大规模铌酸锂光子集成系统的超快激光光刻研究进展

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.