Method for providing separately adjustable voltage dependent optical properties

An electro-optical method comprising steps of

• providing a transparent solid having isolated photo-absorbing centers capable of persistent spectral hole burning when subjected to narrow band light, such burned holes being capable of being filled when the solid is subjected to an electric field;
• maintaining said solid at a temperature at which a process reverse to persistent hole burning cannot take place spontaneously;
• burning a first persistent spectral hole in the solid at a first optical frequency by irradiating the solid with narrow band light of said first frequency while applying a first burning voltage of selected sign, value and temporal course to the solid to adjust the characteristics of the solid in dependence on voltage, that is, the optical response of the solid to applied voltage at said first frequency;
• and burning a second persistent spectral hole in the solid at a second optical frequency by irradiating the solid with narrow band light of said second frequency while applying a second burning voltage of selected sign, value and temporal course to the solid to adjust the optical characteristics of the solid at said second frequency;
• whereby one may separately adjust the optical characteristics at separate frequencies, so that a voltage dimension is introduced as an additional dimension, that is, in addition to the frequency dimension.