Refractive Index Change Research Articles

Unique thermal characteristics of polarization-insensitive metalenses over traditional refractive and diffractive lenses

The thermal characteristics of lenses play an essential role in the performance of optical systems, particularly infrared detection systems. Metalenses, composed of sub-wavelength nanostructured surfaces, have recently emerged as a promising technology to realize flat, lightweight, and mass-producible lenses. However, their thermal behavior remains largely unexplored. This study examines the impact of uniform temperature variations (both theoretically and experimentally) and laser heating (theoretically) on the performance of polarization-insensitive metalens (PIM) at a representative wavelength of 10.6 µm. We compare the thermal performance of PIMs with refractive and diffractive lenses, by a comprehensive structural, thermal, and optical performance (STOP) analysis through finite-element analysis (FEA) and finite-difference-time-domain (FDTD) simulations. A comprehensive analysis of various thermal aberration indicators reveals that the PIM exhibits smaller thermal aberrations than both the aspheric lens and the harmonic diffractive lens, and its performance is closer to that of a traditional diffractive optical element (DOE). We also find that the unique nanostructures of PIM make it highly sensitive to the refractive index change induced by temperature variations, allowing the PIM to achieve unique capabilities compared to other lenses. A typical example is that the PIM consistently demonstrates an opposite shift in focal length and depth of focus, contrary to conventional cases. We also experimentally verify the near-athermal properties of 5-centimeter-aperture metalens, confirming the advantages of large-aperture PIMs over refractive lenses in athermal infrared imaging applications. Additionally, our numerical analysis demonstrates that the broadband achromatic metalens notably outperforms the DOE in simultaneously achromatic (8 to 12 µm) and athermal (-60 to 80°C) performance. It is reasonable to speculate that the thermal diffraction efficiency of the achromatic metalens is likely superior to that of the achromatic multi-level diffractive lens (MDL). Our results confirm the strong potential of metalenses in athermal imaging applications.

FBG-Based UV-Curing Kinetics Analysis by Exothermic Behavior

Since photo-induced polymerization of the ultra-violet (UV)-curing adhesive from a fluid state to a solid state is an exothermic process, the UV curing exothermic behavior can be regarded as a potential evaluation methodology to analyze UV-curing kinetics. Herein, a fiber Bragg grating (FBG)-based UV curing exothermic behavior monitoring is proposed to evaluate the UV-curing dynamic process and analyze a series of thermal and mechanical properties changes during curing. The exothermic behavior of the UV curing adhesive during curing and the feasibility of FBG-based curing kinetic analysis scheme are verified experimentally, full cycle cure monitoring of the UV curing adhesive can be realized by this FBG-based curing kinetic analysis scheme, and the UV-curing kinetics of four different types of the UV curing adhesive are corresponding to different exothermic behaviors. Compared with curing process evaluation based on refractive index variation, this FBG-based exothermic behavior monitoring has the ability to extract more details of the curing process, and some curing stages with negligible refractive index changes also can be distinguished. By using this proposed scheme, the UV-curing dynamic process and multiple characteristic parameters, such as curing time, time constant, transient temperature rise, and residual stress, can be evaluated, which may contribute to evaluating and analyzing UV-curing kinetics more comprehensively.

Designing a terahertz optical sensor based on helically twisted photonic crystal fiber for toxic gas sensing

A novel helically twisted photonic crystal fiber (PCF) is designed and proposed for sensing toxic gases with refractive indices ranging from 1.00 to 1.08. The PCF consists of twelve hollow pipes arranged circularly around the hollow core to support THz radiation propagation. Low-loss polymer Topas is used as the background material of cladding. The fiber is twisted 360° over 50 cm to enhance anti-resonance in the THz region. The fundamental LP01 mode is analyzed using the finite-difference eigenmode (FDE) method. The sensor operates across four frequency bands (0.2 to 3.0 THz) with minimal transmission loss (~ 10⁻⁴ 1/cm). Key parameters such as refractive index sensitivity, relative sensitivity, resolution, and figure of merit (FOM) are evaluated. The average refractive index sensitivities are 1450, 2250, 3000, and 2550 for Bands 1 to 4, respectively, with 100% relative sensitivity across all bands. The sensor detects refractive index changes as small as 10⁻⁴. The FOM, defined as the inverse of the full width at half maximum, exceeds 30 1/RIU, reaching up to 250 1/RIU due to sharp resonance peaks. Compared to other THz sensors, this design offers enhanced performance in sensing gases like SOx, NOx, and CO, while maintaining a simple structure.

Optical properties of polyvinyl alcohol-glass waste powder composites

This study investigates the effect of glass waste powder content on the UV–Vis spectroscopy of polyvinyl alcohol (PVA). The glass powder was obtained from the waste of fluorescent tubes. The solution casting method was utilized to prepare PVA- glass composite films by adding glass powder with 10, 20, 30, and 40 wt. %. UV–Vis absorption spectra of PVA- glass samples were recorded in the range 220–1100 nm. The optical parameters were calculated as follow: absorbance, absorption coefficient, transmittance, refractive index, extinction coefficient, dielectric constant, and imaginary dielectric constant. Based on the XRD results, it is revealed that the PVA become more amorphous with increasing amount of glass waste. UV–Vis spectroscopy studies demonstrated that, for all samples, the absorbance, absorption coefficient, extinction coefficient, and Ei increases with the increase in the amount of glass waste. On the other hand, transmittance decreases with increasing amount of glass waste. The change of the studied properties with wavelength depends strongly on the amount of glass waste powder. At visible region, the transmittance is stable with increasing wavelength for samples containing 20, 30 and 40%. Glass waste, while the pure sample and the sample containing 10% glass waste, the transmittance increases with the wavelength. On the other hand, the absorbance and absorption coefficient for all samples decreases rapidly up to a specific wavelength and then the change is very slight at longer wavelengths. Also, the increase of extinction coefficient and imaginary dielectric constant with wavelength is related to the amount of glass powder added. The change of dielectric constant and refractive index with wavelength depends on the amount of the filler, where the pure and the sample filled with 10% glass powder show normal dispersion, while the other samples show anomalous dispersion. Finally, the pure sample had the highest energy gap (5.7 eV) while the sample containing 30% glass powder had the lowest value (4.8 eV). Through this study, it become possible to change the optical properties of PVA by adding glass waste powder, which allows the possibility of benefiting from the new composites to be used in different applications according to their response to different wavelengths. From an economic and environmental point of view, these wastes can be utilized instead of being thrown away by reusing them as polymer fillers, taking into consideration the change in the optical properties of the matrix polymer.

Lasing in a femtosecond-laser-written single-scan waveguide fabricated in Tm-doped BGG glass.

We report lasing action in a femtosecond-laser-inscribed waveguide in thulium-doped barium-gallium-germanium oxide (BGG) glass. A laser cavity was assembled with this waveguide that provided a single-mode output of 62 mW when pumped at 1.6 µm. The waveguide was fabricated using a single laser scan to create a near-circular cross section with a positive refractive index change of approximately 3.5 × 10-3. Analysis of the laser-modified region was performed using electron-probe microanalysis and Raman spectroscopy. These findings establish BGG glass as a promising platform for the fabrication of mid-infrared integrated photonic devices.

3D printing fiber-tip integrated Fabry-Perot interferometers for ultrasensitive RI sensing with an enhanced Vernier effect.

An ultrasensitive refractive index (RI) sensing technology based on an enhanced Vernier effect is proposed, which integrates a polymer Fabry-Perot interferometer (FPI) with an open cavity FPI on the tip of a seven-core optical fiber. Interference spectra of the polymer FPI and the open cavity FPI shift to opposite directions as the ambient RI changes, thus leading to the enhanced Vernier effect. Investigations of RI sensitivity and temperature dependence of the proposed fiber sensors are carried out. Taking advantage of the enhanced Vernier effect, we demonstrate a remarkable sensitivity of 19742.86 nm/RIU within the RI range from 1.39 to 1.395. The sensor exhibits substantial advantages such as ease of fabrication, compact structure, high sensitivity, and good repeatability, providing a practical and competitive solution for RI sensing.

Multiplexed Bio‐detection on an Interferometric Optical Waveguide Assembly

AbstractMultiplexed remote bio‐detection is demonstrated through an optical waveguide assembly coated with interferometric layers. Image conduits (IC)s, composed of 3012 individual cores, are coated with interferometric layers of tantalum pentoxide (Ta2O5) and silica (SiO2) to transform each core into a sensitive sensor. The spectral response of the IC as a function of refractive index (RI) changes is obtained and compared with the simulated one. The experimental sensitivities and resolutions of individual cores of the waveguide are assessed in remote detection mode by imaging through the optical assembly. For 75% of the cores, a sensitivity better than 510%. RIU−1 (RI Unit) is obtained, corresponding to a resolution better than 7 × 10−4 RIU. Furthermore, the coated face of IC is functionalized with two localized arrays of hundred‐micrometer droplets containing two different oligonucleotide (ODN) probes using a polymeric 3D‐printed microcantilever. Hybridization of complementary ODN strands is detected for one of the probes, the second being a negative control. Interaction kinetics are monitored in functionalized areas by grouping several cores or on individual cores. Thus, multiplexed bio‐detection on the surface of an interferometric waveguide is demonstrated for the first time paving the way for applications in multiplex in situ biosensing, and, ultimately, in vivo endoscopic diagnosis.

Frequency locked whispering evanescent resonator (FLOWER) for biochemical sensing applications.

Sensitive, rapid and label-free biochemical sensors are needed for many applications. In this protocol, we describe biochemical detection using FLOWER (frequency locked optical whispering evanescent resonator)-a technique that we have used to detect single protein molecules in aqueous solution as well as exosomes, ribosomes and low part-per-trillion concentrations of volatile organic compounds. Whispering gallery mode microtoroid resonators confine light for extended time periods (hundreds of nanoseconds). When light circulates within the resonator, a portion of the electromagnetic field extends beyond the cavity, forming an evanescent field. This field interacts with bound analytes resulting in a change in the cavity's effective refractive index, which can be tracked by monitoring shifts in the resonance wavelength. The surface of the microtoroid can be functionalized to respond specifically to an analyte or biochemical interaction of interest. The frequency-locking feature of frequency locked optical whispering evanescent resonator means that the instruments respond to perturbations in the surface by very rapidly finding the new resonant frequency. Here we describe microtoroid fabrication (4-6 h), how to couple light into these devices using tapered optical fibers (20-40 min) and procedures for coupling antibodies as well as G-protein coupled receptors to the microtoroid's surface (from 1 h to 1 d depending on the target analyte). In addition, we describe our liquid handling perfusion system as well as the use of a rotary selector valve and custom fluidic chamber to optimize sample delivery. Step-by-step details on how to perform biosensing experiments and analyze the data are described; this takes 1-2 d.

Toward Resolving Heterogeneous Mixtures of Nanocarriers in Drug Delivery Systems through Light Scattering and Machine Learning.

Nanocarriers (NCs) have emerged as a revolutionary approach in targeted drug delivery, promising to enhance drug efficacy and reduce toxicity through precise targeting and controlled release mechanisms. Despite their potential, the clinical adoption of NCs is hindered by challenges in their physicochemical characterization, essential for ensuring drug safety, efficacy, and quality control. Traditional characterization methods, such as dynamic light scattering and nanoparticle tracking analysis, offer limited insights, primarily focusing on particle size and concentration, while techniques like high-performance liquid chromatography and mass spectrometry are hampered by extensive sample preparation, high costs, and potential sample degradation. Addressing these limitations, this work presents a cost-effective methodology leveraging light scattering and optical forces, combined with machine learning algorithms, to characterize polydisperse nanoparticle mixtures, including lipid-based NCs. We prove that our approach provides quantification of the relative concentration of complex nanoparticle suspensions by detecting changes in refractive index and polydispersity without extensive sample preparation or destruction, offering a high-throughput solution for NC characterization in drug delivery systems. Experimental validation demonstrates the method's efficacy in characterizing commercially available synthetic nanoparticles and Doxoves, a liposomal formulation of Doxorubicin used in cancer treatment, marking a significant advancement toward reliable, noninvasive characterization techniques that can accelerate the clinical translation of nanocarrier-based therapeutics.

SPR Biosensor Based on Bilayer MoS2 for SARS-CoV-2 Sensing.

The COVID-19 pandemic has highlighted the urgent need for rapid, sensitive, and reliable diagnostic tools for detecting SARS-CoV-2. In this study, we developed and optimized a surface plasmon resonance (SPR) biosensor incorporating advanced materials to enhance its sensitivity and specificity. Key parameters, including the thickness of the silver layer, silicon nitride dielectric layer, molybdenum disulfide (MoS2) layers, and ssDNA recognition layer, were systematically optimized to achieve the best balance between sensitivity, resolution, and attenuation. The optimized configuration, consisting of a 45 nm silver layer, a 13 nm silicon nitride layer, 2 MoS2 layers, and a 5 nm ssDNA layer, demonstrated superior performance for detecting SARS-CoV-2 in PBS solution. The biosensor exhibited high sensitivity at low viral concentrations, achieving a sensitivity of 375.01°/RIU, a detection accuracy of 0.002, and a quality factor of 38.34 at 1.0 mM SARS-CoV-2 concentration. Performance metrics validated the sensor's capability for reliable detection, particularly in early-stage diagnostics where timely intervention is critical. Moreover, the biosensor's linear response to refractive index changes confirmed its potential for quantitative viral concentration analysis. This study underlines the significance of integrating advanced materials, such as MoS2 and silicon nitride, to enhance SPR biosensor performance. The findings establish the proposed biosensor as a robust and precise diagnostic tool for SARS-CoV-2 detection, with potential applications in clinical diagnostics and epidemiological monitoring.

Fiber Optic Micro-Hole Salinity Sensor Based on Femtosecond Laser Processing.

This study presents a novel reflective fiber Fabry-Perot (F-P) salinity sensor. The sensor employs a femtosecond laser to fabricate an open liquid cavity, facilitating the unobstructed ingress and egress of the liquid, thereby enabling the direct involvement of the liquid in light transmission. Variations in the refractive index of the liquid induce corresponding changes in the effective refractive index of the optical path, which subsequently influences the output spectrum. The dimensions and quality of the optical fiber are meticulously regulated through a combination of femtosecond laser cutting and chemical polishing, significantly enhancing the mechanical strength and sensitivity of the sensor's overall structure. Experimental results indicate that the sensor achieves salinity sensitivity of 0.288 nm/% within a salinity range of 0% to 25%. Furthermore, the temperature sensitivity is measured at a minimal 0.015 nm/°C, allowing us to neglect temperature effects. The device is characterized by its compact size, straightforward structure, high mechanical robustness, ease of production, and excellent reproducibility. It demonstrates considerable potential for sensing applications in the domains of biomedicine and chemical engineering.

Innovative MIM diplexer with neural network enhanced refractive index detection for advanced photonic applications

This study introduces a high-performance 4-channel Metal-Insulator-Metal (MIM) diplexer, employing silver and Teflon, optimized for advanced photonic applications. The proposed diplexer, configured with two novel band-pass filters (BPFs), operates across four distinct wavelength bands (843 nm, 1090 nm, 1452 nm, 1675 nm) by precisely manipulating the passband dimensions. Utilizing Finite-Difference Time-Domain (FDTD) simulations, the designed diplexer achieves exceptional sensitivity values of 3500 nm/RIU, 4250 nm/RIU, 3375 nm/RIU, and 4003 nm/RIU, along with high figures of merit (FOM) ranging from 113.4 to 124.7 1/RIU. Also, the compact design (400 nm × 830 nm) underscores its suitability for integrated photonic circuits and advanced sensing applications. Furthermore, to further enhance accuracy in detecting refractive index (RI) changes, a multilayer perceptron (MLP) neural network was employed, ensuring the highest sensor accuracy. The accuracy of the MIM diplexer’s RI measurements was statistically validated through a one-sample t-test, confirming the sensor’s reliability. Comparative analysis with existing sensors highlights the diplexer’s superior sensitivity and efficiency, setting a new benchmark in optical communication and photonic sensing technologies. This work paves the way for future advancements in miniaturized, high-sensitivity optical devices, offering robust solutions for next-generation communication and sensing systems.

Gold Ring and Graphite-Based Plasmonic Photonic Crystal Sensor for Biomedical Applications

Introduction: This research puts forward a cost-efficient high-efficiency plasmonic photonic crystal sensor for biomedical applications that functions in the near-infrared range. Method: The sensor design is composed of multiple two-dimensional photonic crystal layers stacked in the order of SiO2 foundational layer, graphite layer, MgF2 waveguide, and finally a gold ring over the top. The graphite layer is deposited for optimum sensing and high absorption peaks and is state-of-the-art in this research work. Metal deposition of the gold layer is used for harnessing plasmonic properties that play a vital role in detecting small refractive index changes. Result: The sensor design is investigated for a range of coupling incident angles and it is found that the sensor is responsive to a broad range of angles i.e., 0o to 80o. The proposed sensor has given output peak values of more than 90% in the whole range of incident source angles. Conclusion: Finally, water and 25% concentration of glucose samples are used for investigating sensor performance and it is noted that the sensor’s sensitivity reaches as high as 1675 nm/RIU-1 with a Figure of Merit (FOM) of 20.94 RIU-1. The sensor’s numerical simulations have been performed using Finite Element Method (FEM) and Finite Difference Time Domain (FDTD).

Unveiling with Density Functional Theory the Optical Property Variations of Three Kinds of Graphene for Acetaminophen Sensor Design.

Understanding the interactions between molecules and sensing elements is crucial to improving sensors. We present one step toward getting closer to the breach between theory and empirical sensor development. Through density functional theory (DFT) calculations, we explored the changes in some optical properties of pristine graphene (G), graphene oxide (GO), and reduced graphene oxide (rGO) interacting with one molecule of acetaminophen (APAP). The main goal is to unveil which graphene-G, GO, and rGO-works better as a substrate to detect APAP for sensor applications based on UV/vis and near-infrared absorption, refractive index changes, and plasmon resonances. For this effort, we used Quantum ESPRESSO software. We calculated each supercell's adsorption energy and recovery time containing the APAP and one graphene variant. Afterward, we calculated the optical absorption, refractive index, reflectivity, and electron energy loss spectroscopy (EELS), a technique to identify the material's plasmons. Then, we analyzed the changeovers in the optical properties mentioned for each graphene layer with and without APAP. We found that G works for UV/vis and plasmon sensors operating in blue and UV-C regions; GO has the highest performance range in UV/vis and plasmonic sensors operating in UV-C; rGO has the highest performance range in UV/vis sensors working on near-infrared and UV-C. Additionally, rGO plasmonic sensors present an "oscillation of percentage variations" from visible to UV. Our study offers a strategy for creating a map to select the best substrate to develop selective APAP optical sensors.

Fractional Solitons in Optical Twin-Core Couplers with Kerr Law Nonlinearity and Local M-Derivative Using Modified Extended Mapping Method

This study focuses on optical twin-core couplers, which facilitate light transmission between two closely aligned optical fibers. These couplers operate based on the principle of coupling, allowing signals in one core to interact with those in the other. The Kerr effect, which describes how a material’s refractive index changes in response to the intensity of light, induces the nonlinear behavior essential for generating solitons—self-sustaining wave packets that preserve their shape and speed. In our research, we employ fractional derivatives to investigate how fractional-order variations influence wave propagation and soliton dynamics. By utilizing the modified extended mapping method (MEMM), we derive solitary wave solutions for the equations governing the behavior of optical twin-core couplers under Kerr nonlinearity. This methodology produces novel fractional traveling wave solutions, including dark, bright, singular, and combined bright–dark solitons, as well as hyperbolic, Jacobi elliptic function (JEF), periodic, and singular periodic solutions. To enhance understanding, we present physical interpretations through contour plots and include both 2D and 3D graphical representations of the results.

Measurement of refractive index in liquid mixtures using interferometry

The main parameters that govern the changes in the speed of light when interacting with matter are polarizability and electronic density. The first relates to the ability of a group of atoms to deform under the action of an electromagnetic field, while the second is directly linked to the mass of the substance. If a beam of reference light and another that is incident in the medium whit molecular variation are superimposed, they will be producing a pattern of interference fringes by the phase shift. In this paper we report the results obtained in the measurement of the change in refractive index of liquids substances using patterns of interference fringes. To check the applicability of the technique, two mixtures of different liquid substances were used in the experiment. Water and gasoline were used as solvents and ethanol and gasoline additive were used as solutes, each at different percentages. The results suggest that it is feasible to analyze the variation of the concentration, density and change of refractive index of a substance, through the direct relationship between the molecular changes of the substance analyzed and the phase difference.

High-resolution, high-speed, chromotropic color printing based on fs-laser-induced gold/graphene HSFLs

Through achieving high-spatial-frequency laser-induced periodic surface structures (HSFLs) on a gold/graphene hybrid film, we introduce a high-speed, high-resolution, and wide-gamut chromotropic color printing technique. This method effectively addresses the trade-off between throughput and resolution in laser coloring. To realize Au HSFL, disordered lattice structures and high transmittance of amorphous Au (a-Au) thin film are used to overcome the rapid hot-electron diffusion and loss of plasmonic coherence typically observed on low-loss metal surfaces, respectively. Coupled with crystallization in Au and modulated surface plasmon polaritons by artificial “seed” pre-structure growing in a SiO2/Si substrate, HSFL emerged with a period of 100 nm on crystalline Au after single and rapid femtosecond laser scanning. This equips the proposed color printing with high-resolution and high-speed features simultaneously. In addition, the crystallization process is demonstrated to initiate change in the complex refractive index of Au, which causes wide-gamut colors. The chromotropic capability, which facilitates the background color to be tailored in color as well as into desirable shapes independently, enables three-level anti-counterfeiting based on the proposed color printing. Therefore, the proposed color printing is amenable for practical implementation in diverse applications, including security marking and data storage, ranging from nanoscale to large-scale fabrication.

Surface plasmon resonance to trace and measure cancer cell apoptosis using morphological and refractive index changes

Morphological changes of cancer cells are often used as an important indicator within efficiency studies of anticancer drugs. Morphological cell analysis on cell size and shape distribution is typically performed using microscopic methods, which are time consuming and require skilled personnel. Recently, more advanced image processing and pattern recognition have enabled identification and quantitative analysis of the cell’s abnormality and classification in an automated way. However, these methods usually involve multiple staining steps. In addition to computational complexity, the processes greatly compromise real-time applications of the system. Therefore, a non-invasive, real-time method allowing for assessment of living cells’ reactions to a death inducer is very much needed. Here, we present an SPR biosensor that measures the changes in cancer cells’ size and detachment, relating the cell confluency with the changes of the refractive index on the cell-substrate interface. As a proof-of-concept, we chose HeLa cell and hydrogen peroxide (H2O2) induced apoptosis as the model system to study the morphological changes of the cell. The results show that the SPR response to cell apoptosis agreed with the cellular morphological changes observed via microscopy. Interestingly, we observed simultaneous apoptosis and necrosis at high H2O2 concentrations. This simultaneous occurrence was verified using a mathematical model which incorporated other important factors such as cell thickness and intercellular refractive index. This model helped resolve the disagreement between SPR signal and cell confluency at high H2O2 concentrations. Our results show the potential of SPR as a label free and real time monitoring method for morphological changes and surface detachment of cancer cells. This method can be fully expanded to other cell-based sensing applications.

Photo-physical mechanism of near-IR femtosecond laser-induced refractive-index change in PMMA

Micromodification in bulk undoped polymethylmethacrylate (PMMA) by single focused (numerical aperture (NA) = 0.25), 1030-nm 250-fs laser pump pulses was explored by pump self-transmittance; optical, 3D-scanning confocal photoluminescence (PL); Raman micro-spectroscopy; and optical polarimetric and interferometric microscopy. Starting from the threshold pulse energy Eth = 0.4 ± 0.1 μJ (peak laser intensity Ith ≈ 8 TW/cm2), visible bright micro-voxels emerged inside PMMA at the 100 ÷ 300-μm depth, with their PL-acquired dimensions increasing versus pulse energy. Optical phase change was interferometrically measured in the voxels at the 532-nm wavelength, exhibiting versus the pulse energy the isotropic refractive index increase Δn = +(4 ÷ 10) × 10−4, and a new 1640-cm−1 peak of C=C vibrations emerged in the Raman spectra. Pump self-transmittance measurements demonstrated the predominating eight-photon absorption (excited energy level ≈ 9.7 eV, coefficient β8 ≈ 3 × 10−5 cm13/TW7) at the sub-threshold I < Ith, implying photoionization of the PMMA chains (the ionization potential of MMA molecule ≈ 9.7 eV). At higher peak intensities I > Ith, inverse brems-strahlung absorption (coefficient ∼103cm−1) of near-critical micro-plasma (density >5 × 1020 cm−3) predominates over the multi-photon PMMA absorption, providing the bulk energy density >6 × 102 J/cm3 and the temperature rise ΔT > 2.2 × 102 K, which are sufficient for PMMA (de)polymerization near the equilibrium bulk temperature TP ≈ 220°C. These results uncover the quantitative mechanism of fs-laser modification of PMMA, justifying the previous qualitative findings and enabling controllable energy deposition during fs-laser PMMA micromachining of diverse functional applications.

INVESTIGATION OF TUBERCULOSIS SENSING USING GRAPHENE COATED METAMATERIAL FIBER

Abstract Detection of tuberculosis (TB) is being showed a greater interest since it affects the
vital human organ (lungs). In this paper, a biosensor based on optical fiber sensing for
detecting TB is proposed. Here, a hollow core fiber protected with a graphene coated
metamaterial (MM) cladding is numerically investigated in the visible region using finite
element method (FEM). The analyte under test (mycobacterium TB affected haemoglobin) is
filled in the core and the change in refractive index is obtained to calculate the sensitivity.
Further, the proposed fiber is optimized by varying graphene thickness and concentration of
MM and investigated in terms of confinement loss, effective area, power confined to the core
and relative sensitivity. The proposed fiber reports an average relative sensitivity of 92.8%
depicting a power confinement of upto 97.7% and numerical aperture of 0.24. Performance
comparison with other designs is carried out in order to project the efficacy of the proposed
sensor. The obtained sensitivity enables the proposed sensor to be a suitable design in
detection of TB and can be employed in medical diagnosis.