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At least 19 records

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NASA NTRS2005

Single mode fiber array for planet detection using a visible nulling interferometer

We report the design, fabrication, and testing of a coherent large mode field diameter fiber array to be used as a spatial filter in a planet finding visible nulling interferometer. The array is a key component of a space instrument for visible-light detection and spectroscopy of Earth like extrasolar planets. In this concept, a nulling interferometer is synthesized from a pupil image of a single aperture which is then spatially filtered by a coherent array of single mode fibers to suppress the residual scattered star light. The use of the fiber array preserves spatial information between the star and planet. The fiber array uses a custom commercial large mode field or low NA step-index single mode fiber to relax alignment tolerances. A matching custom micro lens array is used to couple light into the fibers, and to recollimate the light out of the fiber array. The use of large mode field diameter fiber makes the fabrication of a large spatial filter array with 300 to 1000 elements feasible.

fiber arrays↗

NASA NTRS1985

Particle phase function measurements by a new Fiber Array Nephelometer: FAN 1

A fiber array polar nephelometer of advanced design, the FAN I is capable of in-situ phase function measurements of scattered light from man-made or natural atmospheric particles. The scattered light is measured at 100 different angles throughout 360 degrees, thus providing a potential measurement of the asymmetry of irregularly shaped particles. Phase functions can be measured at 10 to 100 Hz rates and the range of measurable single particle sizes is from 5 micron m to as large as 8mm. For particles smaller than 5 micro m the ensemble average can be measured. The FAN I is microprocessor controlled and the data may be stored on floppy disk or printed out in tabular and/or graphical form. The optical head may be separated from the computer system for operation in field or adverse conditions. Examples of laboratory measured scattering phase functions obtained with the FAN I for spherical particles is given to illustrate its measurement capabilities.

Farmer, W. M.↗

NASA NTRS2011

Optical Fiber Array Assemblies for Space Flight on the Lunar Reconnaissance Orbiter

Custom fiber optic bundle array assemblies developed by the Photonics Group at NASA Goddard Space Flight Center were an enabling technology for both the Lunar Orbiter Laser Altimeter (LOLA) and the Laser Ranging (LR) Investigation on the Lunar Reconnaissance Orbiter (LRO) currently in operation. The unique assembly array designs provided considerable decrease in size and weight and met stringent system level requirements. This is the first time optical fiber array bundle assemblies were used in a high performance space flight application. This innovation was achieved using customized Diamond Switzerland AVIM optical connectors. For LOLA, a five fiber array was developed for the receiver telescope to maintain precise alignment for each of the 200/220 micron optical fibers collecting 1,064 nm wavelength light being reflected back from the moon. The array splits to five separate detectors replacing the need for multiple telescopes. An image illustration of the LOLA instrument can be found at the top of the figure. For the laser ranging, a seven-optical-fiber array of 400/440 micron fibers was developed to transmit light from behind the LR receiver telescope located on the end of the high gain antenna system (HGAS). The bundle was routed across two moving gimbals, down the HGAS boom arm, over a deployable mandrel and across the spacecraft to a detector on the LOLA instrument. The routing of the optical fiber bundle and its end locations is identified in the figure. The Laser Ranging array and bundle is currently accepting light at a wavelength of 532 nm sent to the moon from laser stations at Greenbelt MD and other stations around the world to gather precision ranging information from the Earth to the LRO spacecraft. The LR bundle assembly is capable of withstanding temperatures down to -55 C at the connectors, and 20,000 mechanical gimbal cycles at temperatures as cold as -20 C along the length of the seven-fiber bundle (that is packaged into the gimbals). The total bundle assembly is 10 meters long with two interconnections requiring precise clocking of the seven-fiber array pattern.

Ott, Jelanie↗

NASA NTRS2008

Development, Qualification and Integration of the Optical Fiber Array Assemblies for the Lunar Reconnaissance Orbiter

The NASA Goddard Fiber Optics Team in the Electrical Engineering Division of the Applied Engineering and Technology Directorate, designed, developed and integrated the space flight optical fiber array hardware for the Lunar Reconnaissance Orbiter (LRO). The two new assemblies that were designed and manufacturing at GSFC for the LRO exist in configurations that are unique in the world for the application of ranging and LIDAR. Described here is an account of the journey and the lessons learned from design to integration for the Lunar Orbiter Laser Altimeter and the Laser Ranging Application on the LRO.

Ott, Melanie N.↗

NASA NTRS2008

The Optical Fiber Array Bundle Assemblies for the NASA Lunar Reconnaissance Orbiter

The United States, National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC), Fiber Optics Team in the Electrical Engineering Division of the Applied Engineering and Technology Directorate, designed, developed and integrated the space flight optical fiber array hardware assemblies for the Lunar Reconnaissance Orbiter (LRO). The two new assemblies that were designed and manufactured at NASA GSFC for the LRO exist in configurations that are unique in the world for the application of ranging and lidar. These assemblies were developed in coordination with Diamond Switzerland, and the NASA GSFC Mechanical Systems Division. The assemblies represent a strategic enhancement for NASA's Laser Ranging and Laser Radar (LIDAR) instrument hardware by allowing light to be moved to alternative locations that were not feasible in past space flight implementations. An account will be described of the journey and the lessons learned from design to integration for the Lunar Orbiter Laser Altimeter and the Laser Ranging Application on the LRO. The LRO is scheduled to launch end of 2008.

Ott, Melanie N.↗

NASA NTRS2002

The Surface Interface Characteristics of Vertically Aligned Carbon Nanotube and Graphitic Carbon Fiber Arrays Grown by Thermal and Plasma Enhanced Chemical Vapor Deposition

The development of nano-arrays for sensors and devices requires the growth of arrays with the proper characteristics. One such application is the growth of vertically aligned carbon nanotubes (CNTs) and graphitic carbon fibers (GCFs) for the chemical attachment of probe molecules. The effectiveness of such an array is dependent not only upon the effectiveness of the probe and the interface between that probe and the array, but also the array and the underlaying substrate. If that array is a growth of vertically aligned CNTs or GCFs then the attachment of that array to the surface is of the utmost importance. This attachment provides the mechanical stability and durability of the array, as well as, the electrical properties of that array. If the detection is to be acquired through an electrical measurement, then the appropriate resistance between the array and the surface need to be fabricated into the device. I will present data on CNTs and GCFs grown from both thermal and plasma enhanced chemical vapor deposition. The focus will be on the characteristics of the metal film from which the CNTs and GCFs are grown and the changes that occur due to changes within the growth process.

Delzeit, Lance↗

NASA NTRS2007

High-Reliability Pump Module for Non-Planar Ring Oscillator Laser

We propose and have demonstrated a prototype high-reliability pump module for pumping a Non-Planar Ring Oscillator (NPRO) laser suitable for space missions. The pump module consists of multiple fiber-coupled single-mode laser diodes and a fiber array micro-lens array based fiber combiner. The reported Single-Mode laser diode combiner laser pump module (LPM) provides a higher normalized brightness at the combined beam than multimode laser diode based LPMs. A higher brightness from the pump source is essential for efficient NPRO laser pumping and leads to higher reliability because higher efficiency requires a lower operating power for the laser diodes, which in turn increases the reliability and lifetime of the laser diodes. Single-mode laser diodes with Fiber Bragg Grating (FBG) stabilized wavelength permit the pump module to be operated without a thermal electric cooler (TEC) and this further improves the overall reliability of the pump module. The single-mode laser diode LPM is scalable in terms of the number of pump diodes and is capable of combining hundreds of fiber-coupled laser diodes. In the proof-of-concept demonstration, an e-beam written diffractive micro lens array, a custom fiber array, commercial 808nm single mode laser diodes, and a custom NPRO laser head are used. The reliability of the proposed LPM is discussed.

micro lens array↗

NASA NTRS2013

Fiber Scanning Array for 3 Dimensional Topographic Imaging

We report on the design and development of a fiber optic scanning 3-D LIDAR employing a switched fiber array. This design distributes ns length laser pulses over a sample field, collects the return pulses, and assembles them into a 3-D image. This instrument is a reduced size version consisting of 35 beams, and will serve as a proof-of-principle demonstration for a planned 1000 beam instrument for Earth and planetary topographical missions.

3D↗

NASA NTRS2011

Monolithic, High-Speed Fiber-Optic Switching Array for Lidar

Current fiber switch technologies use mechanical means to redirect light beams, resulting in slow switch time, as well as poor reliability due to moving parts wearing out quickly at high speeds. A non-mechanical ability to switch laser output into one of multiple fibers within a fiber array can provide significant power, weight, and costs savings to an all-fiber system. This invention uses an array of crystals that act as miniature prisms to redirect light as an electric voltage changes the prism s properties. At the heart of the electro-optic fiber-optic switch is an electro- optic crystal patterned with tiny prisms that can deflect the beam from the input fiber into any one of the receiving fibers arranged in a linear array when a voltage is applied across the crystal. Prism boundaries are defined by a net dipole moment in the crystal lattice that has been poled opposite to the surrounding lattice fabricated using patterned, removable microelectrodes. When a voltage is applied across the crystal, the resulting electric field changes the index of refraction within the prism boundaries relative to the surrounding substrate, causing light to deflect slightly according to Snell s Law. There are several materials that can host the necessary monolithic poled pattern (including, but not limited to, SLT, KTP, LiNbO3, and Mg:LiNbO3). Be cause this is a solid-state system without moving parts, it is very fast, and does not wear down easily. This invention is applicable to all fiber networks, as well as industries that use such networks. The unit comes in a compact package, can handle both low and high voltages, and has a high reliability (100,000 hours without maintenance).

Suckow, Will↗

NASA NTRS1992

Reconfigurable optical interconnection network for multimode optical fiber sensor arrays

A single-source, single-detector architecture has been developed to implement a reconfigurable optical interconnection network multimode optical fiber sensor arrays. The network was realized by integrating LiNbO3 electrooptic (EO) gratings working at the Raman Na regime and a massive fan-out waveguide hologram (WH) working at the Bragg regime onto a multimode glass waveguide. The glass waveguide utilized the whole substrate as a guiding medium. A 1-to-59 massive waveguide fan-out was demonstrated using a WH operating at 514 nm. Measured diffraction efficiency of 59 percent was experimentally confirmed. Reconfigurability of the interconnection was carried out by generating an EO grating through an externally applied electric field. Unlike conventional single-mode integrated optical devices, the guided mode demonstrated has an azimuthal symmetry in mode profile which is the same as that of a fiber mode.

Chen, R. T.↗

NASA NTRS1991

Multiple-mode reconfigurable electro-optic switching network for optical fiber sensor array

This paper reports the first switching network compatible with multimode fibers. A one-to-many cascaded reconfigurable interconnection was built. A thin glass substrate was used as the guiding medium which provides not only higher coupling efficiency from multimode fiber to waveguide but also better tolerance of phase-matching conditions. Involvement of a total-internal-reflection hologram and multimode waveguide eliminates interface problems between fibers and waveguides. The DCG polymer graft has proven to be reliable from -180 C to +200 C. Survivability of such an electrooptic system in harsh environments is further ensured. LiNbO3 was chosen as the E-O material because of its stability at high temperatures (phase-transition temperature of more than 1000 C) and maturity of E-O device technology. Further theoretical calculation was conducted to provide the optimal interaction length and device capacitance.

Chen, Ray T.↗

NASA NTRS2011

Three-dimensional range imaging apparatus and method

A three-dimensional range imager includes a light source for providing a modulated light signal, a multiplexer, an optical fiber connecting the light source to the multiplexer, a plurality of optical fibers connected at first ends to the multiplexer and at second ends to a first fiber array, and a transmitter optic disposed adjacent the first fiber array for projecting a pixel pattern of the array onto a target.

Scott, Vibart Stan↗

NASA NTRS2006

Templates for Fabricating Nanowire/Nanoconduit-Based Devices

An effort is underway to develop processes for making templates that could be used as deposition molds and etching masks in the fabrication of devices containing arrays of nanowires and/or nanoconduits. Highly-ordered, optical-fiber arrays consisting of dissimilar polymers comprise the template technology. The selective removal of the fiber cores in specific solvents creates the porous templates to be filled with a "top-down" deposition process such as electrochemical deposition, sputter deposition, molecular beam epitaxy, and the like. Typically, the fiber bundles consist of polystyrene (PS) fiber cores, which are clad with varying thickness poly(methyl methacrylate) (PMMA). When arranged in hexagonal, close-packed configuration and pulled, the fibers form highly-ordered arrays comprised of PS fiber cores surrounded by a continuous matrix of PMMA. The ratio of PMMA cladding thickness to PS core diameter determines the spacing between PS fiber cores and typically ranges from 3:1 to 1:1. Essentially, the simultaneous heating and drawing or pulling in the longitudinal direction of polymer-fiber arrays fuses the fibers together.

Sakamoto, Jeffrey↗

NASA NTRS1993

An analysis of fiber-matrix interface failure stresses for a range of ply stress states

A graphite/bismaleimide laminate was prepared without the usual fiber treatment and was tested over a wide range of stress states to measure its ply cracking strength. These tests were conducted using off-axis flexure specimens and produced fiber-matrix interface failure data over a correspondingly wide range of interface stress states. The absence of fiber treatment, weakened the fiber-matrix interfaces and allowed these tests to be conducted at load levels that did not yield the matrix. An elastic micromechanics computer code was used to calculate the fiber-matrix interface stresses at failure. Two different fiber-array models (square and diamond) were used in these calculations to analyze the effects of fiber arrangement as well as stress state on the critical interface stresses at failure. This study showed that both fiber-array models were needed to analyze interface stresses over the range of stress states. A linear equation provided a close fit to these critical stress combinations and, thereby, provided a fiber-matrix interface failure criterion. These results suggest that prediction procedures for laminate ply cracking can be based on micromechanics stress analyses and appropriate fiber-matrix interface failure criteria. However, typical structural laminates may require elastoplastic stress analysis procedures that account for matrix yielding, especially for shear-dominated ply stress states.

Crews, J. H.↗

NASA NTRS2012

NDT and SHM of Carbon Fiber Composites using Linear Drive MWM-Arrays

Carbon fiber composites are used in a wide range of structural applications due to their excellent specific strength and stiffness. However, the anisotropic mechanical and electrical properties associated with the fibers within each composite layer present challenges, and opportunities, for Nondestructive Testing (NDT) methods used to characterize and assess the structure condition. This includes composite condition after manufacture (such as fiber orientation and density, porosity, delamination, and bond strength) and during usage (such as damage from impact, fiber breakage, thermal exposure or applied stress). Ultrasonic and thermographic methods can address some of these challenges, but eddy current methods provide an alternative method for composite structures that contain a conducting material, such as carbon fibers or a metallic liner. This presentation reviews recent advances in the development of eddy current sensors and arrays for carbon fiber composite NDT and Structural Health Monitoring (SHM) applications. The focus is on eddy current sensor constructs with linear drive windings, such as MWM -Arrays, that induce currents primarily within the linear fibers of the composite. By combining this type of sensor construct with micromechanical models that relate composite constituent properties to measurable sensor responses, insight is obtained into the volumetric distribution of electrical properties within the composite and the associated manufacturing, damage, or strain conditions. With knowledge of the fiber layup, this MWM-Array technology is able to detect damage and strain/stress as a function of depth and fiber orientation. This work has been funded by NASA, NA V AIR and the Army for applications ranging from composite overwrapped pressure vessels (COPVs) to aircraft structures and rotorcraft blades. This presentation will specifically present background on the MWM-Array technology, results from the micromechanical modeling effort, and results from ongoing efforts for high resolution imaging and volumetric strain sensing.

Washabaugh, Andrew↗

NASA NTRS2004

Testing the Predictive Capability of the High-Fidelity Generalized Method of Cells Using an Efficient Reformulation

The High-Fidelity Generalized Method of Cells is a new micromechanics model for unidirectionally reinforced periodic multiphase materials that was developed to overcome the original model's shortcomings. The high-fidelity version predicts the local stress and strain fields with dramatically greater accuracy relative to the original model through the use of a better displacement field representation. Herein, we test the high-fidelity model's predictive capability in estimating the elastic moduli of periodic composites characterized by repeating unit cells obtained by rotation of an infinite square fiber array through an angle about the fiber axis. Such repeating unit cells may contain a few or many fibers, depending on the rotation angle. In order to analyze such multi-inclusion repeating unit cells efficiently, the high-fidelity micromechanics model's framework is reformulated using the local/global stiffness matrix approach. The excellent agreement with the corresponding results obtained from the standard transformation equations confirms the new model's predictive capability for periodic composites characterized by multi-inclusion repeating unit cells lacking planes of material symmetry. Comparison of the effective moduli and local stress fields with the corresponding results obtained from the original Generalized Method of Cells dramatically highlights the original model's shortcomings for certain classes of unidirectional composites.

Arnold, Steven M.↗

NASA NTRS2016

The Fiber Optic System for the Advanced Topographic Laser Altimeter System (ATLAS) Instrument

The Advanced Topographic Laser Altimeter System (ATLAS) Instrument has been in integration and testing over the past 18 months in preparation for the Ice, Cloud and Land Elevation Satellite - 2 (ICESat-2) Mission, scheduled to launch in 2017. ICESat-2 is the follow on to ICESat which launched in 2003 and operated until 2009. ATLAS will measure the elevation of ice sheets, glaciers and sea ice or the "cryosphere" (as well as terrain) to provide data for assessing the earth's global climate changes. Where ICESat's instrument, the Geo-Science Laser Altimeter (GLAS) used a single beam measured with a 70 m spot on the ground and a distance between spots of 170 m, ATLAS will measure a spot size of 10 m with a spacing of 70 cm using six beams to measure terrain height changes as small as 4 mm. The ATLAS pulsed transmission system consists of two lasers operating at 532 nm with transmitter optics for beam steering, a diffractive optical element that splits the signal into 6 separate beams, receivers for start pulse detection and a wavelength tracking system. The optical receiver telescope system consists of optics that focus all six beams into optical fibers that feed a filter system that transmits the signal via fiber assemblies to the detectors. Also included on the instrument is a system that calibrates the alignment of the transmitted pulses to the receiver optics for precise signal capture. The larger electro optical subsystems for transmission, calibration, and signal receive, stay aligned and transmitting sufficiently due to the optical fiber system that links them together. The robust design of the fiber optic system, consisting of a variety of multi fiber arrays and simplex assemblies with multiple fiber core sizes and types, will enable the system to maintain consistent critical alignments for the entire life of the mission. Some of the development approaches used to meet the challenging optical system requirements for ATLAS are discussed here.

global climate changes↗

NASA NTRS2021

Novel Fiber Optic Sensing Arrays with Enhanced Sensitivity in Cryogenic Temperatures

State-of-the-art instrumentation techniques have provided an opportunity to obtain greater insight into the characteristics of cryogenic liquid storage. Optical fiber sensors that utilize fiber Bragg gratings are a viable option for temperature sensing in volatile liquid such as liquid oxygen because there is no risk of electrical sparking and no electromagnetic interference. The National Aeronautics and Space Administration (NASA) Armstrong Flight Research Center (Edwards, California) has developed a novel, simple-to-fabricate fiber array sensor that has been tested and found to be three times more sensitive than typical fiber sensors under cryogenic condition (traditional fiber sensors can suffer from reduced sensitivity below 100 K). Cryogenic temperature monitoring using the NASA fiber optic sensing system is demonstrated in a simulated cryostatic condition, as well as in an elevated pressure environment under liquid nitrogen. Measurement accuracy is compared with traditional silicon diodes. Instrument installation, sensor characteristics, and experimental results are discussed in detail.

Hon Man Chan↗