大规模铌酸锂光子集成系统的超快激光光刻研究进展

Progress on ultrafast laser lithography of large-scale lithium niobate integrated photonics

飞秒光刻辅助化学机械刻蚀技术(photolithography assisted chemo-mechanical etching,PLACE)实现了在薄膜铌酸锂(thin-film lithium niobate,TFLN)上高品质大规模光子集成电路(photonic integrated circuit,PIC)的制造,并推动了光子集成电路重大应用领域的持续发展,产生了一系列高性能PIC应用,诸如高Q微谐振器、低损耗波导、波导放大器、阵列波导光栅(arrayed waveguide grating,AWG)和电光(electro-optic,EO)可调谐/可编程光子器件等.针对PIC器件和光刻系统的大规模生产,本文介绍了一种超高速高分辨率激光光刻制造系统,采用高重复频率飞秒激光器和高速多边形激光扫描仪,可实现200 nm分辨率下4.8 cm2/h的光刻制造效率,并且展示了基于TFLN光子器件的晶圆级制造、晶圆级微电极结构等的应用.

The combination of advanced functional materials with high optical performance and cutting-edge micro/nano fabrication technology has ushered in a new era for integrated photonics.Thin-film lithium niobate(TFLN)has emerged as a promising material platform for the next generation photonic integrated circuits(PICs),owing to its wide transparency window from UV to mid-IR,moderately high refractive index that enables dense photonic integration while maintaining a suitable mode-size in the single-mode lithium niobate(LN)ridge waveguide,and large electro-optic(EO)as well as nonlinear optical coefficients which are critical for high-speed EO tuning and high-efficiency wavelength conversion applications.Photolithography assisted chemo-mechanical etching(PLACE),a technique developed specifically for fabricating high quality(high-Q)large-scale PICs on TFLN,has enabled fabrication of a series of building blocks of PICs ranging from high-Q micro-resonators and low-loss waveguides to waveguide amplifiers,arrayed waveguide grating(AWG)and electro optically tunable/programmable photonic circuits,showing high optical performance,such as,1.2×108-ultra-high-Q micro-resonator,0.025-dB/cm ultra-low-loss continuously tunable delay line,20-dB gain waveguide amplifier and 1.5-mW total power consumption matrix operation devices.Aiming at high-throughput manufacturing of the PIC devices and systems,we have developed an ultra-high-speed high-resolution laser lithography fabrication system employing a high repetition-rate femtosecond laser and a high-speed polygon laser scanner,achieving infinite field of vision(IFOV)processing,by which a lithography fabrication efficiency of 4.8 cm2/h has been achieved at a spatial resolution of 200 nm.Using the high-speed femtosecond laser lithography system,we successfully fabricate photonic structures of large footprints with reasonable propagation loss.By combining the previous femtosecond scan scheme for smoothing mask edges with a high-speed polygon scan scheme for patterning the waveguide groove part,we further improve the propagation loss.We also demonstrate wafer-scale fabrication of microelectrode structures,showing high uniformity in the fabrication process,and high-speed Mach-Zehnder interferometer(MZI)modulators.By characterizing EO performance of the MZI modulator,we achieve a voltage-length product of 1.86 V cm and a measured 3-dB bandwidth up to 70 GHz.With the continuous advances in the high-repetition-rate femtosecond laser,high-speed electronic shutter/controller and high-speed host data transmission technology,we expect the fabrication efficiency and propagation loss can be further promoted by 1–2 orders of magnitude.This will have a profound implication as miniaturization will play a central role in future society.