1. Department of Electrical and Computer Engineering, Northwestern University, Evanston, Illinois 60208, United States
2. Center for Smart Structures and Materials, Department of Mechanical Engineering, Northwestern University, Evanston, Illinois 60208, United States
3. Key Laboratory of Specialty Fiber Optics and Optical Access Networks, Joint International Research Laboratory of Specialty Fiber Optics and Advanced Communication, Shanghai University, Shanghai 200444, China