The bleaching irradiation will usually be UV or visible light, blue light being preferred in most instances. Suitable potoresists in general are known as "dyed resists." They include those marketed by Hoechst AG under the names of AZ 6618-2DG, AZ 6218B-3DG, which both absorb at 436 nm, and AZ 7510-2DG, which absorbs at 365 nm. Other dyed resists are those marketed by Shipley under the name microposit (S1813-J2, S1818-J2, S1400-27 D1, S1400-31 D1). If the bleaching irradiation has a wavelength in the range of from 200-300 nm, many conventional photoresists can be employed as a bleaching mask. Templates which are partially transparent and partially opaque to UV irradiation have been described in DD 114717, for use in making printed circuit boards.
If an electro-optically active waveguide is made, it is possible to refrain from removing the metal mask, as it can be used as an electrode. However, in that case the electrodes will have the same shape as the bleaching mask, which is a serious design limitation. For passive waveguide components and thermo-optic waveguide components, the metal layer is always redundant and has to be removed.