Fiber optical repeaters are used to amplify and regenerate optical signals in fiber optical communication systems .they are used to extend the reach of fiber optical links and improve the signal quality .fiber optical repeaters are used in a wide variety of ampliifcations ,including : 

Telecommunications : Fiber optical repeaters are used by telecommunications companies to extend the reach of their fiber optical networks and provide high-spped internet and other services to customers in remote areas . 

CATV: Fiber optical repeaters are used by cable television companies to deliver high-quality video and audio signals to their customers . 

Data centers : fiber optical repeater are used in data centers to connect servers and other equipment and allow for high-speed data transfer between different parts of the data center . 

Research and development : fiber optical repeaters are used in research and development to test new fiber optical technologies and to create new fiber optic-based applications . 

Military : fiber optical repeaters are used by the military to create secure and reliable commnication networks . 

Here are some specific examples of how fiber optical repeaters are used in different application scenarios : 

Undersea fiber optical cables : fiber optical repeaters are used to amplify the signal in undersea fiber optical cables ,which can be thousands of miles long . 

Long-distance terrestrial fiber optical networks : fiber optical repeaters are used to extend the reach of long-distance terrestrial fiber optical networks ,which can be hundreds of miles long . 

FTTH(fiber to the home)networks :fiber optical repeaters are used to extend the reach of the FTTH networks ,which deliver fiber optical service directly to homes and businesses . 

Fiber optical LANs(local area networks ) :fiber optical repeaters are used to extend the reach of fiber optical LANs,which are high-speed networks that connect computers and devices within a building or campus .

Fiber opitcal sensors :fiber optical repeaters are used to extend the reach of fiber optical sensors ,which are used to measure a variety of parameters ,such as temperature ,pressure ,and strain . 

Fiber optical repeaters are an essential components of many fiber optical communication systems ,they allow for the transmission of optical signals over long distances withtout loss of signal quality .