1. Beijing Engineering Research Center of Laser TechnologyInstitute of Laser EngineeringBeijing University of Technology Beijing 100124 China
2. Guangdong Provincial Key Laboratory of Optical Fiber Sensing and CommunicationsInstitute of Photonics TechnologyJinan University Guangzhou 510632 China
3. Laboratory of Optical PhysicsInstitute of PhysicsChinese Academy of Sciences Beijing 100190 China