Abstract: Apparatus for the transmission of information by a laser beam and laser oscillators therefore are disclosed. This apparatus includes at least one laser oscillator for generating a laser beam and means associated with the laser oscillator for varying a characteristical quantity of the laser beam. The laser may take the form of a surface-emitting semiconductor laser, in which case the variable quantity is the spatial mode content of the laser beam. The laser may be provided with externally controllable means for extracting wave energy from a laser wave in the resonator of the laser, in which case the varying quantity is the spatial mode content or the frequency of the laser beam.

Abstract: Devices for controlling and guiding waves, such as electromagnetic waves, acoustic waves, and the like are disclosed which include at least one wave-transmitting medium and a diffraction grating, associated with the transmitting medium, for scattering wave energy into or out of the guided waves. The device may take the form of a "sandwich"-type or thin film waveguide, in which case the transmitting medium has at least one curvi-planar boundary, or it may take the form of a "rod"-shaped or cylindrical waveguide, in which case the transmitting medium has a substantially cylindrical boundary. According to the invention, the diffraction grating comprises a large number of substantially closed loop grating lines consecutively enclosing each other from inner to outer, with all of the grating lines extending substantially parallel to the phase fronts of the guided waves.