With higher complexity of optical networks there is an increasing demand for components which allow to manipulate the optical signals without conversion to the electronic domain. Besides modulation the key functions needed for advanced telecom applications are multiplexing and demultiplexing in the time and frequency domains, wavelength flutering, routing, switching, dispersion equalising. This paper describes the state-of-the art of planar guided wave circuits (integrated optical devices) made from Si02, InP, LiNbO3 and polymers, which are going to replace discrete components based on fibres, thin film technologies and bulk optics. Special emphasis will be put on scalability and the capability for higher monolithic or hybrid integration. As wafer scale integration, i.e. one circuit occupies a whole wafer, has been reached for specific components such as high channel count arrayed waveguide grating devices (Phasars) and switch matrices, new device structures which consume less real estate have to be elaborated.
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