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A novel highly sensitive D-shaped photonic crystal fiber-based surface plasmon resonance (PCF-SPR) sensor for dual parameters of refractive index and temperature detecting is proposed. A PCF cladding polishing provides a D-shape design with a gold (Au) film coating for refractive index (RI) sensing (Core 1) and a composite film of silver (Ag) and polydimethylsiloxane (PDMS) for temperature sensing (Core 2). Comsol Multiphysics 5.5 is used to design and simulate the proposed sensor by the finite element method (FEM). The proposed sensor numerically provides results with maximum wavelength sensitivities (WSs) of 51,200 and 56,700 nm/RIU for Core 1 and 2 as RI sensing while amplitude sensitivities are -98.9 and -147.6 RIU-1 with spectral resolution of 1.95 × 10-6 and 1.76 × 10-6 RIU, respectively. Notably, wavelength sensitivity of 17.4 nm/°C is obtained between -20 and -10 °C with resolution of 5.74 × 10-3 °C for Core 2 as temperature sensing. This sensor can efficiently work in the analyte and temperature ranges of 1.33-1.43 RI and -20-100 °C. Due to its high sensitivity and wide detection ranges, both in T and RI sensing, it is a promising candidate for a variety of applications, including chemical, medical, and environmental detection.

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For the polarization multiplexing requirements in all-optical networks, this work presents a compact all-fiber polarization beam splitter (PBS) based on dual-core photonic crystal fiber (PCF) and an elliptical gold layer. Numerical analysis using the finite element method (FEM) demonstrates that the mode modulation effect of the central gold layer effectively reduces the dimensions of the proposed PBS. By determining reasonable structural parameters of the proposed PCF, the coupling length ratio (CLR) between X- and Y-polarized super-modes can approach 2, achieving a minimal device length of 0.122 mm. The PBS exhibits a maximum extinction ratio (ER) of - 65 dB at 1.55 µm, with an operating bandwidth spanning 100 nm (1.5-1.6 µm) and a stable insertion loss (IL) of ~ 1.5 dB at 1.55 µm. Furthermore, the manufacture feasibility and performance verification scheme are also investigated. It is widely anticipated that the designed PBS will play a crucial role in the ongoing development process of miniaturization and integration of photonic devices.

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In order to achieve a high-precision synchronous detection of two different refractive index (RI) analytes, a D-type surface plasmon resonance (SPR) photonic crystal fiber (PCF) RI sensor based on two channels is designed in this paper. The sensor uses a D-shaped planar region of the PCF and a large circular air hole below the core as the sensing channels. Surface plasmon resonance is induced by applying a coating of gold film on the surface. The full-vector finite-element method (FEM) is used to optimize the structural parameters of the optical fiber, and the sensing characteristics are studied, including wavelength sensitivity, RI resolution, full width at half maximum (FWHM), figure of merit (FOM), and signal-to-noise ratio (SNR). The results show that the channel 1 (Ch 1) can achieve RI detection of 1.36-1.39 in the wavelength range of 1500-2600 nm, and the channel 2 (Ch 2) can achieve RI detection of 1.46-1.57 in the wavelength range of 2100-3000 nm. The two sensing channels can detect independently or simultaneously measure two analytes with different RIs. The maximum wavelength sensitivity of the sensor can reach 30,000 nm/RIU in Channel 1 and 9900 nm/RIU in Channel 2. The RI resolutions of the two channels are 3.54 × 10-6 RIU and 10.88 × 10-6 RIU, respectively. Therefore, the sensor realizes dual-channel high- and low-RI synchronous detection in the ultra-long wavelength band from near-infrared to mid-infrared and achieves an ultra-wide RI detection range and ultra-high wavelength sensitivity. The sensor has a wide application prospect in the fields of chemical detection, biomedical sensing, and water environment monitoring.

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In this article, we have presented a new cancer sensor with a square core Photonic Crystal Fiber (PCF) to detect the cancerous tissues of the cervix, breast, and skin. This process is thus streamlined and separated by PCF due to its excellent detection characteristics. All required configurations using the finite element method are developed, and various performances of the model are studied using MATLAB. The results depict a mathematical analysis regarding the effectiveness of the sensor within the frequency range of 1.0-2.8 THz. Its relative sensitivity becomes around 99.85% at 2.2 THz with 8.49 × 10-14 dB/m for CL. This PCF has a spot size 3.06 × 10-4 µm that further contributes an effective area of 9.078 × 10-8 m2. Moreover, it has a very small EML of 0.00182 cm-1. This device uses the unique photonic properties of cancer cells to provide quick, reliable, and really very accurate methods for cancer cell identification, such as in breast, cervical, and skin cancers. Due to small size and flexibility, only minimally invasive operations are possible. Real-time monitoring can also be provided, hence improving immediate evaluation and therapy efficacy. This article introduces a novel integration of PCF technology with THz radiation to create a highly sensitive sensor for early cancer detection. By utilizing THz waves' non-invasive and high-resolution properties, this sensor overcomes the sensitivity limitations of traditional methods. It also addresses scattering issues from conventional air hole shapes through optimized geometric configurations, setting a new standard in biomedical sensing and potentially revolutionizing early cancer diagnostics.

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In today's medical research, breast cancer is a severe problem, so it is imperative to develop a reliable and efficient approach for identifying cancerous breast cells. PCF, with its exceptional sense-making abilities, simplifies and distinguishes that procedure. The research presents a unique structural hybrid PCF for detecting breast cancer cells using sensors based on PCF that are specifically built for the terahertz-frequency range. The improvement in sensor sensitivity and specificity in identifying cancer cells at these frequencies is a notable progress compared to conventional approaches, which could potentially result in earlier and more precise diagnosis. In our analysis, we discovered the most common malignancies in breast cancer. We investigate the features of the cancerous cell detector using the COMSOL-Multiphysics 5.6 software. This PCF detector achieves a Confinement Loss of 4.75 × 10-12 and 3.42 × 10-13 dB/m for Type-1 and Type-2 cancer cells, respectively, at 1.2 THz, as well as about 99.946% and 99.969% relative sensitivity. This sensor ensures the highest level of sensitivity for the identification of cancerous breast cells. This sensor's physical architecture is quite straightforward, making it simple to build using current manufacturing techniques. Therefore, it seems that this sensor will pave a new path for identifying and treating cancerous cells.

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The advent of nanotechnology has motivated a revolution in the development of miniaturized sensors. Such sensors can be used for radiation detection, temperature sensing, radio-frequency sensing, strain sensing, and more. At the nanoscale, integrating the materials of interest into sensing platforms can be a common issue. One promising platform is photonic crystal fibers, which can draw in optically sensitive nanoparticles or have its optical properties changed by specialized nanomaterials. However, testing these sensors at scale is limited by the the need for specialized equipment to integrate these photonic crystal fibers into optical fiber systems. Having a method to enable rapid prototyping of new nanoparticle-based sensors in photonic crystal fibers would open up the field to a wider range of laboratories that could not have initially studied these materials in such a way before. This manuscript discusses the improved processes for cleaving, drawing, and rapidly integrating nanoparticle-based photonic crystal fibers into optical system setups. The method proposed in this manuscript achieved the following innovations: cleaving at a quality needed for nanoparticle integration could be done more reliably (≈100% acceptable cleaving yield versus ≈50% conventionally), nanoparticles could be drawn at scale through photonic crystal fibers in a safe manner (a method to draw multiple photonic crystal fibers at scale versus one fiber at a time), and the new photonic crystal fiber mount was able to be finely adjusted when increasing the optical coupling before inserting it into an optical system (before, expensive fusion splicing was the only other method).

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In order to rapidly identify various species of cancer cells in the tissues of person, a unique diamond shaped hollow-core photonic crystal fiber (PCF)-formed by optical waveform is developed and computationally studied. In this investigation, we found the most prevalent cancers, such as HeLa-derived cervical carcinoma. Since normal and cancer cells differ in their refractive indices (RIs), other significant optical properties can be assessed using this information. With the use of the finite element method, a computational tool for solving simultaneous equations, the defining characteristics the suggested cancer cell sensor are examined using COMSOL-Multiphysics software. Additionally, strict mesh parts are used to preserve the utmost level of modeling realism. At 2.4 THz, the PCF detector attains a Relative Sensitivity of around 97.51% and 96.29%, Confinement Loss of 6.1 × 10 -09db/m and 4.39 × 10-07db/m with respect to cervical carcinoma cell and cervical normal cell. The straightforward PCF structure provides a wide chance of application using the continuing fabrication technique, based on these conventional values of performance indices. This biosensor utilizes the distinctive refractive characteristics of cancer cells, providing a highly accurate and dependable approach for the early identification of cervical cancer. This has the potential to significantly transform the process of cervical cancer screening. The novel method boosts the ability to detect and identify certain conditions, leading to increased diagnostic capabilities for early treatment and better results for patients.

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We propose a single material microstructured optical fiber with more than five octave spanning supercontinuum generation. Due to using single material, compatibility checking between core and cladding material need not required. Moreover, the material is such chosen that optical transmission range is quite high in comparison to others. The fiber is designed in COMSOL platform and according to finite element method (FEM), numerical analysis is accomplished. Dispersion, confinement loss, nonlinearity etc. are investigated and exposed for a wavelength range of 2000-3000 nm. The proposed fiber reveals zero dispersion at 2200 nm, nonlinearity of 14,370 W-1km-1 and confinement loss around 10-9 order in dB/m. Finally, supercontinuum generation has been investigated inside the structure and obtained high coherence that span (from 1500 nm to 34,500 nm) over five octave. The generated spectrum fulfills the requirements for being applicable in frequency metrology, fiber laser and biophotonics. With the best of our knowing, such coherent and widened supercontinuua for single material fiber is yet to be proposed.

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Immunosensors capable of ultralow-concentration and single-molecule detection of biomarkers are garnering attention for the early diagnosis of cancer. Herein, a fiber-optic Fabry-Perot interferometer (FPI)-based immunosensor was used for the first time for single-molecule detection of progastrin-releasing peptide (ProGRP). The cascaded FPI structure of the immunosensor introduces a high-order harmonic Vernier effect (HVE). A piece of a side-polished D-shaped hollow-core photonic crystal fiber (HCPCF) was used as a sensing FPI, on which the biomarker was deposited to detect ProGRP. Compared with traditional FPIs with open-cavity structures, this structure provided a larger contact area and improved the sensitivity of the immunosensor. The polished side surface of the D-shaped HCPCF was modified using a gold nanoparticle-graphene oxide (AuNP@GO) nanointerface to enhance refractive index (RI) modulation via antigen-antibody binding and achieve selective energy enhancement of the binding site. The antigen binding changes the RI of the D-shaped HCPCF and the effective RI of the transmitted light in the sensing FPI, thereby changing the spectrum of the immunosensor. Experimental results showed that the high-order HVE and AuNP@GO nanointerface considerably improved the immunosensor sensitivity, exhibiting a liquid RI sensitivity of 583,000 nm/RIU. After functionalization with an anti-ProGRP antibody, the limit of detection of the immunosensor for ProGRP reached 17.1 ag/mL; moreover, the immunosensor could perform detection at the single-molecule level. The proposed novel immunosensor overcomes the sensitivity limitations of optical devices and achieves single-molecule detection of a protein.

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Designing Photonic Crystal Fibers incorporating the Surface Plasmon Resonance Phenomenon (PCF-SPR) has led to numerous interesting applications. This investigation presents an exceptionally responsive surface plasmon resonance sensor, seamlessly integrated into a dual-core photonic crystal fiber, specifically designed for low refractive index (RI) detection. The integration of a plasmonic material, namely silver (Ag), externally deposited on the fiber structure, facilitates real-time monitoring of variations in the refractive index of the surrounding medium. To ensure long-term functionality and prevent oxidation, a thin layer of titanium dioxide (TiO2) covers the silver coating. To optimize the sensor, five key design parameters, including pitch, air hole diameter, and silver thickness, are fine-tuned using the Taguchi L8(25) orthogonal array. The optimal results obtained present spectral and amplitude sensitivities that reach remarkable values of 10,000 nm/RIU and 235,882 RIU-1, respectively. In addition, Artificial Neural Network (ANN) optimization techniques, specifically Multi-Layer Perceptron (MLP) and Particle Swarm Optimization (PSO), are used to predict a critical optical property of the sensor confinement loss (αloss). These predictions are derived from the same input structure parameters that are present in the full L32(25) design experiment. A genetic algorithm (GA) is then applied for optimization with the goal of maximizing the confinement loss. Our results highlight the effectiveness of training PSO artificial neural networks and demonstrate their ability to quickly and accurately predict results for unknown geometric dimensions, demonstrating their significant potential in this innovative context. The proposed sensor design can be used for various applications including pharmaceutical inspection and detection of low refractive index analytes.

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An intensity-demodulated fiber-optic magnetometer is proposed and experimentally investigated, which is fabricated via fusion splicing a segment of photonic crystal fiber (PCF) between single-mode fibers (SMFs), with the cladding air holes of PCF filled with magnetic fluid. Using the magneto-optical properties of the magnetic fluid, the transmission spectrum is changed with an external magnetic field. Based on the intensity variations in the transmission spectrum, the magnetic field is detected, and a sensitivity of 0.238 dB/mT is obtained at 1550.03 nm with the length of PCF 5.5 cm. By converting light signals into electrical signals, a sensitivity of 0.003 V/mT is achieved. The fiber-optic magnetometer possesses the advantages of simple fabrication, compact/robust structure, and low cost.

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Raman enhancement techniques are essential for gas analysis to increase the detection sensitivity of a Raman spectroscopy system. We have developed an efficient Raman enhancement technique called the collision-enhanced Raman scattering (CERS), where the active Raman gas as the analyte is mixed with a buffer gas inside the hollow-core photonic-crystal fiber (HCPCF) of a fiber-enhanced Raman spectroscopy (FERS) system. This results in an enhanced Raman signal from the analyte gas. In this study, we first showed that the intensity of the 587 cm-1 stimulated Raman scattering (SRS) peak of H2 confined in an HCPCF is enhanced by as much as five orders of magnitude by mixing with a buffer gas such as helium or N2. Secondly, we showed that the magnitudes of Raman enhancement depend on the type of buffer gas, with helium being more efficient compared to N2. This makes helium a favorable buffer gas for CERS. Thirdly, we applied CERS for Raman measurements of propene, a metabolically interesting volatile organic compound (VOC) with an association to lung cancer. CERS resulted in a substantial enhancement of propene Raman peaks. In conclusion, the CERS we developed is a simple and efficient Raman-enhancing mechanism for improving gas analysis. It has great potential for application in breath analysis for lung cancer detection.

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We previously developed a hollow-core photonic crystal fiber (HCPCF) based Raman scattering enhancement technique for gas/human breath analysis. It enhances photon-gas molecule interactions significantly but is still based on CW laser excitation spontaneous Raman scattering, which is a low-probability phenomenon. In this work, we explored nanosecond/sub-nanosecond pulsed laser excitation in HCPCF based fiber enhanced Raman spectroscopy (FERS) and successfully induced stimulated Raman scattering (SRS) enhancement. Raman measurements of simple and complex gases were performed using the new system to assess its feasibility for gas analysis. We studied the gas Raman scattering characteristics, the relationship between Raman intensities and pump energies, and the energy threshold for the transition from spontaneous Raman scattering to SRS. H2, CO2, and propene (C3H6) were used as test gases. Our results demonstrated that a single-beam pulsed pump combined with FERS provides an effective Raman enhancement technique for gas analysis. Furthermore, an energy threshold for SRS initiation was experimentally observed. The SRS-capable FERS system, utilizing a single-beam pulsed pump, shows great potential for analyzing complex gases such as propene, which is a volatile organic compound (VOC) gas, serving as a biomarker in human breath for lung cancer and other human diseases. This work contributes to the advancement of gas analysis and opens alternative avenues for exploring novel Raman enhancement techniques.

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A high-sensitivity plasmonic photonic crystal fiber (PCF) sensor is designed and a metal thin film is embedded for achieving surface plasmon resonance (SPR), which can detect the magnetic field and temperature simultaneously. Within the plasmonic PCF sensor, the SPR sensing is accomplished by coating both the upper sensing channel (Ch1) and the lower sensing channel (Ch2) with gold film. In addition, the temperature-sensitive medium polydimethylsiloxane (PDMS) is chosen to fill in Ch1, allowing the sensor to respond to the temperature. The magnetic field-sensitive medium magnetic fluid (MF) is chosen to fill in Ch2, allowing this sensor to respond to the magnetic field. During these processes, this proposed SPR-PCF sensor can achieve dual-parameter sensing. The paper also investigates the electrical field characteristics, structural parameters and sensing performance using COMSOL. Finally, under the magnetic field range of 50-130 Oe, this sensor has magnetic field sensing sensitivities of 0 pm/Oe (Ch1) and 235 pm/Oe (Ch2). In addition, this paper also investigates the response of temperature. Under the temperature range of 20-40 °C, Ch1 and Ch2 have temperature sensitivities of -2000 pm/°C and 0 pm/°C, respectively. It is noteworthy that the two sensing channels respond to only a single physical parameter; this sensing performance is not common in dual-parameter sensing. Due to this sensing performance, it can be found that the magnetic field and temperature can be detected by this designed SPR-PCF sensor simultaneously without founding and calculating a sensing matrix. This sensing performance can solve the cross-sensitivity problem of magnetic field and temperature, thus reducing the measurement error. Since it can sense without a matrix, it further can solve the ill-conditioned matrix and nonlinear change in sensitivity problems in dual-parameter sensing. These excellent sensing capabilities are very important for carrying out multiparameter sensing in complicated environments.

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In this paper, a dual-core photonic crystal fiber (DC-PCF) sensitivity sensor filled with magnetic liquid is introduced and investigated with the finite element method (FEM). To regulate the energy coupling involving the two cores, the magnetic fluid is filled into the pore between the two cores. To adjust the coupling between the supermodes in the DC-PCF, the refractive index (RI) of the air hole filled magnetic fluid may change due to the external magnetic field. This specifically created a magnetic fluid-filled DC-PCF; the magnetic fluid-filled hole is not used as the core for energy transmission, thus avoiding transmission loss. The dip wavelength and the magnetic field displayed an excellent linear connection between 80 and 260 Oe, depending on the numerical data. The detection sensitivity of the magnetic field reached 515.75 pm/Oe at a short fiber length of 482 µm. The designed magnetic fluid-filled DC-PCF has high sensitivity and small volume and has great application prospects in magnetic field detection in the medical and industrial fields.

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In this paper, we propose and design a magnetic field and temperature sensor using a novel petaloid photonic crystal fiber filled with magnetic fluid. The PCF achieves a high birefringence of more than 1.43 × 10-2 at the wavelength of 1550 nm via the design of material parameters, air hole shape and the distribution of the photonic crystal fiber. Further, in order to significantly improve the sensitivity of the sensor, the magnetic-fluid-sensitive material is injected into the pores of the designed photonic crystal fiber. Finally, the sensor adopts a Mach-Zehnder interferometer structure combined with the ultra-high birefringence of the proposed petaloid photonic crystal fiber. Magnetic field and temperature can be simultaneously measured via observing the spectral response of the x-polarization state and y-polarization state. As indicated via simulation analysis, the sensor can realize sensitivities to magnetic fields and temperatures at -1.943 nm/mT and 0.0686 nm/°C in the x-polarization state and -1.421 nm/mT and 0.0914 nm/°C in the y-polarization state. The sensor can realize the measurement of multiple parameters including temperature and magnetic intensity and has the advantage of high sensitivity.

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We propose a surface plasmon resonance (SPR) sensor based on the concave photonic crystal fiber (PCF) coated with molybdenum disulfide (MoS2) and Au layers, which can detect the refractive index (RI) of the analyte. The finite element method (FEM) was used to verify our design, and the loss spectra of the fundamental mode are calculated. Compared with the SPR sensor with only a Au layer, the wavelength sensitivity can be improved by from 3700 to 4400 nm/RIU. Our proposed sensor works in near-infrared band and has a wide RI range from 1.19 to 1.40. The influences of the geometrical parameters of PCF and the thicknesses of Au and MoS2 layers on the loss spectra are discussed in detail, and the maximum wavelength sensitivity of 5100 nm/RIU can be achieved. Meanwhile, a high resolution of 1.96 × 10-5 RIU and the largest FOM of 29.143 can be obtained. It is believed that our findings show the sensor's excellent potential in medical testing, unknown biological detection, environmental monitoring and organic chemical detection.

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In order to detect the refractive index (RI) of high refractive index materials such as trichlorobenzene and aniline in the near-infrared and mid-infrared spectra and expand the detection range of the refractive index, a surface plasmon resonance (SPR) photonic crystal fiber (PCF) sensor based on an elliptical sensing channel is proposed for high refractive index detection. The fiber core and the analyte channel are surrounded by two types of air holes with different sizes. When the surface plasmon resonance effect appears at the interface between the fiber core and the elliptical sensing layer, obvious resonance peaks appear in the near-infrared and mid-infrared bands. The full vector finite element method (FEM) is used to study the sensing characteristics of the sensor and the influence of structural parameters on the resonance peak. The results demonstrate that the sensor achieves detection in the refractive index range of 1.41-1.58, in the wavelength range of 1600-3200 nm. The average wavelength sensitivity is 9217.22 nm/RIU, and the refractive index resolution is 10.85 × 10-6 RIU. The proposed sensor realizes high refractive index detection in the near-infrared and mid-infrared bands, and obtains an ultra-wide detection range and higher sensitivity. The sensor has broad application prospects in chemical detection, biomedical sensing and other fields, and provides a theoretical reference for the design of a photonic crystal fiber surface plasmon resonance sensor.

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This research article proposes and numerically investigates a photonic crystal fiber (PCF) based on a surface plasmon resonance (SPR) sensor for the detecting refractive index (RI) of unknown analytes. The plasmonic material (gold) layer is placed outside of the PCF by removing two air holes from the main structure, and a D-shaped PCF-SPR sensor is formed. The purpose of using a plasmonic material (gold) layer in a PCF structure is to introduce an SPR phenomenon. The structure of the PCF is likely enclosed by the analyte to be detected, and an external sensing system is used to measure changes in the SPR signal. Moreover, a perfectly matched layer (PML) is also placed outside of the PCF to absorb unwanted light signals towards the surface. The numerical investigation of all guiding properties of the PCF-SPR sensor is completed using a fully vectorial-based finite element method (FEM) to achieve the finest sensing performance. The design of the PCF-SPR sensor is completed using COMSOL Multiphysics software, version 1.4.50. According to the simulation results, the proposed PCF-SPR sensor has a maximum wavelength sensitivity of 9000 nm/RIU, an amplitude sensitivity of 3746 RIU-1, a sensor resolution of 1 × 10-5 RIU, and a figure of merit (FOM) of 900 RIU-1 in the x-polarized direction light signal. The miniaturized structure and high sensitivity of the proposed PCF-SPR sensor make it a promising candidate for detecting RI of analytes ranging from 1.28 to 1.42.

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Photonic crystal fiber (PCF) embedded with functional materials has demonstrated diverse applications ranging from ultrafast lasers, optical communication to chemical sensors. Many efforts have been made to fabricating carbon nanotube (CNT) based optical fibers by ex situ transfer method; however, often suffer poor uniformity and coverage. Here, the direct growth of CNTs on the inner walls of PCFs by the chemical vapor deposition (CVD) method is reported. A two-step growth method is developed to control the narrow diameter distribution of CNTs to ensure desirable nanotube optical transitions. In the as-fabricated CNT- embedded fiber, third-harmonic generation (THG) has been enhanced by ≈15 times compared with flat CNT film on fused silica. A dual-wavelength all-fiber mode-locked ultrafast laser (≈1561 and ≈1064 nm) is further demonstrated by integrating the 1.36±0.15 nm-diameter CNTs into two kinds of photonic bandgap hollow core PCF (named HC-1550 and HC-1060) as saturable absorbers, using their S11 (≈0.7 eV) and S22 (≈1.2 eV) interband transition respectively. The fiber laser shows stable output of ≈10 mW, ≈800 fs pulse width, and ≈71 MHz repetition rate at 1561 nm wavelength. These results can enable the large-scale applications of CNTs in PCF-based optical devices.