A novel multi-mode 5-fiber array assembly was developed, manufactured, characterized and then qualified for the Lunar
Orbiter Laser Altimeter (LOLA). LOLA is a science data gathering instrument used for lunar topographical mapping
located aboard the Lunar Reconnaissance Orbiter (LRO) mission. This LRO mission is scheduled for launch sometime
in late 2008. The fiber portion of the array assembly was comprised of step index 200/220μm multi-mode optical fiber
with a numerical aperture of 0.22. Construction consisted of five fibers inside of a single polarization maintaining (PM)
Diamond AVIM connector. The PM construction allows for a unique capability allowing the array side to be "clocked"
to a desired angle of degree. The array side "fans-out" to five individual standard Diamond AVIM connectors. In turn,
each of the individual standard AVIM connectors is then connected to five separate detectors. The qualification test plan
was designed to best replicate the aging process during launch and long term space flight environmental exposure. The
characterization data presented here includes results from: vibration testing, thermal performance characterization, and
radiation testing.
In the past year, a unique capability has been created by NASA Goddard Space Flight Center (GSFC) in support of
Lunar Exploration. The photonics group along with support from the Mechanical Systems Division, developed a seven
fiber array assembly using a custom Diamond AVIM PM connector for space flight applications. This technology
enabled the Laser Ranging Application for the LRO to be possible. Laser pulses at 532 nm will be transmitted from the
earth to the LRO stationed at the moon and used to make distance assessments. The pulses will be collected with the
Laser Ranging telescope and focused into the array assemblies. The array assemblies span down a boom, through
gimbals and across the space craft to the instrument the Lunar Orbiter Laser Altimeter (LOLA). Through use of a LOLA
detector the distance between the LRO and the Earth will be calculated simultaneously while LOLA is mapping the
surface of the moon. The seven fiber array assemblies were designed in partnership with W.L. Gore, Diamond
Switzerland, and GSFC, manufactured by the Photonics Group at NASA Goddard Space Flight Center (GSFC) and
tested for environmental effects there as well. Presented here are the requirements validation testing and results used to
insure that these unique assemblies would function adequately during the Laser Ranging 14-month mission. The data
and results include in-situ monitoring of the optical assemblies during cold gimbal motion life-testing, radiation,
vibration and thermal testing.
This paper is the first in a series of publications to investigate the use of commercial-off-the-shelf (COTS) components
for space flight fiber laser transmitter systems and LIDAR (laser imaging detection and ranging) detection systems. In
the current study, a hermetically sealed COTS LiNbO3 optical modulator is characterized for space flight applications.
The modulator investigated was part of the family of "High-Extinction Ratio Modulators" with part number MXPE-LN
from Photline Technologies in Besancon, France. Device performance was monitored during exposure to a Cobalt60
gamma-ray source. Results from the testing show little change in device operation for a total accumulated dose of 52
krad.
The photonics group in Code 562 at NASA Goddard Space Flight Center supports a variety of space flight programs at NASA including the: International Space Station (ISS), Shuttle Return to Flight Mission, Lunar Reconnaissance Orbiter (LRO), Express Logistics Carrier (ELC), and the NASA Electronic Parts and Packaging Program (NEPP). Through research, development, and testing of the photonic systems to support these missions much information has been gathered on practical implementations for space environments. Presented here are the highlights and lessons learned as a result of striving to satisfy the project requirements for high performance and reliable commercial optical fiber components for space flight systems. The approach of how to qualify optical fiber components for harsh environmental conditions, the physics of failure and development lessons learned will be discussed.
NASA's Goddard Space Flight Center (GSFC) cooperatively with Sandia National Laboratories completed a series of tests on three separate configurations of multi-fiber ribbon cable and MTP connector assemblies. These tests simulate the aging process of components during launch and long-term space environmental exposure. The multi-fiber ribbon cable assembly was constructed of non-outgassing materials, with radiation-hardened, graded index 100/140-micron optical fiber. The results of this characterization presented here include vibration testing, thermal vacuum monitoring, and extended radiation exposure testing data.
"Qualification" of fiber optic components holds a very different meaning than it did ten years ago. In the past,
qualification meant extensive prolonged testing and screening that led to a programmatic method of reliability assurance.
For space flight programs today, the combination of using higher performance commercial technology, with shorter
development schedules and tighter mission budgets makes long term testing and reliability characterization unfeasible.
In many cases space flight missions will be using technology within years of its development and an example of this is
fiber laser technology. Although the technology itself is not a new product the components that comprise a fiber laser
system change frequently as processes and packaging changes occur. Once a process or the materials for manufacturing
a component change, even the data that existed on its predecessor can no longer provide assurance on the newer version.
In order to assure reliability during a space flight mission, the component engineer must understand the requirements of
the space flight environment as well as the physics of failure of the components themselves. This can be incorporated
into an efficient and effective testing plan that "qualifies" a component to specific criteria defined by the program given
the mission requirements and the component limitations. This requires interaction at the very initial stages of design
between the system design engineer, mechanical engineer, subsystem engineer and the component hardware engineer.
Although this is the desired interaction what typically occurs is that the subsystem engineer asks the components or
development engineers to meet difficult requirements without knowledge of the current industry situation or the lack of
qualification data. This is then passed on to the vendor who can provide little help with such a harsh set of requirements
due to high cost of testing for space flight environments. This presentation is designed to guide the engineers of design,
development and components, and vendors of commercial components with how to make an efficient and effective
qualification test plan with some basic generic information about many space flight requirements. Issues related to the
physics of failure, acceptance criteria and lessons learned will also be discussed to assist with understanding how to
approach a space flight mission in an ever changing commercial photonics industry.`
This paper describes a single micro-optical fiber sensor capable of measuring three strains simultaneously in a composite structure subjected to ballistic impact. The development of the sensor fabrication and signal processing techniques and finite element analysis are provided.
This paper investigates a method of producing internal mirrors for Intrinsic Fabry-Perot Sensors that have the potential for improving sensor strength. This approach is based on deposited mirrors on only the core of the fiber. Finite Element stress analysis and reflectivity modeling were used to determine appropriate coating thicknesses. TiO2 sol-gels coatings were then developed to deliver the exact thicknesses and optical properties needed for a thin film partially reflective mirror. A reverse photo resist masking method was developed in order to selectively deposit the TiO2 on the core. The results presented in this paper suggest that the core mirror concept shows promise, but that much work is still required to complete its development.
This paper describes a single micro-optical fiber sensor capable of measuring three strains simultaneously in a composite structure. This single transducer is based on cascading four micro Fabry-Perot cavities to measure three normal strains and one shear strain in the plane of the optical fiber cross-section. The development of the sensor fabrication and signal processing techniques are discussed. This fabrication includes designing and fabricating new optical fibers, optical fiber circuit, and optical fiber multi-strain sensor head. This paper presents 2D and 3D finite element analysis and 2D closed form analysis to establish the transformation between fiber core and composite host strain stats. FEM is also used to design side-hole fiber for maximized sensitivity to transverse strains. Finally, analytical models are presented for expressing the desired strains in the host composite in terms of the measured optical phase shift in the fiber sensor.
An optical fiber sensor for simultaneous measurement of axial strain and temperature is reported. This sensor configuration consists of an in-line fiber etalon cascaded with a in-fiber Bragg grating and demultiplexed using a variation of coherence division multiplexing. The strain/temperature sensor is demonstrated by bonding it to the surface of an aluminum cantilever beam and embedding it into a graphite/epoxy composite cantilever beams. They are found to agree with traditional strain and temperature sensors to within 5 (mu) (epsilon) and 0.5 degree(s)C, respectively for a sensor gage length of approximately 1.0 cm.
A novel compensation technique for polarization-modulated optical fiber sensors is proposed, which employs a single LED to provide the measurement and the reference signals. In the sensor head, a polarization beam splitter is used not only as a polarizer, but also as an analyzer, and the reflective structure is used so that the sensor head is simple, compact and reliable. A loss-compensated temperature sensor based on the thermal effect of birefringent crystal is demonstrated. The experimental results show that this compensation technique can stabilize the sensor output with a high accuracy and better long-term stability.
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