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At least 1,765 records · Page 98

All sources NASA NTRS DOE OSTI

NASA NTRS1985

Development of a new laser Doppler velocimeter for the Ames High Reynolds Channel No. 2

A new two-channel laser Doppler velocimeter developed for the Ames High Reynolds Channel No. 2 is described. Design features required for the satisfactory operation of the optical system in the channel environment are discussed. Fiber optics are used to transmit the megahertz Doppler signal to the photodetectors located outside the channel pressure vessel, and provision is made to isolate the optical system from pressure and thermal strain effects. Computer-controlled scanning mirrors are used to position the laser beams in the channel flow. Techniques used to seed the flow with 0.5-micron-diam polystyrene spheres avoiding deposition on the test-section windows and porous boundary-layer removal panels are described. Preliminary results are presented with a discussion of several of the factors affecting accuracy.

Seegmiller, H. L.↗

NASA NTRS1985

Development of a new laser Doppler velocimeter for the Ames High Reynolds Channel No. II

Seegmiller, H. L.↗

NASA NTRS1991

Growth of Sr(0.61)Ba(0.39)Nb2O6 fibers - New results regarding orientation

The paper describes stable growth of Sr(0.61)Ba(0.39)Nb2O6 (SBN) single-crystal optical fibers (grown by the laser-heated pedestal growth method) along the 100-line and 110-line crystallographic axes. The orientation of SBN fibers was investigated using transmission holograms recorded by focusing two separate, but mutually coherent, optical wavefronts into one end of the fiber. Results showed that the crystal quality of 100-line and 110-line SBN fibers grown at a given pull velocity strongly depended on the fiber diameter; generally, the quality improves with decreasing diameter.

Wilde, Jeffrey P.↗

NASA NTRS1993

Development of simplified external control techniques for broad area semiconductor lasers

The goal of this project was to injection lock a 500 mW broad area laser diode (BAL) with a single mode low power laser diode with injection beam delivery through a single mode optical fiber (SMF). This task was completed successfully with the following significant accomplishments: (1) injection locking of a BAL through a single-mode fiber using a master oscillator and integrated miniature optics; (2) generation of a single-lobed, high-power far-field pattern from the injection-locked BAL that steers with drive current; and (3) a comprehensive theoretical analysis of a model that describes the observed behavior of the injection locked oscillator.

Davis, Christopher C.↗

NASA NTRS2011

Optical source and apparatus for remote sensing

An optical amplifier is configured to amplify an injected seed optical pulse. The optical amplifier may include two or more gain sections coupled to form a continuous solid waveguide along a primary optical path. Each gain section may include: (i) an optical isolator forming an input to that gain section; (ii) a doped optical fiber having a first end coupled to the optical isolator and having a second end; (iii) a plurality of pump laser diodes; (iv) a controller providing drive signals to each of the plurality, the controller being configured to provide at least pulsed drive signals; and (v) an optical coupler having a first input port coupled to the second end, and a second input port coupled to the plurality and an output port.

Coyle, Donald Barry↗

NASA NTRS2011

Optical system and method for gas detection and monitoring

A free-space optical path of an optical interferometer is disposed in an environment of interest. A light beam is guided to the optical interferometer using a single-mode optical fiber. The light beam traverses the interferometer's optical path. The light beam guided to the optical path is combined with the light beam at the end of the optical path to define an output light. A temporal history of the output light is recorded.

Polzin, Kurt A.↗

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 NTRS2016

eLISA Telescope In-field Pointing and Scattered Light Study

The orbital motion of the three spacecraft that make up the eLISA Observatory constellation causes long-arm line of sight variations of approximately ± one degree over the course of a year. The baseline solution is to package the telescope, the optical bench, and the gravitational reference sensor (GRS) into an optical assembly at each end of the measurement arm, and then to articulate the assembly. An optical phase reference is exchanged between the moving optical benches with a single mode optical fiber (“backlink” fiber). An alternative solution, referred to as in-field pointing, embeds a steering mirror into the optical design, fixing the optical benches and eliminating the backlink fiber, but requiring the additional complication of a two-stage optical design for the telescope. We examine the impact of an in-field pointing design on the scattered light performance.

Livas, J↗

DOE OSTI2020

Kinematic chip to chip bonding

The various technologies presented herein relate to integrating an IC having at least one waveguide incorporated therein with a v-groove array IC such that an optical fiber located in a v-groove is aligned relative to a waveguide in the IC maximizing optical coupling between the fiber and the waveguide. The waveguide IC and the v-groove array IC are bonded in a stacked configuration. Alignment of the waveguide IC and the array IC in the stacked configuration enables advantage to be taken of lithographic accuracy of features formed with respect to the Z-direction. Further, kinematic pins and sockets are utilized to provision accuracy in the X- and Z-directions, wherein advantage is taken of the placement accuracy and fabrication tolerance(s) which can be utilized when forming the and sockets. Accordingly, automated alignment of the waveguide IC and the array IC is enabled, facilitating accurate alignment of the respective waveguides and fibers.

42 ENGINEERING↗

NASA NTRS1988

Application of optical and photomechanical techniques in the study of mechanical joints

A fiber-optic technique and the conventional photoelastic technique were applied to the investigation of pin-loaded specimens which simulate pin joints and bolted joints. The angle of contact between the pin and the hole was measured by these techniques and compared with finite element results. The stress distributions obtained form the otoelastic response were also compared with the finite element results. Such comparisons are needed to verify the finite element model and to assess the role of important joint variables such as friction.

Prabhakaran, R.↗

NASA NTRS1997

Poling of Microwave Electro-Optic Devices

The desire to transmit high frequency, microwave RF signals over fiber optic cables has necessitated the need for electro-optic modulation devices. However, in order to reap these potential benefits, it is necessary to develop the devices and their associated fabrication processes, particularly those processes associated with the poling of the devices. To this end, we entered into a cooperative research agreement with Richard Kunath of NASA LeRC. A graduate student in my group, Tony Kowalczyk, worked closely with the group at NASA to develop processes for construction of a microwave frequency electro-optic modulator. Materials were commercially obtained from Amoco Chemical and in collaboration with Lockheed-Martin. The photolithography processes were developed at NASA LeRC and the electric-field poling process was carried out in our laboratory at CWRU. During the grant period, the poling process conditions were investigated for these multilayer devices. Samples were poled and the resulting nonlinear optical properties were evaluated in our laboratory. Following the grant period, Kowalczyk went to NASA under a NRC fellowship, and I continued to collaborate as a consultant. Publications listed at the end of this report came out of this work. Another manuscript is in preparation and will be submitted shortly.

Singer, Kenneth D.↗

NASA NTRS2008

Data Optical Networking Architecture Using Wavelength-Division Multiplexing Method for Optical Sensors

Recently there has been a growth in the number of fiber optical sensors used for health monitoring in the hostile environment of commercial aircraft. Health monitoring to detect the onset of failure in structural systems from such causes as corrosion, stress corrosion cracking, and fatigue is a critical factor in safety as well in aircraft maintenance costs. This report presents an assessment of an analysis model of optical data networking architectures used for monitoring data signals among these optical sensors. Our model is focused on the design concept of the wavelength-division multiplexing (WDM) method since most of the optical sensors deployed in the aircraft for health monitoring typically operate in a wide spectrum of optical wavelengths from 710 to 1550 nm.

Nguyen, Hung D.↗

NASA NTRS2004

Reannealed Fiber Bragg Gratings Demonstrated High Repeatability in Temperature Measurements

Fiber Bragg gratings (FBGs) are formed by periodic variations of the refractive index of an optical fiber. These periodic variations allow an FBG to act as an embedded optical filter, passing the majority of light propagating through a fiber while reflecting back a narrow band of the incident light. The peak reflected wavelength of the FBG is known as the Bragg wavelength. Since the period and width of the refractive index variation in the fiber determines the wavelengths that are transmitted and reflected by the grating, any force acting on the fiber that alters the physical structure of the grating will change the wavelengths that are transmitted and reflected by it. Both thermal and mechanical forces acting on the grating will alter its physical characteristics, allowing the FBG sensor to detect both the temperature variations and the physical stresses and strains placed upon it. This ability to sense multiple physical forces makes the FBG a versatile sensor. To assess the feasibility of using Bragg gratings as temperature sensors for propulsion applications, researchers at the NASA Glenn Research Center evaluated the performance of Bragg gratings at elevated temperatures for up to 300 C. For these purposes, commercially available polyimide-coated high-temperature gratings were used that were annealed by the manufacturer to 300 C. To assure the most thermally stable gratings at the operating temperatures, we reannealed the gratings to 400 C at a very slow rate for 12 to 24 hr until their reflected optical powers were stabilized. The reannealed gratings were then subjected to periodic thermal cycling from room temperature to 300 C, and their peak reflected wavelengths were monitored. The setup shown is used for reannealing and thermal cycling the FBGs. Signals from the photodetectors and the spectrum analyzer were fed into a computer equipped with LabVIEW software. The software synchronously monitored the oven/furnace temperature and the optical spectrum analyzer as well as processed the data. Experimental results presented in the following graph show typical wavelength versus temperature dependence of a reannealed FBG through six thermal cycles (80 hr). The average standard deviation of the temperature-to-wavelength relationship ranged from 1.86 to 2.92 C over the six thermal cycles each grating was subjected to. This is an error of less than 1.0 percent of full scale throughout the entire evaluation temperature range from ambient to 300 C.

Adamovsky, Grigory↗

DOE OSTI2021

Dynamic Tuning of Moiré Excitons in a WSe 2 /WS 2 Heterostructure via Mechanical Deformation

Moiré superlattices in van der Waals (vdW) heterostructures form by stacking atomically thin layers on top of one another with a twist angle or lattice mismatch. The resulting moiré potential leads to a strong modification of the band structure, which can give rise to exotic quantum phenomena ranging from correlated insulators and superconductors to moiré excitons and Wigner crystals. Here, in this study, we demonstrate the dynamic tuning of moiré potential in a WSe 2 /WS 2 heterostructure at cryogenic temperature. We utilize the optical fiber tip of a cryogenic scanning near-field optical microscope (SNOM) to locally deform the heterostructure and measure its near-field optical response simultaneously. The deformation of the heterostructure increases the moiré potential, which leads to a red shift of the moiré exciton resonances. We observe the interlayer exciton resonance shifts up to 20 meV, while the intralayer exciton resonances shift up to 17 meV.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

NASA NTRS1986

Investigation of breadboard temperature profiling system for SSME fuel preburner diagnostics

The feasibility of measuring temperatures in the space shuttle main engine (SSME) fuel preburner using spontaneous Raman scattering from molecular hydrogen was studied. Laser radiation is transmitted to the preburner through a multimode optical fiber. Backscattered Raman-shifted light is collected and focused into a second fiber which connects to a remote-located spectrograph and a mutlichannel optical detector. Optics collimate and focus laser light from the transmitter fiber defining the probe volume. The high pressure, high temperature preburner environment was simulated by a heated pressure cell. Temperatures determined by the distribution of Q-branch co-vibrational transitions demonstrate precision and accuracy of 3%. It is indicated heat preburner temperatures can be determined with 5% accuracy with spatial resolution less than 1 cm and temporal resolution of 10 millisec at the nominal preburner operation conditions.

Shirley, J. A.↗

NASA NTRS1989

Optical pressure sealing coupling apparatus

Apparatus for optically coupling and pressure sealing sections of an instrumentation probe, one of the sections being at a high pressure cryogenic environment and the other section being an ambient pressure. The apparatus includes a housing having a passageway within which elements are mounted for precisely locating a rigid optical fiber coupler and the probe sections so as to optically connect and maintain the ends of the probe sections together to permit signals to pass in both directions through the joint in two or more discrete channels. An adjustable positioning member acts to connect the external section of the probe to the housing in axial and rotation alignment with the interior section.

Timothy B Irvin↗

NASA NTRS1989

High pressure gas scintillation drift chambers with wave shifter fiber readout. I

The authors present results from a prototype xenon-gas scintillation drift chamber. It was operated at pressures up to 20 atm, and the scintillation light yield was measured at various pressures and reduced fields. Scintillation-reduced fields ranged from 1.3 to 3 kV/cm/atm in a 5.4-mm scintillation gap. Drift fields ranged from 45 to 100 V/cm/atm in an 8-cm drift region. The chamber was exposed to an 241Am source in a port either 2.7 or 5.4 cm from the secondary scintillation region. The authors also describe the high-voltage problems encountered during operation at high pressures. Further tests with the wave shifter fiber readout showed that the problem of gas contamination by the fibers is manageable but that the interaction between the optical fibers and the high-pressure xenon gas can lead to fiber damage. A solution to this problem is described.

Parsons, A.↗

NASA NTRS1991

Evaluation and Analysis of the ANSI X3T9.5 (FDDI) PMD and Proposed SMF-PMD as Influenced by Various Fiber Link Characteristics

The purpose of this project is to evaluate the operational parameters of the Kennedy Space Center (KSC) fiber optic cable plant. The evaluation is based on the Fiber Distributed Data Interface (FDDI) Physical Medium Dependent (PMD) and Single Mode Fiber (SMF) PMD standards. From the KSC fiber profile, it would be necessary to develop the modifications needed in existing FDDI PMD and proposed SMF-PMD standards to provide for FDDI implementation and operation at KSC. This analysis should examine the major factors that influence the operating conditions of the KSC fiber plant. These factors would include, but are not limited to the number and type of connectors, attenuation and dispersion characteristics of the fiber, non-standard fiber sizes, modal bandwidth, and many other relevant or significant fiber plant characteristics that effect FDDI characteristics. This analysis is needed to gain a better understanding of overall impact that each of these factors have on FDDI performance at KSC.

Wernicki, M. Chris↗