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Taking advantage of the development of optical-fiber communication technologies, the fiber-optic gyroscope (often abbreviated FOG) started to be investigated in the mid-1970s, opening the way for a fully solid-state rotation sensor. It was firstly seen as dedicated to medium-grade applications ( 1 ° / h range), but today, it reaches strategic-grade performance ( 10 − 4 ° / h range) and surpasses its well-established competitor, the ring-laser gyroscope, in terms of bias noise and long-term stability. Further progresses remain possible, the challenge being the ultimate inertial navigation performance of one nautical mile per month corresponding to a long-term bias stability of 10 − 5 ° / h . This paper is also the opportunity to recall the historical context of Sagnac's experiment, the origin of all optical gyros.

Taking advantage of the development of optical-fiber communication technologies, the fiber-optic gyroscope started to be investigated in the mid 1970s, opening the way for a fully solid-state rotation sensor. It was firstly seen as dedicated to medium-grade applications, but today, it reaches strategic-grade performance and surpasses its well-established competitor, the ring-laser gyroscope, in terms of bias noise and long-term stability. Further progresses remain possible, the challenge being the ultimate inertial navigation performance of one nautical mile per month corresponding to a long-term bias stability of 10 −5 °/h.

A shearography system, that measures two displacement derivative components, using polarisation switching is described. This is achieved using wavelength tuning and highly birefringent optical fibre. Interferometer pathlength imbalance with wavelength tuning provides the phase-stepping.

In this paper, we present a novel method for calibration of the current induced optical frequency shift in LDs. The spatial synchronous phase measurement technique is developed for phase shift measurement. Two OPDs in the unbalanced Michelson mterferometer are independently introduced in order to calibrate the current tuning rate.

We describe a fiberoptic sensor that uses a frequency modulated laser to simultaneously measure both the position and velocity of a reflecting target. We also discuss the effects ofresidual amplitude modulation and multiple reflections.

A new flow-cell for test of fiber optic chemical sensors was designed and tested. The head was made of plexiglass and consisted of the main body and sensor compartments, in which optomembranes and optical fibers were mounted. The performances of the head were determined with pH sensors working in different pH ranges.

Interferometric fiber-optic sensing is used for monitoring the vibrations inside a medium-power transformer. Disturbances are present in the measurement, mainly associated to mechanical transduction to the accessing path cords and to the interrogation scheme. Mechanical vibrations other than of interest are characterized and an optoelectronic and processing scheme is proposed to avoid them.

Both piezoelectric and fiber-optic hydrophones are sensitive to acceleration. The acceleration can be a major noise source in rough environment. The pressure to acceleration responsivity ratio is therefore a figure of merit for a hydrophone.

Velocity vector sensing by using fiber-optic low coherent interferometer is proposed and demonstrated. The velocity vector component is measured directly from a peak position of correlation signal between two backscattering lights from flow.

Optical fibres operating by the photonic bandgap effect offers an alternative approach to evanescent field waveguides for opticai sensing applications. In addition to this, these photonic crystal fibres provide completely new waveguiding properties, which include different macro-bending loss performance compared to standard optical fibres. A first estimation of these new properties is demonstrated for air-guiding fibre designs by combining accurate vectorial mode analysis and an adaptation of more traditional macro-bending loss theory.

We propose a temperature fiber sensor based on CdSe-nanocrystal-doped phosphate glass. This glass demonstrates a reversible temperature-induced absorption edge shift at temperatures less than annealing temperature ofthe glass (

A Quasi-distributed pH sensing system was developed to utilise information derived from evanescently excited fluorescence signals originating from sensor sites fabricated on an optical fibre. The sensor sites comprise a fluorophore immobilised covalently within a hydrogel matrix.

A pH sensor has been fabricated using a tapered single-mode optical fiber coated with cellulose and direct dyes. A range from 3 to 7.4 and from 8 to 1 1 (pH) was achieved without using UV light.

We have proposed and demonstrated a high-resolution interrogation system for fiber Bragg grating strain sensor with prominent temperature stability using long period grating pair and EDF inserted between the two gratings.

Photosensitive materials, i.e., a photochromic dye and a silver halide, were used for fabricating optical fiber devices. Variable transmiUaixe was demonstmted with a photochmmic liquid-core fiber. A periodic photodarkening pattern was induced in an infrared silver halide fiber.

We present the design of a fibre optic system for both intra-cavity and ring down absorption measurements in trace gas detection. The system is constructed from standard fibre optic components with a micro-optic gas cell.

Optical fiber sensors have been embedded in structural elements for over fifteen years in order to obtain information regarding the internal stress, strain, or temperature states of the structures. However, the degree to which the mechanical reliability and data stream integrity are maintained will strongly depend on the type of sensor being used, the measurement application, and the structural integration method. In this paper we present a fiber optic sensor that demonstrates higher sensitivity than the typical fiber Bragg grating sensor, and it is capable of monitoring the state of its own health. The sensor design uses an induced phase discontinuity in the fiber Bragg grating to create a narrow pass-band within the reflection spectrum of the grating. The position of this narrow window within the Bragg spectrum is used to monitor the sensor's health.

The temperature insensitive fiber-optic bending sensor with high resolution and high sensitivity based on a pair of long period fiber gratings will be discussed. Dependence of the resonant wavelength shift and change of peak depth on the curvature change was investigated experimentally.

This paper reports on the first realisation of embedding fiber Bragg grating temperature sensors inside the stator bars of a large air cooled power generator. Furthermore first measurements of the conductor temperature inside the bushings have been carried out during a generator prototype test run.

An FBG-based inclinometer is presented. The opto-mechanical principle is based on a differential method, allowing the temperature, pressure influences and mechanical hysteresis to be compensated for. Metrological qualifications performed in laboratory as well as data gained from a civil engineering field trial are presented.

This work presents a novel fiber optic rotation rate sensor based on the characteristics of an OEO with feedback loop tuned by Sagnac interferometer. Experimental results, which agree with theoretical predictions, show high sensitivity.

A fiber optic hydrophone array with four sensor elements ofthe air-backed mandrel type has been manufactured and tested. Frequency response, crosstalk, noise and directional response have been measured in an acoustic tank.

A self-referenced fibre optic intensity sensor supported by a multiple beam SagnaC Configuration is investigated. Sensor linearity and sensitivity are analysed. Theoretical and experimental results are Compared, being Considered the sensor design and its optimisation.

We report on the first results of a fiber optic acceleration sensor which consists of two partially spectral overlapping Bragg gratings. The motion of an inertial mass shifts the Bragg reflections of the gratings in different spectral directions and thus modulates the overall amount of reflected light.

A fibre-based optical preamplifier system has been used to improve the signal-to-noise capabilities of a Brillouin-based fibre-optic distributed temperature sensor. A 17dB optical signal-to-noise improvement in a 23km sensor is demonstrated.

The significant advantages of optical fiber sensor systems for spacecraft applications have been established through demonstration projects on both prototype exemplars and flight articles. These include distributed strain sensing using embedded and surface-mounted fiber Bragg grating arrays and ultrahigh sensitivity strain and temperature sensing with fiber cavity etalon sensors. These projects will be discussed with emphasis on sensor performance, reliability, and survivability during composite fabrication, including egress of the fiber lead from the part.

Visibility of a core region in a high temperature gas cooled reactor is poor. Realization of optical diagnostics there will improve safety and maintenancibility. Applicability optical fibers for diagnostics there was studied in the study.

We have used the electrostatic self-assembly process to grow nanostructured thin films, molecular layer-by- molecular layer, on the ends of silica optical fibers. Such films form optical cavities that allow measurement of temperature by Fizeau interferometiy.

Distribution of Brillouin shift frequencies along optical fibers are measured by a newly developed Brillouin loop amplification scheme. The frequency shift measurement for a 40-km test fiber has been successfully carried out.

A fibre optic Bragg grating sensor measures strain on the chest of patients as a method to detect the frequency spectrum of the respiration process. The apparatus can be used to trigger electric ventilation pulses.

We present a robust, temperature and vibration insensitive fiber-optic current sensor. The sensor has been integrated into a high-voltage circuit breaker. One year field experience has been gained in two substations of the Italian railways.

New fiber-optic carbon dioxide sensors utilizing a sensitive film containing an indicator dye on a polymer clad optical fiber (PCF) are demonstrated. The sensitive film is a SiO2 gel film including an indicator dye of thymol blue or phenolphthalein, which is dip-coated by a sol-gel method. The attenuation of this sensor changes at the wavelength range of 500 to 700nm detecting CO2 gas.

By using fiber Bragg grating sensors for temperature measurement in high-voltage transformers a new technique for the enhancement of the sensing element's sensitivity is developed and two low cost detector units for the measurement of the Bragg wavelength are presented.

Initial attempts to photo-induce refractive mdcx changes in bulk poly methyl methacrylate (PMMA) and in PMMA based plastic optical fibres (POF) using UV light are described. Optimum changes have been achieved at 216 nm, causing path length changes of 10π, corresponding to possible refractive index modulation of between 5 and 14 % over thicknesses up to 100 μm. The effects of refractive index changes on the far field modal distribution of tapered PMMA plastic optical fibres are described.

The evanescent wave optical fibre probe for Cu2+ ions detection was elaborated. As an optical transducer a porphrine (H2TMePvP) was used. The detection limit of the probe as evaluated to be 5x10-5 mol/1 (3ppm).

Angle Division Multiplexing (ADM) has recently been proposed for fibre-based parallel short distance interconnects. Here, practical issues are discussed such as robustness against environmental stress, alignment requirements for micro-integration and the interconnection of 8 workstations as a demonstration.

A system for producing and demultiplexing large numbers of fiber Bragg grating sensors is described. Three thousand gratings were multiplexed in four optical fibers and demonstrated on a large test article. Preliminary results of a strain sensing system in unaltered fiber using OFDR measurements of the Rayleigh scatter is also described.