Method for bulk periodic poling of congruent grown ferro-electric nonlinear optical crystals by low electric field

An apparatus for effectively reducing the coercive field and stabilizing the reversed domain by inhibiting the relaxation of spontaneous polarization in the periodical poling process of congruent grown ferro-electric non-linear optical crystals, in which said congruent grown ferro-electric non-linear optical crystal is adequately doped with oxide so as to reduce the coercive and internal field in the congruent grown bulk congruent grown ferro-electric non-linear optical crystal;

• in which the coercive field and the associated fringe field effects in preparing the periodically poled structures can be reduced;
• in which the axial anisotropy when bulk type of periodical poling of the congruent grown ferro-electric non-linear optical crystals are being implemented can be reduced, and preparing the periodically poled structures from the congruent grown ferroe-lectric nonlinear optical crystals and real-time measurement of the periodical process, the fabrication system comprising:
• a high voltage supply, which either can be of direct current (DC) type or pulse type and provides the congruent grown ferro-electric nonlinear optical crystals with the source supply to implement the domain reversal, that is, polarization switching, process on said crystal;
• a computer, which is connected to a data acquisition card (DAQ) and a general purpose interface board (GPIB), in which said DAQ is controlled by said computer to make the timing control of said DAQ so as to further control said high voltage supply, and said GPIB is used to connect with a current monitor and said computer to provide real-time monitoring of applied poling voltage and polarization switching current;
• an oscilloscope, which is connected to said GPIB to provide the real-time monitoring of applied voltage and polarization switching current pulses;
• a current monitor, which is connected to a set of current monitoring resistors so as to monitor the magnitude of the polarization switching current;
• a set of monitoring resistors that are connected to said non-linear optical crystal so as to measure the polarization switching current flowing through said congruent grown ferro-electric non-linear optical crystals;
• a rectifier, which is connected to the end of said current monitoring resistors so as to stabilize the reversed domains by inhibiting the relaxation of the spontaneous polarization back to its original direction through the process of charge back flow as the high voltage power supply is switched off at the termination of the poling process.