This PDF file contains the front matter associated with SPIE Proceedings Volume 7817, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

A novel transistor based quantum well modulator structure is presented and analyzed for applications in RF photonic links. The modulator has been realized in the GaAs epitaxial system using both GaAs/AlGaAs and InGaAs/AlGaAs modulation-doped quantum wells. The modulator operates on the principle of charge filling of a quantum well to shift the absorption edge to shorter wavelengths (blue shift). A generalized absorption model is presented for the modulator in which the relaxed k-selection rule and Lorentzian weighting function are used to represent the absorption coefficient in terms of the carrier Fermi energy. Then the blue shift of the absorption edge is determined by the channel charge density in which the Fermi level is controlled by the applied gate-to-source voltage. From this charge control model the transmission of the modulator is determined to be an increasing function of gate-to-source voltage. Absorption spectra and relative transmission curve for both devices are then calculated and validated by comparison to measurement data. It is found that the enhancement interface offers better performance. It is also found that deionization of charge sheet sets the upper limits on input optical power. The analytical T(V) response enables full distortion analysis. Thus RF link performance is studied based on calculation results and SFDR of 120 dB·Hz^2/3 and 127 dB·Hz^2/3 are predicted for the two modulators respectively.

Optical power limiters (OPLs) are nonlinear optical (NLO) devices that limit the amount of energy transmitted in an optical system. At low incident optical power or pulse energy, the transmission of the system is high enough to allow nominal operation of the system. At high incident optical power or pulse energy, the transmission decreases to protect sensitive components such as optical receivers or transmitters. The interest OPLs for use in the space environment is due to the increasingly large number of space based missions and devices that require laser protection from laser beam is coming from, an enemy, misaligned laser in equipment, etc. Temperature and space radiation-induced effects in optical and electronic materials are well known and they can cause disruption in OPL functions, or in the worst case, failure of the sensor. Recently, certain hyperbranched polymer-based composites containing OPL chromophores have been developed that offer high OPL performance and have been shown to function in a simulated + space environment. One novel high performance polymer material containing carbon nanotubes (CNT) covalently attached to the polymer host is promising. Preliminary light scattering measurements suggest that nonlinear scattering is not the primary mechanism for OPL performance.

Measurements of radiation in space, cosmic rays and Solar energetic particles, date back to the dawn of space flight. Solid state detectors, the basis of most modern high energy charged particle instruments, first flew in space in the 1960's. Modern particle spectrometers, such as ACE/CRIS, ACE/SIS and Ulysses/HET, can measure the elemental and isotopic composition of ions through the iron peak. This is achieved by using position sensing detectors (PSD's) arranged into hodoscopes to measure particle trajectories through the instrument, allowing for pathlength corrections to energy loss measurements. The Angle Detecting Inclined Sensor (ADIS) technique measures particle angle of incidence using a simple system of detectors inclined to the instrument axis. It achieves elemental resolution well beyond iron, and isotopic resolution for moderate mass elements without the complexity of position sensing detectors. An ADIS instrument was selected to fly as the High Energy Particle Sensor (HEPS) on NPOESS, but was de-scoped with the rest of the space weather suite. Another ADIS instrument, the Energetic Heavy Ion Sensor (EHIS), is being developed for GOES-R. UNH has built and tested a engineering unit of the EHIS. Applications for manned dosimetery on the Crew Exploration Vehicle (CEV) are also being explored. The basic ADIS technique is explained and accelerator data for heavy ions shown.

Materials International Space Station Experiment (MISSE) missions provide an opportunity for developing space qualifiable materials by studying the response of novel materials when subjected to the synergistic effects of the harsh space environment. MISSE 6 was transported to the international Space Station (ISS) via STS 123 on March 11. 2008. The astronauts successfully attached the passive experiment containers (PEC) to external handrails of the international space station (ISS) and opened up for long term exposure. After more than a year of exposure attached to the station's exterior, the PEC with several hundred material samples returned to the earth with the STS-128 space shuttle crew that was launched on shuttle Discovery from the Kennedy Space Center, Fla., on Aug. 28. Meanwhile, MISSE 7 launch is scheduled to be launched on STS 129 mission. MISSE-7 was launched on Space Shuttle mission STS-129 on Atlantis was launched on November 16, 2009. This paper will briefly review recent efforts on MISSE 6 and MISSE 7 missions at NASA Langley Research Center (LaRC).

There is a wide spectrum of ionizing radiation present in the space environment. The Linear Energy Transfer (LET) of the radiation determines the nature of damage to materials on a microscopic scale. Microdosimetry describes the dependency of this material damage as a function of particle LET and quality. This is key to understanding the effects of radiation on both biological and electronic systems. An ideal microdosimetric detector would physically be the size of individual particle events. If it were to be useful biologically as well, it should be organic and have a density close to one. This would make the device "tissue equivalent." In the past we developed inter-digitated devices that met these criteria. Now we present a solid state tissue equivalent detector using organic semiconductor as the active region. Many of the difficulties associated with the original inter-digitated devices are overcome by the new structures. We report on the material problems associated with the organic materials used, and the solutions found. The device responses to radiation types are presented. Semiconductor processing techniques similar to those used when producing high speed photon and x-ray detectors are employed.

The improvement of silicone-based materials used in space and aerospace environments has garnered much attention for several decades. Most recently, an Ultra Low Outgassing™ silicone incorporating innovative reinforcing and functional fillers has shown that silicone elastomers with unique and specific properties can be developed to meet applications requiring stringent outgassing requirements. This paper will report on the next crucial step in qualifying these materials for spacecraft applications requiring chemical and physical stability in the presence of ionizing radiation. As a first step in this process, selected materials were irradiated with Co-60 gamma-rays to simulate the total dose received in near- Earth orbits. The paper will present pre-and post-irradiation response data of Ultra Low Outgassing silicone samples exposed under ambient air environment coupled with measurements of collected volatile condensable material (CVCM) and total mass loss (TML) per the standard conditions in ASTM E 595. The data will show an insignificant effect on the CVCMs and TMLs after exposure to various dosages of gamma radiation. This data may favorably impact new applications for these silicone materials for use as an improved sealant for space solar cell systems, space structures, satellite systems and aerospace systems.

Superhydrophobic surfaces may be useful for a variety of optical applications as these surfaces exhibit high contact angles with water (>150°) and low-drag. These properties prevent the accumulation of water droplets on the optical surface that would otherwise occur due to condensation or the adhesion of droplets from precipitation. Challenges to producing robust superhydrophobic surfaces for optical applications include the development of cost-effective processes that are compatible with non-planar optical substrates as well as the identification of material systems that exhibit longterm reliability. We have developed a 3D printing technology to create superhydrophobic surfaces by dispensing arrays of high aspect ratio polymeric features onto optical substrates. In this paper, superhydrophobic surfaces were prepared by dispensing silicone elastomers into arrays of features on glass substrates. These samples were exposed to either Cobalt 60 gammarays or 63.8 MeV protons to simulate ionization-induced total dose environments that could be experienced in some space orbits. In addition exposure to other harsh environments, including salt water and 125°C temperatures were evaluated. The effects of these exposure conditions on superhydrophobic properties, as measured by slip angles, are reported. Near-term potential space applications will be discussed.

The responses of hydrophobic silicone-based coatings following irradiation by Co-60-gamma-rays are reported. The dimethylsilicone (DMS) resin coatings consisted of neat samples and samples incorporating semiconductor metal oxide (SMO) irradiated at photon energies of 1.17 and 1.33 MeV. Pre-and post-irradiation measurements indicated that at a total dose of ~ 185 krad(Si) there was no significant change to the coating static hydrophobic contact angles, surface molecular structure and biocide neutralization efficiency. The data was compared with previously irradiated and reported DMS/SMO coatings at a proton fluence of ~1.5 x 10¹² p/cm². Potential space applications for the radiation resistant coating self- cleaning properties are presented as well as a discussion of other environmental testing required to qualify the technology for transition to photonic space applications.

We review our previous results on frequency upconversion. Frequency upconversion of laser pulses at 10.26 μm to those at 1.187 μm was measured in the presence of Nd:YAG laser pulses based on differencefrequency generation in a 10-mm-long GaSe crystal. The highest power conversion efficiency for the parametric conversion was determined to be 20.9%, corresponding to the photon conversion efficiency of 2.42%. This value is two orders of magnitude higher than the highest value reported on GaSe in the literature. The saturation of the output power at 1.187 μm as the input power at 10.26 μm was increased, due to the back conversion, i.e. 1.187 μm + 10.26 μm → 1.064 μm, was clearly evidenced. Besides the midinfrared region, we have also investigated frequency upconversion of the input signals at 1.27 μm and 1.57 μm in the presence of the pump beam at 1.064 μm in bulk periodically-poled LiNbO₃ (PPLN) crystals. The quantum efficiencies of 11.2% and 13.2% have been achieved at these two input wavelengths. The detections of low-level photons at these two wavelengths are important to the NASA Active Sensing of CO₂ Emissions over Nights, Days, and Seasons (ASCENDS) mission.

Intersubband absorption is reported in a new modulation doped structure using strained InGaAs quantum wells (QWs) that support transistor operation. Well defined absorption peaks (1000 cm^-1 to 1700 cm^-1) from 8μm to 11.5μm have been obtained using either n- or p- type modulation doped wells. The absorption wavelength may be extended to as low as 3.2μm by using quantum dots placed within the quantum well. Both n and p well responses show strong polarization dependence with maximum values at incident angles of 65-70° and peak positions which are adjusted by the quantum well parameters. The p well shows a double peaked response with a peak separation of about 1.5μm which results from heavy and light hole contributions. A thyristor infrared detector model has been established based upon the intersubband absorption mechanism and simulation results are shown.

Multi-layer thin-film optics based on alternating sub-wavelength layers of silicon and air provide high index contrast to create improved components with just a few layers. Applications include ultra-high reflectivity mirrors, band-pass and band-blocking filters, anti-reflection coatings, and compact high-resolution Fabry-Perot spectrometers with broad freespectral- range. Such components may be integrated directly into airborne/satellite and man-portable sensing instrumentation. We demonstrate a process to produce ultrathin silicon optical elements with an integral raised spacer rim to provide the requisite air gap when these elements are combined directly into a Bragg stack. Laboratory measurements confirm theoretical design specifications. Individual elements may be stacked and bonded to form Bragg mirrors and other thin-film optics.

The research towards more efficient organic molecules for second-order nonlinear optical (NLO) applications has resulted in substantial improvements of the molecular nonlinear polarizabilities. Different strategies for increasing NLO responses at the molecular level in ionic chromophores are reviewed. However, only a small subset of the highly efficient non-centrosymmetric molecules also forms non-centrosymmetric crystals at the bulk level. Examples of success in achieving polar crystals of molecular salts are presented. Such crystals with a high number density of aligned dipolar chromophores are promising materials for efficient second-order NLO applications, such as terahertz generation via difference frequency mixing.

Quad photoreceivers, namely a 2 × 2 array of p-i-n photodiodes followed by a transimpedance amplifier (TIA) per diode, are required as the front-end photonic sensors in several applications relying on free-space propagation with position and direction sensing capability, such as long baseline interferometry, free-space optical communication, missile guidance, and biomedical imaging. It is desirable to increase the active area of quad photoreceivers (and photodiodes) to enhance the link gain, and therefore sensitivity, of the system. However, the resulting increase in the photodiode capacitance reduces the photoreceiver's bandwidth and adds to the excess system noise. As a result, the noise performance of the front-end quad photoreceiver has a direct impact on the sensitivity of the overall system. One such particularly challenging application is the Laser Interferometry Space Antenna (LISA), which proposes to detect gravity waves in space by measuring distance at 1064 nm wavelength with ~10 pm/√Hz accuracy over a baseline of 5,000,000 kilometers. Currently, LISA's sensitivity is restricted by the noise arising from ~20 pF capacitance per quadrant demonstrated by typical 1 mm diameter InGaAs quad photodiodes. We present a 1 mm diameter quad photoreceiver having an equivalent input current noise density of <3.2 pA/√Hz per quadrant up to a 3 dB bandwidth of ~20 MHz. This performance is primarily enabled by a rad-hard-by-design dualdepletion region InGaAs quad photodiode having 2.5 pF capacitance per quadrant, which allows ~17dB improvement in sensitivity over the state-of-the-art. Moreover, the quad photoreceiver demonstrates a crosstalk of <-52 dB between the neighboring quadrants, which ensures a direction sensing resolution of <30 nrad in LISA.

An overview of fiber based components is presented that lead to robust all-fiber lasers and optical amplifiers suitable for space environments. Critical issues impacting the monolithic integration of high power rare earth doped fiber based optical lasers and amplifiers are presented. Optical performance of various all fiber components are reported with emphasis on temperature effects of fiber based pump combiners with polarization maintaining (PM) fiber feed throughs. The all fiber pump combiner is a key component that enables efficient high power pump coupling into double clad rare earth doped optical fibers. A new pump combiner design that injects two fiber coupled pumps plus one PM signal fiber directly into a single polarization maintaining double clad fiber is reported.

In this paper, we reviewed our previous work concerning the responses of rare-earth (RE) doped fibers (Yb, Er and Er/Yb) to various types of radiations like γ-rays, X-rays and protons. For all these harsh environments, the main measured macroscopic radiation-induced effect is an increase of the linear attenuation of these waveguides due to the generation of point defects in the RE-doped core and silica-based cladding. To evaluate the vulnerability of this class of optical fibers for space missions, we characterize the growth and decay kinetics of their radiation-induced attenuation (RIA) during and after irradiation for various compositions. Laboratory testing reveals that this class of optical fibers is very sensitive to radiations compared to passive (RE-free) samples. As a consequence, despite the small length used for space applications, the understanding of the radiation-induced effects in this class of optical fibers becomes necessary before their integration as part of fiber-based systems like gyroscopes or communication systems. In this paper, we more particularly discussed about the relative influence of the rare-earth ions (Er³⁺ and/or Yb³⁺) and of the glass matrix dopants (Al, P, ...) on the optical degradation due to radiations. This has been done by using a set of five prototype optical fibers designed by the fiber manufacturer iXFiber SAS to enlighten the role of these parameters. Additional spectroscopic tools like confocal microscopy of luminescence are also used to detect possible changes in the spectroscopy of the rare-earth ions and their consequences on the functionality of the active optical fibers.

The RD50 collaboration (sponsored by the European Organization for Nuclear Research CERN) has been exploring the development of radiation hard semiconductor devices for very high-luminosity colliders since 2002. The target fluence to qualify detectors set by the anticipated dose for the innermost tracking layers of the future upgrade of the CERN large hadron collider (LHC) is 10¹⁶ 1 MeV neutron equivalent (n_eq) cm⁻². This is much larger than typical fluences in space, but is mainly limited to displacement and total dose damage, without the single-event effects typical for the space environment. RD50 investigates radiation hardening from many angles, including: Search for alternative semiconductor to replace silicon, improvement of the intrinsic tolerance of the substrate material (p- vs. n-type, initial doping concentration, oxygen concentration), optimization of the readout geometry (collection of holes or electrons, surface treatment), novel detector designs (3D, edge-less, interconnects).

Fiber laser is becoming an enabling technology for coherent Lidar applications and free space communications due to its high efficiency, compact size and reliable operation. In these applications, high extinction rate and high OSNR are musts for a fiber laser. However, current Q-switched fiber lasers and solid state lasers cannot meet these criteria. Innovative approach has to be conceived to meet the requirements. In this paper, we will discuss our researches on high energy/power ns pulsed fiber lasers. Modulation schemes for seed laser in getting various optical waveforms to accommodate pulse narrowing in high power amplification and reduce SBS, high power operation of fiber amplifiers, nonlinearity mitigation in high power fiber lasers, and trade-offs among the parameters such as OSNR, power/energy scaling, extinction ratio, interpulses background noise (contrast ratio), and efficiency will be discussed.

Optical fibers are small-in-diameter, light-in-weight, electromagnetic-interference immune, electrically passive, chemically inert, flexible, embeddable into different materials, and distributed-sensing enabling, and can be temperature and radiation tolerant. With appropriate processing and/or packaging, they can be very robust and well suited to demanding environments. In this paper, we review a range of complete end-to-end fiber optic sensor systems that IFOS has developed comprising not only (1) packaged sensors and mechanisms for integration with demanding environments, but (2) ruggedized sensor interrogators, and (3) intelligent decision aid algorithms software systems. We examine the following examples: • Fiber Bragg Grating (FBG) optical sensors systems supporting arrays of environmentally conditioned multiplexed FBG point sensors on single or multiple optical fibers: In conjunction with advanced signal processing, decision aid algorithms and reasoners, FBG sensor based structural health monitoring (SHM) systems are expected to play an increasing role in extending the life and reducing costs of new generations of aerospace systems. Further, FBG based structural state sensing systems have the potential to considerably enhance the performance of dynamic structures interacting with their environment (including jet aircraft, unmanned aerial vehicles (UAVs), and medical or extravehicular space robots). • Raman based distributed temperature sensing systems: The complete length of optical fiber acts as a very long distributed sensor which may be placed down an oil well or wrapped around a cryogenic tank.

A transceiver technology with in-situ diagnostic optical power monitoring for defense applications is presented. The transceiver transmits and receives CWDM optical data signals over a single multimode fiber. Multimode fibers are preferred in many defense applications due to their elevated connectorization ruggedness compared to single mode connectors. The transmitter optical subassembly includes an array of vertical cavity surface emitting lasers, each directly modulated at 10.3125 Gbps resulting in aggregate data rates scalable to 160 Gbps. A small fraction of the optical power emitted from each VCSEL is used to monitor the output power from each individual laser.

A technology for monolithic device integration of lasers and transistors is described. It is based on a GaAs double modulation-doped epitaxial structure creating both n type and p type conduction channels. In the epitaxy, there are total four levels of contacts including a top level p contact, a bottom level n contact, and two intermediate level channel contacts. The device operation is determined by the contact utilization. The laser operation is achieved within a vertical cavity structure. In laser fabrication, ion implantation is used instead of an oxidized AlAs layer to steer the injection current. The main advantage of ion implantation is accuracy in control of the aperture dimension. For a 12μm diameter VCSEL, the threshold is about 1.7mA. Complementary HFETs are obtained using the n and p channels for the n-HFET and p-HFET respectively. The top p layer and the p-channel are used as n-HFET gate contact and collector (back-gate ) contact respectively. The bottom n layer and the n-channel are used as p-HFET gate contact and collector contact respectively. Complementary HFET operation is demonstrated with balanced threshold voltages of about 0.5V and -0.5V for n-HFETs and p-HFETs, respectively. For 1μm gate length n-HFETs, gm~170ms/mm at Vg=1.2V and Vds=4V, which is similar to that of comparable HEMTs. For 1μm gate length p-HFETs, gm~6.5ms/mm at Vg=1.1V and Vds=4V. With better lithography and shorter gate features, higher gm can be expected. These first results indicate that optoelectronic device performance has not been sacrificed by the monolithic integration.

Next generation navigation systems demand performance enhancements to support new applications with longer range capabilities, provide robust operation in severe thermal and vibration environments while simultaneously reducing weight, size and power dissipation. Compact, inexpensive, advanced guidance components are essential for such applications. In particular, Inertial Reference Units (IRUs) that can provide high-resolution stabilization and accurate inertial pointing knowledge are needed. For space applications, an added requirement is radiation hardening up to 300 krad over 5 to 15 years. Manufacturing specifications for the radiation-induced losses are not readily available and empirical test data is required for all components in order to optimize the system performance. Interferometric Fiber-Optic Gyroscopes (IFOGs) have proven to be a leading technology for tactical and navigational systems. The sensors have no moving parts. This ensures high reliability and a long life compared to the mechanical gyroscopes and dithered ring laser gyroscopes. However, the available architectures limit the potential size and cost of the IFOG. The work reported here describes an innovative approach for the design, fabrication, and testing of the IFOG and enables the production of a small, robust and low cost gyro with excellent noise and bandwidth characteristics with high radiation tolerance. The development is aimed at achieving a sensor volume < 5 cubic inches. The new IFOS gyro uses an open loop configuration, utilizes extremely small diameter radiation-hard fiber with customized all-digital signal processing. The optics is packaged using a combination of highly-integrated optical component assemblies with an allfiber approach that leads to a more flexible yet lower cost optical design. The IFOS gyro prototypes are implemented using a distributed architecture, where the light source, electronics and receiver are integrated in an external package, while the sensor head is integrated in a robust and environmentally rigid package. The sensor package design is compatible with the most severe environmental requirements foreseen for the target applications. This paper presents the current state-of-the-art performance of the prototype gyros and the potential for further reduction of size with improved performance. The gyro sample and data rates are extremely high and can be close to the modulation frequency (up to 80 kHz). IFOS has shown that the noise at high frequencies is not flattening out and extremely high bandwidth operation is possible without any degradation of the operational stability. IFOS has also demonstrated the potential for a future, smaller and extremely robust IFOG. The next phase design will include highly radiation-resistant integrated, compact optical circuits based on InP technology that includes the light source, splitter and receiver in one package, a gyro coil that utilizes small diameter, radiation-hard fiber and a small fiber phase modulator with > 300 krad radiation tolerance. This gyro offers the low noise, low drift, low vibration sensitivity, high accuracy, high bandwidth and high radiation tolerance solution required for next generation systems. We will present both theoretical modeling and experimental results obtained to date