Thin F-doped cladding, pure silica core optical fibers might be excellent candidates for space applications due to their good resistance to high ionising radiation doses. However, besides radiation, thermally-induced microbending losses might also degrade the transmission of such polyimide-coated fibers at telecommunication wavelengths. In the infrared, this attenuation can reach levels comparable to radiation-induced loss in the visible. To evidence this effect, a worst-case experiment was conducted in which fiber samples (10 m) were wrapped around 54mm diameter aluminum mandrels and heated up to 60°C during irradiation. We compared the results with those obtained by in situ spectral measurements of transmission loss on similar but unirradiated samples. Here, the temperature was cycled between room temperature and 120 °C. Infrared transmission loss increased with temperature but disappeared after cooling back to room temperature. At a wavelength of 1 tm, the temperature-induced loss (reference loss at room temperature) in a polyimide-coated fiber reached 0.4, 0.9 and 2.0 dB/m at 50 °C, 73 °C and 114 °C respectively. Whereas the behavior of polyimide-coated radiation-resistant fibers is strongly influenced by temperature-induced microbending losses, acrylate-coated fibers, however, showed practically no sensitivity of transmission loss to temperature. An aluminium-coated radiation-resistant fiber showed an intermediate sensitivity.

High quality optical fiber to OEIC pigtailing, using non-conventional technology, is required to create a real integrated optical system for optical communications, computing, signal processing, control, and sensing. In this paper, Physical Optics Corporation (POC) presents a novel singlemode fiber to singlemode GaAs channel waveguide pigtailing approach. This pigtailing approach involves two key technologies. First, a fiber end-face lensing technology was used to improve modeprofile matching between singlemode fiber and singlemode channel waveguide, so fiber to waveguide coupling efficiency could be improved. Second, resistance layer assisted dual-carrier-soldering (RLADCS) technology was introduced to facilitate fiber and waveguide chip alignment and fixing, so accurate, convenient, and reliable fiber to optoelectronic integrated cicuit (OEIC) pigtailing could be achieved. By using radiation hardened fiber and special OEIC, this pigtailing and packaging technology has potential applications in a space environment. This publication addresses all aspects of this pigtailing approach, including theoretical analysis, design, fabrication, testing, and measurement results.

Commercial InGaAsP laser diodes were tested for radiation-induced changes in their characteristics when irradiated by gamma and proton radiation at several temperatures. The spectral output, threshold current and frequency response of the laser diodes were measured as a function of dose while maintaining the devices at the three temperatures, 71°C, near ambient and -30°C during the exposures. The laser diodes showed small changes to the threshold current under radiation but in general were resistant to the radiations. The details of the experiments and the temperature dependence observed are presented and the comparative effects of gamma and proton radiation are discussed.

The Midcourse Space Experiment (MSX) is a Ballistic Missile Defense Organization (BMDO) demonstration and validation satellite program that has both defense and civilian applications. MSX has UV, visible, and infrared instruments including the SPIRIT 3 cryogenic telescope. It also has several contamination measuring instruments for measuring pressure, gas species, water and particulate concentrations and condensable gas species. A cryogenic quartz crystal microbalance (CQCM) and four temperature controlled microbalances (TQCMs) are part of this suite of contamination measuring instruments. This paper describes some of the flight QCM data obtained and analyzed to date. The CQCM is located internal to the SPIRIT 3 cryogenic telescope and is mounted adjacent to the primary mirror. Real-time monitoring of contaminant mass deposition on the primary mirror is provided by the CQCM which is cooled to the same temperature as the mirror -20 K. The four TQCMs are mounted on the outside of the spacecraft and monitor contaminant deposition on the external surfaces. The TQCMs operate at -50°C and are positioned strategically to monitor the silicone and organic contaminant flux arriving at the UV and visible instruments, or coming from specific contaminant sources such as the solar panels. During the first week of flight operation, all QCMs recorded deposition in the 10-20 ng/cm2-day (1-2 A/day) range. These TQCM deposition rates have continuously decreased, and after 270 days mission elapsed time (MET), the rates have fallen to values between 0 and 0. 15 A/day depending on TQCM location. Thermogravimetric analyses (TGAs) on the CQCM and TQCMs have provided valuable insight into the amount and species of contaminants condensed.

Free space optical communication between satellites networked together can permit high data rates between different places on earth. In order to establish optical communication between two satellites, the line of sight of their optics must be aligned during the entire communication time. Due to the large distance between the satellites and the required accuracy, the pointing from one satellite to another is complicated. The problem is further complicated due to vibrations of the pointing system caused by two fundamental stochastic mechanisms: 1) tracking noise created by the electro-optic tracker and 2) vibrations deriving from mechanical mechanisms. Vibration of the transmitter beam in the receiver plane causes a decrease in the received optical power. Vibrations of receiver telescope relative to the received beam decrease the heterodyne mixing efficiency. These two factors increase the bit error rate (BER) of the network. In this work we derive simple mathematical models of the network BER versus the system parameters, and the transmitter and receiver vibration statistics. Considering this simple model, we propose four methods to decrease the effects of the vibration on the network performance and to converge to desired performance requirements. An example of a practical optical heterodyne free space satellite optical communication network is presented. From this research it is clear that even low amplitude vibration of the satellite pointing systems decreases dramatically network performance.

Typical camera designs include optical glass elements that ma be affected by the ionizing radiation present in the natuml space environment. Ordinary optical glasses darken at low (10 mcI) dose levels when exposed to ionizing radiation. This darkening decreases the sensitivity ofoptical sensors. Optical glass flats ofFK 51, LaK 9, PK 51A, and ZK N7 were exposed to a 10.6 krad dose of ionizing mdiation. Spectrophotometer tmces determined the transmittance of the samples as a function ofwavelength in the range 350 to 850 nm befoie and at various time inteivals after the irradiation. These measured values were then used to evaluate the rate of recovery or "bleaching" of the exposed samples. To prevent celemted bleaching, the samples were kept at room temperature and away fmm light, except during measurement. Tables of the measuied data and plots of the tmnsmissivity vs. wavelength at various times after irradiation are presented.

A previous paper presented long term bleaching data on various glasses exposed to 10.6 krad of ionizing radiation. All the glasses mported except FK 51 have readily available "G" glass equivalents that are stabilized to the natural space environment. Yet, FK 51, because of its location on the Abbe diagram is extremely useful in certain lens design applications. To more fully explore the bleaching ofFK 51, after the initial dose of 10.6 had at 1 1.8 krad/hour, we inadiated three more samples at a similar dose rate but to different total doses. Since the dose rate for this study was significantly higher than the dose rate anticipated for glasses in a shielded space-based lens system (-3 md/day), additional data wei obtained at a lower rate of 7 md/hour. While this dose rate is still higher than the anticipated operational rate, it is more than 1000 times lower than the dose rate used for our initial studies. The bleaching rate for the samples exposed at the lower dose rate is considerably less than for the samples exposed at the higher rate.

Existing manned airborne platforms are becoming increasingly loaded with additional mission performance requirements. These requirements severely stress weight, mission performance, size and electromagnetic interference (EM!) constraints. In addition, as platforms are reduced in size - such as space-based platforms - these limitations become extremely critical. Optical fiber-based systems can be used to provide both data and RF signal distribution for sensors and avionics. These photonic-based systems are lighter weight, smaller in size, lower in loss, and reduce or eliminate signal interference as compared to existing metallic-based signal distribution systems. These fiber based systems apply to both RF and data transmission in manned and unmanned space-based and airborne platforms as well as ground based applications. Photonics also provides non-frequency dependent true time delay RF signal distribution. This results in the additional benefit of improved interferometric direction finding and beam nulling through software applications in sensor and avionics systems. This paper will discuss research which is underway at Rome Laboratory to develop actively reconfigurable photonic-based signal distribution systems, using either all optical techniques - including optical switching - or through a combination of optics and electronics, to meet the future requirements for avionics and sensors in airborne and space-based platforms.

Many image processing applications require small, low-power, low-cost pattern recognition systems that are capable of locating and identifying objects. Space applications require additional features such as environmental ruggedness, stability, and maintenance-free operation. Miniature optical correlators can perform two-dimensional pattern recognition at greater rates than digital platforms of equivalent size, power and/or weight. The patented Miniature Ruggedized Optical Correlator (MROC) module is built to meet the environmental, size, power, maintenance-free operation and weight requirements of military and commercial space applications, and at a cost that permits wide deployment of the capability. The second version of the MROC module consists of a ferroelectric liquid crystal (PLC) device in the input plane for high light efficiency and incorporates a reflective magneto optic spatial light modulator (RMOSLMTM) device in the filter plane for very high speed operation. MROC II breadboard tests demonstrated excellent correlation peaks, i.e. excellent discrimination (SNR>25), at pattern matching rates of 1920 per second on images of military vehicles.

In some applications of optical communication systems, such as satellite optical communication and atmospheric optical communication, the optical beam wanders on the detector surface due to vibration and turbulence effects, respectively. The wandering of the beam degrades the communication system performance. In this research, we derive a mathematical model of an optical communication system with a detection matrix to improve the system performance for direct detection pulse position modulation (PPM) We include a centroid tracker in the communication system model. The centroid tracker tracks the center of the beam. Using the position of beam center and an apriori model of beam spreading we estimate the optical power on each pixel (element) in the detection matrix. Based on knowledge of the amplitudes of signal and noise in each pixel, we tune adaptively and separately the gain of each individual pixel in the detection matrix for communication signals. Tuning the gain is based on the mathematical model derived in this research. This model is defined as suboptimal due to some approximations in the development and is a suboptimum solution to the optimization problem of n multiplied by m free variables, where U,mare the dimensions of the detection matrix. Comparison is made between the adaptive suboptimum model and the standard model. From the mathematical analysis and the results of the comparison it is clear that this model improves significantly communication system performance.

This paper discusses the pressure spike phenomenon measured by the Total Pressure Sensor (TPS) on the Midcourse Space Experiment (MSX) spacecraft as it passes through aurora! regions. The TPS is an inverted magnetron, cold cathode gauge that has a range of 10'° to i0 Ton and is sampled at a 1 Hertz rate. The operation of the instrument depends uponthe conversion of neutral molecules to ions and the measurement of the resultant current. The TPS has monitored large (>10 fold increase) pressure transients in the auroral regions of the Earth, which have very short temporal width (< 3 seconds). It is shown experimentally that the injection of electrons into the TPS orifice results in a higher apparent pressure measurement, presumably due to an increase in the ion formation rate. An equivalent positive ion flux, however, does not noticeably effect the TPS pressure measurement. It is therefore believed that the on-orbit transients seen by the MSX TPS are consistent with an increased flux of electrons from the auroral regions into the entrance aperture of the gauge. This paper describes ground experiments to quantify the phenomenon with a flight spare TPS and correlates these results to the measurements made onboard the MSX spacecraft.

High quality optical fiber to OEIC pigtailing, using non-conventional technology, is required to create a real integrated optical system for optical communications, computing, signal processing, control, and sensing. In this paper, Physical Optics Corporation (POC) presents a novel singlemode fiber to singlemode GaAs channel waveguide pigtailing approach. This pigtailing approach involves two key technologies. First, a fiber end-face lensing technology was used to improve modeprofile matching between singlemode fiber and singlemode channel waveguide, so fiber to waveguide coupling efficiency could be improved. Second, resistance layer assisted dual-carrier-soldering (RLADCS) technology was introduced to facilitate fiber and waveguide chip alignment and fixing, so accurate, convenient, and reliable fiber to optoelectronic integrated cicuit (OEIC) pigtailing could be achieved. By using radiation hardened fiber and special OEIC, this pigtailing and packaging technology has potential applications in a space environment. This publication addresses all aspects of this pigtailing approach, including theoretical analysis, design, fabrication, testing, and measurement results.

Some of the optical fiber sensors for space in china is presented in this paper. It includes the sensors for measuring nuclear radiation, temperature, strain and stress.

The principle andstructure of a novel fiber optic nuclear radiation sensor (mainly measuthig gamma ray) based on the principle of radiation-induced loss are presented in this paper. Its great advantages over conventional nuclear radiation sensors are discussed as well. Experiment results about radiation-induced losses of different doped elements and different doped concentration of the same element in sensitive fibers as well as iniluences of different read-out wavelengths on experiment results are presented and analyzed. Experiment results and analyses show that this kind of fiber optic nuclear radiation sensor has a vast range ofprospects in many application fields ofnuclear radiation detection.

In this paper some significant developments of guided-wave devices and recent technological advances in optoelectronics for space are described. The performance limits of these devices are highlight in terms of technological problems, power consumption, operating frequency, sizes and weight.