It is well known that when a silica optical fiber is irradiated by neutrons or heavy ions, there is an attenuation of the transmission of the signal which is due to the creation of specific radiation damage. We have been able to show the creation of alpha radiation damage in borosilicate glass and glass used for radioactive waste confining in studying their properties of thermostimulated luminescence after high alpha irradiation. We have been able to correlate these radiation damages with interatomic bond break which implies oxygen. To extend this research to all silica optical fiber, the thermostimulated luminescence mechanisms of vitreous silica have been analysed. To exalt its properties in thermostimulated luminescence it has been doped with aluminium. Then, the creation of alpha radiation damage has been searched in this vitreous silica doped with aluminium. The next step of the study is an extending of this method to detect the effect of neutronic or heavy ions irradiation on vitreous silica samples which constitutes the basic material of optical fiber used in nuclear harsh environment.
Induced optical losses and paramagnetic Ge(n)-centres have been investigated in germanium doped silica glass and optical fibers after gamma- and UV-irradiation. It has been found that all the excitations created the similar effects. By means of selective photoexcitation Ge(1 and 3)-centres were identified in optical spectra presumably as the induced absorption bands at 4.4 eV and 6.2 eV, respectively. Moreover, for Ge(1)-centre photobleaching takes place under 266 nm excitation. In optical fibers we have observed no difference in ∝- and UV-induced loss spectra in the wavelength range from 480 nm to 1900 nm. We have found partial reversibility of the photo-colouration. The comparison of samples prepared by MCVD, VAD and PCVD techniques has been made. The origin of the dominant colour centres and their contributions to the irradiative induced losses are discussed.
This paper addresses two effects of transient irradiation on optical fibers. The recovery of the induced attenuation was measured from 100 ns to 1 ms in several fibers, including two pure silica fibers and three fibers with doped silica cores. Measurements were performed at various optical power levels up to 28 mW at -55 and 23 C to investigate the temperature dependence and possible photobleaching effects at short times. We also report studies of the luminescence induced by the transient irradiation for the same group of fibers.
Hard Clad Silica optical fibers, fabricated from pure silica preforms with differing levels of OH and Cl, were exposed to continuous gamma irradiation. The low OH, high Cl containing fibers were irradiated under a variety of environmental conditions and at two testing facilities. The reproducibility of the radiation response is presented. Further the fiber type, the operating power level, the irradiation temperature and the dose rate and level were varied to help rationalize the response of these fibers. The results are given and then discussed in light of their implications on mechanisms of defect growth and recovery and for special applications such as space platform, aircraft, satellite or cold remote stations.
Influences of the impurities in fiber materials on radiation resistivity of pure-silica core fibers were studied by using 60Co as the gamma ray source at room temperature and at -55°C in terms of impurities in cladding materials and Cl and OH contents in core materials. As to the influence of the impurities in cladding materials, MRT (Modified Rod-in-tube) multi-mode fibers with natural. silica and synthetic silica as the support layer were tested. After 104 R exposure at -55 °C, radiation-induced loss of the fiber with synthetic silica was 3.9 dB/km at 1300 nm, while that of the fiber with natural silica was 31.1 dB/km. Similar results were obtained on single-mode fibers, indicating that the cladding material without impurities is effective in improving radiation resistivity Measurements of radiation-induced loss spectra in the wavelength range from 400 nm to 1100 nm during the irradiation revealed that Cl in the core particularly increases radiation-induced losses at low temperatures. Cl-free fibers demonstrated loss increase ranging from 0.2 to 0.4 dB/m at 400 nm after 3 x 104 R exposure at -55 °C while Cl-containing fibers showed radiation-induced losses over 0.8 dB/m. OH ions were found to improve the radiation resistivity at short wavelengths irrespective of Cl contents. Measurements of loss spectra in ultraviolet region revealed that Cl and OH ions are closely related with the formation of color centers.
This paper reports the results of low dose rate (< 1 rad/hr) exposures of several different kinds of polarization-maintaining (PM) fibers. In addition, the relationship between stress and radiation sensitivity has been investigated using otherwise identical fibers in which varying levels of both symmetric and asymmetric stress have been induced by grinding the preform to varying depths.
This paper investigates the radiation behavior of low water, Hard Clad Silica (HCS*) fibers at ambient temperature and below and to doses between 1.5 and 10 krad[SiO2] . The dose rates are 5 and 23 rads/second. The radiation induced attenuation growth and subsequent recovery out to 1,000/3,000 seconds are reported for each irradiation condition.
Radiation resistivity of pure-silica core image guides were investigated in terms of incremental spectral loss and quality of pictures transmitted through the image guides. Radiation-induced spectral losses were measured so as to clarify the dependences of radiation resistivity on such parameters as core materials (OH and Cl contents), picture element dimensions (core packing density and cladding thickness), number of picture elements and drawing conditions. As the results, an image guide with OH-and Cl-free pure-silica core, 30 - 45% in core packing density, and 1.8 - 2.2 μm in cladding thickness showed the lowest loss. The parameters to design the image guide were almost the same as those to obtain a image guide with good picture quality. Radiation resistivity of the image guide was not dependent on drawing conditions and number of picture elements, indicating that the image guide has large tolerances .in production conditions and that reliable quality is constantly obtained in production. Radiation resistivity under high total doses was evaluated using the image guide with the lowest radiation-induced loss. Maximum usable lengths of the image guide for practical use under specific high total doses and maximum allowable total doses for the image guide in specific lengths were obtained by the extrapolating method. Picture quality in terms of radiation-induced degradation in color fidelty in the pictures transmitted through image guides was quantitatively evaluated on the a chromaticity diagram based on the CIE standard colorimetric system and on the color specification charts according to three attributes of colors. The image guide with the least spectral incremental loss gives the least radiation-induced degradation in color fidelty in the pictures as well.
This paper reports progress in the derivation of an empirical model for predicting the radiation induced loss in matched clad single-mode optical fibers. We have drawn fibers from a set of MCVD preforms which were produced over a range of fabrication conditions intended to span the variations encountered in commercial MCVD fiber production. Conclusions regarding dependence of fallout radiation sensitivity on fabrication parameters were drawn from the data through orthogonal matrix analysis.
Multimode optical fibers have been applied to many data transmission requirements over the last 15 years. Many of these applications have required that the fibers operate in adverse environments, in some cases characterized by intense radiation levels. More recently, single mode fibers and their support technologies have advanced to the point where applications of these fibers are increasing throughout the world. Such single mode fibers offer significantly higher bandwidths than their multimode relatives. Single mode fibers will also be utilized under a range of adverse environmental factors.
General trends in radiation sensitivity of optical fibers have been studied using a number of commercially available fiber products. These fibers differ in core doping and type: single mode, multi-mode (graded index) or polarization retaining. For applications with a radiation tolerance requirement, selection beginning with a pure silica core fiber, optimized for operation at 1300 nm is indicated.
As part of a measuring program that should give us a survey of the radiation sensitivity of present commercial optical fibres we tested four more single mode (SM) and three graded index (GI) fibres at wavelengths of 850 nm (GI fibres only), 1300 nm and 1550 nm. All fibres were exposed to electron pulses of 500 rd, 3 krd, 10 krd and 100 krd as well as to the continuous gamma radiation of a Co-60 source upto 10 krd and 100 krd. At 10 krd additional measurements with fibre temperatures of +100°C and -50°C were made at both irradiation facilities.
The growth and recovery rates of X-ray and gamma-ray-induced infrared adsorption in a germanium-silicate multimode fiber can be qualitatively explained by assuming that two types of color centers are responsible for the absorption. One color center (type A) recovers at a fast rate and reaches a steady state concentration during irradiation. The second color center recovers at a slow rate and shows an increase in concentration during irradiation. The formation of color center type A can be suppressed during irradiation by the addition of molecular hydrogen.
Hydrogen plays a significant role in the response to ionizing radiation and subsequent recovery kinetics of pure silica optical fibers near 0.85 μm, especially noticeable at low temperature and low transmitted optical powers . Under these conditions recovery is controlled by the diffusion of molecular hydrogen. This hydrogen may be derived either from radiolytic decomposition of hydroxyl groups present as impurities, or, in the case of low-OH silica fibers, from previous exposure to hydrogen gas. Identification of compounds formed during and after irradiation suggests types of defect centers associated with radiation-induced optical attenuation. Spectroscopic analysis before and after irradiation of as-received and hydrogen impregnated, low-OH fibers from 0.4 to 1.6 μm reveals that SiH is formed both during low-temperature irradiation and the subsequent recovery, that there is more than one 'simple' absorption band, and that these bands are not equally suppressed by hydrogen impregnation.
The radiation resistance of undoped and F-doped synthetic silica is investigated at 840 nm and 1308 nm wavelength. At both wavelengths the F-doped silica shows improved radiation resistance compared to that of the undoped water-free silica. The recovery behaviour after pulsed irradiation of both materials can be devided into three phases with different recovery coefficients. Our results are compared with those from earlier work.
A preliminary investigation into the optical effects of steady-state 1-irradiation of fiber optic delay lines has been completed. The tests in this investigation involve exposing fibers potted in high and low bend stress configurations to 1300 rads/min. (Si02) 1.3 Mev γ-rays. Common optical attenuation kinetics are observed during the growth and recovery phases of the experiment for both high and low bend stress configurations. However, no measureable bendstress related phenomena was observed.
Fiber Optics (FO) testing is required to assure reliability and functional operability of the many FO products currently being developed. It is essential to test end product optical performance under a stringent environment which duplicates temperature extremes, mechanical stresses and caustic atmospheric conditions commonly found in military FO applications. The Naval Air Systems Command (NAVAIR) is currently revising MIL-STD-1678, "Fiber Optic Test Methods," to provide a comprehensive set of current and technically accurate Fiber Optic Test Methods (FOTMs) for evaluation of Military systems, subsystems and components. The goal of this revision is to provide a cost effective standard that will ensure commonality throughout Navy, Army, Air Force and National Aeronautics and Space Administration (NASA) FO programs. Also, it will allow design engineers to avoid duplication in testing and it will aid in selecting appropriate test methods. The standard will be organized to provide a basis for the development of an automated tracking and referencing system. This revision will not only meet current needs, but will also be designed such that it can easily grow to accommodate future needs. Highlights of this revision include development of: (1) Guidelines to identify the essential contents of an FOTM, (2) A standard test method format, (3) An intelligent, user friendly FOTM numbering or identification system, (4) A standard laboratory validation process for test methods to ensure both effectiveness and military applicability prior to inclusion in MIL-STD-1678.
The Navy is currently involved with the development of component specifications and standards for the procurement, installation, and maintenance of fiber optic shipboard systems. This effort has been complicated by the lack of pertinent test data, calibration standards, and adopted test methods. Furthermore, shipboard requirements for fiber optic systems often contrast with those typical of industrial applications. Specifically, the Navy is concerned with short-haul networking, high data rates, enhanced survivability and reliability, and deployment in adverse environments. To reduce component costs and to facilitate procurement processess for shipboard fiber optic systems, the initial effort involved reviewing and evaluating existing military and industry test standards, and adopting or modifying them as necessary. Here is presented an overview of the initial effort to standardize Navy test concepts for fiber optic shipboard applications. These concepts will provide the foundation for system maintenance standards and lend predictability to reliability modelling.
The development of steady state modal conditions in several short length concatenations was studied. The resultant steady state distribution was identified as approximately equivalent to a 70/100 beam optics launch into a short reference fiber. Mechanical methods of reproducing the distribution in a short length of fiber with an initial overfill condition were also studied.
Radiation effects on optical fibers result in two different bffects: accumulated radiation damage resulting in a substantial loss of transmission and transient radiation response in which light is generated in the fiber material itself during exposure .too radiation. In various medical applications, optical fibers are often exposed to radiation during certain clinical procedures which makes their radiation response an effect of concern to the medical community. Thus, this effect needs to be studied and quantified in that kind of environment. This study involves radiation-resistant fibers and the quantification of their light emission response as a function of dose rate and irradiation field size for photon and electron beams at the various energises used in radiation therapy.
In this paper we present the performances obtained with an analog optical baseband link, using a red GaAIAs LED and a common silicon PIN photodiode for the transmission of a single combined TV signal through a PMMA core plastic optical fiber.
A fiber optic multisensor methane detection system matched to topology and environment of a coal mine is reported. The system involves time domain multiplexed (TDM) methane sensors based on selective absorption of source radiation by atomic or molecular species in the gas sensing heads. A two-wavelength ratiometric approach allows simple self referencing, cancels out errors arising from other contaminants, and improves the measurement contrast. The laboratory system consists of a high radiance LED source, multimode fiber, optical sensing head, optical bandpass filters, and involves synchronous detection with low noise photodiodes and a lock-in amplifier. Detection sensitivity upon spectral resolution of the optical filters has also been investigated and described. The system performance was evaluated and the results are presented.
This paper is directed at the use of high power continuous wave and repetitive pulsed lasers used in conjunction with fiber optical components. Until very recently, high power lasers have not been an environment that one would have to be concerned with. Given that some investigators are presently looking at high power lasers for transmission in optical fibers, the problem of laser damage and subsequent catastrophic failure are issues that must be addressed. Equations are provided for determining the maximum threshold damage due to coating interfaces and thermal shock in optical fiber materials. Laser damage at interfaces due to thermal shock is one of the major elements to be dealt with. As it turns out, the cladding on the fiber optic becomes an important player in the maximum threshold of the fiber. The outcoupling surface is the most sensitive to laser damage because this component of damage is a manifestation of the electric field and the mechanical bonding of the coatings.
An All-Silica fiber consisting of a pure silica core/doped silica cladding/hard polymer coating/fluoropolymer buffer was developed and characterized. The All-Silica fiber utilizes a 5-15μm thick proprietary hard polymer coating which is very adherent to the silica surface. The coating is shown to impart similar strength and fatigue characteristics to an All-Silica fiber as is achieved on standard (pure silica core) Hard Clad Silica (HCS®) fiber products. Characteristic strengths of 720 kpsi and static fatigue (n) parameter of 24 are typically observed on the All-Silica fiber presented. The dynamic strength and attenuation are also shown to remain stable during and after temperature cycling (-65 to 125°C) and temperature soak (up to 200°C). Buffered and unbuffered fibers were tested for biocompatibility, achieving a Class VI, Non-Toxic rating.
Polymer coated, silica-based optical fibers are being rapidly deployed for telecommunications. As the use of such fibers grows, they are likely to be exposed to a wide variety of chemicals, especially on customer premises. The effect of four such chemicals, household ammonia, bleach, gasoline, and pesticide, on the strength and static fatigue properties of glass fibers from four manufacturers is examined in this paper. It is found that ammonia and bleach significantly reduce the strength of silica fibers.
Hydrogen permeation rates have been measured for fibers coated with a CVD applied amorphous carbon hermetic barrier. The H2 permeation was characterized by measuring optical loss increases at elevated temperatures at both high and low hydrogen pressures. Very low predicted values for the rates of hydrogen permeation over a wide range of operating temperatures were found, with an experimentally determined activation energy of 23.7 kcal/mole. In-situ measurements of loss increases upon exposure to hydrogen have shown the existence of a lag time where no hydrogen reaches the core of the fiber. Fiber strengths for the carbon coated hermetic fibers are typically 500-600 ksi. Fatigue properties are markedly improved by the presence of this type of hermetic coating. Dynamic fatigue results show extremely high n values on the order of 350-1000. Static fatigue tests in 21 ° C air and 50% relative humidity give n values of about 200. This is a great improvement over the fatigue results for non-hermetic fibers which exhibit n values of approximately 20.
The technology used to make lithium niobate waveguide devices has matured to the point where commercial devices in prototype numbers are available from a large variety of sources. Concomitantly, methodologies and data for assessing device reliability have begun to appear more frequently. The starting material, chip fabrication processes, and packaging techniques all affect device reliability and hence must be examined for their long-term effects. As of now, lithium niobate devices have operated successfully in a variety of systems for times up to two and a half years, and the prospects are excellent for demonstrating the dependability necessary to secure a role in future photonic products
Results of industry-wide round robin comparisons administered by the National Bureau of Standards and the Electronic Industries Association are presented. Multimode fiber parameters include attenuation, bandwidth, core diameter, and numerical aperture. Single-mode fiber parameters include cut-off wavelength and mode-field diameter.
The specification of an optical fiber's mode field diameter (MFD) is explored. Monte Carlo methods are used to generate cumulative density functions of intrinsic splice loss between similar and dissimilar fiber types in order to analyze different MFD specifications. Finally, an improvement to the MFD specification is proposed which is shown to virtually eliminate the compatibility issue of splicing fibers from different suppliers.
A novel technique for analyzing commercially available Optical Time Domain Reflectometers (OTDRs) , to be used in fiber diagnostic and characterization tests, is described. Three OTDR models are selected for evaluation. A series of optical fiber loss and length measurements are made on several single mode fibers to evaluate the performance capability of each of the selected OTDRs. The OTDR properties examined are pulse recovery following a Fresnel reflection, measurement accuracy, and distance accuracy/fault detection capability. The measurements are accomplished both manually and automatically under ambient and low temperature conditions. Pulse recovery immediately following a Fresnel reflection is given primary attention in this paper. A novel measurement technique is adopted for the collection of discrete optical loss data in the region immediately following the Fresnel reflections. An exponential-type curve is assumed for the drop off of the Fresnel reflections. It is found that bases much greater than e (2.72) gives the best fit to the optical loss data. The minimum distance beyond the Fresnel reflection zone at which the backscattered signal is obscured or distorted is determined from the data and model comparison. The minimum extent of the Fresnel reflection zone ranges from 180m to 600m depending the OTDR type and operating mode. Results of preliminary analysis of the measurement accuracy and distance accuracy/fault location capability for each OTDR are also given in this paper.
A new technique for the multimode fiber bandwidth prediction based on a preform profile is suggested. It allows to calculate the output pulse distortion and the bandwidth of a fiber to be drawn dependently of the excitation conditions under which it will operate. It is shown that the accuracy of the bandwidth prediction for 1.5-2.5 km fibers is about 10 %, the bandwidth being 1..1.5 GHzxkm. To achieve this accuracy it is necessary that the excitation conditions and differential mode attenuation be exactly reproduced in the calculation. And the profile variations along length should not be considerable. The predic-tion technique was adapted to P101 Preform Analyser (York Technology) and can replace alpha-approximation curve-fitting during routine manufacture of multimode preforms.
Characteristics of light, such as intensity, phase, polarization, and wavelength have been exploited for fiber optic devices. Recently, use of the modal characteristic of light in a multimode fiber was demonstrated for sensing and modulating applications. Initial studies, using an Automated Mode Analyzer (AMA), a specially developed experimental system designed for the characterization of devices based on modal power redistribution (MPR), is reported.
A method for accurately measuring the coupling ratio of single mode fiber directional couplers is described. The method is insensitive to source fluctuations and eliminates the need for calibrated detectors. Accuracies of ± 0.50% have been demonstrated. The dependence of coupling ratio on input polarization state can also be measured using the technique. Measured coupling ratios on a sample quantity of 20 commercially-available couplers are compared to vendor specifications.
In this paper details and results will be given of the performance of fiber optic couplers when subjected to a variety of environmental tests. These tests include a high humidity/high temperature life test, excessive temperature cycling, vibration and altitude experiments. Results have shown that passive components can be fabricated and packaged to operate reliably under many adverse conditions with negligible change in optical performance.
The linewidth and wavelength tuning characteristics of the distributed feedback and distributed Bragg reflector type single wavelength laser diodes are described. Continuously tunable sources of this type are useful for multichannel coherent transmission systems.
An analytical tool to investigate the arc fusion splicing of optical fibers is developed. The physical model incorporates heat transfer and thermal, visco elastic strain. The heat transfer equations governing radiation, conduction and convection during arc heating are formulated. The radiation heat flux impinging on the fiber optics is modeled based on reported experimental analysis of a generic type arc discharge. The fusion process considers deformation of the fiber due to thermal, viscous and elastic strain. A Maxwell stress-strain relationship is assumed. The model assumes an initial gap at the beginning of the arc which is closed by a press-stroke during the heating cycle. All physical properties of the fused silica glass fibers are considered as functions of temperature based on available experimental data. A computer algorithm has been developed to solve the system of governing equations and parametric studies carried out.
Responsivity is a very important parameter in characterizing the photo-detectors and optical receivers. It is defined as the ratio of photo-current generated to the amount of optical power incident onto the photo-detector. Actual measurement of the optical power being transmitted into the pigtailing fiber is not straight forward and contributes most of the error in the responsivity measurements. In this paper, a repeatable responsivity measurement method is discussed. The essence of this method is to measure the optical power first and attempt to achieve 100% coupling between this optical source fiber and the photo-detector fiber. Using a multimode fiber for the source to couple into the multimode pigtailed photo-detector gives inconsistent measurements and the results are not repeatable. Experiments have been performed using single mode fiber as the source for responsivity measurements, the result has been found to be very consistent. This method is being used as standard operating procedure for manufacturing.
InGaAsP/InP double heterostructure light-emitting diodes (LEDs) provide an excellent source for fiber optic transmitters because of the low transmission losses and minimal material dispersion in silica fibers, which is characteristic of 1.3 μm wavelength transmission. Life testing is performed on a line of commercially available LEDs at both DC and a typical pulse condition. Homogeneous degradation kinetics are derived for current and temperature acceleration.
ABSTRACT The effect of heavy doping (ND>1020cm-3) in n+p region of n+p junction devices were studied. The experimental investigation was done by fabricating different specially fabricated n+ junctions with different carrier concentrations ranging 1 x 1018 - 5 x 1020 cm-3 on a p-type boron doped silicon substrate. The heavy doping was found to have introduced a narrowing of bandgap energy. The contradictory behavior of bandgap shrinkage above 2 x 1020 cm-3 donor density was explained on the basis of FermiDirac Statistics. Lastly, the experimental data had been utilized to arrive at an empirical equation which through iteratively least squares reweighted techniques described the dependence of FDSE on doping concentration.
Surface recombination is very high for unpassivated GaAs photodiodes and hinders performance by lowering Jph while increasing Jo. Present passivation techniques use a GaA1As window layer to reduce recombination at the GaAs surface. However, problems of chemical instability and ohmic contact formation make GaAlAs less than the ideal material. Other potential window materials may better passivate the surface of GaAs while not incorporating the same problems as GaA1As. A new device design is presented which uses localized liquid phase epitaxy (L2PE) to obtain a multilevel structure. This device is useful in testing the performance of different passivating candidates for GaAs by allowing comparison of identical photodiodes with and without passivation. The structure avoids ohmic contact problems to the window layer and permits non-destructive testing of all semiconductor layers.