This PDF contains the front matter associated with SPIE Proceedings Volume 8370, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Photonic crystal fibers are pure silica optical fibers with an array of air holes that run along the length of the fiber. The development of these fibers, in both solid and hollow core varieties, has been significant over the past 15 years and they are increasingly finding new applications in a variety of sensing areas where they can offer opportunities distinct from conventional optical fibers.

Fiber-optic long-period grating (LPG) operating near the dispersion turning point in its phase matching curve (PMC), referred to as a Turn Around Point (TAP) LPG, is known to be extremely sensitive to external parameters. Moreover, in a TAP LPG the phase matching condition can be almost satisfied over large spectral range, yielding a broadband LPG operation. TAP LPGs have been investigated, namely for use as broadband mode convertors and biosensors. So far TAP LPGs have been realized in specially designed or post-processed conventional fibers, not yet in PCFs, which allow a great degree of freedom in engineering the fiber's dispersion properties through the control of the PCF structural parameters. We have developed the design optimization technique for TAP PCF LPGs employing the finite element method for PCF modal analysis in a combination with the Nelder-Mead simplex method for minimizing the objective function based on target-specific PCF properties. Using this tool we have designed TAP PCF LPGs for specified wavelength ranges and refractive indices of medium in the air holes. Possible TAP PCF-LPG operational regimes - dual-resonance, broadband mode conversion and transmitted intensity-based operation - will be demonstrated numerically. Potential and limitations of TAP PCF-LPGs for evanescent chemical and biochemical sensing will be assessed.

This paper presents the results of the finite element modeling of a unique 6-rod bundled sapphire photonic crystal fiber. The structure is composed of five rods of single crystal sapphire fiber 70μm in diameter symmetrically arranged around a solid single crystal sapphire core region, which is 50μm in diameter. The modeling work focuses on the optimization and modal analysis of this photonic crystal fiber using Comsol Multiphysics 4.2a. In sensor design and realization, reduction of the modal volume of the fiber can offer significant advantages, and as such, this research work is focused on computational determination of the structures, which may minimize the number of modes of the sapphire photonic crystal fiber. The fiber design being analyzed in this paper may be especially important for sensors operating in harsh high temperature environments.

I will expose a Computational analysis method for a design of a strain fiber optic sensor. I will use three different software programs. The first program will be MAPLE for the develop of the numerical and symbolic computations, the second program will be ANSYS for the structural analysis and the third one will be OPTIFIBER for the analysis of electromagnetic modes in the optic fiber. The design strategy is to translate the deformations of structures in changes in the refractive index of the optic fiber and the subsequent modification of the electromagnetic modes of the fiber. This strategy will be presented in detail from a computational mathematic point of view. Is hoped that this design method proposed be useful for engineers working with optic fiber.

This article introduces an approach for modeling the fiber optic low-finesse extrinsic Fabry-Pérot Interferometers (EFPI), aiming to address signal processing problems in EFPI demodulation algorithms based on white light interferometry. The main goal is to seek physical interpretations to correlate the sensor spectrum with the interferometer geometry (most importantly, the optical path difference). Because the signal demodulation quality and reliability hinge heavily on the understanding of such relationships, the model sheds light on optimizing the sensor performance.

I will present a computational method for the analysis and design of a temperature sensor based on optical fiber. I will combine symbolic and numerical computations using the following software: Maple, for symbolic computation; Ansys: and Quick-Field for the numerical-graph computation of temperature profiles; Opticfiber for the numerical-graph computation of the electromagnetic modes in the fiber optics. The design strategy is to convert the patterns of temperature in changes of the refractive index of the fiber and the detection of changes in the electro-optical normal modes in the fiber. The proposed method has many advantages for the design of optical fiber sensors nowadays, for temperature measurements as well for other physical variables. We will use many special functions of Mathematical Physics such as the error function, Bessel functions, Kummer functions, Heun functiions, Whittaker functions and Laguerre functions. We will use Maple to make very complex computations with such functions.

We have fabricated both pressure and temperature sensors based on chiral fiber gratings that can operate in harsh environments over wider measurement ranges than conventional fiber Bragg gratings (FBGs). Chiral fiber sensors are made by twisting one or more standard or custom optical fiber with a noncircular or non-concentric core as they pass though a miniature heat zone. Because the resulting structures are as stable as the glass material, they can operate in harsh environments. Excellent temperature stability up to 900°C is found in pure silica chiral fiber temperature sensors. We developed a correlation algorithm for use with a standard FBG interrogator to accurately measure the shift in the transmission spectrum as the environment of the sensor changes. We developed a calibration procedure, which allows the chiral temperature sensor to operate at temperatures from 200 to 900°C with a maximum difference in temperature reading from a calibrated thermocouple of +/- 2°C. We have fabricated a transducerless pressure sensor (i.e. no moving parts) operating from 1 atm. (14.7 psi) up to 12 kpsi with a resolution of 1 psi that can operate at temperatures as high as 700°C.

A gas composition sensor based on Raman spectroscopy using reflective metal lined capillary waveguides is tested under field conditions for feed-forward applications in gas turbine control. The capillary waveguide enables effective use of low powered lasers and rapid composition determination, for computation of required parameters to pre-adjust burner control based on incoming fuel. Tests on high pressure fuel streams show sub-second time response and better than one percent accuracy on natural gas fuel mixtures. Fuel composition and Wobbe constant values are provided at one second intervals or faster. The sensor, designed and constructed at NETL, is packaged for Class I Division 2 operations typical of gas turbine environments, and samples gas at up to 800 psig. Simultaneous determination of the hydrocarbons methane, ethane, and propane plus CO, CO₂, H₂O, H₂, N₂, and O₂ are realized. The capillary waveguide permits use of miniature spectrometers and laser power of less than 100 mW. The capillary dimensions of 1 m length and 300 μm ID also enable a full sample exchange in 0.4 s or less at 5 psig pressure differential, which allows a fast response to changes in sample composition. Sensor operation under field operation conditions will be reported.

In this article a novel advanced fiber-optic fluorescent sensor is demonstrated. The sensor is based on collection of the fluorescence from the sidewall of the multimode optical fiber which is partly de-cladded and covered by the sample under the test (SUT). The most part of the fluorescent intensity is carried by the leaky rays which are inaccessible in traditional evanescent-wave fluorescence fiber sensors. In the proposed structure, some part of a refracting power is collected in the de-cladded segment and used to excite the lower order lossless modes in cladded part by a sidewall mode mixer. In addition to the higher level of fluorescence collection, the architecture allows us to multiplex several different channels along one fiber, since we use only a small segment of the normal (not tapered) sidewall for each channel.A highly efficient fluorescence turn-on molecular probe is applied to this advanced fiber-optic structure, for sensitive and selective detection of Cu⁺² in water. The fluorescence turn-on molecular probe is a mixture of a fluorophore polymer P1and M1 as a Cu receptor and a fluorescent quencher. The P1 is used as an indicator which generates the fluorescence centered at the wavelength of 650 nm and then, with a proper amount of M1 solution, the fluorescence is quenched up to 53% of its maximum intensity. The P1-M1 pair is broken by absorption of Cu with the M1 and the fluorescence is released again. This turn-on effect is used for detection of Cu with a low detection limit of 0.02689 g/ml.

Fiber optic modal interferometry has been around as a sensing concept since the outcome of fiber optic sensing. Initially supported by the utilization of standard Hi-Bi fibres associated to polarimetric modal interference, later this sensing approach evolved to modal interference based on spatial modes propagating in the core, on spatial modes propagating in the core and in the cladding with coupling performed by fibre devices such as long period gratings and tapers, and more recently on several types of modes propagating in photonic crystal fibers. This paper will address fiber optic sensing based on modal interferometry, and configurations of different type researched in last years will be presented and their performance compared.

Temperature measurement in an extremely harsh environment, such as in a coal gasifier and gas turbine, presents significant challenges to any conventional temperature sensing technology, including thermocouples, IR camera, pyrometer, and blackbody radiation measuring methods. The commonly used fiber Bragg grating (FBG)-based temperature sensors have many advantages, making them very successful in structural health monitoring application. However, conventional FBGs have poor thermal stability and survivability when environmental temperature is beyond 500^oC. A band-gap engineering method has been used to transform amorphous fiber material into tetrahedral dominated microstructures, and the mass density modulated grating structure has shown the same fundamental characteristics as conventional FBG but the tetrahedral dominated fiber material enables such grating structure more tolerable to extremely temperature without losing structure integrity. The developed tetrahedral fiber Bragg grating (TFBG) have been prototyped for coal gasification radial and axial distributed temperature measurements. The field validations have demonstrated these TFBG sensors can provide reliable temperature measurement under 1200^oC harsh conditions.

The increasing need of energy and the increasing share of renewables in electric power generation demands higher flexibility in the operation of conventional power plants. Turbo generators have to face higher stress during operation without consuming additional life time. For the first time in a shop test a new generator design was extensively evaluated by using about 250 fibre optic sensors - mostly new developed - to control temperature, strain, movement and vibration.

It is well known that using a single-mode lead-in fiber, a multi-mode fiber section as a Fabry-Perot cavity, and an additional single-mode fiber as the tail results in a structure that generates strong interference fringes while remaining robust. Due to their compact size, sensitivity, and ability to be multiplexed, intrinsic Fabry-Perot interferometers (IFPIs) are excellent candidates for almost any multi-point temperature or strain application. Four of these sensors were to be installed on a 2"x2" coupon for installation in a simulated gas turbine environment. Though the basic principles behind these sensors are well known, serious issues associated with geometric constraints resulting from the size of the test coupon, sensor placement, and mechanical reinforcement of the fiber arose; fabricating a sensor chain with appropriate sensor spacing and excellent temperature response characteristics proved a significant challenge. Issues addressed include inter-sensor interference, high-temperature mechanical reinforcement for bare fiber sections, and high bending losses. After overcoming these problems, a final sensor chain was fabricated and characterized. This chain was then subjected to a battery of tests at the National Energy Technology Laboratory (NETL). Final results are presented and analyzed.

A reliable and low-cost two-wavelength quadrature interrogating method has been developed to demodulate optical signals from diaphragm-based Fabry-Perot interferometric fiber optic sensors for multipoint partial discharge detection in power transformers. Commercial available fused-silica parts (a wafer, a fiber ferrule, and a mating sleeve) and a cleaved optical single mode fiber were bonded together to form an extrinsic Fabry-Perot acoustic sensor. Two lasers with center wavelengths separated by a quarter of the period of sensor interference fringes were used to probe acousticwave- induced diaphragm vibration. A coarse wavelength-division multiplexing (CWDM) add/drop multiplexer was used to separate the reflected two wavelengths before two photo detectors. Optical couplers were used to distribute mixed laser light to each sensor-detector module for multiplexing purpose. Sensor structure, detection system design and experiment results are presented.

An innovative system that allows the measurement of velocity, position, temperature and pressure during burn, deflagration and detonation of energetic materials has been developed. An initial demonstration of this system has been able to measure pressures up to 1,200,000 psi, and temperature changes of 400° C over a period of 25 microseconds. Both measurements were instrument limited. Improved instrumentation will allow extensions to 4,000,000 psi measurements and enhanced resolution of over and order of magnitude. This is the first time to our knowledge that measurements of velocity, position, temperature and pressure have been made interior to highly energetic materials during burn, deflagration and detonation. The technology is in its very early stages. It has great potential to make important near term measurements with significant further improvements being made as the technology begins to mature. Immediate application areas include assessment of the performance of solid rocket motor propellant materials, insensitive munitions and detailed measurements of high speed, energetic events. Additionally, continuous detonation wave velocities were measured inside of large explosive charges greater than 200 millimeters in length.

We present a high-sensitivity fiber-optic ultrasonic sensor based on a π-phase-shifted fiber Bragg grating (πFBG). A π- phase-shift at the center of a traditional fiber Bragg grating results in the formation of a narrow-bandwidth notch in the reflection spectrum, leading to much higher sensitivity than standard fiber-Bragg-grating (FBG) sensors. A method of fabrication is introduced, including a method of removing introduced polarization dependence. A tunable-cavity diode laser is used to interrogate the πFBG by locking the wavelength to the linear slope of the spectral notch. High-sensitivity detection of ultrasonic waves is demonstrated. The directivity of the grating is characterized. The effect of strain induced polarization dependence is investigated. Preliminary tests using ultrasonic pressure waves in water are performed.

Fiber based sensors have come of age commercially and are now increasing in volume deployment. The sensors are used to measure acceleration, pressure, electric current and more. To achieve the performance required from the sensor requires improvements over key performance aspects of a standard telecommunication fiber such as SMF28. Key design considerations are addressed, reduction of bend loss, joining two fibers, reliability, in particular the fiber lifetime, and mechanical stiffness together with features of birefringence or photosensitivity. Application areas such as Fiber Optic Gyroscope (FOG), acoustic and seismic sensors and sensing of electric current have specific demands of specialist optical fibers and these areas are used to illustrate the technical design considerations.

Non-contacting interferometric fiber optic sensors offer a minimally invasive, high-accuracy means of measuring a structure's kinematic response to loading. The performance of interferometric sensors is often dictated by the technique employed for demodulating the kinematic measurand of interest from phase in the observed optical signal. In this paper a white-light extrinsic Fabry-Perot interferometer is implemented, offering robust displacement sensing performance. Displacement data is extracted from an estimate of the power spectral density, calculated from the interferometer's received optical power measured as a function of optical transmission frequency, and the sensor's performance is dictated by the details surrounding the implementation of this power spectral density estimation. One advantage of this particular type of interferometric sensor is that many of its control parameters (e.g., frequency range, frequency sampling density, sampling rate, etc.) may be chosen to so that the sensor satisfies application-specific performance needs in metrics such as bandwidth, axial displacement range, displacement resolution, and accuracy. A suite of user-controlled input values is investigated for estimating the spectrum of power versus wavelength data, and the relationships between performance metrics and input parameters are described in an effort to characterize the sensor's operational performance limitations. This work has been approved by Los Alamos National Laboratory for unlimited public release (LA-UR 12-01512).

Fiber optical interferometers belong to highly sensitive equipments that are able to measure slight changes like distortion of shape, temperature and electric field variation and etc. Their great advantage is that they are insensitive on ageing component, from which they are composed of. It is in virtue of herewith, that there are evaluated no changes in optical signal intensity but number interference fringes. To monitor the movement of persons, eventually to analyze the changes in state of motion we developed method based on analysis the dynamic changes in interferometric pattern. We have used Mach- Zehnder interferometer with conventional SM fibers excited with the DFB laser at wavelength of 1550 nm. It was terminated with optical receiver containing InGaAs PIN photodiode. Its output was brought into measuring card module that performs on FFT of the received interferometer signal. The signal rises with the composition of two waves passing through single interferometer arm. The optical fiber SMF 28e in one arm is referential; the second one is positioned on measuring slab at dimensions of 1x2m. A movement of persons around the slab was monitored, signal processed with FFT and frequency spectra were evaluated. They rose owing to dynamic changes of interferometric pattern. The results reflect that the individual subjects passing through slab embody characteristic frequency spectra, which are individual for particular persons. The scope of measuring frequencies proceeded from zero to 10 kHz. It was also displayed in experiments that the experimental subjects, who walked around the slab and at the same time they have had changed their state of motion (knee joint fixation), embodied characteristic changes in their frequency spectra. At experiments the stability of interferometric patterns was evaluated as from time aspects, so from the view of repeated identical experiments. Two kinds of balls (tennis and ping-pong) were used to plot the repeatability measurements and the gained spectra at repeated drops of balls were compared. Those stroked upon the same place and from the same elevation and dispersion of the obtained frequency spectra was evaluated. These experiments were performed on the series of 20 repeated drops from highs of 0,5 and 1m. The evaluation of experiments displayed that the dispersion of measured values is lower than 4%. Frequency response has been verified with the loudspeaker connected to signal generator and amplifier. Various slabs have been measured and frequency ranges were compared for particular slab designs.

Fizeau sensors constitute a large proportion of the fiber optic interferometric type sensors in use today. These include EFPI, FFPI, certain MEMS devices and in-line fiber intrinsic dual-reflector type sensors. The vast majority of the published literature covering these sensor types models them with a "2-beam" interferometer approximation, and implement interrogation approaches considering the same. Analysis performed and results presented show that the 2-beam model is not sufficient when reflection coefficients exceed 1% and traditional quadrature interrogation can result in linearity or distortion errors roughly in directly proportion to the reflectivity coefficients of the Fizeau sensor. A 4-beam multi-path interferometer model is developed and exercised to demonstrate this problem. Further this model shows that the "errors" in comparison to an ideal 2-beam interferometer model are symmetric across the unit circle and suggests that linear interrogation may be accomplished if orthonormal sample sets over the entire unit circle are used to replace the traditional (simple) quadrature sampling. This is shown to be true in both modeling and lab evaluations. The resulting approach has capabilities of remote, passive sensor operation, high frequency response, large, linear dynamic range and low noise. The interrogation technique demonstrated involves a phase generated carrier with full fringe sampling and quadrature determination which cancels the errors experienced from simple quadrature determination. Such an improvement enables higher reflectivity, higher SNR, high-fidelity fiber Fizeau sensor designs. Applications include embedded sensors, line sensors, or mechanically adapted for acoustic, pressure, vibration, acceleration or seismic sensing.

An Interferometric Polymer Optical Waveguide Sensor (IPOWS) for intravascular optoacoustic signal detection has been fabricated by UV-imprinting method. The sensor has been characterized in sensitivity, dynamic range and frequency bandwidth. We have compared experimentally the performance of the IPOWS with a piezoelectric ultra wideband sensor and other optical fiber sensors based on single-mode silica and polymer optical fibers. All sensors are designed for the detection of optoacoustic wave sources with a frequency bandwidth that exceed 10MHz.

The current schemes of detecting the status of passengers in airplanes cannot satisfy the more strict regulations recently released by the United States Transportation Security Administration. In basis of investigation on the current seat occupancy sensors for vehicles, in this paper we present a novel scheme of seat occupancy sensors based on Fiber Bragg Grating technology to improve the in-flight security of airplanes. This seat occupancy sensor system can be used to detect the status of passengers and to trigger the airbags to control the inflation of air bags, which have been installed in the airplanes of some major airlines under the new law. This scheme utilizes our previous research results of Weight-In- Motion sensor system based on optical fiber Bragg grating. In contrast to the current seat occupancy sensors for vehicles, this new seat occupancy sensor has so many merits that it is very suitable to be applied in aerospace industry or high speed railway system. Moreover, combined with existing Fiber Bragg Grating strain or temperature sensor systems built in airplanes, this proposed method can construct a complete airline passenger management system.

A National Instruments (NI) DAQ card PCI 5105 is installed in a high-speed demodulation system based on Fiber Fabry-Pérot Tunable Filter. The instability of the spectra of Fiber Bragg Grating sensors caused by intrinsic drifts of FFP-TF needs an appropriate, flexible trigger. However, the driver of the DAQ card in the current development environment does not provide the functions of analog trigger but digital trigger type. Moreover, the high level of the trigger signal from the tuning voltage of FFP-TF is larger than the maximum input overload voltage of PCI 5105 card. To resolve this incompatibility, a novel converter to change an analog trigger signal into a digital trigger signal has been reported previously. However, the obvious delay time between input and output signals limits the function of demodulation system. Accordingly, we report an improved low-cost, small-size converter with an adjustable delay time. This new scheme can decline the delay time to or close to zero when the frequency of trigger signal is less than 3,000 Hz. This method might be employed to resolve similar problems or to be applied in semiconductor integrated circuits.

In this paper it is shown that a fundamental technology of hybrid system combining Sagnac interferometer and FBG. Fiber optic sensor array, i.e. two sensors in the Sagnac loop was suggested. Fiber optic sensor array was fabricated in the transformer oil and external sound applied to the sensor directly using by piezoelectric. Tunable laser source was used as a light source. Applied sound frequency range is from 5kHz to 90kHz. From this experiment it is confirmed that fiber optic sensor using Sagnac interferometer in the transformer oil can detect applied sound frequency. In real electric transformer system suggested fiber optic sensor array can be applied to monitoring physical quantities such as internal temperature, sound pressure and vibration due to partial discharge.