Two variable optical delay schemes based on polarization and interference

Variable optical delays have wide application in scientific research and optical communications. In this paper two different schemes to realize a variable optical delay are proposed, one based on polarization and the other on interference. A phase modulator is employed to restrict the signal pulse within an optical loop, and to release it when required. The delay time can be varied by adjusting the length of the loop and the number of cycles the pulse travels around it. Both types of delays are suitable for fiber systems, and can be made into a small package by means of integrated optics technology. The polarization scheme is also convenient for optical delays in free space.