The present relates to a quantum communication system for free space quantum key distribution. An emitter and a receiver, the emitter and the receiver are two points distanced by a free space quantum communication channel, the emitter being designed for wirelessly transmitting data to the receiver via said free space optical communication channel. The receiver includes an optical device capable of receiving the data within a predetermined field of view extending from said optical device toward the receiver. The system is characterized in that the emitter further comprises a light protecting device attached on said emitter. The light protecting device is configured to prevent any light coming from the environment beyond the emitter to enter within the field of view of the receiver. The invention further relates to a method for optimizing free space quantum key distribution.