F 2 -laser microwelding of optical fibers and glass substrates

Abstract

Laser welding of optical glasses remains a challenging area today because of the weak optical absorption typically available with most commercial lasers and the brittle nature of glass. In this paper, we demonstrate for the first time to our best knowledge, the laser welding of telecommunication optical fiber onto a fused silica substrate. The 157-nm F 2 laser was selected for the wide processing window that drives strong absorption at high fluence exposure > 1 J/cm 2 without inducing microcrack formation. The method of second surface ablation was applied to the contact point between the glass plate and glass fiber to locally heat, melt, and reflow the glass and thereby weld together the two similar glasses. Mechanical pressure was applied while the laser beam was scanned along the sample contact to produce a line of overlapping welds of 25-um spot size each. Fused silica samples of up to several hundreds of microns thick could be welded owing to a large 157-nm penetration depth of 1/a ≈ 1 mm. A narrow 3.31 to 3.66 J/cm 2 fluence window was found for laser welding through 160-um thick fused silica substrates. The F 2 -laser welding window is constrained by the need for sufficient transmitted fluence to melt the interface without too much fluence that will damaged the interface structure at the onset of ablation or induce front surface ablation.