Wavelength Interrogation Research Articles

Broadband Enhancement of Magneto-Optical Effects in Hybrid Waveguide-Plasmonic Surfaces for Sensing.

Conventional magnetophotonic nanostructures typically function within narrow wavelength and incident angle ranges, where resonance is observed and magneto-optical (MO) effects are amplified. Expanding these operational ranges may allow for improved applications, including in (bio)sensing devices. In this study, we describe a hybrid magnetoplasmonic waveguide grating (HMPWG) in which the coupling of plasmonic resonances and waveguide modes leads to enhanced MO effects and sensitivity, according to full-wave electromagnetic simulations. High transverse magneto-optical Kerr effect (TMOKE) signals were observed for the full range of wavelengths and angles investigated, i.e., for θinc ≥ 1° and 500 nm ≤ λ ≤ 850 nm. As a proof-of-concept we verified that using the HMPWG nanostructure with an aqueous solution as superstrate one may obtain a sensitivity in variation of the refractive index unit (RIU) of S = 166°/RIU and S = 230 nm/RIU in angle and wavelength interrogation modes, respectively. Upon comparing with conventional magnetoplasmonic gratings, which only enable excitation of plasmonic resonances, we demonstrate that HMPWG nanostructures can be further optimized to reach not only high sensitivity but also high resolution in sensing and biosensing.

Integrated Photonic Sensors for the Detection of Toxic Gasses—A Review

Gas sensing is crucial for detecting hazardous gasses in industrial environments, ensuring safety and preventing accidents. Additionally, it plays a vital role in environmental monitoring and control, helping to mitigate pollution and protect public health. Integrated photonic gas sensors are important due to their high sensitivity, rapid response time, and compact size, enabling precise recognition of gas concentrations in real-time. These sensors leverage photonic technologies, such as waveguides and resonators, to enhance performance over traditional gas sensors. Advancements in materials and fabrication techniques could further improve their efficiency, making them invaluable for environmental monitoring, industrial safety, and healthcare diagnostics. In this review, we delved into photonic gas sensors that operate based on the principles of evanescent field absorption (EFA) and wavelength interrogation methods. These advanced sensing mechanisms allow for highly sensitive and selective gas detection, leveraging the interplay of light with gas molecules to produce precise measurements.

3D- printed modular spr platform integrated with ellipsometer for in-situ label-free optical sensing applications

The present work focuses on advancing optical sensing abilities through the instrumentation of Surface Plasmon Resonance Spectroscopy (SPR) with a commercial ellipsometer. This approach involves the incorporation of an in-house-built 3D-printed SPR module to circumvent the complexity of optical alignments with the ellipsometer. Currently, no commercially available SPR-enhanced Ellipsometry (SPRE) system exists, and previous systems are mostly custom-designed. Our work addresses this gap by introducing an in-house-built SPR module compatible with Ellipsometry and constructed using 3D printing technology. The 3D-printed SPR module is user-friendly, durable, lightweight, and cost-effective, incorporating a flow cell crucial for liquid media operation. This integrated tool provides a highly surface-sensitive, non-invasive, and label-free optical sensing platform. The developed SPR-Ellipsometry platform demonstrates excellent performance in detecting biochemical analytes and multilayer adsorption of poly-electrolytes. The bulk refractive index sensitivity measurement was performed to calibrate the Au sensor chip. The Wavelength (SPR mode), amplitude (Ψ), and phase interrogation (∆) exhibit bulk refractive index sensitivities of 3098 ± 177 nm/RIU, 835 ± 22 °/RIU and 5839 ± 229 °/RIU, respectively. We obtained the refractive index resolution around 1.712 × 10−7 RIU. Protein-protein (BSA/Anti-BSA) interactions were also conducted, achieving a detection limit of 3 pM for Anti-BSA. This work will significantly expand the functionality of SPRE sensors by offering enhanced sensitivity, rich information, and high precision, as well as opening avenues for more efficient and accessible optical sensing technologies. Moreover, the study establishes a foundational framework for researchers, shedding light on the potential of 3D printers in laboratories and expediting the development of cost-effective integrated sensing platforms.

Copper and Tungsten Disulfide Based Highly Sensitive Fiber Optic Surface Plasmon Resonance Sensor

ABSTRACT Fiber optic surface plasmon resonance (SPR) sensor based on copper and tungsten disulfide is presented experimentally. The method of wavelength interrogation is used to analyze the sensor. Outcomes of thicknesses of these materials on the sensitivity of the sensor have been shown in detail. The presence of tungsten disulfide layer of certain thickness in the copper-based sensor has been shown to improve the sensitivity. The SPR sensor with 40 nm thick copper-10 nm thick tungsten disulfide layers exhibits highest sensitivity.

Ultra-wide range non-contact surface profilometry based on reconfigurable fiber interferometry.

Surface characterization is essential for a technical evaluation of device performance and to assess surface dynamics in fabrication units. In this regard, a number of surface profiling techniques have been developed that accurately map sample topography but have significantly limited detection range. Here, we demonstrate a cascaded non-contact fiber interferometer-based approach for real-time high-precision surface profiling with ultrawide detection range (nm to mm). This compact interferometers' system operates by wavelength interrogation that provides a scope to study several types of surfaces and has a tunable cavity configuration for varying the sensitivity and range of the detectable features' size. The proposed system enables nanoscale profiling over 10-1000 nm with resolution of 10 nm and microscale mapping over 1-1000 µm with resolution of 0.2 µm. The technique is utilized to map the features of nanostructured surfaces and estimate the surface roughness of standardized industrial samples.

A unique wheel-shaped exposed core LSPR-PCF sensor for dual-peak sensing: Applications in the optical communication bands, M-IR region and biosensing

Photonic Crystal Fibers (PCF) effectiveness in practice decreases if the fabrication of the sensor becomes too complex. Keeping this in mind, we propose a one-of-a-kind wheel shaped PCF sensor with an exposed core containing only three air holes with exceptional sensing features. The sensor is equipped with dual plasmonic layers, Indium Tin Oxide (ITO, 10 % wt) and silver (Ag) with a coating of TiO2 to enhance the sensing capabilities and provide protection against oxidation. The sensor's distinctive configuration enables it to exhibit two distinct peaks within a range of refractive index from 1.32 to 1.38 for y-polarization and from 1.35 to 1.38 for x-polarization. The sensor specifications have been optimized to achieve the maximum levels of wavelength sensitivity (WS) and double peak shift sensitivity (DPSS). The sensor portrays a WS of 50,652 nm/RIU and the highest DPSS ever recorded, measuring 50,000 nm/RIU. Additionally, the sensor exhibits a significantly high scale of amplitude sensitivity (AS) of 1668.34 RIU−1 which is a very remarkable value considering silver as plasmonic material along with an outstanding figure of merit (FOM) of 1017.11 RIU−1. In addition, our sensor is able to manifest resolutions in the order of 10−6, demonstrating a resolution of 5.94 × 10−6 RIU with the deployment of amplitude interrogation method and 1.97 × 10−6 RIU with the wavelength interrogation method. The design spans an extensive spectrum, covering ultraviolet to mid-infrared wavelengths, enabling detection of biomolecules and biochemicals, along with operation in the optical communication band.

Numerical analysis and detection of cancer cells using a dual-core gold coated plasmonic biosensor

In this research, a simple dual-core photonic crystal fiber (PCF) that leverages surface plasmon resonance (SPR) to operate as a bio-sensor in the visible to near-infrared range is proposed. An external analyte channel is constructed by putting a gold plasmonic metal layer over the fiber sensor. A numerical investigation employing the wavelength interrogation approach reveals that the maximal wavelength and amplitude sensitivity are 22000 nm/RIU and 1561.4 RIU-1, respectively. The high wavelength resolution for this suggested sensor is 4.54 × 10−6 RIU, and that suggests a high detection range. The proposed sensor is designed for the detection of any molecules from the RI range 1.33 to 1.42, and it can detect six different types of cancerous cells (the refractive index of different cancerous cells varied from 1.380 to 1.401) in this range. According to the obtained numerical results, MCF-7 cells exhibit the highest wavelength sensitivity of 6428.6 nm/RIU and amplitude sensitivity of 766.361 RIU-1. Furthermore, the sensor will be able to detect different viruses, proteins, DNA/RNA strands, and other things in this sensing range. This sensor offered the potential to detect biochemical solutions and biological samples due to its high sensitivity and simple shape.

Exploring tunable single-wavelength detection schemes for guided-mode resonance sensors

We explore guided-mode resonant (GMR) structures in an unconventional way for low-cost yet effective bio-sensing applications. In contrast to regular broadband source-based wavelength interrogation techniques, single wavelength-based measurements can successfully eliminate the requirement of a costly spectrometer for rapid label-free detection and analysis. We have fabricated a silicon–nitride grating-waveguide structure and investigated it theoretically as well as experimentally under normal, angular, and conical incidences following an all-in-one transmission geometry. Such studies avoid unnecessary fabrication of multiple chips and promote a wide operational range of the GMR sensor. To validate the proposed cost-effective intensity-based sensing, we have analyzed our fabricated single GMR chip under different combinations of two-axis rotation to confirm its suitability under commonly available laser sources. Finally, using a He-Ne laser, a sensitivity of ∼ 166 mW/RIU is recorded experimentally on an average for the fabricated GMR device, operating at the resonant wavelength of 632.8 nm. The current study provides an in-depth investigation to promote possibilities for utilizing GMR structures in an inexpensive intensity-based bio-detection scheme through the demonstrated proof-of-concept.

Enhancing Precision in Fuel Adulteration Detection: Utilizing a Wavelength Interrogation Surface Plasmon Resonance Approach

Enhancing Precision in Fuel Adulteration Detection: Utilizing a Wavelength Interrogation Surface Plasmon Resonance Approach

Temperature-insensitive cascaded micro-ring resonator silicon photoelectric sensor based on wavelength interrogation for HSA detection

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.

Performance analysis of PLC-based 32-channel arrayed waveguide grating used for FBG interrogator

The Fiber Bragg grating (FBG) is an optical fiber component that reflects or diffracts optical signals of specific wavelengths through periodic refractive index changes inside it. Currently, the use of arrayed waveguide grating (AWG) to interrogate such optical signals is a popular research topic at present. Using the planar lightwave circuit, we designed and fabricated a 32-channel AWG. The AWG has an insertion loss of less than 4 dB, a 3 dB bandwidth of about 1.76 nm, and a crosstalk of non-adjacent channels of less than −28 dB. Additionally, we integrated the AWG with a photodetector (PD) array and built a corresponding wavelength interrogation system, which was tested using three different interrogation methods. The test results indicate that when using the linear fitting, this AWG provides the best results using the dual-channel edge filtering method with an interrogation range of 1.6 nm and an interrogation accuracy of 18.9–20.1 pm. The interrogation accuracies of the relative intensity method are 9.4 pm and 3.7 pm when Gaussian and Lorentzian fittings are used.

On-Chip Sub-Picometer Continuous Wavelength Fiber-Bragg-Grating Interrogator

Miniaturized fiber-Bragg-grating (FBG) interrogators are of interest for applications in the areas where weight and size controlling is important, e.g., airplanes and aerospace or in-situ monitoring. An ultra-compact high-precision on-chip interrogator is proposed based on a tailored arrayed waveguide grating (AWG) on a silicon-on-insulator (SOI) platform. The on-chip interrogator enables continuous wavelength interrogation from 1 544 nm to 1 568 nm with the wavelength accuracy of less than 1 pm [the root-mean-square error (RMSE) is 0.73 pm] over the whole wavelength range. The chip loss is less than 5 dB. The 1 × 16 AWG is optimized to achieve a large bandwidth and a low noise level at each channel, and the FBG reflection peaks can be detected by multiple output channels of the AWG. The fabricated AWG is utilized to interrogate FBG sensors through the center of gravity (CoG) algorithm. The validation of an on-chip FBG interrogator that works with sub-picometer wavelength accuracy in a broad wavelength range shows large potential for applications in miniaturized fiber optic sensing systems.

Guided mode resonance based phase sensing with spectral interferometry

In photonic biosensor designs, the phase-detection methods offer better sensing capabilities and lower detection limits in contrast to other conventional interrogation schemes. However, this class of detection scheme is explored very limitedly for realizing compact biosensing detection schemes. Predominantly, complex experimental setups involving bulk optical components are required for the phase interrogation scheme, which constrains the practical applicability of phase detection apart from the laboratory environment. Here, we present a common-path spectral interferometric technique utilizing a birefringent crystal and spectrometer to evaluate the phase of the guided mode resonance (GMR) signal operating in transmission mode. The common path method offers better stability and constitutes a simple and compact detection modality that can be incorporated into the practical world. A Window Fourier Transform method is implemented to extract the phase of the GMR signal. From the proposed technique, a sensitivity of 103.4 rad/RIU and a limit of detection of 9.8 × 10−5 RIU could be obtained experimentally. This method provides an improved limit of detection as compared to the conventional wavelength interrogation techniques, which also use a spectrometer as the detection system. Hence, this proposed simple and compact detection system enables the realization of highly sensitive portable biosensors.

Theoretical Design of Near-Infrared Tunable Surface Plasmon Resonance Biosensors Based on Gate-Controlled Graphene Plasmons

A tunable near-infrared surface plasmon resonance (SPR) biosensor based on gate-controlled graphene plasmons is numerically investigated by using the finite element method (FEM) and the transfer matrix method (TMM). The novel properties of chemical potential sensing make the proposed sensor promising in the application of ultra-sensitive and highly specific biosensing technology. The sensitivity of chemical potential sensing in wavelength interrogation mode can be calculated to be 1.5, 1.89, 2.29, 3.21, 3.73 and 4.68 nm/meV, respectively, at the resonance wavelengths of 1100, 1200, 1310, 1550, 1700 and 1900 nm. The figure of merit (FOM) achieves 129.3, 101.1, 84.5, 67.7, 69.5 and 59.7 eV−1, respectively, at these resonance wavelengths. The sensitivity of chemical potential sensing in gate voltage interrogation mode also can be calculated to be 156.9822, 143.6147, 131.0779, 111.0351, 101.3415 and 90.6038 mV/meV, respectively, at the incident wavelengths of 1100, 1200, 1310, 1550, 1700 and 1900 nm. The FOM achieves 135.6, 103.0, 88.9, 62.2, 66.6 and 61.5 eV−1, respectively, at these incident wavelengths. Theoretical estimates suggest that the limit of detection (LOD) of the sensor’s DNA sensing can reach the level of femtomolar or even attomolar, comparable to and even lower than that of 2D nanomaterial-enhanced metal SPR sensors with AuNPs as a sensitivity enhancement strategy. The feasibility of preparation and operation of this new concept SPR biosensor is also analyzed and discussed.

Sensitivity enhancement of the surface plasmon resonance sensor based on gallium-doped zinc oxide and silicon for cancer detection: A wavelength interrogation approach

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.

Design and analysis of arc-shaped single core photonic crystal fiber sensor based on surface plasmon resonance

The selection of a suitable plasmonic material is crucial for achieving high-performance photonic crystal fiber-based surface plasmon resonance (PCF-SPR) sensors. However, most numerical investigations have been limited to PCF-SPR sensors with conventional circularly coated plasmonic metals due to their availability and rigid properties. In this work, a single-core arc-shaped PCF is designed and studied with sensing ingredients coated outside the fiber. The simulation and numerical analyses are performed using the full-vector finite element method to examine the effects of using gold as an active metal and also the deposition of Ta2O5 on gold. The results show that the arc-shaped sensor with gold film can obtain the maximum wavelength interrogation sensitivity (WIS) of 9500 nm/RIU within the refractive index (RI) range of 1.25–1.39 while the maximum amplitude interrogation sensitivity (AIS) reaches 579.26 RIU−1 at 1.39 and resolution is 1.05 × 10−5. However, depositing Ta2O5 on the gold gives an improved maximum WIS and AIS of 22,000 nm/RIU and 1209.21 RIU−1, respectively. With the coating of Ta2O5, the resolution improves to 4.55 × 10−6, making the proposed sensor design undoubtedly effective in detecting food chemicals such as butyl acetate and hydrocarbons along with different bio-analyte samples with a wide range of RI.

From Bloch surface waves to cavity-mode resonances reaching an ultrahigh sensitivity and a figure of merit

We report on a new sensing concept based on resonances supported by a one-dimensional photonic crystal (1DPhC) microcavity resonator in the Kretschmann configuration. For a 1DPhC comprising six bilayers of TiO2/SiO2 with a termination layer of TiO2 employed to form a microcavity, we show that when the angle of incidence is changed, the Bloch surface waves (BSWs) can be transformed into cavity-mode resonances exhibiting an ultrahigh sensitivity and a figure of merit. Using wavelength interrogation, we demonstrate that Bloch surface TE wave excitation shows up as a sharp dip in the reflectance spectrum with a sensitivity and a figure of merit (FOM) of 70 nm per refractive index unit (RIU) and 19.5 RIU−1, respectively. When the angle of incidence decreases, cavity-mode resonances for both TE and TM waves are resolved for RI in a range of 1.0001–1.0005. The sensitivity and FOM can reach 52,300 nm/RIU and 402,300 RIU−1 for the TE wave, and 14,000 nm/RIU and 2154 RIU−1 for the TM wave, respectively. In addition, resonances are confirmed experimentally for a humid air with a sensitivity of 0.073 nm per percent of the relative humidity (%RH) for BSW resonance and is enhanced to 1.367 nm/%RH for the TM cavity-mode resonance. This research, to the best of the authors’ knowledge, is the first demonstration of a new BSW-like response that can be utilized in a simple sensing of a wide range of gaseous analytes.

Highly sensitive dual core photonic crystal fiber-based LSPR sensor with simultaneous multi-analyte detection of a wide refractive index range

This manuscript introduces an anisotropic highly sensitive dual core photonic crystal fiber sensor based on localized surface plasmon resonance, possessing the ability to detect multiple analytes simultaneously. Liquid analytes having a refractive index (RI) within the range of 1.25 to 1.5 RIU have been investigated using the proposed sensor. The numerical analysis of the sensing parameters for the proposed sensor shows a maximum wavelength sensitivity of 47,500 nm/RIU for x-polarization (Channel 1) and 18,050 nm/RIU for y-polarization (Channel 2), respectively using the wavelength interrogation technique. Maximum amplitude sensitivity of 625 RIU−1 and 437 RIU−1 is obtained for x−pol. and y−pol., respectively using the amplitude interrogation technique. Maximum sensor resolution of 2.11 × 10−6 RIU and 5.01 × 10−6 RIU is obtained for x−pol. and y−pol., respectively. The linear relationship of the resonant wavelength with the RI produces R2 = 0.9976 and R2 = 0.9979, corresponding to a degree (3) for x−pol. and y−pol., respectively. The figure of merit for x−pol. and y−pol. are 84 RIU−1 and 123 RIU−1.

Design of bio-alcohol sensor based on waveguide-coupled photonic crystal cavity

Detection of bio-alcohol is crucial in diverse industries, including forensics, medicine, and food production. This paper presents a novel biosensor for bio-alcohol detection in water, integrating three micro-cavities with two waveguides within a hexagonal photonic crystal array. Employing a wavelength interrogation approach and finite-difference time-domain (FDTD) simulations, the proposed biosensor demonstrates a high sensitivity of 610 nm/RIU (nanometers per refractive index unit) and a low detection limit of 7 × 10-3 RIU. Simulation results validate the effectiveness of this photonic crystal biosensor for detecting organic substances in water, showcasing its potential for practical applications.

Low-Cost ZnO Spray-Coated Optical Fiber Sensor for Detecting VOC Biomarkers of Diabetes.

A non-invasive optical fiber sensor for detecting volatile organic compounds (VOCs) as biomarkers of diabetes is proposed and experimentally demonstrated. It offers a low-cost and straightforward fabrication approach by implementing a one-step spray coating of a ZnO colloidal solution on a glass optical fiber. The structure of the optical fiber sensor is based on a single-mode fiber-coreless silica fiber-single-mode fiber (SMF-CSF-SMF) structure, where the CSF is the sensor region spliced between two SMFs. The ZnO layer of a higher refractive index coated over the sensing region improves the light interaction with the surrounding medium, leading to sensitivity enhancement. The optical properties, morphology, and elemental composition of the ZnO layer were analyzed. The sensing mechanism of the developed sensor is based on a wavelength interrogation technique showing wavelength shifts when the sensor is exposed to various VOC vapor concentration levels. Various concentrations of the three VOCs (including acetone, isopropanol, and ethanol) ranging from 20% to 100% were tested and analyzed. The sensor noticeably shows a significant response towards acetone vapor, with a better sensitivity of 0.162 nm/% vapor than for isopropanol (0.082 nm/% vapor) and ethanol (0.075 nm/% vapor) vapors. The high sensitivity and selectivity towards acetone, a common biomarker for diabetes, offers the potential for further development of this sensor as a smart healthcare system for monitoring diabetic conditions.