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Imaging platforms that enable long-term, high-resolution imaging of biofilms are required to study cellular level dynamics within bacterial biofilms. By combining high spatial and temporal resolution and low phototoxicity, lattice light sheet microscopy (LLSM) has made critical contributions to the study of cellular dynamics. However, the power of LLSM has not yet been leveraged for biofilm research because the open-on-top imaging geometry using water-immersion objective lenses is not compatible with living bacterial specimens; bacterial growth on the microscope's objective lenses makes long-term time-lapse imaging impossible and raises considerable safety concerns for microscope users. To make LLSM compatible with pathogenic bacterial specimens, we developed hermetically sealed, but optically accessible, microfluidic flow channels that can sustain bacterial biofilm growth for multiple days under precisely controllable physical and chemical conditions. To generate a liquid- and gas-tight seal, we glued a thin polymer film across a 3D-printed channel, where the top wall had been omitted. We achieved negligible optical aberrations by using polymer films that precisely match the refractive index of water. Bacteria do not adhere to the polymer film itself, so that the polymer window provides unobstructed optical access to the channel interior. Inside the flow channels, biofilms can be grown on arbitrary, even nontransparent, surfaces. By integrating this flow channel with LLSM, we were able to record the growth of S. oneidensis MR-1 biofilms over several days at cellular resolution without any observable phototoxicity or photodamage.

International audience; Evanescent-wave scattering is a topic in classical electrodynamics and in the study of colloidal particles near a boundary. However, how such near-surface scattering at subcellular refractive-index heterogeneities degrades the excitation confinement in biological total internal reflection fluorescence microscopy has not been well studied. An elegant theoretical work by Axelrod and Axelrod now addresses this very relevant question and reveals that-even when scattered-evanescent light preserves some of its surprising optical properties.

Critical angle refractometry is an established technique for determining the refractive index of liquids and solids. For transparent samples, the critical angle refractometry precision is limited by incidence angle resolution. For lossy samples, the precision is also affected by reflectance measurement error. In the present study, it is demonstarted that reflectance error can be practically eliminated, provided that the sample’s extinction coefficient is a priori known with sufficient accuracy (typically, better than 5%) through an independent measurement. Then, critical angle refractometry can be as precise with lossy media as with transparent ones.

Phycobiliproteins are a class of light-harvesting fluorescent proteins existing in cyanobacteria and microalgae, which harvest light and convert it into electricity. Owing to recent demands on environmental-friendly and renewable apparatuses, phycobiliproteins have attracted substantial interest in bioenergy and sustainable devices. However, converting energy from biological materials remains challenging to date. Herein, we report a novel scheme to enhance biological light-harvesting through light-matter interactions at the biointerface of whispering-gallery modes (WGMs), where phycobiliproteins were employed as the active gain material. By exploiting microdroplets as a carrier for light-harvesting biomaterials, strong local electric field enhancement and photon confinement at the cavity interface resulted in significantly enhanced bio-photoelectricity. A threshold-like behavior was discovered in photocurrent enhancement and the WGM modulated fluorescence. Systematic studies of biologically produced photoelectricity and optical mode resonance were carried out to illustrate the impact of the cavity quality factor, structural geometry, and refractive indices. Finally, a biomimetic system was investigated by exploiting cascade energy transfer in phycobiliprotein assembly composed of three light-harvesting proteins. The key findings not only highlight the critical role of optical cavity in light-harvesting but also offer deep insights into light energy coupling in biomaterials. Ministry of Education (MOE) Nanyang Technological University This research is supported by the Ministry of Education Singapore (Tier 1-RG 158/19(S)). We would like to thank Internal Grant NAP SUG -M4082308.040 from NTU.

Refereed/Peer-reviewed A multifunction, high-sensitivity, and temperature-compensated optical fiber DNA hybridization sensor combining surface plasmon resonance (SPR) and Mach–Zehnder interference (MZI) has been designed and implemented. We demonstrate, for the first time to our knowledge, the dual-parameter measurement of temperature and refractive index (RI) by simultaneously using SPR and MZI in a simple single-mode fiber (SMF)–no-core fiber (NCF)–SMF structure. The experimental results show RI sensitivities of 930 and 1899 nm/RIU and temperature sensitivities of 0.4 and −1.4 nm/°C for the MZI and SPR, respectively. We demonstrate a sensitivity matrix used to simultaneously detect both parameters, solving the problem of temperature interference of RI variation-based biosensors. In addition, the sensor can also distinguish biological binding events by detecting the localized RI changes at the fiber’s surface. We realize label-free sensing of DNA hybridization detection by immobilizing probe DNA (pDNA) onto the fiber as the probe to capture complementary DNA (cDNA). The experimental results show that the sensor can qualitatively detect cDNA after temperature compensation, and the limit of detection (LOD) of the sensor reaches 80 nM. The proposed sensor has advantages of high sensitivity, real time, low cost, temperature compensation, and low detection limit and is suitable for in situ monitoring, high-precision sensing of DNA molecules, and other related fields, such as gene diagnosis, kinship judgment, environmental monitoring, and so on.

For biomedical photoacoustic applications, an ongoing challenge in simultaneous volumetric imaging and spectroscopic analysis arises from ultrasonic detectors lacking high sensitivity to pressure transients over a broad spectral bandwidth. Photoacoustic impulses can be measured on the basis of the ultrafast temporal dynamics and highly sensitive response of surface plasmon polaritons to the refractive index changes. Taking advantage of the ultra-sensitive phase shift of surface plasmons caused by ultrasonic perturbations instead of the reflectivity change [as is the case for traditional surface plasmon resonance (SPR) sensors], a novel SPR sensor based on phase-shifted interrogation was developed for the broadband measurement of photoacoustically induced pressure transients with improved detection sensitivity. Specifically, by encoding the acoustically modulated phase change into time-varying interference intensity, our sensor achieved an almost five-fold sensitivity enhancement (∼98 Pa noise-equivalent pressure) compared with the reflectivity-mode SPR sensing technologies (∼470 Pa) while retaining a broadband acoustic response of ∼174 MHz. Incorporating our sensor into an optical-resolution photoacoustic microscope, we performed label-free imaging of a zebrafish eye in vivo, enabling simultaneous volumetric visualization and spectrally resolved discrimination of anatomical features. This novel sensing technology has potential for advancing biomedical ultrasonic and/or photoacoustic investigations.

The optical properties of colloidal solutions of nonionic surfactant Triton X-100 are studied via turbidimetry, optical microscopy, refractometry, and polarimetry. It is shown that its micelles have the form of elongated ellipsoids of revolution, are optically active, retain their orientational order, and move under the action of a directed light flux, depending on the concentration of the solution.

In modern large-sized tokamaks and those under construction, for example, in ITER, when measuring the average plasma electron density using the refractometry technique, it becomes necessary to study different effects that affect the measurement accuracy. This paper presents the results from studies of the high-temperature effects that can affect the interpretation of delay time measurements of the probing microwave signal in the ITER refractometry diagnostics. The criteria for applicability of different plasma models (“cold” plasma, modified “cold” plasma, and “hot plasma”) are obtained for calculating the plasma refractive index and interpreting the delay times that will be measured using the refractometry diagnostics of the ITER plasma. In the second article, based on the results obtained in this article, we will consider the influence of the high-temperature effects on the accuracy of determining the mean density using the refractometry diagnostics.

In this work, the splitting of resonance lines in a Fabry-Perot resonator formed by a section of a standard curved single-mode fiber with metal-coated ends is investigated numerically and experimentally. It is shown that this splitting is similar to the Autler-Townes splitting and results from a strong coupling between the fundamental mode of the core and the whispering gallery mode of the cladding of the curved fiber. The influence of all basic parameters of the curved resonator on the splitting of its resonance lines in the reflection and transmission spectra is considered. Prospects for the practical application of the effects studied for high-resolution optical refractometry, as well as the direction of further research are outlined.

We present a numerical and experimental study of resonance splitting in the transmission and reflection spectra of the Fabry–Perot resonator made of a bent section of a conventional single-mode optical fiber with metallized end faces. We show the splitting to be similar in nature to the well-known Autler–Townes effect and to arise from the strong coupling between the core mode and cladding whispering gallery mode of the bent fiber. The effect of all major parameters of the bent resonator on the splitting of its resonances is demonstrated. Potential applications of the observed effects in the field of precision optical refractometry as well as further research directions are discussed.

Herein, we demonstrate a cavity-enhanced hyperspectral refractometric imaging using an all-dielectric photonic crystal slab (PhCS). Our approach takes advantage of the synergy between two mechanisms, surface-enhanced fluorescence (SEF) and refractometric sensing, both based on high-Q resonances in proximity of bound states in the continuum (BICs). The enhanced local optical field of the first resonance amplifies of 2 orders of magnitude the SEF emission of a probe dye. Simultaneously, hyperspectral refractometric sensing, based on Fano interference between second mode and fluorescence emission, is used for mapping the spatially variant refractive index produced by the specimen on the PhCS. The spectral matching between first resonance and input laser is modulated by the specimen local refractive index, and thanks to the calibrated dependence with the spectral shift of the Fano resonance, the cavity tuning is used to achieve an enhanced correlative refractometric map with a resolution of 10-5 RIU within femtoliter-scale sampling volumes. This is experimentally applied also on live prostate cancer cells grown on the PhCS, reconstructing enhanced surface refractive index images at the single-cell level. This dual mechanism of quasi-BIC spatially variant gain tracked by quasi-BIC refractometric sensing provides a correlative imaging platform that can find application in many fields for monitoring physical and biochemical processes, such as molecular interactions, chemical reactions, or surface cell analysis.

Objectives: For dental resin composites, high translucency is important. Therefore, the aim of the study was to create a biocompatible and highly translucent resin-based composite, and to investigate the effect of material thickness on translucency. Methods: A biocompatible ORMOCER® resin matrix was reinforced with dental glass powder as fillers. To reach a high translucency, refractive index matching of the matrix and fillers was done in the two ways: (1) Highly refractive ZrO2 nanoparticles were incorporated into the resin. (2) The resin was modified via addition of 4-Methylthiophenol. The corresponding refractive indices were acquired on an Abbe refractometer (n = 5). In both cases, the dental glass powder was added and translucency of the resulting minifilled and nanohybrid composites were measured using spectral photometry (n = 5). Additionally, the translucency of the experimental composites was determined as a function of specimen thickness in the range 10 mm-2 mm (n = 5). One-way ANOVA was performed to determine the significant differences in various optical parameters among different amounts of modifications and thicknesses at a = 0.05. Furthermore, cytotoxicity tests (extract and direct contact tests) were conducted according to ISO 10993 to classify the biocompatibility of the composites (n = 6). Results: The translucency values of the composites with 47 wt.-% dental glass powder and a specimen thickness of 2 mm, could be increased from 26% up to 71% by increasing the refractive index of the matrix through incorporating ZrO2 nanoparticles. Moreover, it can also be increased to 67% via addition of 4-Methylthiophenol. Further results showed that the translucency significantly depended on the sample thickness following an exponential function. The effect of all tested parameters was significant among the materials (p < 0.001). The composites did not show any cytotoxic effect. Significance: Highly translucent and biocompatible resin composites were developed. They show attractive properties for the use as dental enamel material in direct and indirect restorations.

Digital holographic microscopy (DHM) is an important technique that may be used for quantitative phase imaging of unstained biological cell samples. Since the DHM technology is not commonly used in clinics or bioscience research labs, at present there is no well-accepted focusing criterion for unstained samples that users can follow while recording image plane digital holograms of cells. The usual sharpness metrics that are useful for auto-focusing of stained cells do not work well for unstained cells as there is no amplitude contrast. In this work, we report a practical method for estimating the best focus plane for unstained cells in the digital hologram domain. The method is based on an interesting observation that for the best focus plane the fringe pattern associated with individual unstained cells predominantly shows phase modulation effect in the form of bending of fringes and minimal amplitude modulation. This criterion when applied to unstained red blood cells shows that the central dip in the doughnut-like phase profile of cells is maximal in this plane. The proposed methodology is helpful for standardizing the usage of DHM technology across different users and application development efforts. LAY DESCRIPTION: Digital holographic microscopy (DHM) is slowly but steadily becoming an important microscopy modality and gaining acceptability for basic bio-science research as well as clinical usage. One of the important features of DHM is that it allows users to perform quantitative imaging of unstained transparent cells. Instead of using dyes or fluorescent labelling, DHM systems use quantitative phase as a contrast mechanism which depends on the natural refractive index variation within the cell samples. Since minimal wet lab processing is required in order to image cell samples with a DHM, cells can be imaged in their natural state. While DHM is gaining popularity among users, the imaging protocols across the labs or users need to be standardized in order to make sure that the same quantitative phase parameters are used for tasks such as quantitative phased based cell classification. One of the important operational tasks for any microscopy work is to focus the sample under study. While focusing comes naturally to users of brightfield microscopes based on image contrast, the focusing is not straightforward when samples are unstained so that they do not offer any amplitude contrast. When performing quantitative phase imaging, defocus can actually change the phase profile of the cell due to near-zone (Fresnel) diffraction effects. So unless a standardized focusing methodology is used, it will be difficult for multiple DHM users (potentially at different sites) to agree on quantitative results out of their phase images. DHM literature has prior works which perform numerical focusing of recovered complex wave-field in the hologram plane to find the best focus plane. However such methods are not user friendly and do not allow user the same focusing experience as in a brightfield microscope. The numerical focusing is therefore a reasonably good method for an optics researcher but not necessarily so for a microscopy technician looking at cell samples with a DHM system in a clinical setting. The present work provides a simple focusing criterion for unstained samples that works directly in the hologram domain. The technique is based on an interesting observation that the when an unstained cell sample is in the best-focus plane, its corresponding hologram (or fringe pattern) predominantly shows phase modulation manifested by bending of fringes at the location of the cell. This criterion can be converted into a simple numerical method as we have used to find the best-focus plane using a stack of through focus holograms. We believe that the technique can be used manually by visually observing the holograms or can be converted to an auto-focus algorithm for a motorized DHM system.

We propose and experimentally demonstrate a highly flexible and applicable configuration, namely, the “ v ertical-fluid-array i nduced o ptic microfiber l ong per i od grati n g” (VIOLIN), for fully exploring the characteristics of liquids. The presence of flowing liquid in the periodically carved grooves of the designated substrate can activate a long-period grating resonance, as the microfiber is attached. Since the features of the resonance depend strongly on the refractive index of the fluid, the VIOLIN can be utilized as a refractometer with a high sensitivity of 2443 nm/RIU. Modeling and simulation are employed to investigate the mechanism of the sensor, which can be described as follows briefly: “Liquid renders the resonance to light. Light deciphers the secret of liquid.” Moreover, due to the highly elastic control of the fluidic array and the detachable configuration, multiple sensing and easy reconfiguration of the VIOLIN can be realized. The VIOLIN is expected to be highly suitable for microfiber-based chemo/biosensing applications.

A novel refractometer based on multimode fiber (MMF) embedded single mode-no core-single mode (ME-SNS) fiber structure is presented and investigated in detail. The ME-SNS structure has a higher refractive index (RI) sensitivity because of the stronger evanescent field generated by RI modulation. There is an obvious attenuation dip when 3 segment MMFs are embedded in single mode-no core-single mode (SNS) fiber structure. Total length of sensing unit is only 1.8 mm. Experimental results show that the maximal RI and the temperature sensitivity of the ME-SNS fiber structure are 567.158 nm/RIU and 0.009 nm/°C.

This letter reports a novel fused silica microfluidic device with pressure sensing capability that is fabricated by integrated additive and subtractive manufacturing (IASM) method. The sensor consists of a capillary and a 3D printed glass reservoir, where the reservoir volume change under pressure manifests liquid level deviation inside the capillary, thus realizing the conversion between small pressure change into large liquid level variation. Thanks to the design flexibility of this unique IASM method, the proposed microfluidic device is fabricated with liquid-in-glass thermometer configuration, where the reservoir is sealed following a novel 3D printing assisted glass bonding process. And liquid level is interrogated by a fiber-optic sensor based on multimode interference (MMI) effect. This proposed microfluidic device is attractive for chemical and biomedical sensing because it is flexible in design, and maintains good chemical and mechanical stability, and adjustable sensitivity and range.

The comparative analysis of glasses based on refractive index (RI) is a widely used method in forensic examinations. However, it cannot be directly applied if the control sample has previously been altered by heat or fire, since RI can change significantly in this process. For this reason, the refractive index of the fragments recovered from the perpetrator's clothing can also differ from the control sample recovered after the fire, although they originate from the same source. In the present study, annealing was used as a possible way for the examination of glass microfragments exposed to heat. The appropriate conditions of annealing were investigated first. Then fragments from a toughened and a non-toughened glass were heated in a furnace for various times at 450 and 650 °C and cooled down immediately to model different heat expositions. It resulted in a significant change in the RIs in all cases. These fragments, together with the non-treated samples from the same pane of glasses, were annealed using the optimized parameters. In a similar process, further glasses exposed to real fire were examined. It was found, both in the model experiments and for the fragments exposed to fire, that - regardless of the heat exposure conditions - annealing resulted in the same RI for fragments from the same source, while for different samples different values were observed. Altogether, 11 glasses were examined in 38 experiments, and it was found that annealing combined with refractive index measurement could be a possible way for the examination of heated fragments. The changes in RIs and standard deviations observed during the experiments are consistent with literature data.

In modern 3D microscopy, holding and orienting arbitrary biological objects with optical forces instead of using coverslips and gel cylinders is still a vision. Although optical trapping forces are strong enough and related photodamage is acceptable, the precise (re-) orientation of large specimen with multiple optical traps is difficult, since they grab blindly at the object and often slip off. Here, we present an approach to localize and track regions with increased refractive index using several holographic optical traps with a single camera in an off-focus position. We estimate the 3D grabbing positions around several trapping foci in parallel through analysis of the beam deformations, which are continuously measured by defocused camera images of cellular structures inside cell clusters. Although non-blind optical trapping is still a vision, this is an important step towards fully computer-controlled orientation and feature-optimized laser scanning of sub-mm sized biological specimen for future 3D light microscopy., Optical manipulation of large objects is challenging as optical trap positions are blindly chosen. Here, the authors present off-focus interferometric tracking, which localises optimal grabbing positions with increased refractive index, by analysing the beam deformations of several holographic optical traps.

Developing technologies capable of constantly assessing and optimizing day-to-day activities has been a research priority for several years. A key factor in such technologies is the use of highly sensitive sensors to monitor in real-time numerous parameters, such as temperature and load. Due to their unique features, optical fiber sensors became one of the most interesting and viable solutions for applications dependent on those parameters. In this work, we present an optical fiber load sensor, called load cell, based on Fabry–Pérot hollow cavities embedded in a polymeric material. By using the load cells in a parallel configuration with a non-embedded hollow cavity, the optical Vernier effect was generated, allowing maximum sensitivity values of 0.433 nm N−1 and 0.66 nm °C−1 to be attained for vertical load and temperature, respectively. The proposed sensor’s performance, allied with the proposed configuration, makes it a viable and suitable device for a wide range of applications, namely those requiring high thermal and load sensitivities.

The optical fiber grating sensors have strong potential for the detection of biological samples. However, a careful effort is still in demand to enhance the performance of existing grating sensors especially in biological sensing. Therefore, in this work, we have introduced a novel plus shaped cavity (PSC) in optical fiber model and used it for the detection of haemoglobin (Hb) refractive index (RI). The numerical analysis of designed model is done by the testing of single and double vertical slots cavity in optical fiber core structure. The testing of designed sensor model is done at the wavelength of 800 nm at which the RI of oxygenated and deoxygenated Hb is 1.392 and 1.389, respectively. The analysis of reported PSC sensor model is done in the wide range of Hb RI from 1.333 to 1.392. The tested range of RI corresponds to the Hb concentration from 0 to 140 gl-1. The obtained results states that for the tested range of RI, the autocorrelation coefficientt of R2 = 99.51 % is achieved. The analysis of projected work is done by using finite difference time domain (FDTD) method. The introduction of PSC can increase in sensitivity. In proposed PSC, the length and width of created slots are 1.8 μm and 1 μm, respectively, which is quite enough to observe the response of analytes RI. This can minimize the creation of multiple gratings required for observing the analyte response.

Optical fiber ball resonators based on single-mode fibers in the infrared range are an emerging technology for refractive index sensing and biosensing. These devices are easy and rapid to fabricate using a CO2 laser splicer and yield a very low finesse reflection spectrum with a quasi-random pattern. In addition, they can be functionalized for biosensing by using a thin-film sputtering method. A common problem of this type of device is that the spectral response is substantially unknown, and poorly correlated with the size and shape of the spherical device. In this work, we propose a detection method based on Karhunen−Loeve transform (KLT), applied to the undersampled spectrum measured by an optical backscatter reflectometer. We show that this method correctly detects the response of the ball resonator in any working condition, without prior knowledge of the sensor under interrogation. First, this method for refractive index sensing of a gold-coated resonator is applied, showing 1594 RIU−1 sensitivity, then, this concept is extended to a biofunctionalized ball resonator, detecting CD44 cancer biomarker concentration with a picomolar-level limit of detection (19.7 pM) and high specificity (30–41%).

In this work, a high-sensitivity terahertz (THz) biosensor is achieved by using a graphene/Bragg reflector hybrid structure. This high-sensitivity THz biosensor is developed from the sharp Fano resonance transmission peak created by coupling the graphene Tamm plasmons (GTPs) mode to a defect mode. It is found that the proposed THz biosensor is highly sensitive to the Fermi energy of graphene, as well as the thickness and refractive index of the sensing medium. Through specific parameter settings, the composite structure can achieve both a liquid biosensor and a gas biosensor. For the liquid biosensor, the maximum sensitivity of &gt, &nbsp, 1000&nbsp, °/RIU is obtained by selecting appropriate parameters. We believe the proposed layered hybrid structure has the potential to fabricate graphene-based high-sensitivity biosensors.

In this work, we present a theoretical model of a near-infrared sensitive refractive index biosensor based on the truncate 1D photonic crystal (1D PC) structure with Dirac semimetal. This highly sensitive near-infrared biosensor originates from the sharp reflectance peak caused by the excitation of Bloch surface wave (BSW) at the interface between the Dirac semimetal and 1D PC. The sensitivity of the biosensor model is sensitive to the Fermi energy of Dirac semimetal, the thickness of the truncate layer and the refractive index of the sensing medium. By optimizing the structural parameters, the maximum refractive index sensitivity of the biosensor model can surpass 17.4 × 103/RIU, which achieves a certain competitiveness compared to conventional surface plasmon resonance (SPR) or BSW sensors. Considering that bulk materials are easier to handle than two-dimensional materials in manufacturing facilities, we judge that 3D Dirac semimetal and its related devices will provide a strong competitor and alternative to graphene-based devices.

Refractive index (RI) sensing as a label-free and non-invasive method has been playing an important role in industrial metrology, biochemical detection, and environmental analysis. Due to the combined advantages of microoptics and microfluidics, optofluidic RI sensors have attracted growing interest. Despite a variety of prototypes of optofluidic RI sensors, comprehensive improvement in sensitivity, detection range, fabrication procedures and cost can still bring substantial benefits to the field. In this work, we fabricated a 3D-cascade-microlens optofluidic chip (3DCMOC) for RI sensing. Two-photon stereolithography was employed to fabricate the chip mold, with which the 3DCMOC could be easily manufactured via mold replication. By virtue of integrating four detection channels configured with different numbers (1, 3, 5, and 7) of cascaded microlenses within the 3DCMOC, adjustable sensitivity for RI sensing has been demonstrated through measuring standard sucrose solutions. It was found that the seven-microlens configuration achieved an excellent sensitivity (mean: 21 ± 5 AU·RIU (refractive index unit)-1) and resolution (mean: 3.8 × 10-5 ± 0.9 × 10-5 RIU) at a cost of a narrow linear dynamic range (LDR, 1.3326-1.3548). In contrast, the single-microlens configuration led to an extended LDR (1.3326-1.5120 tested) despite the lower sensitivity (mean: 2.6 ± 0.2 AU·RIU-1) and resolution (mean: 1.5 × 10-4 ± 0.1 × 10-4 RIU). Furthermore, the use of the 3DCMOC was investigated via real-time salinity sensing and analysis of urine specific gravity.

PURPOSE Optical rehabilitation for hemianopia includes the prescription of partial aperture prismatic lenses. Fresnel lenses for this purpose have poor optical quality, while bonded lenses have poor cosmesis and can only be made in glass, creating a potential hazard. Here we present an alternative lens type, which does not reduce contrast sensitivity and which can be made in plastic materials. METHODS A rotated Franklin split lens was prescribed for the right eye only to provide a full aperture prismatic lens without using a Fresnel prism or bonded lenses. Using different refractive indices in each lens provided a minimal transition in thickness and an acceptable cosmetic appearance. This lens was prescribed to a 34-year-old woman with homonymous right hemianopia. Her contemporaneous comments are presented. RESULTS The rotated Franklin split lens provided 18Δ over the temporal edge of the lens. The wearer noticed chromatic aberration with this lens, but was able to cycle comfortably when wearing the lens without any reduction in contrast. CONCLUSIONS A rotated Franklin split lens can be used for the optical rehabilitation of hemianopia. In this case study, cycling was possible with this lens.

In recent years, the chemical modification of optical fibers (OFs) has facilitated the manufacture of sensors because OFs can identify several analytes present in aqueous solutions or gas phases. Nevertheless, it is imperative better to understand the chemical interactions in this molecular system to generate low-cost and efficient sensors. This work presents a theoretical and experimental study of organic polymeric functionalized OF structures and proposes a cost-effective alternative to monitor breathing and humidity. The device is based on silicon optical fibers functionalized with (3-Aminopropyl) triethoxysilane (APTES) and alginate. The theoretical analysis is carried out to validate the activation of the silicon dioxide fiber surface, moreover, the APTES–alginate layer is discussed. The computational simulation suggests that water can be absorbed by alginate, specifically by the calcium atom linked to the carboxylic acid group of the alginate. The analysis also demonstrates a higher electrostatic interaction between the water and the OF–APTES–alginate system, this interaction alters the optical fiber activated surface’s refractive index, resulting in transmission power variation. The humidity analysis shows a sensitivity of 3.1288 mV/RH, a time response close to 25 s, and a recovery time around 8 s. These results were achieved in the range of 50 to 95 %RH. Moreover, the recovery and response time allow the human breath to be studied. The proposed mechanism or device is competitive with prior works, and the components involved made this sensor a cost-effective alternative for medical applications.

Refractometry is a powerful technique for pressure assessments that, due to the recent redefinition of the SI system, also offers a new route to realizing the SI unit of pressure, the Pascal. Gas modulation refractometry (GAMOR) is a methodology that has demonstrated an outstanding ability to mitigate the influences of drifts and fluctuations, leading to long-term precision in the 10−7 region. However, its short-term performance, which is of importance for a variety of applications, has not yet been scrutinized. To assess this, we investigated the short-term performance (in terms of precision) of two similar, but independent, dual Fabry–Perot cavity refractometers utilizing the GAMOR methodology. Both systems assessed the same pressure produced by a dead weight piston gauge. That way, their short-term responses were assessed without being compromised by any pressure fluctuations produced by the piston gauge or the gas delivery system. We found that the two refractometer systems have a significantly higher degree of concordance (in the 10−8 range at 1 s) than what either of them has with the piston gauge. This shows that the refractometry systems under scrutiny are capable of assessing rapidly varying pressures (with bandwidths up to 2 Hz) with precision in the 10−8 range.

A hybrid structure composed of periodic monolayer graphene nanoribbons and a dielectric multilayer structure was designed to generate a Fano resonance (FR). The strong interaction between the surface plasmon resonance of graphene and the dielectric waveguide mode results in the FR. The finite element method is utilized to investigate the behaviors of the FR, and it matches well with the theoretical calculations using rigorous coupled wave theory. The results demonstrate that the profile of the FR can be passively tuned by the period of the graphene nanoribbons and actively tuned by the Fermi level of the graphene. The decoupled nature of the FR gives it potential applications as a self-calibrated refractive index biosensor, and the sensitivity can reach as high as 4.615 μm/RIU. Thus, this work provides a new idea for an excellent self-referencing refractive index biosensor.

Endoscopic optical coherence tomography of large airways poses unique challenges. A hybrid lens is described that consists of a section of coreless fiber and graded index fiber (GIF), followed by a ball lens section. This design produces low numerical aperture beams better suited for large airway imaging. The performance of this lens is compared against conventional GIF and ball lens designs. Forward- and side-viewing probes were modeled, fabricated, and tested. The impact of a sheath on the beam profile was also investigated. Probes with working distances larger than 10 mm and depth-of-focus exceeding 12 mm are demonstrated with the proposed design.

This paper is devoted the base principles of the method of laser refractography and the results of its application in experimental visualization of optically inhomogeneous liquids. Laser refractography is a novel information-measurement technique based on the probing of fluid flows with a structured laser beams, digital recording of the refraction images obtained, and their computer processing with a view to reconstructing the parameters of the flows. Block diagrams of measuring laser systems are shown, and typical refracrograms are presented.

Purpose Fabrication of a suitable flow model or phantom is critical to the study of biomedical fluid dynamics using optical flow visualization and measurement methods. The main difficulties arise from the optical properties of the model material, accuracy of the geometry and ease of fabrication. Methods Conventionally an investment casting method has been used, but recently advancements in additive manufacturing techniques such as 3D printing have allowed the flow model to be printed directly with minimal post-processing steps. This study presents results of an investigation into the feasibility of fabrication of such models suitable for particle image velocimetry (PIV) using a common 3D printing Stereolithography process and photopolymer resin. Results An idealised geometry of a cerebral aneurysm was printed to demonstrate its applicability for PIV experimentation. The material was shown to have a refractive index of 1.51, which can be refractive matched with a mixture of de-ionised water with ammonium thiocyanate (NH4SCN). The images were of a quality that after applying common PIV pre-processing techniques and a PIV cross-correlation algorithm, the results produced were consistent within the aneurysm when compared to previous studies. Conclusions This study presents an alternative low-cost option for 3D printing of a flow phantom suitable for flow visualization simulations. The use of 3D printed flow phantoms reduces the complexity, time and effort required compared to conventional investment casting methods by removing the necessity of a multi-part process required with investment casting techniques.

Remote detection of hydrogen, without the utilization of electronic component or elevated temperature, is one of the hot topics in the hydrogen technology and safety. In this work, the design and realization of the optical fiber-based hydrogen sensor with unique characteristics are proposed. The proposed sensor is based on the gold-coated multimode fiber, providing the plasmon properties, decorated by the IRMOF-20 layer with high selectivity and affinity toward hydrogen. The IRMOF-20 layer was grown by a surface-assisted technique, and its formation and properties were studied using X-ray photoelectron spectroscopy, Raman, X-ray diffraction, and Brunauer-Emmett-Teller techniques. Simultaneous ellipsometry results indicate the apparent changes of the refractive index of the IRMOF-20 layer due to hydrogen sorption. As results, the presence of hydrogen led to the pronounced changes of plasmon band wavelength position as well as its intensity increase. The proposed hydrogen sensors were favorably distinguished by a high response/recovery rate, excellent selectivity toward the hydrogen, very low temperature dependency, functionality at room or lower temperature, insensitivity toward the humidity, and the presence of CO2, CO, or NO2. Additionally, the proposed hydrogen sensor showed good reversibility, reproducibility, and long-term stability.

Sugar concentration in floral nectars is an assessment required in several diverse fields of application. The widely used analysis, consisting of nectar extraction with a microcapillary and sugar concentration measurement with a light refractometer, is not reliable when the nectar is secreted in small quantities, unextractable with a microcapillary. Ancillary methods adopted in such cases are destructive, rather complicated and often provide much less precise and accurate results. The microscopic-size, low cost and biocompatibility of optical fibers were exploited to deliver light directly inside the flower with minimal invasiveness and measure instantaneously the refractometric properties of the nectar without extracting it. After comparing the new and old methods using two known nectariferous species, the new approach was validated on Primula palinuri, whose nectar is unextractable with microcapillaries. The fiber-optic probe was able to measure the nectar refractive index in P. palinuri flowers making it possible to highlight a previously undetected significant trend of the sugar concentration throughout the long anthesis of the single flowers. Changes in nectar concentrations are similar in both longistylous and brevistylous flowers. The fiber-optic refractometer is an advancement of light refractometer analysis. Further customization of the laboratory set-up into portable equipment will boost applications.

A new method for the molecular weight (MW) determination of chitosans by asymmetric flow field flow fractionation (AF-FFF or AF4) coupled with multi-angle light scattering (MALS) and differential refractive index (RI) detectors is proposed. The method allows the separation of polymer from molecular aggregates typically found in chitosan solutions making possible the accurate determination of MW distribution of the polymer. The effect of different experimental conditions on the obtained results has been evaluated and compared with those obtained from SEC-MALS-RI (size exclusion chromatography-MALS-RI). The chitosans analysed were from different biological sources and of varying degree of acetylation. AF4-MALS-RI results revealed that although aggregates are minimised when using a good solvent, a fraction still remains, and it is only completely eliminated by filtration through small pore sizes (≤0.45μm). This represents a limitation for the characterisation of high MW chitosan, where filtration can lead to considerable sample loss in the filter. The method described here has the advantage of not only allowing the identification and separation of the aggregates present, but also the accurate determination of the MW distribution for a wide range of chitosans of varying type where results are well correlated with those obtained by more conventional techniques.

The reflectance of a hybrid fiber Fabry–Perot interferometer modulated by the Fresnel reflection at the fiber tip was used to assess the refractive index (RI) of liquid samples. Notwithstanding the closeness of RI values between samples and fiber core, well-defined interference spectra in Fourier domain were obtained after a robust signal processing algorithm. Then, the analysis of these spectra allowed us to derive a mathematical expression to obtain the RI value of the fiber tip surrounding media. Next, to assess the fiber refractometer measuring capability a series of liquid samples, typically used for RI calibration, with values ranging from 1.3924 to 1.5882 were measured. A standard deviation of 7 × 10−4 between the measured and actual RI values was estimated. Finally, the refractometer was used to monitor the RI of a sample, with a high thermo-optic coefficient, while it was heated. The accurate and compact all-fiber refractometer proposed here exhibited immunity to optical power fluctuations and one of the largest dynamic ranges reported. This set of combined features make it very attractive for real-time label-free biosensing applications.

A simple, convenient, and inexpensive method to fabricate optical fiber based biosensors which utilize periodic hole arrays in gold films for signal transduction is reported. The process of hole array formation mainly relies on self-assembly of hydrogel microgels in combination with chemical gold film deposition and subsequent transfer of the perforated film onto an optical fiber tip. In the fabrication process solely chemical wet lab techniques are used, avoiding cost-intensive instrumentation or clean room facilities. The presented method for preparing fiber optic plasmonic sensors provides high throughput and is perfectly suited for commercialization using batch processing. The transfer of the perforated gold film onto an optical fiber tip does not affect the sensitivity of the biosensor ((420 ± 83) nm/refractive index unit (RIU)), which is comparable to sensitivities of sensor platforms based on periodic hole arrays in gold films prepared by significantly more complex methods. Furthermore, real-time and in-line immunoassay studies with a specially designed 3D printed flow cell are presented exploiting the presented optical fiber based biosensors.

Purpose To determine the agreement and validity of keratometric measurements in children with the Nidek ARK-510A auto-refractokeratometer compared to rotating Scheimpflug imaging with Pentacam and biograph with Lenstar LS 900. Methods This study was conducted on 5620 schoolchildren aged 6–12 years in Shahroud, Iran. Minimum and maximum keratometry values and corneal astigmatism magnitude were compared by calculation of Paired difference, interclass correlation coefficient, and 95% limits of agreement (LoA) between devices. Results After applying the exclusion criteria, 4215 right eyes were enrolled into the study. Mean minimum keratometry with Nidek ARK-510A, Pentacam, and Lenstar was 43.13 ± 1.51, 43.14 ± 1.48, and 42.87 ± 1.46 diopters (D), respectively, and mean maximum keratometry was 43.97 ± 1.59, 44.00 ± 1.56, and 43.75 ± 1.54 D, respectively. Nidek ARK-510A overestimated minimum and maximum keratometry by 0.25 ± 0.37 and 0.22 ± 0.41, respectively, compared to Penatcam. The LoA between Nidek ARK-510A and Pentacam for minimum and maximum keratometry measurements were −0.98 to 0.47 D and −1.02 to 0.57 D, respectively. The LoA between Nidek ARK-510A and Lenstar for minimum and maximum keratometry measurements were −0.70 to 0.72 D and −0.79 to 0.85 D, respectively. The agreement between devices was best in emmetropes, worst in hyperopes. For astigmatic vector components, the agreements between devices were poor but best agreement was between Nidek ARK-510A and Pentacam. Conclusions Keratometry measurement with Nidek ARK-510A was not significantly different from Pentacam and Lenstar, and this device can be used in screening programs in emmetropes.

Significance Polyvinyl alcohol is a wetting agent that could reduce the symptoms of dry eye and contact lens discomfort. Currently, only one lens type, nelfilcon A (DAILIES AquaComfort Plus), releases polyvinyl alcohol. The concept of releasing this agent from contact lenses could be applied to other lens materials. Purpose The purpose of this study was to measure the release of polyvinyl alcohol from commercially available hydrogel daily disposable contact lenses using refractive index and iodine-borate methods. Methods Etafilcon A, omafilcon A, and nelfilcon A were soaked in phosphate-buffered saline and 0.2% trifluoroacetic acid/acetonitile for 24 hours to remove residual blister pack components. The lenses were then incubated in a 10-mg/mL solution of polyvinyl alcohol for 24 hours. After the incubation period, the lenses were placed in 2 mL of phosphate-buffered saline. At specified time intervals, t = 0.5, 1, 2, 4, 8, 12, and 24 hours, the samples were evaluated using refractive index and an iodine-borate assay. Polyvinyl alcohol uptake was determined by extracting the lenses with methanol for 24 hours. Results There were no differences in the uptake of polyvinyl alcohol between lens types (P > .05). The release of this wetting agent for all lens types followed a burst-plateau profile after the first 30 minutes (P > .05). Nelfilcon A had a slightly higher release of polyvinyl alcohol (P .05). Conclusions The results suggest that the contact lenses tested in this study have similar efficiency in delivering polyvinyl alcohol.

Ring resonators are well-known optical biosensors thanks to their relatively high Q-factor and sensitivity, in addition to their potential to be fabricated in large arrays with a small footprint. Here, we investigated the characteristics of a polymer ring resonator with a partially tapered waveguide for Biomedical Sensing. The goal is to develop a more sensitive biosensor with an improved figure of merit. The concept is more significant field interaction with the sample under test in tapered segments. Waveguide width is hereby gradually reduced to half. Sensitivity improves from 84.6 to 101.74 [nm/RIU] in a relatively small Q-factor reduction from 4.60 × 103 for a strip waveguide to 4.36 × 103 for a π/4 partially tapered one. After the study, the number of tapered parts from zero to fifteen, the obtained figure of merit improves from 497 for a strip ring to 565 for a π/4 tapered ring close to six tapered ones. Considering the fabrication process, the three-tapered one is suggested. The all-polymer material device provides advantages of a low-cost, disposable biosensor with roll-to-roll fabrication compatibility. This design can also be applied on silicon on isolator, or polymer on silicon-based devices, thereby taking advantage of a higher Q-factor and greater sensitivity.

Ionic liquids (ILs) are becoming important solvents in commerce, but monitoring their purity and performance in industrial applications presents new challenges. Fiber welding technology utilizes ILs to mold and shape natural fibers (cotton, hemp, flax, silk, and wool) into morphologies that are typically attained only using synthetic, petroleum-based non-biodegradable plastics. The result is an atom-efficient process that up-converts fibrous substrates to value-added products and materials. A key aspect of bringing this and other IL-enabled technologies to market relies on efficient monitoring and recycling of IL-based solvents. Implementing online IL quality monitoring enhances the unit economics of these processes. Here, we characterize and report conductivity measurements, refractometry, and ATR-FTIR spectroscopy techniques for online IL monitoring during an industrial fiber welding process. The online analysis enables more efficient recycling of the IL solvent, increasing the process efficiency and product quality.

Waveguide enhanced Raman spectroscopy (WERS) utilizes simple, robust, high-index contrast dielectric waveguides to generate a strong evanescent field, through which laser light interacts with analytes residing on the surface of the waveguide. It offers a powerful tool for the direct identification and reproducible quantification of biochemical species and an alternative to surface enhanced Raman spectroscopy (SERS) without reliance on fragile noble metal nanostructures. The advent of low-cost laser diodes, compact spectrometers, and recent progress in material engineering, nanofabrication techniques, and software modeling tools have made realizing portable and cheap WERS Raman systems with high sensitivity a realistic possibility. This review highlights the latest progress in WERS technology and summarizes recent demonstrations and applications. Following an introduction to the fundamentals of WERS, the theoretical framework that underpins the WERS principles is presented. The main WERS design considerations are then discussed, and a review of the available approaches for the modification of waveguide surfaces for the attachment of different biorecognition elements is provided. The review concludes by discussing and contrasting the performance of recent WERS implementations, thereby providing a future roadmap of WERS technology where the key opportunities and challenges are highlighted.

In this article, we summarize our investigations on optimized 248 nm deep ultraviolet (UV) fabrication of highly stable epoxy polymer Bragg grating sensors and their application for biomedical purposes. Employing m-line spectroscopy, deep UV photosensitivity of cross-linked EpoCore thin films in terms of responding refractive index change is determined to a maximum of Δn = + (1.8 ± 0.2) × 10−3. All-polymer waveguide Bragg gratings are fabricated by direct laser irradiation of lithographic EpoCore strip waveguides on compatible Topas 6017 substrates through standard +1/-1-order phase masks. According near-field simulations of realistic non-ideal phase masks provide insight into UV dose-dependent characteristics of the Bragg grating formation. By means of online monitoring, arising Bragg reflections during grating inscription via beforehand fiber-coupled waveguide samples, an optimum laser parameter set for well-detectable sensor reflection peaks in respect of peak strength, full width at half maximum and grating attenuation are derived. Promising blood analysis applications of optimized epoxy-based Bragg grating sensors are demonstrated in terms of bulk refractive index sensing of whole blood and selective surface refractive index sensing of human serum albumin.

Digital holographic microscopy (DHM) is a technique that has high potential for analyzing biological samples and has been successfully applied to the study of cells and cell lines providing information about important parameters such as refractive index, morphology, and dry mass, among others; it has also found applicability to study the effects of therapeutic treatments. Finding the size and shape of cells is important since they tend to change in the presence of some pathologies. In this research work, we obtain the morphology thickness and refractive index of the A375 melanoma cell line through a slight tilting of the cell in a DHM setup. Further, the development of a novel mathematical expression based on this tilt and in the optical phase difference is presented. We show images of melanoma cells with the refractive index information included, and their morphology thickness as rendered from the holographic phase maps recorded with DHM.

A biosensor platform based on the plasmonic resonance of graphene in the terahertz (THz) range (0.1 to 10 THz) is designed and investigated. The initial design is to create a nanofluidic channel as a sensing layer in the substrate of a biosensor grounded by metal. The sensor consists of a rectangular graphene patch over the substrate, which can be fed by either an external near-field source or an antenna. The presence of molecules in the nanosensing layer causes small changes in the channel’s properties, detectable through the scattering parameters of the designed biosensor. Since biomolecules are poorly absorbed in the initial biosensor, it can be grounded by a graphene sheet that is the same size as the graphene sheet over the substrate, which results in a performance improvement of the biosensor. It is shown that, by increasing the number of graphene sheets between the ground and the patch, high absorption occurs that enhances the sensitivity of the initial surface plasmon resonance THz biosensor. With varying refractive index of the sensing layer (Ns) in the range of 1.3–1.6, the proposed biosensors are investigated and compared with the initial biosensor. It is shown that by applying a graphene sheet between the two graphene sheets in the substrate, a maximum sensitivity of 8470 nm/RIU is achieved, which is a significant improvement, and also a sensitivity improvement of 4130 nm/RIU is achieved at N s = 1.3 . In the final section, it is shown that changing the substrate material from silicon (Si) to silica ( S i O 2 ) brings a significant sensitivity enhancement in the proposed biosensor with three graphene sheets, which accounts for 15410 nm/RIU in the best scenario.

Three-dimensional (3D) optical microscopy with a high numerical aperture (NA) remains challenging for thick biological specimens owing to aberrations arising from interface refractions. We developed a variable immersion lens (VIL) to passively minimize these aberrations. A VIL is a high-NA concentric meniscus lens and was used in combination with an aberration-corrected high-NA reflecting objective (TORA-FUJI mirror). Wave-optics simulation at a wavelength of 488 nm showed that a VIL microscope enables diffraction-limited 1.2-NA imaging in water (refractive index of 1.34) at a depth of 0.3 mm by minimizing aberrations due to refraction of a sample interface. Another aberration due to the refractive index mismatching between a mounting medium, and an object can also be corrected by the VIL system, because various fluids with different refractive indices can be used as mounting media for the VIL. As a result of correcting the two aberrations at the same time, we experimentally demonstrated that a 6 µm diameter fluorescent bead can be imaged to the true dimensions in 3D.

Optical refractometry techniques enable realization of both pressure and temperature directly from properties of the gas. The NIST refractometer, a fixed length optical cavity (FLOC) has previously been evaluated for operation as pressure standard, and now in this paper, is evaluated for the feasibility of operation as a primary temperature standard as well. The challenge is that during operation, one cavity is filled with gas. Gas dynamics predicts that this will result in heating which in turn will affect the cavity temperature uniformity, impeding the ability to measure the gas temperature with sufficient accuracy to make the standard useful as a primary standard for temperature or pressure. Temperature uniformity across the refractometer must be less than 0.5 mK for measurements of the refractivity to be sufficiently accurate for the FLOC. This paper compares computer modeling to laboratory measurements, enabling us to validate the model to predict thermal behavior and to accurately determine the measurement uncertainty of the technique. The results presented in this paper show that temperature of the glass elements of the refractometer and ‘thermal-shell’ copper chamber are equivalent to within 0.5 mK after an equilibration time of 3000 s (when going from 1 kPa to 100 kPa). This finding enables measurements of the copper chamber to determine the gas temperature to within an uncertainty (k = 1) of 0.5 mK. Additionally, the NIST refractometer is evaluated for feasibility of operation as temperature standard.

A technique for high-precision and high-accuracy assessment of both gas molar (and number) density and pressure, Gas Modulation Refractometry (GAMOR), is presented. The technique achieves its properties by assessing refractivity as a shift of a directly measurable beat frequency by use of Fabry-Perot cavity (FPC) based refractometry utilizing the Pound-Drever-Hall laser locking technique. Conventional FPC-based refractometry is, however, often limited by fluctuations and drifts of the FPC. GAMOR remedies this by an additional utilization of a gas modulation methodology, built upon a repeated filling and evacuation of the measurement cavity together with an interpolation of the empty cavity responses. The procedure has demonstrated an ability to reduce the influence of drifts in a non-temperature stabilized dual-FPC (DFPC)-based refractometry system, when assessing pressure, by more than three orders of magnitude. When applied to a DFPC system with active temperature stabilization, it has demonstrated, for assessment of pressure of N2 at 4304 Pa at room temperature, which corresponds to a gas molar density of 1.7 × 10−6 mol/cm3, a sub-0.1 ppm precision (i.e. a resolution of 0.34 mPa). It is claimed that the ability to assess gas molar density is at least as good as so far has been demonstrated for pressure (i.e. for the molar density addressed, a resolution of at least 1.2 × 10−13 mol/cm3). It has recently been argued that the methodology should be capable of providing an accuracy that is in the low ppm range. These levels of precision and accuracy are unprecedented among laser-based techniques for detection of atomic and molecular species. Since the molar polarizability of He can be calculated by ab initio quantum mechanical calculations with sub-ppm accuracy, it can also be used as a primary or semi-primary standard of both gas molar (and number) density and pressure.

By measuring the refractivity and the temperature of a gas, its pressure can be calculated from fundamental principles. The most sensitive instruments are currently based on Fabry–Perot cavities where a laser is used to probe the frequency of a cavity mode. However, for best accuracy, the realization of such systems requires exceptional mechanical stability. Gas modulation refractometry (GAMOR) has previously demonstrated an impressive ability to mitigate the influence of fluctuations and drifts whereby it can provide high-precision (sub-ppm, i.e., sub-parts-per-million or sub- 10 − 6) assessment of gas refractivity and pressure. In this work, two independent GAMOR-based refractometers are individually characterized, compared to each other, and finally compared to a calibrated dead weight piston gauge with respect to their abilities to assess pressure in the 4–25 kPa range. The first system, referred to as the stationary optical pascal (SOP), uses a miniature fixed point gallium cell to measure the temperature. The second system, denoted the transportable optical pascal (TOP), relies on calibrated Pt-100 sensors. The expanded uncertainty for assessment of pressure ( k = 2) was estimated to, for the SOP and TOP, [ ( 10 mPa ) 2 + ( 10 × 10 − 6 P ) 2 ] 1 / 2 and [ ( 16 mPa ) 2 + ( 28 × 10 − 6 P ) 2 ] 1 / 2, respectively. While the uncertainty of the SOP is mainly limited by the uncertainty in the molar polarizability of nitrogen (8 ppm), the uncertainty of the TOP is dominated by the temperature assessment (26 ppm). To verify the long-term stability, the systems were compared to each other over a period of 5 months. It was found that all measurements fell within the estimated expanded uncertainty ( k = 2) for comparative measurements (27 ppm). This verified that the estimated error budget for the uncorrelated errors holds over this extensive period of time.

Diabetes mellitus is a chronic metabolic condition that affects millions of people worldwide. The present paper investigates the bulk sensitivity of silicon and silicon nitride strip waveguides in the transverse electric (TE) mode. At 1550 nm wavelength, silicon on insulator (SOI) and silicon nitride (Si3N4) are two distinct waveguides of the same geometry structure that can react to refractive changes around the waveguide surface. This article examines the response of two silicon-based waveguide structures to the refractive index of urine samples (human renal fluids) to diagnose diabetes mellitus. An asymmetric Mach–Zehnder interferometer has waveguide sensing and a reference arm with a device that operates in the transverse electric (TE) mode. 3D FDTD simulated waveguide width 800 nm, thickness 220 nm, and analyte thickness 130 nm give the bulk sensitivity of 1.09 (RIU/RIU) and 1.04 (RIU/RIU) for silicon and silicon nitride, respectively, high compared to the regular transverse magnetic (TM) mode strip waveguides. Furthermore, the proposed design gives simple fabrication, contrasting sharply with the state-of-the-art 220 nm wafer technology.