Electro-optic (E-O) materials are essential to modern information society, especially for optical switches, modulators, and filters in optical communication. In this paper, ultrahigh transparent (1-x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3) (PMN-PT) relaxor ferroelectric ceramics are fabricated. The effect of Sm-doping content (0, 0.5, 1.0, 1.5, and 2.0 mol%) on PMN-PT transparent ceramics is systematically investigated on the optical transparency, electro-optic coefficient, extinction ratio, and half-wave voltage. Results indicate that 0.5 mol% Sm-doped PMN-PT ceramic shows the optimal comprehensive performance, including high transparency of 69.6%, large quadratic E-O coefficient of 35 x 10(-16) m(2) V-2, decent extinction ratio of 32 dB, and low half-wave voltage (113 V at d = L = 1 mm). An electro-optic modulator is designed based on the PMN-PT transparent ceramics and its application in optical communication is realized, such as rapid information modulation, analog signal (audio frequency), and digital signal (graphic patterns) transmission. These results indicate that Sm-doped PMN-xPT transparent ceramics are promising candidates for E-O modulation applications.