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At least 181 records · Page 10

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NASA NTRS2008

Vibration Performance Comparison Study on Current Fiber Optic Connector Technologies

Fiber optic cables are increasingly being used in harsh environments where they are subjected to vibration. Understanding the degradation in performance under these conditions is essential for integration of the fibers into the given application. System constraints oftentimes require fiber optic connectors so subsystems can be removed or assembled as needed. In the present work, various types of fiber optic connectors were monitored in-situ during vibration testing to examine the transient change in optical transmission and the steady-state variation following the event. Inspection of the fiber endfaces and connectors was performed at chosen intervals throughout the testing.

Ott, Melanie N.↗

NASA NTRS1988

Optical isolator system for fiber-optic uses

A low loss optical isolator suitable for fiber-optic uses has been assembled from commercial components. The isolator exhibits reverse isolation of greater than 70 dB, with a forward loss of less than 1.3dB. This system provides an effective approach for reducing instabilities encountered in the output signal of semiconductor lasers in certain applications of fiber-optic systems. The paper presents a phenomenological explanation for the superior performance of the isolator system.

Lutes, George↗

DOE OSTI2023

Glass Additive and Subtractive Manufacturing of a Fiber Optic Rotary Encoder for Downhole Pressure Sensing

This article presents a fiber optic rotary encoder-based pressure sensor for downhole applications. The rotary encoder, which is composed of an encoding pad and an all-glass optical fiber sensing head, converts the rotation angles of a pressure transducer to digital codes. The optical fiber only serves as the telemetry channel to directly transmit the data in digital format such that the environmental temperature influence and the long-time drift are minimized. The glass additive and subtractive manufacturing (ASM) techniques are used to embed the multichannel optical fibers into a bulk-fused silica glass substrate. Because the fused silica glass shares a similar material property to the optical fiber (e.g., thermal expansion coefficient), the optical fiber sensing head is well sealed and fixed even at an elevated temperature. The picosecond laser blackening technique is used to fabricate the high reflectivity contrast encoding pad with high accuracy. Here, the proposed pressure sensor was manufactured and experimentally verified to have a signal-to-noise ratio (SNR) of 23 dB and a linear pressure response with a root-mean-square error (RMSE) of 0.37. During the 400-h 250 °C long-term stability test, there was no digital code variation. In addition, a mathematical model to study the relationships between the sensor’s performances and design parameters was established. According to the model, a 12-bit encoder (0.02% pressure sensitivity) can be achieved with a radius of 20 mm.

02 PETROLEUM↗

NASA NTRS2002

Detection, Evaluation, and Optimization of Optical Signals Generated by Fiber Optic Bragg Gratings Under Dynamic Excitations

The dynamic response of a fiber optic Bragg grating to mechanical vibrations is examined both theoretically and experimentally. The theoretical expressions describing the consequences of changes in the grating's reflection spectrum are derived for partially coherent beams in an interferometer. The analysis is given in terms of the dominant wavelength, optical bandwidth, and optical path difference of the interfering signals. Changes in the reflection spectrum caused by a periodic stretching and compression of the grating were experimentally measured using an unbalanced Michelson interferometer, a Michelson interferometer with a non-zero optical path difference. The interferometer's sensitivity to changes in dominant wavelength of the interfering beams was measured as a function of interferometer unbalance and was compared to theoretical predictions. The theoretical analysis enables the user to determine the optimum performance for an unbalanced interferometer.

Adamovsky, Grigory↗

NASA NTRS1991

Annealing of linear birefringence in single-mode fiber coils - Application to optical fiber current sensors

Annealing procedures that greatly reduce linear birefringence in single-mode fiber coils are described. These procedures have been successfully applied to coils ranging from 5 mm to 10 cm in diameter and up to 200 or more turns. They involve temperature cycles that last 3-4 days and reach maximum temperatures of about 850 C. The residual birefringence and induced loss are minimized by proper selection of fiber. The primary application of these coils is optical fiber current sensors, where they yield small sensors that are more stable than those achieved by other techniques. A current sensor with a temperature stability of 8.4 x 10 to the -5th/K over the range from -75 to 145 C has been demonstrated. This is approximately 20 percent greater than the temperature dependence of the Verdet constant. Packaging degrades the stability, but a packaged sensor coil with a temperature stability of about 1.6 + 10 to the -4th/K over the range from -20 to 120 C has also been demonstrated.

Tang, Dingding↗

NASA NTRS1994

Fiber-Optic Terahertz Data-Communication Networks

Network protocols implemented in optical domain. Fiber-optic data-communication networks utilize fully available bandwidth of single-mode optical fibers. Two key features of method: use of subpicosecond laser pulses as carrier signals and spectral phase modulation of pulses for optical implementation of code-division multiple access as multiplexing network protocol. Local-area network designed according to concept offers full crossbar functionality, security of data in transit through network, and capacity about 100 times that of typical fiber-optic local-area network in current use.

Chua, Peter L.↗

NASA NTRS1987

Integrated optics implementation of a fiber optic rotation sensor - Analysis and development

The Jet Propulsion Laboratory is developing a fiber optic rotation sensor (FORS) for use on the Mariner Mark II series of planetary explorer craft and in other space applications. FORS is a closed-loop phase-nulling device and embodies a number of interesting innovations. Chief among these are the incorporation of the device's couplers, phase modulators, and polarizer on a single lithium niobate (LinbO3) integrate optics chip and a novel means of reading out angular position and rotation rate based on optical beat detection. Various aspects of the FORS design and operation are described and discussed. Particular attention is paid to analyzing errors attributable to polarizer imperfection and the so-called residual Michelson effect.

Bartman, R. K.↗

NASA NTRS1993

Flight testing of a fiber optic temperature sensor

A fiber optic temperature sensor (FOTS) system consisting of an optical probe, a flexible fiber optic cable, and an electro-optic signal processor was fabricated to measure the gas temperature in a turbine engine. The optical probe contained an emissive source embedded in a sapphire lightguide coupled to a fiber-optic jumper cable and was retrofitted into an existing thermocouple probe housing. The flexible fiber optic cable was constructed with 200 micron core, polyimide-coated fiber and was ruggedized for an aircraft environment. The electro-optic signal processing unit was used to ratio the intensities of two wavelength intervals and provided an analog output value of the indicated temperature. Subsequently, this optical sensor system was installed on a NASA Dryden F-15 Highly Integrated Digital Electronic Control (HIDEC) Aircraft Engine and several flight tests were conducted. Over the course of flight testing, the FOTS system's response was proportional to the average of the existing thermocouples sensing the changes in turbine engine thermal conditions.

Finney, M. J.↗

NASA NTRS1987

Fiber optic and laser sensors IV; Proceedings of the Meeting, Cambridge, MA, Sept. 22-24, 1986

The conference presents papers on industrial uses of fiber optic sensors, point and distributed polarimetric optical fiber sensors, fiber optic electric field sensor technology, micromachined resonant structures, single-mode fibers for sensing applications, and measurement techniques for magnetic field gradient detection. Consideration is also given to electric field meter and temperature measurement techniques for the power industry, the calibration of high-temperature fiber-optic microbend pressure transducers, and interferometric sensors for dc measurands. Other topics include the recognition of colors and collision avoidance in robotics using optical fiber sensors, the loss compensation of intensity-modulating fiber-optic sensors, and an embedded optical fiber strain tensor for composite structure applications.

De Paula, Ramon P.↗

NASA NTRS2001

Utilization of Infrared Fiber Optic in the Automotive Industry

Fiber optics are finding a place in the automotive industry. Illumination is the primary application today. Soon, however, fiber optics will be used for data communications and sensing applications. Silica fiber optics and plastic fibers are sufficient for illumination and communication applications however, sensing applications involving high temperature measurement and remote gas analysis would benefit from the use of infrared fiber optics. Chalcogonide and heavy metal fluoride glass optical fibers are two good candidates for these applications. Heavy metal fluoride optical fibers are being investigated by NASA for applications requiring transmission in the infrared portion of the electromagnetic spectrum. Zirconium-Barium-Lanthanum-Aluminum-Sodium-Fluoride (ZBLAN) is one such material which has been investigated. This material has a theoretical attenuation coefficient 100 times lower than that of silica and transmits into the mid-IR. However, the measured attenuation coefficient is higher than silica due to impurities and crystallization. Impurities can be taken care of by utilizing cleaner experimental protocol. It has been found that crystallization can be suppressed by processing in reduced gravity. Fibers processed in reduced gravity on the KC135 reduced gravity aircraft were found to be free of crystals while those processed on the ground were found to have crystals. These results will be presented along with plans for producing continuous lengths of ZBLAN optical fiber on board the International Space Station.

Tucker, Dennis S.↗

NASA NTRS1982

Optical crystal temperature gauge with fiber optic connections

An optical temperature gauge uses a semiconductor crystal with a band-edge shift property which is temperature dependent. An external narrow band light source provides optical excitation through a optical fiber and light energy thus passed through the crystal is conveyed by a second optical fiber to a light-to-electric transducers at an external location. The crystal can be located in cryogenic or other systems, to provide remote read-out. The light wavelength is varied (scanned) in a repetitive pattern in source with the instantaneous wavelength passing over the band-edge wavelength during each cycle of the scan. The timing of the crossover is related to the temperature of the crystal by electronic means. Several alternative elements of instrumentation are disclosed. A variation in the basic measurement apparatus is also disclosed, in which the band gap voltage of a light source such as a laser diode is evaluated at the time of band-edge crossover in the crystal and converted to a temperature value.

Sharma, M. M.↗

NASA NTRS1987

AVIRIS foreoptics, fiber optics and on-board calibrator

The foreoptics, fiber optic system and calibration source of the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) are described. The foreoptics, based on a modified Kennedy scanner, is coupled by optical fibers to the four spectrometers. The optical fibers allow convenient positioning of the spectrometers in the limited space and enable simple compensation of the scanner's thermal defocus (at the -23 C operating temp) by active control of the fiber focal plane position. A challenging requirement for the fiber optic system was the transmission to the spectral range 1.85 to 2.45 microns at .45 numerical aperture. This was solved with custom fluoride glass fibers from Verre Fluore. The onboard calibration source is also coupled to the spectrometers by the fibers and provides two radiometric levels and a reference spectrum to check the spectrometers' alignment. Results of the performance of the assembled subsystems are presented.

Chrisp, Michael P.↗

NASA NTRS1988

AVIRIS foreoptics, fiber optics and on-board calibrator

Chrisp, M. P.↗

NASA NTRS1979

Multiwavelength monolithic integrated fiber-optic terminal

The paper presents the Multiwavelength Monolithic Integrated Fiber Optic Terminal (MMIFOT) developed under NASA sponsorship. The program aims to utilize the advantage of optical fiber and integrated optical device technology to achieve parallel transmission of many data channels over the same optical fiber link, and to develop an eight channel wavelength multiplexed fiber optic link that transmits eight bit words in a parallel format at a nominal rate of 20 Mw/s; in the second phase of the program a transmitter/multiplexer chip will be developed. The MMIFOT configuration, the receiver/demultiplexer development, and the waveguide detector development are discussed, concluding that the first phase of the MMIFOT program will culminate in the demonstration of an eight channel receiver/demultiplexer chip with a four channel breadboard multiplexer with the data rate of 20 Mbps per channel with a dynamic range of minimum 20 dB.

Rice, R. R.↗

NASA NTRS2001

Virtual Instrumentation for a Fiber-Optics-Based Artificial Nerve

A LabView-based computer interface for fiber-optic artificial nerves has been devised as a Masters thesis project. This project involves the use of outputs from wavelength multiplexed optical fiber sensors (artificial nerves), which are capable of producing dense optical data outputs for physical measurements. The potential advantages of using optical fiber sensors for sensory function restoration is the fact that well defined WDM-modulated signals can be transmitted to and from the sensing region allowing networked units to replace low-level nerve functions for persons desirous of "intelligent artificial limbs." Various FO sensors can be designed with high sensitivity and the ability to be interfaced with a wide range of devices including miniature shielded electrical conversion units. Our Virtual Instrument (VI) interface software package was developed using LabView's "Laboratory Virtual Instrument Engineering Workbench" package. The virtual instrument has been configured to arrange and encode the data to develop an intelligent response in the form of encoded digitized signal outputs. The architectural layout of our nervous system is such that different touch stimuli from different artificial fiber-optic nerve points correspond to gratings of a distinct resonant wavelength and physical location along the optical fiber. Thus, when an automated, tunable diode laser sends scans, the wavelength spectrum of the artificial nerve, it triggers responses that are encoded with different touch stimuli by way wavelength shifts in the reflected Bragg resonances. The reflected light is detected and a resulting analog signal is fed into ADC1 board and DAQ card. Finally, the software has been written such that the experimenter is able to set the response range during data acquisition.

Lyons, Donald R.↗

NASA NTRS2002

High speed demodulation systems for fiber optic grating sensors

Fiber optic grating sensor demodulation systems are described that offer high speed and multiplexing options for both single and multiple parameter fiber optic grating sensors. To attain very high speeds for single parameter fiber grating sensors ratio techniques are used that allow a series of sensors to be placed in a single fiber while retaining high speed capability. These methods can be extended to multiparameter fiber grating sensors. Optimization of speeds can be obtained by minimizing the number of spectral peaks that must be processed and it is shown that two or three spectral peak measurements may in specific multiparameter applications offer comparable or better performance than processing four spectral peaks. Combining the ratio methods with minimization of peak measurements allows very high speed measurement of such important environmental effects as transverse strain and pressure.

Udd, Eric↗

NASA NTRS1995

Dynamic Light Scattering With Improved Fiber-Optic Probes

Improved fiber-optic probes developed for use in dynamic light-scattering measurements. Intended for measuring dynamic backscattering of laser light from concentrated suspensions of particles in liquids, for purpose of determining statistical distributions of sizes of particles. Offers advantages of compactness and ruggedness, and more suitable for industrial environments. Probes immersed in suspensions characterized. Associated lasers, photodetectors, and signal-processing circuits located remotely in safer environments, coupled to probes via optical fibers.

Dhadwal, Harbans Singh↗

NASA NTRS1995

Ophthalmic Diagnostics Using a New Dynamic Light Scattering Fiber Optic Probe

A new fiber optic probe is developed to study different parts of the eye. The probe positioned in front of an eye, delivers a low power light from a laser diode into the eye and guides the light which is back scattered by different components (aqueous humor, lens, and vitreous humor) of the eye through a receiving optical fiber to a photo detector. The probe provides rapid determination of macromolecular diffusivities and their respective size distributions in the eye lens and the gel-like material in the vitreous humor. We report alpha-crystalline size distributions, as a function of penetration depth, inside the lens and hyaluronic acid molecular size distribution in the vitreous body. In a clinical setting, the probe can be mounted on a slit-lamp apparatus simply by using a H-ruby lens holder. The capability of detecting cataracts, both nuclear and peripheral, in their early stages of formation, in a non invasive and quantitative fashion, has the potential in patient monitoring and in developing and testing new drugs or diet therapies to 'dissolve' or slow down the cataract formation before surgery is necessary. The ability to detect biochemical and macromolecular changes in the vitreous structure can be very useful in identifying certain diseases of the posterior chamber, e.g., posterior vitreous detachment.

Ansari, Rafat R.↗