Tip Of Multimode Fiber Research Articles

Refractive index measurements of ethanol-water binary liquid solutions using a graded-index fiber tip sensor

The refractometric analysis of ethanol-water mixtures is hampered because this type of binary solution does not present a linear behaviour. In this work it is proposed a multimode Graded-Index Fiber (GIF) tip sensor for the measurement of ethanol in binary liquid solutions of ethanol-water. The probe is fabricated by fusion-splicing a 500 µm GIF to a Single Mode Fiber (SMF) and it operates as a refractometric sensor in reflection. Samples of ethanol-water mixtures were measured at different temperatures (20°C to 60°C) to evaluate the probe’s capability to detect variations in ethanol refractive index. The samples have different % (v/v) of ethanol, in a range between 0% and 100%.

Dual-channel temperature-compensated vector magnetic field sensor based on lab-on-a-fiber-tip.

Fiber-optic magnetic field sensors based on magnetic fluid (MF) is encountering with thermal effects and demand for vectorization for several years. A common solution is to use axially processed fiber cascaded with fiber Bragg grating (FBG). However, the length of such sensors is usually in centimeter-level, which restricts the sensing applications in narrow space and gradient field cases. In this work, we present an ultracompact reflection-type dual-channel sensor for vector magnetic field (Channel 1, referred as CH1) and temperature (Channel 2, referred as CH2) monitoring, which is composed of a pair of gold-plated wedge-shaped multimode fiber (MMF) tip and gold-plated multimode-no-core fiber (MNF) tip. The surface plasmon resonance (SPR) effect was adopted. The two sensor probes are coated with magnetic-field-sensitive MF and temperature-sensitive polydimethylsiloxane (PDMS), respectively. The issue of vector magnetic field and temperature cross-sensitivity is tactfully resolved. Importantly, the proposed sensing probes are ultracompact and the spatial resolution is extremely small (615 µm for CH1 based on wedge-shaped fiber tip and 2 mm for CH2 based on MNF), which is very helpful for narrow space and gradient magnetic field detection. The obtained magnetic field intensity sensitivities are 1.10 nm/mT (90° direction) and -0.26 nm/mT (0° direction), and temperature sensitivity is -3.12 nm/°C.

Optical cavitation in non-absorbent solutions using a continuous-wave laser via optical fiber

Optical cavitation can be induced by short pulse lasers focused into a solution with a low absorption coefficient or using a continuous-wave laser focused into highly absorbent solutions. In this work, we report the generation of cavitation bubbles in ethanol using a continuous-wave fiber optic laser with emission at 450 nm wavelength. Silver and copper nitrate nanoparticles were immobilized on the flat end-face of a multimode optical fiber tip using the photodeposition technique and then immersed into the solution. Laser light transmitted through the optical fiber is strongly absorbed by both nanoparticles causing an abrupt increase in temperature around the tip of the optical fiber, reaching the spinodal limit of ethanol (∼187 °C). At this temperature, an explosive phase transition (liquid–gas) occurs causing the generation of a microbubble, which grows until reaches its maximum radius (∼1072 μm in 132 µs) and subsequently collapses, emitting a shock wave. The dynamic behavior of the gas bubble was studied as a function of the laser power using a high-speed video camera, and the shock wave emitted immediately after the bubblés collapse was detected by a microphone. The pressure of the shock wave was analyzed photodepositing different thin films of silver nanoparticles at the tip of the optical fiber, causing optical attenuations of 1, 3, 5, and 7 dB. The experimental results obtained showed that when a thin film of copper nitrate nanoparticles was photodeposited on a film of silver nanoparticles (5 dB), the pressure of the shock wave increases up to ∼ 13-fold, in comparison, if we use only one film of silver nanoparticles. Energetic shock waves have potential applications in a variety of areas such as medicine, biological sciences, material processing, liquid microjets generation, among others.

Gold filled in Fresnel zone plate fabricated by femtosecond laser on fiber tip

We present a method to fabricate Fresnel zone plate (FZP) on the multimode fiber (MMF) tip by combining femtosecond laser direct writing with coating, polishing and chemical etching. After laser processing, the fiber tip coated by gold was polished to obtain a clear unprocessed region with high transmittance and a processed area filled with gold. By launching an 850 nm laser into the MMF, the light intensity distribution and coupling law of the fabricated FZP are studied. The experimental results indicate that the laser is focused at a distance of 900 μm out of the FZP.

Multilayer SiC/C Thin Film Coating on Fiber Tip for Raman Probe Application

A novel technique in the fabrication of an optical filter that is made up of multilayer thin film is introduced in this study. Multiple layers of silicon carbide and carbon with high and low refractive index materials respectively will be deposited alternatively with a various thickness on a glass substrate by radio frequency magnetron sputtering of 99% purity of silicon carbide as the target. The variation of structure and optical properties of the films are studied by using X-ray reflectivity (XRR), Raman scattering spectroscopy, and UV–vis-NIR spectroscopy until it reached the desired results and meet the specification as Raman optical filter. The thin film is then placed on a multimode fiber tip as Raman edge filter. Raman fingerprint of specific alcohol (ethanol) obtained is tested using a fabricated filter with the standard spectrum. The preliminary result of SiC thin film fabrication for 30, 60 and 90 minutes by sputtering process showed rate of deposition obtained is 3.17nm/min. The results demonstrate that the optical properties of silicon carbide thin film can be monitored by modifying the condition of silicon carbide and carbon deposition.

Deep Learning for Estimating Deflection Direction of a Multimode Fiber From Specklegram

This study presents a novel approach and proof-of-concept for measuring the deflection direction of a multimode fiber's tip through analysis of the shape and structure of speckle patterns. First, we utilize a pendulum-based apparatus to construct a comprehensive dataset for studying the association between speckle patterns and the deflection of a multimode fiber tip. Then, we train a convolutional neural network (CNN) model to learn the relationship between a fiber optic deformation parameter and the variations in the shape and structure of speckle patterns. Finally, the ability of the model in estimating the deflection direction is evaluated by using unseen images from the test set. Our experimental results show that speckle patterns provide a feasible solution for measuring the deflection direction of the multimode fiber's tip. Moreover, our results provide insights into the generalization capabilities of speckle patterns analysis for sensing the direction of deflection.

Simultaneous trapping of low-index and high-index microparticles using a single optical fiber Bessel beam

We propose and experimentally demonstrate a fiber-based Bessel optical trap for the simultaneous trapping of both high-refractive-index particle and a low-refractive-index particle. We obtain the Bessel beam by incident 980 nm beam into the designed integrate fiber structure, which is fabricated by coaxial splice a section of step-index multimode fiber to the single mode fiber. A high refractive index glass microsphere, which is stuck on the tip of multimode fiber, is utilized to converge the Bessel beam to produce a bright focal spot and a dark cage along the axial direction. The high-refractive-index particle and the low-refractive-index particle are trapped in the bright focal spot and the dark cage, respectively. Our simulation verifies the feasibility that particles with high refractive index and low refractive index can be trapped and manipulated at the same time. The proposed optical trap which can simultaneously trap the particles with different refractive index makes it easier to manipulate cells or molecules with different properties and explore the multi-molecule interaction, which can facilitate the research related to biology and chemistry.

Cavity-coupled conical cross-section gold nanohole array fiber tip localized surface plasmon resonance sensor

A conical cross-section gold nanoholes array is fabricated on a multi-mode optical fiber tip with an electron-beam lithography process. Underneath the conical gold nanoholes, nanocavities are etched into the substrate fiber glass to increase the light–matter interaction volume. Localized surface plasmon resonance of the fabricated fiber optical device is characterized by measuring the optical transmittance through the fiber tip in the visible and near infrared spectral range. The fiber optical device is used as an index of refraction sensor to detect isopropyl alcohol, ethanol, and methanol. A largely enhanced sensitivity of 652 nm per refractive index unit due to the conical cross-section gold nanoholes and the nanocavities in the fiber glass substrate is observed. Additionally, the response and recovery times of the fiber-tip plasmon sensor are measured for the first time.

Multiphoton fluorescence excitation and detection with a single negative curvature hollow core fibre

In this letter, we propose a single fiber-based sensor setup allowing for simultaneous excitation and detection of multiphoton fluorescence. Presented sensor’s key element is the negative curvature hollow core fiber (NCHCF) with three transmission bands in the visible spectral range (414–423 nm, 510–552 nm and 680–784 nm), allowing for nearly dispersion-free guidance of 160 fs-long laser pulses at 730 nm photon wavelength. Total temporal broadening of a laser pulse propagating in the proposed sensor setup is only (7 ± 1) fs. The NCHCF output beam was additionally focused with a microlensed, multimode fiber tip, increasing the efficiency of multiphoton absorption. The usefulness of the sensor for the multiphoton spectroscopy experiments is tested on the solutions of fluorescein and flavin adenine dinucleotide. This optical fiber sensor combines simplicity, minimal size, and good optical properties, and can be found an interesing solution for the non-linear optical methods used in chemistry, biology and medicine.

法布里-珀罗薄膜干涉的光纤温度传感器

In order to develop a miniature fiber-optic temperature sensor with simple structure, low cost and mass production, the principle of optical coating interference-based temperature sensor was analyzed. The coating formula of temperature sensing probe was designed by TFCalc formula designing software using ZrO2 and Al2O3 materials. The thin film was deposited on the tip of multimode fiber by using electron-beam evaporation in Nanguang ZZS1100-8/G box type vacuum coating machine. The measurement system of coating interference-based temperature sensor was interrogated. The experimental result shows that the wavelength shift of the fiber-optic temperature sensor is linear in the range of 200-600℃, and the correlation coefficient was calculated to be 99.7%, the sensitivity of temperature is 8.3710-6/℃. The temperature sensor based on Fabry-Perot interference is suitable for mass production with stable performance, accurate point measurement, narrow installation position or higher application requirements for integrated sensor.

Single fiber dual-functionality optical tweezers based on graded-index multimode fiber

We propose and demonstrate single fiber dual-functionality optical tweezers based on a graded-index multimode fiber. By using the multi-angle fiber grinding and polishing technology, we fabricate the multimode fiber tip to be a special tapered shape, contributing to focus the outgoing beam with a large intensity gradient for the first functionality—three-dimensional contactless trapping of a microparticle. By adjusting the radial direction offset between the lead-in single mode fiber and the graded-index multimode fiber, we perform the second functionality—axial shift of the trapped microparticle with respect to the fiber tip without need of moving the fiber probe itself. It is convenient for practical applications. The theoretical and experimental results about the relationship between the radial offset and the equilibrium positions of the microparticle have the good consistency. Tailoring the trap and axial shift of the microparticle based on the graded-index multimode fiber provides convenient avenues for fiber optical tweezers applied in practical researches.

Multimode fiber tip Fabry-Perot cavity for highly sensitive pressure measurement

We demonstrate an optical Fabry-Perot interferometer fiber tip sensor based on an etched end of multimode fiber filled with ultraviolet adhesive. The fiber device is miniature (with diameter of less than 60 μm), robust and low cost, in a convenient reflection mode of operation, and has a very high gas pressure sensitivity of −40.94 nm/MPa, a large temperature sensitivity of 213 pm/°C within the range from 55 to 85 °C, and a relatively low temperature cross-sensitivity of 5.2 kPa/°C. This device has a high potential in monitoring environment of high pressure.

Miniature fiber-optic temperature sensor based on optical coating interference

A temperature sensor with Fabry–Perot cavity formed by dielectric film on the tip of multimode fiber is theoretically simulated and experimentally demonstrated. The sensor is proved to be simple in configuration, low cost and easy for batch fabrication. The thermo-optic effect and thermal expansion property of the thin-film materials, and optical coating interference theory were analyzed by MATLAB in the simulation. Experimental result shows that the repeatability error of the fabricated temperature sensor is 6.67%, when the environment temperature changes from 200°C to 700°C, and the temperature characteristic of interference fringes is almost the same as in simulation. The simulation analysis can be used to choose thin film materials and coating formula which is sensitive to temperature and robust for tolerance.

Quantification of the fluorescence sensing performance of microstructured optical fibers compared to multi-mode fiber tips.

Microstructured optical fibers, particularly those with a suspended-core geometry, have frequently been argued as efficient evanescent-field fluorescence-based sensors. However, to date there has not been a systematic comparison between such fibers and the more common geometry of a multi-mode fiber tip sensor. In this paper we make a direct comparison between these two fiber sensor geometries both theoretically and experimentally. Our results confirm that suspended-core fibers provide a significant advantage in terms of total collected fluorescence signal compared to multi-mode fibers using an equivalent experimental configuration.

Dynamic response of tapered optical multimode fiber coated with carbon nanotubes for ethanol sensing application.

Ethanol is a highly combustible chemical universally designed for biomedical applications. In this paper, optical sensing performance of tapered multimode fiber tip coated with carbon nanotube (CNT) thin film towards aqueous ethanol with different concentrations is investigated. The tapered optical multimode fiber tip is coated with CNT using drop-casting technique and is annealed at 70 °C to enhance the binding of the nanomaterial to the silica fiber tip. The optical fiber tip and the CNT sensing layer are micro-characterized using FESEM and Raman spectroscopy techniques. When the developed sensor was exposed to different concentrations of ethanol (5% to 80%), the sensor reflectance reduced proportionally. The developed sensors showed high sensitivity, repeatability and fast responses (<55 s) towards ethanol.

Reversible NO2 Optical Fiber Chemical Sensor Based on LuPc2 Using Simultaneous Transmission of UV and Visible Light.

In this paper, an NO2 optical fiber sensor is presented for pollution monitoring in road traffic applications. This sensor exploits the simultaneous transmission of visible light, as a measurement signal, and UV light, for the recovery of the NO2 sensitive materials. The sensor is based on a multimode fiber tip coated with a thin film of lutetium bisphthalocyanine (LuPc2). The simultaneous injection of UV light through the fiber is an improvement on the previously developed NO2 sensors and allows the simplification of the sensor head, rendering the external UV illumination of the film unnecessary. Coatings of different thicknesses were deposited on the optical fiber tips and the best performance was obtained for a 15 nm deposited thickness, with a sensitivity of 5.02 mV/ppm and a resolution of 0.2 ppb in the range 0–5 ppm. The response and recovery times are not dependent on thickness, meaning that NO2 does not diffuse completely in the films.

An in-line optical fiber refractometer with porous thin film coating

An in-line refractive-index sensor is proposed and demonstrated. The sensor is based on Fresnel reflection modulated by Fabry–Perot interference, which consists of a section of multi-mode fiber (MMF) tip coated with porous dielectric multilayer. The measure is conducted by monitoring the shift of the interference fringe, which is correlated to different refractive indices. When the external refractive index (RI) changes from 1.333 to 1.443, the RI sensitivity is 135.5nm/RIU with good linearity. The miniature size, simple physical structure, small temperature dependence, linear response and ability for batch fabrication make the device attractive for chemical and biological sensing.

Reflectance Response of Optical Fiber Coated With Carbon Nanotubes for Aqueous Ethanol Sensing

Ethanol is a highly flammable chemical and is widely used for medical and industrial applications. In this paper, optical sensing performance of aqueous ethanol with different concentrations is investigated using multimode fiber coated with carbon nanotubes (CNT). The multimode optical fiber tip is coated with CNT via a drop-casting technique and is annealed at 70 $^{\circ}\hbox{C}$ to improve the binding of the nanomaterial to the silica fiber. The optical fiber tip and the CNT sensing layer are microcharacterized using field emission scanning electron microscopy, Raman spectroscopy, and X-ray diffraction techniques. The reflectance response of the developed fiber sensor is measured using a spectrophotometer in the optical wavelength range of 500–800 nm. Upon exposure to ethanol with concentration ranges of 5%–80%, the sensor reflectance reduced proportionally. The dynamic response decreased by 4% when the sensor is exposed to ethanol with concentration of 80% in distilled water. It is found that the sensor shows fast response and recovery as low as 38 and 49 s, respectively.

Reflectance response of tapered optical fiber coated with graphene oxide nanostructured thin film for aqueous ethanol sensing

In this work, optical sensing performance of tapered multimode fiber tip coated with graphene oxide (GO) nanostructured thin film towards aqueous ethanol with different concentrations is investigated. The tapering process of the optical fiber is done by a glass processing machine. The multimode optical fiber tip is dip-coated with GO and annealed at 70°C to enhance the binding of the nanomaterials to the silica fiber. FESEM, Raman microscopy and XRD analyses are performed to micro-characterize the GO thin films. The morphology of the GO is observed to be in sheets forms. The reflectance response of the GO coated fiber tip is compared with the uncoated tip. The measurements are taken using a spectrophotometer in the optical wavelength range of 550–720nm. The reflectance response of the GO coated fiber tip reduced proportionally, upon exposure to ethanol with concentration range of 5–80%. The dynamic response of the developed sensor showed strong reversibility and repeatability when it is exposed to ethanol with concentrations of 5%, 20% and 40% in distilled water. At room temperature, the sensor shows fast response and recovery as low as 19 and 25s, respectively.

Reflective Refractometer Based on a Thin-Core Fiber Tailored Multimode Fiber Bragg Grating

A temperature-independent reflective refractometer configuration based on a core-diameter-mismatch is proposed and experimentally demonstrated. The configuration consists of a short section of thin-core fiber (TCF) with a multimode fiber (MMF) tip inscribed with a fiber Bragg grating (FBG). The TCF excites cladding modes into the downstream MMF via the mismatch-core splicing interface, and the parts of the core and cladding modes are reflected back to the lead-in fiber core by the MFBG. The recoupling efficiency of the core and cladding modes is highly dependent on the surrounding refractive index (SRI) of the TCF and MMF. Experimental results show that some recoupled modes show a high sensitivity to SRI. Power-referenced and temperature-independent SRI measurement with improved sensitivity for resolutions with SRI values near 1.33 is achieved through the wavelengths of selective mode monitoring.