Electrostatic self-assembly (ESA) methods have been used to synthesize multilayered thin film organic/inorganic materials and devices. The ESA method involves the dip coating of charged substrates with alternating layers of anionic and cationic molecules, and the properties of the resulting multilayered structures depend on both the characteristics of the individual molecules and the spatial order of the layers. Since the process is performed at room temperature and pressure by dipping substrates into separate solutions containing the charged molecules, coatings may be formed on substrates of virtually any composition, shape and size. Materials that have been investigated for incorporation into such coatings include noble metal nanoclusters, metal oxide nanoclusters, polymers, cage- structured molecules such as fullerenes, proteins, and dipolar chromophore molecules. Such materials have potential applications in photonic and electronic devices.

The behavior of two nonlinear polymer-modulator materials irradiated by 63.3 MeV protons to a dose of 1 Mrad(Si) is reported. The effects of proton induced ionization and heating in disperse red 1/poly(methylmethacrylate) and in poly(ethylene dioxythiophene)/poly styrene sulphonate/poly(vinyl alcohol) thin films are discussed. Attenuation of the light transmission at an optical wavelength of (lambda) equals 0.6328 micrometers was measured in the polymer films, conductive coatings and their respective substrates. Comparison of these results with a recently reported study of related nonlinear polymer modulator materials exposed to protons is discussed. Conclusions and recommendations regarding the potential application of polymers in the near-Earth space environment are presented.

A nonlinear optic polymer blend of disperse red 1 in poly methyl methacrylate, spin cast on an indium tin oxide coated borosilicate glass substrate and a conductive polymer blend of polyethylene dioxythiophene/poly styrene sulphonate (Baytron P) in poly vinyl alcohol, spin cast on an uncoated borosilicate glass substrate were irradiated by 63.3 MeV proton to a dose of 1 Mrad (Si) of proton particles. The pre and post irradiated optical transmission characteristics of these polymer films over a wavelength range of 400 - 2000 nm, as well as in-situ thermal heating generated by irradiation are presented.

We present a new class of thiophene-based oligomers and polymers with widely tunable photo and electroluminescence properties and which offer great potential for many different areas of application. We were able to synthesize materials displaying high solid-state fluorescence efficiency across the entire visible range. Electroactive polymers emitting light in the near IR were obtained by chemical and/or electrochemical polymerization of oligomers of different length. The polymers also displayed electrochromism, i.e. color change when electric current flowed through the material. All compounds were characterized by great thermo and photooxidative stability. With some of these materials efficient electroluminescent devices were fabricated and characterized.

Recent developments in electro-optic polymer materials and devices have led to new opportunities for integrated optic devices in space environments. The results of numerous tests have indicated that polymer materials have many properties that are suitable to be used in space. These results coupled with recent advances in device and material technology will allow very large bandwidth modulators and switches with drive voltages less than 1 V. At IPITEK, we have already designed and fabricated new polymeric modulators with halfwave voltages less than 0.8 V and a halfwave voltage-interaction product of 2.2 V-cm. The low drive voltage allows electro-optic modulators and switches to be driven directly by high-speed logic devices without the use of broadband amplifiers.

Organic materials for optical applications have received considerably attention in recent years. A particularly large effort has been placed on organic materials for nonlinear optical applications. Organic materials are of special interest because they have the potential to provide unusually large nonlinear optical effects compared to inorganic materials and they can be designed by molecular modeling techniques. We currently know much about the type of materials that make good NLO materials, but useful materials for optical components have been difficult to find because of light absorption at the wavelengths of interest, symmetric crystal formation, and poor physical properties. For long term space applications, an additional concern is the need for the materials to withstand ionizing radiation. The net effect is that most of the materials that are synthesized are not generally useful. We have involved molecular modeling techniques (quantum mechanics and molecular mechanics) as well as crystal engineering in order to reduce the number of materials that must be synthesized. We have had good success with molecular modeling techniques, but crystal modeling methods still need improvement. In our synthetic work we have put a great deal of emphasis on compounds related to dicyanovinylbenzene because of their processability.

Transparent polymeric materials are being designed and utilized as solar concentrating lenses for spacecraft power and propulsion systems. These polymeric lenses concentrate solar energy onto energy conversion devices such as solar cells and thermal energy systems. The conversion efficiency is directly related to the transmissivity of the polymeric lens. The Environmental Effects Group of the Marshall Space Flight Center's Materials, Processes, and Manufacturing Department exposed a variety of material to a simulated space environment and evaluated them for change in optical transmission. These materials include Lexan^TM, polyethylene terephalate, several formulate of Tefzel^TM and Teflon^TM, and silicone DC 93 - 500. Samples were exposed to a minimum of 1000 equivalent sun hours of near ultraviolet radiation (250 - 400 nm wavelength). Prolonged exposure to the space environment will decrease the polymer film's transmission and thus reduce the conversion efficiency. A method was developed to normalize the transmission loss and thus rank the materials according to their tolerance to space environmental exposure. Spectral results and the material ranking according to transmission loss are presented. Power loss over time for a typical solar cell was calculated based on degraded transmission of the polymer material.

We discuss plastic optical fiber technology in the context of its relationship to glass optical fiber technology. POF technology serves as a low cost way to investigate innovative optical fiber material structures. POFs offer some application advantages, especially in low cost broad bandwidth easily interconnected local area networks. Applications to space technology include scintillation sensing and other specialty sensing fibers.

The materials and process technology necessary to fabricate free- standing, circularly-polarizing thin films based on chiral polymer liquid crystalline materials has recently been demonstrated. Free-standing membranes with thicknesses on the order of 10 microns and diameters in excess of 7 cm have been fabricated. The spectrally selective films possess exceptional optical and mechanical properties, exhibiting polarization contrast in excess of 250 with out-of-band transmission greater than 95%. The theory and performance of these filters are presented with specific attention given to the predicted effects of space environments on the durability of this materials technology. Environmental effects to be discussed include wide temperature cycling, radiation and atomic oxygen scavenging.

Optical fiber technology is considered now for communication and sensing applications in various radiation environments, like space and nuclear industry. We report on results from an on-going experimental program, which aims at using multiplexed Fiber Bragg gratings (FBGs), essential photonic components, for in-pile temperature monitoring in a nuclear reactor. To the best of our knowledge, it is the first time that multiplexed FBG-sensors are used in such conditions.

The many advantages of optical fibers for their use in various nuclear environments ushered the respective communities to extensive studies over the last decades. Forecasting the behavior of fiber-optic links exposed to ionizing radiation still remains an important issue. We have developed an industry-aimed pragmatic method based on a simple model for the prediction of radiation induced losses in commercially available optical fibers exposed to ⁶⁰Co gamma rays. When environmental and measurement conditions are well defined, long-term losses could be predicted with a precision of about 15%, for dose rates ranging between 100 Gy/h and 3 kGy/h and total doses up to MGy levels. Thermally induced effects were also considered, between ambient temperature and 80 degree(s)C. From an interpretation of these results, we discuss its applicability and potential further improvements.

In this paper we discuss the dark current increase in CMOS Active pixel Sensors (APS) due to total dose and proton induced damage. We describe measurement results on several diodes that were used to investigate the degradation of the pixel photodiode under ionizing radiation. This study resulted in the design of radiation tolerant pixels that have proven to tolerate at least 200 kGy(Si) total dose from a ⁶⁰Co source. Standard APS sensors show already large degradation after less than 100 Gy(Si) due to a strong surface leakage current increase. Standard CMOS imagers were also evaluated with respect to proton induced damage. Highly energetic protons can displace atoms from their lattice position, giving rise to an increase in mean level of dark current and non-uniformity.

A CMOS APS image sensor test chip, which was designed employing the physical design techniques of enclosed geometry and guard rings and fabricated in a 0.5-micrometers CMOS process, underwent a Co⁶⁰ (gamma) -ray irradiation experiment. The experiment demonstrated that implementing the physical design techniques of enclosed geometry and guard rings in CMOS APS image sensors is possible. It verified that employing these design techniques does not represent a fundamental impediment for the functionality and performance of CMOS APS image sensors. It further proved that CMOS APS image sensors that employ these physical design techniques yield better dark signal performance in ionizing radiation environment than their counterpart that do not employ those physical design techniques. For one of the different pixel designs that were included in the test chip pixel array, the pre- radiation average dark signal was approximately 1.92 mV/s. At the highest total ionizing radiation dose level used in the experiment (approximately 88 Krad(Si)), average dark signal increased to approximately 36.35 mV/s. After annealing for 168 hours at 100 degree(s)C, it dropped to approximately 3.87 mV/s.

The detection of light in the ultraviolet (UV) portion of the electromagnetic spectrum is critical to a number of commercial and military applications. Until very recently, the primary means of light detection in the UV was with either silicon photodiodes or photomultiplier tubes, both of which have serious drawbacks. With the advent of optoelectronic devices fabricated in the ternary alloy of AlGaN, the possibility exists to produce high- performance solid-state photodetector arrays that are sensitive to the visible-blind and solar-blind regions of the spectrum. In this paper, we discuss recent advances in the area of ultraviolet photodetectors fabricated on GaN and AlGaN.

Dynamic scanning and focusing of a laser beam using a robust integrated solid state platform is desirable for many space-based applications including free-space optical communications, target tracking, and optical data storage/processing. Electro-optic devices offer promise as an ideal platform for such applications. However, the relatively low focal powers and scan angles of existing electro-optic devices have limited their use in these areas. Recently, we have applied state of the art fabrication techniques and design optimization to achieve the first integrated lens and scanner device capable of collimating and focusing beams with input diameters of a few microns, then scanning the beam through a large angular range (nearly 20 degrees). The device, fabricated in a bulk LiTaO₃ crystal, is deal for coupling light into or out of channel waveguide or fiber optic systems. We will discuss the expected performance of the existing device in a radiation environment for space-based applications. In addition, we will discuss the expected performance of similarly optimized devices fabricated in other ferroelectric materials, radiation hardened and otherwise.

As a complement to our work developing rapidly-tunable (approximately 10 - 100 kHz) CO₂ lasers for differential absorption lidar (DIAL) applications, we have developed a rapidly-tunable spectrometer. A rapid spectral diagnostic is critical for a high speed DIAL system, since analysis of the return signals depend on knowing the spectral purity of the transmitted beam. The spectrometer developed for our lidar system is based on a double-passed large- (75 mm) aperture acousto-optic deflector, a grating, and a fast single-element room temperature mercury-cadmium-telluride detector. The spectrometer has a resolution of approximately 0.5 cm^-1, a tuning range of 9.0 - 11.4 micrometers , a random-access tuning speed of greater than 80 kHz and a S/N ratio of greater than 100:1. We describe the design and performance of this device, as well as of future devices featuring improved resolution, higher speed and easier and more robust alignment. We will also briefly discuss the applications and limitations of the technique in a space environment.

A MEMS-based, low-power, incandescent light source is being developed. This light source is fabricated using three bonded chips. The bottom chip consists of a reflector on Silicon, the middle chip contains a Tungsten filament bonded to Silicon and the top layer is a transparent window. A 25-micrometers -thick spiral filament is fabricated in Tungsten using lithography and wet- etching. A proof-of-concept device has been fabricated and tested in a vacuum chamber. Results indicate that the filament is electrically heated to approximately 2650 K. The power required to drive the proof-of-concept spiral filament to incandescence is 1.25 W. The emitted optical power is expected to be approximately 1.0 W with the spectral peak at 1.1 micrometers . The micromachining techniques used to fabricate this light source can be applied to other MEMS devices.

The MEMS Technology Group is part of the Microdevices Laboratory (MDL) at the Jet Propulsion Laboratory (JPL). The group pursues the development of a wide range of advanced MEMS technologies that are primarily applicable to NASA's robotic as well as manned exploration missions. Thus these technologies are ideally suited for the demanding requirements of space missions namely, low mass, low power consumption and high reliability, without significant loss of capability. End-to-end development of these technologies is conducted at the MDL, a 38,000 sq. ft. facility with approximately 5500 sq. ft. each of cleanroom (class 10 - 100,000) and characterization laboratory space. MDL facilities include computer design and simulation tools, optical and electron-beam lithography, thin film deposition equipment, dry and wet etching facilities including Deep Reactive Ion Etching, device assembly and testing facilities. Following the fabrication of the device prototypes, reliability testing of these devices is conducted at the state-of-the-art Failure Analysis Laboratory at JPL.

We present an original MOEMS architecture that combines the optical feedback properties of a VCSEL cavity with the nanometer- scale resolution of a GaAs micromachined tip. First, we investigate the effects of external optical feedback on the threshold and spectral characteristics of VCSELs. Second, theoretical analysis and experimental evidence demonstrate the practicability of VCSEL feedback as a principle of optical detection for SNOM microscopy. Finally, we propose a compact architecture of a SNOM sensor with a microtip integrated beneath the VCSEL, report the preliminary results of fabrication of the device, and discuss the opportunity of such architecture in space applications.

Radiation damage in 1310 nm InGaAsP/InP multi-quantum-well lasers caused by 0.8 MeV neutrons is compared with the damage from other radiation sources, in terms of the increase in laser threshold current. The annealing behavior is then presented both in terms of both temperature and forward-bias current dependence. The annealing can be described by a model where radiation induced defects have a uniform distribution of activation energies for annealing. This model can then be used to predict the long-term damage expected for lasers operating inside the CMS tracker.

The CMS tracker slow control system will use approximately 1000 digital optical links for the transmission of timing, trigger and control signals. In this system, the 80 Mbit/s optical receiver at the detector end of each optical link has to be radiation hard since it will operate in the severe radiation environment of the CMS tracker (10 Mrad in 10 years). We have developed a prototype circuit in a 0.25 micrometers commercial CMOS process using radiation tolerant layout practices to achieve the required radiation tolerance. This effective technique consists in the systematic use of enclosed (edgeless) NMOS transistors and guardrings, and relies in the natural total dose hardness of the thin gate oxide of deep submicron processes. The circuit features an Automatic Gain Control loop allowing detection of wide dynamic range input signals (-20 to -3 dBm) with minimum noise, compatible with the maximum expected radiation-induced drop in quantum efficiency of the PIN photodiode. A second feedback loop compensates a photodiode leakage current up to 100 (mu) A, and the circuit outputs an LVDS signal. Four receiver channels were integrated in a 2 X 2 mm² chip, out of which two were simultaneously bonded to two PIN photodiodes, and their Bit Error Rate performance was measured before and after an irradiation with 10 keV x-rays up to 20 Mrad (SiO₂).

ATLAS is a large general-purpose experiment, which will be located at the Large Hadron Collider, LHC. The performance of electronic and optoelectronic components for a 1.28 Gb/s radiation tolerant optical read-out link for the ATLAS liquid argon calorimeter system has been studied. A demonstrator optical link based around the use of the commercial G-link serializer chipset, Vertical Cavity Surface Emitting Laser Diodes and multimode optical fibers, has been built and tested in neutron and gamma radiation environments. The components have been found to be radiation tolerant up to at least a neutron fluence of 1.7 X 10¹³ n(1MeV(Si))/cm² and an ionizing dose of 800 Gy(Si). However, Single-Event Upsets (SEU) in the G-link serializer chip were observed during neutron irradiations. An estimate of the expected ATLAS SEU rate, based on the use of Burst Generation Rate curves for silicon has been performed and leads to an error rate prediction of 2 +/- 1 errors every 100 hours of LHC running.

This paper reports the radiation hardness of optical components to be used in the binary readout of one of the next generation of detectors in high energy physics. The optical components will have to sustain a total ionizing dose of 500 kGy and a 1 MeV equivalent neutron fluence of 10¹⁵ n cm^-2. Emitters of VCSEL type have been chosen and have shown a shift of 1 mA in the laser threshold current after irradiation, but are still suitable for our purpose. The epitaxial Si PIN photodiode receivers have an acceptable 30% drop in responsivity providing a higher reverse bias is applied. Speed and lifetime of both components appear to be unaffected by the radiation damage. Temperature characteristics showing differences from un- irradiated materials will be also presented.

The ATLAS experiment is currently in the final pre-production design phase to allow timely installation at the CERN Large Hadron Collider in 2005. The sub-systems closest to the interaction point--the tracking detectors, will be subject to significant total radiation dose at high flux. Optical data transmission has been chosen for the Pixel and SemiConductor Tracker to both deliver timing and control information to the detector modules and transmit tracking data to the remote counting room. Of considerable concern is the radiation hardness, both transient and total dose, of not just the optoelectronic components but also the driver/receiver electronics. In this paper we report on total dose radiation testing of the VCSEL driver and photodiode receiver ASICs designed using a range of techniques in a nominally radiation-soft process. Both ASICs will be shown to be tolerant to a total gamma dose of 100 kGy and a total neutron fluence (1 MeV equiv.) of 2 X 10¹⁴ n/cm², as required for this system. Single-event upset (SEU) studies have also been carried out using a high-energy pion beam, showing the system to be sufficiently robust to SEU at an ATLAS- like particle flux.

The effect of radiation damage on carrier lifetime in 1310 nm InGaAsP/InP multi-quantum-well lasers irradiated with 0.8 MeV neutrons, was investigated for fluences up to 6.9 X 10¹⁴ n/cm². The damage to the carrier lifetime was studied by measuring the transient response of irradiated lasers to incident optical pulses of 1064 nm and 532 nm wavelength, and by relative intensity noise measurements. The carrier lifetime was determined to be degraded to a similar extent in both the InGaAsP laser cavity and the surrounding InP material following radiation damage.

Predicting the effective life of materials for space applications has become increasingly critical with the drive to reduce mission cost. Programs have considered many solutions to reduce launch costs including novel, low mass materials and thin thermal blankets to reduce spacecraft mass. Determining the long-term survivability of these materials before launch is critical for mission success. This presentation will describe an analysis performed on the outer layer of the passive thermal control blanket of the Hubble Space Telescope. This layer had degraded for unknown reasons during the mission, however ionizing radiation (IR) induced embrittlement was suspected. A methodology was developed which allowed direct comparison between the energy deposition of the natural environment and that of the laboratory generated environment. Commercial codes were used to predict the natural space IR environment, model energy deposition in the material from both natural and laboratory IR sources, and design the most efficient test. Results were optimized for total and local energy deposition with an iterative spreadsheet. This method has been used successfully for several laboratory tests at the Marshall Space Flight Center. The study showed that the natural space IR environment, by itself, did not cause the premature degradation observed in the thermal blanket.

Vacuum degrades the transmittance and catastrophic damage performance of fused-silica surfaces, both bare and silica-sol anti-reflective coated. These effects may be important in certain space application of photonics devices. When exposed to hundreds of 355-nm, 10-ns laser pulses with fluences in the 2 - 15 J/cm² range, transmittance loss is due to both increased reflectance and absorption at the surface. Spectroscopic measurements show that the absorbed light induces broadband fluorescence from the visible to infrared and that the peak photoluminescence wavelength depends cumulative fluence. The effect appears to be consistent with the formation of surface SiO_{x4/ (x < 2} with progressively lower x as cumulative fluence increases. Conversely, low fluence CW UV irradiation of fluorescent sites in air reduces the fluorescence signal, which suggests a photochemical oxidation reaction back to SiO₂. The occurrence of catastrophic damage (craters that grow on each subsequent pulse) also increases in a vacuum relative to air for both coated and uncoated samples.

Intra-core Fiber Bragg Gratings is a candidate technology for a number of future applications in satellite payloads that plan to use multi-wavelength optical links for communicating with other satellites or with ground stations. Applications include wavelength multiplexing and demultiplexing units in multi- wavelength inter-satellite links as well as Add/Drop Multiplexers in the context of broadband satellite constellations using optical networking with on board optical routing. The main advantages of fiber Bragg gratings is that these devices are passive requiring no electric al power, have low mass, and can be compactly packaged. When considered for applications in space the main parameters of concern to be controlled are the stability in wavelength selectivity and throughput loss.

Radiation sensitivity of glass is a general concern for the designer of space optical instruments. It has been proposed that the effect of radiation can be described within the dose coefficient approximation. In the paper we discuss the effect of gamma and proton radiation on the transmission and the refractive index of a number of commercial optical glasses. This experimental study is intended for establishment of a data-base, which will be useful to predict the effect of space radiation on optical systems.

A highly advanced experimental-analytical x-ray diffraction technique for the unique determination of material structure is discussed with respect to its possible application for the characterization of materials used in photonic space devices. The PRXRD technique allows one to determine, in great detail--at the level of a few angstrom, the physical dimensions and fine structure of crystalline materials. During the recent years the technique has been used successfully to determine the defects and fine structure of 1- and 2-D crystal-lattice strain distributions in SiGe- and GaAs-based heterostructures and in silicon crystals implanted with high-energy ions. There are materials that presently used in design of semiconductor lasers, detectors and ultra-high frequency telecommunication devices suitable for space applications. Recent atomic spatial resolution studies have allowed, for the first time, observation and preliminary analysis of surface and interface nano-scale sub-layers, where the crystal structure-factor may noticeably differ from the bulk material.

Research on optical communication behavior in radiative environments is a key point for the design of diagnostic links for the large physic instruments (Laser MegaJoule at CEA, Large Hadron Collider at CERN). For years, the radiation tolerance of several types of emitters (light emitting diode and laser diode (LD)) have been tested with promising results for the LDs. New technologies and devices (Vertical-Cavity Surface-Emitting Lasers (VCSEL)) have recently appeared as promising candidates to replace conventional edge emitting LDs. The shorter wavelength VCSELs (below 1 micrometers ) are well adapted for short distance data links, due to their low threshold current, high efficiency and large possibilities for integration.

Based on a Predevelopment Program, initiated by the European Space Agency, an automatically operating RendezVous Sensor (RVS) is currently developed. This paper describes in more detail the RVS concept emphasizing the electro-optical elements of the sensor.

Based on an ATV RendezVous Predevelopment Program initiated by ESTEC, an automatically operating Rendez Vous Sensor has been developed. The sensor--a Scanning Tele-Goniometer--shall guide docking and retreat of the European Automatic Transfer Vehicle as well as berthing and retreat of the Japanese H-II Transfer Vehicle. The sensor performance will be strongly connected with the properties of cooperative targets, consisting of an arrangement of retro reflectors mounted on ISS each.

This paper describes the design and expected performance of the Laser Range Finder (LRF) as part of the Rendez-Vous Sensor (RVS) on the Automatic Transfer Vehicle and the H II Transfer Vehicle for the International Space Station. The LRF determines the distance between the RVS and a target (retro-reflector) by measuring the time-of-flight of a short laser pulse.

The concentration effect of the spectroscopic properties of Yb³⁺-doped phosphate glasses have been determined from absorption and emission measurements at room temperature. The systematic variations of the spectroscopic properties and laser performance parameters with activator concentration can be used to optimize the doping concentration.

The properties of high rare-earth-containing borosilicate glass have been investigated to assess the potential for using this material to construct electromagnetic calorimeters for particle physics. We report here on measurements of scintillation yield, transmission and decay time, on large blocks of Ce³⁺-doped Gd₂O₃-based glasses, the samples were excited by a high energy X-ray beam and the associated scintillation yield and decay time were measured. The optical transmission of the samples was measured. It was observed that scintillation yield of present scintillation glass is 10 - 20% of BGO scintillation yield, decay time is in range of 60 - 80 ns, glass density is 5.40 g/cm(superscript 3$. It was concluded that higher density and availability and low cost makes this glass become promising candidate for cerium doped dense scintillator.

We have demonstrated that it is possible to product organic light emitting diodes containing lanthanide ions which provide sharp electroluminescence emission at a range of wavelengths in the near infrared including 0.9 micrometers , 0.98 micrometers , 1.064 micrometers , 1.3 micrometers and 1.5 micrometers . For devices grown on ITO substrates we have demonstrated bright electroluminescence at drive voltages of approximately 12 V. We have shown that these diodes can be integrated onto silicon substrates and use the silicon as the anode of the device. For erbium based devices which emit at a wavelength of 1.5 micrometers we have demonstrated devices with room temperature internal efficiencies of approximately 0.01% at a drive voltage of 33 V.