1. Department of Electrical Engineering California Institute of Technology Pasadena CA 91125 USA
2. Photonics Research Center U.S. Military Academy West Point NY 10996 USA
3. Photonics Institute Vienna University of Technology Vienna 1040 Austria
4. Department of Physics Norwegian University of Science and Technology Trondheim N‐7491 Norway
5. BAE Systems P. O. Box 868, MER15‐1813 Nashua NH 03061‐0868 USA