A hydrogel-coated optical fiber surface plasmon resonance (SPR) sensor based on MMF-SMF-MMF structure has been fabricated for pH measurements. When the solutions with difference pH values contacting the sensing probe, the amount of the dissociated carboxylic ions in the hydrogel will change according to the pH value of the solution. This process will modify the volume and refractive index of the hydrogel, which results in a shift of the SPR wavelength. The experimental sensor is able to indicate pH variations in a wide pH range from 1 to 12, and the maximum pH sensitivity of the proposed sensor can reach 13 nm/pH at higher pH region (8–10 pH). The influence of temperature (in the range of 20 °C–40 °C) on SPR wavelength is found to be weak. Further, the sensor possesses remarkable repeatability and excellent stability. Due to the wide measuring range and simple fabrication process, the sensor is promising to be used for the pH measurements.

制备了基于MMF-SMF-MMF结构的水凝胶包覆的光纤表面等离子体共振（SPR）传感器，用于pH值测量。当具有不同pH值的溶液接触传感探针时，水凝胶中解离的羧酸根离子的量将根据溶液的pH值而变化。该过程将改变水凝胶的体积和折射率，从而导致SPR波长的偏移。实验传感器能够指示从1到12的宽pH范围内的pH变化，建议的传感器的最大pH灵敏度在较高pH区域（8-10 pH）下可以达到13 nm / pH。发现温度（在20°C–40°C的范围内）对SPR波长的影响很小。此外，该传感器具有卓越的可重复性和出色的稳定性。