Gamma Radiation Sensing using Cladding Modes of Specialty Optical Fibers

Optical fibers are widely used in ionizing-radiation environments such as reactors, space systems, and high-energy facilities. Fibers serve both as communication links and sensing elements. Radiation creates microscopic defects in silica that can induce attenuation and refractive-index changes, directly impacting optical performance. These effects depend strongly on glass composition and dopants. Deployment in radiation environments faces an inherent contradiction: fibers optimized for low-loss transmission tend to be poor radiation detectors, whereas radiation sensitive fibers may suffer unacceptable degradation for data transmission. This motivates strategies to decouple transmission and radiation response.

In the proposed approach, the sensing function is spatially separated from the main transmission channel while remaining accessible to optical interrogation. A comparatively radiation-resilient fiber core is used for data transmission, while a radiation-sensitive doped ring is embedded within the cladding to act as the primary interaction region. Radiation-induced changes in the ring can be detected through the coupling of guided light to cladding modes, whereas the core mode remains mostly unaffected. Controlled coupling between the core and selected cladding modes is implemented through either permanent Bragg gratings or Brillouin dynamic gratings, which provide a localized coupling mechanism along the fiber. Measurements of coupling spectra enable spatially distributed readout of radiation-induced changes in the cladding region. This architecture is intended to support simultaneous radiation-resilient transmission and distributed radiation monitoring within a single fiber platform. Preliminary results of gamma radiation effects on the coupling to cladding modes of the fiber will be presented.

Ph.D. student Under the supervision of Prof. Avi Zadok.