Fiber-optic sensors available in the market used to measure physical quantities such as electrical and magnetic fields, electrical current, temperature, pressure, acceleration, flow of liquids and gases, and measurement of fluid levels in various industries. As of today, due to the growing use of fiber optics, manufacturers of many machineries and control systems have been keen on using these sensors in manufacturing products. In this paper, due to the increasing importance of optical sensors, especially in wireless sensor networks, in the Internet of things, and in optical fiber networks, these types of sensors have been widely studied over the past decades to date, and in terms of technical and their applications, have been reviewed and reported. The results of this article can be used for designers of these sensors in various industries and universities at undergraduate, post-graduate students, and senior physics and engineering departments.