April 8, 2025. Researchers at Fraunhofer IZM have realized an adhesive-free laser welding process for coupling photonic integrated circuits (PICs) with optical fibers, which can also potentially be used in cryogenic environments of up to four Kelvin, i.e. -269.15°C. The technology opens up a more reliable, faster and cheaper fibre-PIC coupling through a direct quartz-quartz connection and thus revolutionizes applications in the field of quantum technologies.
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A cryogenic environment is essential for observing quantum effects. The latter can have an enormous benefit for people’s quality of life, for example, the handling of big data today can only be solved with quantum computing, for example in personalized medicine and the management of information in hospitals. The development of cryogenic systems for quantum computing is currently being intensively promoted. Quantum technology systems with implemented PIC-based modules offer a compact solution for secure communication and networking in quantum computing. However, reliable fiber optic connections are a basic requirement for such photonic quantum systems. Other areas such as biophotonics or sensor technology also benefit from this.
As part of the QWeld research project, the researchers at IZM developed a laser welding process for vertical optical connections using a “PICWeld” process system prototype, which had already been built and installed in a previous research project. The system was the first time ever that a direct edge connection between a glass fiber and a PIC made of quartz glass could be created using a laser welding process. The longevity and thermal robustness offer a clear advantage over the conventional connection method using adhesives.
The focus in QWeld is on realizing this connection technology for applications in cryogenic environments. PICs manufactured using the standard CMOS process are used, but with one fundamental requirement: a top layer of silicon dioxide (SiO2) is required for glass-to-glass laser welding. A special feature is the vertical coupling of the fiber with the PIC, usually with a specific angle of attack. During welding, the laser hits the contact point between the PIC and the glass fiber on both sides and creates the material bond within a few seconds. This manufacturing process therefore offers immense time savings. The changed boundary conditions, in particular the SiO2-SiO2 material pairing and high precision requirements for the alignment to each other, have required a far-reaching further development of the process and the associated system. For example, local preheating, extended alignment options and measurement technology were integrated. The welded joint is durable, reproducible and can be automated, for example for the series production of PICs, which are so urgently needed in quantum systems.
After the successful realization of this technology for quantum photonics, the project coordinator and scientist from Fraunhofer IZM Dr. Alethea Vanessa Zamora Gómez summarizes: “In the newly developed laser welding process, a CO2 laser is used to preheat a certain area of the SiO2 layer of the PIC in order to minimize the temperature difference between the fiber and the PIC during welding. This innovative preheating process promises to solve all current challenges of fiber bonding for PICs at cryogenic temperatures. Thanks to the use of CO2 lasers, the automated process is cheap and reliable to manufacture, making it attractive for use in industry.” Dr. Zamora Gómez and process developer Marco Queisser can thus confirm the aim of the project with satisfaction: To research a novel laser welding process for fiber-PIC coupling in order to realize future cooperation opportunities in the field of cryogenics and quantum PICs. In addition, further potential applications are possible in biophotonics, sensor technology and high-power lasers.
The QWeld project was funded by the “Wissenschaftliche Vorprojekte (WiVoPro): Photonics and quantum technologies 100% funded by the Federal Ministry of Education and Research (BMBF). The QWeld project ran from 01.08.2022 to 31.12.2024 in the “Quantum technologies – from the basics to the market” program. The project was coordinated by Dr. Alethea Vanessa Zamora Gómez from Fraunhofer IZM.
(Text: Lotta Jahnke)
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Photo: Fraunhofer IZM
