Direct Laser Welding Enables Adhesive-Free Fiber-to-Chip Connection

Fraunhofer IZM researchers and partners have developed a laser welding technique to fix optical fibers to photonic integrated circuits (PICs), removing the need for adhesive bonding. The technology was developed in response to proposed biophotonic sensing techniques involving miniaturized PIC-based systems utilizing highly stable fiber connections.

Traditionally, fiber interconnection strategies for PICs involve adhesives. Adhesive connections, however, can introduce optical degradation in the long term, leading to optical transmission losses. The softness of the adhesive can cause the position of the component to change over time and can create an interference point between the two layers of glass. This can lead to signal attenuation and a brittle connection as the adhesive ages.

CO₂ laser welding creates reliable fiber couplings for glass-based photonic integrated circuits. Credit: Fraunhofer IZM.

Developed in the context of the “PICWeld” Eurostars project, the method can be used to attach optical fibers directly to PICs based on fused silica glass substrates. Led by Alethea Vaness Zamora Gómez at Fraunhofer IZM, the team sought to develop glass-glass joints which are simpler, more robust, and more durable. To circumvent the problems of longevity in adhesive bonding, the team developed a CO₂ laser welding method to create a direct, thermally robust, and transparent glass-glass joint.

Because the glass fibers and substrates have different volumes, the heat capacities of the two parts to be joined are unequal, and therefore have different behaviors in terms of heating and cooling. Without proper compensation for the discrepancies, this can lead to deformation and cracks during cooling. To solve this, the team preheated the substrate evenly using a separate individually adjustable laser, enabling the melting phase of the fiber and substrate to occur simultaneously.

The technology developed through the project goes beyond an experimental setup. The system the team developed was designed for use in industrial settings. In collaboration with ficonTEC Service, the process was implemented in an automated system offering high reproducibility and scalability. It’s equipped with thermal process monitoring up to 1300 ºC, a positioning system accurate to 1 μm, and imaging recognition processes and control software.

“The high automation potential in particular allows customers to use PICs with maximum coupling efficiency. Industrial integration means a leap forward for the areas in which biophotonics can be applied, but also for quantum communication and high-performance photonics,” Gómez said.