Polarization-effect controllability in recirculating delay-line systems

A complete polarization analysis of fiber-recirculating delay line is conducted with particular emphasis given to controllability. An appropriate method of analyzing the polarization eigenmode structure of a general system is presented. It is shown that the eigenmode structure of a recirculating system constructed from normally birefringent fibers may be controlled through the use of in-line birefringence control devices such as fiber squeezers. As a result of this controllability, a nondestructive test for determining the splice-misalignment angle in the system is developed and demonstrated. The use of a recirculating delay-line filter as an in-line polarization control element is also developed from the eigenmode controllability. An additional investigation into the eigenmode structure of this type of system is also conducted. Excellent agreement between theoretical and experimental studies is achieved.