Core-guided Mode Research Articles

Numerical analysis of a single channel exposed core elliptical shaped PCF based highly sensitive SPR sensor for wide RI sensing

This study presents a numerical study of a highly sensitive photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor capable of detecting five types of cancer and bacterial contamination in water. By precisely arranging only two air holes in a single channel of an elliptical-shaped PCF, the sensor maximizes interaction between core-guided modes and surface plasmon polaritons (SPP) along the fiber. Evaluation using COMSOL Multiphysics simulation software, based on finite element method (FEM), demonstrates outstanding sensor performance across a wide refractive index (RI) range (1.33 to 1.43). With a maximum wavelength sensitivity (WS) of 188,000 nm/RIU and amplitude sensitivity (AS) of -22,377.99 RIU−1, the sensor achieveStructural Design and Methodologys a sensor resolution (SR) of 5.3191 × 10−7 RIU and figure of merit (FOM) of 854.55 RIU−1. Notably, it exhibits AS and WS values tailored for specific cancer cell types and water contamination. These results endorse the sensor’s potential in diverse biological and molecular analyte RI detection applications within the visible to near-infrared (VNIR) range (0.55 to 4 µm), offering high sensitivity, affordability, wide sensing range, good linearity, low propagation loss, and simplicity in construction.

Cancer cell detection by plasmonic dual V-shaped PCF biosensor

In this paper, a highly sensitive plasmonic photonic crystal fiber (PCF) biosensor is reported for cancer cell detection. The modal analysis of the reported biosensor is performed using the full vectorial finite element method. The suggested PCF sensor has dual V-shaped groves to enhance the sensor sensitivity where two gold nano-rods are mounted on the etched surfaces. The main idea of the optical sensors is to track the electromagnetic coupling between the leaky core mode and the surface plasmon mode (SPM) at the metal/dielectric interface. When the SPM and one of the fundamental core modes are phase-matched, strong coupling occurs. Therefore, maximum confinement loss is achieved for the core-guided mode at the resonance wavelength, which depends on the analyte refractive index (RI). The V-shaped groove enhances the core/SPM coupling where high RI sensitivity of 24,000 nm/RIU is achieved along the RI range from 1.38 to 1.39, with a resolution of 2.703×10−6RIU. The potential of using the suggested RI sensor for cancer cell detection is then demonstrated. In this context, high sensitivities of 23,700 nm/RIU, 8,208 nm/RIU, and 14,428.6 are obtained for basal, cervical, and breast cancer cells with resolutions of 4.22×10−6RIU, 12.18×10−6RIU, and 6.93×10−6RIU, respectively. The achieved sensitivity and resolution are higher than those of the recently reported cancer biosensors. Moreover, the developed label-free biosensor is safer than other chemical and surgical techniques.

High refractive index sensing highly sensitive and low loss SPR sensor based on hollow-core D-shaped optical fiber

A hollow-core D-shaped optical fiber-based surface plasmon resonance (SPR) sensor for low-loss and highly sensitive liquid analytes detection is theoretically investigated. The gold (Au) metal nanolayer is coated on the cladding etched D-shaped flat surface to develop the plasmonic effect. The nanolayer coating on the outer flat surface is very easy compared to the inside hollow-core, so our hollow-core sensor manufacturing is too easy compared to other hollow-core refractive indices (RIs) detection sensors. The resonance effect between analytes filled fundamental guided core mode and surface plasmon polariton mode of the D-shaped hollow-core optical fiber sensor is used to obtain the detections of analytes RIs variations. We have found good linear results ([Formula: see text]) in analytes RIs versus resonance wavelength for gold layers thicknesses for the analytes RIs range of 1.45–1.52. This hollow-core D-shaped optical fiber sensor achieves the maximum wavelength sensitivity of 23500[Formula: see text]nm RIU[Formula: see text] and a corresponding resolution of [Formula: see text] RIU. We have obtained the maximum figure of merit (FOM) of 228 1/RIU. The proposed sensor may be highly active in detecting the biological and chemical liquid analytes.

Side-polished photonic crystal fiber sensor with ultra-high figure of merit based on Bloch-like surface wave resonance

A Bloch surface wave (BSW) resonance configuration is introduced for biosensing with an ultra-high figure of merit (FOM). The BSW excitation is realized through the evanescent field of the core-guided fundamental mode of a side-polished photonic crystal fiber (PCF). By taking advantage of the air hole periodic microstructure of the PCF cladding, the BSW platform can be achieved with only a single high refractive index dielectric layer on its flat surface. The dielectric layer deposited on the polished surface of the PCF modifies the local effective refractive index, allowing direct manipulation of the BSWs, whereby the resonance wavelength of the surface wave can be adjusted by choosing the material and thickness of this layer. Here, we numerically investigate Bloch-like surface wave (BLSW) resonance conditions around telecom wavelengths for silicon, titanium dioxide, copper monoxide, and aluminum oxide termination layers. The BLSW excitation platform materials have low loss, which results in higher surface field enhancements and narrower resonances, which are advantageous properties for the sensors. The obtained results open new avenues for the application of optical surface waves in biosensing with high FOM. Furthermore, these results show a much higher figure of merit (FOM) than traditional approaches, allowing for increased sensitivity and accuracy.

Improving Temperature-Sensing Performance of Photonic Crystal Fiber via External Metal-Coated Trapezoidal-Shaped Surface

This article describes a photonic crystal fiber (PCF) temperature sensor that utilizes a flat, metal-coated trapezoidal surface. The PCF is made up of two layers of elliptical air holes and a polished trapezoidal surface that allows temperature sensing. An external sensing approach is used to deposit a thin silver layer on the reflective surface, while a thin SiO2 film acts as an oxidation-resistant coating. The top elliptical air hole serves as the interface for energy transformation from the core-guided mode to the surface plasmon-polariton (SPP) mode. Simulations carried out using the finite element method indicate that the proposed SPR-PCF temperature sensor can achieve a maximum temperature sensitivity and resolution of up to 5200 pm/°C and 0.01923 °C, respectively, across a temperature range of 10 to 60 °C. This research has significant potential for sensor design and real-time temperature remote sensing applications.

A Fiber Bragg Grating Sensor Based on Cladding Mode Resonance for Label-Free Biosensing

A fiber-optic biosensing platform based on ultra-narrowband cladding mode resonances was developed on a high-reflectivity fiber Bragg grating (FBG) for targeting biomolecular detection. The multiple cladding modes with a high sensitivity to the refractive index (RI) were excited in the FBG by coupling between the forward-propagating guided core mode of the multimode fiber and the backward-propagating guided cladding mode of the FBG without any damage to the fiber structure or any change to the standard FBG manufacturing process. The full width at half maximum and the Q-factor of the typical cladding mode resonance operation of the proposed sensor are 80 pm and 19,270, respectively, which are better than those of most fiber-optic biosensors reported to date. In addition, the FBG sensor demonstrated a high sensitivity in protein detection and a high selectivity in serum sample assays. The sensitivity of this sensor was further increased simply by coating it with graphene oxide (GO) sheets on the sensing surface without using a signal amplification strategy. Furthermore, an ultra-low limit of detection (LOD) of 32 pM was obtained by the GO-coated FBG sensor for IgG detection. The proposed FBG sensor provides a competitive fiber-optic platform for biomolecular detection. It has a great potential for applications in label-free biosensing.

Side-Opening Grapefruit Fiber-Based SPR Sensor for Simultaneous Measurement of Refractive Index and Temperature

A novel side-opening grapefruit fiber-based SPR sensor is designed to realize simultaneous measurement of refractive index (RI) and temperature. The open section of the grapefruit fiber is coated with a gold layer, which can support two main resonance peaks. The variations of RI and temperature can influence the coupling efficiency between core-guided mode and plasmon mode, thus lead to the two peaks shifts that can be used to determine the variations of RI and temperature. Simulation results demonstrate that the RI coefficients of Peak I and Peak II are 1400 nm/RIU and 226 nm/RIU, respectively. The temperature coefficients of Peak I and Peak II are 34 pm/°C and 527.2 pm/°C, respectively.

Micro-Channel Plasmon Sensor Based on a D-Shaped Photonic Crystal Fiber for Malaria Diagnosis With Improved Performance

In this paper, a D-shaped photonic crystal fiber (PCF) sensor based on surface plasmon resonance with a micro-rectangular opening is proposed. The micro-rectangular opening introduces strong coupling between the metal layer and the core-guided mode as it helps in reducing the distance between the sensing channel and the core of the PCF. Gold (Au) is a noble plasmonic material, which is deposited on the micro-rectangular opening in order to generate an ample amount of surface plasmon on the micro-opening area’s surface. This micro opening also allows for the ease of fabrication while maintaining strong bio-detection capabilities. The obtained results as maximum wavelength sensitivity, resolution, and figure of merit are 67,000 nm/RIU, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${1.5} \times {10}^{-{6}}$ </tex-math></inline-formula> RIU and 279.16 RIU <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula> respectively. These results indicate that they are significantly finer than those existing in the related state of the art, and that the proposed fiber sensor is easy to fabricate. Further, the proposed fiber sensor is utilized for the detection of malaria disease. The proposed sensor’s computed sensitivities for ring stage, trophozoite stage, and schizont stage RBCs of malaria disease are 25,715.30 nm/RIU, 33,157.89 nm/RIU, and 44,827.58 nm/RIU, respectively.

Sensitivity-Tunable Temperature SPR Sensor Based on Side-Opening Grapefruit Fiber With Liquid Mixture

We demonstrate a sensitivity-tunable temperature SPR sensor based on side-opening grapefruit fiber. The opening sections of the fiber are coated with gold layer and then filled with a liquid mixture of ethanol and chloroform as the sensing medium. The variation of the temperature will lead to different coupling efficiencies between the core-guided mode and the plasmonic mode, and then resulting in the change of loss spectra of the fiber that will be detected. Simulation results indicate that the temperature sensitivity of the sensor is 19.9 nm/°C at 10°C when the volume fraction of ethanol in the mixture is 0.1. Moreover, by adjusting the volume fraction, the sensitivity of proposed sensor can achieve the upper limit for a certain temperature range without the excitation of higher order plasmonic modes.

Understanding the impact of cladding modes in multi-mode hollow-core anti-resonant fibres

Multi-moded, anti-resonant hollow-core fibre shows great promise for a range of applications from high power laser delivery to novel, non-linear experiments. Anti-resonant fibers typically guide multiple transverse modes due to their large core size, albeit with often large differential modal loss. Understanding the behaviour of higher order modes in these fibres is of crucial importance if we are to exploit the benefits of hollow-core optical guidance in few- and multi-moded applications, or to design more robustly single mode fibres. In this work we conduct thorough numerical investigations into the origins of confinement loss in tubular anti-resonant fibres and its dependence on the fibre’s key structural parameters.We show that away from the resonances in the glass, leakage loss can be interpreted as originating from resonant out-coupling between the core modes of interest and the lossy modes of the cladding tubes, and is highest when these are phase-matched. Using this insight, we show that the loss can be estimated a posteriori from knowledge of the fields of the core-guided and cladding tube modes and their propagation constants. Such a quantitative estimate is satisfactory by considering only the three lowest mode groups of the cladding tube. This deeper understanding paves the way to a more informed approach to designing few and multi-moded hollow-core fibers for various applications.

A Highly Versatile Porous Core Photonic Quasicrystal Fiber Based Refractive Index Terahertz Sensor.

Miniaturized real-time fiber optic sensing systems with high sensing performance are in extreme demand. In this work, we propose a novel photonic quasicrystal fiber sensor in the terahertz region and test its sensing characteristics using the finite element method. The proposed simulated sensor numerically investigates the cancer-infected cells from the normal cells in the human cervix, blood, adrenal glands, and breast based on the difference in their refractive index changes. The effective refractive index of core-guided mode is due to the interaction of light between the refractive index of the fiber material and infiltrated normal and cancer cells, respectively. The proposed sensor exhibits a high birefringence of 0.03, a low dispersion of 0.35 ps/THz/cm, along with a high numerical aperture of 0.99. Besides, the sensor holds a less-effective material loss of 2.53 × 10 (dB/cm), a maximum power fraction of 88.10, a maximum relative sensitivity of 82.67%, and an effective mode area of 3.16 mm. The results envisage that the proposed sensor displays high sensing performances with a rapid cancer detection mechanism.

Line Position-Dependent Effect in Line-by-Line Inscribed Fiber Bragg Gratings.

Line-by-line direct writing by femtosecond laser has been proved to be a simple and effective method for the fabrication of low-loss fiber Bragg gratings (FBGs), and is more flexible compared with the traditional ultraviolet exposure method. In this paper, the line-position-dependent characteristics of cladding modes coupling in line-by-line FBGs have been studied, to the best of our knowledge, for the first time. Both theoretical and experimental results show that off-center inscribing could compress the bandwidth of the Bragg resonance and excite more abundant cladding mode coupling, in which the core-guided fundamental mode would couple to the cladding-guided LP0n and LP1n simultaneously. By aligning the line positions across the core region, the first apodized line-by-line FBG was achieved. This work enriches the theories of line-by-line FBGs and provides an inscription guidance to meet different application requirements.

Long-range surface plasmon resonance sensor based on side-polished D-shaped hexagonal structure photonic crystal fiber with the buffer layer of magnesium fluoride

In this paper, we demonstrate a long-range surface plasmon resonance (LRSPR) sensor based on D-shaped hexagonal structure photonic crystal fiber (PCF) with buffer layer of magnesium fluoride (MgF2). The theoretical analysis is first introduced to reveal surface plasmon polariton (SPP) mode excitation by the y-polarized core-guided mode. The influences exerted by different thicknesses of Au film and MgF2 buffer layer are theoretically investigated with the full vectorial finite element method for optimizing structure parameters. A novel status of electric field boundary (SEFB) technique is proposed to analyze the reciprocal sensing performance of symmetric LRSPR (sLRSPR) sensor. Theoretical simulation reveals that the LRSPR with PCF/MgF2 (100 nm)/Au (50 nm) architecture exhibits the significant performance and has an intensity sensitivity improvement of 160.13% compared with conventional SPR (cSPR) sensor. With the simulation providing the theoretical basis, a proof-of-concept experiment is performed with the D-shaped PCF fabricated by a wheel polishing system. The experimental results show good agreement with the theoretical calculations, and both of them consistently indicate that the LRSPR-based sensor has an improved intensity sensitivity (−490.625% RIU−1) and an increased penetration depth. Furthermore, focusing on the sensing principle, the proposed SEFB method can be applied in the analysis of other types of multilayer SPR sensor. The optimal LRSPR sensor with improved detection accuracy shows great promise for applications in the field of biochemical measurement.

Preparation of tapered photonic crystal fiber material to employ the evanescent wave for sensing applications

Optical fibre tapers have recently been intensively studied for a variety of applications, including telecommunications, medical, and biochemical sensing. In this research, we fabricate photonic crystal fiber taper without collapsing air holes and describe how steering air-cladding increases the evanescent-field sensitivity of microstructure fibres. The enhancement of the microstructure fibre's performance is based on the decrease of the diameter of the fiber core to a minimal width by tapering, where a specified part power of light is directed by an evanescent field passing through the air holes in the axial cladding. The initial structure of the fiber with outer diameter of 5 μm was reduced (100, 80,60) um for improving the very limited. The guided core mode and axial air holes have a high intensity overlap at 1.55 m wavelength.Some simulation results have been achieved by using the COMSOL multiphysics program. It used to design the photonic crystal fiber large-mode area and with different taper waist diameter and find mode intensity distributions guiding of 1550 nm inside the optical crystal fiber.

Novel Bloch wave excitation platform based on few-layer photonic crystal deposited on D-shaped optical fiber

With the goal of ultimate control over the light propagation, photonic crystals currently represent the primary building blocks for novel nanophotonic devices. Bloch surface waves (BSWs) in periodic dielectric multilayer structures with a surface defect is a well-known phenomenon, which implies new opportunities for controlling the light propagation and has many applications in the physical and biological science. However, most of the reported structures based on BSWs require depositing a large number of alternating layers or exploiting a large refractive index (RI) contrast between the materials constituting the multilayer structure, thereby increasing the complexity and costs of manufacturing. The combination of fiber–optic-based platforms with nanotechnology is opening the opportunity for the development of high-performance photonic devices that enhance the light-matter interaction in a strong way compared to other optical platforms. Here, we report a BSW-supporting platform that uses geometrically modified commercial optical fibers such as D-shaped optical fibers, where a few-layer structure is deposited on its flat surface using metal oxides with a moderate difference in RI. In this novel fiber optic platform, BSWs are excited through the evanescent field of the core-guided fundamental mode, which indicates that the structure proposed here can be used as a sensing probe, along with other intrinsic properties of fiber optic sensors, as lightness, multiplexing capacity and easiness of integration in an optical network. As a demonstration, fiber optic BSW excitation is shown to be suitable for measuring RI variations. The designed structure is easy to manufacture and could be adapted to a wide range of applications in the fields of telecommunications, environment, health, and material characterization.

High amplitude sensitivity gold‐coated trichannel photonic crystal fibre for refractive index sensor

We propose highly sensitive trichannel photonic crystal fibre (TCPCF) refractive index (RI) sensor based surface plasmon resonance (SPR). In this design, we have been integrated the sensing layer with thin gold metal deposited over the surface of the TCPCF for fabrication feasible and easy liquid infiltration. Then, Y-shaped channel is formed through reducing the diametre of air holes for controlling the direction of light through photonic crystal fibre to attain high sensitivity. Also, effective coupling between surface plasmon polariton mode at the metal layer and the core-guided mode is obtained by numerical simulation of finite element method. The optimized TCPCF sensor exhibits maximum amplitude sensitivity of 1938.5 RIU−1 and wavelength sensitivity of 11,000 nm.RIU−1 within the analyte range from 1.34 to 1.39. Further, we have achieved amplitude resolution of 5.2 × 10−6 RIU and wavelength resolution of 9.1 × 10−6 RIU. It is confirmed high detection accuracy for small changes in RI analyte. Moreover, high figure of merit of 623.9 RIU−1 is obtained for the proposed sensor. Therefore, the proposed TCPCF RI sensor can be utilized in the chemical, bio and gas sensing applications.

Plasmonic micro-channel based highly sensitive biosensor in visible to mid-IR

A strong light coupling between core-guided mode and metal layer leads to the enhancement of plasmonic sensor performance significantly. In this work, a plasmonic metal coated micro-channel based surface plasmon resonance sensor is proposed where a micro-channel is introduced to increase the mode coupling by reducing the distance between the core and analyte channel. Gold (Au) is considered to coat the micro-channel and generate surface plasmon on the fiber surface. Titanium dioxide (TiO2) is employed to stick the Au layer tightly with the silica which assists in shifting the sensing wavelength from visible to mid-IR region. The light-guiding and bio-sensing properties of the proposed D-shaped sensor performance is numerically investigated by employing the finite element method. The sensor obtained maximal wavelength and amplitude sensitivities of 1,21,000 nm/Refractive index unit (RIU) and 1,405 RIU−1, respectively in the x-polarized mode. Moreover, the sensor exhibits an extremely high resolution of 8.26 × 10−7 RIU and the limit of detection (LOD) is 6.83 × 10−12 RIU2/nm, respectively, in the wavelength interrogation technique. To the best of our knowledge, the proposed sensor shows the highest wavelength sensitivity, resolution and LOD when compared to the existing PCF based SPR sensors. Due to the extremely sensitive response, the proposed sensor will enhance the unknown analyte detection capability significantly. Furthermore, the broad sensing range of analyte refractive index (RI) variation from 1.33 to 1.44 makes the sensor suitable for biochemical as well as medical diagnostic applications.

Simulation design of silver nanoparticle coated photonic crystal fiber sensor based on surface plasmon resonance

Surface Plasmon Resonance (SPR) is the charge density excitation oscillation (surface Plasmon’s, (SP)) caused by the polarized light along with the metal-dielectric interface by agreeing to phase-matching condition between polarized light and SPR. SPR method has unusual advantages like label-free, real-time and high resolutions with less than 10-7 RIU which is not consenting with other sensing methods. Photonic Crystal Fiber (PCF) presents unique features like design elasticity, geometric flexible and extraordinary guiding mechanism which head for better performance contrast conventional optical fibre, Additionally, the presence of air holes gives the possibility to insert multi able materials, that can recognize the interaction of travelling light and materials operatively. Adding the advantages of PCF to the properties of SPR, lead to design very strong and unique devices in different applications. In this paper, the PCF sensor based on SPR technique had been presented. The inner holes of PCF were coated with silver and then filled with air and ethanol. This was achieved theoretically by Finite Element Method (FEM). When the phase-matching condition was achieved at a fixed wavelength, the energy of the core-guided mode is shifted to the plasmon area and a resonant loss peak is observed at this wavelength. The simulated results show that a blue shifting is obtained when the outer air holes of PCF is filling with ethanol while the inner ring is filled with silver nano-particles. The maximum resolution and sensitivity are 5.66*10-4 RIU, 132.3 nm/RIU respectively in the sensing range of air refractive index to ethanol refractive index are obtained. The submitted design could be very useful in many fields like refractive index and temperature sensing applications.

Building-up and suppression of cladding mode coupling in fiber Bragg gratings

The building-up and suppression of cladding-mode coupling in UV exposure fiber Bragg gratings (FBGs) is investigated experimentally and theoretically. Experimental results reveal that fundamental mode can simultaneously couple to cladding modes from different groups in the un-tilted FBGs as the transmission spectrum takes on multilevel. Theoretical results indicate that due to the non-uniform refractive index profile on the transverse plane of the FBGs, core-guided fundamental mode not only couples to axis-symmetrical cladding modes LP0n, but also transfers to circular-symmetrical cladding modes like LP1n if they distribute in the core region. Based on the symmetry property of the coupled cladding modes, the ‘ring-by-ring’ inscription is theoretically proposed to suppress the cladding mode coupling for the first time, which plays a significant role in high-power fiber lasers research and application.

Analysis of a Single Solid Core Flat Fiber Plasmonic Refractive Index Sensor

In this article, a single solid core flat fiber (SSCFF) refractive index sensor based on surface plasmon resonance (SPR) is proposed and analyzed numerically using the finite element method (FEM). The proposed flat fiber consists of a single array of five circular holes. Among them the central hole is made of GeO2-doped silica which is forming the core. Other holes are filled with air and situated symmetrically on both sides of the central solid core. The upper flat surface of the fiber is coated with a thin plasmonic gold layer which is protected by an active titanium dioxide layers. Analyte is situated on top of these layers. The wavelength interrogation technique is applied to study the coupling characteristics between the core-guided mode and the surface plasmon mode as well as for the refractive index measurement. Numerical analysis results show that this sensor is able to detect high refractive index analytes from 1.49 to 1.54 with a good linear response. Additionally, the dependence of surface plasmonic resonance wavelength on analyte refractive index is studied. The maximum wavelength sensitivity of this sensor is found to be 4782 nm/RIU with a high resolution of 2.09 × 10−5 RIU. The effects of different structural parameters on loss spectrum are studied in detail to optimize this SSCFF structure. In comparison to traditional PCF, this SSCFF structure is fabrication complexity free as well as a suitable candidate for developing portable devices and high refractive index analyte sensors, particularly chemical and protein sensors.