Search

The paper presents the research results to increase the probability of mass fractions measuring control of liquefied petroleum gas components, which has various temperatures by defining the density of the liquid phase. The thermooptical method for measuring control of mass fractions of liquefied petroleum gas components is presented in the paper. The measuring conversion function of the refractive index of liquefied petroleum gas was improved based on the proposed method. Based on research conducted it was developed the device of optoelectronic mass fraction measuring of liquefied petroleum gas components. The estimation of static metrological characteristics of control device measuring channel for the liquefied petroleum gas components mass fractions. The control device basic errors are defined as well.

Cu6PS5I-based thin films were deposited onto silicate glass substrates by magnetron sputtering. Chemical composition of the thin films was determined by energy-dispersive X-ray spectroscopy. With increasing Cu content, a red shift of the exponential absorption edge energy position as well as a decrease of the Urbach energy are observed. Optical transmission spectra of Cu8.05P0.68S3.54I0.73 thin film were investigated in the temperature interval 77–300 K; the temperature behaviour of the optical absorption spectra and the refractive index dispersion was studied. Temperature dependences of the energy position of the absorption edge, the Urbach energy, and the refractive index of the Cu8.05P0.68S3.54I0.73 thin film were analysed. The influence of structural disorder on the optical properties of the Cu6PS5Ibased thin films is discussed.

The objective of this study is to propose and introduce nonlinear modal propagation analysis (NMPA) method being a viable way to study the application of graphene based multimode interference (MMI) coupler as an optical refractive index sensor. The purpose of using graphene in this study is because of its high optical nonlinearity as well as having a small bandgap due to its thin layer. The graphene based sensor can be tuned for highest sensitivity in wavelength and refractive index to detect the clad material. Graphene will act as the core of the sensor which will be placed on top of the sample. The clad refractive index value can be obtained by observing and analyzing the change in the output facet intensity of the sensor. The result also shows that the sensor has high sensitivity due to the usage of graphene and nonlinear region.

Aberration correction was one of the most important and challenging parts of optical trapping systems. Many works try to overcome aberration which is due to trapping setup itself or refractive index mismatch of glass slab and nanoparticles solutions. In this article, we investigate a new method for aberration correction based on a nonlinear refractive index of materials. With the emitting laser to the trapped particle, the refractive index of the trapping site increases and as a result, its aberration reduce. In accordance, this method offers a simple and low-cost way for increasing trapping stiffness.

In this paper, we have employed the L 2 waveguides in order to guide the light into two different arms constructed by the inclusion of an engineered obstacle in front of the input optical port. The light which travels inside the core liquid is coupled into these two arms experiencing different optical paths due to the asymmetric geometry of the obstacle and also the different used cladding liquids. We have used several sets of coupled hydrodynamic-electromagnetic simulations to characterize the interferometer based on the output intensity of the waveguide. The simulation results indicate that this technique has a maximum sensitivity of 595%/RIU and a maximum resolution of 3.3×10 -6 RIU which depends on the range of flow rate.

Electromagnetically induced transparency (EIT), a pump-induced narrow transparency window within the absorption region of a probe, had offered new perspectives in slow-light control in atomic physics. For applications in nanophotonics, the implementation on chip-scaled devices has later been obtained by mimicking this effect by metallic metamaterials. High losses in visible and near infrared range of metal-based metamaterialls have recently opened a new field of all-dielectric metamaterials; a proper configuration of high refractive index dielectric nanoresonators can mimick this effect without losses to get high Q, slow-light response. The next step would be the ability to tune their optical response, and in this work we investigate thin layers of phase change materials (PCM) for all-optical control of EIT-like all-dielectric metamaterials. PCM can be nonvolatively and reversibly switched between two stable phases that differ in optical properties by applying a visible laser pulse. The device is based on Si nanoresonators covered by a thin layer of PCM GeTe; optical and transient thermal simulations have been done to find and optimize the fabrication parameters and switching parameters such as the intensity and duration of the pulse. We have found that the EIT-like response can be switched on and off by applying the 532nm laser pulse to change the phase of the upper GeTe layer. We strongly believe that such approach could open new perspectives in all-optically controlled slow-light metamaterials.

Particle image velocimetry (PIV) is a well-established tool to collect high-resolution velocity and turbulence data in the laboratory. PIV measurements are based on using a laser sheet to illuminate a flow seeded with small particles and taking quick successive images or image pairs of the illuminated particle field with a CCD or CMOS camera. The movement of the particles between images can be used to infer flow field velocities over an image area. During experiments at the Simulated Turbulence and Turbidity Environment (SiTTE) laboratory tank, we observed a marked influence of optical turbulence, i.e. strong temperature gradients leading to changes in the index of refraction, on particle imaging in PIV. The particles look blurred and have a “shooting star” appearance. PIV is routinely used in flows with very high temperature gradients, such as nuclear reactor cooling rods, but the optical path length is typically very short (on the order of cm), and no such effect is generally considered for measurements in liquids. We investigated the effect of optical turbulence on PIV imaging for various optical path lengths (0.5m to 2m) and turbulence strengths. Velocities from the PIV measurements were calculated using the algorithms provided within Dantec’s Dynamic Studio and compared to velocities from concurrent velocity point measurements with a Laser Doppler Velocimetry system. The results indicate that optical turbulence can affect PIV measurements in liquids, and that depending on the strength of the optical turbulence and path length, care needs to be taken to mediate this effect using appropriate post-processing techniques when inferring velocities from PIV data.

Image sensing technologies and systems operating from the ultraviolet (UV) to long-wave infrared (LWIR) spectral range are being developed for a variety of defense and commercial systems applications. Reflection loss of a significant portion of the incident signal limits the performance of image sensing systems. One of the critical technologies that will overcome this limitation and enhance image sensor performance is the development of advanced antireflection (AR) coatings. In this paper, we review our latest work on high-quality nanostructure-based AR structures, including recent efforts to deposit nanostructured AR coatings on substrates transparent to infrared (IR) radiation. Nanostructured AR coatings fabricated via a scalable self-assembly process are shown to enhance the optical transmission through transparent optical components by minimizing reflection losses in the spectral band of interest to less than one percent, a substantial improvement over conventional thin-film AR coating technologies. Step-graded AR structures also exhibit excellent omnidirectional performance, and have recently been demonstrated in medium wavelength and long wavelength IR spectral bands.

Silicon oxycarbide (SiOC) thin films are produced with reactive rf magnetron sputtering of a silicon carbide (SiC) target on Si (100) and SiO2/Si substrates under varying deposition conditions. The optical properties of the deposited SiOC thin films are characterized with spectroscopic ellispometry at multiple angles of incidence over a wavelength range 300- 1600 nm. The derived optical constants of the SiOC films are modeled with Tauc-Lorentz model. The refractive index n of the SiOC films range from 1.45 to 1.85 @ 1550 nm and the extinction coefficient k is estimated to be less than 10-4 in the near-infrared region above 1000 nm. The topography of SiOC films is studied with SEM and AFM giving rms roughness of 0.9 nm. Channel waveguides with a SiOC core with a refractive index of 1.7 have been fabricated to demonstrate the potential of sputtered SiOC for integrated photonics applications. Propagation loss as low as 0.39 ± 0.05 dB/mm for TE and 0.41 ± 0.05 dB/mm for TM polarizations at telecommunication wavelength 1550 nm is demonstrated.

The measurement of refractive index of very thin films at the order of ten to hundred nanometers is cumbersome and usually requires employing sophisticated techniques such as the spectral ellipsometry. In this paper we describe a simple contact method for measuring the refractive index of thin films. Here we have used the prism-coupling technique for characterizing samples prepared as four-layer slab waveguides. The waveguide resonance condition can be calculated by solving simple analytic transcendental equations for the slab waveguide. Then the captured mode position as a function of cladding thickness is used for probing the refractive index of cladding layer. We used indium-tin-oxide layer on glass as the substrate and polysulfone with known refractive index as the material for testing the method. In the paper we provide the theoretical background of the method, demonstrate the experimental results obtained during the implementation of the technique as well as discuss its main strengths and flaws.

In this work we correlate the dimension of the waveguide with small variations of the refractive index of the material used for the waveguide core. We calculate the effective modal refractive index for different dimensions of the waveguide and with slightly variation of the refractive index of the core material. These results are used as an input for a set of Finite Difference Time Domain simulation, directed to study the characteristics of amorphous silicon waveguides embedded in a SiO 2 cladding. The study considers simple linear waveguides with rectangular section for studying the modal attenuation expected at different wavelengths. Transmission efficiency is determined analyzing the decay of the light power along the waveguides. As far as near infrared wavelengths are considered, a-Si:H shows a behavior highly dependent on the light wavelength and its extinction coefficient rapidly increases as operating frequency goes into visible spectrum range. The simulation results show that amorphous silicon can be considered a good candidate for waveguide material core whenever the waveguide length is as short as a few centimeters. The maximum transmission length is highly affected by the a-Si:H defect density, the mid-gap density of states and by the waveguide section area. The simulation results address a minimum requirement of 300nm×400nm waveguide section in order to keep attenuation below 1 dB cm -1 .

To improve the transmittance of THz component and overcome the difficulties of fragile structure as well as ensuring precise alignment of existing methods, a new method involving the mature 3DIC through-silicon via (TSV) technology has been proposed to make anti-reflection layer with suitable effective refractive index based on the robustness of Si wafer. Cu wire-grid polarizers were also fabricated on wafer. The THz polarizers were completed after wafer bonding with Cu sealing ring and In/Sn guard ring. Not only the new method is easier for production with better performance, but also the silicon substrate has several advantages. The novel method has proven that THz optical component could be constructed with a nearly 100% transmittance, or widened the transmittance spectrum range from 0.5 to 2 THz when transmittances is sacrificed to 70% instead of a near 100%. Furthermore, a robust structure could also be expected with broadband transmission and excellent extinction ratio. It is properly optimized for mass production because the fabrication method could be easily done and does not required high cost.

Organic microstructures attract much attention due to their unique properties originating from the design of their shape and optical parameters. In this work we discuss the linear, second- and third-order nonlinear optical effects in arrays and in individual organic microstructures composed by self-assembling technique and formed randomly on top of a solid substrate. The structures under study consist of micro-spheres, -hemispheres or -frustums made of red laser dye and reveal an intense fluorescence (FL) in the visible spectral range. Importantly, that due to a high value of the refractive index and confined geometry, such micro-structures support the excitation of whispering gallery modes (WGM), which brings about strong and spectrally-selected light localization. We show that an amplification of the nonlinear optical effects is observed for these structures as compared to a homogeneous dye film of similar composition. The obtained data are in agreement with the results of the FDTD calculations performed for the structures of different dimensions. Perspectives of application of such type of organic nonlinear microresonators in optical devices are discussed.

Propagation and diffraction of a light beam through nonlinear materials are effectively compensated by the effect of selftrapping. The laser beam propagating through photo-sensitive polymer PVA/AA can generate a waveguide of higher refractive index in direction of the light propagation. In order to investigate this phenomenon occurring in light-sensitive photopolymer media, the behaviour of a single light beam focused on the front surface of photopolymer bulk is investigated. As part of this work the self-bending of parallel beams separated in spaces during self-writing waveguides are studied. It is shown that there is strong correlation between the intensity of the input beams and their separation distance and the resulting deformation of waveguide trajectory during channels formation. This self-channeling can be modelled numerically using a three-dimension model to describe what takes place inside the volume of a photopolymer media. Corresponding numerical simulations show good agreement with experimental observations, which confirm the validity of the numerical model that was used to simulate these experiments.

One-dimensional dynamic photonic crystal was formed by a periodic spatial modulation of dielectric permittivity induced by the two ultrashort laser pulses interference in semiconductor quantum dots CdSe/ZnS (QDs) colloidal solution intersecting at angle θ. The fundamental differences of dynamic photonic crystals from static ones which determine the properties of these transient structures are the following. I. Dynamic photonic crystals lifetimes are determined by the nature of nonlinear changes of dielectric permittivity. II. The refractive index changing is determined by the intensity of the induced standing wave maxima and nonlinear susceptibility of the sample. We use the pump and probe method to create the dynamic one-dimensional photonic crystal and to analyze its features. Two focused laser beams are the pump beams, that form in the colloidal solution of quantum dots dynamic one-dimensional photonic crystal. The picosecond continuum, generated by the first harmonic of laser (1064 nm) passing through a heavy water is used as the probe beam. The self-diffraction of pumping beams on self induced dynamic one-dimensional photonic crystal provides information about spatial combining of laser beams.

The Borrmann effect is known as an increase of the X-rays transmission of a perfect crystal in the Laue diffraction scheme when the Bragg diffraction condition are satisfied. Following the trend of the transfer of the X-ray phenomena into the optical spectral range, we experimentally observed and studied the optical analogue of the Borrmann effect for the case of one-dimensional photonic crystals (PhC). For the experiments we made the samples of PhCs based on porous fused silica, which reveal periodical modulation of the refractive index and light absorption. We show that in such structures the Borrmann effect reveals itself as increasing transmission when light propagates through a PhC at the Bragg angle of incidence. Pronounced differences of the Borrmann effect are observed for the PhC structures with light losses concentrated in high or low refractive index layers. The spectral features of the effect are analyzed both experimentally and theoretically.

Silver halide emulsions have been considered one of the most energetic sensitive materials for holographic applications. Nonlinear recording effects on holographic reflection gratings recorded on silver halide emulsions have been studied by different authors obtaining excellent experimental results. In this communication specifically we focused our investigation on the effects of refractive index modulation, trying to get high levels of overmodulation that will produce high order harmonics. We studied the influence of the overmodulation and its effects on the transmission spectra for a wide exposure range by use of 9 μm thickness films of ultrafine grain emulsion BB640, exposed to single collimated beams using a red He-Ne laser (wavelength 632.8 nm) with Denisyuk configuration obtaining a spatial frequency of 4990 l/mm recorded on the emulsion. The experimental results show that high overmodulation levels of refractive index produce second order harmonics with high diffraction efficiency (higher than 75%) and a narrow grating bandwidth (12.5 nm). Results also show that overmodulation produce diffraction spectra deformation of the second order harmonic, transforming the spectrum from sinusoidal to approximation of square shape due to very high overmodulation. Increasing the levels of overmodulation of refractive index, we have obtained higher order harmonics, obtaining third order harmonic with diffraction efficiency (up to 23%) and narrowing grating bandwidth (5 nm). This study is the first step to develop a new easy technique to obtain narrow spectral filters based on the use of high index modulation reflection gratings.

Holographic Optical Elements (HOEs) cover nowadays a relevant position as dispersing elements in astronomical spectrographs because each astronomical observation could take advantage of specific devices with features tailored for achieving the best performances. The design and manufacturing of highly efficient and reliable dispersive elements require photosensitive materials as recording substrate where it is possible to precisely control the parameters that define the efficiency response (namely both the refractive index modulation and the film thickness). The most promising materials in this field are the photopolymers because, beside the ability to provide the tuning feature, they bring also advantages such as self-developing, high refractive index modulation and ease of use thanks to their simple thin structure, which is insensitive from the external environment. In particular, Bayfol HX photopolymers were characterized with the purpose to use them as new material for astronomical Volume Phase Holographic Gratings. We designed and manufactured VPHGs for astronomical instrumentation and we demonstrated how photopolymers are reliable holographic materials for making astronomical devices with performances comparable to those provided by VPHGs based on Dichromated Gelatins (DCGs), but with a much simpler production process. Moreover, the versatility of these materials allowed us to propose and realize novel architectures of the spectroscopic dispersive elements. A compact and unique single prism device was realized for a FOSC spectrograph and new multi-layered devices are proposed, stacking VPHGs one on top of the other to obtain many spectra in the instrument’s detector, with advantages as increase of resolution and signal to noise ratio with respect to the classical single dispersive element.

We demonstrate holography in a traditional two-component holographic photopolymer in which the solid polymer host matrix has three distinct sets of material properties: 1) an initially liquid state appropriate for formulation and casting into the desired final shape, 2) a rubbery state with low glass transition temperature appropriate for holographic recording, and 3) a final higher modulus state with improved mechanical robustness. The general chemical scheme is to form the second stage rubbery polymer network via a thiol-acrylate Michael addition with an excess of one functional group. Holographic recording then takes place via radically initiated photopolymerization of a mobile high refractive index monomer, per the common two-chemistry process. During final flood illumination of the material, the remaining monomer and excess functional groups are polymerized to increase crosslink density and improve the mechanical properties of the matrix. We described three such material schemes and report general trends. We demonstrate high (96%) efficiency holographic recording, low (1.1%) shrinkage, no oxygen sensitivity and stage 2 glass transition temperatures at or above room temperature, sufficient to enable self-supporting films.

Optically-driven diffusion of high refractive index molecules within a transparent thermoset polymer matrix is a promising platform for hybrid optics that combines a wide range of optical structures from large scale holograms to micron-scale gradient index waveguides in a single integrated optical system. Design of such a system requires characterization of the optical response of the material at a wide range of spatial scales and intensities. While holographic analysis of the photopolymers is appropriate to probe the smaller spatial scales and lower intensity optical response, quantitative phase mapping of isolated structures is needed to probe the response to the higher intensities and lower spatial frequencies used in direct write lithography of waveguides. We apply the transport of intensity equation (TIE) to demonstrate quantitative refractive index measurements of 10 μm-scale localized gradient index structures written into diffusive photopolymer materials using both single- and two-photon polymerization. These quantitative measurements allow us to study the effect of different exposure conditions and material parameters such as writing beam power, exposure time, and wt% loading of the writing monomer on the overall profile of the refractive index structure. We use these measurements to probe the time scales over which diffusion is significant, and take advantage of the diffusion of monomer with a multiple-write scheme that achieves a peak refractive index contrast of 0.025.

We report on the characterization of volume holographic gratings recorded in photopolymerizable nanocomposites incorporated with hyperbranched polymer (HBP) acting as transporting organic nanoparticles. The HBP possesses ultrahigh index of refraction owing to the inclusion of triazine and aromatic ring units. Such an HBP was easy to disperse into acrylate monomer without any aggregation, so that films with good optical quality are available. A transmission volume grating with refractive index changes up to 2.3×10-2 was obtained at 27 vol.% HBP concentration and 7 vol.% multifunctional acrylate monomer at a wavelength of 532 nm.

Diarylethenes are P-type photochromic systems showing reversible light-induced modulation of optical properties, e.g., transmittance and refractive index, in the visible and near infrared regions. Transmittance can be progressively tuned according to the illumination dose, and the pattern written and erased several times with light. We demonstrated binary Computer Generated Holograms based on of photochromic materials, to be used as adaptable reference surfaces in interferometric tests. We encoded by Direct Laser Writing binary amplitude Fresnel Zone Plates into photochromic substrates and successfully tested them into an interferometric setup. More recently, we exploited the non-threshold behavior of photochromic materials to encode grayscale CGHs, which give a better wavefront reconstruction than binary holograms. We propose to use a device based on a Digital Micro-mirror Device as a real-time reconfigurable mask. We recorded for the first time amplitude grayscale CGHs and reconstructed them with high fidelity in shape, intensity and size.

In this research, we present new holographic material based on fluoride photo-thermo-refractive glass(PTR) - chloride PTR glass. One of the benefit of this type of PTR glass is positive refractive index change. During this work, for the first-time volume Bragg gratings were recorded in this kind of material. The first experiments revealed that such gratings are mixed i.e. possess both absorption and phase components. Complex analysis shows that both refractive index and absorption coefficient are modulated inside the grating structure. We found out that at first there is no strict dependence of the refractive index change from dosage, but as we continue the process of thermal treatment – dependence is appear. Exposure influence on the refractive index change for this glass differs from fluoride one and shows some sort of saturation after the exposure of 4-6 J/cm 2 . We distinguished refractive index change and absorption coefficient change and observed both behavior with increasing thermal treatment time. We found out that the increase of thermal treatment time results in the significant refractive index change. At the same time the absorption does ‘not practically change. It was found that maximum modulation of refractive index is comparable with fluoride PTR glass and achieves value of 1600 ppm. The modulation of absorption is equal to induced absorption caused by silver nanoparticles and depends from reading wavelength. Our study shows that almost all absorption is modulated inside the grating.

The photopolymerizable nanoparticle-polymer composites (NPCs) have thus far shown their excellent performance in practical applications, such as holographic data storage, nonlinear optics and neutron optics. We have demonstrated twofold enhancement of the saturated refractive index modulation (Δn sat ) of ZrO 2 NPC volume gratings recorded at high spatial frequencies by doping with a single functional thiol as a chain transfer agent (CTA). This result suggested that the incorporation of a CTA in an NPC is very useful for holographic applications of volume gratings in light and neutron optics. Such chemical modification of NPC volume gratings may be more effective by doping with multifunctional thiols. This is so because polymer features such as the molecular weight and the crosslinking network density can be tailored more diversely by introducing multifunctional thiols in photopolymers. The influences of varying functionalities of thiols as chain transfer agents on the thermal stability of a volume grating recorded in a photopolymerizable ZrO 2 nanoparticle-polymer composite film have been investigated.

Two-beam holographic exposure and subsequent monitoring of the time-dependent first-order Bragg diffraction is a common method for investigating the refractive index response of holographic photopolymers for a range of input writing conditions. The experimental set up is straightforward, and Kogelnik’s well-known coupled wave theory (CWT)[1] can be used to separate measurements of the change in index of refraction (Δn) and the thickness of transmission and reflection holograms. However, CWT assumes that the hologram is written and read out with a plane wave and that the hologram is uniform in both the transverse and depth dimensions, assumptions that are rarely valid in practical holographic testing. The effect of deviations from these assumptions on the measured thickness and Δn become more pronounced for over-modulated exposures. As commercial and research polymers reach refractive index modulations on the order of 10-2, even relatively thin (< 20 μm thick) transmission volume holograms become overmodulated. Peak Δn measurements for material analysis must be carefully evaluated in this regime. We present a study of the effects of the finite Gaussian write and read beams on the CWT analysis of photopolymer materials and discuss what intuition this can give us about the effect other non-uniformities, such as mechanical stresses and significant absorption of the write beam, will have on the analysis of the maximum attainable refractive index in a material system. We use this analysis to study a model high Δn two-stage photopolymer holographic material using both transmission and reflection holograms.

Sapphire windows are routinely being used in demanding aerospace applications due to their high strength and desirable optical and material properties. Sapphire is particularly useful in addressing the increasing need for systems that provide a wider range of capabilities in a single package. In general, refractive index homogeneity of the component materials can have a significant impact on overall optical system performance. This leads to the need for a deeper understanding of the shape and magnitude of index inhomogeneity in large sapphire windows to ensure predictable, high quality operation. Thin, sapphire slices from a sapphire crystal boule grown via the Heat Exchanger Method (HEM) have been previously evaluated for refractive index homogeneity over a 25.4cm (10.0”) aperture. The resultant transmitted wavefront error (TWE) from those measurements has now been used to model typical optical systems to quantify the effects on system-level performance attributed to representative amounts of index inhomogeneity in the sapphire window. The results of this modeling effort are presented in the following paper.

In this study, two-dimensional photonic crystal (PhC) was developed using functionalized polymers and nanoimprint lithography (NIL) for biosensing applications. In addition, using functionalized polymer-based PhC, detection of DNA hybridization or potassium ion were successfully applied by changing of PhC design and base material. For detection of DNA hybridization, PhC cavity was fabricated using polymer. By introducing of cavity into PhC, surrounding refractive index change due to the DNA hybridization could be detected high sensitively. Furthermore, for detection of potassium ion, PhC was fabricated using ionophore contained plasticized poly (vinyl chloride) (PVC). By using ionophore contained PVC-based PhC, potassium ion was specifically extracted into the PhC by ionophore. Then, potassium ion could be detected by the optical characteristics change that attributed by the physical and chemical property change of base material. From these result shows that the functionalized polymer-based PhC enables to apply for developing of high sensitive optical biosensor.

Dimensional Optical Metrology and Inspection for Practical Applications VI, Anaheim, California, United States of America, 9 April 2017

In this study, a numerical model based on finite element method was proposed to evaluate the thermo-mechanical behavior of a composite structure material. The composite structure consisted of substrate, thermal spray coating, and an embedded optical fiber. The stress level of the composite structure especially the embedded fiber at the end of elaboration process was analyzed. The variations of refractive index of the embedded fiber due to the thermo-optic effect and the elasto-optic effect were investigated. The results showed that the the variation of stress and refractive index during the elaboration process had an insignificant effect on the embedding quality of the optical fiber under the presented optimized experimental conditions.

In this article, an Adiabatic Tapered Optical Fiber — Fabry Perot (ATOF-FP) Sensor is introduced as a simple refractive index sensor. This FP Cavity relies upon reflection from two cleave ends of ATOF sensor's arms. Its spectrum was investigated with Distributed Feedback (DFB) tunable laser and photo detector. With analyzing the change in Optical Transmission Power (OTP) versus refractive index changes, the sensitivity of ATOF was −66.21 dB/RIU. In addition, the visibility of FP was studied. Its RI sensitivity was −0.975 1/RIU. The sensor resolution was 2.3 × 10−5 RIU with consideration of minimum detectable signal of acquisition system.

This work presents the proof of concept of the detection of global and surface optical index variations by surface plasmon resonance (SPR) thanks to optical fiber bundles. This work is the first necessary step for the future design of a lab-on-fiber tool dedicated to molecular analysis for endoscopic diagnosis. Our approach is based on nanostructured optical fiber bundles comprising several thousands of individual optical fibers. These nanostructures were coated by a thin gold layer in order to gain interesting optical properties such like SPR. The sensitivity and resolution of the bundle to global optical index changes were measured in retro-reflection. We performed numerical simulations in order to optimize the fiber tip geometry, gold coating thickness and finally enhance their analytical performances. We achieved a resolution of 10−4 refractive index unit, which is fully compatible with the detection of biological interactions involving large proteins or bacteria. Finally, we proved that our sensor was sensitive to surface optical index variations and able to detect the adsorption of a thin self-assembled molecular layer.

The design and modelling of a novel magnetic field sensor based on a long period fiber grating coated with a thin film of N doped ZnO is reported. The parameters of both, the grating and the thin film were carefully chosen to operate in the transition mode and near to the dispersion turning point. At this point, an LPFG shows its maximum sensitivity to external refractive index variations. The magnetic field induces variations in the coating refractive index, which changes the effective refractive index of the cladding mode and the consequent spectral response. In this work a sensitivity to the surrounding magnetic field of 2.9 nm/mT is reported with a maximum theoretical resolution of 2 μT.

We report on a thermal stability study of the resonant wavelength of fiber Bragg gratings fabricated by femtosecond laser. We propose a new method to analyze the decay of the central wavelength shift of Bragg gratings based on isothermal and isochronal processes up-to a maximum temperature of 800 °C. The obtained thermal decay follows a typical power-law function, which allowed us to fit theoretical equations to our experimental data and simulate the refractive index decay. A method to mitigate this decay is proposed and the results demonstrate the potential of using femtosecond fiber Bragg gratings as high temperature sensors.

We present a slot optical waveguide ring resonator that can be used as a refractive index sensor. The proposed ring resonator works on the principle of coupling of the mode from the bus waveguide to the ring waveguide. The ring resonator was analyzed using the finite-difference time-domain method. Our proposed waveguide structure showed a sensitivity of 42 nm/RIU. Our aim is to design a chalcogenide ring resonator for refractive index sensing in mid-infrared wavelengths.

We reported a simple, robust, and highly sensitive temperature sensor using intrinsic Mach-Zehnder interferometer formed by means of bending a tapered microfiber, embedded in polydimethylsiloxane. The outer temperature perturbations modulate the refractive index of the polymer through thermo-optic and thermal expansion effects of the polymer. This leads to a phase difference between interfering guided modes through the bent-microfiber, which ultimately results prominent wavelength shift in the transmission spectrum. The sensor exhibits a linear temperature response with a sensitivity as high as −6.25nm/°C over the temperature range from 24° to 40 °C. The sensitivity of the sensor increases as wavelength increases.

A four-channel fibre optic measurement system for fibre Bragg grating (FBG) sensors was used to measure the refractive index of fluids with Fresnel reflectometer sensors prepared from SMF28e singlemode fibres. The fibre optic measurement system was calibrated with five high-purity organic fluid samples in the refractive index range between 1.3 and 1.6. The light source had a wavelength of 1550 nm and the fluid samples were held at 24 °C. In total, 400 refractive index measurements were performed. The calibration of the fibre optic measurement system was performed with a linear correction function. The combined uncertainty of the refractive index measurements with the fibre optic measurement system was found to be in the order of 10−4.

An optical fiber sensor based on Fabry-Perot interferometer to measure the refractive index changes due to oxygenation level changes in hypoxic tumors for radiotherapy treatments is proposed. The sensors have an outer diameter of 220μm with a 20–30μm length air-cavity and a 30μm thickness end cap located at the tip of the sensor. The sensors are used to measure the phase change in the received optical spectrum when there is a change in refractive index using a Fast Fourier Transform based analysis method. The refractive index change is measured in order to determine the oxygenation level in hypoxic tumors. In this paper, different concentrations of iso-propanol solution are prepared to produce refractive index values between 1.3438 and 1.3655 in order to mimic the refractive index of hemoglobin. The sensors are coated with a 100 nm thick gold layer and a comparison is made with non-coated sensors. The coated sensors have a resolution in order of 10−3 RIU.

This paper presents a multimode fiber sensor that uses surface plasmon resonance on a metallic wire to measure refractive index. Numerical simulations based on the finite element method reveal the sensor supports several plasmon modes in the wire capable of coupling with the multiples optical fiber modes. Therefore, the sensor configuration creates multiple resonances at different wavelengths, with different values of the loss, sensitivity, among other parameters. Choosing the appropriate mode and filtering out the rest of the modes allows to optimize the sensor performance. In the present work a sensitivity of 5340nm/RlU and resolution of 1.87×10−6RlU were found.

An optical fibre long period grating (LPG) modified with a thin film of HKUST-1, a material from metal organic framework (MOF) family, was employed for the detection of carbon dioxide. The sensing mechanism is based on the measurement of the change of the refractive index (RI) of the coating that is induced by the penetration of CO 2 molecules into the HKUST-1 pores. The responses of the resonance bands in the transmission spectrum of an LPG modified with 40 layers of HKUST-1 upon exposure to carbon dioxide in mixture with nitrogen were investigated.

This work presents combined long-period grating (LPG) and a micro-cavity in-line Mach-Zehnder interferometer (μIMZI), both induced in the same single-mode optical fiber. In order to increase refractive index (RI) sensitivity of the LPG, it has been nanocoated with aluminum oxide (Al 2 O 3 ). Next, the μIMZI has been fabricated as a cylindrical cavity (d = 60 μm) in the center of the LPG. In transmission measurements for various RI in the cavity and around the LPG we have observed two effects coming from two independently working sensors. There was no significant impact on one or the other in terms of their functional properties. Such a combination of sensorial effects can be applied for cross-reference measurements of the two different parameters at the same time or for discrimination of influence of other parameters on the RI measurements.

A novel method for distributionally evaluating the effective refractive index differences, Δn eff , in multimode optical fibers is presented based on the Brillouin spectrum analysis. The proposed method is successfully demonstrated in GeO 2 -doped step-index 2-mode fibers, for evaluating Δn eff between LP 01 and LP 11 modes, and the method could be straightforwardly expanded to fibers containing higher-order modes, by using a mode demultiplexer supporting the higher-order mode. To the authors' best knowledge, this is the first report of distributional measurements of the effective refractive index differences in multimode optical fibers.

We propose a highly sensitive hybrid-plasmonic sensor based on thin-gold nanoslit arrays. The transmission characteristics of gold nanoslit arrays are analyzed as changing the thickness of gold layer. The surface plasmon polariton mode excited on the sensing medium, which is sensitive to refractive index change of the sensing medium, is strengthened by reducing the thickness of the gold layer. A design rule is suggested that steeper dispersion curve of the surface plasmon polariton mode leads to higher sensitivity. For the dispersion engineering, hybrid-plasmonic structure, which consists of thin-gold nanoslit arrays, sensing region and high refractive index dielectric space is introduced. The proposed sensor structure with period of 700 nm shows the improved sensitivity up to 1080 nm/RIU (refractive index unit), and the surface sensitivity is extremely enhanced.

Temperature dependent refractive index of DNA-cetyltrimethylammonium chloride (CTMA) thin-solid-film was measured 20 to 90°C to obtain its thermo-optic coefficient of −3.6× 10−4 (dn/dT). DNA-CTMA film has high thermosoptic coefficient than other polymers. The film was deposited on coreless silica fiber (CSF) to serve as a multimode interferometer optical fiber temperature sensor. It is immersed in a water that changed temperature from 40 to 90°C. It has sensitivity of 0.25nm/°C.

In this work we review the concept of optical fiber meta-tips, recently introduced by the authors. Optical fiber meta-tips come from the integration of plasmonic optical metasurfaces and the fiber optics technology. In particular, this integration is a major breakthrough in the recently emerged "Lab-On-Fiber" technology, where nanostructured platforms with special capabilities of light manipulation are integrated onto the tip of an optical fiber. Optical fiber meta-tips can, on one side, boost the real world applicability of optical metasurfaces, and, on the other side, bring about more advanced capabilities of on-fiber control and manipulation of light wavefront and polarization. With a view towards possible practical applications to label-free chemical and biological sensing, we inspect the potentialities of optical fiber meta-tips to work as sensors of local refractive index variations, and aim at studying the effect that the phase gradient impressed by the metasurface has on the surface sensitivity of proposed devices.

A single mode fiber is used in this study, in a Y-coupler mode; the mirror tip which is coated with bromothymol blue (BTB), homogeneously mixed in polyvinyl alcohol (PVA) matrix. The setup operated at 1550 nm, and was used to sense extremely small quantities of ammonia gas, at room temperature. The sensor was able to detect ammonia in the range of 1.5 ppm to 150 ppm; with observed sensitivity in terms of wavelength shift of 0.7 nm. The sensor showed excellent reversibility with fast response and recovery time of the order of few seconds. The possible interaction of dye with ammonia was studied and compared with chloroform.

In this study, we develop a plastic optical fiber (POF) sensor with a double-layer structure cladding consisting of a swelling polymer lower layer and a dye-doped swelling polymer upper layer. Both cladding layers swell and decrease their refractive indices when exposed to alkane vapor. Then, the structure of the POF sensor changes from leaky to waveguide mode. Therefore, the intensity of transmitted light changes remarkably, depending on the presence of alkane. The absorption of light due to the dye in the upper cladding layer increases the change in transmitted light intensity. In this study, we fabricated a POF sensor by using the electrospray deposition method and examined its response to alkane vapor. The results indicate an improvement in the sensitivity of the POF alkane sensor due to the effect of the double-clad layer.

A few-mode microfiber knot resonator (FM-MKR) incorporating a polyvinyl alcohol (PVA) is investigated for measurement of relative humidity (RH). Two modes, such as HE 11 and HE 12 , are excited and interfered in a nonadiabatically tapered structure of the single-mode fiber (SMF). After making a tie with the few-mode microfiber, the FM-MKR is fabricated. In the FM-MKR, two modes, such as HE 11 and HE 12 , must be circulated within the optical knot and cross-coupled independently with a phase delay. By optimizing the diameter of the microfiber, the difference of group effective refractive indices between two modes is dramatically suppressed resulting in the improvement of RH sensitivity of the proposed FM-MKR.

A novel, low cost and highly sensitive optical fibre probe sensor for concentration measurement of ethanol solvent (C2H5OH) corresponding to bio-ethanol production rate by an algae is reported. The principle of operation of the sensor is based on inter-fibre light coupling through an evanescent field interaction to couple the light between two multimode fibres mounted parallel to each other at a minimum possible separation i.e. ∼ < 1mm. The sensor was fabricated using a low cost 1000um plastic optical fibre (POF) and was characterized for real time measurement in the broadband spectrum including visible and near infra-red. The wavelength dependency of this sensor design was also investigated by post processing analysis of real time data and hence the optimum wavelength range determined. The proposed sensor has shown significant response in the range of 0.005–0.1 %v/v (%volume/volume or volume concentration) which depicts the high sensitivity for monitoring very minute changes in concentration corresponding refractive index changes of the solution. Numerically, sensor has shown the sensitivity of 21945 intensity counts/%v/v or 109.7 counts per every 0.0050 %v/v.

Refereed/Peer-reviewed A Mach-Zehnder interferometer was created from a cavity milled in the taper region next to a microfiber knot resonator. A focused ion beam was used to mill the cavity with 47.8 mu m in length. The microfiber knot resonator was created from an 11 mu m diameter taper, produced using a filament fusion splicer. After milling the cavity, the microfiber knot resonator spectrum is still visible. The final response of the presented sensor is a microfiber knot resonator spectrum modulated by the Mach-Zehnder interference spectrum. A preliminary result of -8935 +/- 108 nm/RIU was obtained for the refractive index sensitivity of the cavity component in a refractive index range of n = 1.333 to 1.341. Simultaneous measurement of refractive index and temperature using this combined structure is a future goal.