1. St. Petersburg Academic University, Khlopina 8/3, 194021 St. Petersburg, Russia
2. State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, P.O. Box 66, #10 Xitucheng Road, Haidian District, Beijing 100876, China
3. Ioffe Physical Technical Institute of the Russian Academy of Sciences, Politekhnicheskaya 26, 194021 St. Petersburg, Russia