The idea of using hollow waveguides to pipe electromagnetic radiation from place to place,as an alternative to free-space propagation,goes back a long way.Hollow metallic tubes,with transverse dimensions chosen so tha...The idea of using hollow waveguides to pipe electromagnetic radiation from place to place,as an alternative to free-space propagation,goes back a long way.Hollow metallic tubes,with transverse dimensions chosen so that only the fundamental mode is supported,have been routinely used since the 1940s to build microwave circuitry,for example in radar installations.Indeed,many of the first scientists and engineers working with lasers had a background in microwaves,which strongly influenced early work on optical telecommunications.Hollow metal waveguides are highly lossy at optical frequencies,so that shortly after the laser emerged in the early 1960s,attempts were made to build free-space optical data links using chains of lenses mounted in underground pipes.Although this would overcome beam diffraction,it was soon realised that beam-steering errors,driven for example by vibrations from traffic,would build up rapidly with distance,rendering such systems impractical over the distances needed for telecommunications[1].展开更多
文摘The idea of using hollow waveguides to pipe electromagnetic radiation from place to place,as an alternative to free-space propagation,goes back a long way.Hollow metallic tubes,with transverse dimensions chosen so that only the fundamental mode is supported,have been routinely used since the 1940s to build microwave circuitry,for example in radar installations.Indeed,many of the first scientists and engineers working with lasers had a background in microwaves,which strongly influenced early work on optical telecommunications.Hollow metal waveguides are highly lossy at optical frequencies,so that shortly after the laser emerged in the early 1960s,attempts were made to build free-space optical data links using chains of lenses mounted in underground pipes.Although this would overcome beam diffraction,it was soon realised that beam-steering errors,driven for example by vibrations from traffic,would build up rapidly with distance,rendering such systems impractical over the distances needed for telecommunications[1].
