The use of glass as an assembly carrier in electronics production enables the additional transmission of optical signals via the carrier material and can therefore contribute to significantly higher data transmission for applications in the automotive and telecommunications sectors as well as for AI applications. In the research project 'Integrated Electro-Photonic Panel Systems' (EPho), a system was developed to automatically characterize the propagation losses of integrated optical waveguides.

The rapidly growing volumes of data in an increasingly digitalized world require new solutions in order to process and transmit data efficiently. This requires more and more transistors, tiny electronic components on a chip that are responsible for carrying out computing operations. In data centers and high-performance computers in particular, the miniaturization of transistors and their contacting is reaching the limits of what is technically feasible. In modern chips, the smallest structures are only a few silicon atoms wide. This requires extreme manufacturing precision for more and more transistors per chip, which leads to a lower yield in production and therefore to high costs.

In order to increase the number of transistors per package in an economical manner in accordance with Moore's law and thus achieve a further increase in power density, attempts are increasingly being made not to place all transistors on one chip, but to distribute them over several so-called chiplets. However, this principle only works profitably if the chiplets are effectively interconnected.

This places high demands on the substrate on which the chiplets are placed. The connections between the chiplets must fulfill ever smaller structure sizes. The current target is 3 μm (line/space), which can no longer be reliably processed on organic substrates.

Industry-leading companies, such as Intel, therefore rely on glass as a substrate material. Fraunhofer IZM is also pursuing this approach. This is because glass is a substrate material into which optical waveguides can also be integrated. This means that an electro-optical circuit board can conduct both electrical and optical signals, thereby significantly increasing data transmission.

Fraunhofer IZM has developed a process running on commercial equipment that produces low-attenuation single- and multi-mode waveguides in large-format (>450 mm x 300 mm) thin glass using an ion exchange process. Since many hundreds of waveguides can be fabricated in one glass, the inspection of these glass panels is very challenging. This is also due to the fact that, unlike electrical cables, glass panels allow crossings and therefore complex layouts can be integrated into a single layer. To complete the process chain, a system has now been developed that automatically characterizes the propagation losses of integrated optical fibres. This also includes waveguides written using femtosecond lasers or waveguides in other substrate materials. The measurement procedure is always the same:

1. A sample is inserted into the system.
2. The layout is uploaded, the waveguides to be measured are selected and the measurement is started.
3. The system automatically detects the edges of the substrate, any existing marks, the exact position of the measuring fiber, takes a reference measurement and uses all this information to then automatically measure the insertion losses of all selected waveguides.

The system enables comprehensive process control for the production of optical fibers. In addition, many thousands of parameter sets can be examined to determine new process parameters when developing processes for fiber optic production. Especially in technologies with many variable process parameters, such as laser writing of optical fibers, the system enables great progress to be made in a short time.

The EPho project (16ES0806) was successfully completed in 2022 and funded by the Federal Ministry of Education and Research (BMBF) with a sum of 1.33 million euros. Other project partners were the companies Ilfa, Schröder Spezialglas and Ficontec Service.