The invention relates to the technical field of
laser communication, in particular to a
free space optical communication system, device and method. According to the
free space optical communication system provided by the invention, the space
light beam is firstly coupled with the multimode
optical fiber, and the characteristic that the
diameter of a
fiber core of the multimode
optical fiber is larger is utilized, so that the
coupling efficiency is improved, and the
energy loss in the
coupling process can be effectively reduced. Then, a mode
demultiplexer is used, and a mode conversion technology is adopted to separate and convert
multiple modes of light in the multimode
optical fiber, so that the obtained LP01 mode is separated and converted into a fundamental mode of the single-mode optical
fiber to serve as an output optical
signal, and the problem that the
modes of the multimode optical
fiber and the single-mode optical fiber are not matched is solved through the mode conversion technology; and finally, the converted fundamental mode
signal in the single-mode fiber is used for communication, so that a high-speed communication module can be better matched.