Fiber optic interferometers to sense various physical parameters including temperature, strain, pressure, and refractive index have been widely investigated. They can be categorized into four types: Fabry-Perot, Mach-Zehnder, Michelson, and Sagnac. In this paper, each type of interferometric sensor is reviewed in terms of operating principles, fabrication methods, and application fields. Some specific examples of recently reported interferometeric sensor technologies are presented in detail to show their large potential in practical applications. Some of the simple to fabricate but exceedingly effective Fabry-Perot interferometers, implemented in both extrinsic and intrinsic structures, are discussed. Also, a wide variety of Mach-Zehnder and Michelson interferometric sensors based on photonic crystal fibers are introduced along with their remarkable sensing performances. Finally, the simultaneous multi-parameter sensing capability of a pair of long period fiber grating (LPG) is presented in two types of structures; one is the Mach-Zehnder interferometer formed in a double cladding fiber and the other is the highly sensitive Sagnac interferometer cascaded with an LPG pair.

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This article presents an investigation of the phase equilibria in the Sn-Bi-In ternary alloy system, performed both by theoretical and experimental methods. Following the regular solution model and a standard thermochemical calculation, a theoretical evaluation of the phase equilibrium in the entire ternary system is conducted. The thermodynamic parameters required for the calculation are initially obtained by fitting the model to existing data available from prior studies. The theoretical results are then validated and further improved by experimental work in which alloys with several critical compositions were chosen and examined. In the experimental work, differential scanning calorimetry (DSC), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX) spectroscopy were jointly used to identify the transition temperatures and the phases in the microstructure. The resulting phase diagram agrees well both with the existing data and with the data from the current experiments. However, different from previous findings, this study finds a nonbinary nature of the Sn-BiIn and Sn-BiIn 2 quasi-binaries and nine invariant reactions, one eutectic, six peritectic and two peritectoid. The phase-reaction scheme (Scheil diagram), the liquidus projection, and the phase diagram, covering entire compositional ranges, are established.

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