conductive membrane modulator 10 constructed over the waveguide 14 sometimes referred to as a channel waveguide fabricated by the ion exchange process although a diffused channel glass waveguide is shown in fig1 the principles that facilitate the operation of the conductive membrane modulator 10 are more generally applicable to a range of waveguide configurations including those defined as being ribs strip loaded embossed and diffused and to waveguides constructed on substrates other than glass including silicon sapphire silicon carbide gallium arsenide and indium phosphide all of which are well understood in the art the conductive membrane modulator 10 is constructed so that it can be moved from the first position shown in fig1 to the second position shown in fig2 in the first position the conductive membrane 20 is separated from the waveguide 14 by a finite gap 26 electrodes 22 and 24 are provided and disposed so as to facilitate the movement of the conductive membrane 20 between the first and second positions in a preferred embodiment this is accomplished by using standard photolithography and thin film deposition techniques to define the lower electrode 22 the lower electrode 22 the substate 12 and the waveguide 14 are then coated with a protective overcoat layer 15 of tantalum pentoxide the preferred characteristics of the protective overcoat layer 15 am a it should effectively withstand the action of the wet chemical etchants which are used later in.