Refractive Index memory effect of ferroelectric materials by domain control

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Refractive Index memory effect of ferroelectric materials by domain control Kazuhiko INOUE and Takeshi MORITA Graduate School of Frontier Sciences, The University of Tokyo. 5-1-5 Kashiwanoha, Chiba, Kashiwa 277-8563, Japan. ABSTRACT Ferroelectric electro-optics materials are widely studied for optical applications, such as optical switches, optical scanners, and optical shutters. However, conventional operation of those devices requires a continuous external electrical field. On the other hand, our group proposes an optical property memory effect by controlling domain structure as either full-polarized or depolarized state using asymmetric voltage operation. The optical property memory effect can keep its optical value, such as refractive index and light transmittance without any external electrical field. In this study, it was confirmed that the refractive index state had two stable values depending on domain conditions. This memory effect should be useful for innovative optical switch or scanner in the future. INTRODUCTION Lead lanthanum zirconate titanate (PLZT) is a ferroelectric electro-optic material that has excellent transparency from a visible to an infrared wavelength, and shows variable light transmittance and refractive index with an applied electric voltage1-4. Until now, the practical device applications, such as optical switches, optical scanners and optical shutters have been widely studied5-6. Such conventional devices require a continuous external electrical field. Alternatively, our group has focused on the memory effects by using an imprint electrical field. An imprint electrical field is observed mainly in ferroelectric thin films and most studies have focused to remove the imprint electrical field7. With the imprint electrical field, ferroelectric properties, such as strain, permittivity, light transmittance and refractive index shifts to the direction of the axis of the electric field and ferroelectric materials have two different states at zero electric field. Same to the thin film, bulk ferroelectric materials can also have this imprint electrical field, which is induced by applying a high voltage to ferroelectric material at high temperature. Using this method, ferroelectric properties memory effects such as, strain, permittivity, refractive index and light transmittance had been demonstrated8-11. In other words, the devices using memory effect can be driven by pulse voltage operation. However, with those studies, it was clarified that the strain memory gap was reduced by successive pulse operations around 104 times8. This tendency is expected to be in the PLZT optical memory effect if the imprint electrical field is used for the memory effect. To overcome this fatigue problem, following principle was developed for the memory effects without the imprint electrical field. With this principle, the strain and light transmittance memory effect, which have two stable states at zero electric field were successfully demonstrated12-13. This method uses an asymmetric voltage operation to control its

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