A fiber optic sensor for simultaneous measurement of refractive index and temperature is presented. The sensing probe is realized by introducing a multimode interference device inside a high birefringence fiber loop mirror resulting in a configuration capable of refractive index and temperature discrimination. The multimode interference peak is sensitive to the surrounding refractive index (90 nm/RIU) and slightly responsive to the temperature (0.01 nm/°C). On the other hand, the birefringent fiber loop mirror is highly sensitive to temperature (2.36 nm/°C) and it has almost no response to refractive index. Using a power ratiometric peak detection scheme, a temperature independent refractive index measurement can be achieved with a resolution of ±2.25 × 10-5 RIU. © 2012 Elsevier B.V.177 17171723Fan, X.D., White, I.M., Shopova, S.I., Zhu, H.Y., Suter, J.D., Sun, Y.Z., Sensitive optical biosensors for unlabeled targets: A review (2008) Analytica Chimica Acta, 620, pp. 8-26Kim, C.-B., Su, C.B., Measurement of the refractive index of liquids at 1.3 and 1.5 micron using a fibre optic Fresnel ratio meter (2004) Measurement Science and Technology, 15 (9), pp. 1683-1686. , DOI 10.1088/0957-0233/15/9/002, PII S0957023304758701Suhadolnik, A., Babnik, A., Mozina, J., Optical-fiber reflection refractometer (1995) Sensors and Actuators B: Chemical, 29, pp. 428-432Kumar, A., Subrahmanyam, T.V.B., Sharma, A.D., Thyagarajan, K., Pal, B.P., Goyal, I.C., Novel refractometer using a tapered optical fibre (1984) Electronics Letters, 20 (13), pp. 534-535Pereira, D.A., Frazao, O., Santos, J.L., Fiber Bragg grating sensing system for simultaneous measurement of salinity and temperature (2004) Optical Engineering, 43, pp. 299-304Asseh, A., Sandgren, S., Ahlfeldt, H., Sahlgren, B., Stubbe, R., Edwall, G., Fiber optical bragg grating refractometer (1998) Fiber and Integrated Optics, 17 (1), pp. 51-62Laffon, G., Ferdinand, P., Tilted short-period fibre-Bragg-grating-induced coupling to cladding modes for accurate refractometry (2001) Measurement Science and Technology, 12 (7), pp. 765-770. , DOI 10.1088/0957-0233/12/7/302, PII S0957023301203713, Optical Fibre SensorsHan, M., Guo, F.W., Lu, Y.F., Optical fiber refractometer based on cladding-mode Bragg grating (2010) Optics Letters, 35, pp. 399-401Patrick, H.J., Kersey, A.D., Bucholtz, F., Analysis of the response of long period fiber gratings to external index of refraction (1998) Journal of Lightwave Technology, 16 (9), pp. 1606-1612. , PII S0733872498066699Allsop, T., Reeves, R., Webb, D.J., Bennion, I., Neal, R., A high sensitivity refractometer based upon a long period grating Mach-Zehnder interferometer (2002) Review of Scientific Instruments, 73, pp. 1702-1705Díaz-Herrera, N., Gonzalez-Cano, A., Viegas, D., Santos, J.L., Navarrete, M.C., Refractive index sensing of aqueous media based on plasmonic resonance in tapered optical fibres operating in the 1.5 μm region (2010) Sensors and Actuators B: Chemical, 146, pp. 195-198Zamarreno, C.R., Sanchez, P., Hernaez, M., Del Villar, I., Fernandez-Valdivielso, C., Matias, I.R., Arregui, F.J., Dual-peak resonance-based optical fiber refractometers (2010) IEEE Photonics Technology Letters, 22, pp. 1778-1780Fukano, H., Matsumoto, Y., Taue, S., High-sensitivity optical fiber refractive index sensor using multimode interference structure (2012) IEICE Electronics Express, 9, pp. 302-306Jung, Y., Kim, S., Lee, D., Oh, K., Compact three segmented multimode fibre modal interferometer for high sensitivity refractive-index measurement (2006) Measurement Science and Technology, 17, pp. 1129-1133Silva, S., Pachon, E.G.P., Franco, M.A.R., Hayashi, J.G., Malcata, F.X., Frazao, O., Jorge, P., Cordeiro, C.M.B., Ultrahigh-sensitivity temperature fiber sensor based on multimode interference (2012) Applied Optics, 51, p. 2542Biazoli, C., Silva, S., Franco, M.A.R., Frazao, O., Cordeiro, C.M.B., Multimode interference tapered fiber refractive index sensors (2012) Applied Optics, 51 (24), pp. 5941-5945. , 10.1364/AO.51.005941Zhao, Y., Wu, H.K., Wang, Q., Advances of high-birefringence fiber loop mirror sensors (2011) Journal of Optoelectronics and Advanced Materials, 13, pp. 457-465Frazao, O., Marques, L.M., Santos, S., Baptista, J.M., Santos, J.L., Simultaneous measurement for strain and temperature based on a long-period grating combined with a high-birefringence fiber loop mirror (2006) IEEE Photonics Technology Letters, 18 (22), pp. 2407-2409. , DOI 10.1109/LPT.2006.886139Frazao, O., Marques, B.V., Jorge, P., Baptista, J.M., Santos, J.L., High birefringence D-type fibre loop mirror used as refractometer (2008) Sensors and Actuators B: Chemical, 135, pp. 108-111Kang, J., Dong, X.Y., Zhao, C.L., Zhang, Z.X., Jin, S.Z., Measurement of refractive index with a PM-LPG based Sagnac loop sensor (2011) Spectroscopy and Spectral Analysis, 31, pp. 902-905Zibaii, M.I., Frazao, O., Latifi, H., Jorge, P.A.S., Controlling the sensitivity of refractive index measurement using a tapered fiber loop mirror (2011) IEEE Photonics Technology Letters, 23, pp. 1219-1221Zhong, C., Shen, C., You, Y., Chu, J., Zou, X., Dong, X., Jin, Y., Wang, J., A polarization-maintaining fiber loop mirror based sensor for liquid refractive index absolute measurement (2012) Sensors and Actuators B: Chemical, 168, pp. 360-364Jesus, C., Caldas, P., Frazao, O., Santos, J.L., Jorge, P., Baptista, J.M., Simultaneous measurement of refractive index and temperature using a hybrid fiber Bragg grating/long-period fiber grating configuration (2009) Fiber and Integrated Optics, 28 (6), pp. 440-449Silva, S., Santos, J.L., Malcata, F.X., Kobelke, J., Schuster, K., Frazao, O., Optical refractometer based on large-core air-clad photonic crystal fibers (2011) Optics Letters, 36 (6), pp. 852-854Zibaii, M.I., Kazemi, A., Latifi, H., Azar, M.K., Hosseini, S.M., Ghezelaiagh, M.H., Measuring bacterial growth by refractive index tapered fiber optic biosensor (2010) Journal of Photochemistry and Photobiology B: Biology, 101 (DECEMBER 3), pp. 313-320Zibaii, M.I., Latifi, H., Karami, M., Gholami, M., Hosseini, S.M., Ghezelayagh, M.H., Non-adiabatic tapered optical fiber sensor for measuring the interaction between alpha-amino acids in aqueous carbohydrate solution (2010) Measurement Science and Technology, 21 (10), p. 105801