Integrated optic time delay network for phased array antennas

An integrated optic time delay unit (TDU) is described. The TDU relies on a folded path optical waveguide to achieve time delays ranging from a few picoseconds to several nanoseconds. The folded path configuration utilizes thick phase gratings as reflective elements. These elements provide large angle deflection, high diffraction efficiency or reflectivity, and wavelength multiplexing capabilities and form the basis for an electronically addressable switch. As a switching element they also offer high isolation due to their high diffraction efficiency. By cascading gratings or alternatively utilizing long gratings, the transmitted optical signal is expected to be reduced to -40 dB to -60 dB or better, thus offering excellent isolation. The folded path configuration is the key to a small compact package. Using low-loss waveguides, it is projected that time delays up to 10 ns can be achieved in a package size of 25 mm by 75 mm. The delay line concept, with the exception of active switching, has been demonstrated using ion-exchange waveguides and surface relief gratings