This PDF file contains the front matter associated with SPIE Proceedings Volume 8028, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Fiber Bragg gratings with grating planes inclined relative to the fiber cross section can be used to excite a large number of cladding modes in a few tens of nm of spectral bandwidth. Each of these modes responds differentially to various perturbations, thereby enabling many sensing modalities from a single sensor design. In particular, we show here that the polarization state of the input core mode light further enhances the sensing options and show that polarization dependent loss (PDL) can be used to increase the sensitivity of refractometric and surface plasmon resonance sensors.

We have fabricated chiral fiber long-period gratings (CLPGs) for radiation sensing by co-twisting two standard optical fibers or twisting a single custom optical fibers with nonconcentric core as the fibers pass though a miniature oven. The wavelength shift of transmission dips in the CLPGs have proven to be much more sensitive to ionizing radiation than are fiber Bragg gratings. The radiation sensitivity of these CLPGs was investigated in a wide variety of twisted fibers at the Fraunhofer Institute for Technological Trend Analysis by Henschel et al.⁷. Because chiral fiber gratings do not rely on glass photosensitivity, as is the case for fiber Bragg gratings (FBGs), chiral radiation sensors can be fabricated from a range of glass combinations selected strictly for their sensitivities to radiation in different circumstances. The fiber may also be made of glass selected to be radiation insensitive so that the fiber can be used to sense temperature in high-radiation environments. Radiation-induced shifts of up to 10 nm are observed in transmission dips of CLPGs for doses of 100 kGy of Co-60 gamma radiation. With such high sensitivity, these gratings can be used as radiation sensors for doses below 10 Gy. The wavelength shift was found to depend upon the radiation dose rate. This dependence is found to vary with glass composition. This opens up the possibility of using two CLPGs to simultaneously measure both the dose and rate of radiation.

Optical fibers are ideal for environmental sensing applications because of their ability to transmit optical signals to and from the sensing region without the use of free-space optics. By accessing the evanescent field, the fiber itself can act as the sensing element and long interaction lengths can be achieved. Microstructured optical fibers are particularly suited to such applications as the species of interest can occupy the air spaces within the fiber. Here we use a suspended nanowire design that provides the high evanescent overlap of a nanowire with the long interaction length and robustness of a conventional fiber. The fluorescence-detection approach proposed in this paper is attractive because of its simplicity. When one end of the fiber is dipped into the sample, capillary forces draw the liquid into the voids within the fiber. The evanescent field of the pump light excites the fluorescent labels and a portion of the fluorescence is captured by the fiber core and propagates to the fiber tips. The aim of this work is to improve the sensing architecture to increase the sensitivity of the sensor, and to examine the primary factors such as the background glass fluorescence currently restricting the detection limit in this type of sensor. This work is focused on biological detection in liquid samples using Quantum dots, but through careful selection of the fluorescent dye this can be extended to a large number of alternative applications. Using this system we are able to detect quantum dot concentrations as low as 10 pM.

We present thermally regnenerated fiber Bragg grating in air-hole microstructured fibers for high temperature hydrostatic pressure sensing application. Saturated type I gratings were inscribed in hydrogen-loaded two-hole optical fibers using 248-nm KrF laser, and regenerated during annealing at 800ºC. The fiber Bragg grating resonance wavelength shift and peak splits were studied as a function of external hydrostatic pressure from 15 psi to 2400 psi. The grating pressure sensor shows stable and reproducible operation up to 800ºC. This paper demonstrates a multiplexible pressure sensor network technology for high temperature harsh environment using a single fiber feedthrough.

Fiber grating sensors may be used to monitor high-speed events that include catastrophic failure of structures, ultrasonic testing and detonations. This paper provides insights into the utility of fiber grating sensors to measure structural changes under extreme conditions. An emphasis is placed on situations where there is a structural discontinuity. Embedded chirped fiber Bragg grating (CFBG) sensors can track the very high-speed progress of detonation waves (6-9 km/sec) inside energetic materials. This paper discusses diagnostic instrumentation and analysis techniques used to measure these high-speed events.

Traumatic brain injury (TBI, also called intracranial injury) is a high potential threat to our soldiers. A helmet structural health monitoring system can be effectively used to study the effects of ballistic/blast events on the helmet and human skull to prevent soldiers from TBI. However, one of the biggest challenges lies in that the pressure sensor installed inside the helmet system must be fast enough to capture the blast wave during the transient period. In this paper, an ultrafast optical fiber sensor is presented to measure the blast signal. The sensor is based on a Fabry-Pérot (FP) interferometeric principle. An FP cavity is built between the endface of an etched optical fiber tip and the silica thin diaphragm attached on the end of a multimode optical fiber. The sensor is small enough to be installed in different locations of a helmet to measure blast pressure simultaneously. Several groups of tests regarding multi-layer blast events were conducted to evaluate the sensors' performance. The sensors were mounted in different segments of a shock tube side by side with the reference sensors, to measure a rapidly increasing pressure. The segments of the shock tube were filled with different media. The results demonstrated that our sensors' responses agreed well with those from the electrical reference sensors. In addition, the home-made shock tube could provide a good resource to study the propagation of blast event in different media.

Various spectral-encoded fiber optic sensor concepts and advanced system solutions for application in energy facility monitoring have been investigated. The technological maturity, high performance and reliability of multiplexed fiber Bragg grating (FBG) sensor arrays and networks for the measurement of temperature, dynamic strain, air flow, and magnetic field distributions in electric power generators increasing their efficiency will be demonstrated by selected examples of field testing under harsh environmental conditions. For high-temperature combustion monitoring in gas turbines, beside silica FBGs with enhanced temperature stability also sapphire FBGs and Fabry-Perot sensors have been tested and evaluated as well as fiber-based black-body thermal radiation sensors. Finally, the potential of FBG sensors for application in cryo-energetic facilities such as super-conductive high-power motors and experimental nuclear fusion reactors will be discussed.

The idea of fabricating fiber Bragg gratings already during the drawing of a fiber dates back almost 20 years. The application of a transverse holographic writing method on a draw tower offers a promising solution for a highly effective Bragg grating production. Because of the high technology requirements it took more than 10 years to develop the method into a reliable process. During the last five years the improvements in the technical development enables cost effective industrial production of draw tower gratings (¹DTG^®). In this paper we report about new possibilities of the improved process with respect to the grating type (type I gratings, type II gratings), the coating type (²ORMOCER^®, metals) and the fiber type and diameter (125μm, 80μm and below). Furthermore, we present examples for the application of draw tower fiber Bragg gratings in sensing technologies for medical applications.

The large multiplexing number of FBGs exposes a requirement for the effective and repeatable fabrication method. In this paper we report the development of an automatic FBG fabrication system, which meets the requirement of mass production. There are four major functional parts in the system: fiber feeding system, CO₂ laser coating removal system, FBG writing system and fiber collecting system. The fiber feeding system uses motors and gears to accurately move an optical fiber to where the FBGs will be made. The coating removal system is based on the heat effect of a CO₂ laser, which will decompose and evaporate the selected coating of the optical fiber. The FBG writing system is based on the UV photosensitivity of the fiber. A phase-mask is placed between the UV light and the optical fiber to produce periodic interference pattern, which further modulates the refractive index along the fiber periodically. The fiber collecting system is driven by a linear motor and the fiber can be wound around a spool tightly and smoothly at a moderate speed. The whole FBG fabrication system is controlled and synchronized by a computer via some interface circuits and a Graphical User Interface (GUI). With this system, it takes 48 seconds to fabricate one FBG, and up to 500 FBGs can be made continuously, which is limited by the leakage of the gas inside the excimer laser. This mass production line not only improves the fabrication efficiency but also contributes to the multiplexing capability by reducing the splicing loss.

A robust embeddable Fiber Bragg Grating based sensing cable has been developed by Monitor Optics Systems. This sensor sees an array of Bragg Gratings encapsulated in a pultruded Glass Fiber Reinforced Polymer rod. The sensors are easy to install and more robust than telecom standard optical fibers and can be used in a number of different applications. An example is illustrated where the sensors have been used to instrument a section of a main highway in Australia to measure ground strains in the road pavement as part of a pavement monitoring system. The monitoring system is being used to monitor the effects of mining induced subsidence on the road as the main component of an early warning safety system. The monitoring system has been continuously expanded over the last 3 years in accordance with the advancement of the mining activity and now fields over 800 Fiber Bragg Gratings. The system proved to be reliable and accurate and is now the primary tool for alarm triggering and response. The sensing cables are now being used to monitor instability in embankments.

A fast spectrometer based FBG interrogator will be discussed. This unit is constructed around a fast linear InGaAs array with 1024 pixels and capable of reading out 40000 lines per second. This array is integrated in a double reflective grating spectrometer, dispersing the spectra in the [1510 - 1590 nm] band. The signal treatment electronics is capable of determining the peak wavelength position of at least 8 birefringent FBG sensors or 16 single FBG sensors at the data rate, supplied by the image sensor.

A discrete liquid level sensor based on fiber Bragg grating (FBG) that is suitable for liquid level monitoring is proposed. FBG (fiber Bragg grating) is embedded in a cantilever beam which is made of carbon fiber composite. And an iron sheet is bonded with the end of cantilever beam. For the float, a magnet is bonded with the float. When the liquid level rises or fall, the float will move up or down. The cantilever beam will bend downward or upward, it will induce strain on the FBG. Therefore, the Bragg wavelength of FBG will shift. An extra reference grating was utilized for temperature compensation.

Fiber laser strain sensors achieve fundamentally limited strain resolution, resulting in their ability to resolve axial fiber displacements at the sub-femtometer level. This ultra-high resolution enables the development of miniaturized sensors capable of achieving the performance necessary for high resolution marine sensing. The reduction in size also facilitates an increased operating bandwidth for broadband acoustic transducers. The last decade has seen considerable development of this technology, moving it from a laboratory curiosity to deployable demonstrations. Significant advances have been made in understanding the fundamental properties of erbium fiber laser strain sensors as well as laser multiplexing, signal demodulation and sensor design. This talk will describe the basic properties of fiber laser strain sensors and show how the technical challenges involved in developing deployable, multiplexed arrays of miniature transducers have been overcome. In particular the development of miniature wideband hydrophones, low power DC magnetometers with sub-nT resolution and miniature acoustic vector sensors will be described. Finally, a view towards potential future applications of this technology will be given.

The management of threats such as pandemics and explosives, and of health and the environment requires the rapid deployment of highly sensitive detection tools. Sensors based on Surface Plasmon Resonance (SPR) allow rapid, labelfree, highly sensitive detection, and indeed this phenomenon underpins the only label-free optical biosensing technology that is available commercially. In these sensors, the existence of surface plasmons is inferred indirectly from absorption features that correspond to the coupling of light to the surface plasmon. Although SPR is not intrinsically a radiative process, under certain conditions the surface plasmon can itself couple to the local photon states, and emit light as first described byKretschmann. Here we show that by collecting and characterising this re-emitted light, it is possible to realise new SPR sensing architectures that are more compact, versatile and robust than existing approaches. This approach addresses existing practical limitations associated with current SPR technologies, including bulk, cost and calibration. It is applicable to a range of SPR geometries, including optical fibres, planar waveguides and prism configurations, and is in principle capable of detecting multiple analytes simultaneously. Moreover, this technique allows to combine SPR sensing and fluorescence sensing into a single platform which has never been demonstrated before and consequently use these two methods for a more reliable diagnostic. As an example, this approach has been used to demonstrate the rapid detection of the seasonal influenza virus.

Researchers have long sought to improve collection efficiencies in scattered-light sensing applications. Herein, we demonstrate efficient collection of Raman scattered light from gaseous samples. This enables the accurate, real-time, simultaneous measurement of otherwise difficult to distinguish molecular gasses or hydrocarbons. Hollow capillary waveguides, lined with a metal and dielectric over-coating, have often been used to deliver IR laser light to a target. We show that these waveguides can be used as both a sample holder for Raman gasses and as a laser-pumped optical cell which can collect Raman scattered light from these gasses. We extend existing low mode-order capillary waveguide analysis to treat higher order modes. This extension allows a robust computer simulation to accurately predict the spontaneous Raman scattering power that can be collected by the waveguide. We verify our new theoretical models with experimental measurements of Raman signals from a nitrogen filled waveguide. We demonstrate a cutback experiment which verifies our new theoretical predictions of the variation of scattering collection efficiency with guide dimensions. The prediction accuracy of our simulations allows us to design spectrometers and detectors to maximize Raman-light throughput in a high-sensitivity gas detection system.

Distributed Fiber Optic Sensor for Position Determination is a novel position sensor and can be used as a monitoring system in communication main of long distances. Single fiber is employed as the sensor in the system to pick up the disturbances in the environment. The principle of the system is that for a disturbance signal applied at a particular position along the fiber, the response, in the frequency domain, presents a series of periodic maxima and minima (or nulls). These minima depend on the position of the disturbance along a fiber. An intelligent, reliable and real-time signal processing method is needed in such a system to determine the position of disturbance. It is not enough to process the signal of the system just using FFT (fast Fourier transform) algorithm. By using power spectral estimation and wavelet transforming as the method of signal processing, the position of a random disturbance is successfully determined.

Fractional flow reserve (FFR) has proven to be very useful in diagnosis of narrowed coronary arteries. It is a technique that is used in coronary catheterization to measure blood pressure difference across a coronary artery stenosis in maximal flow. In-vivo blood pressure measurement is critical in FFR diagnosis. This paper presents a novel miniature all-optical fiber blood pressure sensor. It is based on Fabry-Perot (FP) interferometry principle. The FP cavity was fabricated by directly wet etching the fiber tip. Then, a diaphragm with well-controlled thickness was bonded to the end face of the fiber using the thermal bonding technique. Finally, the sensor was packaged with a bio-compatible and flexible coil for animal tests. A 25-50 kg Yorkshire swine model was introduced as the animal test target. The left anterior descending coronary artery (LAD) was exposed, and beyond the takeoff of the largest diagonal branch, a 3.0 mm vascular occluder was secured. Firstly, standard invasive manometry was used to obtain the blood pressure as baseline. Next, a guiding catheter was introduced into the ostium of the left main coronary artery, and the miniature blood pressure sensor was advanced into the LAD at a point beyond the vascular occlude. The blood pressure beyond the vascular occlude was recorded. The sensor successfully recorded the blood pressure at both near-end and far-end of the vascular occluder.

A non-metallic interferometric optical fiber ultrasonic wideband sensor is presented for optoacoustic imaging applications. The ultrasonic sensitivity of intrinsic fiber optic interferometric sensors depends strongly of the material which is composed of. We compare experimentally the acoustic sensitivity of two fiber optic sensors based on singlemode silica optical fiber and multimode graded-index perfluorinated polymer optical fiber, respectively. Both sensors are designed for detection of optoacoustic wave sources with frequencies in the range from 100 kHz to 5 MHz. These results are also compared with a PVDF ultra wideband sensor. We evaluated detection of real world optoacoustic signals, generated from an optically absorbing object embedded in a tissue mimicking phantom, between our silica optical fiber sensor and an array of piezoelectric transducers. Reconstructed two dimensional acoustic images of the phantom are presented and compared with images obtained with the Laser Optoacoustic Imaging System, LOIS-64B, demonstrating the feasibility of our fiber optic sensor as a wideband ultrasonic sensor.

Dendrometers, dendrographs and dry weight measurements have been successfully used for measurements of plant growth. These sensors have been used with Linear Variable Differential Transformer (LVDT) based data logging systems for continuous monitoring. In this paper the preliminary results for a prototype technique is presented as a proof of concept for the continuous monitoring of plant growth using an approach based on fiber-optic interferrometric sensing. The advantage of this sensing technique over the others is the ability to measure and analyze with very high sensitivities such as micron changes in dimensions allowing measurements over short time spans. The sensor was mounted on a Dracaena Sanderiana (Lucky Bamboo) shoot and the change in shoot length dimensions resulted in changes in the output signal display which is in the form of interferrometric fringes. The data acquisition is performed over a long duration using labVIEW based data logging. Filtered output of the data has been presented where an attempt has been made to relate the fringes to length changes. The sensing system is nondestructive and noninvasive and has been targeted to respond to changes in stem length due to changes in plant growth parameters. The objective is to provide a measurement system to do research in optimizing plant growth in greatly reduced time spans. This form of sensing application is also applicable for monitoring the growth of plants growing at much slower rates.

Currently, fiber optic sensors are covering a great part of the automobile field, due to their precision, practicality and viability. At present, there are many theoretical and practical developments of fiber optic sensors focused towards the monitoring of thermal, torque and deformity variables, among other ones that are present in transportation vehicles. However, there is still a lot of exploration and investigation on this subject to be done, so that new analysis can be recognized and, consequently, new applications too. This work explains through MAPLE software, the computational analysis of the transverse electric and transverse magnetic modes generated in terms of Bessel functions, as a result of the light propagation through a fiber optic with different settings, proper of the type of sensor analyzed. This research exposes fundamental characters of measurement focused on the register of attributes of an object through. At the end, exposures and comments are made about the results obtained in graphics, showing the relation with the physical mathematical model described. The research for applications of this kind of technology is still scarce, for which it results necessary to investigate new types of analysis that can make possible the expansion of the technique to other fields of knowledge.

An analysis based on the Jones matrix theoretical analysis is presented to study the polarization effect of the distributed optical fiber sensor which was based on interferometer for disturbance location. A new improved distributed optical fiber location system is designed by using a Faraday rotation mirror ,the system is insensitive to the change of the polarization in the sensing part of the optic fiber, remove the linear birefringence and the orientation birefringence, the practicability of the system is increased.

A novel distributed fiber-optic sensor system based on phase generated carrier (PGC) for determining the position of disturbance is presented. The configuration and the operating principle of the system are illustrated, and the location mechanism is analyzed. The location of certain disturbance is obtained by means of the PGC demodulation technology with a new frequency domain location algorithm.Theory analysis and experiment results show that the proposed technology can realize the detection and location of the disturbing signals rapidly and effectively. This method is simply and can be obtained easily, it can eliminate the differences induced by the instability of detection signal, and can greatly improve the position accuracy.

An optical fiber sensor was developed to control the cleaning efficiency of surfactants. Prior to the measurements, the sensing part of the probe is covered with a uniform standardized soil layer (lipid multilayer), and a gold mirror is deposited at the end of the optical fiber. For the lipid multilayer deposition on the fiber, Langmuir-Blodgett technique was used and the progress of deposition was followed online by ultraviolet spectroscopy. The invention provides a miniaturized Surface Plasmon Resonance dip-sensor for automated on-line testing that can replace the cost and time consuming existing methods and develop a breakthrough in detergent testing in combining optical sensing, surface chemistry and automated data acquisition. The sensor is to be used to evaluate detergency of different cleaning products and also indicate how formulation, concentration, lipid nature and temperature affect the cleaning behavior of a surfactant.