Funding for this research was provided by:
Natural National Science Foundation of China (No. 61671055, No.61605004)
the Fundamental Research Funds for the Central Universities, China (No. FRF-TP-19-016A2)
the State Key Laboratory of Advanced Optical Communication Systems Networks, China
Article History
Received: 13 May 2019
Accepted: 4 October 2019
First Online: 4 March 2020