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Controllable beating signal using stored light pulse * Wang Lei(王 磊) a) , Yang Qing-Yu(杨庆禹) a)b) , Wang Xiao-Xiao(王潇潇) a) , Luo Meng-Xi(罗梦希) a) , Fan Yun-Fei(范云飞) a) , Kang Zhi-Hui(康智慧) a) , Dai Tian-Yuan(戴天缘) a) , Bi Sheng(毕 升) a) , Wang Hai-Hua(王海华) a)c) † , Wu Jin-Hui(吴金辉) a) ‡ , and Gao Jin-Yue(高锦岳) a) a

BaTiO3 crystal films, possessing advanced electrooptic (EO) properties, have spurred a broad interest in research and development of EO modulators for fiber-optic communications. However, the EO coefficient is still at uncontrollable and unoriented states despite it playing a crucial role in developing applicable industrial devices. In this work, accurate measurements of the EO coefficient r 51 and birefringence b e o of BaTiO3 crystal films are implemented with a theorem-based theoretical model, an embedded waveguide/electrode device configuration and a complementary modulation of both the linear and ellipse polarizations. Then, with two state-of-the-art device samples on different crystal films, the final average values of the r 51 and b e o are 410 ± 8 pm V−1 and −0.0208 ± 0.0003 for Sample-1 and 624 ± 31 pm V−1 and −0.0138 ± 0.0015 for Sample-2, respectively. Furthermore, a theoretical model for analyzing the measurement accuracies of r 51 and b e o is proposed and the accuracy dependences on the two key variables, drive voltage and optic–electric interaction efficiency, are investigated. Finally, the limitations to the measurement accuracy of this methodology are discussed, including the effect of temperature on the measurement accuracy of r 51 .

For the BaTiO3 crystal thin-film waveguides, a new electro-optic (EO) modulating scheme of a two-dimensional (2D) matching method between the optical field of the lightwave working signal and the electric field of the microwave driving signal is investigated with an embedded device regime. In this 2D matching method, the two central parameters for determining the optical refractive index modulation (RIM) efficiency are (i) the overlap integral between optic and electric fields and (ii) the electric-field strength of the modulating signal, both of which are dependent of the allowable electrode gap. As a result, the higher the electric-field strength is created by the imposed drive voltage crossing the electrode gap, the higher an overlap integral is reached, and consequently, at the smallest allowable electrode gap of 4.5 μm, the usual maximum 65% overlap integral of the traditional co-planar waveguide (CPW) regime based one-dimensional (1D) matching method has been improved to 88%. Thus, for a given BaTiO3 crystal thin-film having EO coefficient r51 = 500 pm/V, when the birefringence values are −0.001 and −0.005, with the CPW device regime, the optical RIM efficiencies are 4.88 × 10−4/V and 1.83 × 10−4/V, respectively, while with the embedded regime based 2D EO matching scheme, the RIM efficiencies are improved to 8.84 × 10−4/V and 3.31 × 10−4/V, respectively, leading to the modulation efficiency improvement of 81% for any birefringence.

Coherent storage of optical image in a coherently-driven medium is a promising method with possible applications in many fields. In this work, we experimentally report a controllable spatial-frequency routing of image via atomic spin coherence in a solid-state medium driven by electromagnetically induced transparency (EIT). Under the EIT-based light-storage regime, a transverse spatial image carried by the probe field is stored into atomic spin coherence. By manipulating the frequency and spatial propagation direction of the read control field, the stored image is transferred into a new spatial-frequency channel. When two read control fields are used to retrieve the stored information, the image information is converted into a superposition of two spatial-frequency modes. Through this technique, the image is manipulated coherently and all-optically in a controlled fashion.