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This letter proposes a new magnetic field sensor using phase-shift fiber loop ring-down (PS-FLRD) technique combined with single mode-no core-single mode fiber (SNS) structure. This is the first time the PS-FLRD technique has been applied to magnetic field sensing. The magnetic fluid (MF) coated SNS structure is the sensing head. Among them, we have creatively proposed and derived the discrete PS-FLRD model. We calculated and experimentally verified the linear region of the system and achieved $R^{2}$ above 0.999. Finally, we have used the linear region in combination with the SNS structure to measure the magnetic field, achieving a sensitivity of ${5\times 10}^{-5}$ /Gs in the measurement range of 0-200Gs. This work demonstrates the significant potential of the PS-FLRD technique combined with interferometric structures in sensing.

Radiation measurement is critical in ensuring astronauts' safety during space exploration. Although various radiation monitoring techniques have been developed, achieving high-precision measurements remains a significant challenge. This study proposes an improved phase shift fiber loop ring-down (PS-FLRD) system for measuring radiation levels. To enhance the accuracy of the PS-FLRD model, we have constructed a more precise model under discrete conditions, which reduces the fitting error of the phase versus loss equation. Moreover, we have implemented a dual optical path design to mitigate errors arising from environmental changes and ensure the long-term stability of the radiation measurement process. As a result of these improvements, our system can achieve high resolution and low uncertainty, with values of 80 $\mu$dB and 13 mdB, respectively. This level of precision enables the detection of loss variations of 1 m erbium-doped fiber at a radiation dose of 1 Gy, which is one to two orders of magnitude higher than that of commercial instruments. Our proposed system is highly beneficial for measuring the exposure of astronauts to the radiation environment, providing a strong safety guarantee for future surface exploration of the moon and Mars.