Searching for optimal sensitivity of single-mode D-type optical fiber sensor in the phase measurement

To improve the sensitivity of a single-mode D-type optical fiber sensor, we selected a D-type optical fiber sensor with 4 mm long and 4 μm core thickness made of a single-mode fiber, a Au-coating on the sensor with a thickness range of 15–32 nm, a light wavelength of 632.8 nm, and an incident angle of 86.5–89.5° for different refractive index (1.33–1.40) sensing. These simulations are based on the surface plasmon resonance (SPR) theory using the phase method which shows that the sensitivity is proportional to the refractive index, Au film thickness and lower incident angle on the sensing interface. The sensitivity is higher than 4000 (degree/RIU), and the resolution is better than 2.5 × 10−6(RIU) as the minimum phase variation is 0.01°. This device is used to detect the refractive index or gas or liquid concentration in real-time. The proposed sensor is small, simple, inexpensive, and provides an in vivo test.