Optical fibers include communication-grade, erbium-doped amplifier, polarization-preserving singlemode, power-delivery, cutoff singlemode and sensor-grade types. Communication-grade fibers are available in standard, high-temperature and hermetically sealed configurations. Erbium-doped fibers suit broadband optical networks and cable-TV applications in the 1550-nm fiber-optic transmission window. Polarizing-preserving fibers are used for polarized optical power, polarization-state sensors, and coherent transmission and detection. Moderate and high-power-density fibers have a pure silica core and a high damage threshold.