This PDF file contains the front matter associated with SPIE Proceedings Volume 6758, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

There is a broad range of security sensing applications in transportation that can be facilitated by using fiber optic sensors and photonic sensor integrated wireless systems. Many of these vital assets are under constant threat of being attacked. It is important to realize that the threats are not just from terrorism but an aging and often neglected infrastructure. To specifically address transportation security, photonic sensors fall into two categories: fixed point monitoring and mobile tracking. In fixed point monitoring, the sensors monitor bridge and tunnel structural health and environment problems such as toxic gases in a tunnel. Mobile tracking sensors are being designed to track cargo such as shipboard cargo containers and trucks. Mobile tracking sensor systems have multifunctional sensor requirements including intrusion (tampering), biochemical, radiation and explosives detection. This paper will review the state of the art of photonic sensor technologies and their ability to meet the challenges of transportation security.

Fiber grating based techniques have proven themselves as low cost, small size and low weight solutions for sensing strain and/or temperature in various applications, including structural health monitoring of aircrafts, ships and other man-made structures. However, normal fiber gratings are sensitive to both strain and temperature in a manner that is impossible to distinguish from the sensor response. Methods devised to circumvent this problem rely on combinations of gratings with different sensitivity to these two perturbations. Simultaneous measurements on two gratings then provide the necessary information to decode strain and temperature values but this requires special grating configurations and packaging to maximize the differential sensitivity. We will present experimental results of an alternative approach where we use a single very weakly tilted fiber Bragg grating (TFBG), to achieve the same effect. The grating couples light from the fundamental mode guided in the core to a large number of cladding modes, depending on the wavelength of interrogation. We propose and demonstrate a novel configuration in which many high order cladding mode resonances are removed by bonding the TFBG in a pre-bent state on a metal plate. After bonding, only a few low order mode resonances are left and occupy less than 5 nm of bandwidth (thereby allowing multiplexing). These resonances all have the same temperature sensitivity but very different behavior when the plate vibrates, bends or stretches statically. Differential measurements of the resonance power levels and shifts then provide valuable information about the mechanical state of the sensor.

An overview of ultrasound fiber guides, their transmission properties, and their applications in sensing is presented. Ultrasound fiber guides are structures similar to optical fibers that are used for transmission of acoustic waves. They consist of a core region surrounded by a cladding layer to help confine the wave to the core. Ultrasound fiber guides may be fabricated with glass materials such as pure and doped fused silica, using fiber optics manufacturing technology. The underlying principles of fiber optic sensing in many cases are also applicable to ultrasound fiber guides, hence the potential applications of these waveguides in sensing and health monitoring of infrastructures. Propagation properties of ultrasound fiber guides are reviewed. Attention is focused on guides with small differences between the parameters of the core and cladding, often a necessary requirement for single-mode operation. Various types of guided modes including flexural, torsional, and radial modes are discussed. These modes are predominantly shear type. Ultrasound fiber guides also support another group of modes with complex propagation constants, which are referred to as leaky longitudinal modes. These modes lose power as propagate along the guide through radiation. Similarities and differences between optical and ultrasound modes in fiber guides are addressed.

Mass replicable digital micro-optical technology is the basis of our novel high resolution accelerometer and shock sensors. Such sensors are intended to sense the direction as well as the magnitude of the successive shocks, with the highest possible accuracy, for either real time monitoring or analysis of information stored in a memory buffer over a given time, which makes them perfect candidates for the transportation industry (real time monitoring and deferred time analysis).

The sensor is primary used as pressure sensor or as a touch sensor. It consists of one optical waveguide. Its optical attenuation depends strongly on the local pressure and takes advantage of the evanescent field properties. The optical waveguide core is similar to a normal plastic optical fiber. There is a light-absorptive layer in the optical cladding. The transmitter is placed on one side of the sensor with a signal source, such as an LED and there is a receiver on the other side with one photosensitive element, such as a PIN diode. In the normal state (no pressure), there is a total reflection at the boundary between the core and the cladding. The optical rays do not reach the absorptive layer. Under pressure, since the optical ray is skin-deep in the optical coating, the light will absorb in the absorptive layer. This results in a strong rise of optical attenuation.

Commercial and military launch vehicles are designed to use cryogenic hydrogen as the main propellant, which is very volatile, extremely flammable, and highly explosive. Current detection system uses Teflon transfer tubes at small number of vehicle location through which gas samples are drawn and stream analyzed by a mass spectrometer. A concern with this approach is the high cost of the system. Also, the current system does not provide leak location and is not in real time. This system is very complex and cumbersome for production and ground support measurement personnel. This paper describes the successful test of a multipoint fiber optic hydrogen microsensors system on the Linear Aerospike X-33 rocket engine at NASA's Stennis Flight Center. The system consisted of a reversible chemical interaction causing a change in reflective of a thin film of coated Palladium. The sensor using a passive element consisting of chemically reactive microcoatings deposited on the surface of a glass microlens, which is then bonded to an optical fiber. The system uses a multiplexing technique with a fiber optic driver-receiver consisting of a modulated LED source that is launched into the sensor, and photodiode detector that synchronously measures the reflected signal. The system incorporates a microprocessor to perform the data analysis and storage, as well as trending and set alarm function. The paper illustrates the sensor design and performance data under field deployment conditions.

Internal components of the planetary stage of a helicopter transmission have proven difficult to diagnose due to the complex geometry of the gearbox and the inability to place sensors inside the planetary gear system. The goal of the research presented in this paper is to use fiber optic sensors to monitor the strain response of planetary gears on the surface of the ring gear. As the planetary gears traverse the locations of the fiber optic strain sensors, a local strain profile will be recorded. By synchronous data processing of the strain profiles of each planetary gear, an average response signal will be generated. Deviations from the average response profile will provide an indication to the existence of damage within the planetary stage. This paper will present results from experiments conducted on a transmission test rig at the University of Maryland. Fiber Bragg grating sensors were selected because of their multiplexing capabilities and localized strain measurement attributes. Initial test results have proven the feasibility of using FBG sensors to monitor the strain response due to the planetary stage. Research to be conducted includes the development and application of advanced damage detection algorithms that take advantage of the novel attributes of this approach.

Advances in sensors and sensors networks have significantly shaped the fundamental approach to dealing with traditional health monitoring problems within the aerospace community. Sensors with increased networking capability are seen to constitute the nervous system for any envisaged aircraft diagnostics, prognostics and health management (DPHM) system. Highly multiplexed fiber Bragg grating optical fibers immerged as one of the leading technologies for potential development of an integrated global airframe DPHM system. In this paper, we identify key limitations of this technology and propose an approach to address two of these limitations; namely, temperature compensated measurement and miniaturized demodulation system. Our experimental development illustrated the potential of the approach taken to deal with temperature compensation and suggest proper selection of gratings wavelength. Moreover, it demonstrates the suitability of the developed demodulation system for interrogating highly multiplexed gratings.

We present a compact and fast wavelength monitor capable of resolving pm wavelength changes. A photosensor array or position detector element is coated with a linear variable filter, which converts the wavelength information of the incident light into a spatial intensity distribution on the detector. Differential read-out of two adjacent elements of the photosensor array or the position detector is used to determine the centroid of this distribution. A wavelength change of the incident light is detected as a shift of the centroid of the distribution. The performance of this wavelength detector was tested with a wavelength tunable light source. We have demonstrated that our device is capable of detecting wavelength changes as small as ~0.1 pm. The wavelength monitor can be used as read-out unit for any optical sensor that produces a wavelength shift in response to a stimulus. In particular, changes in the reflection properties of one and two-dimensional photonic crystals can been detected. The performance of this interrogation method has been tested for the case of temperature and strain sensors based on Fiber Bragg Gratings (FBG).

Fiber Bragg grating sensors (FBGs) have gained rapid acceptance in aerospace and automotive structural health monitoring applications for the measurement of 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 and heavy 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 integrated optic sensor (InOSense) microchip technology. The hybrid InOSense microchip technology enables the 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. The sponsor of this program is NAVAIR under a DOD SBIR contract.

This paper describes the successful test of a multi-point fiber optic oxygen sensor system during the static firing of an Evolved Expandable Launch Vehicle (EELV)/Delta IV common booster core (CBC) rocket engine at NASA's Stennis Flight Center. The system consisted of microsensors (optrodes) using an oxygen gas sensitive indicator incorporated onto an optically transparent porous substrate. The modular optoelectronics and multiplexing network system was designed and assembled utilizing a multi-channel opto-electronic sensor readout unit that monitored the oxygen and temperature response of the individual optrodes in real-time and communicated this information via a serial communication port to a remote laptop computer. The sensor packaging for oxygen consisted of two optrodes - one doped with an indicator sensitive to oxygen, and the other doped with an indicator sensitive to temperature. The multichannel oxygen sensor system is fully reversible. It has demonstrated a dynamic response to oxygen gas in the range of 0% to 100% with 0.1% resolution and a response time of ≤10 seconds. The sensor package was attached to a custom fiber optic ribbon cable, which was then connected to a fiber optic trunk communications cable (standard telecommunications-grade fiber) that connected to the optoelectronics module. Each board in the expandable module included light sources, photo-detectors, and associated electronics required for detecting oxygen and temperature. The paper illustrates the sensor design and performance data under field deployment conditions.

Hydrogen is used as the main propellant for space shuttles, as an energy source in fuel cells, in oil refineries, and for many other applications. Hydrogen is extremely volatile, easily flammable, and highly explosive. Storage and handling of hydrogen is a challenging task and a good hydrogen sensor is highly desirable. An ideal hydrogen sensor should be fast, reversible, highly selective, compact in size, easy to fabricate, and cheap in price. Unfortunately such a sensor to date is not available. In this paper we propose a multi-channel integrated optical sensor for detection of hydrogen. The sensor consists of a high index waveguide on a low index substrate and uses Pd or Pd alloy thin film as the sensing medium. Since a single channel hydrogen sensor will be affected by the presence of other gases and the variations of temperature, humidity, and input power; a multi-channel sensing scheme and differential measurements are proposed to correct for some of these effects. All the components of the multi-channel sensor can be realized using planar technology and the complete sensor can be fabricated on a single chip. The sensor is compact and the response time is expected to be very short. The concept of multi-channel sensing presented in this work is very general and can be extended to other gas sensors as well.

A system for interrogation of high-frequency events with an FBG array in the presence of large quasi-static fluctuations has been developed at Intelligent Optical Systems (IOS). The system allows highly sensitive detection of periodic or transient events up to the MHz range while automatically compensating for slow changes in the FBG center frequency using a closed loop tracking system. Both the high frequency signal and the low frequency parts of the sensor spectrum are available for further processing. The system components, setup, and applications are presented and discussed.

Since the TWA flight 800 accident in July 1996, significant emphasis has been placed on fuel tank safety. The Federal Aviation Administration (FAA) has focused research to support two primary methods of fuel tank protection - ground-based and on-board - both involving fuel tank inerting. Ground-based fuel tank inerting involves some combination of fuel scrubbing and ullage washing with Nitrogen Enriched Air (NEA) while the airplane is on the ground (applicable to all or most operating transport airplanes). On-board fuel tank inerting involves ullage washing with OBIGGS (on-board inert gas generating system), a system that generates NEA during aircraft operations. An OBIGGS generally encompasses an air separation module (ASM) to generate NEA, a compressor, storage tanks, and a distribution system. Essential to the utilization of OBIGGS is an oxygen sensor that can operate inside the aircraft's ullage and assess the effectiveness of the inerting systems. OBIGGS can function economically by precisely knowing when to start and when to stop. Toward achieving these goals, InnoSense LLC is developing an all-optical fuel tank ullage sensor (FTUS) prototype for detecting oxygen in the ullage of an aircraft fuel tank in flight conditions. Data would be presented to show response time and wide dynamic range of the sensor in simulated flight conditions and fuel tank environment.

Laser Communications offer a viable alternative to established RF communications for inter-satellite links and other applications where high performance links are a necessity. 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. This paper will focus on the requirements of the lasers and optics used for beam forming, as well as receiver antenna gain and detectors used in free space communications. Also discussed are the critical parameters in the Transmitter, Channel, Receiver, and link budget that are employed in successful inter-satellite communications system.

Panoramic technologies are experiencing new and exciting opportunities in the transportation industries. The advantages of panoramic imagers are numerous: increased areas coverage with fewer cameras, imaging of multiple target simultaneously, instantaneous full horizon detection, easier integration of various applications on the same imager and others. This paper reports our work on panomorph optics and potential usage in transportation applications. The novel panomorph lens is a new type of high resolution panoramic imager perfectly suitable for the transportation industries. The panomorph lens uses optimization techniques to improve the performance of a customized optical system for specific applications. By adding a custom angle to pixel relation at the optical design stage, the optical system provides an ideal image coverage which is designed to reduce and optimize the processing. The optics can be customized for the visible, near infra-red (NIR) or infra-red (IR) wavebands. The panomorph lens is designed to optimize the cost per pixel which is particularly important in the IR. We discuss the use of the 360 vision system which can enhance on board collision avoidance systems, intelligent cruise controls and parking assistance. 360 panoramic vision systems might enable safer highways and significant reduction in casualties.

We are presenting a novel shock sensor device based on multimode optical fiber. This device is an elementary fiber sensor tailored for the transportation industry, and especially the automotive industry, allowing detection of shocks and the measurement of the deformation of surface external of the system. We also show how a plurality for such sensors can be combined in order to detect and characterize the shock in order to trigger an adapted response from the vehicle for added safety.

Many applications need fast measurement systems that capture their environment in three dimensions. Adequate measurement sensors are required that provide fast, accurate, and reliable 3-D data. Automotive applications long for real time and reliable data, not only for driving assistance systems but for safety, also. Until now, most solutions, like multi image photogrammetry, radar sensors or laser scanners, lack in one of these aspects at least. With the upcoming range imaging cameras, new sensors with a performance never seen before are to be taken into consideration. Range imaging has already been proved as an emerging technology for automotive applications. These cameras provide a distance measurement system in each pixel and therefore produce 3-D data with up to video frame rates with a single sensor. But because of their new measurement concept classical calibration approaches cannot be used. This paper will present results of research about the calibration of the SwissRanger^TM, a range imaging camera introduced by CSEM Switzerland. Special emphasis is given to the determination of the influence of the diverse parameters on the distance measurement accuracy. These parameters are the temperature, the reflectivity and the distance itself, for example. The influences are represented in functional dependencies in order to reach high accuracy of the system. Temperature compensation by means of a specialized setup is addressed. A successful implementation of a temperature drift compensation by means of a differential setup is presented.

In this article we will introduce a Light Emitting Diode (LED) lighting diffuser plate which diffuses light by optical microstructure. In LED lighting, LED array is the most popular method to attain the illuminance requirement, but this method will produce the glaring and non-uniform illuminance problems. Traditionally, diffuser, which is comprised of diffuser particles, is used to solve the above problems, but it also produces another problem which is low lighting efficiency. Therefore, we use optical microstructure to replace the diffuser particles to solve the problems of LED lighting but only reduce a little lighting efficiency. Moreover, we could control the lighting area of the LED lamp by designing the optical microstructure.