Abstract: A fast optical (with or without a photonic crystal) switch is fabricated/constructed, utilizing a phase change material, activated by either an electrical pulse (a voltage pulse or a current pulse) and/or a light pulse and/or pulses in terahertz (THz) frequency of a suitable field strength. The applications of such a fast optical switch for an on-demand optical add-drop subsystem, integrating with (a) a light slowing/light stopping component (based on metamaterials and/or nanoplasmonic structures) and (b) with or without a wavelength converter are also described.