Optical fibers have been involved in the area of sensing applications for more than four decades. Moreover, interferometric optical fiber sensors have attracted broad interest for their prospective applications in sensing temperature, refractive index, strain measurement, pressure, acoustic wave, vibration, magnetic field, and voltage. During this time, numerous types of interferometers have been developed such as Fabry-Perot, Michelson, Mach-Zehnder, Sagnac Fiber, and Common-path interferometers. Fabry-Perot interferometer (FPI) fiber-optic sensors have been extensively investigated for their exceedingly effective, simple fabrication as well as low cost aspects. In this study, a wide variety of FPI sensors are reviewed in terms of fabrication methods, principle of operation and their sensing applications. The chronology of the development of FPI sensors and their implementation in various applications are discussed.

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Major factor effects the durability of a concrete structures is cracks formation induced by expansion of reinforcement corrosion. Therefore, monitoring and evaluating the corrosion level of structure is essential for its safety. In order to monitor corrosion, an innovative methodology based on Fiber Bragg Grating sensing technique was developed and tested in this paper. The method uses the volume of corrosion products to detect the evolution of corrosion. The corrosion process was accelerated by impressed current technique. A correlation between the FBG wavelength shift and corrosion percentage of reinforcement was found.

This letter reports a fiber optic sensing technology for the detection of salinity and liquid level of a given solution. The operation principle is based on the displacement measurement in a large measuring range by generating a variety of outputs for various sensing objectives. The proposed sensor is investigated analytically and experimentally. The achieved salinity sensitivity is 8.589 /%, in addition, the proposed sensor exhibits an excellent liquid level sensitivity of 0.4421 /mm in the experiment.Index Terms-Fiber optic displacement sensor, refractometer, plastic optical fiber, intensity modulation.

With the pace of increasing online transactions and communication, the demand for security and privacy increases. To protect confidential information and to authenticate people electronically, several solutions already introduced. Traditional biometric systems that are based on single biometric usually suffer from problems like impostors' attack or hacking, unacceptable error rates. To improve security and privacy and system's reliability two or more biometrics of the same identity could be combined in a method that enhances the efficiency of the system. The biometric information, however, is irreplaceable information, when it is compromised. Thereby, one must give a special attention to protection of such information. We propose a novel protection technique for the biometric information, especially the feature information and the templates. The point of our proposal is securely embeds and extracts an iris template in a fingerprint image using a combined DWT and LSB based biometric watermarking algorithm in each authentication. The embedded data travel through insecure communication line like the internet, and they are used in matching process. This technique causes security against eavesdropping and replay attacks on the internet, because the watermark embedded transmitted data are used in the authentication session after watermark extraction.