Fabrication of hydrothermal PPKTP and its spontaneous parametric down-conversion characteristics

High-voltage electric field polarization, selective corrosion, current monitoring, and other methods are used to develop hydrothermal PPKTP. It is found that the reversal domain nucleation of hydrothermal-grown KTP crystals has four kinds of microscopic morphology, namely, strip shape, spindle shape, bullet shape and irregular shape, in the process of high voltage electric field polarization. Compared with the leakage current in the process of polarization of flux-grown KTP crystals, the hydrothermal-grown KTP crystals only exist when the applied electric field is much larger than the coercive field. The leakage current can be suppressed by multiple loading of short pulses, and the PPKTP with a poled period of 10 μm and 46 μm were fabricated, respectively. Subsequently, based on the fabricated PPKTP, the SPDC characteristics are studied. To the PPKTP with a poled period of 10 μm, the quantum entanglement source whose brightness exceeds 2.1 kHz @ 810 nm is prepared by the SPDC technique. Otherwise, the PPKTP with a poled period of 46 μm is used for SPDC, and the brightness of entangled photon pairs in channel 1 and channel 2 are 3.21 kHz @ 1560 nm and 5.31 kHz @ 1560 nm, respectively.