1. Nanophotonics Lab, St. Petersburg National Research Academic University of the Russian Academy of Sciences, St. Petersburg 194021, Russia
2. Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA
3. Department of Photonics Engineering, Technical University of Denmark, DTU Fotonik, Kgs. Lyngby, DK 2800, Denmark
4. Optoelectronics Department, St. Petersburg State Electrotechnical University “LETI,” St. Petersburg 197376, Russia