Das Susobhan, Uddin Md Gius, Li Diao, Wang Yadong, Dai Yunyun, Toivonen Juha, Hong Hao, Liu Kaihui, Sun Zhipei
Department of Electronics and Nanoengineering, Aalto University, Espoo, Finland.
QTF Centre of Excellence, Department of Applied Physics, Aalto University, Aalto, Finland.
Light Sci Appl. 2025 Jan 9;14(1):41. doi: 10.1038/s41377-024-01660-6.
Coherent broadband light generation has attracted massive attention due to its numerous applications ranging from metrology, sensing, and imaging to communication. In general, spectral broadening is realized via third-order and higher-order nonlinear optical processes (e.g., self-phase modulation, Raman transition, four-wave mixing, multiwave mixing), which are typically weak and thus require a long interaction length and the phase matching condition to enhance the efficient nonlinear light-matter interaction for broad-spectrum generation. Here, for the first time, we report octave-spanning coherent light generation at the nanometer scale enabled by a phase-matching-free frequency down-conversion process. Up to octave-spanning coherent light generation with a -40dB spectral width covering from ~565 to 1906 nm is demonstrated in discreate manner via difference-frequency generation, a second-order nonlinear process in gallium selenide and niobium oxide diiodide crystals at the 100-nanometer scale. Compared with conventional coherent broadband light sources based on bulk materials, our demonstration is ~5 orders of magnitude thinner and requires ~3 orders of magnitude lower excitation power. Our results open a new way to possibly create compact, versatile and integrated ultra-broadband light sources.
相干宽带光的产生因其在从计量、传感、成像到通信等众多领域的应用而备受关注。一般来说，光谱展宽是通过三阶及更高阶非线性光学过程（如自相位调制、拉曼跃迁、四波混频、多波混频）实现的，这些过程通常较弱，因此需要长相互作用长度和相位匹配条件来增强用于产生广谱的高效非线性光与物质的相互作用。在此，我们首次报道了通过无相位匹配的频率下转换过程在纳米尺度实现倍频程相干光的产生。通过在100纳米尺度的硒化镓和二碘化铌氧化物晶体中进行差频产生（一种二阶非线性过程），以离散方式展示了高达倍频程相干光的产生，其-40dB光谱宽度覆盖约565至1906纳米。与基于块状材料的传统相干宽带光源相比，我们的展示薄了约5个数量级，所需激发功率低了约3个数量级。我们的结果为创建紧凑、通用和集成的超宽带光源开辟了一条新途径。
