The PolaStay™ polarization tracker automatically adjusts the state of polarization (SOP) towards a reference SOP, counteracting continuous input SOP variations as fast as 0.7 ms with no resets. The reference SOP is determined by a feedback signal which can be provided either internally or externally. The internal feedback version (POS-002-I) consists of a fiber squeezer polarization controller, in-line polarization monitor, digital and analog circuits, and proprietary algorithm. The error signal from the polarization monitor is fed back to the polarization controller to maintain a linear SOP at the output. The external feedback version (POS-002-E) replaces the internal polarization monitor with an external analog electrical feedback signal of the user’s choice, such as a voltage proportional to the degree of polarization (DOP) measured by a polarimeter, the bit-error rate (BER) from a BER chip, the RF spectrum of a detected signal, or the optical power after a polarizer. The output fiber can be either single mode fiber or PM fiber with the SOP aligned to its slow axis. This module can be used for PMD compensation, polarization division demultiplexing, elimination of polarization fading in coherent detection and fiber sensor systems, suppression of noise figure in optical amplifiers, and reduction of PDL effects.