1. Z. Chen, M. Mitchell, M. Segev, Electrical Engineering Department and Center for Photonics and Optoelectronic Materials (POEM), Princeton University, Princeton, NJ 08544, USA.
2. T. H. Coskun and D. N. Christodoulides, Department of Electrical Engineering and Computer Science, Lehigh University, Bethlehem, PA 18015, USA.