To improve the detection limit of optical sensors, it is of paramount importance to understand light–matter interaction processes at a fundamental level. At room temperature, the ultimate detection limit is governed amongst others by fundamental thermodynamic fluctuations. Their effect on the properties of light that propagates in amorphous materials is not well understood. Here, we unveil and model for the first time a dominating high-frequency (terahertz-range) noise contribution in the phase of laser light having propagated in optical waveguides, leading to Raman-like sidebands in the optical output spectrum. A salient feature of our approach is to consider a mean relaxation time of the spontaneous random heat flux in the medium, which leads to a spatial correlation of the thermo-refractive noise. The resulting phase noise can be several orders of magnitude larger than what was predicted by earlier models. Our model allows us to explain the origin and specificities of the background that is observed in the Raman optical spectra of silicon nitride waveguides and silica optical fibers. Not only do these findings add a previously unknown dimension to the fundamental knowledge about noise in light–matter interaction, they also need to be taken into account in any optical system in which dynamic fluctuations at the picosecond (ps) or sub-ps level play a role.

中文翻译：

---

基本热力学波动对光在非晶材料制成的光子波导中传播的影响

为了提高光学传感器的检测极限，从根本上了解光与物质的相互作用过程至关重要。在室温下，最终检测极限主要受基本热力学波动的控制。它们对在非晶材料中传播的光的性质的影响尚不十分清楚。在这里，我们首次揭示并建模了在光波导中传播的激光相位中占主导地位的高频（太赫兹范围）噪声贡献，从而在光输出光谱中产生了类似拉曼的边带。我们方法的一个显着特征是考虑介质中自发随机热通量的平均弛豫时间，这会导致热折射噪声的空间相关性。所产生的相位噪声可能比早期模型所预测的大几个数量级。我们的模型使我们能够解释在氮化硅波导和二氧化硅光纤的拉曼光谱中观察到的背景的起源和特异性。这些发现不仅为光-物质相互作用中的噪声的基本知识增加了一个以前未知的维度，而且在皮秒内动态波动的任何光学系统中都需要考虑到这些发现（ps）或sub ps级别起作用。