**5. Conclusions**

In this work, the analyses for the ion etching-based SWR of a rectangular dielectric waveguide led to the categorization of the horizontal and vertical components, and the P-V definition of type surface roughness of CLSM measurements also showed the ability to scan the etched surface at the two directions. Then, the possible different contributions of two components to OPL of waveguide could be imaged and reconstructed as the measurement results. Therefore, with the accurate measured values of the SWR and the theoretical/experimental combinative model, the accurate OPL coefficient was composed, and the important simulation results of the SWR-caused optical loss were found with this model. Therefore, the conclusions obtained in this article are very sustainable in considering the ensemble effect of SWR and the SOI waveguide structure in the research and development of high-quality industrial devices and systems. As an additional conclusion from this work, the upper limit of the correlation length was calculated to be 130 nm, and in any similar work in the future, this parameter is necessary to be discussed. With the above simulation results and conclusions, the coating works of silicon dioxide films of both the BOX layer and the upper cladding layer could be specifically designed to compress the optical loss.

**Author Contributions:** Conceptualization, H.S. and D.S.; methodology, H.S., P.Y., B.W. and T.L.; validation, H.S. and D.S.; formal analysis, D.S., H.S. and H.J.; investigation, D.S., H.S. and T.Y.; data curation, H.S. and B.W; writing—original draft preparation, H.S.; writing—review and editing, H.J. and D.S.; visualization, P.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work is co-sponsored by the Natural Science Foundation of Jilin Provincial Science & Technology (Foundation Grant: 20180101223JC).

**Acknowledgments:** The authors thank the Chang Guang Yuanchen Optoelectronics, Ltd., for their help in Si etching and PECVD coatings of SOI wafer samples. Else, the authors would like to thank Guozheng Wang of the School of Science at the CUST, China, for his help in wafer processing, and want to thank a graduate, Xueping Wang, for her support in testing.

**Conflicts of Interest:** The authors declare no conflict of interest.
