1. State Key Laboratory of Modern Optical Instrumentation, College of
Optical Science and Engineering, Zhejiang University, Hangzhou 310027, China
2. MacDiarmid Institute
for Advanced Materials and Nanotechnology, Dodd-Walls Centre for Photonic
and Quantum Technologies, Department of Physics, University of Otago, P.O. Box 56, Dunedin 9016, New Zealand