Tapered Single-Mode Optical Fiber pH Sensor Coated with Hydrogel Working at the Dispersion Turning Point

A pH sensor based on the dispersion turning point (DTP) is proposed, with a structure involving a thin layer of calcium alginate hydrogel coated on a tapered single-mode fiber (SMF). The tapered SMF with a waist diameter of 3.85 μm and a length of 7000 μm is fabricated using a two-step tapering method. Experimental results indicate that the sensitivity of the sensor to pH values ranging from 7.03 to 8.45 is 58.11 nm/pH. The pH sensor we proposed features high sensitivity, low cost, and simple fabrication process, among other advantages.