Silicon is the dominant material in the microelectronic industry and silicon photonics is rapidly gaining importance as a
technological platform for a wide range of applications in telecom, and optical interconnect. It allows the implementation
of many photonic functions through the use of wafer-scale technologies normally used for advanced CMOS-processing.
In this paper some of the most important issues toward a practical implementation of Silicon photonics into an industrial
device will be addressed: low loss waveguides, polarization handling, tunability, hitless switching. A tunable Add-Drop
multiplexer has been chosen as a case study of a fully integrated device.
In this paper system applications, geometry, physical effects and materials of optical switching devices are reviewed. Main system scenarios are presented and some key features such as size, loss, speed, scalability and granularity are highlighted. Two principal categories of optical switches are considered, i.e. guided-wave switches and free-space switches. In the first category some sub- classes have been identified according to their geometrical configuration, principle of operation and, then physical mechanism and materials. As for the geometry, the most frequently used configurations are briefly described together with their advantages and disadvantages. Different physical effects suitable to obtain the index change, which the switching function is based on, are also described with reference to the material substrates. Switches based on semiconductor optical amplifier gate are also analyzed. In the free-space category the main sub-classes are represented by the opto-mechanical devices and micro-opto-electro- mechanical systems switches. The last technology combines the free-space interconnecting with the integration capability on a single silica chip. The main advantages such as the ability to scaling up to large switch fabric and some issues such as packaging and reliability are analyzed. Finally, devices based on polarization change, acousto- optics interaction, total internal reflection and holography are illustrated.