A reflector chamber, used to couple a light source to a downstream light-transport medium, includes a forward reflector which folds the light impinging upon it forward and a backward reflector that folds backwards the light received from the light source or the forward reflector. The two reflectors are judiciously shaped so as to maximize the energy density at the output aperture with an angle of emission within the numerical aperture of the downstream medium. The forward reflector is preferably shaped substantially flat and coplanar with the light source. The backward reflector is preferably a concave section. A diverging light reflector may be added to the output aperture of the coupler in order to increase its efficiency.