Amplitude Interrogation Method Research Articles

Microchannel-based plasmonic refractive index sensor for low refractive index detection.

A microchannel incorporated photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor for detection of low refractive index (RI) at near-infrared wavelength is presented in this paper. To attain a simple and practically feasible mechanism, plasmonic material gold (Au) and sensing medium are placed outside the fiber. A thin layer of TiO2 is employed as an adhesive layer to strongly attach the Au with the silica glass. In the sensing range of 1.22 to 1.37, maximum sensitivities of 51,000nm/RIU (RI unit) and 1872 RIU-1 are obtained with resolutions of 1.96×10-6 and 9.09×10-6 RIUs using wavelength and amplitude interrogation methods, respectively. To the best of the authors' knowledge, the obtained maximum wavelength sensitivity and resolution are the highest among reported PCF-based SPR sensors to date. The sensor also exhibits a maximum figure of merit of 566. Therefore, the proposed sensor would be an excellent candidate for a wide range of RI detection with higher accuracy for applications such as pharmaceutical inspection and leakage monitoring, bio-sensing, and other low RI analytes.

Propagation Controlled Photonic Crystal Fiber-Based Plasmonic Sensor <italic>via</italic> Scaled-Down Approach

Light trapping capability is the key phenomena of the photonic crystal fiber (PCF) which paves the broad range of applications. In this work, we control the light-guiding direction of the proposed PCFs via scaled-down approach to enhance the coupling between core-guided mode and surface plasmon polariton (SPP) mode resulting in the increase of sensitivity. We introduce the scaled-down air-holes in the first and second rings of the proposed PCF which provides the light guiding capability through the desire scaled-down region. A chemically stable plasmonic material gold is used outside the PCF structure to facilitate the detection of unknown analyte externally. Finite element method is used for numerical investigations, and the sensor performance is investigated by following the wavelength and amplitude interrogation methods. The proposed sensor shows the maximum wavelength sensitivities of 30000 and 22000 nm/RIU, and the maximum amplitude sensitivities of 1212 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and 1506 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> for x- and y-polarized modes, respectively in the analyte refractive index (RI) range of 1.33 to 1.39. It also shows high sensor wavelength resolution of 3.33 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> RIU and 4.54 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> RIU, and a figure of merit about 508 and 500 for x- and y-polarized modes, respectively. It should be noted that the proposed PCF SPR sensor shows the significant sensing response for both polarization modes, as a result it will provide more freedom in choosing light source during practical implementation. Furthermore, the finding results indicates the proposed sensor will be effective for the detection of organic chemicals, biomolecules and medical diagnostics.

Highly amplitude-sensitive photonic-crystal-fiber-based plasmonic sensor

Simple structure, quick response, and highly sensitive miniaturized sensors are highly desirable for the broad range of sensing applications. In this work, we numerically investigated a highly sensitive photonic-crystal-fiber (PCF)-based plasmonic sensor for refractive index sensing. We consider gold as the plasmonic material, which is used outside the fiber structure to exhibit the plasmonic phenomena and to help detect the surrounding medium refractive index. The proposed PCF is designed to enable the evanescent field to interact with an external sensing medium leading to a highly sensitive response. The sensor performance has been investigated by wavelength and amplitude interrogation methods. The proposed sensor exhibits the maximum amplitude sensitivity of 2,843 RIU−1 with the sensor resolution of 3.5×10−6 RIU, which is the highest among the reported PCF SPR sensors, to the best of our knowledge. It also shows wavelength sensitivity of 18,000 nm/RIU and sensor resolution of 5.6×10−6 RIU. The figure of merit of the proposed sensor is about 400. The sensor response also allows us to detect the refractive index variation in the range of 1.33 to 1.41. Such promising results and broad sensing range ensure that the proposed sensor will be a suitable candidate for biological analytes and biochemical and organic chemical detections.

Twin Core Photonic Crystal Fiber Plasmonic Refractive Index Sensor

This paper presents a highly sensitive plasmonic refractive index (RI) sensor on a dual-core photonic crystal fiber (PCF). The performance of the RI sensor is weighed in terms of amplitude sensitivity, wavelength sensitivity, wavelength resolution, and linearity of the resonance wavelength. Numerical result shows that the maximum amplitude sensitivity of 725.8918 RIU $^{-1}$ and 1085 RIU $^{-1}$ are achieved for $x$ - and $y$ -polarization, respectively, by using amplitude interrogation method. In addition, the wavelength interrogation method gives the maximum wavelength sensitivity of around 9000 nm/RIU for both $x$ - and $y$ -polarized modes. Moreover, the maximum wavelength resolution of $1.11\times 10^{-5}$ RIU and the value of the co-efficient of determination ( $\text{R}^{2}$ ) of 0.9784 are reported. The proposed high-performance plasmonic RI sensor can be a favorable candidate for the detection of biological and biochemical analytes.

Dual core photonic crystal fiber based surface plasmon resonance biosensor

This article proposed a dual core photonic crystal fiber (DC-PCF) biosensor based on surface plasmon resonance (SPR). The finite element method (FEM), wavelength and amplitude interrogation methods are used to analyze the performance of the proposed sensor. The maximum wavelength sensitivity of 9000 nm/RIU and 25,000 nm/RIU, with analyte refractive index (RI) of 1.38, are numerically achieved for x-and y-polarized modes, respectively. Besides that, the structure shows the maximum amplitude sensitivity of around 470 RIU−1 and resolution as high as 1.11 × 10−5 RIU ∼4 × 10−6 RIU for both polarizations. Therefore, the proposed high sensitive biosensor can be useful in different wavelength ranges for the simultaneous detection of biological and biochemical analytes.

Gold-coated photonic crystal fiber biosensor based on surface plasmon resonance: Design and analysis

The particularly sensitive circular lattice Photonic Crystal Fiber (PCF) based Surface Plasmon Resonance (SPR) sensor is proposed to gain high sensitivity for the detection of unknown analytes. In this model, two-layer PCF based on the SPR has been designed. A plasmonic chemically inactive material gold (Au) with thickness 35 nm is used to the outside of the PCF structure which exhibits negative real permittivity. A circular perfectly match layer (PML) outside the structure is applied to evaluate the performance of the sensor. The raised design has consisted of symmetric air-hole. Three small air-holes are used in second layer and center which help us to produce more evanescent field. Using the wavelength interrogation method the proposed model shows the maximum wavelength sensitivity of 9000 nm/RIU (Refractive Index Unit) and using the amplitude interrogation method it shows the maximum amplitude sensitivity of 318 RIU−1 with maximum sensor resolution 1.11 × 10−5 in the sensing range among analyte 1.34–1.37. Here the proposed model is investigated how phase matching points are varied with changing parameters as like diameter, PML, thickness of gold (Au), sensing layer and pitch. The obtained result reveals that the proposed model may be used in biochemical and biological analyte detection to find out the important application.

Photonic crystal fiber-based plasmonic biosensor with external sensing approach

We propose a simple photonic crystal fiber (PCF) biosensor based on the surface plasmon resonance effect. The sensing properties are characterized using the finite element method. Chemically stable gold material is deposited on the outer surface of the PCF to realize the practical sensing approach. The performance of the modeled biosensor is investigated in terms of wavelength sensitivity, amplitude sensitivity, sensor resolution, and linearity of the resonant wavelength with the variation of structural parameters. In the sensing range of 1.33 to 1.37, maximum sensitivities of 4000 nm/RIU and 478 RIU−1 are achieved with the high sensor resolutions of 2.5×10−5 and 2.1×10−5 RIU using wavelength and amplitude interrogation methods, respectively. The designed biosensor will reduce fabrication complexity due to its simple and realistic hexagonal lattice structure. It is anticipated that the proposed biosensor may find possible applications for unknown biological and biochemical analyte detections with a high degree of accuracy.

A Novel Diamond Ring Fiber-Based Surface Plasmon Resonance Sensor

We propose a highly sensitive novel diamond ring fiber (DRF)-based surface plasmon resonance (SPR) sensor for refractive index sensing. Chemically active plasmonic material (gold) layer is coated inside the large cavity of DRF, and the analyte is infiltrated directly through the fiber instead of selective infiltration. The light guiding properties and sensing performances are numerically investigated using the finite element method (FEM). The proposed sensor shows a maximum wavelength and amplitude interrogation sensitivity of 6000 nm/RIU and 508 RIU−1, respectively, over the refractive index range of 1.33–1.39. Additionally, it also shows a sensor resolution of 1.67 × 10−5 and 1.97 × 10−5 RIU by following the wavelength and amplitude interrogation methods, respectively. The proposed diamond ring fiber has been fabricated following the standard stack-and-draw method to show the feasibility of the proposed sensor. Due to fabrication feasibility and promising results, the proposed DRF SPR sensor can be an effective tool in biochemical and biological analyte detection.

Highly Sensitive D-Shaped Photonic Crystal Fiber-Based Plasmonic Biosensor in Visible to Near-IR

A simple D-shaped photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) biosensor is proposed for refractive index sensing in visible to near infrared (IR) region. A thin Titanium di-oxide (TiO2) layer is used as an adhesive layer to strongly attach the plasmonic gold (Au) layer with silica fiber surface. TiO2 also helps to tune the operating sensor wavelength from visible to near IR (550–1770-nm wavelength). Finite-element method has been used to investigate the guiding properties. The proposed sensor shows the maximum wavelength interrogation sensitivity of 46 000 nm/RIU and the average sensitivity of 9,800 nm/RIU in the sensing range of 1.33–1.43. It also shows the maximum amplitude sensitivity of 1,086 RIU $^{-1}$ . Using the wavelength and amplitude interrogation methods, proposed sensor gives the theoretical maximum resolution of 2.2 $\times 10^{-6}$ and 9.2 $\times 10^{-6}$ RIU, respectively. To the best of our knowledge, it has the highest sensitivity and sensor resolution among the reported PCF SPR sensors. The proposed D-shaped PCF has been fabricated following the standard stack-and-draw method to show the feasibility of the proposed sensor. Due to the promising results over the broad range of analyte RI, it would be an excellent candidate for the detection of biomolecules, organic chemicals, chemical, and other analytes.

A Highly Sensitive Gold-Coated Photonic Crystal Fiber Biosensor Based on Surface Plasmon Resonance

In this paper, we numerically demonstrate a two-layer circular lattice photonic crystal fiber (PCF) biosensor based on the principle of surface plasmon resonance (SPR). The finite element method (FEM) with circular perfectly matched layer (PML) boundary condition is applied to evaluate the performance of the proposed sensor. A thin gold layer is deposited outside the PCF structure, which acts as the plasmonic material for this design. The sensing layer (analyte) is implemented in the outermost layer, which permits easy and more practical fabrication process compared to analyte is put inside the air holes. It is demonstrated that, at gold layer thickness of 40 nm, the proposed sensor shows maximum sensitivity of 2200 nm/RIU using the wavelength interrogation method in the sensing range between 1.33–1.36. Besides, using an amplitude interrogation method, a maximum sensitivity of 266 RIU−1 and a maximum sensor resolution of 3.75 × 10−5 RIU are obtained. We also discuss how phase matching points are varied with different fiber parameters. Owing to high sensitivity and simple design, the proposed sensor may find important applications in biochemical and biological analyte detection.

Plasmonic Fiber-Optic Refractometers Based on a High Q-Factor Amplitude Interrogation

A nano-scale gold-coated tilted fiber Bragg grating sensor with clear surface plasmon resonance is proposed and experimentally demonstrated. The transmission spectrum of the sensor provides a fine comb of narrowband resonances that overlap with the broader absorption of the surface plasmon and thus provides a unique tool to measure small shifts of the plasmon and identify the changes of the surrounding refractive index (SRI) with high accuracy. Meanwhile, our proposed sensor provides an amplitude interrogation method for SRI measurement, which is much simpler and cost-effective than the traditional wavelength monitoring. Experimental results obtained in sucrose solutions with different refractive indices ranging from 1.3330 to 1.3410 show that the sensitivities of our proposed sensor are 450 nm/RIU and 2040 dB/RIU by using the wavelength and amplitude interrogation methods, respectively. Furthermore, the Q-factor of amplitude interrogation signal has been increased from $\sim 70$ to $\sim 6000$ by using the narrowband cladding resonance instead of broader SPR absorption.

Surface Plasmon Resonance Sensor Based On Exposed-Core Microstructured Optical Fiber Placed With A Silver Wire

We propose a surface plasmon resonance (SPR) sensor based on the exposed-core microstructured optical fiber (EC-MOF) placed with a silver wire. The exposed section of the EC-MOF as a microfluidic channel is placed with the silver wire to avoid the metal coating and is then deposited with the analyte to avert the analyte filling. The proposed SPR sensor can support two polarized resonance peaks (x-polarized and y-polarized) caused by the silver wire. We theoretically investigate the sensitivities of the two polarized peaks both in the wavelength and amplitude interrogation methods and analyze the influences of the silver wire location on the sensing performances. The results show that the sensitivities of the two polarized peaks are similar and relatively stable for random locations of the silver wire. Moreover, the x-polarized peak provides a higher resolution for wavelength sensitivity and needs a shorter silver wire for the maximum amplitude sensitivity. This paper demonstrates that using the EC-MOF placed with the silver wire can simultaneously solve the metal coating and analyte filling problems in the other SPR sensors with no sacrifice in sensitivity.

High Refractive Index Surface Plasmon Resonance Sensor Based on a Silver Wire Filled Hollow Fiber

A surface plasmon resonance (SPR) sensor based on a hollow fiber (HF) is proposed to realize high analyte refractive index (RI) detection. The hole in the HF as a microfluidic channel for the analyte is filled with a silver wire to replace the metal coating. The sensitivity of the proposed SPR sensor with analyte RI from 1.47 to 1.51 is theoretically investigated both in the wavelength and amplitude interrogation methods. The results show that the sensor can support two disparate resonance peaks, with orthogonal polarizations (x-and y-polarized peaks), and the sensitivity of the y-polarized peak is higher than that of x-polarized peak. Moreover, contrary to the performances of the resonance peaks supported by the low RI SPR sensors, the two polarized peaks shift to shorter wavelength as analyte RI increasing and show a higher sensitivity at low analyte RI. These results and analyses, including the abnormal behaviors of resonance peaks and the coupling condition between the core modes and the plasmon modes, are very helpful for the design and improvement of high RI SPR sensors.

Surface Plasmon Resonance Photonic Crystal Fiber Biosensor: A Practical Sensing Approach

We propose a simple, two rings, hexagonal lattice photonic crystal fiber biosensor using surface plasmon resonance phenomenon. An active plasmonic gold layer and the analyte (sample) are placed outside the fiber structure instead of inside the air-holes, which will result in a simpler and straight forward fabrication process. The proposed sensor exhibits birefringent behavior that enhances its sensitivity. Numerical investigation of the guiding properties and sensing performance are conducted by finite element method. Using wavelength and amplitude interrogation methods, the proposed sensor could provide maximum sensitivity of 4000 nm/RIU and 320 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , respectively. The resolutions of the sensor are 2.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> and 3.125 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> RIU for wavelength and amplitude interrogation modes. The proposed sensor design shows promising results that could be used in biological and biochemical analytes detection.