  Wireless optical communications (WOC) has carriers up to several hundred
terahertz, which offers several advantages, such as ultrawide bandwidth and no
electromagnetic interference. Conventional WOC that uses light transmitters
such as light emitting diodes (LEDs), directed LEDs, and lasers are facing
major challenges in attenuation or tracking. Resonant beam communications
(RBCom) meets the requirements of low attenuation, non-mechanical mobility, and
multiple access. Yet, RBCom channel undergoes echo interference in contrast to
common non-echo channels. An interference elimination method based on optical
filtering is presented along with an exemplary interference-free RBCom system.
