Xia L, van der Slot P J M, Toebes C, Boller K-J
Opt Express. 2025 Mar 24;33(6):12530-12543. doi: 10.1364/OE.547344.
We experimentally investigate on-chip control and analysis of spatially multimode nonlinear interactions in silicon nitride waveguide circuits. Using widely different dispersion of transverse supermodes in a strongly-coupled dual-core waveguide section, and using integrated pairs of input and output single-mode waveguides, we enable controlled excitation of nonlinear processes in multiple supermodes, while a basic physical mode decomposition aids the identification of parallel and cascaded processes. Pumping with ultrashort pulses at 1.5-m wavelength (around 195-THz light frequency), we observe simultaneous dual-supermode, near-infrared supercontinuum generation having different spectral widths, in parallel with third-harmonic generation at around 515 nm (582 THz). Cascaded four-wave mixing with supercontinuum components upconverts the third-harmonic radiation toward a set of four shorter blue wavelengths emitted in the range between 485 and 450 nm (617 to 661 THz). The approach taken here, i.e., using chip-integrated spatial multiplexing and demultiplexing for excitation and analysis of broadband transverse nonlinear conversion, can be an advanced tool for better understanding and control in multimode nonlinear optics, such as for extending frequency conversion to wider spectral ranges via extra phase matching paths.
我们通过实验研究了氮化硅波导电路中空间多模非线性相互作用的片上控制和分析。利用强耦合双核波导段中横向超模的广泛不同色散，并使用集成的输入和输出单模波导对，我们能够在多个超模中实现非线性过程的受控激发，同时基本的物理模式分解有助于识别并行和级联过程。用波长为1.5微米（光频率约为195太赫兹）的超短脉冲泵浦，我们观察到同时产生具有不同光谱宽度的双超模近红外超连续谱，同时在约515纳米（582太赫兹）处产生三次谐波。与超连续谱分量的级联四波混频将三次谐波辐射上转换为一组在485至450纳米（617至661太赫兹）范围内发射的四个较短的蓝光波长。这里采用的方法——即使用芯片集成的空间复用和解复用进行宽带横向非线性转换的激发和分析——可以成为更好地理解和控制多模非线性光学的先进工具，例如通过额外的相位匹配路径将频率转换扩展到更宽的光谱范围。
