A hybrid interferometric optical fiber temperature-salinity-depth sensor based on Fabry-Perot interferometer(FPI)cascaded Mach-Zehnder interferometer(MZI)is proposed.A 28 μm FPI micro cavity is fabricated by using two single-mode fiber and silica capillary.The single-mode fiber derived from FPI is aligned and fused with multi-mode fiber with large core diameter and fine-core fiber successively,and the single-mode fiber is misaligned and fused behind the fine-core fiber.The single mode-multimode-thin-core-misaligned fusion single mode fiber derived from FPI is composed of MZI.Theoretical analysis and experimental study are carried out on the temperature,refractive index and depth response characteristics of the sensor.By monitoring the reflection spectrum and transmission spectrum,different characteristic wavelengths are selected.Experimental results show that FPI is not sensitive to refractive index changes,and the sensitivity of temperature and depth is 0.578 nm/tC and 1.297 2 nm/cm.The sensitivity of two characteristic troughs of MZI to temperature is 0.052 4 nm/℃ and 0.0552 nm/℃,and the refractive index sensitivity is-35.157 nm/RIU and-27.581 nm/RIU,which is insensitive to depth change.The sensor has the advantages of simple fabrication and low cost.
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