[论文解读] Hybrid Nonlinear Effects in Photonic Integrated Circuits

Arghadeep Pal, Alekhya Ghosh+6 more|ArXiv.org|May 2, 2025

Photonic and Optical Devices被引用 3

一句话总结

该论文通过将熔融二氧化硅包层中的拉曼散射与Si3N4芯中的克尔频率梳产生相结合，展示了混合光学非线性在单一器件中实现拉曼激光与宽带拉曼-克尔梳的能力。实验观测到在片上泵浦功率143 mW时出现拉曼激光阈值，色散工程使泵浦、斯托克斯与反斯托克斯波长周围形成约400 nm宽的梳形谱。

ABSTRACT

Nonlinear optics in photonic integrated circuits is usually limited to utilizing the nonlinearity of a single material. In this work, we demonstrate the use of hybrid optical nonlinearities that occur in two different materials. This approach allows us to observe combined Raman scattering and Kerr frequency comb generation using silicon nitride (Si3N4) microresonators with fused silica cladding. Here, the fused silica cladding provides Raman gain, while the silicon nitride core provides the Kerr nonlinearity for frequency comb generation. This way we can add Raman scattering to an integrated photonic silicon nitride platform, in which Raman scattering has not been observed so far because of insufficient Raman gain. The Raman lasing is observed in the silica-clad silicon nitride resonators at an on-chip optical power of 143 mW, which agrees with theoretical simulations. This can be reduced to mw-level with improved optical quality factor. Broadband Raman-Kerr frequency comb generation is realized through dispersion engineering of the waveguides. The use of hybrid optical nonlinearities in multiple materials opens up new functionalities for integrated photonic devices, e.g. by combining second and third-order nonlinear materials for combined supercontinuum generation and self-referencing of frequency combs. Combining materials with low threshold powers for different nonlinearities can be the key to highly efficient nonlinear photonic circuits for compact laser sources, high-resolution spectroscopy, frequency synthesis in the infrared and UV, telecommunications and quantum information processing.

研究动机与目标

• Motivate and demonstrate the use of hybrid nonlinearities across two materials to enable functionalities not possible with a single material.
• Show that Raman gain in fused silica cladding can drive Kerr frequency comb generation in a Si3N4 core.
• Engineer waveguide dispersion to achieve broadband Raman-Kerr combs spanning pump, Stokes, and anti-Stokes wavelengths.
• Quantify the Raman lasing threshold and illustrate the dependence on resonator geometry and quality factor.

提出的方法

• Fabricate Si3N4 microresonators with a fused silica cladding to introduce Raman gain in the cladding.
• Couple a continuous-wave pump into the microring and observe Raman lasing and subsequent Kerr comb formation.
• Engineer waveguide width to control dispersion and align free spectral ranges (FSRs) between mode families to enable broadband combs.
• Use finite element method (FEM) to calculate cladding mode overlap and effective mode volume contributing to Raman scattering.
• Provide a theoretical threshold model for Raman lasing and compare with experimental threshold (Pm threshold ~143 mW).
• Characterize resonator Q factors and dispersion to understand the transition from Raman Stokes lasing to Raman-assisted Kerr frequency combs.]
• research_questions: [
• Can hybrid nonlinearities from two distinct materials enable Raman lasing in Si3N4-based photonic circuits where Raman gain is typically insufficient?
• How does dispersion engineering of Si3N4 microresonators influence the bandwidth and efficiency of Raman-assisted Kerr frequency combs?
• What are the threshold conditions and optimal geometries (e.g., core thickness, Q-factor) for low-power Raman lasing in silica-clad Si3N4 resonators?
• How do interactions between Raman scattering and Kerr four-wave mixing (FWM) enable cascaded or broadband comb formation?
• Can hybrid material approaches extend nonlinear optical functionality to new spectral regions or applications (e.g., supercontinuum generation, self-referencing of combs)?

实验结果

主要发现

• Raman lasing is observed in fused silica-clad Si3N4 resonators with an on-chip pump power of 143 mW, in agreement with theory.
• Broadband Raman-Kerr frequency combs spanning pump, Stokes, and anti-Stokes wavelengths are achieved by dispersion engineering of the Si3N4 waveguide.
• Engineered dispersion (e.g., 1.9 μm core width) enables cascaded Raman combs around the Stokes and anti-Stokes lines, with comb lines overlapping across mode families.
• The Raman lasing threshold depends on core thickness and Q-factor, with a minimum predicted at ~250 nm Si3N4 core thickness for Q ~2.2×10^6, and far lower thresholds possible with higher Q.
• FSR matching between TE00 and TE10 mode families near the Raman Stokes wavelength is key to achieving Raman-assisted Kerr comb generation and wider bandwidths.
• The work demonstrates a pathway to combine materials with different nonlinearities (second- and third-order) for enhanced nonlinear photonic devices.