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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Fiber-Optic Sensor for Aircraft Lightning Current Measurement

An electric current sensor based on Faraday rotation effect in optical fiber was developed for measuring aircraft lightning current. Compared to traditional sensors, the design has many advantages including the ability to measure total current and to conform to structure geometries. The sensor is also small, light weight, non-conducting, safe from interference, and free of hysteresis and saturation. Potential applications include characterization of lightning current waveforms, parameters and paths, and providing environmental data for aircraft certifications. In an optical fiber as the sensing medium, light polarization rotates when exposed to a magnetic field in the direction of light propagation. By forming closed fiber loops around a conductor and applying Ampere s law, measuring the total light rotation yields the enclosed current. A reflective polarimetric scheme is used, where polarization change is measured after the polarized light travels round-trip through the sensing fiber. The sensor system was evaluated measuring rocket-triggered lightning over the 2011 summer. Early results compared very well against a reference current shunt resistor, demonstrating the sensor's accuracy and feasibility in a lightning environment. While later comparisons show gradually increasing amplitude deviations for an undetermined cause, the overall waveforms still compared very well.

Nguyen, Truong X.↗
NASA NTRS2012

Fiber-Optic Sensor for Aircraft Lightning Current Measurement

An electric current sensor based on Faraday rotation effect in optical fiber was developed for measuring aircraft lightning current. Compared to traditional sensors, the design has many advantages including the ability to measure total current and to conform to structure geometries. The sensor is also small, light weight, non-conducting, safe from interference, and free of hysteresis and saturation. Potential applications include characterization of lightning current waveforms, parameters and paths, and providing environmental data for aircraft certifications. In an optical fiber as the sensing medium, light polarization rotates when exposed to a magnetic field in the direction of light propagation. By forming closed fiber loops around a conductor and applying Ampere s law, measuring the total light rotation yields the enclosed current. A reflective polarimetric scheme is used, where polarization change is measured after the polarized light travels round-trip through the sensing fiber. The sensor system was evaluated measuring rocket-triggered lightning over the 2011 summer. Early results compared very well against a reference current shunt resistor, demonstrating the sensor s accuracy and feasibility in a lightning environment. While later comparisons show gradually increasing amplitude deviations for an undetermined cause, the overall waveforms still compared very well.

Nguyen, Truong X.↗
NASA NTRS1974

Study of glass preforms for glass fiber optics applications (study of space processing of ceramic materials)

The feasibility, and technical and economic desirability was studied of space processing of glass preforms for optical fiber transmission applications. The results indicate that space processing can produce glass preforms of equal quality at lower cost than earth bound production, and can produce diameter modulation in the glass preform which promotes mode coupling and lowers the dispersion. The glass composition can be modified through the evaporative and diffusion processes, and graded refractive index profiles can be produced. A brief summary of the state of the art in optical fiber transmission is included.

Wang, F. F. Y.↗
NASA NTRS1981

Fiber optics transmission of LV signal

The first use of a long optical fiber for transmitting megahertz frequencies in a laser velocimeter (LV) receiver system is reported. The fiber comprises a 600-micron diameter fused silica core, a silicon polymer cladding and a plastic jacket. The fiber numerical aperture is 0.22, corresponding to a maximum entrance half-angle of 0.22 rad. The 10-m length used results in a 5.6% attenuation loss. The fiber is found to transmit an 80-MHz signal with excellent resolution. It is established that an LV receiver using fiber optics sends a clean signal in electronically noisy and high-pressure environments and allows velocity measurements in places too small for a photomultiplier tube.

Young, A. D.↗
NASA NTRS1985

Remote displacement measurement using a passive interferometer with a fiber-optic link

Remote displacement measurement is demonstrated using a Fabry-Perot cavity with a multimode optical fiber link. The sensing cavity modulates, as a function of its length, the spectrum of a light-emitting diode (LED). The light returns via the fiber and is analyzed by a tunable reference cavity. A closed-loop control causes the reference cavity to track the sensing cavity length within 2 x 10 to the -12th m. Displacement range is 2 x 10 to the -6th m. The reference cavity length is measured interferometrically, using a laser, to obtain the sensing cavity length. Advantages of this sensing technique include compatibility with multimode fiber-optic components, high immunity to optical losses, and large dynamic range.

Beheim, G.↗
NASA NTRS1989

Advanced Components For Fiber-Optical Systems

Paper reviews statuses of some advanced passive and active optical components for use with optical fibers. Emphasis on highly birefringent components controling polarization, because control of polarization critical in applications as fiber-optical gyroscopes, interferometric sensors, and coherent communications.

Depaula, Ramon↗
NASA NTRS1988

Use of optical fibers in spectrophotometry

The use of single or small numbers of fiber optic fibers in astronomical spectroscopy with the goal of greater spectrophotometric and radial velocity accuracy is discussed. The properties of multimode step index fibers which are most important for this application are outlined, as are laboratory tests of currently available fibers.

Ramsey, Lawrence W.↗
NASA NTRS1991

Active control for vibration suppression in a flexible beam using a modal domain optical fiber sensor

An account is given of the use of a modal-domain (MD) fiber-optic sensor as an active control system component for vibration suppression, whose output is proportional to the integral of the axial strain along the optical fiber. When an MD sensor is attached to, or embedded in, a flexible structure, it senses the strain in the structure along its gage length. On the basis of the present integration of the sensor model into a flexible-structure model, it becomes possible to design a control system with a dynamic compensator which adds damping to the low-order modes of the flexible structure. This modeling procedure has been experimentally validated.

Cox, D. E.↗
NASA NTRS1993

Silicon-Etalon Fiber-Optic Temperature Sensor

Developmental temperature sensor consists of silicon Fabry-Perot etalon attached to end of optical fiber. Features immunity to electrical interference, small size, light weight, safety, and chemical inertness. Output encoded in ration of intensities at two different wavelengths, rather than in overall intensity, with result that temperature readings not degraded much by changes in transmittance of fiber-optic link.

Beheim, Glenn↗
NASA NTRS1994

Fiber Optic Switch For Broadband Emission Spectroscopy

Many high-temperature processes comprise large-scale phenomena. Studying spatial and temporal correlations of physical processes between several locations within characteristic scales provides desired information on macroscopic physical processes. Achieved with emission spectroscopy by use of multiple optical fibers. Simultaneous coupling of light from these fibers into single available spectrometer and/or monochromator not accomplished without added expense of two-dimensional array and increased complexity of calibration. Quasi-simultaneous coupling, while maintaining optimum alignment and maximum throughput of broadband emission, achieved by use of fiber optic multiscanner. Instrument used successfully in study of frozen-flow losses internal to flow of plasma inside nozzle of arc jet. Instrument includes two hollow disks of different sizes and stepping motor.

De Groot, Wim↗
NASA NTRS2001

Application of a Fiber Optic Distributed Strain Sensor System to Woven E-Glass Composite

A distributed strain sensing system utilizing a series of identically written Bragg gratings along an optical fiber is examined for potential application to Composite Armored Vehicle health monitoring. A vacuum assisted resin transfer molding process was used to fabricate a woven fabric E-glass/composite panel with an embedded fiber optic strain sensor. Test samples machined from the panel were mechanically tested in 4-point bending. Experimental results are presented that show the mechanical strain from foil strain gages comparing well to optical strain from the embedded sensors. Also, it was found that the distributed strain along the sample length was consistent with the loading configuration.

Anastasi, Robert F.↗
NASA NTRS2004

The Application of Fiber Optic Wavelength Division Multiplexing in RF Avionics

This paper demonstrates a successful application of wavelength division multiplexing (WDM) to the avionics environment to support analog RF signal transmission. We investigate the simultaneous transmission of four RF signals (channels) over a single optical fiber. These four analog channels are sequentially multiplexed and demultiplexed at different points along a fiber optic backbone to more closely emulate the conditions found onboard aircraft. We present data from measurements of signal-to-noise ratio (SNR), transmission response (loss and gain), group delay that defines phase distortion, and dynamic range that defines nonlinear distortion. The data indicate that WDM is well-suited for avionics applications.

Ngo, Duc↗
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 NTRS2014

An Intrinsic Fiber-Optic Sensor for Structure Lightning Current Measurement

An intrinsic optical-fiber sensor based on Faraday Effect is developed that is highly suitable for measuring lightning current on aircraft, towers and complex structures. Originally developed specifically for aircraft installations, it is light-weight, non-conducting, structure conforming, and is immune to electromagnetic interference, hysteresis and saturation. It can measure total current down to DC. When used on lightning towers, the sensor can help validate other sensors and lightning detection network measurements. Faraday Effect causes light polarization to rotate when the fiber is exposed to a magnetic field in the direction of light propagation. Thus, the magnetic field strength can be determined from the light polarization change. By forming closed fiber loops and applying Ampere's law, measuring the total light rotation yields the total current enclosed. A broadband, dual-detector, reflective polarimetric scheme allows measurement of both DC component and AC waveforms with a 60 dB dynamic range. Two systems were built that are similar in design but with slightly different sensitivities. The 1310nm laser system can measure 300 A - 300 kA, and has a 15m long sensing fiber. It was used in laboratory testing, including measuring current on an aluminum structure simulating an aircraft fuselage or a lightning tower. High current capabilities were demonstrated up to 200 kA at a lightning test facility. The 1550nm laser system can measure 400 A - 400 kA and has a 25m fiber length. Used in field measurements, excellent results were achieved in the summer of 2012 measuring rocket-triggered lightning at the International Center for Lightning Research and Testing (ICLRT), Camp Blanding, Florida. In both systems increased sensitivity can be achieved with multiple fiber loops. The fiber optic sensor provides many unique capabilities not currently possible with traditional sensors. It represents an important new tool for lightning current measurement where low weight, complex shapes, large structure dimension, large current, and low frequency capabilities are important considerations.

Nguyen, Truong X.↗
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↗
NASA NTRS1994

Fiber optic attenuator

A fiber optic attenuator of the invention is a mandrel structure through which a bundle of optical fibers is wrapped around in a complete circle. The mandrel structure includes a flexible cylindrical sheath through which the bundle passes. A set screw on the mandrel structure impacts one side of the sheath against two posts on the opposite side of the sheath. By rotating the screw, the sheath is deformed to extend partially between the two posts, bending the fiber optic bundle to a small radius controlled by rotating the set screw. Bending the fiber optic bundle to a small radius causes light in each optical fiber to be lost in the cladding, the amount depending upon the radius about which the bundle is bent.

Buzzetti, Mike F.↗
NASA NTRS1983

Fiber optic temperature sensor

A temperature sensor has been developed that utilizes the temperature dependent absorption of a rare earth doped optical fiber. The temperature measurement is localized at a remote position by splicing a short section of the rare earth fiber into a loop of commercial data communication fiber that sends and returns an optical probe signal to the temperature sensitive section of fiber. The optical probe signal is generated from two different wavelength filtered LED sources. A four port fiber optic coupler combines the two separate wavelength signals into the fiber sensing loop. Time multiplexing is used so that each signal wavelength is present at a different time. A reference signal level measurement is also made from the LED sources and a ratio taken with the sensor signal to produce a transmission measurement of the fiber loop. The transmission is affected differently at each wavelength by the rare earth temperature sensitive fiber. The temperature is determined from a ratio of the two transmission measurements. This method eliminates any ambiguity with respect to changes in signal level in the fiber loop such as mating and unmating optical connectors. The temperature range of the sensor is limited to about 800 C by the temperature limit fo the feed fibers.

Morey, W. W.↗