P. A. S. Jorge

Interferometric optical fiber inclinometer with dynamic FBG based interrogation

The development of an interferometric optical fiber inclinometer is described in this paper. A weak tapered region is induced in a standard single mode fiber in the vicinity of the cleaved fiber tip, using a standard fusion splicer. In this situation an in-fiber Michelson interferometer is constructed that is sensitive to curvature applied in the tapered region. It is shown that depending on the angular range, fringe visibility and/or peak position depend strongly on the applied curvature enabling low cost dielectric inclinometer to be setup that is suitable for high voltage applications. It is presented an analysis of the sensor response by means of experimental measurements and manipulation of these experimental data through computational simulations. The results coming from the numerical simulations indicate a good performance of the sensor within range of angular variation between 3 and 6 degrees and 10 and 14 degrees. A low cost strategy to interrogate the response of sensor using electrically modulated fiber Bragg gratings, a photodetector and frequency analysis is described. The results presented by this electric interrogation technique show a good sensitivity in the range 3.5 to 5.5 degrees.

DNA-Aptamer optical biosensors based on a LPG-SPR optical fiber platform for point-of-care diagnostic

Surface Plasmon Resonance (SPR) is the base for some of the most sensitive label free optical fiber biosensors. However, most solutions presented to date require the use of fragile fiber optic structure such as adiabatic tapers or side polished fibers. On the other hand, long-period fiber gratings (LPG) present themselves as an interesting solution to attain an evanescent wave refractive index sensor platform while preserving the optical fiber integrity. The combination of these two approaches constitute a powerful platform that can potentially reach the highest sensitivities as it was recently demonstrated by detailed theoretical study [1, 2]. In this work, a LPG-SPR platform is explored in different configurations (metal coating between two LPG – symmetric and asymmetric) operating in the telecom band (around 1550 nm). For this purpose LPGs with period of 396 μm are combined with tailor made metallic thin films. In particular, the sensing regions were coated with 2 nm of chromium to improve the adhesion to the fiber and 16 nm of gold followed by a 100 nm thick layer of TiO2 dielectric material strategically chosen to attain plasmon resonance in the desired wavelength range. The obtained refractometric platforms were then validated as a biosensor. For this purpose the detection of thrombin using an aptamer based probe was used as a model system for protein detection. The surface of the sensing fibers were cleaned with isopropanol and dried with N2 and then the aminated thrombin aptamer (5’-[NH2]- GGTTGGTGTGGTTGG-3’) was immobilized by physisorption using Poly-L-Lysine (PLL) as cationic polymer. Preliminary results indicate the viability of the LPFG-SPR-APTAMER as a flexible platforms point of care diagnostic biosensors.

Characterization of a novel dissolved CO2 sensor for utilization in environmental monitoring and aquaculture industry

A novel optical fiber sensor is presented for measuring dissolved CO2 for water quality monitoring applications, where the optical signal is based either on refractive index changes or on color change. The sensing chemistry is based on the acid-basic equilibrium of 4-nitrophenol, that is converted into the anionic form by addition quaternary ammonium hydroxide. The CO2 sensitive layer was characterized and tested by using simple absorbance/reflectance measurement setups where the sensor was connected to a fiber optic CCD spectrometer. A prototype simulating a real shallow raceway aquaculture system was developed and its hydraulic behavior characterized. A commercially available partial-pressure- NDIR sensor was used as a reference for dissolved CO2 tests with the new optical fiber sensor under development. Preliminary tests allowed verifying the suitability of the new optical sensor for accurately tracking the dissolved carbon dioxide concentration in a suitable operation range. Direct comparison of the new sensor and the reference sensor system allowed to demonstrate the suitability of the new technology but also to identify some fragilities there are presently being addressed.

Special diffractive elements for optical trapping fabricated on optical fiber tips using the focused ion beam

In this work, spiral phase lenses and Fresnel zone lenses for beam tailoring, fabricated on the tip of optical fibers, are reported. The spiral phase lenses allow tailoring the fundamental guided mode, a Gaussian beam, into a Laguerre - Gaussian profile without using additional optical elements. Whereas, the Fresnel lenses are used as focusing systems. The lenses are fabricated using Focused Ion Beam milling, enabling high resolution in the manufacturing process. The output optical intensity profiles matching the numerical simulations are presented and analyzed.

Fabrication of a spun elliptically birefringent photonic crystal fiber and its characterization as an electrical current sensor

In this paper a spun elliptically birefringent photonic crystal fiber is fabricated and characterized. Its performance as a current sensor, using a polarimetric configuration, was tested and compared against single mode fiber at 633 nm. In particular the sensor sensitivity and linearity was investigated using fiber loops with different radius or number of turns around the conductor. The results obtained show that the spun fiber (40 rotation per meter) is able to suppress quite effectively the effects of the bend induced birefringence as compared to the standard fiber.

LPG based fiber optic sensor for carbon dioxide

In this work a novel optical-fiber sensor for carbon dioxide measurement is presented. A polymeric sensitive layer based on the acid-base equilibrium of phenol and of its derivative 4-nitro-phenol is used for carbon dioxide determination. The sensitive material presents changes in color and in its refractive index. Colorimetric and refractometric measurements were performed. The results show the sensor is more sensitive for lower concentrations and a saturation effect occurs for higher levels. For the colorimetric response, a resolution of ±0.15% was estimated and a response time of 30s was measured. For the refractometric measurements, a resolution of ±0.50% could be estimated and a response time of 12s was measured. Reversibility and reproducibility were also demonstrated.

Colorimetric and refractometric measurements of carbon dioxide

In this work, a polymeric sensitive layer based on the acid-base equilibrium of phenol and of its derivative p-nitro-phenol is presented for carbon dioxide measurements. Thin films casted on glass slides were tested, using a LED source (λc at 410 nm) and an Ocean Optics USB4000 spectrometer, in the 0% to 15.25% CO2 concentrations range, showing a 40% maximum transmittance variation with a 51s response time and a 0.15% resolution. Preliminary results indicate that CO2also induces refractive index changes in the sensitive layer. Using a fiber based interferometric setup, a CO2 dependent refractive index change of ~0.045 RIU was observed, in the 0%-90% CO2 concentration range.

Fibre optic hot-wire flowmeter based on a metallic coated hybrid LPG-FBG structure

In this work an all optical hot-wire flowmeter based on a silver coated fibre incorporating a long period grating and a Bragg grating is demonstrated. Optical energy at 1480 nm propagating down the fibre is coupled by the long period grating into the fibre cladding and absorbed by the metallic coating deposited on the fibre surface over the Bragg grating position. This absorption acts like a hot-wire raising locally the fibre temperature, which is effectively detected by the FBG resonance shift. The temperature raise depends on the flow speed of the surrounding air that has the effect to cool the fibre. In this way, the FBG Bragg wavelength shift can be related with the flow speed. Results obtained demonstrate the working principle and a flow speed resolution of 0.08 m/s is demonstrated.

Intrinsic Fabry-Pérot cavity sensor based on chemical etching of a multimode graded index fiber spliced to a single mode fiber

An intrinsic Fabry-Pérot cavity for high temperature and strain measurement is presented. The in-fibre cavity is formed by a chemical etched graded index optical fiber spliced to a single mode fiber. The intrinsic sensor obtained shows high sensitivity to strain (6.2 pm/με) and rather low sensitivity to temperature (0.9 pm/°C), being suitable for applications as a strain gauge at high temperature.

Polymeric optical fiber tweezers as a tool for single cell micro manipulation and sensing

In this paper a new type of polymeric fiber optic tweezers for single cell manipulation is reported. The optical trapping of a yeast cell using a polymeric micro lens fabricated by guided photo polymerization at the fiber tip is demonstrated. The 2D trapping of the yeast cells is analyzed and maximum optical forces on the pN range are calculated. The experimental results are supported by computational simulations using a FDTD method. Moreover, new insights on the potential for simultaneous sensing and optical trapping, are presented.