The wide variety of optoelectronics applications in NASA flight systems and instruments require that optoelectronic technologies meet the demanding requirements of the space environment throughout mission life. These requirements vary widely from intense radiation near Jupiter to the very cold temperatures on the Martian surface to the effects of solar flares in Earth orbit. Considerable work has been performed under the NEPP Program to meet these assurance needs and minimize the risk of insertion of optoelectronics in NASA systems. In this paper we provide recent examples of this work for a variety of NASA mission applications that employ various optoelectronic devices.
With the rapidly increasing insertion of photonic devices, circuits and subsystems into NASA spacecraft, a variety of issues associated with reliability and radiation tolerance have arisen. In this paper, we discuss these issues from the perspective of the work currently ongoing in the NASA Electronic Parts and Packaging (NEPP) Program. This Program is focused on evaluating the reliability and radiation response of advanced and emerging microelectronics and photonics technologies of interest to NASA spacecraft system designers. Examples to be discussed include radiation studies of various optoelectronic devices and reliability of photonic components. These studies have been motivated in part by problems observed in space that include the failure of optocouplers on TOPEX/Poseidon, and the observation of single event-induced transients in the Hubble Space Telescope.
Radiation testing of 980 nm single mode optical fiber, at 120 krads total dose was performed at three temperatures (minus 30 degrees Celsius, plus 96 degrees Celsius, and room temperature). Testing was also performed on samples from different sections of the optical fiber drawn from a single preform that was designed for a lower cutoff wavelength this fiber is referred to as (Flight), and an off-the-shelf (OTS) 980 nm optical fiber from the same manufacture. The results of this data are discussed in this paper and a projection of the damage to the optical fibers over a five year period was done using the nth order kinetic model developed by J. Friebele et al.
A review is given of the effects of radiation on various photonic modulator materials and devices including polymer-based structures, insulator-based devices, semiconductor-based devices, and spatial light modulators. We conclude by providing recommendations for further work in the area of radiation effects in photonic modulators.
The effects of radiation on fused biconical taper wavelength division multiplexers are presented. The polarization sensitivity of these devices before and after irradiation is discussed. Preliminary results on the effects of irradiating different regions of the device, and comparisons between the effects of proton and Co60 radiation sources are also given. A theoretical model that takes into account the index change in the Ge-doped cores of the optical fibers used to make these devices agrees well with experimental observations. This indicates that index changes in the fiber may be primarily responsible for the effects of radiation on these devices.
Following a brief review of the radiation environment encountered by NASA spacecraft, we present examples of the use of fiber optic and optoelectronic components in this environment. Initial results of the fiber optic experiments on the recently retrieved Long Duration Exposure Facility (LDEF) will be presented. Very little radiation induced attenuation was observed during the LDEF flight. Next, we discuss the application of a Fiber Optic Rotation Sensor (FORS) on the JPL CRAF/Cassini missions. For these relatively long missions, reliability is expected to be more of an issue than radiation damage. Finally, we briefly discuss the application of fiber optic data busses to NASA spacecraft. Because of the short fiber lengths required, radiation is not expected to be a serious problem with data link applications.
The effects of neutron irradiation on several properties of both single and multiple stripe laser diodes have been examined. Prior to fast neutron irradiation, total light output as a function of laser current, threshold current, near-field pattern, far-field pattern, and laser output wavelength spectra were measured at room temperature. These measurements were then repeated at intermittent neutron fluence levels. It was observed that the threshold current increased with neutron fluence for all devices examined. In contrast, neutron irradiation had only an indirect effect on the remainder of the laser diode properties in that the higher currents required for operation after irradiation caused variations in these properties.
On the NASA Space Station, the requirement for high speed data transfer between the exterior experimental bays and the interior research facilities has generated the need for fiberoptics. The adverse vacuum effects in space, temperature extremes, and natural space radiation place extreme conditions on optical fiber interconnects. This report addresses the adverse space environmental effects of temperature and radiation on optical fibers.