We propose a technique to measure in situ the refractive index changes induced by ionizing radiation in single-mode optical fibers. This change can be derived from the channel drift appearing in narrow channel wavelength-division-multiplexing couplers exposed to gamma radiation. We measured a radiation-induced refractive index change of about 5 10/sup -6//kGy[H/sub 2/O] at low doses and 5 10/sup -7//kGy[H/sub 2/O] at higher doses. No saturation was observed up to a total gamma dose of 13 MGy.

In situ measurement of refractive index changes induced by gamma radiation in germanosilicate fibers

Thermonuclear reactors will require permanent monitoring under high-gamma dose rates and high neutron flux. We propose to get rid of the digital data transmission limitations in highly radioactive environments by implementing an analog fiber-optic link based on directly modulated vertical-cavity surface-emitting laser (VCSELs). In this paper, we introduce an architecture for highly radiation-tolerant instrumentation data links based on the intrinsic wavelength division multiplexing capabilities of fiber-optic data transmission. The potential radiation acceptance level of the analog fiber-optic link is estimated on the basis of irradiation results on individual COTS photonic components such as VCSELs, fiber-optic passive multiplexers, and optical fibers.

Toward the development of radiation-tolerant instrumentation data links for thermonuclear fusion experiments

Fiber optics are being effectively utilized in an increasing range of data and information transfer applications. A less mature, but equally challenging, application of fiber optics concerns their use for a host of sensor technologies. Fiber sensors have now been developed for measurement of many physical parameters. These sensor systems frequently exploit several general attributes of fibers, including: cost, an all-dielectric trans-mission medium, freedom from electrical interference, bandwidth, resistance to degradation in severe or adverse environments, light weight, etc. This paper summarizes the use of fiber optics or guided optical systems for radiation sensors. It is limited to passive systems wherein electrical power is not required at the sensor location. However, electrically powered light sources, receivers and/or recorders may still be required for detection and data storage in sensor system operation. This paper emphasizes sensor technologies that permit high bandwidth measurements of transient radiation levels, and will also discuss several low bandwidth applications. In addition to discussion of several specific sensor concepts, an extensive bibliography is included to guide research into these, or other, forms of radiation sensors. The bibliography is subdivided into four major categories. In the bibliography, each paper is listed only once, even though a given paper may include data appropriate to several sections. Furthermore, to avoid long reference lists within the text, only a few of the bibliographical entries are referenced therein. The present conference is not included in the reference list, but includes several related papers. Four other general reviews of related technologies may be of particular benefit.1-4

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Review of high bandwidth fiber optics radiation sensors

Multiple-beam Fizeau fringes in transmission have been applied to gamma -irradiated blue Cashmeline fibres, to determine their refractive indices for plane-polarised monochromatic light at gamma =5461 AA, vibrating parallel and perpendicular to the fibre axis, and the birefringence over the range from 5 Mrad up to 200 Mrad.

https://iopscience.iop.org/article/10.1088/0022-3727/22/6/011/pdf

Effect of gamma irradiation on the refractive indices, birefringence and optical absorption of blue Cashmeline fibre

Multiple-beam fringes of the Fizeau-type transmission and on reflection were utilised for the studies of the optical properties of gamma -irradiated Dralon fibres. Irradiation was carried out over a period of 24-1948 h. The dose rate was maintained at 14.7+or-0.2 rad s-1. Empirical formulae were suggested to represent the variation of refractive indices and birefringence with the dose. Variation of the mean refractive index with the wavelength of light has been studied, and the constants A and B of Cauchy's dispersion formula were calculated. This multiple-beam interferometric method was also applied to determine the thermal coefficient of refractive index of the fibres. Micro-interferograms are given for illustration.

https://iopscience.iop.org/article/10.1088/0022-3727/19/12/023/pdf

Effect of gamma irradiation on the optical properties of fibres

An interferometric method is discussed which enables changes in refractive index of irradiated optical fibers to be determined. The method was used to determine the changes of step-index fibers irradiated with 1 krad of γ rays from a 60Co source. In one case, relative changes in the core and cladding radii of 3.9‰ and 1.8%, respectively, and in the core and cladding refractive indices of 2.8‰ and 2.26‰, respectively, have been determined.

A. Ferrari

Papers

Differential interferometry of γ-irradiated optical fibers

RADII and refractive index changes in γ - irradiated optical fibers