Optical variable delay line and variable-frequency fiber-optic multiplexer

A fiberoptic-coupled free-space variable delay line is provided wherein the phase adjustment of the signal can be accurately set. A microscope-objective lens collimates a signal beam which is received by a focusing lens. The focusing lens is provided on an adjustable carrier to allow one to accurately adjust the distance travelled by the collimated signal base and thereby accurately adjust the off-set. A plurality of these variable delay lines can be arranged to form a multiplexer. If the threads on each drive rod moving a carrier are different, the carrier can be adjusted to accommodate changes in frequency of the signal.