Doughan Isaac, Halder Atri, Reduto Igor, Koivurova Matias, Aalto Timo, Roussey Matthieu, Turunen Jari
Center for Photonics Sciences, University of Eastern Finland, P.O. Box 111, 80101, Joensuu, Finland.
VTT Technical Research Ctr. of Finland Ltd., Espoo, Finland.
Sci Rep. 2024 Nov 19;14(1):28665. doi: 10.1038/s41598-024-80054-5.
We show that the mode strengths of a guided field in an arbitrary asymmetric channel waveguide can be uniquely determined from self-referencing interferometric measurements at the exit plane of the waveguide. This requires knowledge of both the amplitude and phase of the complex electric field distribution. Although the amplitude can be obtained from the measured intensity profile easily, the phase retrieval is usually non-trivial. We develop an innovative, alternative and promising technique, where the complex cross-spectral density (CSD) function is measured using a customized wavefront folding interferometer. We then construct the total electric field (complex valued), from which we can determine the strengths of the allowed modes for an asymmetric strip waveguide. Our retrieval algorithm also provides the phase information (intermodal dispersion) associated with each mode, directly from the measured electric field distribution. Moreover, we experimentally demonstrate the developed scheme for different in-coupling (butt-coupling) conditions, resulting in different modal strength distributions.
我们表明，在任意非对称通道波导中，导模场的模式强度可以通过在波导出射面进行自参考干涉测量唯一确定。这需要知道复电场分布的幅度和相位。虽然幅度可以很容易地从测量的强度分布中获得，但相位恢复通常并非易事。我们开发了一种创新、替代且有前景的技术，即使用定制的波前折叠干涉仪测量复交叉谱密度（CSD）函数。然后我们构建总电场（复数值），从中可以确定非对称条形波导中允许模式的强度。我们的恢复算法还直接从测量的电场分布中提供与每个模式相关的相位信息（模间色散）。此外，我们通过实验展示了针对不同的入射耦合（对接耦合）条件所开发的方案，这些条件会导致不同的模式强度分布。
