Optical Waveguide Theory

We report a miniaturized fiber inline Fabry-Perot interferometer (FPI), with an open micro-notch cavity fabricated by one-step fs laser micromachining, for highly sensitive refractive index measurement. The device was tested for measurement of the refractive indices of various liquids including isopropanol, acetone and methanol at room temperature, as well as the temperature-dependent refractive index of deionized water from 3 to 90 degrees C. The sensitivity for measurement of refractive index change of water was 1163 nm/RIU at the wavelength of 1550 nm. The temperature cross-sensitivity of the device was about 1.1x10(-6) RIU/degrees C. The small size, all-fiber structure, small temperature dependence, linear response and high sensitivity, make the device attractive for chemical and biological sensing.

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Temperature-insensitive miniaturized fiber inline Fabry-Perot interferometer for highly sensitive refractive index measurement

Sensing via fiber optics has occupied R&D groups for over 40 years, and some important transitions into the commercial sector have been achieved. We look at the fundamental concepts involved in the various sensing approaches, and the differentiators which have led to commercial impact. We also look to the future of fiber-optic sensors.

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Fiber-Optic Sensing: A Historical Perspective

The deposition of an overlay of higher refractive index than the cladding in a Long Period Fiber Grating (LPFG) permits to improve the sensitivity to ambient refractive index changes in a great manner. When the overlay is thick enough, one of the cladding modes is guided by the overlay. This causes important shifts in the effective index values of the cladding modes, and henceforward fast shifts of the resonance wavelength of the attenuations bands in the transmission spectrum. This could be applied for improving the sensitivity of LPFG sensors. The problem is analysed with a numerical method based on LP mode approximation and coupled mode theory, which agrees with so far published experimental results.

Optimization of sensitivity in Long Period Fiber Gratings with overlay deposition.

Remarkable developments can be seen in the field of optical fibre biosensors in the last decade. More sensors for specific analytes have been reported, novel sensing chemistries or transduction principles have been introduced, and applications in various analytical fields have been realised. This review consists of papers mainly reported in the last decade and presents about applications of optical fiber biosensors. Discussions on the trends in optical fiber biosensor applications in real samples are enumerated.

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Recent Development in Optical Fiber Biosensors

The application of an etching process in a single-mode multimode single-mode (SMS) fiber allows monitoring the change of refractive index of wind turbine gearbox oil due to temperature and degradation. The SMS was designed for operating at short wavelengths, where the setup is less expensive.

Detection of wind turbine gearbox oil degradation with etched single-mode multimode single-mode (SMS) fiber

Ordered titanium dioxide nanotubes on indium tin oxide as a structure supporting lossy-mode resonance is reported. Capability for application of the structure for optical humidity sensing is shown as an application example.

Ordered Titanium Dioxide Nanotubes for Lossy-mode Resonance-based Humidity Sensing

The society of the information is based on the ability of humans to communicate in real time. This is possible thanks to the emission of electromagnetic waves. In this work it is discussed, by analyzing the round trip time (RTT) parameter, if it is possible to expand the society of the information out of the Earth. The results show that the value of the speed of light limits this expansion. Real time applications, such as videogaming, remote surgery, or voice conversations, are only possible on Earth and its proximities, which indicates that there could be a relation between real time telecommunications on Earth and the anthropic principle.

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Telecommunications on Earth and their possible relation with the anthropic principle

The widespread industrial use of per- and polyfluoroalkyl substances (PFAS) have engendered the release of these manmade chemicals in the environment with harmful effects on animal and human health. To monitor PFAS levels in drinking waters, sensitive and versatile sensing strategies are urgently required. Since many perfluoroalkyl carboxylic acids, such as perfluorooctanoic acid (PFOA), are fatty acid-mimic, delipidated human serum albumin (HSA) can be applied as biorecognition element for the design of novel PFAS sensors. Here, two albumin-based biosensing strategies are described and compared: i) a lossy mode resonance (LMR) fiber optic one and ii) an impedimetric portable one developed on screen-printed electrodes. In both biosensing platforms, HSA was covalently immobilized via EDC/NHS chemistry using the carboxylic moieties of the polymeric layers previously deposited at the transducer surface. Afterwards, the conformational changes related to the formation of HSA/PFOA complex were followed considering: i) the LMR spectral shifts for the optical platform and ii) the changes of absolute impedance for the impedimetric one. The performance and future developments of both PFOA biosensors are discussed. 

Albumin-Based Optical and Electrochemical Biosensors for PFAS Detection: A Comparison

An optical waveguide coated by a thin film affects the propagation of the light generating a type of resonances called lossy mode resonances (LMR), very interesting for sensing purposes.

Ignacio Del Villar

Papers

Detection of wind turbine gearbox oil degradation with etched single-mode multimode single-mode (SMS) fiber

Ordered Titanium Dioxide Nanotubes for Lossy-mode Resonance-based Humidity Sensing

Telecommunications on Earth and their possible relation with the anthropic principle

Albumin-Based Optical and Electrochemical Biosensors for PFAS Detection: A Comparison

Fiber Optic Sensors based on Lossy Mode Resonances