Areas where our knowledge and understanding of the response of fibre optics to ionizing radiation are incomplete include effects at extreme temperatures, the role of photobleaching, and transient behaviour at visible wavelengths. Recent measurements are discussed and a model for the radiation impulse response of undoped core fibres, where photobleaching is important, is presented.

Under past radiation test results, it was observed that various combinations of coatings changed the radiation response characteristics of pure fused silica core step index fibers. The most radiation resistant fiber was that coated with a polyimide, which is cured with a high temperature. Based on this fact, additional testing was performed on polyimide coated fibers fabricated from different preform core/clad ratios. Our preliminary results indicated that the smaller the core/clad ratio the better the performance of the radiation response of the fiber. These results are fortuitous for space applications, since the polyimide coating is also a low-outgassing, wide-temperature range, small size fiber coating material. The test results indicate that the variations in radiation response may be due to a post-drawing anneal occurring during coating cure which minimizes drawing-induced defects.

The OH-content of an undoped core all-glass fiber is modified within the range from 1 to 100 ppm. At 860 nm wavelength the radiation resistance expressed by recovery coefficient in the long-term annealing after pulsed irradiation (10 ms - 10 s) increases with increasing water-content and with additional hydrogen-treatment. At 1310 nm wavelength the induced loss at short times after the radiation pulse is smaller due to hydrogen-treatment. The long-term recovery decreases with increasing OH-content, in contrast to 860 nm.

This paper investigates photobleaching at a low temperature in a multi-mode step index pure-silica-core optical fiber. Radiation-induced attenuation and subsequent recovery were measured over a wide range of transmitted optical power levels. These measurements were performed at a wavelength of 850 nm and a temperature of -55 °C using the NATO/FOTP-49 test procedures. When low levels of optical power were used, the maximum attenuation increased by a factor of ten and the recovery time increased by a factor of thirty compared with results at high optical power. Complete recovery required several hours at the lowest optical powers.

Photobleaching at 340 and 1300 nm wavelengths of three multimode silica fibers under steady-state gamma irradiation (2 x 480 Gy, 120 Gy/h) at room temperature was studied as regards induced loss and recovery kinetics. Significant differences in behaviour between two pure silica-core fibers (plastic clad QSF 200 A and fluorine doped-clad AS 200 -300 from Quartz et Silice) and a germanium doped-core fiber 7020/250 from Compagnie Lyonnaise de Transmissions Optiques are presented. The hardening up to 0.1 MGy of a short bidirectional data link designed to operate a servomanipulator in a hot cell is described as an example of application.

Two long-term reliability issues for silica based optical waveguides used in adverse environments are strength degradation by static fatigue and optical loss increases due to hydrogen diffusion into the lightguide structure. Hermetic coatings can prevent the reaction of OH and H2 with the optical fiber thus overcoming these long-term aging effects which can degrade fiber performance. Processing techniques for the in-line deposition of a hermetic coating will be discussed and fiber performance evaluated.

Telecommunications has provided the primary impetus for the explosive growth in fiber-optics technologies over the last decade. However, although standard telecommunications is the largest volume-user of optical fibers, other applications that exploit the unique attributes of photonics systems are becoming increasingly prominent. Many of these systems require that the fiber properties remain acceptable while exposed to a challenging variety of adverse environments. Many of these environments include exposure to ionizing radiation. Radiation-induced modifications to optical materials have been studied for several decades, so it was to be anticipated that such effects would be present in optical fibers. Many papers and several comprehensive reviews",3,4 have been devoted to better understand-ing of such phenomena.

Experimental investigation has been carried out demonstrating mode-selective amplification in fibers by the backward stimulated Raman scattering process, thereby improving signal bandwidth in the fiber compared to an unamplified transmission. The feasibility of simultaneously amplifying multiple data channels using a single flashlamp-pumped dye laser was also shown.

Design, analysis, manufacturing and testing of an electro-opto-mechanical (EOM) cable incorporating metal tube protected single-mode fibers is discussed with respect to application in undersea towing of fiber optic interferometric sensor arrays. An explaination for observed low-noise phase data transmission capability of this lead tow cable is given. Constraints related to the cable operational environment are considered in conjunction with cable analytical modelling and performance prediction.

Responsible electrical equipment should be controlled during the work in care of their high reliability. Traditional control measurement systems cannot fulfil the task because of the hard conditions in which the equipment may operate (various electrical potentials, electromagnetic interferences, changes of temperature, etc.). The development of fibre optic transmission media and fibre optic sensors allows the construction of new control measurement systems for cooperation with such electrical equipment as: converters, generators, treLnsforniens, switch bays, busbards, etc. Those optical fibre structures, composed of bu-ses and sensors are subject of this paper. The main attention is paid to the structure of the systems including couplers and area extention of the networks depending on the functions in the electric systems. The authors present the first stage of laboratory and field tests for optical fibre sys-tems in control-measurement networks for HV/HP substations, power everhead lines, electrical equip-ment etc.

We have been able to show the creation of irradiation damages to a irradiated silicate glass, basic material in optical fiber, by studying its thermostimulated luminescence. The phenomenon whose importance could be essential in particular situations is the subject of a research programm'in collaboration with the C.E.A. (SDHA, Marcoule, F) concerning borosilicate glass that is the basic frit of glass used for radioactive waste confining. The created damages are correlated to bond breaks such as Si-0 or B-0. We are considering the possibility of extending this research to optical fibers.

We discuss preliminary measurements of the response of gallium arsenide integrated optical waveguides to radiation from a Febetron. The Febetron produces electrons in the 300-700 keV rangelA in approximately 3-ns FWHM pulses, with a maximum dose rate of approximately 10 rad/sec. "Prompt" radiation effects were monitored on a streak camera recording system.

Four kinds of high reliability optical components; LD module, APD module, optical coupler and optical shutter, have been developed for undersea repeaters. These components have sufficient reliability for undersea system applications, as the result of environmental reliability tests which were carried out for 10,000 hours with 200 samples.

Plastic optical fiber transmission link (POFTL) becomes an atractive option for short distance LAN's and industrial applications. In this work, we investigate the influence of LED optical characteristic variations due to its junction temperature changements on performances of a PMMA core POFTL. A selective loss As is introduced for this purpose. The value of As is found to be 0.33dB/km°C.

The radiation sensitivity of several silicon optoelectronic sensors (photodiodes, linear arrays, CCD) has been measured under pulsed gamma irradiation. The transient effects are presented as a function of both dose and dose rate .

The paper consists of three major parts: 1) general idea of special purpose optical fibres manufacturing, 2) technological process and material considerations, 3) applications considerations and conclusions. Special-purpose optical fibres were assembled in this work of glass rods (rectangular or circular) to give eventually more or less classical structure containing one or multiple core and one homogeneous or nonhomogeneous optical-supporting cladding. Some modifications of this basic assembling technology may also include multistage hybrid process like multicrucible and multirod-in-tube. These processes give only intermediate preforms. We suggest here a namelMOSAIC FIBRESIfor optical filaments manufactured by the preform assembling technology. Several technological experiments have been performed to manufacture some basic kinds of mosaic optical fibres. Several kinds of specialty optical fibres like: multicore, noncircular core, nonhomogeneous core, ring-like core, attenuation/dispersion/birefringence/polarization tailored, polarizing/modulating/amplifying etc, have been used to build optical fibre compatible devices and censors. Some of these devices and sensors have been applied in laboratory simulated hostile environments.

In this paper will be described the analytical expressions which will provide the damage thresholds of infrared and visible imaging systems when subjected to high power continuous wave and repetitive pulsed laser devices. The primary optical components that comprise a system are generally optical substrates that have vapor deposited reflective metal films or are diamond turned metallic substrates to maximize reflectivity. Additionally, one will find optical thin films used to enhance reflectivity and transmission through the optical train. For those systems that are designed for the infrared, the materials that have the best reflectivity at 10.6 p.m. 1.06 p,m, etc. are very highly absorbing in the visible portion of the spectrum. This enhanced absorption in the visible portion of the spectrum provides for very low damage thresholds when subjected to visible continuous wave and repetitive pulsed lasers. Thereare, of course, visible optical systems which are very sensitive to the visible portion of the spectrum, i.e., the eyes of a human being. Equations are provided for one and three dimensional analysis of temperature gradients in the optical thin films and slip and melt thresholds for metallic substrates. Further, equations are provided for both the semi-infinite plate boundary condition and for those substrates that have a thickness less than required for semi-infinite plate boundary using the Reverse Thermal Wavemodel. Pictures of in band and out of band damage are provided and curves are plotted for the various coatings on commonly used substrate materials.

In the framework of the development of an extrinsic type fiber-optic interferometric sensor, the design and the qualification tests of the sensing microprobe are presented. The microprobe is the end-termination of a fiber-optic instrument devised for the monitoring of the end-turn vibrations of large generators. Since the monitoring must be made in real operating conditions, the microprobe must survive in real harsh environment: 100°C average temperature, very high electromagnetic field (30000 Amp. average current), pure hydrogen at 4 atmosphere pressure, high mechanical noise. The microprobes were developed following two approaches: conventional and stacked micro-optics concept. Several thermal tests showed a better behaviour by the stacked-optic microprobe. During the test, autointerference modulation phenomena appeared on the control beams. A hypothesis of a polyetalon existence inside the microprobe was formulated and its correctness was supported by a computer simulation. Preliminary qualification tests of the whole interferometric instrument, ended by the stacked-optic microprobe, showed an excellent response over the whole thermal operating range.