The development of compact systems operating in the long-wave infrared wavelength range is of high interest for spectroscopic and sensing applications. There is currently a wide interest toward the development of optical frequency-combs to enhance the performances of these systems. Amongst the different techniques to obtain optical frequency-combs, electro-optic frequency-comb generation presents major advantages thanks to the tunable repetition rate only limited by the bandwidth of the used electro-optical modulator. However, the development of integrated and efficient electro-optical modulators operating in a wide long-wave infrared spectral band is still at its infancy, and electro-optical frequency-comb has not been demonstrated so far beyond 3 $\mu \mathrm{m}$ wavelength. In this work, a Schottky-based modulator embedded in a Ge-rich graded SiGe waveguide is used for electro-optic frequency-comb generation. Considering the limited efficiency of the modulator, harmonically-rich RF signals are used to enhance the generation of comb lines around the optical carrier. Interestingly, this allows us to demonstrate the generation of electro-optical combs spanning over 2.4 GHz around 8 $\mu \mathrm{m}$ wavelength. This paves the way toward fully integrated and tunable mid-infrared electro-optic frequency-comb generation systems.

中文翻译：

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8 μm 波长下可调谐片上电光频率梳生成

在长波红外波长范围内工作的紧凑型系统的开发对于光谱和传感应用具有很大的意义。目前人们对开发光学频率梳以增强这些系统的性能产生了广泛的兴趣。在获得光学频率梳的不同技术中，电光频率梳产生具有主要优势，因为可调谐重复率仅受所用电光调制器的带宽限制。然而，在宽长波红外光谱带中工作的集成高效电光调制器的开发仍处于起步阶段，并且电光频率梳迄今为止尚未被证明超过3$\mu \mathrm{米}$波长。在这项工作中，嵌入在富Ge梯度SiGe波导中的基于肖特基的调制器用于电光频率梳生成。考虑到调制器的效率有限，谐波丰富的射频信号被用来增强光载波周围梳状线的生成。有趣的是，这使我们能够演示跨越 2.4 GHz 大约 8 的电光梳的生成$\mu \mathrm{米}$波长。这为完全集成和可调谐中红外电光频率梳发生系统铺平了道路。