Dam

Dams generally serve the primary purpose of retaining water or prevent water flow into specific land regions. But dams are not completely waterproof structures. Hydropower and pumped-storage hydroelectricity are often used in conjunction with dams to provide generate electricity. Infact stored water could be released through turbines to a generator. To boost the power generation capabilities of a dam, the water may be run through a large pipe called a penstock before the turbine.
During an armed conflict, a dam is to be considered as an "installation containing dangerous forces" and shall not be made the object of attack.

@B Do you know Three Gorges Dam?

@ More about Pumped storage hydroelectricity

Diode

A diode is a two-terminal electronic component that conducts electric current in only one direction. Usually it is a crystalline piece of semiconductor material connected to two electrical terminals.
The most common function of a diode is to allow an electric current to pass in one direction while blocking current in the opposite direction, and is used to convert alternating current to direct current, and to extract modulation from radio signals in radio receivers.

Diode electric symbol

Optical fiber

An optical fiber or optical fibre is a thin, flexible, transparent fiber that acts as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. Fibers are used instead of metal wires because signals travel along them with less loss and are also immune to electromagnetic interference. Furthermore, because optical fibers transmit only the light, while this is produced by an external generator, they can directly pass through hostile environments for electrical cables, such as water.

optical fiber pool lighting

@ Watch how optical fiber work

PATENT: Method of producing optical waveguide fibers, Keck et al. 1970