SPR turbidity sensor using microstructured POF coated with gold film

In this study, a turbidity sensor utilizing a polymer optical fiber is fabricated through micromachining and coated with a gold film is presented and validated (termed mm-POF_Au). The mm-POF_Au turbidity sensor employs intensity modulation principles, leveraging alterations in transmitted light intensity induced by interactions with the light field and surface plasmon resonance phenomena. UV laser is used for micromachining to create a narrow groove structure, and subsequently, a uniform gold coating is applied to the fiber's sensor section. Examinations are conducted on the influence of the machining pitch on the sensor's turbidity response. The experimental results revealed that the mm-POF_Au turbidity sensor exhibits a linear response behavior, exhibiting a resolution of approximately 0.04 NTU, with a functional detection range from 0 to 400 NTU. The sensor's output response is obtained when the machining pitch is set at 400 μm, accompanied by an enhanced sensitivity of 2.4 nW/NTU, thereby also contributing to a more stable performance. In addition to its precision and sensitivity, the sensor's repeatability and susceptibility to temperature variations are also meticulously characterized. Furthermore, this method paves the way for an indirect evaluation of turbidity by exploiting the variations in heat transfer rates attributable to escalating turbidity levels, thereby enriching the scope of turbidity assessment techniques.