An optical scheme for polarization encoding BB84 protocol is described. Fiber electro-optical LiNbO<sub>3</sub> phase modulators based on Pockels cells provide both polarization states generation for Alice and basis choosing for Bob at high frequency, requiring low operation voltages (V<sub>π</sub> < 5V). Proposed scheme uses only one laser source, which guarantee the indistinguishability of the pulses and active basis choosing allows the system to have two single photon detectors in contrast to the four in the standard polarization encoding schemes. Two phase modulators compensate each others’ polarization mode dispersion, caused by the natural birefringence of the lithium niobate crystal. The system consists of standard components and has simple configuration. The principle of operation is experimentally demonstrated.