A fiber squeezer polarization controller is attractive for use in a coherent optical fiber trunk line system because of low insertion loss and low power penalty. A fiber squeezer polarization controller to be used practically requires 1) stable endless operation, 2) high response speed in the endless operation, and 3) protection from fiber break, which is a particular problem in a fiber squeezer polarization controller. The authors developed a fiber squeezer polarization controller satisfying these requirements. The developed controller realized a stable endless operation with less than 0.1-dB power penalty under 40-degrees-C fiber squeezer temperature change. In addition, a practically sufficient response speed of 15-pi rad/s was obtained in an endless operation. A metal-coated fiber used in the fiber squeezers was confirmed to be effective in preventing fiber break by repetitive load application test (5-10 kg, one million times) to the metal-coated fiber. These techniques could realize a practical and high-performance polarization controller for a coherent transmission system.
