Logic gates are circuits that perform logical operations such as OR, AND, NOT, NOR and NAND. Any complex logic circuit can be composed of these logic gates. The future communication network will develop towards the goal of the all-optical network. All-optical logic gate devices are important components in fast and high-capacity all-optical information processing such as all-optical addressing identification, optical packet switching, and photon computation. At present, all-optical logic gates are mainly made of waveguide fiber, which is difficult to be integrated on small integrated chips. The defect waveguide in the photonic crystal has the characteristics of small size and strong light control ability, which makes it a key method to design a miniaturized optical logic gate. Lithium niobate has unique electro-optic, acousto-optic, piezoelectric and other physical properties, so it is an ideal material for developing integrated optical path in the future. The development of all-optical logic gate based on lithium niobate optical platform is of great significance to integrated photonic chip and all-optical calculation.

Based on cylindrical two-dimensional lithium niobate photonic crystal, Xianfeng Chen and Yuping Chen's research group at Shanghai Jiao Tong University studied the dual-light interference process of a lithium niobate photonic crystal with W1 defect waveguide, and the influence of defect microcavity of lithium niobate photonic crystal L2 on the waveguide light. The new type of all-optical logic gate taking advantage of lithium niobate material combined with micro-cavity structure was designed. The defect cavity is used to improve the extinction ratio of different logic output signals. The designed all-optical logic gate has a maximum extinction ratio of 23 dB. Then, according to the designed basic logic gate devices, the structure of all-optical half adder is designed, and the basic functions of logic operation are successfully realized. This work has been published in Chinese Optics Letters, Volume 17, Issue 7, 2019 (Chenghao Lu, et al., All-optical logic gates and a half-adder based on lithium niobate photonic crystal micro-cavities).

"This work provides an efficient implementation for the design of integrated photonic chip and all-optical calculates based on lithium niobite on insulator thin film in future." said Professor Yuping Chen, "In future work, we will extend the design of all-optical logic gates and adder/subtractor structures in lithium niobate on insulator (LNOI) thin film, and try to fabricate the lithium niobate photonic crystal structure in LNOI effectively, which will help us to develop the all-optical computing on chip."

Schematic structure of the all-optical half-adder in an LN PhC