Optical element having dielectric layers formed by ion-assisted deposition and method for fabricating the same

A method for fabricating an optical element, comprising:

• providing a substrate;
• and
• forming a plurality of first dielectric layers, a plurality of metal layers of Ag or its alloy and a plurality of second dielectric layers over the substrate, wherein the plurality of first dielectric layers and the plurality of metal layers are alternately formed over the substrate, and the plurality of second dielectric layers are formed on one side away from the substrate of the plurality of metal layers and between the plurality of metal layers and the plurality of first dielectric layers, wherein the plurality of first dielectric layers are formed by performing high-power ion-assisted deposition and the plurality of second dielectric layers are formed by performing low-power ion-assisted deposition, wherein the high-power ion-assisted deposition has a beam voltage which is in a range from about 1,000V to about 1,500V and has a beam current which is in a range from about 1,000 mA to about 1,500 mA, and the low-power ion-assisted deposition has a beam voltage which is in a range from about 100V to about 500V and has a beam current which is in a range from about 100 mA to about 800 mA.