A simple CCD-camera spectrometer was deployed at the Los Alamos Spallation Radiation Effects Facility to characterize fast neutron irradiation effects in several silica-based optical fibers over the wavelength range ~450-1100 nn. The experimental arrangement allowed optical loss spectra to be developed from remotely recovered frame grabs at various times during irradiation without necessary resort to “cut back” methods. Data recorded for a pure-silica-core/F-doped-silica-clad fiber displayed a peculiar artifact which is described and mathematically modelled in terms of leaky modes propagating in an optical cladding which is substantially less susceptible to radiation-induced optical attenuation than is the core. Evidence from optical time-domain reflectometry supports the postulate that mode leakage into the cladding may be due to light scattering from the tracks of ions displaced by the 14-MeV neutrons. These results suggest that fibers with fluorine doping in the core, as well as in the cladding, would be relatively resistant to radiation-induced attenuation in the UV-visible spectral region

The sensitivity of high NA single mode optical fibers to both steady state and transient radiation environments over the -55 to 80 C temperature range has been evaluated. In accord with prediction, the initial incremental losses are equal to or less than that in comparable telecommunications fibers.< >

The effect of varying single mode fiber fabrication factors such as core and clad dopant concentrations, deposition conditions, and draw parameters on the recovery of the nuclear radiation-induced attenuation at 1.3 μm has been studied. Statistically significant correlations of core factors have been established with a 24 experimental design, and separate one-dimensional experiments revealed the effect of clad [Ge] and [F].

Recent studies have indicated that the birefringent-inducing stress of polarization-maintaining (PM) fibers decreases the long term, permanent loss induced by ionizing radiation and that light polarized along the two orthogonal axes of PM fibers may be attenuated differently by exposure to irradiation sources. This paper reports the results of specific studies of this differential attenuation induced in a series of PM fibers by both steady state and transient irradiations. It has been found that the response to ionizing radiation depends on the materials properties of the fiber, i.e. the core and clad dopants and/or degree of stress, and that the magnitude of the differential attenuation is small relative to the total or one-axis incremental loss.

The low optical attenuation of 1.3-μm single-mode fibers in telecommunication systems can be compromised by exposure to ionizing radiation sources. In spite of a number of prior studies characterizing the radiation response of these waveguides,1 there is a large diversity of sensitivities and recovery behaviors. An example is shown in Fig. 1: the initial loss immediately following exposure can vary from 2.5 to 30 dB/km, and the fibers can either recover completely in 24 h or contain permanent losses of as much as 3 dB/ km.

Optical fiber waveguides may be subjected to unique adverse environments onboard spacecraft, including wide temperature ranges and low dose rate radiation exposures. Since fiber reliability is essential, an accelerated lifetest has been designed to simulate deployment on the Space Station. The initial induced losses following exposure at -150 C are much lower in the fibers with pure than in those with doped silica cores. Good long term recovery is evident at this low temperature in fibers which do not contain P provided light is being transmitted in the waveguide since photobleaching is the dominant recovery mechanism in both types of fiber at -150 C. Except for the P-doped waveguides, the worst-case incremental losses are extrapolated to be < 10 dB/km for a 10 year, 1 rad/day exposure at -150 C with a -20 dBm signal in the fiber. Thus, optical fibers are attractive for use in spacecraft exposed to low dose rate natural space radiation environments.

A set of both pure and doped silica core multimode fibers was irradiated in either pure gamma, pure proton, or mixed neutron-gamma irradiation fields. All parameters were maintained as nearly identical as practical so that a comparison of the effects of each type of irradiation could be made.

Fiber waveguides will be exposed to low-dose- rate nuclear environments in many commercial systems: typical values are ~0.1 rad/year for sea level cosmic ray background and ≳1 rad/day in some spacecraft and nuclear power applications. Most previous studies of radiation effects on optical fibers have employed either pulsed sources or steady-state sources with moderate (10-104-rad/ min) dose rates.1

The response of optical fiber waveguides to radiation has been previously well characterized only at room temperature (except for Ref. 3) for a large number of commercially available and prototype fibers at both 0.85 and 1.3 μm using dose rates of either ~1012 rad/sec for pulsed irradiations or 102-104 rad/min for steady state irradiation.1-3 This paper is the first report of the effect of temperature on the induced loss and recovery of a suite of both single-mode and multimode fibers at 0.85 and 1.3 μm over the —55-80°C typical Mil Spec temperature range and the first measurements of the dose rate dependence of the induced loss over the 0.0007 - 104-rad/min range simulating reactor environs, fallout, or an accelerated cosmic background exposure. The results characterize optical fibers in these important field conditions.

The radiation-induced attenuation of pure silica core fibers measured at 0.85 μm has been reduced by treating the soot preforms in various oxidizing atmospheres; the most effective of the treatments used in this study was SOCl 2 . Fibers treated in SOCl 2 or Cl 2 also have low OH contents. The radiation-induced loss of the treated fibers has been found to follow the square root of the drawing-induced absorption band height at 0.63μm.

Substantial decay of the radiation-induced attenuation in optical fibers within a period of 1 h following a moderate exposure of several kilorads is a requirement envisioned for some optical communication systems. This paper extends previous measurements of recovery following pulsed irradiation1 and long term recovery in some fibers at 0.85 μm3 to include additional multimode fibers, recovery data at 1.3 μm, and the first report of the behavior of single-mode fibers in a radiation environment.

Ge-doped silica-core optical fiber waveguides are attractive for optical communication systems requiring all-glass fibers with low loss and high bandwidth; indeed, many of the all-glass fibers now commercially available are based on the germanium-silica system. In spite of their attractive intrinsic properties, we showed at the Second Topical Meeting on Optical Fiber Transmission1 and in more-recent studies2,3 that these fibers suffer severe degradation in optical transmission when exposed to radiation.

: An analysis was made of the optical recording and readout characteristics of the photodichroic KF:LiF crystal containing F sub A defects as the activated medium. The results of a series of measurements indicate, in agreement with the analysis, that this crystal system has the highest photosensitivity of any direct reversible recording material without a gain mechanism (approx. 1 mJ/sq. cm.). The modulation transfer function for a 200-micrometers-thick activated layer was measured to be 40% at 75 lines/mm, and the dynamic range exceeded 40 dB. The crystal can be operated fatigue free at 220 K by use of thermoelectric coolers, although optimum performance is predicted for a temperature of about 100 K. The wavelength range of photosensitivity lies in the blue and green and matches the argon laser lines. (Author)