Analysis of Tapered Fibre Optic Surface Plasmon Resonance Bio-Sensor Chip With Highly Perturbed Taper Profiles.

A numerical model based on the Transfer matrix method (TMM) is proposed for the first time to study the gold coated tapered fibre optic surface plasmon resonance (SPR) with eight different types of taper profiles namely linear, exponential-linear, Gaussian, quadratic, sinusoidal, error function type and highly perturbed taper profile so-called chirp type of profile. The performance in terms of sensitivity, full width at half maximum (FWHM), detection accuracy (D.A.), amplitude dip, and half power points are estimated with respect to tapering ratio and choices of taper profile. It is found that sensitivity increased almost linearly with the taper ratio of each taper choice for the account of the reduction of detection accuracy. It has been found that sensitivity is highest for the case of chirp taper profile and lowest for the case of quadratic taper profile at low taper ratio. In this study, the aqueous solution is considered for sensor development which is adulterated by biomolecules species like DNA, blood samples, etc.

High sensitivity detection of different pH ranges with rGO-nanocomposite coated eFBG sensor.

In the proposed work, a highly sensitive reduced graphene oxide (rGO) coated etched fiber Bragg grating (eFBG) pH sensor is developed and characterized. To create the sensing probe, a nanocomposite layer of rGO is coated over the unclad area of the eFBG. The analysis of rGO material has been done using different characterization tools such as UV-VIS-NIR spectroscopy, x-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). Experiments are performed using pH samples ranging from pH 2 to pH 12 to validate the operational sensing range of the proposed sensor. The effectiveness of the proposed sensor is evaluated with various pH values by monitoring the shift in the resonance peak of the sensor's reflection spectrum in a real-time interrogation system. The sensor performs well in both low and high pH ranges, with a maximum sensitivity of 0.232 nm/pH at pH 12. Due to a shift in the rGO's optical band-gap at both low and high pH values in the samples, the sensor can detect minimal changes in concentration. In the reflected spectrum, the Bragg wavelength (λ B) shifts as a result of the change in the refractive index. The λ B is observed to change as the pH of the aqueous solution is changed experimentally. Its performance is shown to be minimally affected by the ambient temperature (in the range of 19-21∘ C). The sensor also has the capacity for remote sensing, a quick response time, a small size, a low cost, a miniaturized probe, and the ability to reuse the probe.

Recent Advancement in Fiber-Optic-Based SPR Biosensor for Food Adulteration Detection-A Review.

Food safety is a scientific discipline that requires sophisticated handling, production, and storage. Food is common for microbial development; it acts as a source for growth and contamination. The traditional procedures for food analysis are time-consuming and labor-intensive, but optical sensors overcome these constraints. Biosensors have replaced rigorous lab procedures like chromatography and immunoassays with more precise and quick sensing. It offers quick, nondestructive, and cost-effective food adulteration detection. Over the last few decades, the significant spike in interest in developing surface plasmon resonance (SPR) sensors for the detection and monitoring of pesticides, pathogens, allergens, and other toxic chemicals in foods. This review focuses on fiber-optic SPR (FO-SPR) biosensors for detecting various adulterants in food matrix while also discussing the future perspective and the key challenges encountered by SPR based sensors.

A Numerical Study of Different Metal and Prism Choices in the Surface Plasmon Resonance Biosensor Chip for Human Blood Group Identification.

Optimized design of Surface plasmon resonance (SPR) based biosensor in terms of different metal choices and prisms are presented to the first time for the high precision detection of human blood group in near infrared wavelength range. The results are well compared with the earlier published gold coated silicon biosensor chip while discussing the pros and cons of various prism/metal choices. In this study buffer layer onto SPR active metal has been deployed to avoid the oxidation problem and contamination issue related with blood samples. Refractive index of blood samples has been considered in theoretical model based on the experimental data. Si prism has been found to be the best choice as a substrate material with combination of Al as a SPR active metal for blood group identification analysis. SPR dip slope (S), detection accuracy (D.A.) and blood group discrimination factor ( δθSPR ) have been studied with respect to different metal choices with their suitability to the next generation biosensor applications.

SPR Based Biosensing Chip for COVID-19 Diagnosis-A Review.

Surface Plasmon Resonance (SPR) techniques are highly accurate in detecting biomolecular like blood group measurement, food adulteration, milk adulteration and recently developing as a rapid detection for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. In order to validate the clinical diagnosis, Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) of nasopharyngeal swabs has been utilized, which is time consuming and expensive. For fast and accurate detection of the SARS-CoV-2 virus, SPR based biosensing chips are described in this review article. SPR sensors have the potential to be employed for fast, accurate, and portable SARS-CoV-2 virus diagnosis. To combat the SARS-CoV-2 pandemic, there is considerable interest in creating innovative biosensors that are quick, reliable, and sensitive for COVID-19 diagnosis.

Numerical analysis of a grating embedded bidirectional integrated optical coupler pressure sensor.

A numerical analysis of a grating embedded bidirectional optical coupled waveguide structure is presented for the first time, to our knowledge. A finite difference method (FDM) based scheme is devised to extract the allowed eigen TE and TM modes of the structure. Sensing characteristics of the grating employed between two high refractive index couplers are then explored. The influence of strain on the composite structure is numerically analyzed for better understanding of guiding phenomena. A numerical method based on a three-point central finite difference scheme with proper boundary conditions at the point of discontinuity is developed. For an accurate sensitivity analysis, a large number of mesh points (N=1000) are used in the FDM algorithm, while the whole analysis is done on MATLAB software. To the best of the authors' knowledge, Bragg grating sensitivities of individual TE and TM modes have been estimated for the first time. It is found that higher order TE and TM modes show improved sensitivity performance. The physics behind the improved sensitivity of the proposed structure is correlated with existing cases. The proposed technique is based on effective refractive index theory, and hence it is easy to implement. This work can be easily extended to obtain temperature, humidity, and vibration sensitivities of other novel structures.

Real-time interrogation of fiber optic biosensor using TiO2 coated etched long-period grating.

In this work, a TiO2 coated etched long-period grating (e-LPG) fiber optic biosensor is developed for the detection of Escherichia coli (E. coli) bacteria in food items. Label-free Escherichia coli bacteria monitoring is done over the detection range of 0 cfu/ml-50 cfu/ml using an advanced spectral interrogation mechanism. The thin film deposition of 40 nm TiO2 over the e-LPG is confirmed by the microscopy method, such as scanning electron microscopy. In our proposed biosensor design, T4-bacteriophage is covalently immobilized over the TiO2 coated fiber surface. This biosensor system has reached sensitivity at 2.55 nm/RIU. Our experiments confirm the resolution and the limit of detection (3σ/S) of 0.0039 RIU and 10.05 ppm, respectively. The proposed biosensor with enhanced sensitivity is suitable for monitoring harmful pathogens/infectious agents in various food products.

Photonic generation of a parabolic-shaped microwave signal and dual-linear-chirp microwave waveform.

Based on an external modulation technique through a dual-polarized dual-parallel Mach-Zehnder modulator, a photonic technique is proposed for the generation of a microwave signal with a parabolic shape. An optically modulated waveform from the modulator is passed through an optical bandpass filter, which results in parabolic signals of 1 GHz and 9 GHz frequencies at the photo detector. A peak power spectral component of -30dBm power is obtained at 1 GHz and 9 GHz frequencies of the parabolic signal. Based on the present methodology, a parabolic signal of the desired frequency band can be obtained. The obtained signal is processed to generate a dual-linear-chirp signal by passing through the phase modulator. Here, a dual-linear-chirp microwave waveform with a chirp rate of 1.53Π×1019Hz/s is achieved at 6 GHz center frequency. The results are obtained through MATLAB simulation and verified by experimental results. A fair agreement is found between the result obtained through MATLAB simulation and the result obtained by experimental verification.

Photonic-technique-based highly steerable beamforming system incorporating a prism of super Gaussian apodized tunable chirped fiber Bragg grating for X-band applications.

Conventional phased arrays operate over bandwidths that are inversely proportional to the array size. The use of true-time delays (TTDs) instead of phase shifts would eliminate the bandwidth restrictions due to beam squint. Photonic techniques for dynamically controlling the delay at the input of a phased array antenna opens an area of new powerful methods for remarkably precisely increasing the speed of beamsteering of an antenna in a desired direction. In this paper, we demonstrate a photonic-based wideband TTD beamforming network employing super-Gaussian apodized chirped fiber Bragg gratings (SGFBGs) of different lengths such as 1.5 cm, 2 cm, 2.5 cm, and many more, as well as different chirp rates, which can be used as variable TTD lines for controlling the radiation angle of the phased array antenna (the main lobe radiated by the phased array antenna can be steered squint-free between 0° and ±49.63∘), suitable for continuous beamforming at microwave frequencies in the X-band (8-12 GHz). The main purpose of using SGFBGs in a TTD module is the reduction of ripples in delay with respect to wavelength, which results in reduction in ambiguity while tuning the laser wavelength to any particular value within spectral width of FBG. To the best of the authors' knowledge, this is the first experimental demonstration that shows the impact of tuning wavelength on delay change due to SGFBGs in the RF signal fed to the respective element of the antenna array.

Class modal analysis of a thin multi-trench-assisted liquid-filled optical waveguide coupler for simultaneous multi-sensing applications.

In this paper, we present an analysis of, to the best of our knowledge, a novel class of the thin multi-trench-assisted optical coupler for multi-sensing of chemical detection. The design structure is an optical waveguide coupler consisting of closely coupled trenches filled with different liquids for chemical sensing. The refractive index profile of the coupler is allowed to vary due to the chemical filled in these trenches. The scalar finite difference method (FDM) is used to analyze the TE (s polarized) as well as TM (p polarized) modes, and thereafter propagate them along the structure through various trenched sections. We excite the structure with the eigenmode profile, which can be well approximated by the Gaussian shape pulse. The trenches with different chemicals and separation between them are well demonstrated in several examples. The main finding of this paper is that the coupling period of the structure can be changed by altering the refractive index of the trench region. In the FDM analysis, we have used the variable discretization step for better accuracy of these results. A new approach based on a thin multi-trench-assisted optical coupler scheme to analyze and design the chemical sensor is then proposed for the first time, to the best of our knowledge, for the detection of adulteration present in, for example, beverages, and in the medical industry.

Design of optical reversible logic gates using electro-optic effect of lithium niobate based Mach-Zehnder interferometers.

In recent years reversible logic has come as a promising solution in the optical computing domain. In reversible gates, there is one-to-one mapping between input and output, causing no loss of information. Reversible gates are useful for application in low power complementary metal-oxide semiconductors, with less dissipation, and in quantum computing. These benefits can be utilized by implementing reversible gate structures in the optical domain. In this paper, basic reversible Feynman and Fredkin logic gates using a lithium niobate based Mach-Zehnder interferometer are proposed. The different applications utilizing the proposed structures are also explained in this study.