CONCLUSION
In this paper, an all-optical fiber RI sensor based on multimode interference has been proposed and experimentally demonstrated. SCS configuration comprises of CLF section which represent the sensing area spliced between two small pieces of SMF. A various diameters of CLF of 100 and 50 μm with three different tune lengths 20, 25 and 30 mm have been employed as a sensing area to substitute the traditional MMF. The effect of CLF diameter variation on the sensor performance has been examined. Chemical etching process was used to tune the CLF diameter from 100 to 50 μm. The experimental results of the SCS configuration encompassed of the etched CLF at 50 μm diameter with a CLF length of 25 mm exhibited the greatest sensitivity of about 1012 nm/RIU. The SCS structure has attractive benefits such as low cost, high measurement sensitivity, simple structure, and fast response.