1. Department of Electrical and Computer Engineering; National University of Singapore; Singapore 117576 Singapore
2. National University of Singapore; Suzhou Research Institute; Suzhou 215123 China
3. Institute of Microelectronics; Agency for Science, Technology, and Research (A*STAR); 11 Science Park Road, Singapore Science Park II Singapore 117685 Singapore
4. Division of Physics and Applied Physics; Centre for Disruptive Photonic Technologies; School of Physical and Mathematical Sciences; Nanyang Technological University; Singapore 637371 Singapore