefficient materials or supplementary temperature control mechanisms simplifies its practical applications. It can be made by a large array to detect different type protein molecules for high throughput multiparameter analysis. ● The proposed biosensor is temperature-insensitive in wavelength interrogation. ● The vernier effect increases detection sensitivity but not temperature sensitivity. ● The cascaded micro-ring resonators biosensor shows high sensitivity for HSA detection.. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance (SPR) sensors have been applied in a wide range of applications for real-time and label-free detection. In this article, by covering the topological insulators nanosheets on the surface of the noble metal (Au), the sensitivity of the SPR sensor is greatly enhanced because of the strong interaction of light with Au–bismuth selenide (Bi2Se3) heterostructure. It is shown that the sensitivity of proposed SPR sensors depends on the concentration of Bi2Se3 solution or the thickness of the coated Bi2Se3 film. The optimised sensitivity (2929.1 nm/RIU) and figure of merit (33.45 RIU−1) have been obtained after three times drop-casting, and the enhancement sensitivity of proposed sensors is up to 51.97% compared to the traditional Au–SPR sensors. Meanwhile, the reflection spectrum is simulated by using the method of effective refractive index, and the reason for the increase of sensitivity is analysed theoretically. For researching the application of modified SPR sensor, heavy metal detection is employed to detect in the last part. Our proposed SPR sensors have potential applications in heavy metal detections and biosensing.

A highly sensitive dual-polarized 'X' oriented quadruple D-shaped open channel photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor for various analyte detection is proposed in this paper. Gold is taken as a plasmonic material for its stability and compatibility. Silicon nitride (Si3N4) and titanium oxide (TiO2) has been used separately as an adhesive layer of gold to elevate the sustainability of the evanescent field. This paper shows a comparative study and inspects the effect of sensing performance between Si3N4 and TiO2 as an adhesive layer of gold. Numerical investigations have been followed up using the finite element method (FEM). For practical feasibility, analyte and plasmonic materials have been placed at the outer surface of the sensor. After watchful investigation, the maximum wavelength sensitivities of 21,000 nm/RIU (Refractive Index Unit) and 18,000 nm/RIU have been found for the y-polarization when using TiO2 and Si3N4, respectively. The highest amplitude sensitivities are of 914RIU−1 and 625RIU−1 for TiO2 and Si3N4, respectively. Furthermore, minimum wavelength resolutions of 4.76 × 10−6 RIU and 5.55 × 10−6 RIU have been observed in y-polarization for TiO2 and Si3N4, respectively. The sensor evinces a maximum figure of merit (FOM) of 236RIU−1 for TiO2. This sensor has the analyte sensing range of 1.31–1.38RI (Refractive Index) for TiO2 and 1.32–1.39RI for Si3N4. The sensor also delivers low confinement loss for Si3N4 and TiO2, which certifies viability in fabricating the design. Recognizing this sensor’s wavelength sensitivity, amplitude sensitivity, and sensing RI range, it could be a promising candidate for detecting different liquid analytes with excellent accuracy.

Surface plasmon resonance (SPR) sensors have been applied in a wide range of applications for real-time and label-free detection. In this article, by covering the topological insulators nanosheets on the surface of the noble metal (Au), the sensitivity of the SPR sensor is greatly enhanced because of the strong interaction of light with Au–bismuth selenide (Bi2Se3) heterostructure. It is shown that the sensitivity of proposed SPR sensors depends on the concentration of Bi2Se3 solution or the thickness of the coated Bi2Se3 film. The optimised sensitivity (2929.1 nm/RIU) and figure of merit (33.45 RIU−1) have been obtained after three times drop-casting, and the enhancement sensitivity of proposed sensors is up to 51.97% compared to the traditional Au–SPR sensors. Meanwhile, the reflection spectrum is simulated by using the method of effective refractive index, and the reason for the increase of sensitivity is analysed theoretically. For researching the application of modified SPR sensor, heavy metal detection is employed to detect in the last part. Our proposed SPR sensors have potential applications in heavy metal detections and biosensing. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance (SPR) sensors have become an essential tool for the label-free and immediate detection of biomolecular interactions. This paper presents a unique method for increasing the sensitivity of an SPR sensor designed for cancer detection. We offer a sensor design that promises improved detection capabilities using the unique characteristics of silicon (Si) and gallium-doped zinc oxide (GZO). The method uses a wavelength interrogation technique to precisely monitor biomolecular interactions by taking advantage of the spectrum changes SPR brings. The sensor's potential for detecting early-stage cancer is shown by numerical findings that support a considerable improvement in sensitivity to 1711.7 nm/RIU for Basal cancer cells. A promising route for developing biological sensing technologies is the combination of GZO and Si in the SPR sensor, wavelength interrogation, transfer matrix method (TMM)-based reflectance computation, and the attenuated total reflection principle. • The proposed methodology employs a wavelength interrogation technique to accurately track biomolecular interactions by leveraging the spectral modifications induced by surface plasmon resonance (SPR). • The integration of GZO and Si in the SPR sensor, along with wavelength interrogation, reflectance computation using the transfer matrix method (TMM), and the application of the attenuated total reflection principle, presents a highly promising approach for the advancement of biological sensing technologies. • We have successfully detected six different cell types, including Basal, Jurcat, HeLa, PCI-2, MDA-MB-231, and MCF-7, using a wavelength interrogation-based SPR biosensor. • Notably, with a value of 1711.7 (nm/RIU), the sensitivity for identifying basal cancer cells outperforms that of other cancer cell types. [ABSTRACT FROM AUTHOR]

In this manuscript, an optically passive fiber Bragg grating (FBG) interrogation system able to perform high-frequency measurement is proposed. The idea is mainly based on the use of an arrayed waveguide grating (AWG) device which is used to discriminate the fiber optic sensor (FOS) wavelength encoded response under test in function of its output channels. As made clear by the theoretical model studied in the proposed manuscript, the Bragg wavelength shift can be detected as in linear dependence with the proposed interrogation function which changes with the voltage produced by two (or more) adjacent AWG output channels. To prove the feasibility of the system, some experimental analyses are conducted with a custom electrical module characterized by high-speed and low-noise operational amplifiers. As static measurements, three FBGs with different full width at half maximum (FWHM) have been monitored under wide-range wavelength variation; while, as dynamic measurement, one FBG, glued onto a metal plate, in order to sense the vibration at low and high frequency, was detected. The output signals have been processed by a digital acquisition (DAQ) board and a graphical user interface (GUI). The presented work highlights the characteristics of the proposed idea as competitor among the entire class of interrogation systems currently used. This is because here, the main device, that is the AWG, is passive and reliable, without the need to use modulation signals, or moving parts, that affect the speed of the system. In addition, the innovative multi-channel detection algorithm allows the use of any type of FOS without the need to have a perfectly match of spectra. Moreover, it is also characterized by a high dynamic range without loss of sensitivity.

Temperature sensing with enhanced sensitivity based on the spectral interference of polarization modes in a highly birefringent (HB) fiber is proposed and demonstrated. A temperature sensor employs a tandem configuration of a birefringent quartz crystal and HB fiber placed between an analyzer and a polarizer. In the setup a modified channeled spectrum is generated, which shifts with the temperature change of the sensing part of the HB fiber. We analyze the measurement method theoretically and show that the sensitivity of the temperature sensing based on the wavelength interrogation is enhanced in comparison to a standard method with a fiber interferometer. We also demonstrate the enhancement of the temperature sensitivity for three HB fibers under test. Experimental results show that the temperature sensing can reach a sensitivity of −0.30 nm/K, which is enhanced in comparison to −0.10 nm/K reached for a standard measurement. [ABSTRACT FROM AUTHOR]

This paper presents the development of a cost-effective precision fiber Bragg grating (FBG) interrogation system using long-wavelength vertical-cavity surface-emitting laser (VCSEL). Tuning properties of a long-wavelength VCSEL have been studied experimentally. An approximately quadratic dependence of its wavelength on the injection current has been observed. The overall design and key operations of this system including intensity normalization, peak detection, and quadratic curve fitting are introduced in detail. The results show that the system achieves an accuracy of 1.2 pm with a tuning range of 3 nm and a tuning rate of 1 kHz. It is demonstrated that this system is practical and effective by applied in the FBG transformer temperature monitoring. [ABSTRACT FROM AUTHOR]

A highly sensitive measurement of the displacement of an interferometer mirror based on spectral interferometry and Vernier effect is proposed and demonstrated. The displacement measurement employs two interferometers in tandem, an interferometer represented by a combination of a polarizer, a birefrigent quartz crystal and an analyzer, and a Michelson interferometer. In the setup the Vernier effect is generated and the resultant channeled spectrum is with the envelope which shifts with the displacement of the interferometer mirror. We analyze the new measurement method theoretically and show that the sensitivity of the displacement measurement based on the wavelength interrogation is substantially increased in comparison to a standard method with a Michelson interferometer. We also demonstrate the realization of the measurement setup in which the position of the interferometer mirror is controlled via a closed-loop piezo positioning system. Experimental results show that the displacement measurement can reach a sensitivity of 264 nm/μm, which is substantially increased in comparison to −34 nm/μm reached for a standard measurement. [ABSTRACT FROM AUTHOR]

A wavelength-interrogation fiber Fabry–Perot refractive index (RI) sensor based on a sealed in-fiber ellipsoidal cavity is presented. There are two physical cavities in the sensor head: 1) the air cavity and 2) the silica cavity. The result of simulation shows there is only one trough in 1510–1590 nm, the RI can be measured by tracking the trough wavelength shift, and there is no turning point in RI response characteristic between 1 and 2 RIU. The sensitivity and linear range of the RI measurement can be controlled by changing the silica cavity’s length and the sensor end’s roughness. Experiment results match well with the theoretical analysis within the measurement range. High reliability, without turning point and real-time demodulation make it appropriate for practical application. [ABSTRACT FROM PUBLISHER]

• Different kind of FBG wavelength interrogators are compared. • Working mechanism and advantages for periodic edge filter are discussed. • Mathematical principle for FBG wavelength interrogation of crossed HiBi-FLM based periodic edge filter is discussed. • Fast array FBG wavelength interrogation system is proposed to monitor dynamic strain waves. • High resolution interrogation result for the vibration amplitude spectrum of iron pipe is presented. A novel ultrafast wavelength interrogation system for array fiber Bragg gratings (FBGs) has been proposed and experimentally demonstrated, the operation principle is based on pulsed optical source (POS) combined with edge-filtering method and time-division multiplexing (TDM) technique. Thanks to the Gaussian-shape nature and numerous passband channels of the HiBi-FLM transmission, the simultaneous interrogation of array wavelength-division multiplexing (WDM) FBGs can be realized by employing crossed HiBi-FLMs scheme. The HiBi-FLM can provide an individual edge filter for each WDM-FBG and map the FBG reflection spectra into corresponding optical intensity, thus realizing the simultaneous interrogation of multiple WDM-FBGs. The interrogation speed of the proposed system is as high as 200 kHz, which can be further improved to hundreds of megahertz (MHz) by increasing the repetition rate of the POS, the response speed of the photodetector (PD), and the sampling rate of field programmable gate array (FPGA), as well as reducing the pulse width and the lengths of the delay lines. The proposed wavelength interrogation system features high speed, outstanding multiplexing capability, large dynamic range and simple configuration, thus providing a promising solution for various applications, such as quasi-distributed sensing, high-speed communication, medical treatment and the monitoring of ultrafast dynamic phenomena (e.g., molecular dynamics sensing and aircraft engine diagnostics). [ABSTRACT FROM AUTHOR]

A two-step spectral interferometric technique is used to measure a surface plasmon resonance (SPR) phase difference from the spectral interferograms recorded in the Kretschmann configuration. The technique employs a polarimetry setup with a white-light source and birefringent crystal and allows one to obtain a channeled spectrum. Two such spectra, one including reflection of p - and s -polarized waves from the SPR structure for air when the SPR phenomenon does not occur in the source spectral range, and the other one for an analyte when the SPR phenomenon occurs, are used to retrieve the wavelength-dependent SPR phase difference. The new method is applied for aqueous solutions of ethanol with different parameters, the concentration of ethanol in water in a range from 0 to 60 weight percent and the refractive index in a range from 1.333 to 1.362. The sensing scheme uses a wavelength interrogation method and the position of a sharp maximum in the spectral derivative of the SPR phase change is measured as a function of the analyte parameter in a range from 644 to 690 nm. In the same setup, the spectral dependence of the ratio between the reflectances of both polarization states is measured as a function of the analyte parameter. It is revealed that the detection accuracy of the interferometric measurements is more than three times higher than that of the polarimetric measurements. [ABSTRACT FROM AUTHOR]

The spectral interference of polarization modes in a highly birefringent (HB) fiber to measure temperature is analyzed theoretically and experimentally. A tandem configuration of a birefringent delay line and a sensing HB fiber is considered and the spectral interferograms are modelled for the known birefringence dispersion of the HB fiber under test. As the delay line, a birefringent quartz crystal of a suitable thickness is employed to resolve a channeled spectrum. The channeled spectra are recorded for different temperatures and the polarimetric sensitivity to temperature, determined in the spectral range from 500 to 850 nm, is decreasing with wavelength. It is demonstrated that the temperature sensing is possible using the wavelength interrogation, i.e., the position of a given interference maximum is temperature dependent. The temperature sensitivity of the HB fiber under test is −0.25 nm/K and the resolution is better than 0.5 K. [ABSTRACT FROM AUTHOR]

In long period fiber gratings (LPFGs), the fiber modes guided by the core layer can excite surface plasmon resonance (SPR) in the metallic thin-film coated on the cylindrical surface of fibers. In this letter, the LPFG-based fiber optic SPR sensor is analyzed numerically by unconjugated form of coupled mode method. According to the mode analysis, the EH modes can couple with surface plasmon mode and are suitable for refractive index sensing application. In wavelength interrogation, the transmission dip caused by SPR is sensitive to the environmental refractive index. The sensitivity of the sensor achieves 1660 nm/RIU in the aqueous solution. [ABSTRACT FROM PUBLISHER]

This work considered a two-dimensional hybrid organic–inorganic perovskite thin film with various thicknesses within a sandwiched structure of P3HT: PC61BM and PEDOT: PSS (the top and bottom sides). The optical absorption based on the method of attenuated total reflection was calculated. Then, a detailed primeval study on the lossy mode resonance (LMR) behavior of perovskite thin film as a refractive index sensor was theoretically investigated by defining surrounding media with various refractive indices ranging from 1.33 to 1.44. Since one of the efficient ways to improve the performance of the LMR sensor is optimizing the thickness of the lossy layer, herein, both polarization absorption spectra were studied. The results revealed that the transverse magnetic (TM) mode experienced more loss variation with exhibiting higher red-shift versus rather than transverse electric (TE) mode. The highest sensitivity of 3400 refractive index unit (R I U − 1) was achieved; with such high sensitivity to the surrounding environment variations, the proposed structure indicates a versatile prospect. We believe that the perovskite-based LMR sensor can play an influential role in signal detection in biochemical sensors. • A 2D perovskite thin film within a sandwiched structure was studied. • The LMR wavelength interrogation method was explored using ATR was calculated. • The LMR as a function of perovskite thickness exhibited high sensitivity. • This structure revealed that is able to generate multiple LMRs. [ABSTRACT FROM AUTHOR]

In this work, we have proposed graphene decorated Aluminum (Al) nanostructure-based plasmonic device for sensing in the near-infrared region where the same engineered plasmonic device can be used under both angle as well as wavelength interrogation with high sensitivity and Figure of Merit (FOM) simultaneously. A detailed analysis using rigorous coupled-wave analysis is carried out to prove the feasibility of the proposed plasmonic device with the same designed parameters to operate in two interrogation modes, which is impossible in conventional prism configuration. The performance parameters, sensitivity, and FOM are found to be 1000 nm/RIU and 333.33RIU−1 during wavelength interrogation and 119º/RIU and 318.91RIU−1 for the angle interrogation respectively. Finally, the biosensing application is carried out by demonstrating the glucose concentration detection in the urine samples. The proposed Al-based plasmonic device decorated with graphene layer has the advantages of being cost-effective and possessing real-time sensing capability, paving the way for biomedical applications in the near-infrared region. [ABSTRACT FROM AUTHOR]

Abstract: Two types of localized surface plasmon resonance (LSPR)-based optical fiber biosensors using gold nanospheres (GNSs) and gold nanorods (GNRs) have been developed and their performance characteristics evaluated and cross-compared successfully in this work. Based on the results obtained from the optimization of each of these types of biosensor and reported by the authors elsewhere, GNSs with a diameter of 60nm and GNRs with an aspect ratio of 4.1 were specifically chosen in this work for the fabrication of two representative sensor probes, with an aim to create a highly sensitive and wavelength-based LSPR sensor to overcome the limitations arising from other intensity-based sensors. In order to develop effective LSPR biosensors, both GNSs and GRNs respectively were immobilized on an unclad surface of an optical fiber, prior to the functionalization with human IgG in order to create a device for the detection of anti-human IgG, at different concentrations. The experimental results obtained from tests carried out show that the sensitivities of GNSs and GNRs-based LSPR sensors to refractive index variation are 914 and 601nm/RIU respectively; however as biosensors they have demonstrated the same detection limit of 1.6nM for the detection of anti-human IgG. [Copyright &y& Elsevier]

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. [ABSTRACT FROM PUBLISHER]

A differential measurement design employing two nearly collinear optical beams can lead to surface plasmon polariton (SPP) sensors of increased dynamic range and signal-to-noise ratio. We demonstrate a differential measurement device that is based on wavelength interrogation, employs a single incident polarization state, and is combined with a 2-D nanohole array for operation at near-normal incidence, where this approach offers a decrease in the measurement time. [ABSTRACT FROM PUBLISHER]

Abstract: We have proposed and discussed a design of arrayed waveguide grating (AWG) for the application of wavelength interrogation. The spectral responses of a silica-based 16 channel AWG with channel spacing 1.6nm have been simulated when different receiver waveguide spacing are used. It was found that the 3-dB bandwidth is reduced about 50% as the receiver waveguide spacing increasing from 20μm to 30μm. The effect of bandwidth of the spectral response on wavelength resolution of AWG based interrogator has been estimated and discussed. [Copyright &y& Elsevier]

In the fiber Bragg grating sensing using a superluminescent diode as the light source and an arrayed waveguide grating as the wavelength interrogator, the wavelength measurement error due to the spectral modulation of the superluminescent diode is theoretically formulated and quantitatively analyzed by computer simulation. It is shown that the wavelength measurement errors produced with the use of real superluminescent diodes are in very good agreement with the theoretical results. In order to reduce the wavelength measurement error due to the spectral modulation of superluminescent diode, two different types of remedies are proposed that utilize the temperature switching of superluminescent diode and that adjust the bandwidths of fiber Bragg grating and arrayed waveguide grating, and their efficacies are experimentally demonstrated together with good quantitative agreement with the theoretical calculation. [ABSTRACT FROM PUBLISHER]

In this manuscript, an optically passive fiber Bragg grating (FBG) interrogation system able to perform high-frequency measurement is proposed. The idea is mainly based on the use of an arrayed waveguide grating (AWG) device which is used to discriminate the fiber optic sensor (FOS) wavelength encoded response under test in function of its output channels. As made clear by the theoretical model studied in the proposed manuscript, the Bragg wavelength shift can be detected as in linear dependence with the proposed interrogation function which changes with the voltage produced by two (or more) adjacent AWG output channels. To prove the feasibility of the system, some experimental analyses are conducted with a custom electrical module characterized by high-speed and low-noise operational amplifiers. As static measurements, three FBGs with different full width at half maximum (FWHM) have been monitored under wide-range wavelength variation; while, as dynamic measurement, one FBG, glued onto a metal plate, in order to sense the vibration at low and high frequency, was detected. The output signals have been processed by a digital acquisition (DAQ) board and a graphical user interface (GUI). The presented work highlights the characteristics of the proposed idea as competitor among the entire class of interrogation systems currently used. This is because here, the main device, that is the AWG, is passive and reliable, without the need to use modulation signals, or moving parts, that affect the speed of the system. In addition, the innovative multi-channel detection algorithm allows the use of any type of FOS without the need to have a perfectly match of spectra. Moreover, it is also characterized by a high dynamic range without loss of sensitivity. [ABSTRACT FROM AUTHOR]

A highly sensitive dual-polarized 'X' oriented quadruple D-shaped open channel photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor for various analyte detection is proposed in this paper. Gold is taken as a plasmonic material for its stability and compatibility. Silicon nitride (Si 3 N 4) and titanium oxide (TiO 2) has been used separately as an adhesive layer of gold to elevate the sustainability of the evanescent field. This paper shows a comparative study and inspects the effect of sensing performance between Si 3 N 4 and TiO 2 as an adhesive layer of gold. Numerical investigations have been followed up using the finite element method (FEM). For practical feasibility, analyte and plasmonic materials have been placed at the outer surface of the sensor. After watchful investigation, the maximum wavelength sensitivities of 21,000 nm/RIU (Refractive Index Unit) and 18,000 nm/RIU have been found for the y-polarization when using TiO 2 and Si 3 N 4, respectively. The highest amplitude sensitivities are of 914RIU−1 and 625RIU−1 for TiO 2 and Si 3 N 4, respectively. Furthermore, minimum wavelength resolutions of 4.76 × 10−6 RIU and 5.55 × 10−6 RIU have been observed in y-polarization for TiO 2 and Si 3 N 4, respectively. The sensor evinces a maximum figure of merit (FOM) of 236RIU−1 for TiO 2. This sensor has the analyte sensing range of 1.31–1.38RI (Refractive Index) for TiO 2 and 1.32–1.39RI for Si 3 N 4. The sensor also delivers low confinement loss for Si 3 N 4 and TiO 2, which certifies viability in fabricating the design. Recognizing this sensor's wavelength sensitivity, amplitude sensitivity, and sensing RI range, it could be a promising candidate for detecting different liquid analytes with excellent accuracy. [ABSTRACT FROM AUTHOR]