This PDF file contains the front matter associated with SPIE Proceedings Volume 8794, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Over the last years optofluidics has emerged as a very promising field. The integration at microscopic level between optics and microfluidics provides a number of unique characteristics that cannot be obtained with solid materials only. This paper briefly reviews the state of the art on optofluidics for sensing applications. We first describe the different approaches in order to realized optofluidic waveguides. These waveguides allow an increased interaction efficiency between the light and the liquid substance that can be very useful in sensing applications (fluorescence, absorption spectroscopy, etc.). We then illustrate high sensitive optofluidic devices such as Mach-Zehnder interferometers, Fabry- Perot cavities and ring resonators. Examples of applications of optofluidic sensors for chemical and biological analysis are given.

We present the experimental investigations of the Bragg gratings writing process in the microstructured polymer fiber using UV beam of 325 nm wavelength and standard phase mask technique. The good quality higher order peaks placed at λ_B/2=782 nm and 2λ_B/3=1040 nm for the grating with primary peak at λ_B=1555 nm were experimentally demonstrated for the first time. The growth dynamics for all the peaks was investigated.

Focussed Ion Beam (FIB) machining has been demonstrated to be capable of fabricating nano and micro-structure elements. In this paper we demonstrate techniques to design and fabricate a 45° mirror on the end of both conventional single mode and multi-core fibres (MCF) using FIB processing. The mirror is finished by a two step process: first a scanning process is used to make a rough cut followed by a polishing process to create an optical surface finish. The machined 45° mirror can be accurately aligned with optical fibre core, which avoids issues associated with the alignment of external turning mirror components. Proof-of-concept tests demonstrate that the fabricated structure is capable of measuring two axis displacements interferometrically with a maximum displacement up to 1.0mm and an rms error of ~50nm.

A high-temperature fibre optical sensor for the simultaneous measurement of pressure and temperature has been demonstrated and tested over a pressure range of 60 bar and up to 700°C. The sensor is based on a multi-cavity design and employs a monolithic sapphire transducer element. Excellent linearity with pressure < ±0.1% FS across the whole temperature range and low temperature cross-sensitivity to pressure < ±0.03% FS have been demonstrated.

We propose and numerically characterize a design for a photonic crystal fiber based surface plasmonic resonance sensor for an aqueous environment. The coupling properties of the plasmonic modes and core-guided mode are investigated comprehensively by the finite element method. The sensor consists of selectively filled with silver nanowires analyte channels, which enhance the phase matching between the core-guided mode and plasmonic mode. Compared with the entirely filled structure, the selectively filled sensor design demonstrates lower transmission loss and better sensitivity, which is 2800nm/RIU (refractive index unit). Moreover, the resonance wavelength has an increase with the analyte index increase, and the increasing trend of wavelength separation with index change is linear.

Recent progress in the development of ultrasonic fibre-optic sensors for detecting acoustic emission from partial discharge in elastomeric insulations is presented. These sensors are an important part of a proposed comprehensive scheme for the fibre-optic monitoring of cable accessories. After specifying the underlying design goals the improved fibre-optic sensor design is outlined. It is experimentally shown that it offers about ten-fold improvement over a previously investigated resonant cantilever-type design in terms of detection limit, making it competitive with conventional piezoelectric transducers, however with the added compatibility with strong electrical fields and electromagnetically noisy environments.

In this work, Bragg gratings were used to monitor, in real time, the temperature during the diamond deposition process obtained by hot filament chemical vapor deposition (HFCVD). Due to the instability of uniform fiber Bragg gratings (FBGs) to high temperatures, regenerated fiber Bragg gratings (RFBGs) were utilized. The results reveal that the diamond deposition process occurs at about 832 ºC (in the experimental conditions used in this case). The work also suggests that RFBGs are suitable devices to monitor processes which, as in the diamond deposition, the temperature is a critical parameter, and where other traditional methods have a little feasibility due to the own experimental setup or samples type under study.

We report on a feasibility analysis for the development of fiber optic humidity sensors to be applied in high-energy physics applications and in particular in experiments actually running at the European Organization for Nuclear Research (CERN). Due to the stringent sensors requirements concerning radiation hardness capability and low temperature operation, we focus our attention on the investigation of fiber optic humidity sensors based on polyimmide (PI)-coated Fiber Bragg Gratings (FBGs). Data here reported, obtained during a wide experimental campaign carried out in the laboratories of CERN, demonstrate that the selected technological platform is able to perform relative humidity (RH) measurements with percent resolution in the temperature range -15-20°C as well as in presence of ionizing radiations up to 10KGray, largely outperforming conventional humidity sensors, currently employed within CERN environment.

This paper shows the first results we obtained for angular acceleration sensing using a fiber Bragg grating based angular accelerometer (FBGAA). We present measurements of angular accelerations imposed by an oscillating plate. Post processed moving average was used to reduce structural natural oscillation noises. Key structural mounting ideas are shown.

Fiber Bragg gratings (FBG) were inscribed in single crystalline sapphire fibers by fs-laser irradiation. Due to the used multi-mode air clad fiber a sapphire-FBG spectra showa a wide asymmetric peak with a half width of 7 nm. Different mathematical peak functions were tested to determine a fiber Bragg wavelength. It was shown that the shift of the calculated Bragg wavelengths in dependence on temperature is identical for the different peak functions. The determination of the fiber Bragg wavelength shift with a resolution of 10pm allows temperature measurements within an accuracy of ±1°C in the temperature range up to 1500°C. Sapphire FBG were used to measure the temperature distribution and thermal fluctuations within an inductive heated furnace in the range from 100°C to 1500°C.

In this work, the fabrication and characterization of novel humidity sensors based on Lossy Mode Resonances (LMR) is presented. Tin oxide (SnO₂) coatings fabricated onto optical fibers are used as LMR supporting coatings. The SnO₂ based refractometers showed an average sensitivity of 6715 nm/refractive index unit (RIU) in the range 1.333–1.420 RIU. The behavior of this optical fiber device as relative humidity (RH) sensor was also tested, monitoring its response to different surrounding humidity levels. The results show a sensitivity of 0.1 nm/RH% in the range from 20% to 80% RH.

A simple optical inclinometer based on phase-shifted Bragg grating in a taper configuration is proposed. The phase-shifted FBG was fabricated using a DUV femtosecond laser technique in the taper region. The sensing head was characterized for different angle curvatures and also to strain. The angle and strain sensitivities of the inclinometer are 13.15 pm/degree and 8.96 pm/μ(epsilon).

Many optical systems based on Surface Plasmon Resonance (SPR) have been developed for work as refractometers, chemical sensors or even for measure the thickness of metal and dielectric thin films. These kinds of systems are usually large, expensive and cannot be used for remote sensing. Optical fiber sensors based on SPR has been widely studied for the last 20 years with several configurations mostly using multimode optical fibers with large cores and plastic claddings. Sensors based on SPR present very high sensitivity to refractive index variations when compared to the traditional refractive index sensors. Here we propose a SPR sensor based in a single mode fiber. The fiber end is chemically etched by emersion in a 48% hydrofluoric acid solution, resulting a single mode fiber with the cladding removed in a small section. A resonance dip around 1580 nm was attained in good agreement with the simulation scenario that takes into account the real characteristics of the fiber.

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.

We present possibility of demodulation signals with different types of modulation. Our setup gives possibility to obtain high accuracy and precision of measurements. We explain how to optimize the setup to obtain optimum condition to phase demodulation for signals with different types of modulation. Real time phase measurements and stable working conditions are provided experimentally. Thermal stabilization and errors analysis based on geometrical and physical setup parameters is demonstrated and optimized, too. Our phase demodulation method is effective and simple in opposite to other phase decoding methods with are overloaded by digital signal processing steps.

This work describes an all-fiber Fabry-Pérot interferometer (FFPI) that is sensitive to gas pressure variations. The geometry of the air cavity consists on splicing a small section of silica rod with a large offset in between two singlemode fibers. It is shown that the FFPI sensor is sensitive to gas pressure variation and when submitted to different gaseous environments, namely carbon dioxide, nitrogen and oxygen, it presented different sensitivities of 6.2, 4.1 and 3.6 nm/MPa, respectively. This result is obtained due to refractive index difference between gases. The refractive index change on nitrogen environment by means of the gas pressure variation resulted in a sensitivity of 1526 nm/RIU. The response of the sensing device to temperature in air was also determined and a sensitivity of -14 pm/°C was attained.

A triangular nanowire is fabricated by tapering a suspended-core fiber and reducing the core size below one micrometer. The triangular nanowire has a high birefringence with an order of magnitude of 10^-3 and when introduced in a fiber loop mirror presents a sinusoidal interference pattern generated by the fast and slow modes of the nanowire. The suspended nanowires were characterized in temperature and strain and enhanced sensitivities were found for both parameters when compared with untapered structures.

A combined optical fiber pressure/temperature sensing system based on low-finesse extrinsic Fabry-Perot interferometer (EFPI) in conjunction with a fiber Bragg grating (FBG) for biomedical measurement applications is presented. The sensing probe has 200 μm outer diameter, and is biocompatible, meeting the requirements for the most demanding biomedical applications. High accuracy (<1mmHg) is achieved by means of fiber polishing and diaphragm etching in hydrofluoric acid, and optimizing the sensitivity to <1nm/kPa. A white light interrogation system based on spectrometric analysis has been developed which implements several pressure detection algorithms. A measurement campaign has been carried out to validate the proposed system, showing 1mmHg accuracy, air-gap compression linearity, and temperature compensation.

Sensitive optical hydrophone is a key component for the design of compact fully optical acoustic arrays and one major issue about this kind of sensors is their sensitivity to hydrostatic pressure and temperature. We present in this paper a compact hydrophone which is optimized for reduced temperature sensitivity and high static pressure capability. High acoustic sensitivity is obtained through wideband mechanical amplification design. Two mock-ups have been realized and the measurements show good agreements with finite-element model. We present acoustic measurements as well as measurements in environmental conditions (temperature and pressure) obtained with a low noise opto-electronic interrogation system.

A fiber-optic refractive index sensor based on terahertz multimode interference in a singlemode-multimode-singlemode fiber structure (SMS) is numerically demonstrated for the first time in the literature. The shift of spectral transmission is investigated as function of external refractive index. Moreover, the coupling efficiency between optical modes at singlemode and multimode sections are determined. The proposed sensor reaches average sensitivity of ~5 GHz/RIU (refractive index unit) over a refractive index range of 1.4-1.5.

Polarimetric sensitivity of a birefringent holey fiber to strain, temperature and hydrostatic pressure is measured in the spectral domain. In an experimental setup comprising a broadband source, a polarizer, a birefringent holey fiber under a variable physical parameter, a birefringent delay line, an analyzer and a compact spectrometer, the spectral interferograms are resolved. These are characterized by the equalization wavelength at which spectral interference fringes have the largest period due to the zero overall group modal birefringence. The spectral interferograms are processed to retrieve the phase as a function of the wavelength. From the retrieved phase functions corresponding to different values of the physical parameter, the polarimetric sensitivity as a function of wavelength is obtained. Using this approach, the polarimetric sensitivity to strain, temperature and hydrostatic pressure is measured.

For underwater surveillance applications, an all-optical acoustic array technology allows enhanced capabilities compared to conventional piezoelectric antenna in terms of compactness, robustness and large distance remote interrogation through small diameter optical cable. This paper presents the results obtained on a first full optical antenna panel based on an innovative wideband pressure and temperature compensated fiber laser hydrophone. The presented mock-up includes 12 fiber-laser optical hydrophones interrogated through a 4 km lead optical cable.

The intermodal sensitivity of a two-mode birefringent holey fiber to strain, temperature and hydrostatic pressure is measured in the spectral domain. In an experimental setup comprising a broadband source, a polarizer, a twomode birefringent holey fiber under a variable physical parameter, an analyzer and a compact spectrometer, the spectral interferograms are resolved. These are characterized by the equalization wavelength at which spectral interference fringes have the largest period due to the zero group optical path difference between the fundamental, the LP₀₁ mode and the higher-order, the LP₁₁ mode. The spectral interferograms are processed to retrieve the phase as a function of the wavelength. From the retrieved phase functions corresponding to different values of the physical parameter, the intermodal sensitivity as a function of wavelength is obtained. Using this approach, the intermodal sensitivity to strain, temperature and hydrostatic pressure is measured for two orthogonal (x and y) polarizations.

In this work, an ultra compact in line fiber optic Fabry-Perot interferometer is presented. The interferometric structure consists of a thin (< 1 μm) amorphous silicon layer in line integrated into a standard single mode optical fiber by means of an electric arc discharge technique. The device exhibits low loss (1.46 dB) and high interference fringe visibility (~ 30% in linear scale) both in reflection and transmission due to the high refractive index contrast between silica and α-Si. A high linear temperature sensitivity up to 75 pm/°C is demonstrated in the range 15-52 °C. The proposed device is simple, compact, cost effective and attractive for point monitoring sensing application in ultra-high temperature sensing in harsh environments.

We have installed a set of 250 m long borehole optical fiber strainmeters at Piñon Flat Observatory in southern California, USA. These instruments consist of an optical fiber stretched between two positions in the borehole – the upper position is at depth of 4 m and the lower is at a depth of 254 m. The tensioned optical fiber’s length is monitored interferometrically; vertical Earth strain is determined by recording the fiber length change over this interval. We achieve a strain sensitivity of about 0.01 n(epsilon) (10^–11) at periods near 1 s. The noise in the tidal band is 300 n(epsilon)/√Hz (near 1cycle per day). After an initial settling period of about a year, the instrument drift is 1-2 μ(epsilon) per year.

We report a nonlinear temperature dependence of the birefringence in polarization maintaining fibre optics, obtained using Bragg gratings recorded in different types of fibres and thermal regeneration. Results show the birefringence quenching is also reversible but with different final values.

A double closed-loop resonator fiber optic gyro (RFOG) with an improved digital serrodyne scheme is experimentally demonstrated. To overcome the effect of the imperfect serrodyne modulation, an improved frequency shifting module is designed and constructed on a single FPGA. The frequency resolution is improved to 0.01Hz, which is equivalent to a rotation rate of 0.04°/h. A bias stability of 2°/h is achieved in a double closed-loop RFOG with a 14.25-m long fiber ring resonator. This is the best result reported to date, to the best of our knowledge, for closed-loop RFOGs. Moreover, good linearity and large dynamic range are also experimentally demonstrated thanks to the closed-loop operation.

Sensitivity of optical fibers to the temperature, longitudinal strain or pressure, is a very important feature in many applications, such as sensors or telecommunication. The most common way to modify (depending on application - either mitigate or strengthen,) this sensitivity is changing the fiber material properties by appropriate glass doping or by employing appropriate microstructure in the fiber. In some cases the precise adjustment of a doping level and sophisticated design of air-holes arrangement is needed to obtain required features of the fiber. In this paper, for the first time, to the best of our knowledge, we report the investigation of the mode area and geometry influence on the fiber temperature and mechanical sensitivities. To do so, we engaged a dedicated all-fiber interferometer which enables the measurement of the temperature and longitudinal strain sensitivities of different fiber types, including conventional and microstructured fibers with different core diameters.

This paper presents ways to improve the sensitivity of the interferometric hybrid sensor. Hybrid interferometer is defined as a combination of modalmetric sensor and interferometer sensor. Hybrid interferometer is presented as an application to extensive security systems, where particular importance is the early detection of an intruder. Specification of the hybrid sensor is based on the phenomenon of outputting the interferometer from interference as a result of the disorder. Hybrid sensor sensitivity depends therefore on determine when the sensor leaves the interference. Improve the detection sensitivity can be increased by improving the contrast of interference pattern at the output of the interferometer by using polarization balance. This paper presents a preliminary study and the conclusions of using polarization balance in the hybrid interferometer system.

The acoustic pressure sensitivities of hollow-core photonic bandgap fibers (HC-PBFs) with different thicknesses of silica outer-cladding and polymer jacket were experimentally investigated. Experiment with a HC-PBF with 7 μm-thick silica outer cladding and 100 μm-thick Parylene C jacket demonstrated a pressure sensitivity 10 dB higher than the commercial HC-1550-02 fiber and 25 dB higher than a standard single mode fiber. The significant enhancement in sensitivity would simplify the design of fiber hydrophones and increase the number of sensors that could be multiplexed in a single fiber.

In this paper we report on fabrication and characterization of a refractive index sensor based on two concatenated double resonanced long period fiber gratings (LPFGs) with an inter grating space in between them. The inter grating space provides a temperature dependent extra phase difference between the core mode and the participating cladding modes, making the sensor similar to a Mach-Zehnder interferometer with its arms phase shifted. We demonstrate that by adjusting the inter grating space the thermally induced phase difference in the LPG region can be compensated, producing temperature insensitive resonance wavelengths. The interferometer is highly stable over a wide range of temperatures (20-100 °C). The measured refractive index sensitivity for aqueous solutions (1.333-1.393) is 2583.3 nm/RIU, which is highly desirable for precision sensing of biological samples.

Polarimetric optical fiber sensors belong to phase sensors in which polarization state of the output light depends on birefringence of the fiber. In general, external stresses can change birefringence of the fibers. Hence polarimetric sensors may be used for strain monitoring inside composite materials. Length of the sensing fiber of the polarimetric sensor is relatively high, particularly when used to measure strain in composite material, thus light traveling through the sensing fiber may become depolarized and dynamics η of the sensor diminishes. In the paper it is shown that by the use of compensation, depolarization of the light passing through the sensor is significantly reduced. This allows use of less expensive and more robust light sources than laser diodes which are important when the sensor is designed to operate in harsh environment. A comparison of different light sources and sensing fibers for application in strain measurement in composite materials is presented and discussed and an influence of the lamination process on sensor dynamics is evaluated.

In this paper, several configurations of optical fiber refractive index sensors based on a hetero-core structure are presented. These sensors are made by splicing short lengths of several specialty fibers with different core and cladding diameters between two standard single-mode fibers. In addition, two fiber bragg gratings are inscribed in single-mode fiber at both sides of the specialty fibers in order to create an in-fiber Fabry-Perot interferometer and the behavior of the transmission spectra is analyzed. The sensitivities and spectral behavior of the sensors are obtained by immersion in solutions of different refractive index.

Small sections of suspended twin-core fiber are used in reflection configurations to create two parallel Fabry-Pérot cavities. Situations where both cores are excited and where only one core is excited are analyzed and compared. When both cores are excited, two parallel and equivalent cavities are formed and an interference pattern with higher visibility is obtained. The structure is also characterized with respect to temperature and a sensitivity of 12.4 pm/K is achieved.

In this work, the results of a new technique for developing oxygen gas sensors with polymer optical fibers are shown. The transducer is a locally tapered optical fiber with a ruthenium complex directly embedded into the fiber itself. The complete setup is based on a side-illumination scheme in order to get a high signal-to-noise ratio with conventional lowcost optoelectronic devices. Different tests to measure fluorescence intensity spectral distribution, fluorescence lifetime and dynamic response of the sensor have been carried out.

The present work addresses the need for new devices felt in the context of quality control, especially in the food industry. Due to the spectral dependence of the attenuation coefficient, a novel dual-parameter sensor for colour and refractive index was developed and tested. The sensor employs plastic optical fibres to measure the transmitted optical power in three measurement cells each with a different incident wavelength. The performance of the sensor was tested using several dyes at different concentrations and aqueous solutions of glycerine and ethanol. Results show that this technique allows the monitoring of refractive index and colour without cross-sensitivity.

In this work an innovative and low cost optical chemical sensor, based on surface plasmon resonance in plastic optical fiber, is presented and experimentally tested for the detection and analysis of trinitrotoluene (TNT). The fabricated optical chemical sensor was realized removing the cladding of a plastic optical fiber along half the circumference, spin coating on the exposed core a buffer of Microposit S1813 photoresist, and finally sputtering a thin gold film. A Molecularly Imprinted Polymer (MIP) film was deposited on the thin gold film for the selective detection of TNT. It has been found that the sensor recognizes trinitrotoluene, since the SPR signal is affected by the presence of TNT in the polymer, while with a slow response kinetics, probably due to the thickness of the polymeric layer.

This work presents an application of thin zinc oxide (ZnO) films obtained using atomic layer deposition (ALD) for effective tuning of spectral response and the refractive-index (RI) sensitivity of long-period gratings (LPGs). The technique allows for an efficient and well controlled deposition at monolayer level of excellent quality nano-films as required for optical sensors. The effect of ZnO deposition on spectral properties of the LPGs is discussed. We correlated the increase in ZnO thickness with the shift of the LPG resonance wavelength and proved that similar films are deposited on fibers and silicon reference samples in the same process run. The thin overlay effectively changes the distribution of the cladding modes and thus also tunes the device’s RI sensitivity. The tuning can be simply realized by varying number of cycles, which is proportional to thickness of the high-refractive-index (n<1.9 in infrared spectral range) ZnO film. The advantage of this approach is precision in determining the film thickness resulting in RI sensitivity of the LPGs.

An evanescent wave fiber optic sensor for detection of E. coli outer membranes proteins (EcOMPs) is presented. The sensing probe is achieved by the functionalization of a Long Period Grating (LPG) inscribed in a single mode fiber (SMF28) with poly-L-lysine (PLL) resulting in a label-free configuration capable of specific recognition of EcOMPs in waters due to the resonance wavelength shift variation owing to refractive index changes of the medium (≈100 nm/RIU). The sensing head was characterized and tested against EcOMP and applied to spiked environmental water samples. The sensor displayed linear responses in the range of 1×10^-10 M to 1×10^-8 M EcOMP and is regenerated (under low pH conditions) and the deviation of the subsequent detection was less than 0.1 %.

This paper presents the detection and quantification of hogwash oil in soybean oils by means of absorption spectroscopy. Three types of soybean oils were adulterated with different concentrations of hogwash oil. The spectra were measured in the visible band using a white LED and a low-cost spectrometer. The measured spectra were processed by means of multivariate analysis to distinguish the adulteration and, for each soybean oil, to quantify the adulterant concentration. Then the visible spectra were sliced into two bands for modeling a simple setup made of two LEDs only. The successful results indicate potentials for implementing a smartphone-compatible device for self-assessment of soybean oil quality.

In this work we experimentally show how the technology of surface plasmon resonance (SPR) in doubly deposited uniform- waist tapered optical fiber sensors (DLUWTs) can be extended into the visible region (around 520 nm) by changing the thicknesses of the deposited layers. In this way, by using DLUWTs we can cover, in an easy and versatile way, a total wavelength range over 1000 nm wide, having shown in the past how this same kind of sensors can be usable in the communication band. The possibilities of fiber sensors can then be applied to the region of visible wavelengths, which is very interesting from the biological point of view.

A chemical sensor for the detection of cocaine has been developed, based on a molecularly imprinted polymer (MIP) containing a fluorescein moiety as the signalling group. The fluorescent MIP was formed and covalently attached to the distal end of an optical fibre. The sensor exhibited an increase in fluorescence intensity in response to cocaine in an aqueous acetonitrile mixture. Selectivity for cocaine over codeine has been demonstrated.

The use of a PMMA based plastic optical fibre in radiotherapy dosimetry is presented. The optical fibre tip is coated with a scintillation material, terbium-doped gadolinium oxysulfide (Gd2O2S:Tb), which fluoresces under ionising radiation. The emitted signal penetrates the fibre and propagates along the fibre where it is remotely monitored using a fluorescence spectrometer. The results demonstrate good repeatability, with a maximum percentage error of 0.59% and the response is independent of dose rate.

We recently introduced a reliable fabrication process enabling the integration of dielectric and metallic nanostructures directly on the tip of optical fibers¹. It involves conventional deposition and nanopatterning techniques (typically used for planar devices fabrication) suitably adapted to directly operate on the fiber tip. By using this approach, and with a view towards possible applications, here we demonstrate the realization of different technological platforms based on the integration on the fiber facet of periodic and quasi-periodic metallo-dielectric nanostructures supporting localized surface plasmon resonances, that can be used for chemical and biological sensing as well as polarization sensitive devices.

Possibility of a Co/Fe co-doped alumino-silicate optical fiber as a radiation dosimeter application was investigated from the measurement of radiation-induced optical attenuation (RIA). The RIA at 1310 nm of the optical fiber upon gammaray irradiation was found to increase linearly with the radiation dose. The extent of the RIA increase to 11,900 dB/km at radiation dose rate of 20 Gy/min for 1 hour was 70 times larger than that of the reference single mode fiber and the RIA remained almost constant after 5 minutes of the irradiation termination.

In this paper, we report on our study of UV-VIS absorption spectroscopy in suspended-core optical fibres (SCFs) filled with organic-dye solutions. We compare two different dye classes, the anionic dye - bromophenol blue sodium salt (BB) and cationic dye - oxazine 725 perchlorate (OX). While the results obtained with BB are in a good agreement with the spectra measured in a standard reference cuvette, those obtained with OX are different and reveal much stronger absorption of light than in cuvettes. This stronger absorption indicates accumulation of the dye molecules on the short section of the core close to the end of the fibre. This observation demonstrates difference in physicochemical properties of the two dye classes and is important for the development of chemical sensors based on SCFs.

Cardiovascular diseases are one of the primary causes of death in the world. Hemodynamics is the study of the blood propagation and the physics aspects concerned to it, relating pressure, flow and resistance. One of the most important topics on hemodynamics is the evaluation of arterial wave reflections. Recently this physical parameter of the pressure wave propagation through the arterial tree was considered as a novel strong risk factor for cardiovascular diseases. Arterial pressure reflections can be quantified by central pressure profile analysis. In this work we study in the trial of an optical fibre Bragg grating based sensor of assess the central pressure profile, with the goal of to achieve a superior sensitivity, with a better signal quality than electromechanical probes, measured directly in the carotid artery.

We report the fabrication and characterization of surface plasmon resonance (SPR) based optical fiber riboflavin/vitamin B₂ sensor using combination of colloidal crystal templating and molecularly imprinted gel. The sensor works on spectral interrogation method. The operating range of the sensor lies from 0 μg/ml to 320 μg/ml, the suitable amount of intakes of riboflavin recommended for different age group. The SPR spectra show blue shift with increasing concentration of riboflavin, which is due to the interaction of riboflavin molecule over specific binding sites caused by molecular imprinting. The present sensor has many advantageous features such as fast response, small probe size, low cost and can be used for remote/online monitoring.

We report a surface plasmon resonance based fiber optic hydrogen sulphide gas sensor using Cu/ZnO thin films. The sensor works on wavelength modulation scheme. The fiber optic probe was fabricated by removing the cladding of appropriate length from the fiber and depositing copper and ZnO thin films on the unclad core by thermal evaporation technique. The presence of hydrogen sulphide gas around the probe changes the dielectric function of zinc oxide and a dip is observed in transmitted spectrum. With the increase in the gas concentration shift in the resonance wavelength has been observed. The proposed sensor can be used for online monitoring and remote sensing of hydrogen sulphide gas in the environment.

We have experimentally demonstrated the role of the high index dielectric layer of zinc oxide over the metal layer on the performance of the surface plasmon resonance based fiber optic refractive index sensor. The configuration contains copper as a SPR active metallic layer covered by dielectric layer. The configuration of Cu/ZnO shows high sensitivity. Further increase in the thickness of ZnO layer increases the sensitivity of the sensor. A good agreement between experimental results and the simulated ones based on multilayer two dimensional approach is obtained. The additional advantages of ZnO layer, apart from sensitivity enhancement, are protection of metallic layer from oxidation, tunability of the resonance wavelength region, biocompatibility and capability of gas sensing.

We present an experimental study of fiber optic ammonia gas sensor based on the phenomena of surface plasmon resonance working on wavelength modulation scheme. The principle of the sensor is based on the change in dielectric constant of the bromocresol purple (BCP) in the presence of ammonia gas. The sensor works at room temperature. Two different kinds of coating configurations have been considered, namely copper + BCP and silver + BCP, on the unclad portion of the fiber. The experiments have been carried out at the low concentrations (1 ppm − 10 ppm) of ammonia gas around the probe. The sensor with copper and BCP layers has greater sensitivity than sensor with silver and BCP layers. The proposed sensor has small response and recovery times.

In this paper we propose and demonstrate two forms of a device for sensing cladding modes efficiently. The cladding modes, generated by an untilted and tilted fibre Bragg grating (TFBG) written in SMF28 fibre are captured by splicing it to an in-line double-clad fibre coupler (DCFC). A comaprison is made of the capture efficiency of the cladding modes in two configurations; one in which the TFBG is taper spliced to the DCF, or in the other in which an FBG in an SMF28 is etched down to match the outer core of the DCF. In both cases the cladding modes are captured efficiently, but with significantly improved results for the former configuration. We demonstrate surrounding refractive index sensing using a new signal analysis scheme based on the extinction of each cladding mode resolved over a bandwidth of over ~60nm. This robust device has the advantage of faithfully transmitting the cladding modes over a long distance and is therefore suitable for remote sensing over long distances. The sensitivity of the device is discussed. This device may be used in a variety of applications such as for bend, strain, temperature and surrounding refractive index sensing.

A long period grating (LPG) modified with a mesoporous film infused with a functional compound, calix[4]arene, was employed for the detection of volatile organic compounds (VOCs). The mesoporous film consisted of an inorganic part, of SiO₂ nanoparticles (NPs) along with an organic moiety of poly(allylamine hydrochloride) polycation PAH, which was finally infused with functional compound, p-sulphanatocalix[4]arene (CA[4]). The LPG sensor was designed to operate at the phase matching turning point to provide the highest sensitivity. The sensing mechanism is based on the measurement of the refractive index (RI) change induced by the complexion of the VOCs with calix[4]arene (CA). The LPG modified with 5 cycles of (SiO₂ NPs/PAH)₅PAA responded to exposure to chloroform and benzene vapours. The sensitivity to humidity as an interfering parameter was also investigated.

A technique for liquid-level sensors based on a long fiber Bragg grating (FBG) is presented and experimentally demonstrated. The measurement system is based on the measurement of the central frequency distribution of the FBG based on time-frequency domain analysis. A short optical pulse is injected into a 10-cm long FBG mounted in a container. The back-reflected pulse is scanned by means of an oscilloscope. When part of the grating is immersed in a liquid having temperature higher than the surrounding ambient, the structure of the uniform grating is distorted and its time-frequency response changes. A spatial resolution of 2 mm, given by the input pulse duration, and a 10-cm long measurement range are achieved. Liquid-temperature sensing has also been implemented by scanning the spectral response of the FBG by means of a CW laser and an OSA.

We present the fabrication and characterization of regenerated fiber Bragg gratings (RFBG) in high-birefringence optical fiber for high-temperature sensing. The RFBG presents two Bragg resonances corresponding to the slow and fast axis of the optical fiber. The distance between these two Bragg resonances can be used to reduce the cost of the interrogation unit. Two optical filters are used to convert the wavelength shift due to temperature into optical power changes. The use of modal interferometers for the optical filters simplifies the interrogation setup since they can be easily tuned by strain or temperature.

A fiber optic sensor based on a long-period grating (LPG) inscribed in a photonic crystal fiber is investigated for vibration sensing for structural monitoring applications. In this paper, preliminary results are shown demonstrating the sensor ability to detect vibration induced in a test structure. The sensor frequency response when attached to a loudspeaker-acrylic plate stimulation system (tested in the range from 40 Hz to 2.5 kHz) is analyzed using an intensity based scheme with a tunable laser. An alternative interrogation scheme, where the vibration signal is retrieved from a spectral scan, is also demonstrated and analyzed showing promising characteristics for structural health monitoring.

An optical fiber relative humidity (RH) sensor exploiting Localized Surface Plasmon Resonance (LSPR) is designed in order to achieve a linear response over a large dynamic range with an optimized sensitivity. To further enhance the sensitivity, in-house developed gold nanoparticle film was also synthesized onto a U-shaped and an etched-core region of the optical fiber. A throughout linear response over a dynamic range of ~20-90% RH with a very high sensitivity is observed. Importantly, reducing the core diameter resulted in four time sensitivity enhancement. In addition, the sensor response was observed to be highly reversible and repeatable.

In this work the deposition of a tetrakis(4-sulfonatophenyl)porphyrin (TPPS) film onto optical fiber tip is obtained via a non-conventional procedure consisting in a UV-light induced deposition. This leads to the growth of TPPS thin films right at the core region of the fiber end. The simplicity and cost effectiveness of this procedure, as well as the potential of porphyrins as functional materials, enable the design of novel active and passive in-fiber devices. Here, the presence of intense, narrow bands in the reflected spectra is successfully exploited to detect corrosive or toxic vapors, such as strong volatile acids and bases, at room temperature.

In this paper we present preliminary results on the use of Photonic Crystal Fibers (PCFs) in a conventional capillary electrophoresis system to separate and detect fluorescent species. PCFs show interesting advantages over conventional capillaries for this application, including larger surface-to-volume ratio and potential for higher resolution with comparable sensitivity. Our results illustrate some of these advantages, and we point out the need for stringent tolerances in the fabrication of specific PCFs for this application.

This paper presents a study of optical forces acting on dielectric particles in media of distinct refractive index. The radiation pressure forces produced by optical tweezers are calculated using the finite difference time domain method as well as the Lorentz force on electric dipoles. The model considers a 2-dimension structure composed of a waveguide and a dielectric microparticle. Furthermore, the paper presents preliminary experimental results concerning the implementation of fiber optical tweezers system based on polymeric lensed fibers.

Monitoring pH for long periods, usually 24 h, in the stomach and in the esophagus may be essential in the diagnosis of gastro-esophageal diseases. The clinical range of interest is quite extended, between 1 to 8 pH units. Methyl red, after its covalent immobilization on controlled pore glass (CPG), is characterized by a working range which fits well with the clinical one. A novel probe, suitable for gastro-esophageal applications, was designed in order to optimize the performances of the colored CPG. This leads to a very simple probe configuration characterized by a very fast response.

Within the EU project i-Protect fibre optic sensors for measuring heart rate, respiratory rate and skin temperature are being developed. The plastic optical fibre (POF) sensors are based on macrobending effects, photoplethysmography and fluorescence thermometry. The sensors and monitoring units are integrated into underwear and are communicating wireless via body area network and communication unit with the rescue command centre. All sensors can be removed from the underwear to allow washing the textile. First prototypes of the fibre optic sensors were tested in comparison to commercial reference sensors.

High-precision dosimeters are needed in brachytherapy treatments to ensure safe operation and adequate working conditions, to assess the correspondence between treatment planning and dose delivery, as well as to monitor the radiation dose received by patients. In this paper we present the development of a multi-sensor dosimeter platform targeted for brachytherapy environments. The performance of different scintillating materials response is assessed. The emission bands of most common scintillator materials used in ionizing radiation detection are typically below 550 nm, thus they may be prone to stem effect response. To avoid this effect we propose the use of scintillators with longer wavelength emission. Samples of neodymium doped glasses are evaluated as new infrared radioluminescent scintillators for real-time dosimeters, namely lithium lead boron silver (LLB4Ag) and lithium bismuth boron silver (LBiB4Ag) glasses. Their response is compared with the response of organic scintillator BCF-60 with a 530nm response.

This work focuses on the results and analyses performed on long-period optical-fiber gratings (LPFG) designed for use as refractometric sensors. The study was conducted with non-uniform LPFG specially designed for refractometric applications. First, LPFG transmission spectra were calculated for nominal period, propagation constant of the cladding mode and phase shift between the adjacent LPFG sections. Then, a random variation of the above parameters was introduced and the effect of this variation on the transmission spectrum of the LPFG, with the external refractive index as parameter, was evaluated. Finally, a change in the resonant wavelength against the external refractive index was investigated under random variation of parameters. We have found that in some long-period fiber grating refractometric sensors fabrication tolerances should as stringent as 0.2 % of nominal parameter. The methodology of tolerance analysis and quantitative data obtained in this work might be useful in establishing tolerances for fabrication parameters of long-period fiber grating refractometric sensors.

We investigated experimentally the response of the fiber-optical refractometric sensor with semi-cylindrical plastic detection element under different polarization states of the input light. Our results demonstrate that the state of polarization of light in such sensor has a significant effect on the sensor response to external refractive index. This property can be exploited, in particular, for adjusting the form and linearity of the sensor response in situations when such adjustment cannot be achieved by modification of the sensor geometrical parameters and material constants.

We report on a concept of the all-fiber intensity bend sensor, which is based on photonic crystal fibers with asymmetric air-hole structure. The cross-section of these fibers consists of two regions with different air-filling factors on opposite sides of the fiber core. The design enables the measurement of the bending radius as well as the bending orientation. Moreover, the mode field area of our fibers is adjusted to that of standard single mode fibers (SMFs), which allows easy fabrication of the sensor with the use of widely available light sources and detectors pigtailed with SMFs.

At the moment technology allows to miniaturize measurement system to several micrometers. Application of an optical fiber taper in such system needs to manufacture a new one with diameters below single micrometers which is very difficult and expensive. Another way to obtain this level of diameters is the process of tapering from the existing fibers. In the paper, experimental results of propagation light from a supercontinnum sources of the wavelength generates the wavelength of 350-2000 nm, in different optical fiber submicron wires made from tapers manufactured from single mode fibers are presented. Biconical optical fibers’ tapers were manufactured in low pressure gas burner technique. There are presented spectral characteristics of a propagated beam. For the test, there was manufactured an optical fiber submicron wires with a different length of waist region with a diameter near one micrometer. We put to the test a taper made from a standard telecommunication fiber SMF-28 with a cutoff wavelength equal to 1260.

Regenerated Fiber Bragg Gratings have been annealed at high temperatures up to 890°C during 9000 hours in continuous. This test has been conducted in order to experimentally assess the long-term stability of regenerated FBGs dedicated to measurements in high temperature environments. The evolution of both reflectivities and Bragg wavelengths of four wavelength-multiplexed regenerated FBGs simultaneously annealed at respectively 760°C, 810°C, 850°C and 890°C is reported.

Fiber Bragg grating (FBG) inscription efficiencies with a nanosecond (ns) KrF-Excimer laser source at 248 nm and with a ns Q-switched, 5^th-harmonic Nd:VO₄ laser source at 213 nm were compared. With both laser sources the phase mask method was used for FBG inscription. The growth process of the refractive index change during UV-exposure is presented as a function of cumulated fluence for inscription in standard non-hydrogenated SMF28 fibers. The inscription efficiency was found to be significantly higher for the 213 nm than for the 248 nm radiation, indicating a higher photosensitivity at 213 nm compared to 248 nm in low Ge-doped fibers.

In a highly Ge doped photosensitive fiber, co doped with phosphorus and fluorine and with a doped inner cladding, we observed, during annealing experiments, an anomalous variation of the FBG strength as a function of temperature and time. This characteristic only occurred when the fiber had been loaded with hydrogen. During a stepwise temperature increase from room temperature to 1200°C, the gratings showed, after an initial thermal decay, in two distinct temperature ranges a significant increase in reflectivity with time. One range with an increase in reflectivity was found between 850°C and 1000°C. The behaviors of the FBGs in this range were very similar to that known from chemical composition or regenerated gratings. Another temperature range with increasing reflectivity was found between 500°C and 700°C, followed by a strong decrease in reflectivity at temperatures between 750°C to 800°C. Both regimes of regeneration might be associated with changes in the core and doped inner cladding of this type of fiber.

We demonstrate four-port long-period gratings formed by winding an optical microfiber with another thinner microfiber. The surrounding thinner microfiber not only induces a strong refractive-index perturbation in the center microfiber, but also collects and leads out the light resonantly coupled from the fundamental mode to high-order modes, providing flexibility for applications as optical filters and sensors. The devices exhibit temperature sensitivity of 7.6 pm/°C, strain sensitivity of -10.6 pm/μ(epsilon) and refractive-index sensitivity of 2012.6 nm/RIU.

This work reports the fabrication of asymmetric fiber tapers using a pulsed CO₂ laser as a heat source. The laser has its beam focused on the side of the fiber by using a moveable mirror and a convergent lens while the softened fiber is stretched by a translation stage. The tapering process uses a superposition of step tapers that are produced after sweeping the laser spot over a previously calculated length of the fiber. Constant speeds in all the translation stages are used in the process. A pulsed laser source with a low cost power control is also used to fabricate asymmetric tapers having a relatively low loss.

We report on the production and characterization of narrow bandwidth fiber Bragg gratings (FBGs) in two spectral regions using polymer optical fibers (POFs). Narrow bandwidth FBGs are increasingly important for POF transmission systems, WDM technology and sensing applications. Long FBGs with resonance wavelength around 850 nm and 1550 nm were fabricated in several types of polymer optical fibers. The 3 dB FBG bandwidth varies from 0.22 nm down to 0.045 nm considering a Bragg grating length of 10 mm and 25 mm, respectively.

This paper reports on the fabrication of Long Period Gratings (LPGs) in hollow-core air-silica photonic bandgap fibers by using pressure assisted Electrode Arc Discharge (EAD) technique. In particular, the fabrication procedure relies on the combined use of EAD step, to locally heat the HC fiber, and of a static pressure (slightly higher than the external one) inside the fiber holes, to modify the holes. This procedure permits to preserve the holey structure of the host fiber avoiding any hole collapsing and it enables a local effective refractive index change due to the size and shape modifications of core and cladding holes. Periodically repeated EAD treatments permit the fabrication of LPGs based devices in hollow core optical fibers enabling new functionalities hitherto not possible. Here, the experimental fabrication of LPG prototypes with different periods and lengths are discussed. And, the HC-LPGs sensitivity to environmental parameters such as strain and temperature are investigated.

We present a polarizing optical fiber designed to operate at 780 nm with, to date, an unprecedented spectral window. The polarization extinction ratio obtained for a 3 meters long sample of this fiber is greater than 60 dB over a 40 nm window. We will demonstrate these performances by presenting a new method for characterizing the rejection as a function of wavelength. This method presents many advantages; not the least being that it yields rejection values in excess of the individual rejections of polarizers used for the setup.

An analytical model based on geometrical optics and multilayer transfer matrix method is applied to the surface plasmonic resonance supported by fibre taper structures in the context of optical sensing applications. Phase interrogation is considered in particular as a methodology to attain enhanced sensitivities, and the performance of the sensing heads as function of the metal clad and taper parameters is analyzed. General topics concerning the actual relevance of plasmonics are also presented, first in a global perspective and then when applied to sensing.

Fiber Bragg gratings (FBG) are one of the most successful fiber optic technologies with very interesting perspectives for application in fiber optic sensing. It has been already reported that the possibility of its fabrication in novel microstructured fibers (MSF), creating a unique 3D structure, can significantly improve their performance and sensing properties. In this paper we present the results of FBG inscription in a dual-mode highly birefringent (HB) MSF with enhanced polarimetric strain sensitivity of the second order mode, as its mode maxima are closer to the cladding air-holes, where the strain distribution during fiber elongation is the highest. We perform an analysis and comparison of the FBG reflection and transmission characteristics, showing the effects of power coupling to cladding radiation modes. Furthermore we present the results of temperature and longitudinal strain sensitivities of the particular modes visible in the grating reflection spectrum followed by conclusions with reference to our previously reported results of polarimetric strain and temperature measurements of a similar fiber design.

This work proposes a new approach to the design of hollow-core fiber for single-polarization application. The hollow-core fiber has a cladding with high air filling fraction consisted of hexagonal air-holes in a hexagonal lattice. The novelty design consists of changing the diameter of just one radial line of air-holes. The asymmetric cladding leads to obtain fundamental core modes with high birefringence, and fundamental modes with transmission bandgaps in different spectral range. The shift in the bandgaps results in a high polarization dispersion loss (PDL > 20dB/m) with bandwidth of about 38 nm. At the wavelength 1500 nm the PDL is about 3000 dB/m and the confinement loss to the guided mode is about just 0.1 dB/km.

In this paper the photonic crystal fibers (PCFs) with various solid core diameters are presented. The attenuation obtained in the photonic band gap (PBG) mechanism for 37 rods forming the core of PLCFs was 0.16 dB/cm, which is the lowest attenuation reported to date. Reducing the fiber core diameter causes the increase of light penetration in fiber holes, which results in increased losses. The solid core of PCFs structure used in experiment consisted of 1, 7, 19 and 37 rods. The attenuation of PLCFs was measured by using the cut-back technique.

The mode-field expander (MFE) is a microstructured optical fiber (MOF) based device that enlarges the modal field distribution and can couple light from large mode area (LMA) fibers into small core fibers or vice-versa and other optical waveguides. Using our earlier developed analytical field model, we studied the mode-field expansion in MOFs having triangular lattice, and low-loss splicing of MOFs to standard single-mode fibers (SMFs), based on the controlled all airhole collapse method, which leads to an optimum mode-field match at the joint interface of the MOF-SMF. Comparisons with available experimental and simulation results have also been included.

In the paper we present our recent results concerning the orientation of ferroelectric liquid crystal molecules inside silica micro capillaries. We have infiltrated the silica micro capillaries with experimental ferroelectric liquid crystal material W-260K synthesized in the Military University of Technology. The infiltrated micro capillaries were observed under the polarization microscope while both a polarizer and an analyzer were crossed. The studies on the orientation of ferroelectric liquid crystal molecules may contribute to further studies on behavior of this group of liquid crystal materials inside photonic crystal fiber. The obtained results may lead to design of a new type of fast optical fiber sensors.

In this paper we present the theoretical investigation of the phase birefringence in multi-component glasses photonic crystal fiber PCF14(6), selectively infiltrated with 5CB nematic liquid crystal (LC). The PCF14(6) used as a host in our numerical model is made of the PBG08 high-refractive index glass (~1.95). Refractive index of the fiber is much higher than then both ordinary and extraordinary refractive indices of the LC and as a result low-loss and index-guiding propagation is possible. In our calculations we assume that the host PCF is infiltrated with LC only in the center row of the air channels. Such selective infiltration induces initial phase birefringence in the fiber equal to 1.8 ^.10^-5 when molecules are parallel to the fiber axis. The influence of the tilt angle of the liquid crystal molecules alignment on the PLCF birefringence is presented. We show possibility to tune the phase birefringence up to 6.2 ^.10^-5 or down to −2.4 ^.10^-5 depending on the direction of electric field.

Photonic liquid crystal fibers allow for dynamic modification of their guiding and polarization properties. In particular it is possible to dynamically tune phase delay between two orthogonal polarization of the guided mode. In this work an index-guiding photonic liquid crystal fiber with highly tunable retardation, reaching value of 15λ (or 30π in terms of phase difference) is presented. Electric tuning with two sets of electrodes is also discussed and demonstrated proving that photonic liquid crystal fibers can be utilized as a all-in-fiber polarization controllers.

A Fabry-Pérot microcavity tip temperature sensor based on a special design double-cladding optical fiber is proposed. The produced fiber has pure silica core and outer cladding and a silica ring doped with phosphorous. The whole ring region is removed by chemical etching post-processing. Consequently, light will be guided in the core region. In a first step, the double-cladding optical fiber is spliced to single mode fiber. Afterwards, the tip is etched in a solution of 48% hydrofluoric acid. The inner cladding will be etched faster, and the core becomes suspended and surrounded by air. The Fabry-Pérot microcavity tip sensor is subjected to temperature, and a linear sensitivity of 14.6 pm/°C is obtained.

A double-clad photonic bandgap fiber (DCPBGF) can be used to transmit femtosecond signals. This fiber is supposed to be applied in endoscopy in vivo. In the environment of human body, temperature is higher than ambient temperature. For this reason one should consider influence of temperature rise on properties of ultrafast impulse propagation.

An optical fiber bend sensor based on a fiber Bragg grating by using a germano-silicate glass optical fiber with depressed-index structure has been developed and its novel bend sensing characteristics was demonstrated. With the increase of bending, the transmission spectrum was linearly blue-shifted without change of optical transmission loss. Total blue-shift of the Bragg reflection wavelength upon bending in the radius of curvature from 20 m^-1 to 133 m^-1 was − 0.13 nm.

We present a new class of hollow core photonic crystal fibers taking the advantages of quasi-crystals structures. We analyze two structures based on modified 8-fold and 12-fold symmetries and we presente the ability of air guiding propagation having two photonic bandgap in the λ/Λ<1 In this paper bandgap of both structures as well as the behavior of the guided modes via finite element method are investigated.

A cost-effective technique for coupling a plastic optical fiber (POF) to a silica single-mode fiber (SMF) is proposed, which can, by exploiting a multimode fiber (MMF), avoid the damage or burning at the butt-coupled POF/SMF interface. Using this coupling technique, we also show that the Brillouin Stokes power in a POF can be enhanced by combined use of pulsed pump and an erbium-doped fiber amplifier. When the pulsed pump with average optical power of 18 dBm, duty ratio of 15%, and pulse period of 2 μs is launched into a 200-m-long POF, 4-dB enhancement of the Stokes power is obtained compared to that with 18-dBm continuous-wave pump. The relatively small enhancement is probably caused by the high Brillouin threshold of POFs. The Stokes power dependence on duty ratio is non-monotonic, which might originate from a longer phonon lifetime in POFs than that in silica SMFs.

In this paper we have been experimentally investigated thermo-optic properties of a Co nanofluid filled mictrostructured fiber (MSF). We have prepared samples based on pure chemical compounds: cyklohexane and toluene and both of them were used as solvents for Co nanoparticles. MSF filled by cyklohexane and its mixture with Co nanoparticles worked on weakly guided regime and toluene based MSFs samples became the solid core bandgap fibers. We have measured temperature transmission spectral characteristics within the range of 18°C-80°C. Temperature sensitivity of Co nanofluid based on cyklohexane were the strongest in third telecommunication window and reached 0.12dB/°C with dynamic range of 7dB. For toluene based samples we observed bandgaps shifts from the longer to the shorter wavelengths. Temperature sensitivity of these type of samples were close to -5nm/°C.

Following the pioneering work of the Lawrence Livermore National Laboratory, Chirped Fiber Bragg Gratings are investigated as in situ, real-time, wavelength-position discriminators for measuring detonation speeds inside explosives.

The paper presents the results of experimental studies of the temperature dependence of a microfibre coupler (MFC) with a waist diameter of ~4 μm covered with a layer of liquid crystal (LC) material. The microfiber coupler is fabricated by fusing together and tapering of two standard telecom fibers using a microheater brushing technique, followed by partially embedding the structure in a low-refractive index UV curable polymer (Efiron PC-363) for stability and later by placing a thin heated LC layer over the polymer-free uniform taper waist region. The temperature dependence of the embedded in polymer MFC sensor before the application of the LC layer demonstrates a redshift of the coupler’s spectrum with an average sensitivity of ~0.5 nm/°C in the temperature range of 14-70 °C. The application of the LC overlay increases the average temperature sensitivity to ~0.7 nm/°C. The demonstrated device offers several advantages such as ease of fabrication and light coupling, the potential for better stability and the possibility of electric field tuning for realizing temperature, electric field, bio-, chemical sensors and tunable add-drop filters for fiber communication systems. Further work is ongoing to explore various tuning mechanisms of the MFC spectrum.

Recently we have demonstrated that conventional (free-space) Faraday rotation spectroscopy (FRS) can be successfully transitioned into optical fiber-based sensing architectures using paramagnetic gas-filled hollow-core photonic bandgap fibers (HC-PCFs)¹. Our measurements revealed that due to the birefringence properties of the HC-PCFs, behavior of the fiber-optic FRS signals is substantially different compared to free-space FRS systems. Furthermore, magnetic circular dichroism tends to have much higher influence on the FRS signals than in other systems. To explain this behavior we have developed a theoretical model, and shown that close agreement with the experimental data can be achieved. In this paper we focus attention on the detailed explanation and the in-depth discussion of the model and assumptions incorporated within it. This approach can be easily extended to account for parasitic effects that take place in real-world FRS sensor systems such as imperfect polarizers or birefringent gas cell windows.

The response of optical fibre long period gratings (LPGs), fabricated with precise control of the grating period to operate at or near the phase matching turning point (PMTP), to temperature was studied. The effect of the grating period on sensor performance was studied. The sensitivity of the LPG operating at the phase matching turning point to temperature was 0.99 nm/°C for 111.5 μm grating period that is ca. 7 times higher than that of an LPG operating far from turning point. The possibility of using LPG sensors to determine the thermo-optic coefficient of the surrounding material was explored.

High-Q resonators have been widely used for sensing purposes. High Q factors normally lead to sharp spectral peaks which accordingly provide a strong sensitivity in spectral interrogation methods. In this work we employ a low-Q ring resonator to develop a high sensitivity sub-micrometric resolution displacement sensor. We use the slow-light effects occurring close to the critical coupling regime to achieve high sensitivity in the device. By tuning the losses in the cavity close to the critical coupling, extremely high group delay variations can be achieved, which in turn introduce strong enhancements of the absorption of the structure. We first validate the concept using an Optical Vector Analyzer (OVA) and then we propose a simple functional scheme for achieving a low-cost interrogation of this kind of sensors.

We present recent results on the fabrication of metallo-dielectric structures on the optical fiber tip by using a self-assembly technique. Our studies aim to attain advanced nanostructured sensors by exploiting easy and low cost fabrication processes suitable to be employed in massive production of technologically advanced devices in the roadmap of the Lab on Fiber Technology. The pursued approach basically consists in the preliminary preparation of a patterned polymeric film by the breath figure technique, directly on the optical fiber tip, and in the successive metal deposition by evaporation. The experimental results demonstrate the successful creation of a metallo-dielectric honeycomb pattern on the optical fiber tip. The experimental spectral features are in good agreement with the numerical analysis, elucidating the photonic and plasmonic interactions occurring in the Lab onto the optical fiber tip. The sensing properties of the optical fiber probes have been successfully explored in terms of sensitivity to the surrounding refractive index changes demonstrating their potentialities for chemical and biological sensing applications.

In this paper, we report photo-inscription of uniform Bragg gratings in Trans-4-stilbenemethanol-doped photosensitive step-index polymer optical fiber characterized by a core diameter of 8.2 μm. Single-mode gratings were produced at ~1550 nm by the phase mask technique with a Helium-Cadmium emitting at 325 nm with an average power of 30 mW. The grating growth was monitored during the manufacturing process, showing that the reflected band is blue shifted by a few hundreds of picometers. Finally, the gratings were characterized in temperature in the range 25 − 50 °C. Their sensitivity has been computed equal to − 47 pm/°C.

Fibre Bragg gratings (FBGs) are strain sensors that can be embedded into composite materials, without affecting their mechanical performances. In this study, we report the use of a short and weakly tilted FBG inscribed in a single mode highly germanium doped photosensitive optical fibre to discriminate, with a good spatial resolution, strain and temperature effects for structural health monitoring (SHM) application. The transmission spectrum of a weakly tilted FBG (TFBG) presents three regions of interest: the Bragg resonance, the ghost mode resonance and all other cladding mode resonances that are not exploited in this work. We make use of the differential temperature sensitivity of the Bragg mode and the ghost mode to discriminate between temperature and strain effects inside composite materials.

Embedding FBG sensors in carbon fiber structures is a very attractive solution, due to the small fiber diameter, and the possibility to manufacture arrays of many gratings into a single optical fiber. These embedding is particularly useful for the manufacturing of smart structures, able to improve their characteristics thanks to embedded sensors and actuators. In this work a carbon fiber beam of 3 m length, with an array of 30 FBG sensors and 3 piezoelectric actuators, is described. The focus of the work is on the evaluation of the good operation of embedded FBG sensors, that is not easy due to the microstructure of woven carbon fiber layers, producing non-homogeneous strain field, a well known problem for the reliability of FBG strain measurements. The proposed technique looks at the standard deviation of the full width at -6 dB of the spectra of each FBG sensors, during a quasi-static motion producing quasi-static strains. 37% of the 30 FBG sensors have been found to produce measurements corrupted by a small error. At the end, vibration control of the described structure is shown.

Due to their high mechanical and corrosion resistance and their small dimension, optical fibre sensors and more particularly fibre Bragg gratings have demonstrated their high utility in the composite material field for monitoring purpose when there are placed under constrain, vibration or temperature variation. In this context the ingress or egress of optical fibre sensors is an important issue for their application in real applications. However, the optical fibre at these transition points is very fragile and an improper handling of the samples can lead to breakage. In this paper, we describe a new kind of “small form factor” optical fibre connectors well suited to be embedded in composite materials. This new connector, cleavable, allows to obtain a good finish of the composite components that can be used in real applications. We also assess its proper behavior (reflection losses evolution) when this embedded connector is tested under vibration and temperature.

Metal clad single mode optical fibres are successfully embedded into stainless steel using a layer by layer based additive manufacturing technology based on selective laser sintering of powered stainless steel material. The single mode fibre has been coated with a protective Ni metal layer to facilitate thermal protection and bonding to the stainless steel matrix. A loss of ~1 dB is observed after embedding which is attributed to micro bending in the embedded section.

In this work a high-performance optical low-coherence reflectometer (OLCR) has been used to estimate the optical losses in optical fibers and fiber Bragg grating sensors embedded into CFRP material samples. An ASE tunable narrowband light source coupled to a Michelson interferometer allowed the high spatial resolution localization of both the concentrated and the distributed loss for different fiber coatings and type. In particular, acrylate- and polyimidecoated fibers and bend-insensitive fibers were tested. By using the OLCR it was possible to locate and identify the sources of optical loss introduced by the CFRP manufacturing process, therefore obtaining useful information on the efficiency of the embedding process.

Several easy-to-manufacture designs based on a pair of Fiber Bragg Gratings structure embedded in Carbon Fiber Reinforced Plastic (CFRP) have been explored. These smart composites can be used for strain and temperature discrimination. A Finite Elements Analysis and Matlab software were used to study the mechanical responses and its optical behaviors. The results exhibited different sensitivity and using a matrix method it is possible to compensate the thermal drift in a real application keeping a simple manufacture process.

This paper presents the results of strain tests performed with fiber Bragg gratings written by interferometric or phasemask methods. The results show a significant difference on dynamic response these sensors when subject same conditions of temperature and mechanical stress. This effect may suggest a limitation on use of sensors based on this technique in applications requiring precise and fast responses.

Composite structures are made from two or more constituent materials with significantly different physical or chemical properties and they remain separate and distinct in a macroscopic level within the finished structure. This feature allows for introducing highly birefringent polymer microstructured optical fibers into the composite material. These new fibers can consist of only two polymer materials (PMMA and PC) with similar value of the Young modulus as the composite material so any stresses induced in the composite material can be easily measured by the proposed embedded fiber optic sensors.

Results of our research on embedded highly birefringent polymer microstructured fibers are presented. A composite material sample with fibers embedded between two layers of a multi-layer composite structure is fabricated and characterized. Temperature sensitivities of the polymer fibers are measured in a free space and compared with the fibers embedded in the composite material. It appeared that highly birefringent polymer microstructured fibers exhibit a strong increase in temperature sensitivity when embedded in the composite material, which is due to the stress-induced changes in birefringence created by thermally-induced strain.

In this paper a technique for integrating copper coated silica optical fibers into AS-4/PEEK composite for Structural Health Monitoring (SHM) is presented. The integration steps are described in detail. X-ray and microscopic images indicate a successfully integrated optical fiber which does not seem to affect the fiber/matrix distribution around it. Optical backscatter reflectometry shows losses of approximately 2dBm^-1 along the integrated parts of the optical fiber due to temperature induced shrinkage of the composite.

We propose a new scheme of Brillouin optical frequency-domain analysis (BOFDA) for distributed fiber-optic strain and temperature sensing, named linear-configured BOFDA (L-BOFDA). In conventional loop-configured BOFDA, light injection into both ends of a fiber under test (FUT) is needed for counter-propagation of pump and probe waves. In contrast, in L-BOFDA, pump and probe waves are injected into the same end of an FUT, and the probe wave Fresnelreflected (or mirror-reflected) at the other end of the FUT is exploited; thus, one-end access is feasible. We show proof-of-concept results of distributed strain measurement in a silica single-mode fiber with L-BOFDA, and discuss the signal-to-noise ratio degradation and the benefit in developing distributed Brillouin sensors based on polymer optical fibers.

A novel method to perform 3D vector measurement of intense and static magnetic elds is presented. The technique is based on the recently introduced distributed magnetic- eld ber optic sensor, which exploits Faraday rotation of polarization in standard single-mode bers. In the present case, the ber is arranged in several concatenated short coils, and the component of the magnetic eld parallel to the ber axis is measured by the distributed sensor. We show that by analyzing amplitude and spatial phase of the Faraday rotation measured along a coil, the 2D vector component of the magnetic eld parallel to the coil plane can be calculated. By arranging two close coils on orthogonal planes, a 3D reconstruction of the magnetic eld is achieved. Measurement uncertainty of few percents has been experimentally demonstrated over coils of just two loops; better accuracy can be obtained by increasing the number of ber loops.

Fibre optic sensors for monitoring in safety-relevant structures have to be validated in order to proof their reliability under typical structural load conditions. The reliable use of optical fibre sensors depends strongly on an appropriate and qualitative application. Diagnostics of the physical condition of embedded and surface-applied fibre optic strain sensors are demonstrated on field examples. Distributed strain measurement based on Rayleigh backscattering is used to determine breakage of the fibre, interface adhesion problems and to identify application related strain transfer mechanisms.

We report a Brillouin-based fully distributed and dynamic monitoring of a strain wave, propagating at a speed of ~4km/sec in a 6m long fiber. Using an audio speaker, a mechanical impulse was introduced to one end of a 6m long optical fiber, initiating a strain wave propagating towards the other fixed end of the fiber. Employing a simplified version of the Slope-Assisted Brillouin Optical Time Domain Analysis (SA-BOTDA) technique, the whole length of the fiber was interrogated every 1μs (before averaging). A dynamic spatially and temporally continuous map of the strain was obtained, from which the wave velocity could be deduced. With a trade-off among sampling rate, range and signal to noise ratio, kHz sampling rates and hundreds of meters of range can be covered with spatial resolutions down to a few centimeters.

Fibre-optic distributed sensing has the potential to revolutionize well and reservoir surveillance in the oil and gas industry. Benefits include the passive nature of optical fibre sensors, the potential for cost-effective installations, combined with the possibility of densely distributed measurements along the entire length of the fibre. Amongst a range of fibre-optic sensing technologies, Distributed Acoustic Sensing has the potential to provide a low cost alternative for conventional seismic technologies. To widen the geophysical application scope further, the fibre-optic sensing cable should be made more sensitive to incoming seismic waves that arrive at the cable perpendicular (“broadside”) to its axial direction. We introduce the development of such cable concepts, and present results of a successful cable deployment in a surface seismic field trial. Efforts continue to realize cost-effective directionally-sensitive cables for geophysical use, for deployment down-hole and on surface.

Stimulated Brillouin scattering (SBS) in plastic optical fibers (POFs) is observed, for the first time to the best of our knowledge, using pump-probe technique without lock-in detection, and the dependences of the Brillouin gain spectrum on POF length, pump power, and probe power are fully investigated. An optimal POF length exists for SBS observation, because POFs have relatively high propagation loss of 250 dB/km at 1.55 μm; it is found to be 3.8 m when 21.1-dBm pump and 22.2-dBm probe waves are used. As the probe and pump powers grow higher, the Stokes power is also increased but nonlinearly, which indicates that the Brillouin signal observed with this technique can be directly applied to the implementation of POF-based Brillouin optical time-domain analysis systems.

The possibility to customize Simplex coding for long range Brillouin Optical Time Domain Analysis is demonstrated by “colouring” the sequences in the frequency domain. The coding gain is identical to the traditional intensity-modulated Simplex code, though with much simplified series of sequences. The frequency-hopping pulses in return-to-zero intensity-modulated format are generated with a Direct-Digital Synthesizer. The proof-of-concept is experimentally demonstrated with measurements over a 50 km range (100 km fibre-loop) and a 2 meter spatial resolution.

The paper reports results of the long distance (25 km range) distributed optical fiber sensing by means of Tunable Wavelength Coherent Optical Time Domain Reflectometry (TW-COTDR) method. The tests were designed to verify the accuracy and repeatability of the method in long distance measurements, as well as compatibility with various optical fiber types. Results demonstrate the capability of the method to detect strain or temperature changes over long distances. This proposed method is compared to Brillouin sensing techniques, into the same fibers. Unlike the Brillouin-based methods, measurement uncertainty does not increase with increasing distance. We demonstrated 0.16°C uncertainty at 21km.

With their high thermal stability compared with other plastic optical fibers (POFs), partially chlorinated graded-index POFs (PCGI-POFs) are a promising candidate to develop the sensing heads of Brillouin-based distributed strain and temperature sensors. In this study, the Brillouin frequency shift (BFS) and its temperature dependence in a PCGI-POF are estimated by using ultrasonic pulse-echo technique. The estimated BFS is ~4.43 GHz with its temperature coefficient of approximately –6.9 MHz/K at 1550 nm. Its absolute value is ~5.8 times as large as that of silica single-mode fibers, and even larger than that of a perflurointated GI-POF. Its fracture strain of ~3.0% (mostly in elastic region) is small compared with other POFs, and so it appears difficult to estimate the BFS dependence on strain in a PCGI-POF with this technique. These experimental results imply that the Brillouin scattering in PCGI-POFs is potentially applicable to highprecision temperature sensing.

Raman-assistance (RA) has become a promising technique to enhance the sensing range of standard Brillouin Optical Time Domain Analysis (BOTDA) fiber sensors due to its ability to amplify in a distributed way all the interacting signals within the fiber. Unfortunately, Raman amplification introduces a great amount of Relative Intensity Noise (RIN) to the detected low-frequency probe wave. This RIN transfer problem has been widely identified as a major limitation in RABOTDA. In Vector Brillouin Optical Time Domain Analysis (VBOTDA) the detected signal is transferred to a highfrequency carrier where the Raman RIN transfer turns out to be much less harmful. In this work we demonstrate, for the first time to our knowledge, Raman-assistance in a VBOTDA. Our results show significant reduction of the RIN transfer effect in RA-VBOTDA compared to standard RA-BOTDA, making this type of scheme particularly interesting for long range distributed sensing.

Brillouin sensors have the potential to measure strain or temperature distribution along the optical fiber, by determination of the Brillouin frequency shift (BFS). The Brillouin optical correlation domain analysis (BOCDA) is an important technique in Brillouin sensors, having great spatial resolution over a restricted measurement range, comparing to other systems, such as the Brillouin optical time domain analysis (BOTDA). To elongate the restricted measurement range, temporal gating techniques have been proposed and demonstrated, but the influence of these techniques on the performance of the BOCDA system or the parameter requirement for system optimization have not been investigated. In this report, we first determine a simulation method to calculate the BOCDA output with temporal gatings and find out that the phase relation between the gating pulses and the sinusoidal frequency modulation (FM) may change the system output. Although that influence can be neglected for most cases, the phase optimization can make the system output approach the ideal case that the temporal gating is not being applied. Finally, calculations of system output for different gating pulse lengths are held, showing that the pulse length does not have to strictly match one period of the sinusoidal FM of the laser source.

We present the application of a Brillouin distributed sensor for railway traffic monitoring. The field test is performed on the Italian regional line San Severo - Peschici. A single-mode optical fiber was attached along a rail length of about 60 meters. The strain associated to train passage was acquired along the monitored rail length, at 31 Hz acquisition rate and 1-m spatial resolution. The sensor is capable to retrieve useful information in railway traffic monitoring, such as train identification, axle counting, speed detection, and dynamic load calculation.

We report an experimental study on a cantilever beam, aimed to verify the feasibility of modal analysis by distributed Brillouin sensing for structural damage identification. Damage identification was carried out for three defect cases, analyzing the changes of the natural frequencies and mode shapes of the first two bending modes. Comparison with finite element method (FEM) analysis shows that the damage can be detected and localized, within the limitation dictated by the spatial resolution (30 cm) of our sensor.

Phase-sensitive optical time domain reflectometry (ΦOTDR) is a simple and effective tool that allows the distributed monitoring of vibrations along single-mode fibers. In this letter we study the effects of modulation instability (MI) in long-range ΦOTDR over conventional optical fibers. We demonstrate both theoretically and experimentally that MI can induce a position-dependent signal fading which leads to a nearly complete visibility loss in the interference signal recorded at certain positions and therefore to a sensitivity loss at these positions. While this effect is detrimental in the context of distributed vibration analysis using ΦOTDR, we also believe that the technique provides a clear and insightful way to evidence the Fermi-Pasta-Ulam (FPU) recurrence associated to the MI process.

In structural health monitoring, the propagation of ultrasonic waves along a structure can reveal interesting data relevant to the integrity of the whole structure. The availability of a system for distributed sensing of ultrasonic waves could, in some cases (e.g. pipelines) provide extremely valuable information to civil engineers. Phase-sensitive optical time domain reflectometry (ΦOTDR) is a simple and effective tool allowing the distributed monitoring of vibrations along single-mode fibers. Up to now, ΦOTDRs have been used mostly for the measurement of sub-kHz vibrations. In this work, the authors present an experimental characterization of a high-visibility ΦOTDR and its performance when used for ultrasonic vibration measurements. The sensor was able to measure vibrations of up to 39.5 kHz with a resolution of 5 m over a range which could go up to 1.25 km. This is the first time to our knowledge that a ΦOTDR is demonstrated for distributed measurement of ultrasonic waves.

We demonstrate a BOTDA sensor based on the use of the Brillouin phase-shift that performs measurements tolerant to non-local effects. This technique raises opportunities to increase the distance covered by these sensors and the maximum optical power of the probe wave injected to the fiber. As a result, the system has the potential to increase the SNR achieved at the last meters of the fiber. Proof-of-concept experiments demonstrate unaltered measurements of the phase-shift spectrum in a 20Km long fiber for large frequency-dependent distortions of the pump pulse.

In this paper we present an engineering application of optical fiber distributed sensing for monitoring of the ground settlement during a tunnel excavation. The design, installation methods, and implementation of 4D (space plus time) warning system are outlined. The ground settlement was closely monitored for entire 6 months of tunnel construction process, revealing a wide range of geomechanical phenomena. Obtained on-line vertical displacements allowed engineers to control the excavation speed and monitor ground settlement, contributing substantially to the overall reliability and safety.

A random access distributed Brillouin fibre sensor is presented, based on phase modulation using a pseudo-random bit sequence (PRBS) together with time gating. The standard phase-correlation technique is known to show a noise level increasing linearly with the number of measured points due to weak gratings generated randomly along the whole sensing fibre. Here we show how intensity modulated pump and time gated detection significantly improve the signal-tonoise ratio (SNR) of the system with no impact on the spatial resolution. A measurement with 1.1 cm spatial resolution over 3.3 km is demonstrated, representing 300’000 equivalent points. The limitations of the proposed technique are discussed through the paper.

A thorough study of the generation of modulation instability (MI) in distributed Brillouin fibre sensors is presented. ASE noise co-propagating with the pump pulses within the MI gain spectrum has been identified to be an important factor seeding modulation instability and reducing its power threshold. The paper describes how optical narrowband filtering reduces the pump depletion resulting from MI, allowing pump pulses to propagate through longer distances in standard optical single-mode fibres.

In this work, a simple, stable and switchable single- or dual-wavelength fiber laser configuration is proposed and demonstrated. The cavity laser is comprised of two FBGs, encompassing a short length of highly-doped Er-fiber, to create effectively single- or dual-wavelength fiber lasers. The laser performance in terms of the laser output power and laser stability is experimentally investigated in this paper. Application for temperature measurement is also shown.

We report a 10cm spatial resolution in a Brillouin-based distributed sensing system using two simultaneously launched gain and loss pump pulses, having slightly different durations. Post-recording subtraction of the probe signal, excited by the shorter pulse, from the corresponding one, obtained from the longer pump pulse, is no longer required, since it is done automatically by the overlapping parts of the gain and loss pump pulses. Using a 30ns gain pump pulse and a 29ns loss pump pulse we were able to improve upon previously published results, achieving a distributed strain measurement along a standard single mode optical fiber with a spatial resolution of ~10cm. This technique does not broaden the involved Brillouin gain spectra so that the strain/temperature sensitivity is not compromised.

We analytically investigate the case of the Brillouin interaction between probe waves propagating against two modulated pump waves. This investigation is motivated by the sweep-free BOTDA technique, where, to increase the BOTDR sensing speed, the Brillouin gain spectrum is simultaneously interrogated by many probe-pump pairs. It is shown both analytically and experimentally that the Brillouin interaction between a probe and its corresponding pump is negligibly affected by a neighboring pump only when the pump tones separation is much larger than the width of the Brillouin gain spectrum.

We propose to use focused femtosecond laser pulses to create scattering damage in standard singlemode optical fibres as reference points for quasi-distributed sensing applications. Such sensor fibres are interrogated with incoherent optical frequency domain reflectometry (I-OFDR) technique and optical time domain reflectometry (OTDR). A performance comparison of both techniques with the clear advantage of the I-OFDR is presented as well as a quasi-distributed length change measurement application. Also dynamic measurement based on the I-OFDR technique is demonstrated on a femtosecond laser-induced sensor chain.

In this paper we present results of computer simulation of the Optical Frequency Domain Reflectometry system used for measuring distributed radiation-induced absorption. We simulated conditions of an experiment in which a highly radiation sensitive optical fibre doped with aluminium was exposed to gamma-radiation. The total exposed dose was about 50 kGy. We measured two backscattering profiles of the fibre network before and right after irradiation to estimate the induced change of the trace slope which in case of optical fibre dosimetry is used for total dose estimation. Then we simulated this experiment using a MATLAB model imitating an optical fibre backscattering profile. The simulation was based on the operational principles of the OFDR system and imitated its measurement algorithm. As a result of simulation we obtained two backscattering traces which were in good conformity with those measured in the real-life experiment. To our knowledge, this is the first time that distributed measurement of radiation-induced absorption using optical frequency domain reflectometry has been simulated.

A novel configuration for a Brillouin distributed sensor using a phase modulated probe is presented. It offers the combined advantages of a direct implementation using simple devices and a large immunity to noise, shifting the information from the baseband to a higher frequency, which substantially strengthens the robustness to perturbations, interferences and other optical coherent noises. It naturally facilitates the possibility to perform frequency-coding on the probe to realise dynamic and fast measurements, since all frequency tunings are realised at sub-GHz frequencies.

We describe te production and characterization of FC/PC connectorised fibre Bragg grating sensors in polymer fibre. Sensors were recorded in few-moded and single mode microstructured fibre composed of poly (methyl methacrylate).

In this work we tested use of thin film aluminium coating to enhance the temperature sensing features of FBG sensors. Thin film coating was evaporated on the Bragg grating after removal of the original acrylate recoating, using a modified vacuum evaporation system that allows uniform radial deposition around the fibre. Results show that recoating thickness up to 0.5 μm do not produce appreciable effects, whereas thickness of 2.3 μm appreciably increases temperature sensitivity without increasing time response constant.

Acrylate and polyimide coatings are found to have a suitable modulus for micro-seismic sensors whilst carbon coatings are too hard and inelastic for reliable use in this application. Fiber cladding designs can be optimized for mechanical reliability by using 80μm or 50μm cladding diameters and the numerical aperture (NA) increased to give low bend losses. To reduce splice losses, a bridging fiber has been developed, capable of reducing splice losses between telecoms fibers and reduced cladding diameter high NA sensor fibers by <50%.

A simple, yet effective, setup for the simultaneous interrogation of multiple ferrule-top-cantilever sensors for acoustic sensing is here presented and experimentally tested with two ferrule-top-cantilever sensors; results confirm the feasibility of the approach.

In this paper, a 50 Km remote and switchable fiber optic sensing system based on an erbium doped fiber ring laser is proposed. The system allows the integration of different interrogation methods based on the detection of wavelength or amplitude variations of the laser. This integration is carried out by sequentially activating different ring cavities by using an optical switch. With this scheme, the maximum gain zone of the erbium doped fiber amplifier can be used to increase the distance of the sensor system. A bending intensity sensor and a FBG based strain sensor were successfully tested for high and low-strain measurements respectively. This system includes all the active elements inside the monitoring station, enabling the remote monitoring of the sensors.

This paper develops a fiber optical sensor network based on OADM (optical add-drop multiplexer) devices with a bus configuration. Unlike conventional bus sensor networks which need optical couplers to include the sensors, the proposed network uses OADM to incorporate the sensors to the network. These devices make it possible to increase the number of sensors in bus networks in comparison with those that have optical couplers, wherein the transmitted signal into the spine of the bus decreases because of the insertion loss and also because of the coupling ratio. In this work, different intensity sensors have been efficiently employed because the proposed configuration addresses the two main concerns of intensity sensors: on the one hand, each sensor is associated with a different wavelength directly offered by each OADM; and on the other hand, a reference wavelength is included in order to distinguish between power variations induced by the transducer or to detect a fiber failure.

Highly birefringent (Hi-Bi) microfiber-based fiber loop mirrors (FLMs) were studied for tunable comb filters and refractive index (RI) sensors. RI sensitivity of up to 15,441 nm/RIU was experimentally demonstrated for the RI sensors and, for the tunable filter a thermal tuning coefficient of ~-2.35nm/°C was obtained for temperature from 20 to 90°C when it was immersed into water. The use of two cascaded Hi-Bi micro-tapers within a Sagnac loop allows more flexibility in controlling the transmission/reflection spectraums of the FLM. The length of the tapered Hi-Bi microfibers is on the order of centimeters, two orders of magnitude shorter than the conventional Hi-Bi fiber-based devices.

We present a solid-state FBG array interrogator and multiplexer capable of determining absolute FBG wavelengths and of providing high-speed, high-resolution static and dynamic measurements. Using a described procedure, deployable on multiplexing passive-interferometric schemes, the system is able to determine initial sensor wavelengths and thereafter track wavelength changes with interferometric resolution. The scheme allows high-resolution interrogation of FBG sensor arrays to be applied to many industrial applications, where previously the lack of combined absolute and quasistatic wavelength measurement precluded the use of interferometric techniques. Using a preliminary laboratory embodiment, we demonstrate a wavelength determination accuracy of <0.3 nm and a measurement resolution of 10 fm/√Hz, and propose pathways to improved performance and miniaturisation.

The increasing quantity of renewable energy in electric power generation leads to a higher flexibility in the operation of conventional power plants. The turbo generator has to face the influence of frequent start-stop-operation on thermal movement and vibration of the stator end windings. Large indirect cooled turbo generators have been equipped with FBG strain and temperature sensors to monitor the influence of peak load operation. Fiber optic accelerometers measure the vibration of the end windings at several turbine generators since many years of operation. The long term reliability of fiber optic vibration, temperature and strain sensors has been successfully proved during years of online operation. The analysis of these data in correlation to significant operation parameter lead to important diagnostic information.

This paper presents a novel design of a system for using smart mobile robots to deploy a Wireless Sensor Network (WSN) for different optical fibre sensors, allowing for potential applications where there is a remote and harsh monitoring environment and allowing for the advantages of the optical fibre technology for the sensor itself to be used. The platform which was designed is comprised of a smart mobile robot, an optical fibre sensor module and a WSN module integrated with a localization component based on Received Signal Strength Indicator (RSSI), which has important advantages for mobile sensing and tracking, flexible deployment and mesh networking. The design principle and implementation-related issues for the platform have been discussed in this study. To investigate the performance of the mobile WSN platform, an experiment simulating measurement in a real environment has been performed. With the positive experimental data obtained, the functionalities of the platform are successfully demonstrated, which enables the real-time monitoring and transmission of sensor data and in addition estimated positional information. The exploitation of this kind of mobile WSN platform with fibre optic sensors is expected to make an impact on many applications, including those where advanced optical fibre sensing is particularly advantageous, yet where conventional WSNs cannot meet the requirements of the total sensing system.