Tunable thin-film filters: review and perspectives

The development of tunable filters is a key point for the ability of optical telecommunication networks to comply with the continuous evolution of the service providers needs. Among the numerous technologies which can be used to achieve narrow bandpass filtering devices, we concentrate our analysis on Thin-Film Interference Coatings and compare the principles, performances and use constraints of the various schemes allowing to tune such a thin-film structure : tilt of a standard bandpass filter, translation of a linear variable filter, deformation of the substrate of a DWDM filter, implementation of active spacers with controllable optical thickness (thin-films or solid spaced etalons).