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Fringe pattern based measurement techniques are the state-of-the-art in full-field optical metrology. They are crucial both in macroscale, e.g., fringe projection profilometry, and microscale, e.g., label-free quantitative phase microscopy. Accurate estimation of the local fringe orientation map can significantly facilitate the measurement process in various ways, e.g., fringe filtering (denoising), fringe pattern boundary padding, fringe skeletoning (contouring/following/tracking), local fringe spatial frequency (fringe period) estimation, and fringe pattern phase demodulation. Considering all of that, the accurate, robust, and preferably automatic estimation of local fringe orientation map is of high importance. In this paper we propose a novel numerical solution for local fringe orientation map estimation based on convolutional neural network and deep learning called DeepOrientation. Numerical simulations and experimental results corroborate the effectiveness of the proposed DeepOrientation comparing it with a representative of the classical approach to orientation estimation called combined plane fitting/gradient method. The example proving the effectiveness of DeepOrientation in fringe pattern analysis, which we present in this paper, is the application of DeepOrientation for guiding the phase demodulation process in Hilbert spiral transform. In particular, living HeLa cells quantitative phase imaging outcomes verify the method as an important asset in label-free microscopy.

Gold-coated tilted fiber Bragg gratings (TFBG) are refined plasmonic biosensors, highly sensitive to surrounding refractive index (RI) changes. Their interrogation usually relies on insertion loss measurements for single input polarized light, limiting the set of exploitable features. To overcome this limitation, we trigger the Jones formalism to retrieve the polarization enabling optimized plasmonic excitation for both phase and amplitude measurements. We present an experimental phase shift with a sensitivity as high as 45835°/RIU and further assess this approach to HER2 proteins sensing at 1µg/ml. We compare this angular modality with the one relying on the insertion loss using a quality factor that takes the shift as well as the dispersion into account. This strengthens its relevance in terms of precision for ultra-small RI variations.

A high-sensitivity surface plasmon resonance (SPR) sensor based on the coupling of Au grating and Au film is investigated through simulations and experiments. The SPR sensor is designed by using a hybrid method composed of genetic algorithm (GA) and rigorous coupled wave analysis (RCWA). The numerical results indicate the sensor has an angular sensitivity of 397.3°/RIU (refractive index unit), which is approximately 2.81 times higher than the conventional Au-based sensor and it is verified by experiments. Theoretical analysis, by finite-difference time-domain (FDTD) method, demonstrates the co-coupling between surface plasmon polaritons (SPPs) propagating on the surface of Au film and localized surface plasmons (LSPs) in the Au grating nanostructure, improving the sensitivity of the SPR sensor. According to the optimized structural parameters, the proposed sensor is fabricated using e-beam lithography and magnetron sputtering. In addition, the proposed sensor is very sensitive to the detection of small molecules. The limit of detection (LOD) for okadaic acid (OA) is 0.72 ng/mL based on an indirect competitive inhibition method, which is approximately 38 times lower than the conventional Au sensor. Such a high-sensitivity SPR biosensor has potential in the applications of immunoassays and clinical diagnosis.

We propose an optical-fibre metal-insulator-metal (MIM) plasmonic sensor based on the Fano resonances of surface plasmon polaritons (SPPs). Its structure consists of a coupling fibre that connects C-shaped and rectangular cavities and a main fibre that contains a semi-circular resonator. When incident light passes through the main fibre, it excites SPPs along the interface between the metal and medium. The SPPs at the resonator induce Fano resonances, owing to the coupling effect. The results show that the designed optical-fibre MIM plasmonic sensor could flexibly tune the number of Fano resonances by adjusting the structure and geometric parameters to optimise the sensing performance. The full width at half maximum of the Lorentzian resonance spectra formed by the electric and magnetic fields reached 23 nm and 24 nm, respectively. The wavelength of the Fano resonance shifted as the refractive index changed; thus, the proposed sensor could realise the application of sensing and detection. The highest sensitivity achieved by the sensor was 1770 nm/RIU. Finally, we simulated the designed sensor to human blood-glucose-level detection, and observed that the resonance wavelength would increase with the increase of glucose concentration. Our study shows that optical fibres have broad application prospects in the field of electromagnetic switching and sensing.

Terahertz (THz) metamaterials for rapid label-free sensing show application potential for the detection of cancer biomarkers. A novel flexible THz metamaterial biosensor based on a low refraction index parylene-C substrate is proposed. The biomarkers are modified on non-metal areas by a three-step modification method that simplifies the modification steps and improves the modified effectivity. Simulation results for non-metal modification illustrate that a bulk refractive index sensitivity of 325 GHz/RIU is achieved, which is larger than that obtained for the traditional metal modification (147 GHz/RIU). Meanwhile, several fluorescence experiments proved the uniform modification effect and selective adsorption capacity of the non-metal modification method. The concentration of the carcinoembryonic antigen (CEA) biomarkers for breast cancer patients tested using this THz biosensor is found to be consistent with results obtained from traditional clinical tests. The limit of detection reaches 2.97 ng/mL. These findings demonstrate that the flexible THz metamaterial biosensor can be extensively used for the rapid detection of cancer biomarkers in the future.

Refractive index (RI) sensing plays an important role in analytical chemistry, medical diagnosis, and environmental monitoring. The optofluidic technique is considered to be an ideal tool for RI sensor configuration for its high integration, high sensitivity, and low cost. However, it remains challenging to achieve RI measurement in real time with high sensitivity and low detection limit (DL) simultaneously. In this work, we design and fabricate a RI sensor with an arched optofluidic waveguide by monitoring the power loss of the light passing through the waveguide, which is sandwiched by the air-cladding and the liquid-cladding under test, we achieve RI detection of the sample in real time and with high sensitivity. Furthermore, both numerical simulation and experimental investigation show that our RI sensor can be designed with different geometric parameters to cover multiple RI ranges with high sensitivities for different applications. Experimental results illustrate that our sensor is capable to achieve a superior sensitivity better than −19.2 mW/RIU and a detection limit of 5.21×10−8 RIU in a wide linear dynamic range from 1.333 to 1.392, providing a promising solution for real-time and high-sensitivity RI sensing.

The presence of species other than the target biomolecules in the fluidic analyte used in the refractive index biosensor based on the surface plasmon resonances (SPRs) can lead to measurement ambiguity. Using graphene-based acousto-plasmonic biosensors, we propose two methods to eliminate any possible ambiguity in interpreting the measured results. First, we take advantage of the dynamic tunability of graphene SPRs in the acousto-plasmonic biosensor with a surface acoustic wave (SAW) induced uniform grating, performing measurements at different applied voltages. Second, a single measurement employing a similar biosensor but with SAW-induced dual-segment gratings. The numerical results show the capability of both methods in decoupling the effect of the target analyte from the other species in the fluid, enabling interpreting the measurement results with no ambiguity. We also report the results of our numerical investigation on the effect of measuring parameters like the target layer effective refractive index and thickness, and the fluid effective refractive index, in addition to the controlling parameters of the proposed acousto-plasmonic biosensor, including graphene Fermi energy and electrical signaling on the sensing characteristics. Both types of proposed biosensors show promising features for developing the next generation lab-on-a-chip biosensors with minimal cross-sensitivities to non-target biomolecules.

In this research work, an anisotropic photonic crystal fiber (PCF) biosensor working on a refractive index (RI) variation and based on surface plasmon resonance (SPR) is presented. Liquid analytes (LA) having a RI within the range of 1.340 to 1.380 RIU are investigated from the proposed biosensor. Spectroscopy analysis of LA having RI values of 1.340 RIU, 1.360 RIU, and 1.380 RIU is performed from the developed sensing setup for modeling an ultrasensitive biosensor. The numerical analysis of the sensing parameters for the proposed sensor presents a maximum wavelength sensitivity (WS) of 20000 nm/RIU for x- polarization (x − pol.) and 18000 nm/RIU for y- polarization (y − pol.), respectively, using the wavelength interrogation technique. Maximum amplitude sensitivity (AS) of 2158 RIU−1 and 3167 RIU−1 is obtained for x − pol. and y − pol., respectively, using the amplitude interrogation technique. Maximum sensor resolution (SR) of 5.00 × 10−6 RIU and 5.55 × 10−6 RIU is obtained for x − pol. and y − pol., respectively. The linear relationship of the resonant wavelength (RW) with the RI produces R2 = 0.9972 and R2 = 0.9978, corresponding to a degree (2) for x − pol. and y − pol., respectively. The figure of merit (FOM) for x − pol. and y − pol. are 93.45 RIU−1 and 105.88 RIU−1, respectively. The sensing parameters have obtained the maximum value for the LA having a RI value of 1.375 RIU.

Multiple parameters need to be monitored to analyze the kinetics of biological progresses. Surface plasmon polariton resonance sensors offer a non-invasive approach to continuously detect the local change of refractive index of molecules with high sensitivity. However, the fabrication of miniaturized, compact, and low-cost sensors is still challenging. In this paper, we propose and demonstrate a grating-coupled SPR sensor platform featuring dual mode operation for simultaneous sensing of pressure and refractive index, which can be fabricated using a highly-efficient low-cost method, allowing large-scale production. Both sensing functionalities are realized by optical means via monitoring the spectral positions of a surface plasmon polariton mode (for refractive index sensing) and Fabry-Perot or metal-insulator-metal modes (for pressure sensing), which are supported by the structure. Simultaneous measurement of refractive index with the sensitivity of 494 nm/RIU and pressure was demonstrated experimentally. The proposed platform is promising for biomonitoring that requires both high refractive index sensitivity and local pressure detection.

Optical aberrations affect the quality of light propagating through a turbid medium, where refractive index is spatially inhomogeneous. In multiphoton optical applications, such as two-photon excitation fluorescence imaging and optogenetics, aberrations non-linearly impair the efficiency of excitation. We demonstrate a sensorless adaptive optics technique to compensate aberrations in holograms projected into turbid media. We use a spatial light modulator to project custom three dimensional holographic patterns and to correct for local (anisoplanatic) distortions. The method is tested on both synthetic and biological samples to counteract aberrations arising respectively from misalignment of the optical system and from samples inhomogeneities. In both cases the anisoplanatic correction improves the intensity of the stimulation pattern at least two-fold.

In this paper, a novel refractometer based on Mach-Zehnder Interferometer (MZI) is proposed and experimentally investigated. The MZI is composed of 2 micro bending cores (MBCs), one of which excites the cladding modes and the other couples the modes back. This structure is formed by high-frequency CO2 laser polishing and oxyhydrogen flame heating. With the unique deformation method, the interaction between the fiber core and the external status gets enhanced, moreover, higher modes in the cladding are excited, which leads to a high refractive index (RI) sensitivity. Due to the high temperature of the oxyhydrogen flame, the core of CO2 polished fiber is modulated, furthermore, the cladding shape of MBC tends to be circular. Hence, relatively small modulating regions of 500 μm can form for interference. In the experiment, 2 transmission dips are chosen for RI measuring, which possesses the wavelength of 1530.4 nm and 1600.8 nm, respectively. The RI sensitivities of the 2 transmission dips are -271.7 nm/RIU and -333.8 nm/RIU with the RI range of 1.33-1.42. The temperature characteristic is also experimentally analyzed and the temperature sensitivities of which are 0.121 nm/℃ and 0.171 nm/℃ in the range of 34℃-154℃. By solving the matrix equation, the proposed sensor can be applied for simultaneous measurement of RI and temperature.

Infrared refractive index is an indispensable parameter for various fields including infrared photonics. To date, critical-angle refractometers, V-block refractometers, and spectroscopic ellipsometry have been commonly used to measure the refractive index. Although every method has an accuracy of four decimal places for the refractive index, a measurable wavelength region is limited up to about 2 µm. In this study, we demonstrated a metamaterial infrared refractometer for determining broadband complex refractive index. Using the device, a broadband (40–120 THz; wavelength 2.5–7.5 µm) and high-precision(< 5 ×10−3) complex refractive index of polymethyl methacrylate was measured for the first time.

Optical biosensor, which perceptively captures the variety of refractive index (RI) of the surrounding environment, has great potential applications in detecting property changes and types of analytes. However, the disequilibrium of light-matter interaction in different polarizations lead to the polarization-dependence and low sensitivity. Here, we propose a polarization-independent and ultrasensitive biosensor by introducing a one-dimensional topological photonic crystal (1D TPhC), where two N-period 1D photonic crystals (PhC1 and PhC2) with different topological invariants are designed for compressing the interaction region of the optical fields, and enhancing the interaction between the light and analyte. Since the strong light-matter interaction caused by the band-inversion is polarization-independent, the biosensor can obtain superior sensing performance both for TE and TM polarization modes. The sensitivity and Figure of Merit (FOM) of the designed biosensor are 1.5677×106 RIU−1 (1.3497 × 106 RIU−1) and 7.8387×1010 RIU−1deg−1 (4.4990×1010 RIU−1deg−1) for TM (TE) polarization mode, which performs two orders of magnitude enhancement compared with the reported biosensors. With the protection of the topological edge state, this biosensor has high tolerance to the thickness deviations and refractive index (RI) variations of the component materials, which can reduce the requirements on fabrication and working environment. It is anticipated that the proposed biosensor possesses excellent sensing performances, may have great potentials in environmental monitoring, medical detection, etc.

We demonstrated the design of two different structures, a two-sided structure and a top-surface structure, of glucose waveguide Bragg grating (WBG) sensors in a single-mode silicon-on-insulator (SOI) chip. A two-sided WBG structure was fabricated, and chip preparation was realized by lithography and other processes. A photonic platform for testing the two-sided WBG using glucose was built and completed. When the blood glucose concentration changed by 1 mg/mL, the two-sided WBG had a wavelength offset of 78 pm. The experimental results show that the two structures can achieve the sensing of different blood glucose concentrations. The two-sided WBG had better sensing performance and thus has a wide range of application prospects.

We propose a novel intensity diffraction tomography (IDT) reconstruction algorithm based on the split-step non-paraxial (SSNP) model for recovering the 3D refractive index (RI) distribution of multiple-scattering biological samples. High-quality IDT reconstruction requires high-angle illumination to encode both low- and high- spatial frequency information of the 3D biological sample. We show that our SSNP model can more accurately compute multiple scattering from high-angle illumination compared to paraxial approximation-based multiple-scattering models. We apply this SSNP model to both sequential and multiplexed IDT techniques. We develop a unified reconstruction algorithm for both IDT modalities that is highly computationally efficient and is implemented by a modular automatic differentiation framework. We demonstrate the capability of our reconstruction algorithm on both weakly scattering buccal epithelial cells and strongly scattering live C. elegans worms and live C. elegans embryos.

A flexible terahertz (THz) metamaterial biosensor is theoretically and experimentally investigated. The metamaterial unit cell of the periodic structure array was simply composed of three non-overlapping cut wires with different length parameters on a flexible thin-film (parylene-C) to improve sensitivity. The biosensor sample was fabricated using a lithography process and characterized by a THz time-domain spectroscopy (TDS) system. The metamaterial exhibited multi-resonance dips in transmission spectrum at 0.6-2.0 THz, which can self-correct errors in biosensing. Numerical results show that the Q-factor, figure of merit (FOM) and sensitivity can change in dynamic ranges with the geometric parameters (space and width) of three-cut-wire metamaterial. When space distance was 40 µm and other parameters were default, the sensitivity, FOM and Q-factor reached 710 GHz/RIU (Refractive Index Unit), 9, and 20, respectively. Therefore, through proper design and preparation, the metamaterial can be applied to biochemical detection.

In light transmission microscopy, axial scanning does not directly provide tomographic reconstruction of specimen. Phase deconvolution microscopy can convert a raw intensity image stack into a refractive index tomogram, the intrinsic sample contrast which can be exploited for quantitative morphological analysis. However, this technique is limited by reconstruction artifacts due to unoptimized optical conditions, which leads to a sparse and non-uniform optical transfer function. Here, we propose an optimization method based on simulated annealing to systematically obtain optimal illumination schemes that enable artifact-free deconvolution. The proposed method showed precise tomographic reconstruction of unlabeled biological samples.

Novel laser light sources in the mid-infrared region enable new spectroscopy schemes beyond classical absorption spectroscopy. Herein, we introduce a refractive index sensor based on a Mach-Zehnder interferometer and an external-cavity quantum cascade laser that allows rapid acquisition of high-resolution spectra of liquid-phase samples, sensitive to relative refractive index changes down to 10

A multi-diffractive nanostructure is reported for the resonant excitation of surface plasmons that are cross-coupled through a thin metallic film. It consists of two superimposed periodic corrugations that allow diffraction excitation of surface plasmons on the inner side of a thin metal film and their subsequent phase matching with counterpropagating surface plasmons travelling to the opposite direction on its other side. This interaction leads to establishing of a set of cross-coupled Bragg-scattered surface plasmon modes that exhibit an electromagnetic field localized on both metal film interfaces. The reported structure is attractive for surface plasmon resonance biosensor applications, where direct optical probing can be done through the substrate without the need of optical matching to a high refractive index prism. In addition, it can be prepared by mass production – compatible means with UV-nanoimprint lithography and its biosensing performance characteristics are demonstrated by refractometric and biomolecular affinity binding studies.

Optofluidic microlenses are one of the crucial components in many miniature lab-on-chip systems. However, many optofluidic microlenses are fabricated through complex micromachining and tuned by high-precision actuators. We propose a kind of tunable optofluidic microbubble lens that is made by the fuse-and-blow method with a fiber fusion splicer. The optical focusing properties of the microlens can be tuned by changing the refractive index of the liquid inside. The focal spot size is 2.8 µm and the focal length is 13.7 µm, which are better than those of other tunable optofluidic microlenses. The imaging capability of the optofluidic microbubble lens is demonstrated under a resolution test target and the imaging resolution can reach 1 µm. The results indicate that the optofluidic microbubble lens possesses good focusing properties and imaging capability for many applications, such as cell counting, optical trapping, spatial light coupling, beam shaping and imaging.

The rapid and sensitive detection of plant-growth-regulator (PGR) residue is essential for ensuring food safety for consumers. However, there are many disadvantages in current approaches to detecting PGR residue. In this paper, we demonstrate a highly sensitive PGR detection method by using terahertz time-domain spectroscopy combined with metamaterials. We propose a double formant metamaterial resonator based on a split-ring structure with titanium-gold nanostructure. The metamaterial resonator is a split-ring structure composed of a titanium-gold nanostructure based on polyimide film as the substrate. Also, terahertz spectral response and electric field distribution of metamaterials under different analyte thickness and refractive index were investigated. The simulation results showed that the theoretical sensitivity of resonance peak 1 and peak 2 of the refractive index sensor based on our designed metamaterial resonator approaches 780 and 720 gigahertz per refractive index unit (GHz/RIU), respectively. In experiments, a rapid solution analysis platform based on the double formant metamaterial resonator was set up and PGR residues in aqueous solution were directly and rapidly detected through terahertz time-domain spectroscopy. The results showed that metamaterials can successfully detect butylhydrazine and N-N diglycine at a concentration as low as 0.05 mg/L. This study paves a new way for sensitive, rapid, low-cost detection of PGRs. It also means that the double formant metamaterial resonator has significant potential for other applications in terahertz sensing.

Total internal reflection fluorescence (TIRF) microscopy is an important imaging tool for the investigation of biological structures, especially the study on cellular events near the plasma membrane. Imaging at cryogenic temperatures not only enables observing structures in a near-native and fixed state but also suppresses irreversible photo-bleaching rates, resulting in increased photo-stability of fluorophores. Traditional TIRF microscopes produce an evanescent field based on high numerical aperture immersion objective lenses with high magnification, which results in a limited field of view and is incompatible with cryogenic conditions. Here, we present a waveguide-based TIRF microscope, which is able to generate a uniform evanescent field using high refractive index waveguides on photonic chips and to obtain cellular observation at cryogenic temperatures. Our method provides an inexpensive way to achieve total-internal-reflection fluorescence imaging under cryogenic conditions.

We developed two versions of refractometers to measure the refractive index of liquids. One refractometer comprises a glass cell with a surface relief grating on the inner face of one of its walls, while the other one is a microfluidic channel in the form of serpentine that behaves as a grating. Measurements of the liquid refractive index were performed by sensing the first order intensity. Several liquids have been used including an organic one. Calibration plots are shown.

Among five nucleobases, adenine (A), guanine (G), cytosine (C), thymine (T) and uracil (U), uracil is a key distinctive constituent existing only in ribonucleic acid (RNA). RNA shares the common A, G, and C with deoxyribonucleic acid (DNA) made of A-T, G-C hydrogen bonding. We explored a new attempt to combine uracil (U) with DNA, successfully realizing U-doped DNA thin solid films for the first time. Impacts of uracil on optical properties of the films were thoroughly investigated. The method was based on optimal spin-coating of an aqueous solution of DNA and uracil over silicon or silica substrates. Optical absorption of both aqueous solution and U-doped DNA thin solid films was characterized in a wide spectral range covering UV-visible-IR. Immobilization of uracil within DNA thin solid films was experimentally confirmed by FTIR spectroscopy studies. By using an ellipsometer, we measured the refractive indices of the films and discovered that U-doping was a very effective means to control optical dispersion DNA thin solid film. We further investigated thermo-optic behavior to find impacts of U-doping in DNA films. Detailed thin film processes and optical characterizations are discussed.

In this paper, a gas refractometer based on microfiber Sagnac interferometer is demonstrated, which can achieve an ultrahigh sensitivity when operating at the group birefringence turning point. We undertake a theoretical analysis and a simulated calculation to study the device characteristics and obtain the specific parameters of ellipticity and long axis of the elliptic microfiber for the group birefringence turning point. In the experiment, we obtain a positive sensitivity of 0.295 nm/KPa and a negative sensitivity of −0.219 nm/KPa during gas pressure and refractive index (RI) sensing, the obtained highest RI sensitivity can reach 160,938.9 nm/RIU. To further reveal its practical potential in gas detection, we conduct CO2 gas concentration detection and the device also demonstrates ultrahigh sensitivity and good repeatability. Besides, temperature sensing is performed to explore its temperature response wherein it shows a sensitivity of 486.7 pm/ °C. These results show its potential for use in gas- and acoustic-sensing applications.

At present, researchers are exploring biological tissue detection method using terahertz techniques. In this paper, techniques to inspect mouse liver injury by using terahertz spectroscopy were studied. The boxplots were applied to remove abnormal data, and the maximal information coefficient was employed to select crucial features from the absorption coefficient and refractive index spectra. Random Forests and AdaBoost were applied to recognize different levels of liver injury. We found that AdaBoost had better performance on low-level injury classification. This work suggests that terahertz techniques have the potential to detect liver injury at an early stage and evaluate liver treatment strategies.

A biosensor based on electromagnetically induced transparent (EIT) metamaterials (MMs) is proposed owing to the low loss and high Q-factor. The theoretical sensitivity of the biosensor based on EIT-like MMs were evaluated up to 248.8 GHz/RIU (RIU, Refractive Index Unit). In experiments, the cancer cells A549, as an analyte, are cultured on EIT-like MMs surface. The results show that when the cell concentration increases from 0.5 × 105 to 5 × 105 cells/ml, the frequency shift Δf could change from 24 to 50 GHz. Moreover, the coupled oscillators model is applied to explain the effect of the refractive index of analyte in simulations and the cell concentration in experiments on the EIT-like MMs. The fitting results exhibit that the refractive index of analyte and cell concentration significantly affect the radiative damping of the bright mode resonator γ1. The proposed EIT-like MMs biosensors show great potentials for cell measurement because any change that results in the lineshape variation in EIT-like MMs can only be attributed to the change of external dielectric environment due to the suppression of radiative losses.

Concentrations down to 3 nM of the rhS100A4 protein, associated with human tumor development, have been detected in undiluted urine using an integrated sensor based on microring resonators in the emerging Al

A novel biosensor based on a two-dimensional gradient (TDG) guided-mode resonance (GMR) filter was introduced in this study. The TDG-GMR is demarcated in terms of the gradient grating period (GGP) in one dimension and gradient waveguide thickness (GWT) in the other dimension. A single compact sensor can combine these two features to simultaneously provide a broad detection range through GGP and high resolution through GWT. A detection range of 0.109 RIU (0%–60% sucrose content) with a limit of detection of 5.62 × 10−4 was demonstrated in this study by using a TDG-GMR with a size of 140.8 × 125.4 µm2. This value cannot be achieved using one dimensional gradient GMR sensor. Label-free (LF) biomolecule detection through TDG-GMR was also experimentally demonstrated in a model assay of albumin. The result confirms that the GWT-GMR provides a better resolution, whereas the GGP-GMR provides a broader detection range. A device for multiplex measurement could be easily implemented with a compact sensor chip and a simple readout directly from a charge-coupled device. This system would require a narrow-band source such as a light emitting diode or a laser diode, in addition to a limited number of other components such as a polarizer and a collimator. The proposed TDG-GMR could easily be integrated with smartphones and portable devices.

In this study, we present first-time fabrication of FBGs in all ZEONEX-based SMPOFs with a single 25 ns pulse of 248 nm UV irradiation over a 12-month period, which opens up new frontiers in optics and photonics for the effective fabrication of polymer optical fiber Bragg gratings (POFBGs), permitting mass producibility of them. POFBGs were characterized by subjecting them to various physical parameters including temperature and tensile strain. Strain responses of FBGs with similar grating strengths fabricated with 248 nm and 325 nm He-Cd laser irradiations were explored over a year to demonstrate their long-term stability and applicability. Owing to the unique features of the proposed sensing device fabricated by embedding POFBGs in silicone rubber, a good performance in the detection of human heart rate with an amplitude of 4 pm, which is 4 times higher compared to that of silica single mode fiber (SMF) was demonstrated. The response of the sensing device during a human respiration process was also explored where exhalation and inhalation were monitored and distinguished while the breath was held. These revelations signify the importance of ZEONEX-based POFBGs, which allow consistent and effective grating fabrication and are highly promising in the foreseeable future for biomedical applications.

Refractometry is a ubiquitous technique for process control and substance identification in the chemical and biomedical fields. Herein, we present an all-dielectric, wafer-scalable, and compact Fabry-Pérot microcavity (FPMC) device for refractive index (RI) sensing. The FPMC consists of a highly porous SiO2 microcavity capped with a thin, quasi-periodically patterned TiO2 hole array partial reflector that enables rapid, nanoliter-scale analyte transport to and from the sensor. Liquid (alcohols) or condensed-vapor (water from human breath) infiltration resulted in spectral redshifts up to 100 nm, highly apparent visible color change, rapid recovery (< 20 s), and RI sensitivity of up to 680 nm/RIU. The sensor can also be used in spectral or single-wavelength detection modes. Effective-medium and finite-difference time-domain optical simulations identified that Fano-resonant scattering modes induced by the quasi-periodic TiO2 outcoupling layer effectively filter higher-order Fabry-Pérot cavity modes and thereby confer an easily identifiable red-to-green color transition during analyte infiltration.

The structures of flexodomains, which are similar to optical gratings and can be controlled by the amplitude of applied voltage and temperature, were verified through polarizing microscopy and light diffraction techniques. The properties of the optical grating induced by a bent-core nematic liquid crystal in planar cells with varied cell gaps and pretilt angles were studied. The period of optical grating decreases with the increase in the amplitude of the applied voltage and pretilt angle. In addition, the period increases with the increase in cell gap and temperature. The period of optical grating has a linear relationship with temperature. The continuously adjustable period has the potential to become an important and extended application of optical grating.