Process for the preparation of an optical structure and optical structure obtained thereby

DETAILED DESCRIPTION We claim: 1.
A process for producing an optical structure comprising a silicon-based coating on an optical polymeric substrate, comprising the following consecutive steps: (a) plasma-activating a surface of the substrate with plasma based upon a gaseous mixture containing argon to form an activated surface; (b) depositing a first layer of SiO.
sub.
2 onto the activated surface by a plasma enhanced chemical vapor deposition technique from silane and oxygen to form a first layer having a thickness of from about 2 to 5 microns; (c) coating said first layer by a plasma enhanced chemical vapor deposition technique while the substrate is subjected to radio-frequency biasing with a second layer formed of a silicon nitride.
2.
The process for producing an optical structure comprising a silicon-based coating on an optical polymeric substrate, comprising the following consecutive steps: (a) plasma-activating a surface of the substrate with a plasma based upon a gaseous mixture containing argon to form a plasma-activated surface; (b) depositing a first layer of SiO.
sub.
2 onto the activated surface by plasma enhanced chemical vapor deposition from silane and oxygen to form a first layer having a thickness of from 2 to 5 microns; (c) coating said first layer by plasma enhanced chemical vapor deposition with a second layer, said second layer comprising a complex having a composition intermediate between SiO.
sub.
2 and Si.
sub.
3 N.
sub.
4 with a minimum of Si--Si bonds while the substrate is subjected to radio-frequency biasing.
3.
The process according to claim 1 wherein the nitride compound of silicon contains silicon, hydrogen and nitrogen.
4.
The process according to claim 1 wherein said second layer has a thickness of from 2 to 50 microns.
5.
The process according to claim 1 further comprising depositing onto the activated surface a silicon-based under-layer by plasma enhanced chemical vapor deposition from silane.
6.
The process according to claim 2 further comprising depositing onto said activated surface a silicon-based under-layer by plasma enhanced vapor chemical vapor deposition from silane