Refractive index (RI) sensors are of importance in many applications since many physical, biochemical, and environmental parameters can be detected by examining RI variations. In this paper, we describe an intensity-modulated RI sensor using a bismuth telluride (Bi2Te3)–integrated tilted fiber Bragg grating (TFBG) configuration. Bi2Te3 is deposited on the fiber cylindrical surface using magnetron sputtering technology. The light–matter interaction of Bi2Te3 is activated, and the optical tunable feature is used for RI measurement. The maximum RI sensitivity is ~333.4 dB/RIU. Furthermore, when the intensity difference between the cladding mode and the core mode is used for RI measurement, the result is immune to light intensity fluctuation. Moreover, the area occupied by all cladding modes is used in the RI sensitivity calculation, thus a wide RI range measurement is realized. To the best of our knowledge, this is the first time that Bi2Te3 is used for an optical fiber sensor, and we hope that the idea presented can be found interesting by the sensing community.