|
Free Space Optical Communications
Free-space optical communication (FSO) is an optical communication technology that uses light propagating in free space to wirelessly transmit data for telecommunications or computer networking. "Free space" means air, outer space, vacuum, or something similar. This contrasts with using solids such as optical fiber cable. The technology is useful where the physical connections are impractical due to high costs or other considerations. History Optical communications, in various forms, have been used for thousands of years. The ancient Greeks used a coded alphabetic system of signalling with torches developed by Cleoxenus, Democleitus and Polybius. In the modern era, semaphores and wireless solar telegraphs called heliographs were developed, using coded signals to communicate with their recipients. In 1880, Alexander Graham Bell and his assistant Charles Sumner Tainter created the photophone, at Bell's newly established Volta Laboratory in Washington, DC. Bell considere ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Washington, DC
) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan, National Cathedral , image_flag = Flag of the District of Columbia.svg , image_seal = Seal of the District of Columbia.svg , nickname = D.C., The District , image_map = , map_caption = Interactive map of Washington, D.C. , coordinates = , subdivision_type = Country , subdivision_name = , established_title = Residence Act , established_date = 1790 , named_for = George Washington, Christopher Columbus , established_title1 = Organized , established_date1 = 1801 , established_title2 = Consolidated , established_date2 = 1871 , established_title3 = Home Rule Ac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atlantic Wall
The Atlantic Wall (german: link=no, Atlantikwall) was an extensive system of coastal defences and fortifications built by Nazi Germany between 1942 and 1944 along the coast of continental Europe and Scandinavia as a defence against an anticipated Allied invasion of Nazi-occupied Europe from the United Kingdom, during World War II. The manning and operation of the Atlantic Wall was administratively overseen by the German Army, with some support from ''Luftwaffe'' ground forces. The ''Kriegsmarine'' (German Navy) maintained a separate coastal defence network, organised into a number of sea defence zones. Hitler ordered the construction of the fortifications in 1942 through his Führer Directive No. 40. More than half a million French workers were drafted to build it. The wall was frequently mentioned in Nazi propaganda, where its size and strength were usually exaggerated. The fortifications included colossal coastal guns, batteries, mortars, and artillery, and thousands o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
