Reaching mGy resolution in radiation sensing with a slow-light FBG

Fiber sensors offer significant advantages in the field of radiation sensing, including remote sensing capability, compactness, and potentially high sensitivity. These sensors are optimized in terms of either the fiber length (typically meters or longer) or resolution (often unspecified but usually at the grey level at best), which generally calls for a tradeoff. This paper reports a gamma-radiation fiber sensor with record metrics, namely a dose resolution down to the milligray/√Hz level for a length of only 7 mm. The principle is based on the absorption of light due to the color centers induced in the fiber core by irradiation. Measurements are performed after irradiation, as color centers have a long lifetime. Absorption heats up the fiber, and the temperature rise is measured with a slow-light fiber Bragg grating in contact with the irradiated fiber. The temperature rise, measured in three fibers irradiated with different doses, is proportional to the irradiation dose and equal to 140 mK/Gy at an excitation power of 1 W at 1040 nm. The noise in the sensor output, measured using an Allan deviation technique, is as low as 1 mK/√Hz, leading to a dose resolution of 6 mGy/√Hz.