Autofocusing With Out-of-Band Phase Conjugation

Electromagnetic phase conjugation provides an appealing path toward communication and target localization in dynamic media such as the earth's atmosphere. However, realizing phase conjugation-based devices has proven difficult because of the inherent complexity of systems that employ receivers and transmitters working on the same band. In this letter, we propose the concept of out-of-band phase conjugation in which the frequency of the phase conjugated wave is an integer multiple of the incident wave frequency. Remarkably, the out-of-band phase conjugated wave maintains the autofocusing property that makes phase conjugation so powerful and opens the door to imaging technology effective in random and dynamic media.