Melanie N. Ott

Radiation effects data on commercially available optical fiber: database summary

Presented here are the results of a survey performed at NASA Goddard Space Flight Center on radiation data for commercially available optical fiber. The survey includes data from the past decade that can still be used for currently available parts. The objective of this work was to provide a current central location for relevant radiation data on optical fiber that could be useful for space flight projects. Only valid part numbers that are currently relevant to the manufacturers producing the optical fiber and parts that have been verified as changing number but not process, are included in this study. Presented are the currently available optical fiber types with valid part numbers and manufacturer, the relevant radiation data, and the corresponding data reference. Also included in this summary is the recent unreleased radiation data from experiments conducted at Goddard Space Flight Center on OFS (formerly Spectran) 62.5/125/250 micron optical fiber. This database will serve as a tool for engineers when selecting radiation tested optical fiber for future and current optical fiber systems for space flight applications.

Technology validation of optical fiber cables for space flight environments

Periodically, commercially available (commercial off the shelf, COTS) optical fiber cable assemblies are characterized for space flight usage under the NASA Electronic Parts and Packaging Program. The purpose of this is to provide a family of optical fiber cable options to a variety of different harsh environments typical to space flight missions. The optical fiber cables under test are evaluated to bring out known failure mechanisms that are expected to occur during a typical mission. The tests used to characterize COTS cables include: vacuum exposure, thermal cycling and radiation exposure. Presented here are the results of the testing conducted at NASA Goddard Space Flight Center on COTS optical fiber cables over this past year. Several optical fiber cables were characterized for their thermal stability both during and after thermal cycling. The results show how much preconditioning is necessary for a variety of available cables to remain thermally stable in a space flight environment. Several optical fibers of dimensions 100/140/172 microns were characterized for their radiation effects at -125 degree(s)C using the dose rate requirements of International Space Station. One optical fiber cable in particular was tested for outgassing to verify whether an acrylate coated fiber could be used in a space flight optical cable configuration.

On the suitability of fiber optic data links in the space radiation environment: a historical and scaling technology perspective

As NASA, DoD, industry, and others propagate the current spacecraft trends for increasing science data throughput and on-board processing, the use of fiber optic data links between spacecraft subsystems has gained heightened interest. With this is mind, we present a perspective of the use of these fiber optic systems in the space radiation environment that encompasses both the historical past and scaleable future space systems and their requirements.

Twelve-channel optical fiber connector assembly: from commercial off-the-shelf to space flight use

The commercial off the shelf (COTS) twelve channel optical fiber MTP array connector and ribbon cable assembly is being validated for space light use and the results of this study to date are presented here. The interconnection system implemented for the Parallel Fiber Optic Data Bus (PFODB) physical layer will include a 100/140 micron diameter optical fiber in the cable configuration among other enhancements. As part of this investigation, the COTS 62.5/125 micron optical fiber cable assembly has been characterized for space environment performance as a baseline for improving the performance of the 100/140 micron diameter ribbon cable for the Parallel FODB application. Presented here are the testing and results of random vibration and thermal environment characterization of this commercial off the shelf COTS MTP twelve channel ribbon cable assembly. This paper is the first in a series of papers which will characterize and document the performance of Parallel FODBs physical layer from COTS to space flight worthy.

Optical fiber cable assembly characterization for the mercury laser altimeter

For the space flight mission MESSENGER, the Mercury Laser Altimeter (MLA) instrument required highly reliable optical fiber assemblies for the beam delivery system. A custom assembly was designed based on commercially available technologies to accommodate the requirements for the mission. Presented here are the results of environmental testing the MLA optical fiber assemblies. These assemblies consisted of W.L.Gore FLEX-LITETM cable with 200 micron core Polymicro Technologies optical fiber and the Diamond AVIMS connector kits. The assemblies were terminated to the NASA-STD-8739.5 in the Code 562 Advanced Photonics Interconnection Manufacturing Laboratory at NASA Goddard Space Flight Center. The technology validation methods that were used to characterize these assemblies for usage in a space flight environment have been established and well documented. Only the tests that are known to bring out the failure modes typical to optical fiber assemblies have been performed to assess the ability of these assemblies to withstand the environmental parameters that have been established for Mercury Laser Altimeter. Testing involved vacuum, vibration, thermal and radiation exposure and the data with results of those characterization tests are included here. For the radiation characterization, both the 200 micron core FLEX-LITETM (FON1173) and the 300 micron core FLEX-LITETM (FON1174) were tested. For all other environmental tests only the 200 micron core FLEX-LITETM /AVIMs assembly was tested since it was expected that the results of such testing would not differ much with core size.

Recent photonics activities under the NASA Electronic Parts and Packaging (NEPP) program

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.

Applications of optical fiber assemblies in harsh environments: the journey past, present, and future

Over the past ten years, NASA has studied the effects of harsh environments on optical fiber assemblies for communication systems, lidar systems, and science missions. The culmination of this has resulted in recent technologies that are unique and tailored to meeting difficult requirements under challenging performance constraints. This presentation will focus on the past mission applications of optical fiber assemblies, including: qualification information, lessons learned, and new technological advances that will enable the road ahead.

Qualification and Issues with Space Flight Laser Systems and Components

The art of flight quality solid-state laser development is still relatively young, and much is still unknown regarding the best procedures, components, and packaging required for achieving the maximum possible lifetime and reliability when deployed in the harsh space environment. One of the most important issues is the limited and unstable supply of quality, high power diode arrays with significant technological heritage and market lifetime. Since Spectra Diode Labs Inc. ended their involvement in the pulsed array business in the late 1990s, there has been a flurry of activity from other manufacturers, but little effort focused on flight quality production. This forces NASA, inevitably, to examine the use of commercial parts to enable space flight laser designs. System-level issues such as power cycling, operational derating, duty cycle, and contamination risks to other laser components are some of the more significant unknown, if unquantifiable, parameters that directly effect transmitter reliability. Designs and processes can be formulated for the system and the components (including thorough modeling) to mitigate risk based on the known failures modes as well as lessons learned that GSFC has collected over the past ten years of space flight operation of lasers. In addition, knowledge of the potential failure modes related to the system and the components themselves can allow the qualification testing to be done in an efficient yet, effective manner. Careful test plan development coupled with physics of failure knowledge will enable cost effect qualification of commercial technology. Presented here will be lessons learned from space flight experience, brief synopsis of known potential failure modes, mitigation techniques, and options for testing from the system level to the component level.

Electron induced scintillation testing of commercially available optical fibers for space flight

A test to verify the performance of several commercial and military optical fibers available on the market today was conducted, via usage of an electron accelerator, to monitor radiation induced scintillation or luminescence. The test results showed that no significant effects could be detected with the PMT (Photomultiplier Tube) system used, above a noise floor of 50 photons/sec that were due to optical fiber scintillation. Although some data appeared to show events taking place, noise scan results have correlated these events to arcing inside the electron accelerator facility. This test was to simply characterize for space flight, which optical fiber candidates were the largest scintillators among the eighteen optical fiber candidates tested.

Fiber optic cables for transmission of high-power laser pulses

High power pulsed lasers are commonly deployed in harsh environments, like space flight and military missions, for a variety of systems such as LIDAR, optical communications over long distances, or optical firing of explosives. Fiber coupling of the laser pulse from the laser to where it is needed can often save size, reduce weight, and lead to a more robust and reliable system. Typical fiber optic termination procedures are not sufficient for injection of these high power laser pulses without catastrophic damage to the fiber endface. In the current study, we will review the causes of fiber damage during high power injection and discuss methods used to avoid these issues to permit fiber use with high reliability in these applications. A brief review of the design considerations for high peak power laser pulse injection will be presented to familiarize the audience with all the areas that need to be considered during the design phase. The majority of this paper focuses on the proper fiber polishing methods for high power use with an emphasis on laser polishing of the fibers. Results from recently build fibers will be shown to demonstrate the techniques.