OPTICAL CHANNEL WAVE-GUIDE FABRICATION BASED ON ELECTRON-BEAM IRRADIATION OF SILICA

The bombardment of silica by low-energy electrons induces compaction and an increase in refractive index. We have used this phenomenon, combined with photolithographic processing, to make channel waveguides in silica, most of which are monomode, with a depth of 2-7-mu-m and peak index variation between 10(-3) and 10(-2). Channel waveguide widths down to 2-mu-m have been fabricated on fused silica plates and on silica layers grown on silicon by plasma-enhanced chemical vapor deposition (PECVD) methods. The lowest measured linear losses at 633 nm were 0.3 db/cm in PECVD silica and 1.9 db/cm in the fused silica plates, although much lower losses are anticipated in the latter material. Using this method we have fabricated 3 dB directional couplers in both materials.