A Novel Bifolium‐Shaped Fiber Measurement System for Decoupled Detection of Dilution and Adulteration in Beverages via Refractive Index Modulation

Fresh‐squeezed orange juice is one of the most popular and widely consumed drinks worldwide. In fact, it is a pricey product compared to most other juices, thereby increasing the risk of adulteration for economic reasons. In this paper, a novel dual‐channel optical fiber sensor based on a bifolium‐shaped fiber structure for measuring fruit juice dilution and adulteration is proposed and experimentally demonstrated. The bifolium‐shaped fiber structure was made by bending a single‐mode fiber (SMF) to an almost symmetric two‐leaf geometry. Optimizing the leaf diameter caused two distinct resonant dips, namely dip SR1 and dip SR2 , to appear in the transmission spectrum of the bifolium structure, one dip for each leaf. Thereby, each leaf forms a separate sensing region. The first sensing region (SR1) was used to measure the dilution of freshly squeezed orange juice with deionized water, and the second region (SR2) was used to detect its adulteration with commercial orange fruit juices bought from the supermarket. Experimental results indicate that the sensor detects dilution of fresh‐squeezed orange juice and adulteration with cheaper orange juice, with sensitivities of −0.686 and −0.744 nm/%, respectively. The results showed that the bifolium‐shaped structure can serve as a potential dual‐channel sensing method for food liquid quality assurance, reducing both time and device requirements.