摘要
采用飞秒激光直写技术在蒸镀在薄膜铌酸锂的金属铬膜上加工掩模版,结合电感耦合等离子体刻蚀技术,将掩膜图案转移到薄膜铌酸锂上,成功在薄膜铌酸锂平台上制备出了220 nm厚的具有高保真度的达曼光栅器件。采用波长为532 nm的连续激光器作为光源,搭建了测试光路,对光栅结构的衍射性能进行了表征。测试结果表明:制备的二维达曼光栅表现出良好的分光结果,能够衍射出分光阵列数为2×2、3×3、4×4的均匀光强点阵,制备的涡旋达曼光栅具有较高的涡旋光束产生效率,能够衍射出分光阵列数为1×2的涡旋光束阵列,耦合实验结果与理论仿真结果吻合。
Objective As portable terminal devices become increasingly compact and lightweight in recent years,optical devices are gradually being miniaturized and integrated.However,conventional optical components based on lithium-niobate crystals are limited by their large optical volumes,which renders it difficult to satisfy the demand for the high-density integration of photonic chips;moreover,their further development is highly challenging.Breakthroughs in thin-film preparation technology offer a direction for overcoming these challenges.The lithium niobate-on-insulator(LNOI)platform provides the best comprehensive solution to address the longstanding low transmission loss,high-density integration,and low modulation power consumption requirements of photonic integrated chips,thus rendering it an ideal platform for photonic integrated chip technology.However,the current fabrication of photonic integrated devices based on the LNOI platform relies primarily on electron-beam lithography or ultraviolet lithography assisted by etching technology,which is characterized by complex fabrication processes,low processing efficiencies,and high processing costs.In this study,to investigate the potential application of femtosecond lasers in the fabrication of high-performance photonic integrated devices on an LNOI platform,we propose a method that uses femtosecond laser direct writing(FLDW)-assisted inductively coupled plasma(ICP)etching technology to fabricate Dammann grating structures on an LNOI platform.Methods In this study,the finite-difference time-domain(FDTD)method is used to guide the design of Dammann grating structures.First,the relationship between diffraction angle and grating period is obtained via simulation.Subsequently,the calculated parameters are introduced into the FDTD software as initial values for simulation optimization to determine the appropriate grating period and phase-transition point.For device fabrication,a layer of metallic chromium measuring approximately 600 nm thick is deposited on an LNOI platform using vacuum evaporation as a mask.FLDW is used to create a mask pattern of the Dammann grating on the chromium film.Subsequently,the mask pattern is transferred from the chromium film to the LNOI platform via inductively coupled plasma(ICP)etching.The expected depths of the Dammann gratings are obtained by varying the etching time.After removing the metal chromium film using a chromium etching solution,various Dammann grating structures are achieved based on the LNOI platform.Results and Discussions The Dammann grating devices based on the LNOI platform fabricated via ICP etching exhibit high fidelity(Fig.4),good anisotropic etching,and a high depth-to-width etching ratio(Fig.5).The average etching depth of the grating is 250 nm and the grating exhibits good etching uniformity,thus satisfying the etching requirements.A 532 nm continuous laser is used as the excitation source inside the test system to characterize the diffraction performance of the grating structures(Fig.6).The incident laser is expanded using a beam-expansion optical path composed of two lenses and then coupled to the surface of the Dammam grating through a small aperture.The output diffraction beam is obtained on the final charge coupled device(CCD)using an imaging objective lens to observe the intensity distribution of the light field diffracted by the Dammann grating.The test results show that the fabricated two-dimensional Dammann gratings can split beams effectively as well as diffract 2×2,3×3,and 4×4 uniform light intensity arrays.The fabricated vortex Dammann grating is extremely efficient in generating a vortex beam and can diffract a 1×2 high-quality vortex beam array,which is consistent with the theoretical simulation result.Conclusions In summary,two-dimensional Dammann gratings and vortex Dammann grating devices are successfully fabricated on an LNOI platform via FLDW-assisted ICP etching.Compared with the conventional ultraviolet lithography or electron-beam lithography assisted by etching technology,mask-assisted etching technology using FLDW offers high processing freedom,good surface quality,a simple fabrication process,and high fabrication efficiency.Thus,it is extremely advantageous for the fabrication of large-scale high-performance micro-optical devices.This study demonstrates the potential of FLDW-assisted ICP etching technology for the fabrication of high-precision diffraction gratings on LNOI platforms,which can propel the development of high-performance photonic integrated devices on LNOI platforms.
作者
章航舰
庞博宁
郑大怀
陈红云
刘洪亮
Zhang Hangjian;Pang Boning;Zheng Dahuai;Chen Hongyun;Liu Hongliang(Tianjin Key Laboratory of Micro-Scale Optical Information Science and Technology,Institute of Modern Optics,Nankai University,Tianjin 300350,China;State Key Laboratory of Fluid Power and Mechatronic Systems,Zhejiang University,Hangzhou 310027,Zhejiang,China;School of Physical Sciences,Nankai University,Tianjin 300071,China;School of Materials Science and Engineering,Nankai University,Tianjin 300350,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2024年第18期76-81,共6页
Chinese Journal of Lasers
基金
国家自然科学基金(12274236)
流体动力基础件与机电系统全国重点实验室开放基金(GZKF-202320)。
关键词
飞秒激光直写
电感耦合等离子体刻蚀
薄膜铌酸锂
达曼光栅
femtosecond laser direct writing
inductively coupled plasma etching
thin-film lithium niobate
Dammann grating
