| 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. |