Automated direct surface coupling of optical fibers to integrated photonics by laser welding

Integrated photonics is a potential platform technology to enable miniaturization, scalability and cost-effectiveness for applications ranging from traditional optical communications and sensing to innovative quantum technologies. However, photonic integrated circuits (PICs) should be connected to the outside world by optical fibers in order to be of practical use. These connections require assembly methods, e.g. based on the well-known adhesive bonding, to meet the requirements of the application. With a focus on quantum technologies, some quantum experiments need to be developed at cryogenic temperatures (T = 4 K), requiring reliable and robust fiber connections for PIC modules such as sensors, detectors and lasers. Therefore, innovative bonding methods should be explored, as the adhesive method is no longer valid at such temperatures due to its rapid optical and mechanical degradation. As part of the project “QWeld”, the suitability of laser welding for direct fiber coupling to the surface of the fused silica blank substrates and PICs with SiO2-coated gratings is investigated. A similar method has previously been reported using borosilicate glass to interconnect micro-optics. At this point we face the challenge imposed by the fused silica material, being the same material as the fiber, and the thin layer of SiO2 in the case of silicon (Si) wafer-based PICs. Tensile tests were performed on fused silica substrates and compared with borosilicate glass values. Moreover, initial temperature tests down to 77 K were carried out to investigate mechanical stability of fiber-coupled samples.