This paper presents the basic fundamentals in fiber optics and working principle of optical fiber transmission system. Fiber optics transmission system has altered the telecommunication industry. It has likewise made its essence generally felt inside the information organizing group too. Utilizing fiber optic link, optical interchanges have empowered telecommunications connects to be made over substantially more noteworthy separations and with much lower levels of misfortune in the transmission medium and conceivably most imperative of all, fiber optical correspondences has empowered considerably higher information rates to be suited.