Domain Engineering Enabled Giant Linear Electro‐Optic Effect and High Transparency in Ferroelectric KTa_1−xNb_xO₃ Single Crystals

Abstract

A giant linear electro‐optic (EO) effect and high transparency in ferroelectric potassium tantalate niobate [( K T normala 1 − x N normalb x normalO 3 ), KTN] crystal is achieved via a thermally controlled domain engineering method. It involves a two‐step thermal annealing process: 1) a rapid cooling process that forms polar nano‐regions (PNRs), i.e., a cooling rate of 1 . 67 ° C normals − 1 from T normalc + 58 ° C to T normalc + 8 ° C where T normalc is the Curie temperature; and 2) a slow cooling process that facilitates abnormal domain growth (AGG) i.e., a cooling rate of 0 . 0115 ° C s − 1 from T normalc + 8 ° C to T normalc − 15 ° C . Since PNR can have a faceted boundary and high anisotropy, it can promote AGG within single crystals to realize solid‐state domain conversion macroscopically from a multi‐domain to single‐domain crystal within a slow cooling process. The resultant KTN crystal offers high transparency that is equivalent to its paraelectric phase; and a linear EO coefficient ( γ 51 ) as large as γ 51 ≈ 51200 p m normalV − 1 , which is five times the value of conventional KTN crystals with similar composition. This giant linear EO coefficient represents a major technical advance in EO materials and significantly reduces the driving voltage, power, and footprint of many types of EO devices.

Brillouin Scattering Study of Electro-Optic KTa1−xNbxO3 Crystals

“…Moreover, the ferroelectric phase transitions and the associated optical properties of KTN can be customized by changing the Nb content [ 6 , 7 ]. In addition, KTN has drawn much scientific attention because of its excellent quadratic electro-optic (EO) coefficient and large photorefractive effect in the vicinity of the Curie temperature ( T C ) [ 8 , 9 , 10 , 11 ]. Different types of optical devices such as varifocal lenses, modulators, deflectors, and EO switches based on KTN crystals have been developed because of their giant EO effect [ 12 , 13 , 14 , 15 ].…”