What is a Coherent Optical Fiber Communication System? A coherent optical fiber communication system leverages variable properties of light waves, including amplitude, phase, and polarization, to optimize the capacity of a fiber optic link. Coherent optics are typically used for ultra-high bandwidth applications ranging anywhere from 100 Gigabit to 1 Terabit per second. As the world's largest fiber optic components and subsystem manufacturer, Coherent is best positioned to provide the Fast Ethernet and Gig such as Fast Ethernet (125 Mb/s) and Gigabit Ethernet (1 Gb/s). Distances for these links may.