All-optical logic gates and a half-adder based on lithium niobate photonic crystal micro-cavities

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

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."

基于铌酸锂光子晶体微腔的全光逻辑门和半加器

铌酸锂光子晶体中全光半加器的结构示意图

逻辑门是执行“或”、“与”、“非”、“或非”、“与非”等逻辑运算的电路，任何复杂的逻辑电路都可由这些逻辑门组成。未来的通信网将朝着全光网络的目标发展。全光逻辑门器件是用于全光寻址鉴别、光分组交换、光子运算等快速高容量全光信息处理的重要组件。目前全光逻辑门主要采用波导光纤制作，难以集成在小型集成芯片上。光子晶体中的缺陷波导具有尺寸小、控光能力强的特性，使其成为设计小型化光逻辑门的关键方法。到目前为止，全光逻辑门大多是在硅基光子晶体材料上设计和集成的。然而，硅的双光子吸收和三阶非线性会引起非线性损耗和信号串扰，导致硅逻辑门的消光比较低。铌酸锂具有独特的电光、声光、压电等物理特性，是未来开发集成光子芯片的理想材料。基于铌酸锂光学平台开发全光逻辑门对构建集成光子芯片和全光网络具有重要意义。

上海交通大学陈险峰、陈玉萍课题组基于柱形二维铌酸锂光子晶体，研究了铌酸锂光子晶体W1缺陷波导的双光干涉过程，和铌酸锂光子晶体L2缺陷微腔对波导导光的影响。随后，该课题组提出了一种结合二维光子晶体缺陷波导和光子晶体缺陷微腔的全光逻辑门的新型设计。所设计的全光逻辑门的消光比最高能达到23 dB。基于上述基础逻辑门器件，该课题组设计了全光半加器的结构，成功实现了逻辑运算的基本功能。相关研究结果发表于Chinese Optics Letters 2019年第17卷第7期(Chenghao Lu, et al., All-optical logic gates and a half-adder based on lithium niobate photonic crystal micro-cavities)。

该研究团队的陈玉萍教授指出：“这项工作为未来基于铌酸锂薄膜（LNOI）材料上全光水平的光子计算提供了一个高效的实现方案。后续工作主要是在铌酸锂薄膜中设计新型全光逻辑门和加、减法器结构，同时寻找合适的加工方法制作该铌酸锂光子晶体结构，为未来片上全光计算的应用集成奠定基础。”