an open - path / free - space optical communication system using reflected light has modulated optical or laser sources and provides communication between the modulated source and a detector in an obstructed line - of - sight relationship . the system detects backscattered light impinging on a target illuminated by the source of light . barrier objects positioned in a line - of - sight path between the source and detector are circumvented and a first device that provides the modulation signal for the source controls a remote second device .