1. Microelectronics Research Center , The University of Texas at Austin , Austin , TX 78758 , USA
2. Department of Electrical and Computer Engineering , The University of Texas at Austin , Austin , TX 78705 , USA
3. School of Electrical, Computer and Energy Engineering , Arizona State University , Tempe , AZ 85287 , USA
4. Omega Optics, Inc. , 8500 Shoal Creek Blvd., Bldg. 4, Suite 200 , Austin , TX 78757 , USA