Polarizer-relatedJOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 8, NO. 3, MARCH 1990 459 Polarization Control for Coherent Fiber-optic Systems Using Nematic Liquid Crystals Abstract-One of the obstacles to coherent fiber-optic communications is the unpredictable polarization drift which necessitates the use of an active polarization controlling system to match the polarizations of the signal and local oscillator. The polarization match must be maintained during the reset of any of the finite range components to prevent loss of data. A novel and practical system which uses three liquid crystal devices for the polarization matching process is presented, and the required reset control algorithm and its derivation are described in detail. I. INTRODUCTION ODERN fiber-optic communications systems employ direct detecti……