An optomechanical system (1000, 2000, 3000, 4000) for injecting light, especially into a thin optical medium, the system comprising: - an optical coupler (1, 1a, 1") that comprises a body of axis Oz, O being the center of the entrance of the optical coupler, including integrally formed: - a lens of axis coincident with the axis Oz, of preferably subcentimeter-size maximum width W, comprising: - a convex entrance face of radial extent R 1; - a convex central exit face, defined by a central extent, on the axis Oz, called H and preferably smaller than W, and of radial extent RA; and - a peripheral exit face (13, 13a) that comprises a part joined to the central exit face, said part being flat, especially annular, or concave or frustroconical and flared in the direction of the exit of the system; - a cavity, of axis coincident with the axis Oz, comprising a bottom containing the entrance face, and comprising a lateral surface (14, 14a to 14c), called the entrance lateral surface; - a peripheral reflective surface, encircling the lens and the cavity, of axis coincident with the axis Oz, able to totally internally reflect light rays refracted by the entrance lateral surface, said peripheral reflective surface extending beyond the entrance face in the direction of the exit of the optical coupler; - an optical collector of axis coincident with the axis Oz, with as entrance, a surface, called the collecting surface, facing the central exit face, of millimeter-size radial extent RINT, and a numerical aperture NA smaller than 1, the collector comprising a jacket having a given end surface, the central exit face and the peripheral exit face (13, 13a) being spaced apart from the collecting surface, the optical collector comprising a bundle of optical fibers, said optical fibers having a diameter smaller than 1.5 mm; and - a member (30, 30', 30") for aligning the optical collector with the optical coupler, the optical coupler and the aligning member being integrally formed or being indirectly or directly fastened together, the central distance e F on the axis Oz between the collecting surface and the central exit face being nonzero and smaller than 5 mm, and the optomechanical system comprising a stop surface against which the end surface abuts. - an optical coupler (1, 1a, 1") that comprises a body of axis Oz, O being the center of the entrance of the optical coupler, including integrally formed: - a lens of axis coincident with the axis Oz, of preferably subcentimeter-size maximum width W, comprising: - a convex entrance face of radial extent R 1; - a convex central exit face, defined by a central extent, on the axis Oz, called H and preferably smaller than W, and of radial extent RA; and - a peripheral exit face (13, 13a) that comprises a part joined to the central exit face, said part being flat, especially annular, or concave or frustroconical and flared in the direction of the exit of the system; - a cavity, of axis coincident with the axis Oz, comprising a bottom containing the entrance face, and comprising a lateral surface (14, 14a to 14c), called the entrance lateral surface; - a peripheral reflective surface, encircling the lens and the cavity, of axis coincident with the axis Oz, able to totally internally reflect light rays refracted by the entrance lateral surface, said peripheral reflective surface extending beyond the entrance face in the direction of the exit of the optical coupler; - a lens of axis coincident with the axis Oz, of preferably subcentimeter-size maximum width W, comprising: - a convex entrance face of radial extent R 1; - a convex central exit face, defined by a central extent, on the axis Oz, called H and preferably smaller than W, and of radial extent RA; and - a peripheral exit face (13, 13a) that comprises a part joined to the central exit face, said part being flat, especially annular, or concave or frustroconical and flared in the direction of the exit of the system; - a convex entrance face of radial extent R 1; - a convex central exit face, defined by a central extent, on the axis Oz, called H and preferably smaller than W, and of radial extent RA; and - a peripheral exit face (13, 13a) that comprises a part joined to the central exit face, said part being flat, especially annular, or concave or frustroconical and flared in the direction of the exit of the system; - a cavity, of axis coincident with the axis Oz, comprising a bottom containing the entrance face, and comprising a lateral surface (14, 14a to 14c), called the entrance lateral surface; - a peripheral reflective surface, encircling the lens and the cavity, of axis coincident with the axis Oz, able to totally internally reflect light rays refracted by the entrance lateral surface, said peripheral reflective surface extending beyond the entrance face in the direction of the exit of the optical coupler; - an optical collector of axis coincident with the axis Oz, with as entrance, a surface, called the collecting surface, facing the central exit face, of millimeter-size radial extent RINT, and a numerical aperture NA smaller than 1, the collector comprising a jacket having a given end surface, the central exit face and the peripheral exit face (13, 13a) being spaced apart from the collecting surface, the optical collector comprising a bundle of optical fibers, said optical fibers having a diameter smaller than 1.5 mm; and - a member (30, 30', 30") for aligning the optical collector with the optical coupler, the optical coupler and the aligning member being integrally formed or being indirectly or directly fastened together,