Abstract: A method for preparing a periodically poled structure according to this aspect of the present invention comprises the steps of providing a ferroelectric substrate and performing a poling process by applying a poling current to at least one portion of the ferroelectric substrate according to a current waveform. The current waveform include a major phase and a tailed phase accompanying the major phase; the major phase has at least one peak current (Ip) and terminates when the current drops substantially equal to Ip/e, and the charge delivered to the portion of the ferroelectric substrate during the major phase is larger than that delivered during the tailed phase. The nucleation phase is configured to generate nucleation sites in the portion of the ferroelectric substrate and the spreading phase is configured to increase the size of the nucleation sites.

Abstract: A periodic poling structure comprises a ferroelectric substrate including a plurality of tunnels, a plurality of first domains positioned in the ferroelectric substrate between the tunnels and a plurality of second domains interleaved between the first domains in the ferroelectric substrate. Each first domain has a first polarization direction, and each second domain has a second polarization direction different from the first polarization direction. The tunnels are disposed on a top surface and on a bottom surface of the ferroelectric substrate in an equal interval manner or in a variant interval manner. Particularly, the second polarization direction is opposite to the first polarization direction. The periodic poling structure further comprises a plurality of conductive blocks covering the entire base surfaces of the tunnels, or separated from the sidewalls of the tunnels by insulation gaps such that the conductive blocks cover only a portion of the base surfaces of the tunnels.

Abstract: A method for preparing a periodically poled structure according to this aspect of the present invention comprises the steps of providing a ferroelectric substrate and performing a poling process by applying a poling current to at least one portion of the ferroelectric substrate according to a current waveform. The current waveform include a major phase and a tailed phase accompanying the major phase; the major phase has at least one peak current (Ip) and terminates when the current drops substantially equal to Ip/e, and the charge delivered to the portion of the ferroelectric substrate during the major phase is larger than that delivered during the tailed phase. The nucleation phase is configured to generate nucleation sites in the portion of the ferroelectric substrate and the spreading phase is configured to increase the size of the nucleation sites.

Abstract: A periodic poling structure comprises a ferroelectric substrate including a plurality of tunnels, a plurality of first domains positioned in the ferroelectric substrate between the tunnels and a plurality of second domains interleaved between the first domains in the ferroelectric substrate. Each first domain has a first polarization direction, and each second domain has a second polarization direction different from the first polarization direction. The tunnels are disposed on a top surface and on a bottom surface of the ferroelectric substrate in an equal interval manner or in a variant interval manner. Particularly, the second polarization direction is opposite to the first polarization direction. The periodic poling structure further comprises a plurality of conductive blocks covering the entire base surfaces of the tunnels, or separated from the sidewalls of the tunnels by insulation gaps such that the conductive blocks cover only a portion of the base surfaces of the tunnels.