1. Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583
2. Photonics Initiative, Advanced Science Research Center, City University of New York, 85 St. Nicholas Terrace, New York, New York 10031, United States
3. Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78712, United States
4. Physics Program, Graduate Center, City University of New York, New York, New York 10016, United States
5. Department of Electrical Engineering, City College of New York, New York, New York 10031, United States