Scalable and Efficient Nonlinear Photonic Circuits with Segmentally Tuned Thin-film PPLN Waveguides

Nonlinear photonic devices that generate, convert, and interface light signals across different frequencies are fundamental building blocks in contemporary optics, enabling a variety of classical and quantum photonic applications. For example, phase-sensitive amplification of optical communication signals is theoretically noiseless and could break the inherent 3-dB noise figure limit in traditional amplifiers. Spontaneously down-converted photons provide a natural source of entangled photon pairs for quantum information processing. Frequency combs, characterized by equally spaced frequency components and phase-locked repetitive temporal pulses, serve as compact light sources for wavelength-division multiplexed communication systems as well as ultra-precise rulers in astronomy, spectroscopy, and metrology. Among various nonlinear platforms, thin-film periodically poled lithium niobate (PPLN) devices are particularly appealing due the strong material nonlinearity of lithium niobate and the excellent light confinement in thin-film waveguides. However, current thin-film PPLN devices are usually fabricated using chip-scale processes like electron-beam lithography, with compromised throughput, scalability, and uniformity. This significantly limits their applications in large-scale nonlinear photonic systems that require multiple nonlinear components integrated on the same chip with consistent performances. In this proposal, we aim to address this challenge by developing a wafer-scale lithium niobate nonlinear photonic platform based on ultraviolet stepper lithography and automated poling processes. To compensate for the inhomogeneous broadening effects caused by film thickness variation across the wafer, we will design and fabricate segmented thermal-optic tuning modules that can locally adjust and align the quasi-phase-matching spectra in each section for optimal wavelength conversion. Based on the scalable fabrication and tuning schemes developed, we will finally showcase a large-scale nonlinear photonic circuit that includes multiple PPLN devices and other functional photonic components, which together perform efficient phase-sensitive amplification of high-speed optical communication signals. The proposed research is supported by the expertise, infrastructure, and preliminary results in PI’s lab on lithium niobate device fabrication and periodic poling. PI’s team has recently developed a wafer-scale thin-film lithium niobate fabrication process and achieved a series of high-performance linear photonic devices and circuits. Preliminary measurement results on PPLN devices also confirm a reliable and uniform periodic poling process, which will be further optimized, automated, and scaled up in this project. The successful accomplishment of this project will deliver not only a wafer-scale nonlinear photonic platform that is readily compatible with existing lithium niobate photonic components and foundry processes, but more importantly one that enables large-scale integration of nonlinear photonic circuits with unprecedented functionalities. This will open up new possibilities for future quantum and classical photonic applications that require scalable, high-performance, and tunable nonlinear photonic devices.