Optimum sensitivity of single-mode D-type optical fiber sensor in the intensity measurement

To improve the sensitivity of a single-mode D-type optical fiber sensor in the refractive index range 1.33–1.40, we selected parameters such as, a D-type optical fiber sensor made of a single mode fiber with 4 mm long and 4 μm core radius, a Au-coating with a thickness range of 20–60 nm, a wavelength of 632.8 nm, and an incident angle at the range of 88–89.5° to simulate. These reflectance simulations are based on the surface plasmon resonance (SPR) theory. The results show that the optimum sensitivity for a specific refractive index measurement corresponds to a specific Au film thickness. The optimum sensitivity is close to a value of 40 (1/RIU (refractive index unit)). The best resolution is better than 2.5 × 10−5 RIU as the minimum intensity variation is 0.1%. This device is used to detect the refractive index or gas or liquid concentration in real time, and it has some merits such as, small, easy to manufacture, compact and inexpensive and could be in vivo test.