Femtosecond laser direct inscription of surface skimming waveguides in bulk glass

Abstract

We present a detailed study of waveguide inscription near the surface of bulk glass using a femtosecond laser. Three silicate glasses used extensively as hosts for photo-induced photonic devices were examined. Our results show that near-surface waveguides generally present a low-index contrast, as the pulse energy damage threshold decreases sharply at close proximity to the surface. We devised a novel method to allow the formation of optical waveguides that exhibit a high-index contrast up to the surface of any transparent material. As a proof of concept, the inscription of near-surface single-mode waveguides operating at a wavelength of 405 nm is demonstrated.

A simple technique to overcome self-focusing, filamentation, supercontinuum generation, aberrations, depth dependence and waveguide interface roughness using fs laser processing

“…By placing a glass cover slide in optical contact with the top surface of the sample, the air-glass interface is suppressed and the fs-laser passes through unaffected due to the weak Vander Waals attractive forces established between the atoms of the surfaces which form a temporary direct bond 21 . Therefore, it becomes possible to write waveguides at the very edge of the sample surface.…”

“…With its growing advancements and breakthroughs 1–4 such as optical data storage 5, 6 , multiphoton nanofabrication 6, 7 , optofluidic lab-on-a-chip devices 8, 9 , integrated photonics devices 10, 11 , elements of optical quantum computing systems 12 , 3D photonics crystals 13 , micro-mechanical/biological systems 14, 15 , cancer treatment 16 , photonics wire bounding 17 and invisible photonics devices for mobile phone applications 18, 19 , femtosecond laser processing is widely believed to offer a potentially versatile and cheap solution for material processing and device manufacturing. However, several limitations must be overcome to make this technology viable, namely, optical aberrations in focusing optics 20 , undesirable ablation 18, 21 , depth of field 22 , depth of writing limited by the working distance of the lens 23 , pulse stretching 24 , and unavoidable nonlinear optical effects such as supercontinuum generation and filamentation due to Kerr self-focusing 25–29 . Beam shaping has been successfully used to improve some of these problems 30 .…”

“…Recently, an efficient and simple solution was demonstrated by Bérubé et al . 21 using a 150  μ m thick glass cover slide placed in optical contact with the top surface of the sample to be processed. The sample is thus virtually thicker and the sample can be laser processed at the very edge of the surface (see Methods for more information and limitation of this technique).…”

“…The sample is thus virtually thicker and the sample can be laser processed at the very edge of the surface (see Methods for more information and limitation of this technique). Waveguides have also been written close to the surface in toughened glass such as Corning® Gorilla® glass 18, 19, 21 in which ion exchange process forms a compressive layer with high mechanical resistance that limits cracks and surface ablation. Since Gorilla glass is used as screen covers in the display industry, it has a great potential for liquid and gas sensing applications in mobile devices 19 .…”

Single-step fabrication of surface waveguides in fused silica with few-cycle laser pulses

“…Attempts in non-optimized glasses have resulted in surface swelling [6], cracking [19] and ablation [33]. In pure fused silica, the direct fabrication of near-surface waveguides with a good refractive index contrast has even been considered impossible [5]. The main reason is that fs-laser direct writing relies on pulse-to-pulse heat accumulation to induce controlled, localized heating of the substrate.…”