This PDF contains front matter associated with SPIE Proceedings Volume 8026, including Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

This paper describes the first successful Plastic Optical Fiber (POF) cable and glass fiber hydrogen detection sensor systems developed for Delta IV Launch Vehicle. Hydrogen detection in space application is very challenging; the hydrogen detection is priority for rocket industry and every transport device or any application where hydrogen is involved. H2 sensors are necessary to monitor the detection possible leak to avoid explosion, which can be highly dangerous. The hydrogen sensors had to perform in temperatures between -18° C to 60° C (0° F to 140° F). The response of the sensor in this temperature regime was characterized to ensure proper response of the sensors to fugitive hydrogen leakage during vehicle ground operations. We developed the first 75 m combination of POF and glass fiber H2 sensors. Performed detail investigation of POF-glass cables for attenuation loss, thermal, humidity, temperature, shock, accelerate testing for life expectancy. Also evaluated absorption, operating and high/low temperatures, and harsh environmental for glass-POF cables connectors. The same test procedures were performed for glass multi mode fiber part of the H2 and O2 sensors. A new optical waveguides was designed and developed to decrease the impact of both noise and long term drift of sensor. A field testing of sensors was performed at NASA Stennis on the Aerospike X-33 to quantify the element of the sensor package that was responsible for hydrogen detection and temperature.

Guided wave ultrasound is well suited for inspection of laminate composite structures. Compared to nearly flat or gently curved composites, performing accurate NDT on sharply curved structures is more complex with standard ultrasound test methodologies, such as pulse-echo methods. Ultrasound propagation in curved composite structures is investigated for sharply curved geometries. Responses are predicted based on dispersion models. Experimental results are presented on 0.25 inch thick curved carbon fiber reinforced plastic (CFRP) composite geometry of an aircraft structural component and compared with predicted values.

An all optical pressure and temperature compensated fiber optic oxygen sensor (FOxSense^TM) system is under qualification for use in the in-situ closed-loop-control of the inert atmosphere environment inside fuel tanks of military and commercial aircraft. The all-optical oxygen environment control sensor is a passive, intrinsically safe, fiber-optic sensor device with no electrical connections leading to the sensors installed within the fuel tanks of an aircraft. To control the fuel tank environment, an array of multiple sensors is deployed throughout the fuel tanks of an aircraft, and a remote multi-channel optoelectronic system is used to monitor the status of all the sensors in real time to provide feedback oxygen environment information to the on-board inert gas generating system (OBIGS). Qualification testing of the all optical sensor have demonstrated the ability to monitor the oxygen environment inside a simulated fuel tank environment in the oxygen range from 0% to 21% oxygen concentrations, temperatures from (-) 40°C to (+) 60°C, and altitudes from sea level to 40,000 feet. Fiber optic oxygen sensors with built-in temperature compensation as well as the conduit fiber optic cables have passed DO-160E including acoustic noise and burn test.

Cryogenic leak detection is critical to space missions, particularly for avoiding launch delays. The real-time, multi-location, early leak detection of oxygen and hydrogen down to ppm levels is extremely important for safety, reliability, and economic reasons. One of the significant challenges in meeting these requirements has been the drift effect that is caused by the exposure to extreme temperatures. This paper discusses the effect of the development of a sensor supporting matrix to improve the overall behavior of oxygen and hydrogen optical sensors at cryogenic temperatures. These achievements offer great advances in the fiber optic leak detection of cryogenic oxygen and hydrogen, specifically for space applications. Emphasis on operational conditions such as -150 K and vacuum environments, in addition to performance characteristics such as sensitivity (10 ppm) and response time (~ 3 sec), are addressed in this paper.

The intrinsically safe detection of hydrogen leaks in fuel cell vehicles (FCV) is critical for ensuring system operational safety. An early indication of a leak will not only trigger an alarm in unsafe situations, but will also dramatically reduce the risk and cost associated with fuel cell malfunction. This paper discusses the development of hydrogen leak detection technology that is suitable for onboard, real-time, and intrinsically safe monitoring of fuel cells. This technique offers FCV onboard sensing requirements with a sensitivity of 0.05% (500 ppm) in air, a response time of 3-5 seconds, operation at 5-90%RH and 0-55°C, and power consumption ≤0.5 watts.

Passive acoustic monitoring hydrophones with low power consumption for autonomous underwater vehicles (AUVs) are desirable for long term unmanned monitoring of ocean acoustics including marine mammal acoustics as well as those due to human activity. Fiber-optic hydrophones offer wider bandwidth and high sensitivity alternatives to conventional piezoelectric transducer (PZT) devices. Deployment on board AUVs requires operation under a wide range of temperature and pressure conditions that change with depth and location, hence, maintaining the sensitivity and reliability over the operating range is crucial. A read-out mechanism for a resonant hydrophone using a fiber Bragg grating (FBG) transducer is described. The read-out uses a temperature tuned DFB laser diode to compensate for FBG changes with temperature and depth, enabling operation over a wide temperature range. Its compact footprint and battery-powered readout system operation enables portability on AUVs.

Usually manufacturer's specifications do not deal with the ability of linear sheet polarizers to have a constant transmittance function over their geometric area. These parameters are fundamental for developing low cost polarimetric sensors(for instance rotation, torque, displacement) specifically for hybrid car (thermic + electricity power). It is then necessary to specially characterize commercial polarizers sheets to find if they are adapted to this kind of applications. In this paper, we present measuring methods and bench developed for this purpose, and some preliminary characterization results. We state conclusions for effective applications to hybrid car gearbox control and monitoring.

Fiber optic imaging systems are used in many applications, including medical imaging, machinery diagnostics, and remote sensing. Most commonly, coherent bundles of optical fibers are used that maintain the spatial positioning of each fiber throughout the length of the bundle, resulting in a recognizable proximal (camera side) image that is almost identical to the distal image projected into the bundle by the lens. Although coherent fiber bundles provide excellent solutions for many imaging applications, their limited flexibility and thermal stress intolerance may prohibit them from being used in harsh or complex environments. The flexibility and thermal tolerance of a fiber imaging system can be significantly improved by using an incoherent bundle of fibers wherein the spatial positioning of each fiber is not preserved throughout the length of the bundle. Incoherent bundles need to be calibrated to provide the means to reconstruct distal imagery. In reported calibration schemes, the calibration time is strongly dependent on the ratio between the bundle size and the fiber size. The calibration time can thus become prohibitive for highly resolved images using many fibers. A novel calibration scheme is described for incoherent bundles where the calibration time is proportional to the bundle-to-fiber size ratio, resulting in significantly reduced processing time and enabling more highly resolved images. As an added benefit for medical and remote sensing applications, incoherent light guides scramble the scene images, which may provide a desirable level of data privacy.

This paper presents a novel, non-intrusive, non-contact object boundary mapping sensor using a Digital Micromirror Device (DMD) and real-time pixel processing. The presented sensor is ideal for use in environments where brightly illuminated or radiating objects are in a hazardous environment such as in environments with radiation, heat, cold, harmful machine parts, etc. Experimental results demonstrate the boundary mapping sensor for a rectangular target and a multi-square target illuminated by visible wavelengths.

This paper presents a non-intrusive, non-contact object distance mapping sensor using an Electronically Controlled Variable Focus Lens (ECVFL). The proposed sensor is a free-space-based optical sensor that uses ECVFL-based agile optics to direct light from a object that requires terrain height mapping. The presented compact design makes the proposed sensor ideal for use in environments where laser illuminated objects are in a hazardous environment such as in environments with radiation, heat, cold, harmful machine parts, etc. The proposed design uses a few optical components and smart detection optics for making its object distance/terrain measurements. The presented sensor can find potential remote sensing applications in ground and space vehicle maneuvering, machine parts inspection and in chemical, transportation and aerospace industries.

Presented is a novel design of a multimode laser beam analyzer to enable beam measurements of minimum beam waist size, minimum waist location, divergence and the beam propagation parameter called M². Experimental results demonstrate these measurements for a 532 nm multimode test laser beam.

The purpose of this research effort is to develop an in-situ corrosion sensing capability. The technique will permit detection of corrosion on and within aircraft structures. This includes component junctions that are susceptible to corrosion but which are not accessible for visual inspection. The prototype experimental configuration we are developing includes long wave infrared transmitting optical fiber probes interfaced with a Fourier Transform Infrared (FTIR) interferometer for evanescent wave absorption spectroscopic measurements. The mature and fielded technique will allow periodic remote sensing for detection of corrosion and for general onboard aircraft structural health monitoring. An experimental setup using an Attenuated Total Reflection (ATR) crystal integrated with an FTIR spectrometer has been assembled. Naturally occurring corrosion including Aluminum Hydroxide [Al(OH)₃] is one of the main corrosion products of aluminum the principle structural metal of aircraft. Absorption spectra of our model corrosion product, pure Al(OH)₃, have been collected with this ATR/FTIR experimental setup. The Al(OH)₃spectra serve as reference spectral signatures. The spectra of corrosion samples from a simulated corrosion process have been collected and compared with the reference Al(OH)₃ spectra. Also absorption spectra of naturally occurring corrosion collected from a fielded corroded aircraft part have been obtained and compared with the spectra from the simulated corrosion.

This paper addresses the development and real time test validation of an integrated hardware and software environment that will be able to measure real-time in-situ strain and deformation fields using a state-of-the-art wireless sensor system to enhance structural durability and damage tolerance (D&DT), reliability via real-time structural health monitoring (SHM) for sensorized aerospace structures. The tool will be a vital extension of existing suite of structural health monitoring (SHM) and diagnostic prognostic system (DPS). The goal of the extended SHM-DPS is to apply a multi-scale nonlinear physics-based finite element analyses (FEA) to the "as-is" structural configuration to determine multi-site damage evolution, residual strength, remaining service life, and future inspection intervals and procedures. Information from a distributed system of wireless sensors will be used to determine the "as-is" state of the structure versus the "as-designed" target. The approach enables active monitoring of aerospace structural component performance and realization of DPS-based conditioned based maintenance. Software enhancements will incorporate information from a sensor network system that is distributed over an aerospace structural component. As case study DPS application a realistic composite stiffened panel representative of fuselage/wing components is selected. Two stiffened panels is manufactured and instrumented; a) embedded internally between composite layers, and b) surface mounted with wireless sensors; the second of which with an optimized sensor network. The panels will be tested in compression following low-velocity impact. The sensor system output will be routed and integrated with a finite element analysis (FEA) tool to determine the panel's, multi-site damage locations, and associated failure mechanisms, residual strength, remaining service life, and future inspection interval. The FEA model utilizes the web/internet based GENOA progressive failure analysis commercial software suite, durability and damage tolerance (D&DT), and reliability software capable of evaluating both metallic and advanced composite structural panels under service loading conditions. The approach utilizes a building block validation strategy, and real-time structural health monitoring system.

This paper explores the design and development of an all optical O2 sensor system that can be used for monitoring of headspace gases in the ullage of inerting fuel tanks of commercial airplanes. Also included is detailed discussion of the various test and measurement techniques used to estimate the O2 gas concentration .We compare the various intensity based approaches and contrast them with the frequency domain techniques that measure phase to extract fluorescent lifetimes. The various inerting fuel tank requirements are explained and finally a novel compact measurement system using that uses the frequency heterodyning cross correlation technique that can be used for various applications is described in detail while the benefits are explored together with some test data collected.

Lithium-ion batteries have been proven efficient as high power density and low self-discharge rate energy storage systems, specifically in electrical drive vehicles. An important safety factor associated with these systems is the potential hazardous release and outgassing of toxic chemical vapors such as hydrogen fluoride (HF) and hydrogen sulfides (H₂S), and relatively elevated levels of carbon dioxide (CO₂). The release and accumulation of such gases emphasizes an in-line monitoring need. Intelligent Optical Systems, Inc. (IOS) has identified a viable approach for the development of an onboard optical sensor array that can be used to monitor battery outgassing. This paper discusses the potential of developing a battery outgas sensing approach that will meet sensitivity and response time requirements.

Using optical links in space and building high speed laser communications network has proven to be an extremely complicated task and many such schemes were tried without success in the past. However, in the last few years, there has been impressive progress made to bring the concept to fruition in civilian and government-non classified projects. In this paper we will focus on the requirements of the space-based lasers and optics used for beam forming, as well as receiver antenna gain and detectors used in free space communications. High data rate, small antenna size, narrow beam divergence, and a narrow field of view are characteristics of laser communications that offer a number of potential advantages for system design. Space-based optical communications using satellites in low earth orbit (LEO) and Geo-synchronous orbits (GEO) hold great promise for the proposed Internet in the Sky network of the future. Also discussed are the critical parameters in the transmitter, channel, receiver, and link budget that are employed in successful inter-satellite communications system. We cover that Laser Communications offer a viable alternative to established RF communications for inter-satellite links and other applications where high performance links are a necessity.

Recently there has been strong interest in wireless optical (WO) communication link applications in airplanes and avionics platforms for size, weight, power, cost, and electromagnetic interference (EMI) reduction. Wireless optical link has additional advantage of providing network security because the optical signal from wireless optical link is well confined within an airplane or avionics vehicle. In this paper we discuss some potential wireless optical link applications in commercial airplanes and the challenges in the implementation of wireless optical links for these applications. We will present our experimental results on using white LED (WLED), visible laser source and free-space small-form-factor (SFF) optical transceivers to demonstrate the viability of applying wireless optical links in avionics platforms.

There is interest in the rotorcraft community to develop health monitoring technologies. Among these technologies is the ability to monitor the transmission planetary gear system. The gearbox environment does not lend itself to traditional sensing technologies due to the harsh environment and crowed space. Traditional vibration-based diagnostics are based on the output from externally mounted sensors, usually accelerometers fixed to the gearbox exterior. This type of system relies on the ability of the vibration signal to travel from the gears through the gearbox housing. These sensors are also susceptible to other interference including electrical magnetic interference (EMI). For these reasons, the development of a fiber optic-based transmission monitoring system represents an appealing alternative to the accelerometer due to their resistance to EMI and other signal corrupting influences. Aither Engineering has been working on integrating the fiber optic sensors into the gearbox environment to measure strain on the ring gear of the planetary gear system. This application utilizes a serial array of wavelength division multiplexed fiber Bragg grating (FBG) sensors. Work in this area has been conducted at both the University of Maryland, College Park and more recently at the NASA Glenn Research Center (NGRC) OH-58 transmission test rig facility. This paper discusses some of the testing results collected from the fiber optic ring gear sensor array. Based on these results, recommendations for system requirements are addressed in terms of the capabilities of the FBG instrumentation.

We introduce a review concerning hydrogen sensors already validated based on palladium, and we discuss the best ways to proceed to achieve an ideal hydrogen sensor. We discuss the performances regarding the configuration of an optical fiber hydrogen sensor as well as the used materials properties. We conclude that hydrogen sensors using plasmonic effects are a seductive way to follow.

Recently various HUD (Head Up Display) projection engines have been introduced to industry, suited to solve the stringent price/size/functionality constrains the automotive market. Some of the most promising projectors are laser based and project directly a far-field image superimposed onto the driver's field of view by the mean of an optical combiner. One of the major drawbacks of such technology is the parasitic speckle produced by the coherent nature of the illumination (laser light), which has been proven to be very annoying and distracting for the driver. We propose a method to overcome the parasitic speckle phenomenon in the HUD application, not by reducing it directly but rather by uniformizing the speckle within the integration time of the eye, through generation of an orthogonal set of speckle modes for a single projected image.

We report on a technology for multi-level microstructures manufacturing. Results are presented in the field of multilevel diffractive optical elements (DOEs) fabrication. The DOEs presented as examples are Fresnel lenses and Fourier computer generated holograms, calculated by means of a conventional Iterative Fourier Transform Algorithm. The DOEs have a typical pixel dimension of 5x5 μm² and are up to 512 by 512 pixels in size. The fabrication technique is based on polymer laser ablation through a chrome-on-quartz half-tone mask with a demagnifying high NA lens. In our case, the mask is imaged onto the polymer with a 5x, 0.13 NA reduction lens. The experimental results are presented and discussed.