Fig. 1. Schematic of the procedure and simulation results of electric-field distribution. (a) Schematic of the periodic interdigital electrode; (b) simulation results of electric-field distribution under a voltage of 500 V (parameters of the electrodes were as follows: each nickel electrode was 2 μm in width and 200 μm in length, and the electrode period was set to 30 μm, L_inv and L_unwere 21 μm and 9 μm, respectively, and W_dom was set to 100 μm); (c) schematic of the fabrication procedure for head-to-head and tail-to-tail domain structures in x-cut congruent TFLN

Fig. 2. Schematic and parameters of the poling experiment. (a) Schematic of the poling setup; (b) waveform of the poling electric pulse

Fig. 3. Confocal second-harmonic microscopy images and simulation results of electric-field distribution of domain inversion area. (a) U_p=360 V, 10 pulses; (b) U_p=420 V, 10 pulses; (c) U_p=440 V, 10 pulses; (d) U_p=460 V, 10 pulses; (e) U_p=500 V, 10 pulses

Fig. 4. PFM phase image of periodically poled x-cut TFLN. (a) Period is 30 μm; (b) period is 20 μm; (c) phase profile of the periodically poled TFLN along the white dashed line in Figs. (a) and (b)

Fig. 5. Poling voltage waveforms and the electrical conductance of the structure. (a) Poling voltage waveforms under 500 V voltage and 10 pulses; (b) electrical conductance of the structure corresponding to Figs. (c)‒(f); (c) confocal microscopy images and equivalent circuit of the state in which the domains begin to nucleate; (d) domains grow longitudinally; (e) domains merge horizontally; (f) domain inversion is completed.