Regulation of Periodic Poling in KTP Crystals via Electrode Pattern and Connection Design

doi:10.15541/jim20250383

Abstract

Abstract:

Periodically poled potassium titanyl phosphate (PPKTP) crystals, engineered based on the ferroelectric domain structure of KTiOPO₄ (KTP), have emerged as a core component for generating entangled quantum light sources in quantum optics. This is attributed to the entangled photon sources they produce, which exhibit superior performance such as low power consumption, compact size, and high entanglement quality. During the preparation of PPKTP crystals via the electric field poling method, inhomogeneous electric fields can lead to irregular domain structures, adversely affecting their nonlinear optical properties. Therefore, electric field uniformity is a critical control factor in the poling process. To improve the electric field homogeneity during the polarization of PPKTP crystals, this study systematically optimized both the electrode pattern and the electrode connection structure through simulation and experimental validation. Using finite element analysis, the spatial electric field distributions of different electrode patterns were simulated. A double-sided rounded electrode pattern was proposed to mitigate edge electric field concentration, while a parallel multi-contact electrode connection method was introduced to further enhance the uniformity of the electric field distribution. The domain structures of the poled crystals were characterized using metallographic microscopy. Experimental results from the ferroelectric domain morphology analysis confirmed that the double-sided rounded electrode pattern effectively alleviates the tip effect, and the parallel multi-contact connection method significantly improves electric field uniformity, thereby providing key conditions for high-quality domain inversion. Ultimately, hydrothermally grown PPKTP crystals were obtained with straight domain walls, a period of 46 μm, and a duty cycle of approximately (50±1)%. This work offers a simple, efficient, and structurally rational design solution for achieving uniform electric field distribution in the preparation of PPKTP crystals.

Key words: KTiOPO₄, PPKTP, finite element analysis, electric field spatial distribution

CLC Number:

TQ174

TAN Tingting, SONG Xudong, ZHAO Weidi, QIN Qi, HE Xiaoling, ZHANG Changlong. Regulation of Periodic Poling in KTP Crystals via Electrode Pattern and Connection Design[J]. Journal of Inorganic Materials, 2026, 41(8): 1125-1132.

Figures/Tables 12

Table 1 Key parameters used in simulation modeling

Parameter	Numerical value
Polarization period	46 μm
Electrode width	12 μm
Crystal thickness	1 mm
Electrode thickness	0.3 μm
Relative dielectric constant of potassium titanium phosphate	13
Voltage connection end radius	130 μm
Polarization voltage	3 kV

Fig. 1 Different electrode patterns (a) Rectangular electrode; (b) Rectangular electrode with rounded corners on one side; (c) Rectangular electrode with rounded corners on both sides

Fig. 2 Spatial electric field distributions for different electrode patterns (a) Frame-shaped electrode; (b) Single-sided rounded-corner electrode; (c) Double-sided rounded-corner electrode. Colorful figures are available on website

Fig. 3 Edge electric field distributions for different electrode patterns (a) Frame-shaped electrode; (b) Single-sided rounded-corner electrode; (c) Double-sided rounded-corner electrode

Fig. 4 Images of the polarized samples (a) Cracked crystal after polarization of the frame-shaped electrode; (b) Crystal domain morphology after polarization of a single-sided rounded-corner electrode; (c) Crystal domain morphology after polarization of a double-sided rounded-corner wide electrode

Fig. 5 Schematic diagrams of different electrode connection methods (a) Bilateral wiring electrode connection method; (b) Parallel multi- contact electrode connection schematic

Fig. 6 Spatial electric field distribution diagrams for different electrode connection configurations (a-c) Overall simulation: (a) bilateral connection structure, (b) parallel 4-contact connection structure, (c) parallel 8-contact connection structure; (d-f) Surface simulation: (d) bilateral connection structure, (e) parallel 4-contact connection structure, (f) parallel 8-contact connection structure. Colorful figures are available on website

Fig. 7 Spatial electric field distributions on selected internal cross-sections for different electrode connection structures (a) Bilateral electrode connection method; (b) Parallel 4-contact electrode connection method; (c) Parallel 8-contact electrode connection method. Colorful figures are available on website

Fig. 8 Internal spatial electric field distributions on the outer x-z plane of the crystal exterior under different electrode connection configurations (a) Bilateral wiring electrode connection method; (b) Parallel 4-contact electrode connection method; (c) Parallel 8-contact electrode connection method. Colorful figures are available on website

Fig. 9 Electric field distribution maps along the selected line on the crystal surfaces (a) Overall distribution and (b) local magnification of the selected region for the bilateral wiring electrode connection method; (c) Overall distribution and (d) local magnification of the selected region for the parallel 4-contact electrode configuration; (e) Overall distribution and (f) local magnification of the selected region for the parallel 8-contact electrode configuration

Fig. 10 Domain wall morphologies of polarized KTP crystals along the +z plane under different electrode connection configurations (a-c) ×100 magnification: (a) bilateral wiring electrode connection method, (b) parallel 4-contact electrode connection method, (c) parallel 8-contact electrode connection method; (d-f) ×200 magnification: (d) bilateral wiring electrode connection method, (e) parallel 4-contact electrode connection method, (f) parallel 8-contact electrode connection method

Fig. 11 Widths of the reversed domains on the characteristic straight line under different electrode connection methods (a) Bilateral wiring electrode connection mode; (b) Parallel 4-contact electrode connection mode; (c) Parallel 8-contact electrode connection mode

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