**5. Conclusions**

In this work, the SBS induced nonlinear distortion for 10 Gbaud and 28 Gbaud SSB QAM16 transmission over an 80 km SSMF based on a KK receiver is experimentally observed and investigated for the first time. Significantly reduced BER can be induced along with the increase in CSPR due to SBS, which makes SBS an unneglectable issue for KK receiver-based systems. An SBS threshold of about 7 dBm is detected for such an 80 km SSMF link. Different nonlinear distortion performances are found for LSB and RSB signals, and LSB performs better than RSB. Here, a ~2 dB power tolerance improvement is achieved by LSB with optical filtering to remove the SBS. The proof-of-concept results in this work unfold an important issue of SBS-induced nonlinear distortion, which would be of grea<sup>t</sup> significance for KK receiver-based optical transmission applications.

**Author Contributions:** Conceptualization, J.D. and Y.Z.; methodology, J.D. and Y.Z.; experiment investigation, Y.Z. and W.S.; writing—original draft preparation, Y.Z.; writing—review and editing, J.D. and Z.H.; supervision, J.D. and Z.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work is supported by National Key R&D Program of China (2018YFB1801804), National Natural Science Foundation of China (NSFC) (61935011, 61875124).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** Thanks to all the reviewers and editors for their careful work and pertinent suggestions.

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