This PDF file contains the front matter associated with SPIE Proceedings Volume 9202 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Detection of the liquid level in fuel tank becomes a critical element for the safety and efficiency in aerospace operations. Two liquid level sensing techniques are presented in this paper. The first technique is based on optical fiber Long Period Gratings (LPG). In this system, the full length of a specially fabricated fiber is the body of the probe because the length of the sensing fiber that is submerged in the liquid can be detected by the interrogation system. The second system based on Total Internal Reflection (TIR) uses optical fibers to guide light to and from an array of point probes. These probes are specially fabricated, miniature optical components which reflects a substantial amount of light back into the lead fiber when the probe is gas but almost no light when it is in liquid. A detailed theoretical study by computer simulation was carried out on these two techniques in order to determine which technique was more suitable for experimental investigation. The study revealed that although the first technique may provide more potential benefits in terms of weight and easy installation; a number of technical challenges make it not suitable for a short term solution. The second, probe array based technique, on the other hand, is more mature technically. The rest of the research program was therefore focused on the experimental investigation of the probe array detection technique and the test results are presented in this paper.

Using the change in the intrinsic optical properties of YMg-based thin films upon exposure to hydrogen, we observe the presence of hydrogen at concentrations as low as 20 ppm just by a change in color. The eye-visible color change circumvents the use of any electronics in this device, thereby making it an inexpensive H₂ detector. The detector shows high selectivity towards H₂ in H₂-O₂ - mixtures, and responds within 20 s to 0.25% H₂ in the presence of 18% O₂.

We propose the study and the design of an ultra sensitive polarimetric torque sensor. The principle is based on the measurement of the torsion angle  induced on the shaft when a torque T is applied on it. This optical torque sensor has been tested for Aluminum, Steel and Plexiglas shafts with different geometries. The torsion angle has been measured with 0,001° accuracy. The torsion angle is then studied as a function of the applied torque. The comparison between the theoretical and the experimental results give us respectively 4.33%, 1.30% and 1.24% for the Plexiglas, the Aluminum and the Steel shafts. These results permit us good perspectives for our applications

We present a review of optical fiber hydrogen sensors based on Palladium. Palladium hydrogen optical fiber sensing system can be considered as a model for other metal hybrid system. Besides, the Palladium hydrogen, systems are well characterized in bulk, cluster or thin film form. We focus on the fiber principles. We discuss then their performances regarding their configurations. We will conclude by introducing the challenges for designing an ideal hydrogen optical fiber sensor based on metal hybrids approach and which designing direction seen the best to take.

A compact, reliable and safe hydrogen sensor is required for the existing and emerging applications of hydrogen including aerospace and fuel cells. An optical sensor is an attractive option for hydrogen sensing because of its compactness, immunity from electromagnetic interference, and inherent safety. In this work we present the results of experimental demonstrations of a Pd-based hydrogen sensor and a ring resonator based temperature sensor on a siliconon- insulator (SOI) platform. The hydrogen sensor consists of a ridge waveguide with a very thin coating of palladium. The sensor response time is less than 10 seconds for 4% hydrogen concentration, and the sensor response was repeatable under hundreds of cycles of exposure to hydrogen. The response of the hydrogen sensor is affected by variation of temperature, and this effect must be considered in a real life application of the hydrogen sensor. To overcome this limitation we design and experimentally demonstrate a temperature sensor on SOI using a ring resonator, which shows good sensitivity over a wide range of temperature. The hydrogen sensor and the temperature sensor can be integrated on the same chip to implement a sensor capable of reliably measuring hydrogen concentration under varying temperature.

This presentation outlines development work performed to produce internal components (connector insert assemblies & optical terminus assemblies) to be fit into MIL-DTL-38999, or commercial off the shelf (COTS) equivalent, connector housings. Connectors modified with these internal components are then suitable for optical termination and transmission through specialty fibers such as polarization maintaining, small core single-mode, and others, with the ability to achieve high levels of performance in the areas of insertion loss, return loss, polarization extinction ratio (as applicable) and power handling capability (as applicable.) Technical details are presented to illustrate features within the optical terminus, and its insert cavity, which serves to allow for fiber/ferrule polar orientation, concentricity of mated termini ferrules and fibers terminated within, and other attributes designed to support optical performance goals. Finally, optical performance data is given and discussed to illustrate results achieved by production of evaluation cable assemblies. emblies.

Severe environments, demanding performance and cost effectiveness characterize current harsh environment system interconnect needs. The increasing use of fiber optics in these applications mandates reliable, safe and efficient fiber optic (FO) interconnect systems. Reliability, safety, bandwidth, and environmental requirements necessitate the transition from copper wire based to fiber optic based systems. Discussed are the technologies, environments, and performance requirements applicable to these applications, along with the trade decisions necessary to implement solutions. This paper addresses harsh environment fiber optic reliability requirements, fiber optic reliability characterization, potential FO interconnect failure modes, and the how to quantify fiber optic reliability. A case study is presented that encompasses the applicable environments for such interconnects, quantifies the inherent reliability of the FO interconnect system in such environments, and provides fiber optic interconnect reliability risk mitigation strategies. FO interconnect failure prediction is also discussed.

In order to reduce some of the toxic emissions produced by internal combustion engines, the fossil-based fuels have been combined with less harmful materials in recent years. However, the fuels used in the automotive industry generally contain different additives, such as toluene, as anti-shock agents and as octane number enhancers. These materials can cause certain negative impact, besides the high volatility implied, on public health or environment due to its chemical composition. Toluene, among several other chemical compounds, is an additive widely used in the commercially-available gasoline-ethanol blends. Despite the negative aspects in terms of toxicity that this material might have, the Raman spectral information of toluene can be used to achieve certain level of frequency calibration without using any additional chemical marker in the sample or any other external device. Moreover, the characteristic and well-defined Raman line of this chemical compound at 1003 cm⁻¹ (even at low v/v content) can be used to quantitatively determine certain aspects of the gasoline-ethanol blend under observation. By using an own-designed Fourier-Transform Raman spectrometer (FT-Raman), we have collected and analyzed different commercially-available and laboratory-prepared gasoline-ethanol blends. By carefully observing the main Raman peaks of toluene in these fuel blends, we have determined the frequency accuracy of the Raman spectra obtained. The spectral information has been obtained in the range of 0 cm⁻¹ to 3500 cm⁻¹ with a spectral resolution of 1.66 cm⁻¹. The Raman spectra obtained presented only reduced frequency deviations in comparison to the standard Raman spectrum of toluene provided by the American Society for Testing and Materials (ASTM).

We are presenting a new optical encoder architecture for shaft encoding, both in incremental and absolute modes. This encoder is based on a diffractive optics technology platform. We have developed various disk based rotary diffractive encoders previously. This encoder is different in the way it is not a disk composed of successive gratings or computer generated holograms, but rather composed of a single element placed on the shaft. It is thus best suited for hollow shaft or end of shaft applications such as in encoder controlled electrical motors. This new architecture aims at solving some of the problems encountered with previous implementations of diffractive encoders such as disk wobble, disk to shaft centering and also encoding in harsh environments.

We are presenting several techniques to improve the quality of the signals in diffractive optics encoders, for either linear and rotational encoders. We have developed previously various hybrid incremental/absolute disk based rotary diffractive encoders architectures. While the binary signals for absolute encoding were usually of sufficiently good quality to retrieve the entire Gray code signal over the desired resolutions (10, 12 or 14 bits), the quality and integrity of the sinusoidal signals for the incremental part of the encoder needed to be improved, since these are the signals allowing the encoder to go to much higher interpolated resolutions (20 bits or over). A good precision over the interpolated signals assumes very accurate sinusoidal profiles form the raw signals. Strong interpolation can only be done on high quality sinusoidal native signals (also referred to as pulses per revolution or PPR). A typical high resolution incremental encoder might provide 12 to 16 native sinusoidal PPRs, but the interpolation over these signals can reach way over 20 bits of resolution if the signals are of good quality.

This paper reviews the various optical technologies that have been developed to implement HMDs (Head Mounted Displays), both as AR (Augmented Reality) devices, VR (Virtual Reality) devices and more recently as smart glasses, smart eyewear or connected glasses. We review the typical requirements and optical performances of such devices and categorize them into distinct groups, which are suited for different (and constantly evolving) market segments, and analyze such market segmentation.

This paper describes the performances of mold light guide based see-through optics for the production of AR glasses for commercial and professional applications. A monolithic thin mold light guide with surface structure mirror array extracts and project bright and large virtual image into the user eye of sight. The light guide thin form factor allows a new user experience with two possible positions for the virtual image in front of the user eye. A wireless AR glasses based on this concept will be described and demonstrated. A comparison with others light guide based technologies in term of Safety, Brightness efficiency and form factor will be presented and discussed.

We review our work regarding a new class of couplers, resonators and free space gratings that employ the concept of Parity-Time (PT) symmetry in optics. PT structures can be implemented as diffractive gratings having complex refractive index profiles. The complex index profile integrates both phase and loss modulations as in conventional gratings, but also gain modulation. We review our work on integrated waveguide grating structures (Bragg regime) and free space structures (Raman Nath regime). Uni-directionality in free space can be applied to the development of novel optical combiners for the HMD/HUD fields. Such elements can be replicated in mass via lithography/embossing, with similar efficiency as conventional volume HOEs (Holographic Optical Elements) such as photopolymers.

High quality, controlled-structure nanowires (NWs), grown on a transparent flexible substrate, have attracted great interest as a mean of harvesting solar and mechanical energy. Clarifying their optical and piezoelectric properties is essential for this application. In this paper, vertically aligned lithium (Li) doped p-type ZnO NWs were grown, on a micro-patterned transparent flexible polyethylene naphthalate (PEN) substrate, by electrochemical deposition at 88 °C. The substrate was coated with aluminum-doped ZnO (AZO) thin layer, which served as a good seed layer and a transparent conductive oxide layer. Varying the seed layer thickness gave control of the individual NWs’ diameter, density and alignment. The effect of doping on the optical band-gap, crystalline quality and Schottky barrier were investigated by X-ray diffraction (XRD) spectroscopy and piezoelectric characterization. The piezoelectric polarization induced piezo-potential in strained ZnO NWs can drive the flow of electrons without an applied electric bias, thus can be used to harvest mechanical energy and convert it into electricity. To prove this concept, flexible piezoelectric energy harvesters based on an array of ZnO NWs were fabricated. Results show that the patterned p-type NW-based energy harvester produces 26-fold output voltage and 19-fold current compared to the conventional un-doped ZnO NW energy harvester from the same acceleration input.

To integrate polymer fiber based physical layer for avionic data network, it is necessary to understand the impact and cause of harsh environments on polymer fiber optic components and harnesses. Since temperature and vibration have a significant influence, we investigate the variation in optical transmittance and monitor the endurance of different types of connector and splices under extreme aircraft environments. Presently, there is no specific aerospace standard for the application of polymer fiber and components in the aircraft data network. Therefore, in the paper we examine and define the thermal cycling and vibration measurement set up and methods to evaluate the performance capability of the physical layer of the data network. Some of the interesting results observed during the measurements are also presented.

Lasercomm or Free Space Optical (FSO) communication has the potential to provide fiber optic data rates without the need for wired physical connectivity. This paper investigates the feasibility of an Omnidirectional FSO (O-FSO) communications link that utilizes fiber bundles for improved omni-directionality and compares experimental data with modeled results. Current state of the art O-FSO link ranges are limited to 100 meters or so, with data rates of only a few100 kbits/sec. The proposed architecture is formed from commercially available fiber bundle that collects omnidirectional light due to the hemispheric nature of the fiber bundle by exploiting the acceptance cones of the individual fiber exposed to the optical radiation. The experimental transmitter is composed of an LED source that is driven by an On-Off-Keying signal. This paper presents the received optical power while varying the range between the transmitter and receiver. The omni-directionality of this architecture is also verified. The measured results are then compared to the model predictions for omni-directionality and range.

With the phasing out of incandescent lamps in many countries, the introduction of new LED based light sources and luminaries sometimes raise the question of whether the spectral characteristics of the LED and other energy savings Fluorescent lights including the popular CFLs are suitable to replace the traditional incandescent lamps. These concerns are sometimes raised particularly for radiation emissions in the UV and Blue parts of the spectrum. This paper aims to address such concerns for the common ‘white light’ sources typically used in household and other general lighting used in the work place. Recent studies have shown that women working the night shift have an increased probability of developing breast cancer. We like to report on the findings of many studies done by medical professionals, in particular the recent announcement of AMA in the US and many studies conducted in the UK, as well as the European community to increase public awareness on the long term health risks of the optical and opto-biological effects on the human health caused by artificial lighting.

This paper describes recent progress towards the development of an innovative light weight, high-speed, and selfpowered wireless fiber optic sensor (WiFOS™) structural health monitor system suitable for the onboard and in-flight unattended detection, localization, and classification of load, fatigue, and structural damage in advanced composite materials commonly used in avionics and aerospace systems. The WiFOS™ system is based on ROI’s advancements on monolithic photonic integrated circuit microchip technology, integrated with smart power management, on-board data processing, wireless data transmission optoelectronics, and self-power using energy harvesting tools such as solar, vibration, thermoelectric, and magneto-electric. The self-powered, wireless WiFOS™ system offers a versatile and powerful SHM tool to enhance the reliability and safety of avionics platforms, jet fighters, helicopters, commercial aircraft that use lightweight composite material structures, by providing comprehensive information about the structural integrity of the structure from a large number of locations. Immediate SHM applications are found in rotorcraft and aircraft, ships, submarines, and in next generation weapon systems, and in commercial oil and petrochemical, aerospace industries, civil structures, power utilities, portable medical devices, and biotechnology, homeland security and a wide spectrum of other applications.

In this paper, we compare the performance of a Correlation Brillouin Optical Time Domain Analysis (CBOTDA) system using bipolar Golay complementary pairs and unipolar Optical Orthogonal Code. Our simulation studies show that the spatial resolution supported by both schemes are comparable, but the Golay code is preferred due to better peak power to average power ratio (PAPR). We proceed to experimentally demonstrate the detection of a temperature event at the end of a 50 km long sensing fiber using Golay complementary pairs.

A scheme to generate return-to-zero on-off keying (RZ-OOK) high speed all-optical pseudo random bit sequence (PRBS) using binary phase shift keyed (BPSK) signal based on quantum-dot semiconductor optical amplifiers (QD-SOA) has been designed and studied. The PRBS is generated by a linear feedback shift register (LFSR) composed of all-optical logic XOR and AND gates. The XOR gate is composed of a pair of QD SOA Mach-Zehnder interferometers, which can generate BSPK signal to realize all-optical logic XOR gate. Results show that this scheme can mitigate the patterning effects and increase the operation speed to ~250Gb/s.

This paper describes recent progress towards the development of a remote “frequency-domain” fluorescence lifetime (SeePhase™) monitor used for the real time hermetic seal leak inspection of packaged food containers. A multitude of food goods, meets, vegetables, and beverages are typically packaged within an inert environment to reduce the risk of bacteria growth and increase the storage life of the food product. The SeePhase™ system uses a multi-parameter oxygen, carbon dioxide, and moisture sensitive patch that is placed within the hermetic sealed food package. Upon the presence of gases oxygen, carbon dioxide, or moisture inside the hermetic sealed food package, the sensor patch produces a fluorescence lifetime signature characteristic of a hermetic seal leak damage of the package.

In this paper, we propose and demonstrate a self-seeding 1.2 GHz RSOA-based laser by employing 3.5 Gbit/s orthogonal-frequency-division-multiplexing quadrature-amplitude-modulation (OFDM-QAM) with bit-loading algorithm for upstream traffic in a colorless WDM-PON access. To achieve 3.5 Gbit/s traffic data rate and accomplish the forward error correction (FEC) threshold [bit error rate (BER) = 3.8 x 10^-3], a Faraday rotator mirror (FRM) is used to perform self-seeding operation in this experiment. Here, the power penalty is about 2.59 dB at the wavelength of 1550.0 nm wavelength in a 20 km single mode fiber (SMF) transmission. Moreover, the measured BER performances of proposed laser are also discussed and analyzed, while the fiber mirror (FM) is used to replace the FRM in this experiment.

Wireless communication of aviation contains high capacity confidential information and therefore such communication requires secure high speed data communication scheme by using reliable cipher. In this report, the authors propose free space optical communication by utilizing optical intensity-modulated Y-00 cipher for applications of secure aviation systems including unmanned aircraft systems. Y-00 cipher transmitter and receiver with intensity levels of 4096 at data rate of 2.5 Gbit/s are fabricated for secure free space optical communication and a free space Y-00 cipher transmission is experimentally demonstrated.

We experimentally compared different options for interconnection of remote places in precise time transmission infrastructures. We aimed at lines with bidirectional single path amplification, as they provide the best results in term of time uncertainty. For links with high reflections and without accessible midpoints, the distributed Raman amplification has been tested. In case of dark channels with fibre based “last miles”, the Raman amplification in the last miles only has been verified. According to author’s knowledge, this is the first time when the distributed amplification is used for modulated precise time transmission over fiber. For reference, the traditional lumped EDFAs suitable for transmission links or dark channels with accessible mid-point have been compared.

We propose a polarimetric fiber optic vibration sensor. The principle is based on the evolution of polarization when the constraint (vibration) is applied on a sensitive zone of the sensor. We study the effects of a vibration application on our system with a continuous frequency and the polarization evolution on the Poincaré sphere. The study has demonstrated a very good accuracy and a good agreement between the theoretical and the experimental results were achieved.

Spatial Domain Multiplexing/Space Division Multiplexing (SDM) can increase the bandwidth of existing and futuristic optical fibers by an order of magnitude or more. In the SDM technique, we launch multiple single mode pigtail laser sources of same wavelength into a carrier fiber at different angles. The launching angles decide the output of the carrier fiber by allocating separate spatial locations for each channel. Each channel follows a helical trajectory while traversing the length of the carrier fiber, thereby allowing spatial reuse of optical frequencies. In this endeavor we launch light from five different single mode pigtail laser sources at different angles (with respect to the axis of the carrier fiber) into the carrier fiber. Owing to helical propagation we get five distinct concentric donut shaped rings with negligible crosstalk at the output end of the fiber. These SDM channels also exhibit Orbital Angular Momentum (OAM), thereby adding an extra degree of photon freedom. We present the experimental data of five spatially multiplexed channels and compare them with simulated results to show that this technique can potentially improve the data capacity of optical fibers by an order of magnitude: A factor of five using SDM and another factor of two using OAM.

A compact and light weight liquid-level-measuring system based on fiber-optics sensor technology is presented as alternative to systems based on float gauges and other conventional level sensors for liquids that pose fire, corrosion and explosion hazards. These Fresnel reflection based fiber-optic sensors are inherently safer because they do not include electrical connections inside fuel/chemical tanks, and they exploit changes in internal reflection of guided electromagnetic modes as a result of contact between the outer surface of optical fiber and a liquid. Discrete changes in light transmission/reflection are used to indicate that liquid has come into contact with a suitably designed fiber optic probe at the output end of the fiber. This endeavor presents a quasi-continuous fiber optic level detection system that measures liquid level to within known increments of depth, by placing the probes of a number of such sensors at known depths in a tank where each probe effectively serves as a level switch. Due to the fiber optic nature of the design, the system can operate from cryogenic applications to boiling fluids. Experimental results for liquid nitrogen and water are presented.

A true three dimensional camera is described here, that without using the stereoscopic effect can measure the distance from each pixel to the point on the object that is in focus at the pixel. It is useful for providing detailed range information for guiding autonomous vehicles and general robotic vision. It is conventionally assumed that humans have three dimensional vision because each object is observed from a slightly different direction with each eye. That is, humans have stereoscopic vision. This is true. However, there is another mechanism in animal eyes that also contributes to three dimensional vision. The Depth Perception Camera described here also uses this mechanism. The Depth Perception Camera can be be constructed by conventional semiconductor device fabrication technology. It can also be constructed using a three dimensioal printer that can handle differently doped semiconductors.

Atmospheric turbulences can significantly deteriorate the performance of long-range conventional imaging systems and create difficulties for target identification and recognition. Our in-house developed adaptive optics (AO) system, which contains high-performance deformable mirrors (DMs) and the fast stochastic parallel gradient decent (SPGD) control mechanism, allows effective compensation of such turbulence-induced wavefront aberrations and result in significant improvement on the image quality. In addition, we developed advanced digital synthetic imaging and processing technique, “lucky-region” fusion (LRF), to mitigate the image degradation over large field-of-view (FOV). The LRF algorithm extracts sharp regions from each image obtained from a series of short exposure frames and fuses them into a final improved image. We further implemented such algorithm into a VIRTEX-7 field programmable gate array (FPGA) and achieved real-time video processing. Experiments were performed by combining both AO and hardware implemented LRF processing technique over a near-horizontal 2.3km atmospheric propagation path. Our approach can also generate a universal real-time imaging and processing system with a general camera link input, a user controller interface, and a DVI video output.

In this paper, we discuss various aspects of the control and sensing in a flexible wing aircraft using embedded LPFG (Long Period Fiber Grating). Driven by the need to improve aerodynamic efficiency and reduce fuel burn, interest in light-weight structures for next generation aircraft has been on the rise. However, in order to fully exploit novel lightweight structures, there is a critical need for distributed sensing along the entire wing span and its integration with closed-loop control systems. A model of an LPFG sensor string embedded in an Euler-Bernoulli beam is proposed along with an associated control algorithm.

Spatial domain multiplexing (SDM) is a system that allows multiple channels of light to traverse a single fiber, utilizing separate spatial regions inside the carrier fiber, thereby applying a new degree of photon freedom for optical fiber communications. These channels follow a helical pattern, the screen projection of which is viewable as concentric rings at the output end of the system. The MIMO nature of the SDM system implies that a typical pin-diode or APD will be unable to distinguish between these channels, as the diode will interpret the combination of the SDM signals from all channels as a single signal. As such, spatial de-multiplexing methods must be introduced to properly detect the SDM based MIMO signals. One such method utilizes a fiber consisting of multiple, concentric, hollow core fibers to route each channel independently and thereby de-mux the signals into separate fibers or detectors. These de-mux fibers consist of hollow core cylindrical structures with beveled edges on one side that gradually taper to route the circular, ring type, output energy patterns into a spot with the highest possible efficiency. This paper analyzes the beveled edge by varying its length and analyzing the total output power for each predetermined length allowing us to simulate ideal bevel length to minimize both system losses as well as total de-mux footprint. OptiBPM simulation engine is employed for these analyses.

Spatial domain multiplexing (SDM) also known as space division multiplexing adds a new degree of photon freedom to existing optical fiber multiplexing techniques by allocating separate radial locations to different MIMO channels as a function of the input launch angle. These independent MIMO channels remain confined to the designated location while traversing the length of the carrier fiber, due to helical propagation of light inside the fiber core. The SDM technique can be used in tandem with other multiplexing techniques, such as time division multiplexing (TDM), and wavelength division multiplexing in hybrid optical communication schemes, to achieve higher optical fiber bandwidth by increasing the photon efficiency due to added degrees of photon freedom. This paper presents the feasibility of a novel hybrid optical fiber communications architecture and shows that SDM channels of different operating wavelengths continue to follow the input launch angle based radial distribution pattern.

This paper discuses a novel, rollable, mass fabricable, low-concentration photovoltaic sheets for Cubesats providing them with efficient photoelectric conversion of sunlight and secondary diffuse light. The wrap consists of three thin (of order a millimeter or less), cheap plastic-sheet layers, which can be rolled together in a spiral wrapping configuration when stowed. Preliminary simulation based on the above modeling approaches show that the designs achieve comparable photovoltaic power (area for area) and (b) result in a at angular response curve which remains at from normal incidence of over 35 degrees to the normal. The simulation were performed using a ray tracing simulator built in Matlab. In addition, we have constructed a demonstrator using quartz wafers based on the optimized design to show the technology. Details of its fabrication are also provided.

Fiber optic systems are used frequently in military, aerospace and commercial aviation programs. There is a long history of implementing fiber optic data transfer for aircraft control, for harsh environment use in local area networks and more recently for in-flight entertainment systems. The advantages of fiber optics include high data rate capacity, low weight, immunity to EMI/RFI, and security from signal tapping. Technicians must be trained particularly to install and maintain fiber systems, but it is not necessarily more difficult than wire systems. However, the testing of the fiber optic interconnection system must be conducted in a standardized manner to assure proper performance. Testing can be conducted with slight differences in the set-up and procedure that produce significantly different test results. This paper reviews various options of interconnect configurations and discusses how these options can affect the performance, maintenance required and longevity of a fiber optic system, depending on the environment. Proper test methods are discussed. There is a review of the essentials of proper fiber optic testing and impact of changing such test parameters as input launch conditions, wavelength considerations, power meter options and the basic methods of testing. This becomes important right from the start when the supplier test data differs from the user’s data check upon receiving the product. It also is important in periodic testing. Properly conducting the fiber optic testing will eliminate confusion and produce meaningful test results for a given harsh environment application.

To achieve the highest possible turbine inlet temperature requires to accurately measuring the turbine blade temperature. If the temperature of blade frequent beyond the design limits, it will seriously reduce the service life. The problem for the accuracy of the temperature measurement includes the value of the target surface emissivity is unknown and the emissivity model is variability and the thermal radiation of the high temperature environment. In this paper, the multi-spectral pyrometer is designed provided mainly for range 500-1000℃, and present a model corrected in terms of the error due to the reflected radiation only base on the turbine geometry and the physical properties of the material. Under different working conditions, the method can reduce the measurement error from the reflect radiation of vanes, make measurement closer to the actual temperature of the blade and calculating the corresponding model through genetic algorithm. The experiment shows that this method has higher accuracy measurements.

Vertical takeoff and landing (VTOL) aircrafts such as helicopters and drones, add a flexible degree of operation to airborne vehicles. In order to operate these devices in low light situations, where it is difficult to determine slope of the landing surface, a lightweight and standalone device is proposed here. This small optical device can be easily integrated into current VTOL systems. An optical projector consisting of low power, light weight, solid state laser along with minimal optics is utilized to illuminate the landing surface with donut shaped circles and coaxial centralized dot. This device can placed anywhere on the aircraft and a properly placed fiber system can be used to illuminate the surface beneath the bottom of the VTOL aircraft in a fashion that during operation, when the aircraft is parallel to the landing surface, the radius between the central dot and outer ring(s) are equidistant for the entire circumference; however, when there the landing surface of the VTOL aircraft is not parallel to the landing strip, the radial distance between two opposite sides of the circle and central dot will be unequal. The larger this distortion, the greater the difference will be between the opposite sides of the circle. Visual confirmation or other optical devices can be used to determine relative alignment of the projector output allowing the pilot to make proper adjustments as they approach the landing surface to ensure safe landings. Simulated and experimental results from a prototype optical projector are presented here.

Normally, reliable, reproducible, high-yield packaging technologies are essential for meeting the cost, performance, and service objectives for the harsh environment of space applications. This paper describes a new improved micro packaging method of hermetic seal mini-DIL (dual in line) laser diode module. The problem of using a softer solder resulted in failure mechanisms observed in the mini-DIL laser diode module based laser firing unit (LFU) for ordinance ignition of a missile system. These failures included: (1) failure in light output pulse power, (2) fiber pigtail damage inside the package snout which caused low LFU production yield. Our distinctive challenge for this project is the micro packaging of mini-DIL. For this package a new technique for the hermetic sealing using a micro-soldering process was developed. The process is able to confine the solder seal to a small region inside the snout near the fiber feed-through hole on the wall of the mini-DIL package. After completing the development, which included temperature and thermal cycling, X-rays analysis showed the new method had no fiber damage after the microsoldering seal. The new process resulted in 100% success in the packaging design and was granted a patent for the innovative development.

In this paper, a fabrication of IPMC (Ionic Polymer Metal Composites) films with hexagonal electrodes for deformable mirrors applications has been described. With the array of hexagonal electrodes on one side of IPMC membrane, we can control the contour of IPMC by driving voltage selectively. Our fabrication process involves ion-exchange, lithography, and electroless plating steps. A positive photoresist in photolithography is used as the mask in the electroless plating process to selectively grow platinum electrodes in IPMC regions. We have measured the surface resistance of the IPMC. The surface resistance of the hexagonal electrodes is about 5Ω, which is small enough to enable the IPMC to be actuated by low voltage. The other side of the IPMC membrane is smooth and can be used as reflection surface. We have generated deformation on our IPMCs (5 cm X 5 cm) under a low actuation voltage less than 5 volts successfully. The maximum stroke of the IPMC deformable mirror is about 25 um. Due to the low driving voltage of IPMCs, the deformable mirrors made of IPMCs is promising.

A slot metasurface (metascreen) designed to have resonance that couples with the 1733 cm^-1 absorption peak of the C=O molecular bond of PMMA (polymethyl methacrylate) is presented. The metasurface is made of a gold layer perforated with periodically-placed slots and stood off above a reflective ground plane with silicon substrate. The metasurface is modeled using ANSYS HFSS and including measured optical properties for gold, silicon and PMMA in the infrared spectrum. PMMA forms a thin overcoat and exhibits a strong absorption resonance at wavenumber 1733 cm^-1. Coupling between the metasurface and PMMA is observed via normal mode splitting. Mode splitting has been analyzed from classical coupled mass spring oscillators to exciton-photons coupling in microcavities. The coupled systems can be described with a Hamiltonian matrix and solved for the eigenfrequencies. Parametric analysis of coupled response as a function of the design geometry is provided. Coupling energy, reflectance spectrum, and dispersion plots showing the anticrossing behavior of hybrid modes are presented as characterization of resonance coupling and normal mode splitting. Slot metasurface results are compared to the complementary structure (nanorod metasurface) in order to explore the duality of the complentary metasurfaces and their coupled responses. Coupled resonances have application in biosensors for molecule detection, surface-enhanced infrared absorption (SEIRA), and infrared imaging.

We have designed a tapered rib waveguide and numerically studied the generation of supercontinuum using such waveguides. The Air-SF57 glass-SiO₂ waveguide is 2 cm long, with a varying etched depth to manage the total dispersion. Numerical simulations are conducted for input pulses at a wavelength of 1550 nm. The proposed waveguide geometry greatly broadens the output spectrum extending from ~1000 nm to ~ 4600 nm at -30 dB level, caused by continuous modification of the phase matching condition for dispersive wave emission. The coherence property has also been investigated, demonstrating that fully coherent supercontinuum can be obtained with proper pumping conditions.

There are several military or commercial systems operating in very harsh environments that require rugged windows. On some of these systems, windows become the single point of failure. These applications include sensor or imaging systems, high-energy laser weapons systems, submarine photonic masts, IR countermeasures and missiles. Based on the sea or land or air based platforms the window or dome on these systems must withstand wave slap, underwater or ground based explosions, or survive flight through heavy rain and sand storms while maintaining good optical transmission in the desired wavelength range. Some of these applications still use softer ZnS or fused silica windows because of lack of availability of rugged materials in shapes or sizes required. Sapphire, ALON and spinel are very rugged materials with significantly higher strengths compared to ZnS and fused silica. There have been recent developments in spinel, ALON and sapphire materials to fabricate in large sizes and conformal shapes. We have been developing spinel ceramics for several of these applications. We are also developing β−SiC as a transparent window material as it has higher hardness, strength, and toughness than sapphire, ALON and spinel. This paper gives a summary of our recent findings.

A circular polarized (CP) infrared (IR) leaky wave surface design is presented. The metasurface consists of an array of rectangular patches connected by microstrip and operating over the long-wave infrared (LWIR) spectrum with directional wave emission and absorption. The surface is composed of periodically aligned arrays of sub-wavelength metal patches separated from a ground plane by a dielectric slab. The design combines the features of the conventional patch and leaky wave antenna leading to a metasurface that preferentially emits CP IR radiation by use of axial asymmetrical unit cells. This is a deviation from reported structures that mainly employ a phase shifter to combine linearly polarized waves in order to attain circular polarization. The performance of this leaky wave surface is verified through full-wave simulation using the ANSYS HFSS finite element analysis tool. The leaky wave phenomenon is demonstrated by the frequency and angular dependence of the absorption while circular polarization is characterized via stokes parameters. The main beam of this surface can be steered continuously by varying the frequency while maintaining circular polarization within the main beam direction. A CP leaky wave at 10.6 μm with a scanning angle of 30° is demonstrated. Metasurfaces exhibiting spectral and polarization selectivity in absorption/emission hold the potential for impact in IR applications including detection, imaging, thermal management, energy harvesting and tagging.

In normal fiber, the refractive indices of the core and cladding do not change along the length of the fiber; however, by inducing a periodic modulation of refractive index along the length in the core of the optical fiber, the optical fiber grating is produced. This exhibits very interesting spectral properties and for this reason we propose to develop and integrate a distributed sensor network based on long period fiber gratings (LPFGs) technology which has grating periods on the order of 100 μm to 1 mm to be embedded in the wing section of aircraft to measure bending and torsion in real-time in order to measure wing deformation of commercial airplanes resulting in extensive benefits such as reduced structural weight, mitigation of induced drag and lower fuel consumption which is fifty percent of total cost of operation for airline industry. Fiber optic sensors measurement capabilities are as vital as they are for other sensing technologies, but optical measurements differ in important ways. In this paper we focus on the testing and aviation requirements for LPFG sensors. We discuss the bases of aviation standards for fiber optic sensor measurements, and the quantities that are measured. Our main objective is to optimize the design for material, mechanical, optical and environmental requirements. We discuss the analysis and evaluation of extensive testing of LPFG sensor systems such as attenuation, environmental, humidity, fluid immersion, temperature cycling, aging, smoke, flammability, impact resistance, flexure endurance, tensile, vitiation and shock.

In this paper, we discuss optimization of a novel low-concentration photovoltaic system with the following properties: (1) static concentration without the need for tracking (2) thermal uniformity via Diffraction Efficiency Modulation (DEM), and (3) mass-fabricability and rollability. The approach leverages a unique combination of waveoptics modeling, multi-objective thermal-electro-optical optimization, and mass-fabricable, nano-manufacturing technology. We discuss various aspects of the optimization including a novel Helmholtz FD solver and thermal and electrical considerations.

Recent work has demonstrated significant promise for high temperature optical gas sensing based upon optical property responses in a class of high electronic conductivity metal oxides. In this work, we theoretically simulate the response of aluminum-doped zinc-oxide (an exemplary conducting metal oxide) in optical fiber evanescent wave absorption spectroscopy sensor devices through the application of a general model of the optical constants for this class of materials in conjunction with prior published material-specific constants for the systems under investigation. Theoretical simulations are compared with recently published experimental results for Al-doped ZnO thin films and the various factors responsible for optimizing sensing responses in this class of materials will be discussed.

Recent development in fiber optic sensing technology has mainly focused on discrete sensing, particularly, sensing systems with potential multiplexing and multi-parameter capabilities. Bragg grating fiber optic sensors have emerged as the non-disputed champion for multiplexing and simultaneous multi-parameter sensing for emerging high value structural components, advanced processing and manufacturing capabilities and increased critical infrastructure resilience applications. Although the number of potential applications for this sensing technology is large and spans the domains of medicine, manufacturing, aerospace, and public safety; critical issues such as fatigue life, sensitivity, accuracy, embeddability, material/sensor interface integrity, and universal demodulation systems still need to be addressed. The purpose of this paper is to primarily evaluate Commercial-Of-The-Shelf (COTS) Fiber Bragg Grating (FBG) sensors’ sensitivity to pressure, often neglected in several applications. The COTS fiber sensitivity to pressure is further evaluated for two types of coatings (Polyimide and Acrylate), and different arrangements (arrayed and single).

A direct B-integral measurement, and SPM compensation method in fiber optic CPA systems is demonstrated. For a pair of input pulses, the chirped nature of the amplification transforms a nonlinear phase change into a temporal amplitude change resulted in a satellite side pulses generation. The SHG autocorrelation measurement of these satellite pulses is directly correlated to B-integral value. Then the accumulated SPM is removed by precompensation of the spectral phase. The degree of compensation again confirmed the described B-integral measurement result.

There are numerous ways to use video cameras to measure 3D dynamic spatial displacements. When the scene geometry is unknown and the motion is unconstrained, two calibrated cameras are required. The data from both scenes are combined to perform the measurements using well known stereoscopic techniques. There are occasions where the measurement system can be simplified considerably while still providing a calibrated spatial measurement of a complex dynamic scene. For instance, if the sizes of objects in the scene are known a priori, these data may be used to provide scene specific spatial metrics to compute calibration coefficients. With this information, it is not necessary to calibrate the camera before use, nor is it necessary to precisely know the geometry between the camera and the scene. Field-ofview coverage and sufficient spatial and temporal resolution are the main camera requirements. Further simplification may be made if the 3D displacements of interest are small or constrained enough to allow for an accurate 2D projection of the spatial variables of interest. With proper camera orientation and scene marking, the apparent pixel movements can be expressed as a linear combination of the underlying spatial variables of interest. In many cases, a single camera may be used to perform complex 3D dynamic scene measurements. This paper will explain and illustrate a technique for using a single uncalibrated video camera to measure the 3D displacement of the end of a constrained rigid body subject to a perturbation.

This paper describes recent progress towards the development and qualification of a highly distributed, multi-point, all optical pressure and temperature compensated, fiber optic oxygen sensor (FOxSense™) system for closed-loop monitoring and safety of the oxygen ullage environment inside fuel tanks of military and commercial aircraft. The alloptical FOxSense™ system uses a passive, multi-parameter (O2/T&P) fiber optic sensor probe with no electrical connections leading to the sensors install within the fuel tanks of an aircraft. The all optical sensor consists of an integrated multi-parameter fiber optic sensor probe that integrates a fuel insensitive fluorescence based optical oxygen optrode with built-in temperature and pressure optical optrodes for compensation of temperature and pressure variants induced in the fluorescence response of the oxygen optrode. The distributed (O2/T&P) fiber optic sensors installed in the fuel tanks of the aircraft are connected to the FOxSense optoelectronic system via a fiber optic cable conduit reaching to each fuel tank in the aircraft. A multichannel frequency-domain fiber optic sensor read-out (FOxSense™) system is used to interrogate the optical signal of all three sensors in real-time and to display the fuel tank oxygen environment suitable for aircraft status and alarm applications. Preliminary testing of the all optical fiber optic oxygen sensor have demonstrated the ability to monitor the oxygen environment inside a simulated fuel tank in the range of 0% O2 to 40% O2 concentrations, temperatures from (-) 40°C to (+) 60°C, and altitudes from 0-ft to 40,000-ft.

Fiber optic acousto-ultrasonic transducers offer numerous applications as embedded sensors for impact and damage detection in industrial and aerospace applications as well as non-destructive evaluation. Superficial contact transducers with a sheet of fiber optic Bragg gratings has been demonstrated for guided wave ultrasound based measurements. It is reported here that this method of measurement provides highly reproducible guided ultrasound data of the test composite component, despite the optical fiber transducers not being permanently embedded in it.

Fiber optic connector technology is making significant advances for use in aviation and aerospace applications. This increasingly user friendly system has contributed to more novel extremely small multifiber connectors for fiber optic interconnection. With low insertion loss and excellent environmental endurance in harsh environments they meet the requirements of higher integration in optical backplanes. There are two main methods of transmitting an optical signal between two fibers: (1) Physical Contact (PC) and (2) Non-Physical Contact Connectors, Expanded Beam (EB). Expanded beam connectors have been shown to withstand extreme environments without the need for special servicing or cleaning equipment. Protecting the optical fibers behind the lenses ensures that no damage or degradation can occur to the fiber ends. Severe conditions, extreme surroundings, rough weather, rugged and unforgiving environment call for the use of high-performance fiber optic connectors. Appropriate connector selection is essential to assure adequate optical, environmental and mechanical performance. The choice of these items should be specific to the requirements of the system when considering environmental and mechanical limitations. Proper installation, maintenance and repair training is essential. This paper outlines the attributes, environments, requirements, technologies and solutions of fiber optic connectors for harsh environment for aviation and aerospace applications. Furthermore, it describes various state-of-the-art technologies, particularly for aviation industry. Discussion will also place emphasis on physical contact and expanded beam designs which are the fiber optic technologies being used in harsh environments of aviation and aerospace applications. Key

We report an experimental demonstration and characterization of dynamic Brillouin gratings (DBGs) in a 5m long polarization-maintaining fiber (PMF) using heterodyne detection. The dependence of DBG reflectivity on the Brillouin gain and on the pumps and the probe powers is studied and reported.

Effect of scintillations is a serious problem in optical systems which require atmospheric propagation, and various examinations have been implemented to keep communication quality. But combination of optical conditions to optimize communication capability has not been examined. In this paper, optimization of the combination of optical variables, for example transmission beam radius of carrier wave and diameter of receiving aperture, is conducted by using the lognormal distribution model in weak turbulence and the gamma-gamma distribution model, which is suitable for weak to strong turbulence, in moderate to strong turbulence with considering aperture averaging. As a result of the examination, the optimum combination have been successfully found. Moreover, to investigate the propagation mode of carrier wave, comparison of propagation attenuation between Gaussian beam wave and Laguerre-Gaussian beam wave and evaluation of communication quality in optimized optical condition obtained from above-mentioned examination, will be done. The result is that the propagation loss of any of the Laguerre-Gaussian beam waves are smaller than those of the Gaussian beam waves. It is also observed that the propagation loss of (5, 1) Laguerre-Gaussian beam wave is particularly small among those.

In this work two fiber optic sensing techniques are used to study the dimensional stability in fresh state of different cementitious materials. A conventional Portland cement mortar and two commercial grouts were selected. The measurements were performed by using a Bragg grating embedded in the material and a non-contact Fizeau interferometer. The first technique was applied in a horizontal sample scheme, and the second one, by using a vertical configuration. In addition, a mechanical length comparator was used in the first case in order to compare the results. The evolution with time of the dimensional changes of the samples and the analysis of the observed behavior are included.

Camera motion is a potential problem when a video camera is used to perform dynamic displacement measurements. If the scene camera moves at the wrong time, the apparent motion of the object under study can easily be confused with the real motion of the object. In some cases, it is practically impossible to prevent camera motion, as for instance, when a camera is used outdoors in windy conditions. A method to address this challenge is described that provides an objective means to measure the displacement of an object of interest in the scene, even when the camera itself is moving in an unpredictable fashion at the same time. The main idea is to synchronously measure the motion of the camera and to use those data ex post facto to subtract out the apparent motion in the scene that is caused by the camera motion. The motion of the scene camera is measured by using a reference camera that is rigidly attached to the scene camera and oriented towards a stationary reference object. For instance, this reference object may be on the ground, which is known to be stationary. It is necessary to calibrate the reference camera by simultaneously measuring the scene images and the reference images at times when it is known that the scene object is stationary and the camera is moving. These data are used to map camera movement data to apparent scene movement data in pixel space and subsequently used to remove the camera movement from the scene measurements.