Interlaboratory comparison of radiation-induced attenuation inoptical fibers. II. steady-state exposures

For pt.I see ibid., vol.6, no.2, p.165-71 (1988). For pt.III see ibid., vol.8, no.6, p.977-89 (1990). The results of steady-state ⁶⁰ Co irradiations of silica core multimode fiber and silica core single-mode and Ge-doped graded index fibers are reported. These data were acquired over the interval of 1987-9. Several significant differences from the results and measurement procedures presented in pt.I must be accounted for in drawing comparisons between the two sets of reported data. Fiber wrap diameter and launched power level were observed to significantly influence the radiation-induced attenuation measured in silica core multimode and single-mode fibers, while the effect was less in Ge-doped silica core multimode fibers     

In-line fiber etalon (ILFE) fiber-optic strain sensors

This paper describes an optical fiber interferometer that uses a short segment of silica hollow-core fiber spliced between two sections of single-mode fiber to form a mechanically robust in-line optical cavity. The hollow-core fiber is specifically manufactured to have an outer diameter that is equal to the outer diameter of the single mode lead fibers, thereby combining the best qualities of existing intrinsic and extrinsic Fabry-Perot sensors. Uniaxial tension and pure bending strength tests are used to show that the new configuration does not diminish the axial strength of bare fiber and reduces the bending strength by 17% at most. Similar tests confirm that the fiber sensor has 1.96% strain to failure. Axisymmetric finite element analysis is used to investigate the reliability of the in-line etalon when it is embedded in a typical thermoset composite, and parametric studies are performed to determine the mechanically optimal cavity length. The fiber optic sensor is tested using low coherence interferometry with pseudo-heterodyne demodulation under strain and temperature fields. The strain response compares well with resistance strain gages, and the temperature tests confirm the low thermal apparent strain of this sensor     

Radiation Response of Fiber Optic Waveguides in the 0.4 to 1.7? Region

The response of fiber optic waveguides to ionizing radiation has been studied. Measurements of the growth and decay of the radiation-induced loss at 0.82? have revealed that fibers with low OH are more susceptible to damage than those with high OH. The addition of P to Ge-doped silica core fibers has been found to suppress an intense transient absorption. Spectral measurements of the radiation-induced absorption between 0.4 - 1.7? have shown an increase in the OH overtone and combination band intensity with irradiation so that the induced loss at 1.3? is actually less in the low OH content silica core fibers than in the high OH content fibers. Real time spectral measurements of the damage following a pulsed irradiation have lead to an identification of the absorption bands and damage mechanisms responsible for the radiation-induced absorption.     

Interlaboratory comparison of radiation-induced attenuation inoptical fibers. I. Steady-state exposures

A comparison of the losses induced at 0.85 μm in three all glass-pure silica core optical fibers by steady-state radiation exposures has been made among five laboratories. Both the growth of the attenuation during irradiation and the recovery following exposures of 3000 and 10⁵ rads have been measured. Although a standard set of parameters was attempted by all laboratories, the slight divergences (0.45⩽σ⩽0.99 dB/km) observed in some data indicate sensitivity of the results to factors such as photobleaching, injection conditions, and sample coil diameter     

Early Index Growth in Germanosilicate Fiber Upon Exposure to Continuous-Wave Ultraviolet Light

In this paper, high-accuracy measurements of ultraviolet (UV)-induced refractive-index changes (plusmn3times10^-7) in germanosilicate optical fiber as a function of intensity and exposure time are presented. To examine the early growth characteristics of the fiber, samples are irradiated with 244-nm light for 100 s at relatively low intensities (0.007-2.7 W/cm²). The combined growth data is then interpolated to generate a 3-D "index growth surface" of photo-induced index. An empirically derived mathematical expression relates the index growth to the exposure time and intensity. Evidence is presented that, after exposing the fiber at one intensity, additional growth at a different intensity is dictated by the final index change of the first exposure and the intensity of the second exposure. This "compound growth rule" permits the complete calculation of induced-grating structures produced by such a complex exposure history. Using the index-growth surface and the compound-growth rule, the growth and UV erasure of a fiber Bragg grating is successfully predicted using a modified F-matrix algorithm     

Interlaboratory comparison of radiation-induced attenuation inoptical fibers. III. Transient exposures

For pt.II see ibid., p.967-76 (1990). A comparison made over a period of five years of the losses induced in step-index multimode, graded-index multimode, and single-mode fibers by pulsed radiation exposure by 12 laboratories is discussed. The recoveries of the incremental attenuations from 10^-9 to 10¹ s are reported. Although a standard set of measurement parameters was attempted, differences between the laboratories are evident; possible origins for these are discussed     

Radiation-resistant low OH content silica core fibers

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 SOCl2. Fibers treated in SOCl2or Cl2also 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.     

Evidence of Secondary-Phase Separation in an Alkali Borosilicate Glass

Transmission electron micrographs of a borosilicate glass containing CuCl semiconducting microcrystals clearly show that secondary-phase separation is present. There are two minor-phase (droplet) size distributions which indicate that upon heat treatment the initial droplet phase oversaturates, thus causing secondary-phase separation.