Silica-based optical integrated circuits

Silica-based integrated optical waveguide technology is reviewed. Low loss and manufacturable waveguides are made by chemical vapour, flame hydrolysis and electron beam deposition. Fibre to fibre insertion loss is as low as 0.3 dB for a 6 cm long waveguide. Bragg reflective add-drop filters are made with gratings formed by ultraviolet irradiation. The waveguide grating router has found important application as a multiplexer in dense wavelength multiplexed communications systems. Multiplexers with wide pass bands and stop bands are made with Fourier filters: these filters consist of a chain of alternating couplers and delaying arms. The good performance of waveguide grating routers and Fourier filters is due to the high degree of path delay and coupler control achievable by photolithography and processing in this technology.