Proceedings Volume 0506

Fiber Optics in Adverse Environments II

Roger A. Greenwell
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Proceedings Volume 0506

Fiber Optics in Adverse Environments II

Roger A. Greenwell
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Volume Details

Date Published: 15 October 1984
Contents: 1 Sessions, 35 Papers, 0 Presentations
Conference: 28th Annual Technical Symposium 1984
Volume Number: 0506

Table of Contents

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Table of Contents

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Material Dispersion Measurements On Fiber Optic Cables Used At The Nevada Test Site
Vern N. Smiley, Mark A. Peressini, Daniel E. Whitaker
Results of material dispersion measurements on multimode, graded-index, optical fibers are given. An rf phase shift technique was used. The measurement was repeated for several wavelengths over the spectral width of an LED source. Typically, an LED centered at 820 nm was useful from about 790 to 850 nm. Wavelength coverage can be extended further by using LED's with different central wavelengths. Material dispersion values for high-bandwidth fibers fell in the range 100 to 108 ps/(nm x km) at a wavelength of 825 nm.
Gamma-Ray To Cerenkov-Light Conversion Efficiency For Pure-Silica-Core Optical Fibers
B. L. Pruett, R. T. Peterson, D. E. Smith, et al.
We have determined experimentally the absolute gamma-ray to Cerenkov-light conversion efficiency for pure-silica-core optical fibers in the vicinity of metallic Compton-converter slabs. To measure the energy dependence of this process, we used 60Co and 24Na radiation sources. The results show how the conversion efficiency varies with Compton-converter material, thickness, angle of the fiber, and fiber-converter distance. We also performed computer calculations of conversion efficiency. This method employs an electron-photon transport code named SANDYL together with analytical calculations of Cerenkov-light generation. We compare the results of these calculations with experimental results.
Measuring Transient Radiation Effects In Optical Fibers
Mark D. Rotter, Donald R. Jander
We propose a new method for measuring transient radiation effects in optical fibers on a nanosecond timescale. The method, which incorporates a streak camera, allows more precise time resolution than other methods and has the advantage of measuring the radiation-induced attenuation as a function of wavelength and time simultaneously. By choosing different light sources and sweep speeds, radiation-induced attenuation may be measured under a variety of experimental configurations. Examples of the types of out-put obtained with our method are given.
Optical Characterization Of Radiation-Resistant Fibers
Vern N. Smiley, Bruce M. Whitcomb, Mark A. Peressini, et al.
Various measurements have been made on step index fibers having pure silica cores which are expected to have good radiation hardness properties. These measurements include spec-tral attenuation, numerical aperture, and bandwidth. Values for the preceeding quantities are given for several step index fibers of various diameters including the following: plastic-clad silica (PCS), QSF-AS, Raychem VSC, Dainichi Diaguide, and Ensign-Bickford fiber. Computer-controlled instrumentation was developed for these measurements and is described.
A High-Bandwidth Multichannel Fiber Optic System For Measuring Gamma Rays
F. Roeske, D. E. Smith, B. L. Pruett, et al.
We describe an analog fiber optic gamma-ray diagnostic system that can transmit signals through fiber cables 600 to 700 m long with a system bandwidth exceeding 1 GHz and measure the relative timing between signals to within 0.3 ns. Gamma rays are converted to visible light via the Cerenkov process in a short length of a radiation-resistant optical fiber. A graded-index optical fiber transmits this pulse to a recording station where the broadened pulse is compensated for material dispersion and recorded using a streak camera. The streak camera can simultaneously record 20 to 30 data channels on a single piece of film. The system has been calibrated using electron linear accelerators and fielded on two experiments.
A Novel Probe For Determining The Size And Position Of A Relativistic Electron Beam
T. J. Orzechowski, Helmut Koehler, W. Edwards, et al.
In order to determine the size and position of a relativistic electron beam inside the wiggler magnetic field of a Free Electron Laser (FEL), we have developed a new probe which intercepts the electron beam on a high Z target and monitors the resulting bremsstrahlung radiation. The probe is designed to move along the entire three meters of the wiggler. 1 This FEL is designed to operate in the microwave region (2 - 8 mm) and the interaction region is an oversized waveguide with a cross section 3 cm x 9.8 cm. The axial probe moves inside this waveguide. The probe stops the electron beam on a Tantalum target and the resulting x-rays are scattered in the forward direction. A scintillator behind the beam stop reacts to the x-rays and emits visible light in the region where the x-rays strike. An array of fiber optics behind the scintillator transmits the visible light to a Reticon camera system which images the visible pattern from the scintillator. Processing the optical image is done by digitizing and storing the image and/or recording the image on video tape. Resolution and performance of this probe will be discussed.
Radiation Response Of Optical Fibers In A Nuclear Reactor
Judy K. Partin
The Idaho National Engineering Laboratory (INEL) is actively involved in the development and application of fiberoptic-based instrumentation for use in nuclear reactor research. To aid in this development effort, a testing program has been undertaken to quantify optical losses in promising waveguide materials during radiation exposure at elevated temperatures characteristic of reactor environments. This paper reports results of testing conducted during the fuel-conditioning phase of the Severe Fuel Damage Test 1-1A performed at the INEL's Power Burst Facility. Radiation-resis-tant fiberoptic samples were obtained from five manufacturers: the Spectran Corporation, the Quartz Products Corporation, Dainichi-Nippon Cables, LTD., Fiberguide Industries, and Hughes Research Laboratories. Two identical sets of samples were placed in a specially designed test fixture and positioned approximately 60 centimeters above the reactor core. One was held at a temperature of 200°C, while the second remained at 20°C. The radiation-induced optical attenuation was monitored in several spectral bands in the 600-1100 nanometer region. The in situ measurements were recorded over a 125 hour period during which the reactor power varied between 0.1 to 22 MW thermal. The samples were exposed to average fluxes of 2.8 X 109 n/cm2/sec thermal neutrons, 4.4 X 108 n/cm2/sec fast (> 1 MeV) neutrons, and dose rates of approximately 106 rad/hr gamma radiation. The growth and recovery of radiation induced losses as a function of wavelength, temperature, and reactor power level are presented.
Fore-Optics Systems Designed For Electronic Streak Cameras Using Fiber Optics'
Robert P. Reedy
We describe the general principles that should be considered in designing a fore-optics system to image signals from optical fibers onto the photocathode of a streak tube. Important design considerations of these systems include lens design (resolution, magnification, relative aperture, field size, and transmission), use of supplementary field lenses, and the configuration of the fiber arrays. We also discuss provisions made in these systems to evaluate all channels of the complete fiber system and to align the fiber-array images on the photocathode. Typical applications of these fore-optics systems include simultaneous filtering of multiple channels of optical signals, reducing the size of the image, or using a streak camera that has a curved front window.
Development Of The Nuclear Optical Penetration
K. Inoue, K. Koike, Y. Imada
We have developed the nuclear optical penetration to be incorporated in the wall penetration of the shell to introduce a data transmission system using optical fibers into a nuclear power plant with a pressurized water reactor. Radiation-induced coloration in optical glass seriously affects transmission characteristics of optical fibers, whereas it has been revealed that the pure-silica core optical fiber without any dopant in the core has wide applicability in radiation fields thanks to its very low radiation-induced attenuation. The wall penetration of the shell should have airtightness and resistivity to heat, vibration, and pressure, let alone radiation, excellent enough to be invariable in data transmission efficiency even when subjected to severe environmental tests. The sealing modules of this newly developed nuclear optical penetration are hermetically sealed. The gap between the optical fiber rod (100 pm in core diameter and 5 mm in rod diameter) and stainless steel tube is sealed with lamingted glass layer. As the result of He gas leakage test, high airtightness of less than 10 cc/sec was achieved. No thermal deformation of the core was caused by sealing with laminated glass layer, nor was observed transmission loss. Then the sealiing modules were subjected to the irradiation test using 60 Co gamma ray exposure of 2 x 10 rads. Though silica glass layer supporting the fiber rod and sealing glass portion turned blackish purple, transparency of the fiber was not affected. Only less than 0.5 dB of connecting loss was observed at the connecting point with the optical fiber cable. The sealing modules were also found to have resistivity to vibration and pressure as excellent as that of existing nuclear electric penetrations. We expect the nuclear optical fiber penetration will be much effective in improving reliability of data transmission systems using optical fibers in radiation fields.
Laser-Based Data Acquisition In Gas Centrifuge Environments Using Optical Fibers
M. R. Cates, S. W. Allison, B. Marshall, et al.
The operating environment of gas centrifuges poses three basic experimental problems: rotating reference frame, corrosive effects of UF6 gas, and vacuum coupling. Diagnostic experiments in this environment effectively use fiber optics as laser transport systems and data extraction channels. Access to the interior of rotating centrifuges is only from a central nonrotating column assembly. Optical paths are often long and difficult to measure in static conditions with precision necessary in operating conditions. Residual traces of HF gas, from UF6, damage exposed optical components over time. Diagnostic measurements requiring pulsed laser sources and analysis of fluorescence emissions, both from UF6 gas and from temperature-sensitive phosphor are described, with emphasis on optical fiber components and experimental design configurations. The studies were done at Oak Ridge Gaseous Diffusion Plant through the Centrifuge Physics Department of the Centrifuge Division. The advantages of fiber optics methods include: optical path flexibility, small and adaptable size of components, utility in connection with moveable assemblies, and relative ease of vacuum isolation.
Ec-135 Fiber Optic Technology Review
Jan R . Schultz, Harry N. Hodges
Fiber optic technology offers many advantages for upgrading nuclear survivability in systems such as the Airborne Command Post EC-135 aircraft, including weight and cost savings, EMI and EMC immunity, high data rates. The greatest advantage seen for nuclear survivable systems, however, is that a fiber optic system's EMP hardness can be maintained more easily with the use of fiber optics than with shielded cables or other protective methods. TRW recently completed a study to determine the feasibility of using fiber optic technology in an EC-135 aircraft environment. Since this study was conducted for a USAF Logistics Command Agency, a feasible system had to be one which could be realistically priced by an integrating contractor. Thus, any fiber optic approach would have to be well developed before it could be considered feasible. During the course of the study problem areas were encountered which are associated with the readiness of the technology for use rather than with the technology itself. These included connectors, standards, fiber radiation resistance, busing, maintenance, and logistics. Because these problems areas have not been resolved, it was concluded that fiber optic technology, despite its advantages, is not ready for directed procurement (i.e., included as a requirement in a prime mission equipment specification). However, offers by a manufacturer to use fiber optic technology in lieu of conventional technology should be considered. This paper treats these problems in more detail, addresses the areas which need further development, and discusses the hardness maintenance advantages of using fiber optic technology.
New Submerged-Robot Control Optical Fiber Cable With Small-Diameter, High-Strength Frp Covered Optical Fiber
K. Fuse, Y. Shirasaka, H. Yanagawa
Of natural resources on the earth, the utilization of the oceans has the oldest history, and the development of them has been delayed most. However, hot expectation is being placed on the development of the oceans. The element that obstructs the acceleration of such development is the sea itself. From a technical viewpoint, the means to explore the oceans have not been developed sufficiently, and equipment such as special large vehicles and ships has been bulky, requiring a very large sum of money to prepare them. These have been part of the reasons why the development of the oceans has been delayed. For this reason, a large number of exploratory systems will be studied as the ocean development becomes active in the near future. A single optical fiber cable has been considered as a cable for control of an ocean exploratory robot, which weighs approximately 30 to 40 kg at most in air requiring no power feeding to the drive section inside the vehicle and running by self on a built-in battery, as well as for data transfer. This cable is believed most suitable in terms of high speed mobility, transmission characteristics, and system cost. The mode (system) of pay off of the cable paid off by the ship loading such a cable becomes very important in the design of optical fiber cables for control of ocean exploratory robots. This paper introduces a new FRP covered optical fiber cable developed as an optical fiber cable for control of ocean exploratory robots with a small diameter and rotating motion. This cable is considered most suitable for the pay off-system which is simple and offers the highest space utility. The paper describes a basic study made prior to an actual performance test in the sea, as well as its design and characteristics.
A Fiber Optic Digital Uplink For Ocean-Floor Experimentation
John P. Powers
A fiber optic data link has been implemented to carry data from an ocean-floor geomagnetic data collection system to a surface telemetry buoy. The battery-powered link was designed to operate at depths of up to 100 meters although the system margin would allow depths in excess of 1.5 km. Pulse-code modulated data is obtained from sampled analog data, organized into frames, preceded by a synchronizing code word, and applied to the optical transmitter. Data rates of up to 250 kb/s were achieved. Commercial transmitters and receivers were incorporated into waterproof housings with bulkhead penetrators of local design used to provide fiber access. Fiber optic cable with Kevlar strength members was used for the link. A nonmagnetic deployment apparatus was fashioned to to allow for deployment and recovery of the experiment from an oceanographic research vessel. The experiment was sucessfully deployed, operated, and recovered in Monterey Bay on three separate oc-casions.
Single Fibre Cable For Dispensing Applications
Peter G. Hale, J. Garth Lamb, Robert C. McEleny
This paper summarises the design and development of an optical fibre package and ruggedised cable type for use in applications such as high speed or under water dispensing. The potential of this cable generic design is illustrated by reference to a multimode version developed for underwater dispensing. The overall diameter of the cable is 0.84mm and it exhibits a tensile strain of 0.6% at 180N load. The absence of a sheath gives a free-flooding design with inherent stability under pressure. Results are presented which show negligible incremental losses during manufacture, spooling and deployment.
Considerations For Applying Fiber Optic Technology To Increase Electromagnetic Pulse (Emp) System Survivability
J.Philip Castillo
Fiber optics technology is a promising tool which may be applied at the system or subsystem level to help decrease the EMP environment stress to which the system is exposed. The careful replacement of conducting wires with nonconducting fibers can result in a significant decrease of the overall EMP stress which appears at susceptible electronics. However, other problems such as added complexity and redistribution of energy may result and potentially exacerbate the problem if appropriate safeguards are not implemented. This paper will address the generic problems associated with increasing the surviv-ability of systems in an electromagnetic pulse environment. In particular, various protection approaches will be contrasted with the potential application of fiber optics in reducing EMP stress at critical electronics interfaces. This paper will focus on system level aspects which must be taken into account when applying fiber optics technology to new and existing systems.
A Fiber Optic Sensor For Measuring Multimegampere Currents From Flux Compression Generators
L. R. Veeser, R. S. Caird, C. M. Fowler, et al.
We are developing and fielding single mode fiber optic sensors that measure multi-megampere currents in electromagnetically hostile environments aggravated by the use of explosives. Current is measured by detecting the Faraday rotation of polarized laser light from a fiber surrounding the current conductor. Comparisons to accurately calibrated Rogowski loops show agreement to within a few per cent, well within the accuracies of the experiments.
Fiber Optic Aircraft Systems Electromagnetic Pulse (Emp) Survivability
Byron Gage, Roger Greenwell, Michael Summerlin, et al.
Mitigation of EMP coupling into sensitive, mission critical equipment is essential for Aircraft required to operate in adverse nuclear environments. As has been demonstrated in several aircraft test-fix-test programs, traditional hardening can eliminate most EMP problems but generally adds weight, volume, and complexity which impacts system reliability, maintainability and hardness surveillance. Fiber optic technology reduces weight, volume, and complexity while reducing overall life cycle costs and can also mitigate or eliminate many EMP related problems. As requirements for data transfer volume increase, aircraft system expansion utilizing present technology within extended design constraints is hampered by mission requirements for extensive EMI, RFI, EMP, lightning and short circuit shielding and protection. The criticality of excessive weight and space needed for shielding protection is well known and so are the problems of bent pins associated with filter pin connec-tors. The use of non-metallic composite structural materials for the aircraft skin further exacerbates the traditional shielding and filtering problems. The complete elimination of shielding and filtering is not possible. However, the use of fiber optics paths, complex penetrations and other intentional or inherent inadvertent conductors and thereby greatly simplifies EMP hardening. The inherent dielectric nature of fiber optics makes it relatively resistant or immune to the upset/damage potential of EMP. Fiber optic technology is also capable of electromagnetic interference and cross talk. The vulnerability of fiber optic technology to other significant factors in the operational environment, i.e., ionizing radiation, should also be examined and assessed.
Microshell®-Tipped Optical Fibers As Sensors Of High-Pressure Pulses In Adverse Environments
Robert F. Benjamin, Frederick J. Mayer, Robert L. Maynard
We have developed and used an optical-fiber sensor for detecting the arrival of strong pressure pulses. The sensor consists of an optical fiber, tipped with a gas-filled microballoon. They have been used successfully in adverse environments including explosives, ballistics and electromagnetic pulses (EMP). The sensor produces a bright optical pulse caused by the rapid shock-heating of a gas, typically argon or xenon, which is con-fined in the spherical glass or plastic microballoon. The light pulse is transmitted via the optical fiber to a photo detector, usually a streak camera or photomultiplier tube. The microballoon optical sensor (called an optical "pin" by analogy to standard electri-cal "pins"), was originally developed for diagnosing an explosive, pulsed-power generator. Optical pins are required due to the EMP. The optical pins are economical arrival-time indicators because many channels can be recorded by one streak camera. The generator tests and related experiments, involving projectile velocities and detonation velocities of several kilometers per sec have demonstrated the usefulness of the sensors in explosives and ballistics applications. We have also measured the sensitivity of the optical pins to slowly-moving projectiles and found that a 200 m/sec projectile impacting the microballoon sensor produces a flash having a risetime less than 100 ns and a pulse duration (FWHM) of less than 300 ns. The technical and cost advantages of this optical pin make it potentially useful for many electromagnetic, explosive, and ballistics applications.
Application Of Optical-Fiber Pins To Explosive, Pulse-Power Generators
R. S. Caird, R. F. Benjamin, R. G. McQueen, et al.
Arrays of optical-fiber pins, known as microballoon optical pins, have been used to diagnose the dynamic deformation of an explosive pulsed-power generator. The pin data determine the effects of multimegampere electrical current loading on generator performance. The pins are required to work in the adverse environment of the generator, consisting of explosives and explosive products and very large, rapidly-changing electrical currents that give rise to intense electromagnetic interference. The optical pin is a shock arrival-time sensor consisting of an optical fiber tipped with a gas-filled microballoon about 200 microns in diameter. When a strong pressure pulse impinges on the microballoon, the shock-heated gas within the spherical shell emits a bright flash. The light is transmitted via the optical fiber to an electronic streak camera which simultaneously records signals from many pins. The signals from an array of these sensors measure the time profile of the impact of the explosive-driven armature with the stationary conical stator. Details of the microballoon pin are described at this meeting by Benjamin and Mayer. The microballoon pin was compared with the conventional flash-gap technique in which air, confined in a much larger space, is shock-heated to produce a time-of-arrival flash. The two methods gave essentially identical results on the first shot. Since the microballoon was more convenient to use and indicated a greater range of usefulness in future applications, we used it exclusively on the subsequent shots. The microballoon optical-fiber pin gave us the data necessary for the next generator design iteration and will be used extensively in the future.
Colorado Springs Area Emp Hardening Project
Ronald J. Schemmel
Using Fiber Optic technology, Electro-Magnetic Pulse (EMP) protected enclosures were installed in the Colorado Springs Area (CSA). EMP in the communications community is of concern because of the detrimental effect a high altitude nuclear burst would have on electronic and communications equipment. Computer Sciences Corporation, Colorado Springs Operation was tasked by the Air Force to EMP protect critical communications circuits to enable key personnel to communicate to these locations. This system of circuits comprises nine different EMP protected enclosures throughout CSA. The enclosures were inter-connected by either a microwave radio link or a fiber optic link. The fiber optic links utilized a dual, 50/125 micron, multimode, graded index, silica fiber. Two types of modems were used as the light transmitters and receivers. A pair of full duplex digital asynchronous modems were installed to carry the T-1 (1.54 Mbps) data. Dual channel, analog, full duplex modems with a bandwidth of 25 kilohertz were used in the voice circuits. Large EMP shelters were placed at key locations and interconnected by microwave radio links. Co-located with the radios were multiplexers, an uninterruptable power supply and the fiber optic modems. The fiber optic links go out from these sites to terminal loca-tions. Two fiber optic voice channels provide EMP protected telephone communications to select sites. Each of the terminal locations consists of an EMP enclosure containing a self supporting power supply, an AC/DC inverter, telephone signaling equipment (utilizing Single Frequency SF signaling) and fiber optic modems. Each terminal is expected to provide survivable communications although not indefinitely. This project required interfacing a variety of different communications equipment such as microwave radios, fiber optic modems, channel banks and multiplexers. The communica-tions links used twisted pair cable, microwave transmission, coaxial cable and fiber optic cable carrying data rates of 300 baud to 1.544 Mbps. Computer Sciences Corporation had made provisions to allow for expansion and upgrade and is vigorously supporting that effort.
Silicon Oxynitride Coatings To Reduce Mechanical Fatigue And Hydrogen Induced Optical Ageing In Silica Fibres
W. J. Duncan, K. J. Beales, D. M. Cooper, et al.
Monomode silica fibre has been coated during fibre pulling with silicon oxynitride ceramics using an on-line deposition process. The coatings have been tested for their ability to prevent the mechanical and optical ageing of fibre. The ceramic coated fibres are more fatigue resistant than silica having N values of over 100 compared with an N of 25 for silica. rrus ceramic coated fibre need only be proof tested at about half the level required for silica. While silica fibre saturates with hydrogen in 500 hours no hydrogen has been detected in a ceramic coated fibre stored in hydrogen for 1900 hours. This and other experiments at high temperature suggest that silicon oxynitride coatings can prevent the hydrogen content of fibre from reaching unacceptable levels.
Pcs Cable Connector Termination, Radiation Exposure, And Testing
Roger H. Ellis, David Johnson
It has been well established that Plastic Clad Silica (PCS) fibers have shown more resistance to radiation damage at 820 nm than most fibers studied.1,2,3,4,5 However, most plastic clad materials lack the physical properties to provide a good adhesive bond required by military ruggedized fiber optic connectors. A program to develop a PCS fiber optic termination technique suitable for use in military tactical systems was initiated by NOSC.6 The termination characteristics of PCS fiber were evaluated. Emphasis was placed on terminating Maxlight radiation hardened single fiber cables (RSC) into SMA type connectors. Once the termination process was determined; physical, environmental, and optical testing was performed using military specification requirements. The results were compared with test samples which had been subjected to both x-ray pulse (prompt) and two levels of gamma (CO") radiation.
The Application Of Commercial Star Couplers To Increase Signal Dynamic Range
B. M. Whitcomb, V. N. Smiley, R. L. Flurer, et al.
Fused biconical tapered (FBT) fiber optic star couplers have been used in a variety of applications at the Nevada Test Site (NTS) in several diagnostic experiments to provide increased dynamic range for the recording devices or to divide the available signal between different recording devices. A number of installation problems have been manifested in this application of FBT couplers. The most severe problem results from the modal selection mechanism inherent in the design of FBT couplers. Substantial work has been done to characterize a variety of commercial couplers for this application.
Characterization Of Fiber Optic Cables Under Large Tensile Loads
J. W. Ogle, L. D. Looney, R. T. Peterson
Fiber optic cables designed for the Nevada Test Site (NTS) have to withstand an unusually harsh environment. Cables have been manufactured under a 6 year old DOE specification that has been slightly modified as the cable requirements are better understood. In order to better understand the cable properties a unique capability has been established at the NTS. Instrumentation has been developed to characterize the transmission properties of 1 km of fiber optic cable placed under a controlled tensile load up to 1500 lbs. The properties measured are cable tension, cable elongation, induced attenuation, attenuation vs. location, fiber strain, bandwidth, and ambient temperature. Preforming these measurements on cables from the two qualified NTS fiber optic cable manufacturers, Siecor and Andrew Corp., led to a new set of specifications. The relevant new and old specifications will be reported along with the characterization techniques and results on cables manufactured under the old specification.
Transient Attenuation In Connectors To PCS Fibers And In Glass-On-Glass Fibers Induced By Pulsed X-Rays
Joseph Zucker, Ray Clarke, Ralph Narciso
Using Sandia Laboratories' Hermes Ii X-Ray Pulser, We Have Measured The Transient Attenuation Of Connectors To Pcs Fiber Prepared With Raychem Fibersleeves® And Of Glass-On-Glass Silica Core Fiber (Raychem Type Vsc) Induced By 50 Nanosecond X-Ray Pulses With Total Dose Of 5 Krads. No Significant Losses Were Induced In The Connectors Either At 23°C Or At -55°C, Thus Qualifying Them For Use In A High Radiation Environment. The Peak Transient Attenuation Measured For The Fiber With 200 Micrometer Core Diameter At -55°C (7.2 Db/Km/Krad) Is Significantly Lower Than For Any Other Commercially Available Fiber At That Temperature.
New Source Compounds For Fabrication Of Doped Optical Waveguide Fibers
D. A. Thompson, P. L. Bocko, J. R. Gannon
Raw materials used for the fabrication of high purity Si02-Ge02 glasses are typically volatile metal halides. The use of non-halides has been reported but have not been extensively utilized. New compositions for optical fibers have been proposed to extend optical performance and fabrication efficiency but these are often unattainable due to lack of suitably volatile high purity source compounds compatable with CVD systems. A recent approach to obtain waveguides more resistant to detrimental radiation effects is the addition of metal oxides such as cerium oxide that are widely used in specialty glasses to minimize induced absorptions caused by ionizing radiation by creation of hole and electron traps. Optical Waveguide fibers in the Si02-Ge02-Ce02 system have been fabricated by conventional OVD processes utilizing newly developed cerium source compounds. These new compounds are transported from bubblers using argon carrier gas to the burner where methane-oxygen combustion in the presence of SiCl4 and GeCl4 produces ceria containing glass of optical waveguide quality. Cerium (III) and Ce (IV) are observed at 260 and 320nm, respectively, in transmission curves of bulk pieces of glass and also optical fibers. Ceria concentrations over 0.4% (wt) induce phase separation so attenuation measurements have been on fiber containing less Ce02. No deleterous effects of absorption due to CeO2 occur beyond 850nm based upon comparisons of control and doped fibers. Results of preliminary radiation exposure will also be presented.
Radiation Resistance Of Pure-Silica Core Image Guides
A. Utsumi, H. Hayami, H. Tanaka, et al.
Thirteen types of pure-silica core image guides were prepared. They incorporate fibers with varied water content in the core glasses prepared by different fabrication methods, dopants in cladding glasses; structures and dimensions of picture element fibers. Then the image guides were subjected to the tests for influence of each intrinsic factor upon their radiation resistance with varied dose rate of ''Co gamma ray irradiation. It was revealed that pure-silica glass with an adequate amount of OH radicals for the core made by the plasma method and B F-doped glass for the cladding is the most desirable material combination It was proven that radiation resistance improves in proportion to cladding thickness and core diameter. Also it was found that image guides without support layer is more excellent in radiation resistance than those with support layer and that an image guide produced with one of the best materials and irradiated with the dose rate of 2 x 106 R/H. The test showed that the image guide withstands the irradiation of 109 at highest, if irradiated length is as short as 1 m.
Environmental Effects On Hard Clad Silica Optical Fibers
Bolesh J. Skutnik, Ronald E. Hille
Hard clad silica (HCS) optical fibers have been developed which exhibit a unique combination of Properties. The fibers have high tensile strength, and attenuation only minimally affected by wide temperature ranges, humidity and water immersion. The radiation resistance is also excellent. With this combination of properties, the HCS fiber is ideal candidate for fiber optic cable systems for use in adverse environments.
Radiation-Induced Light Emission In Silica Core Fibers
W. Schneider, U. Babst, O. A. Balk, et al.
In various optical fibers we induced light emission either by bremsstrahlung or by electron pulses from a Febetron 705 radiation source. The emitted light was measured and will be explained as function of the dose rate, the radiation-induced loss, the fiber length and direction, the wavelength, and the width of the radiation pulses. The radiation induced excess loss, deducted from the shape of the emitted light pulses, fits reasonably to the excess loss gained with transmission measurements.
Fluorescence Emission By Molecular Impurities In Irradiated And Non-Irradiated Silica
G. Boisde, W. Carvalho, P. Dumas, et al.
In order to gain a better understanding of the optical behaviour of irradiated silica (dry, OH and F-doped) two spectroscopic methods are used. In the first case an Ar.F laser emitting at 193 nm excites preform samples and the fluorescence is examined between 400 and 1000 nanometers. In the second case fibers drawn from these preforms were excited using an Ar+ laser and examined with a Raman microprobe in the various doped zones. The emission spectra confirm that 02 molecule complexes contribute to the optical spectra of pure silica samples. The presence of fluorine as a dopant seems to be associated to an emission band around 600 nm whose nature is so far unknown.
Radiation Response Of Optical Fibers And Selfoc Microlenses At 1.3 Um
E. J. Friebele, K. J. Long, C. G. Askins, et al.
The incremental loss induced at 1.3 μm in multimode and single mode optical fiber waveguides has been studied at 23 C and -55 C in situ as a function of time after high dose rate (9000 rads/min) steady state exposure and as a function of dose during low dose rate (- 1 rad/day) irradiation. Undoped and binary Ge-doped silica core fibers have demonstrated the lower radiation responses and better recoveries at 23 C; the induced losses substantially increase by factors of 8-18 when exposed at -55 C. Selective P doping on the fiber centerline or in the cladding has been found to reduce this temperature dependence, but increased damage and less recovery at 23 C have been noted. Measurements of the radiation response of Selfoc Microlenses have shown that the induced loss in a single lens at 1.3 I'm is only - 1 dB after an exposure of 2 x 104 rads; the SLS lenses are more radiation sensitive than the SLW lenses.
Transient Attenuation In Optical Fibers
A. A. Hopkins, R. E. Kelly, L. D. Looney, et al.
Low and high energy pulsed electron beams were used to generate radiation-induced transient attenuation in high-OH, Suprasil core, PCS fibers, demonstrating the energy dependence of the radiation damage and recovery mechanisms. A radiation resistant low-OH fiber was studied and its performance contrasted to that of high-OH material. Several fibers with differing core compositions were also studied.
The Effect Of Neutron Irradiation On The High Temperature Operation Of Injection Laser Diodes
Charles E. Barnes
Certain optoelectronic applications for which it would be desirable to use an injection laser diode (ILD) require that the light source be exposed to a combined hostile environment of both radiation and high temperature. Because of the complexity of ILD's it is very possi-ble that these two hostile components will have detrimental synergistic effects on the laser. We have studied the effects of fast neutron irradiation on the high temperature (T<100°C) operation of ILD's. In general, it was found that the ILD's were more sensitive to irradia-tion at higher temperatures, and that the lasers with the least temperature variation in threshold current were the least sensitive to irradiation.
A1Gaas/Gaas Radiation Hardened Photodiodes
J . J. Wiczer, C. E. Barnes, T. A. Fischer, et al.
We report on AlGaAs/GaAs double heterojunction photodiodes designed and fabricated to be resistant to the effects of ionizing-radiation. The work described here includes new results comparing optimized, AlGaAs/GaAs photodiodes grown with two different growth processes: liquid phase epitaxy and molecular beam epitaxy. These devices were processed with similar photo-lithographic masks and exposed to high energy neutrons, electrons, and photons. Electrical and optical characterizations were completed before and after each irradiation; degradation trends are reported.
Radiation Response Of A Radiation-Hardened Si Photodiode Incorporating A Sinker Diffusion
T. A. Fischer, J. J. Wiczer
A commercially available, epitaxially-grown, Si photodiode was irradiated with 18 MeV electrons, 1-10 MeV x-rays, and neutrons from a pulsed reactor. The device structure is given, the radiation-hardened design features are discussed and their inherent limitations are identified. The ionizing radiation sensitivity and neutron-induced, permanent damage to quantum efficiency and leakage current have been measured. Empirical fits to the data are presented to aid optoelectronic sub-system designers in predicting device performance in various radiation environments.