Temperature-insensitive sensor based on U-shaped few-mode fiber for blood glucose brix measurement

In this study, a U-shaped few-mode fiber (FMF) sensor for blood glucose brix measurement is proposed, which is temperature-insensitive. These sensors with smaller bending diameters can be obtained by bending single-mode fiber (SMF)-FMF-SMF. The light leaks from fiber core to fiber cladding because the bending, which results in the occurrence of modal interference. The experiments show that the maximum blood glucose brix sensitivity is up to $1.081 \text{nm} / \%$ in the blood glucose brix range of 0%-18%, when the bending diameter is $\sim 1 \text{mm}$. And the sensors are temperature-insensitive in the temperature range of $10^{\circ} \text{C}-40^{\circ} \text{C}$. The sensor has advantages of compact structure and high sensitivity. Therefore, the sensor is suitable for applications in fields such as biomedicine.