Fiber Tip Sensor Research Articles

SPR Fiber Tip Sensor for the Simultaneous Measurement of Refractive Index, Temperature, and Level of a Liquid

This paper provides the design, fabrication, and experimental demonstration of a novel, compact, and simple-to-construct optical fiber-tip sensor for the simultaneous measurement of the refractive index (RI), temperature, and level of liquid samples by means of surface plasmon resonance (SPR) phenomenon. The proposed fiber-tip SPR sensor consists of a multimode fiber spliced to a sensing element, it comprises a gold-coated single-mode fiber tip, whose end face is coated with a metallic mirror. By covering part of the sensing element with a thermo-responsive material, whose thermo-optic coefficient is high, it is possible to measure temperature; whereas the metal-bare section is used to measure the changes in the RI and level of a liquid sample. As the RI and temperature of the liquid sample increase, the position of the resonance wavelengths ( ${\boldsymbol {\lambda }_{\boldsymbol {bare}}}$ and ${\boldsymbol {\lambda }_{\boldsymbol {Covered}}}$ ) shifts toward larger and shorter wavelengths, respectively. On the other hand, as the level of the sensed sample increases, the deepness of ${\boldsymbol {\lambda }_{\boldsymbol {bare}}}$ increases too, but the position of ${\boldsymbol {\lambda }_{\boldsymbol {bare}}}$ and ${\boldsymbol {\lambda }_{\boldsymbol {Covered}}}$ remains constant for a particular liquid and temperature. We expect that this novel sensor becoming a promising candidate for biomedical, food, and/or industrial applications.

A fiber-tip photoacoustic sensor for in situ trace gas detection.

Most trace gas detection methods developed so far largely rely on active sampling procedures, which are known to introduce different kinds of artifacts. Here, we demonstrate sampling-free in situ trace gas detection in millimeter scale volumes with fiber coupled cantilever enhanced photoacoustic spectroscopy. Our 2.4 mm diameter fiber-tip sensor is free from the wavelength modulation induced background signal (a phenomenon that is often overlooked in photoacoustic spectroscopy) and reaches a normalized noise equivalent absorption coefficient of 1.3 × 10-9 W cm-1 Hz-1/2 for acetylene detection. To validate its in situ gas detection capability, we inserted the sensor into a mini fermenter for headspace monitoring of CO2 production during yeast fermentation. Our results show that the sensor can easily follow the different stages of the CO2 production of the fermentation process in great detail.

Determination of thermo-optic coefficient of ethanol-water mixtures with optical fiber tip sensor

Abstract In this work, the thermo-optic coefficient (TOC) of ethanol-water mixtures, through refractive index and temperature measurements are determined using an etched optical fiber tip based on a multimode interferometer. The proposed probe is fabricated by fusion-splicing a 5.2 mm long coreless fiber section to a single mode fiber. To reduce the sensor dimensions and improve its sensitivity towards external medium variations, the fiber tip is subjected to wet chemical etching using a solution of 40% hydrofluoric acid, presenting a final diameter of 24.4 μm. The TOC of each solution is estimated and, in the case of deionized water and pure ethanol, its value is of −1.128 × 10−4 °C−1 and −3.117 × 10−4 °C−1, respectively.

Optical Fiber-Tip Sensors Based on In-Situ µ-Printed Polymer Suspended-Microbeams.

Miniature optical fiber-tip sensors based on directly µ-printed polymer suspended-microbeams are presented. With an in-house optical 3D μ-printing technology, SU-8 suspended-microbeams are fabricated in situ to form Fabry–Pérot (FP) micro-interferometers on the end face of standard single-mode optical fiber. Optical reflection spectra of the fabricated FP micro-interferometers are measured and fast Fourier transform is applied to analyze the cavity of micro-interferometers. The applications of the optical fiber-tip sensors for refractive index (RI) sensing and pressure sensing, which showed 917.3 nm/RIU to RI change and 4.29 nm/MPa to pressure change, respectively, are demonstrated in the experiments. The sensors and their optical µ-printing method unveil a new strategy to integrate complicated microcomponents on optical fibers toward ‘lab-on-fiber’ devices and applications.

Fabry–Perot interferometer fiber tip sensor based on a glass microsphere glued at the etched end of multimode fiber

We demonstrate an optical Fabry–Perot interferometer fiber tip sensor based on a glass microsphere glued at the etched end of a multimode fiber. The fiber device is miniature and robust, with a convenient reflection mode of operation, a high temperature sensitivity of 202.6 pm/°C within the range from 5°C to 90°C, a good refractive index sensitivity of ∼119 nm/RIU within the range from 1.331 to 1.38, and a gas pressure sensitivity of 0.19 dB/MPa.

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.

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.

Liquid-air based Fabry-Pérot cavity on fiber tip sensor.

This paper presents a Fabry-Perot fiber tip sensor based on an air-liquid filled cavity. The cavity is sealed off by a thin gold coated membrane of parylene C, between 300 and 350 nm, creating a particularly flexible diaphragm. In order to retrieve and track the cavity of interest from other cavities formed within the sensor tip, a signal processing of the feedback signal is performed by inverse fast Fourier transform. The experimental sensor has been manufactured and tested for temperature, giving cavity length sensitivities of 6.1 nm/°C and 9.6 nm/°C for temperature increase and decrease respectively. The external gas pressure response gives a sensitivity of 15 nm/kPa. The fiber sensor has also been adapted for force sensing after silicone embedment and has shown a sensitivity of about 8.7 nm/mN. Finally, the sensor has been tested on insertion into a human temporal bone, proving that it could be an interesting candidate for insertion force monitoring for robotic cochlear implantation.

Sensitive Detection of Small Particles in Fluids Using Optical Fiber Tip with Dielectrophoresis.

This work presents using a tapered fiber tip coated with thin metallic film to detect small particles in water with high sensitivity. When an AC voltage applied to the Ti/Al coated fiber tip and indium tin oxide (ITO) substrate, a gradient electric field at the fiber tip induced attractive/repulsive force to suspended small particles due to the frequency-dependent dielectrophoresis (DEP) effect. Such DEP force greatly enhanced the concentration of the small particles near the tip. The increase of the local concentration also increased the scattering of surface plasmon wave near the fiber tip. Combined both DEP effect and scattering optical near-field, we show the detection limit of the concentration for 1.36 μm polystyrene beads can be down to 1 particle/mL. The detection limit of the Escherichia coli (E. coli) bacteria was 20 CFU/mL. The fiber tip sensor takes advantages of ultrasmall volume, label-free and simple detection system.

Ultrasensitive Temperature Sensor Based on a Fiber Fabry–Pérot Interferometer Created in a Mercury-Filled Silica Tube

We demonstrate an ultrasensitive temperature sensor based on a unique fiber Fabry-Perot interferometer (FPI) that was created by means of splicing a mercury-filled silica tube with a single-mode fiber. The air cavity of the fiber FPI was formed by the surface of the mercury column and the endface of the single-mode fiber. Moreover, the mercury-based fiber FPI exhibits an ultrahigh temperature-sensitivity of up to -41.9 nm/°C, which is about one order of magnitude higher than that of the ordinary FPI-based fiber-tip sensors reported so far. Hence, such a mercury-based fiber FPI temperature sensor could be used for highly sensitive ambient temperature sensing applications.

Theoretical investigations for combination optical fiber tip sensors

For the optical fiber biosensor made of combination optical fiber tip, the effects of the refractive index RI of outer medium and the geometrical parameters of combination optical fiber tip on two important quantities have been investigated. One factor is the total intensity of the evanescent wave into fluorescent layer through core-medium interface; the other is the intensity of the fluorescence signal transmitted from fluorescent layer to measurement end. Theoretical investigations show that the two quantities are dependent upon the RI of outer medium, and the total intensity of the evanescent wave into fluorescent layer increases with the increase of taper angle, and the fluorescence signal arrived at the measurement end gets larger value for shorter fiber tip when the RI of outer medium is smaller than the RI of fiber core.

Interference characteristics in a Fabry–Perot cavity with graphene membrane for optical fiber pressure sensors

Due to higher mechanical strength and ultra-thin thickness, graphene is used as a sensitive diaphragm in a Fabry---Perot cavity to improve the sensitivity of pressure sensors. In accordance with the working principle of Fabry---Perot interferometer, a load---deflection mathematical model of fiber-tip pressure sensor with graphene membrane is established based on the large deflection elastic theory of circular membrane. The effects of membrane parameters, including prestressing force and membrane layer number, on deflection mechanical behaviors are studied by using finite element method. Also, the effects of graphene membrane layer and incident light angle on the film reflectivity are obtained according to the refractive index characteristics of the membrane. The simulation results show that an approximate linear relation between loads and deflections exists in the simulated pressure range from 0 to 3.5 kPa, and a theoretical pressure sensitivity of 1,096 nm/kPa for a single-layered graphene membrane can be achieved. To estimate the performance of multi-layered graphene membrane as the diaphragm, an extremely thin 13-layered 125-μm diameter graphene diaphragm is fabricated on the tip of the fiber end, which forms a low finesse Fabry---Perot interferometer. The Fabry---Perot cavity with a length of 40 μm can exhibit a fringe visibility of approximate 0.56 with a measured membrane reflectivity of 1.49 %. The experimental results demonstrate that the use of graphene as diaphragm material would allow highly sensitive and miniature fiber-tip sensors.

Detection of evaporation process of acetone with a microstructured fiber in a reflective configuration

A multimodal interferometer based on a new microstructured fiber tip is proposed for detection of the evaporation process of acetone. The new geometry consists of a capillary tube in which an offset Ge-doped core is fused and spliced at the end of a single-mode fiber. The fiber tip sensor structure was immersed in liquid acetone and the evaporation process of acetone was monitored in real time. Due to the refractive index variation of the external medium with increasing temperature, a short detection time of ∼1 s was achieved.

광섬유 패치코드를 이용한 Fabry-Perot 간섭계 온도센서

In this paper, we propose and demonstrate a Fabry-Perot interferometer (FPI) optical fiber tip sensor fabricated by a blade-sawing technique using a fiber optic patch cord for high-resolution temperature measurement. The sensor head consists of a short air FP cavity near the tip of a single-mode fiber patch cord tip. The temperature which we can measure is determined through a phase variation of the interference fringes in the reflective spectrum of the sensor. The fiber optic FPI sensor in this work can monitor the environmental temperature very accurately from 40 to <TEX>$120^{\circ}C$</TEX>. As a result, the temperature sensitivity is obtained as <TEX>$38.2pm/^{\circ}C$</TEX>.

Fabry-Perot fiber-tip sensor based on an inner air cavity for refractive index sensing

We propose a simple and low-cost Fabry-Perot (F-P) fiber sensor based on an inner air cavity. The air cavity is fabricated at the fiber-tip by splicing a single-mode fiber and a hollow-core photonic crystal fiber (HC-PCF), with un-collapsed section of the HC-PCF being cleaved. Application of F-P fiber-tip sensor in the external refractive index (RI) measurement is experimentally demonstrated. The sensor exhibits a good linear response and high sensitivity of -54.409 dB/RIU in the RI range of 1.333–1.413. Therefore, it is applied to fiber-optic biological and chemical sensing.

Femtosecond laser fabricated in-line micro multicavity fiber FP interferometers sensor

A compact micro multicavity Fabry–Perot (FP) optical fiber tip sensor is presented. In the end of the single-mode fiber (SMF), we drill a short air hole with femtosecond laser, which forms a multicavity together with the fiber flat face tip. The sensor has been experimentally tested for refractive index (RI) and temperature sensing by monitoring its wavelength shift. Simultaneous measurement of both changes in the ambient temperature and the RI can be realized using the sensitivity matrix. Measurement results show that the in-line FP exhibits the gas RI sensitivity of 867.76nm/RIU and the temperature sensitivity of 7.8pm/°C within the range of 24–104°C, and the device is highly stable over time.

Characterization of laser-driven shock waves in solids using a fiber optic pressure probe

Measurement of laser-driven shock wave pressure in solid blocks of polymethyl methacrylate is demonstrated using fiber optic pressure probes. Three probes based on a fiber Fabry-Perot, fiber Bragg grating, and interferometric fiber tip sensor are tested and compared. Shock waves are generated using a high-power laser focused onto a thin foil target placed in close proximity to the test blocks. The fiber Fabry-Perot sensor appears capable of resolving the shock front with a rise time of 91 ns. The peak pressure is estimated, using a separate shadowgraphy measurement, to be 3.4 GPa.

Theoretical investigations for surface plasmon resonance based optical fiber tip sensor

The surface plasmon resonance (SPR)-based optical fiber tip sensor is more convenient for the chemical or biological sensing since it occupies less space than the SPR-based optical fiber sensor using the transmitted spectrum as the sensing signal. In this work, a detail theoretical analysis for the SPR-based optical fiber tip sensor has been finished. First, the effects of the geometric parameters on the reflecting spectrum, resonance wavelength and sensitivity have been investigated. Then, a dispersion function-based explanation for the relationship between resonance wavelength and tip angle has been presented. It can be seen that the increase of tip angle may lead to the increase of resonance wavelength and the broadening of resonance dip because the incident angle of the ray at the tip interface changes in a greater region.

Micro Multicavity Fabry–Pérot Interferometers Sensor in SMFs Machined by Femtosecond Laser

We propose and demonstrate a compact micromulticavity Fabry–Pérot (FP) optical fiber tip sensor for refractive-index (RI) and temperature measurement, which is fabricated by laser micromachining. The fabrication process of the sensor offers a quite simple way to fabricate compact in-line FP at a low cost. At the end of the single-mode fiber, there is a short air FP cavity, which forms a multicavity together with the fiber flat face tip. Two independent cavities exist in our sensor, and the air cavity is used for RI sensing and the glass cavity for temperature sensing, thus, avoiding the temperature and RI cross-sensitivity. The measurement results show that the in-line FPI exhibits an RI sensitivity of 1074.36 nm/RIU and a temperature sensitivity of 10.6 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm pm}/^{\circ}{\rm C}$</tex></formula> .

Optical Response of Fiber-Optic Fabry-Perot Refractive-Index Tip Sensor Coated With Polyelectrolyte Multilayer Ultra-Thin Films

The polyelectrolyte multilayer (PEM) thin film-coated Fabry-Perot (F-P) optical fiber tip sensors had been developed for in situ refractive index (RI) measurement. Using the simple layer-by-layer (LBL) approach, the sensor surfaces had been successfully coated with PEM thin films of poly(diallyldimethyl- ammonium choloride)/poly(styrenesulfonate sodium salt) (PDDA/PSS) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> (n is number of bilayers). Their optical response to the changes of external RI had been investigated and evaluated. The results demonstrated that after coated with PEM thin films, the inflection point of as-formed F-P tip sensor would shift from 1.457 to 1.4623 but its RI sensitivity was slightly reduced from 39 dB/RI to 25 dB/RI. In addition, their fringe contrast exhibited the unique temperature-independent performance. Therefore, owing to these special optical properties, simple operation and easy miniaturization, these novel PEM thin film coated F-P tip sensors have great potential in the detection and sensing of chemical and biological molecules, even at elevated temperature.