Femtosecond laser writing of lithium niobate ferroelectric nanodomains.

Lithium niobate (LiNbO 3 ) is viewed as a promising material for optical communications and quantum photonic chips 1,2 . Recent breakthroughs in LiNbO 3 nanophotonics have considerably boosted the development of high-speed electro-optic modulators 3-5 , frequency combs 6,7 and broadband spectrometers 8 . However, the traditional method of electrical poling for ferroelectric domain engineering in optic 9-13 , acoustic 14-17 and electronic applications 18,19 is limited to two-dimensional space and micrometre-scale resolution. Here we demonstrate a non-reciprocal near-infrared laser-writing technique for reconfigurable three-dimensional ferroelectric domain engineering in LiNbO 3 with nanoscale resolution. The proposed method is based on a laser-induced electric field that can either write or erase domain structures in the crystal, depending on the laser-writing direction. This approach offers a pathway for controllable nanoscale domain engineering in LiNbO 3 and other transparent ferroelectric crystals, which has potential applications in high-efficiency frequency mixing 20,21 , high-frequency acoustic resonators 14-17 and high-capacity non-volatile ferroelectric memory 19,22 .