This PDF file contains the front matter associated with SPIE Proceedings Volume 7675, including the Title Page, Copyright information, Table of Contents, Conference Committee listing and introduction.

This research effort is intended to demonstrate an in-situ optical fiber corrosion sensor that operates in conjunction with a Fourier Transform Infrared (FTIR) interferometer as an evanescent wave absorption spectroscopic technique. This technique will allow periodic remote sensing for onboard structural health monitoring of areas of normally inaccessible structural components. The potential advantages of optical fiber sensors result from the fact that the sensing element, the optical fiber, can be embedded in junctions in aircraft structures, in locations where humidity and corrosion can accumulate, but are such that they can not be directly observed. A fiber-optic-FTIR experimental setup, including several samples of field corrosion material has been assembled in the laboratory to spectrally detect Aluminum Hydroxide [Al(OH)₃] which is one component of corrosion of aluminum. Absorption spectra of Al(OH)₃, have been collected using an Attenuated Total Reflection (ATR) crystal as a reference spectral signature. The spectra of samples from a simulated corrosion process have been collected and compared with Al(OH)₃ spectra. The laboratory experimental setup has included samples from the controlled corrosion conditions.

This paper presents a non-intrusive, non-contact liquid level sensor. The proposed sensor is a free-space-based optical sensor that uses opto-fluidic technology-based agile optics to direct light from a laser source to the Liquid Under Test (LUT). The presented design makes the proposed sensor ideal for use in environments where levels have to be determined for caustic or toxic liquids having a small window interface on the containers carrying them. The proposed design uses very low optical power levels (< 100 μW) making it useful for measuring levels of combustible liquids (e.g., jet fuels) which have a danger of being ignited at higher power levels. The proposed sensor can find potential applications in transportation, chemical and aerospace industries.

Cameras provide excellent in situ coverage of many events of interest in current state-of-the-art aerospace systems. From departing earth footage to booster separation events, cameras provide the eyes in the skies for real-time situational awareness on the ground. One of the principal challenges of using cameras on high-speed aerospace vehicles is designing the necessary environmental protection systems to isolate the cameras from the harsh aerothermal environment. An established approach uses an external fairing or aeropod to provide the requisite isolation. The camera is located within the aeropod, and the image data are sent electrically from the aeropod to the telemetry system. While this approach has been successfully demonstrated on numerous platforms, there are advantages to moving the camera into the interior of the vehicle and reducing the size of the imaging hardware within the aeropod. If the size of the pod hardware can be reduced, multiple imaging sensors can be fit within the same aeropod. Alternatively, a smaller sensor can allow for a reduced aeropod size with commensurate reduced drag and aerothermal heating. A prototype fiber optic imaging system was developed for aerospace applications by combining a modified medical endoscope with a ruggedized camera. With this new configuration, a significantly smaller aeropod can be used to protect only the distal tip of the endoscope in lieu of the entire camera assembly. The data are acquired through a small lens at the distal tip and transmitted optically through a coherent imaging fiber bundle to a camera located within the vehicle. Data from the prototype fiber optic imaging system are compared with data acquired by a standard ruggedized camera. Results of these tests are reported in this paper.

Composite bridges offer many advantages compared to current steel and aluminum bridges including their lightweight and superior corrosion resistance properties. This paper presents the results of a comprehensive on-going research program to develop innovative Diagnostic Prognostic System (DPS) and a structural evaluation of Composite Army Bridge (CAB) system. The DPS is founded on three technologies, namely; optical fiber sensing, remote data transmission,, and virtual testing. In developing this system, both laboratory and virtual test were used in evaluating different potential damage scenarios. Health monitoring of a composite beam with DPS entailed comparing live strain data to archived strained data in various bridge locations. For temporary field repairs, a family of composite chords was subjected simple ramp loads in search of ultimate strength. As such, composite bridge specimens showcased their strengths, heralded the viability of virtual testing, highlighted the efficacy of field repair, and confirmed the merits of health monitoring.

Gas sensing systems based on fibre optic linked near infra red absorption cells are potentially a flexible and effective tool for monitoring accumulations of hazardous and noxious gases in enclosed areas such as tunnels and mines. Additionally the same baseline technology is readily modified to measure concentrations of hydrocarbon fuels - notably but not exclusively methane, and monitoring emissions of greenhouse gases. Furthermore the system can be readily implemented to provide intrinsically safe monitoring over extensive areas at up to ~250 points from a single interrogation unit. In this paper we review our work on fibre coupled gas sensing systems. We outline the basic principles through which repeatable and accurate self calibrating gas measurements may be realised, including the recover of detailed line shapes for non contact temperature and / or pressure measurements in addition to concentration assessments in harsh environments. We also outline our experience in using these systems in extensive networks operating under inhospitable conditions over extended periods extending to several years.

Precise knowledge of laser beam parameters is a key requirement in many photonics applications including for lasers and optics used in the transportation industry. This paper reports on a novel motion-free laser beam characterization system using electronically agile digital and analog photonics such as a Digital Micromirror Device (DMD) and an analog variable focal length lens. The proposed system has the capability of measuring all the parameters of a laser beam including minimum waist size, minimum waist location, beam divergence and the beam propagation parameter (M²). Experimental results demonstrate the measurement of the minimum beam waist size and location for a test 633 nm fundamental mode Gaussian laser beam. The system is also applicable for imaging of arbitrary beams including non-laser beams.

Hydrogen detection is priority for every launch vehicle where hydrogen is involved. Hydrogen sensors are necessary to monitor the detection of every possible leak. For space application is very challenging to pin point exact location of leaks and public acceptance of hydrogen fuel is require the integration of a reliable hydrogen safety sensor. For detecting leakage of cryogenic fluids in spaceport facilities, launch vehicle industry and aerospace agencies are currently relying heavily on the bulky mass spectrometers, which fill one or more equipment racks, and weigh several hundred kilograms. Recently new innovation in optical hydrogen makes these sensors intrinsically safe since they produce no arc or spark in an explosive environment caused by the leakage of hydrogen. Being a very small molecule, hydrogen is prone to leakage through seals and micro-cracks. This paper describes the development of fiber optic innovative technologies for detection of hydrogen in space applications. These systems consisted of Micro Mirror, Fiber Bragg grating, Evanescent Optical Fiber and Colorimetric Technology. The paper would discuss the sensor design and performance data under field deployment conditions.

In the past, Boeing had successfully developed and produced the hermetic ARINC 636 fiber optic transmitter and receiver modules for the PLANET System in the Boeing 777 commercial airplanes. These hermetic fiber optic modules had demonstrated over 4 millions aggregate flight hours with zero failure; the hermetic fiber seal technology is a key contributor to this outstanding reliability record. Recently, we have investigated failure mechanisms in commercial-off-the-shelf (COTS) hermetic mini-dil (dual-in-line) laser diode modules; and developed new hermetic fiber seal process for low cost mini-dil form factor packages. In addition, we are also developing cost effective hermetic multi-channel fiber optic array modules technology for aerospace applications.

Modern vehicles use modern materials, including multiple metallic layers, composites, and ceramics. This has led to significant improvements in quality, reliability, and lifetime, at the cost of significantly increased complexity. It is particularly difficult to test these modern materials for buried defects such as internal corrosion, glue/weld failures, and disbonds, yet these defects can lead to damage and even failure of the part. As one tool in the array of nondestructive evaluation (NDE) technologies, we report on Directed Acoustic Shearography (DAS), which combines the sensitivity of shearography with the speed of ultrasonic imaging, and adds improved depth resolution. We show that DAS is particularly useful in detecting buried defects in modern materials, how it lends itself to automation, and present early tests of DAS detecting buried defects as small as 1/32 inch in a multilayer aluminum structure.

We present a novel implementation of virtual optical interfaces for the transportation industry (automotive and avionics). This new implementation includes two functionalities in a single device; projection of a virtual interface and sensing of the position of the fingers on top of the virtual interface. Both functionalities are produced by diffraction of laser light. The device we are developing include both functionalities in a compact package which has no optical elements to align since all of them are pre-aligned on a single glass wafer through optical lithography. The package contains a CMOS sensor which diffractive objective lens is optimized for the projected interface color as well as for the IR finger position sensor based on structured illumination. Two versions are proposed: a version which senses the 2d position of the hand and a version which senses the hand position in 3d.

An optical fiber containing structured hydrogen sensing points, consisting of Palladium and/or Magnesium alloys is proposed and characterized. The sensitive layer is deposited on the outside of a multimode fiber, after removing the optical cladding. The sensor is based on a measurement technique which uses the Surface Plasmon Resonance effect. Compared to previous work which was performed at a single wavelength of 670nm, this study was done in the range of 450 to 900nm. A continuous change in intensity is observed as a function of the hydrogen concentration between 0.5% and 4% H₂ in Ar. The response shows that the intensity transmitted can either decrease or increase, depending on the selected wavelength. The response time and the reproducibility of the detectors are also discussed. From our experiments and optical simulations we conclude that Pd covered indicator layers based on Mg alloys, such as Mg-Ti, would be even more advantageous compare to Pd layers thanks to their lower hydrogen equilibrium pressures. We will demonstrate an extended sensitivity range by juxtaposing different materials over a fiber section, having different hydrogen equilibrium pressures.

Fiber optic sensors have matured to allow the detection of chemical and physical parameters at multiple points, or in a distributed fashion, along the length of a single optical fiber strand. The electro-optic readout unit connected to the fiber needs to be tailored to the specific sensor application to balance the requirements for spatial and frequency resolution, interrogation intervals, readout time, noise suppression, system size and cost, and other parameters. This paper will discuss different fiber optic sensor configurations and suitable readout strategies to meet the requirements of the sensing application.

Free space optical communication between movable platforms, especially communication with non-cooperative targets, requires detecting low intensity signals in conditions of multiple sources of contaminating signals. In this paper, we review recent achievements in ultra-narrow bandpass filters based on volume Bragg gratings (VBGs) recorded in the bulk of photo-thermo-refractive glass. The new types of transmission filters show unique characteristics such as high throughput and bandwidths as narrow as a few picometers at any wavelength from 500 to 2700 nm. The first filter type is formed by the incoherent combination of a Fabry-Perot etalon and a VBG that enables tunable ultra-narrow band transmission with a single resonance. The filters demonstrate a bandwidth down to a few picometers at 1064 nm, a transmission exceeding 90%, an ultra-broad rejection band (several hundreds of nanometers), and an extinction ratio better than 30 dB. The second filter type is based on multiplexed frequency shifted VBGs that form a volumetric Moiré Bragg grating. The filter provides a single resonance with transmission higher than 90% in the middle of the reflection lobe of the VBG, a bandwidth down to a few picometers and high mechanical stability. Both types of ultra-narrow bandpass filters can be used for many applications requiring to transmit a single frequency and to reject other adjacent frequencies, e.g., in Lidars, or for selection of longitudinal modes in laser resonators. The new filters provide a significant advantage in terms of stability, tunability and achievable throughput for a given bandwidth.

We present a simple concept for a low-cost pressure transducer. The transducer is a polarimetric device consisting of a pressure sensitive dielectric material in-between polarizing optics. The pressure on the sensitive material creates a stress-induced birefringence which is detected through a change in state of polarization. We show the theoretical behaviour of this device and the various ways of optimizing its sensitivity.

Range-gated active imaging systems are more and more used for surveillance and night vision applications. Their ability to improve vision through fog, snow or rain makes them good candidates to be used for automotive safety. But even if they increase safety, expensive options have no chances to come out from the laboratory and to be integrated in a car. Instead of using a complete active imaging system, i.e. a laser diode illuminator coupled with an intensified camera, we propose to control the LED headlights of future cars in a pulsed mode and to synchronize these pulses with a sensitive camera. This paper shows some prototypes we've built and evaluates the performances of these different systems. Furthermore, the problem of sensor saturation due to retroreflecting road signs is investigated and resolved by using a bistatic configuration.

Comprised of heavier hydrocarbon components, jet fuel is much less volatile, with Jet A having a flash point of approximately 100°F and JP-4 having a flash point of approximately 0°F. In contrast, straight-run gasoline has a flash point of approximately -40°F. The flash point is the minimum temperature where a liquid fuel can generate enough vapor to form a flammable mixture with air. If the temperature is below the flash point there isn't enough fuel evaporating to form a flammable fuel-air mixture. Since jet fuel and gasoline have similar flammable concentration limits, gasoline must produce much more vapor at a given temperature to have such a low flash point; hence gasoline is much more volatile than jet fuel. In this paper we explore Fluorescence Technology as applied to the design and development of O2 sensors that can be used for this application and discuss 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.

To the best of our knowledge, proposed is the first liquid lens technology-based 1x2 fiber optic switch using a single Electronically Controlled Variable Focus Lens (ECVFL). By controlling the focal length of the liquid ECVFL, the input optical beam is spatially adjusted to couple into the respective output fiber port. The switch demonstrates a 3-dB bandwidth of 175.67 nm, with a center frequency of 1550 nm, and features low power consumption suitable for mobile applications. The proposed switch can be useful in communication and control systems, in roadway sensor systems, vehicle detection systems, and monitoring systems.

Building high speed communications network using optical links in space 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. 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. Laser Communications offer a viable alternative to established RF communications for inter-satellite links and other applications where high performance links are a necessity. This paper 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. Also discussed are the critical parameters in the transmitter, channel, receiver, and link budget that are employed in successful inter-satellite communications system.

Passive hydrophones with a minimal footprint are useful for a variety of underwater monitoring applications; a fiber optic hydrophone is being investigated. Fiber optic hydrophones have been used in offshore moored applications, and have the capability to cover large areas. A resonant hydrophone using a fiber Bragg grating (FBG) transducer for limited bandwidth operation is described and compared with predicted diaphragm resonances. A battery-power readout system using a laser diode source that can typically operate for a full day, and can be used in off-mooring applications such as in autonomous underwater vehicles, is outlined.

Horus technologies develops novel optical tags based on planar digital micro-optics. These tags are calculated by computer, fabricated as masters via optical microlithography and replicated in mass by plastic embossing. Such tags are composed of several different levels of anti-counterfeating features, ranging from traditional holographic patterns, to OVIDs, to micro-holograms, to machine readable digital holograms storing holographic 1D and 2D bar codes. These tags have a double aim: anti-counterfeating of automotive/avionic parts and providing the engineer using an appropriate tag reader with all the technical information referring to these parts.

Intrinsic optical fiber microphones with the design that we propose have a good sensitivity and dynamic allowing them to address many innovative applications. But their performances induce some defects as noise sensing that has to be separated to the wanted sound signal to obtain a clean usable sound signal. In this paper we introduce the design of an optical fiber sound sensing system and the bases of the adapted signal processing allowing to use all the advantages of this design with a low level of noise. The results are very promising.

Progress in PV conversion efficiency requires optoelectronic breakthroughs. Completing one-step PV conversion by additional new low-energy mechanisms is one of the most important challenges of modern photovoltaics. Si is a basic PV material which cannot be efficient enough in its bulk or thin-film form because of its indirect bandgap. One way has been indicated by multi-interface solar cell on single-crystal Si combining nanostructured Si materials and device improvements leading to a PV metamaterial conditioned simultaneously both electrically and mechanically by the built-in electrical and local stress fields. This allows a two membrane-like conversion cycle where a nanoscale Si-layered system plays a specific role due to an active interface and crystalline defects. We demonstrate a step-like collection efficiency curve proving new low-energy (0.3 eV) carrier generation and multiplication has been measured under solar intensities on dedicated test structures.

Fiber Bragg gratings (FBGs) are a mature sensing technology that has gained rapid acceptance in civil, aerospace, chemical and petrochemical, medicine, aviation and automotive industries. Fiber Bragg grating sensors can be use for a variety of measurements including strain, stress, vibration, acoustics, acceleration, pressure, temperature, moisture, and corrosion distributed at multiple locations within the structure using a single fiber element. The most prominent advantages of FBGs are: small size and light weight, multiple FBG transducers on a single fiber, and immunity to radio frequency interference. A major disadvantage of FBG technology is that conventional state-of-the-art fiber Bragg grating interrogation systems are typically bulky, heavy, and costly bench top instruments that are assembled from off-the-shelf fiber optic and optical components integrated with a signal electronics board into an instrument console. Based on the need for a compact FBG interrogation system, this paper describes recent progress towards the development of a miniature fiber Bragg grating sensor interrogator (FBG-Transceiver^TM) system based on multi-channel monolithic integrated optic sensor microchip technology. The integrated optic microchip technology enables the monolithic integration of all of the functionalities, both passive and active, of conventional bench top FBG sensor interrogators systems, packaged in a miniaturized, low power operation, 2-cm x 5-cm small form factor (SFF) package suitable for the long-term structural health monitoring in applications where size, weight, and power are critical for operation.