PICs

*Updated version of the 2023 article. 

Definition

Conventional computer chips contain circuits with electronic components such as transistors, amplifiers and resistors, which are mounted on a semiconductor disc of silicon, also known as a wafer. Electrons are used for data transmission. Photonic integrated circuits (PICs), on the other hand, integrate complex optical components that generate, modulate and transmit light, such as laser/LED light sources, optical amplifiers, modulators and waveguides, on a single chip. These circuits, then, use light instead of electrons. This has its advantages: Signal transmission with light is much faster and more energy efficient than electron transmission. PICs can therefore speed up data processing in high-performance computers and increase the energy efficiency of data centres. In addition, the integration of the optical components makes it possible to manufacture versatile, chip-based optical components for various photonic applications. 

Current applications and opportunities 

PICs on silicon chips are already a mature, commercially available technology. These optical chips are used in data centres and high-performance computing centres for signal conversion at the computer interfaces between electrical cables and optical fibres – these are known as interconnects. However, because of the enormous increase in data generated by AI applications, these interconnects are reaching their limits. 

Researchers are therefore looking for new semiconductor materials, as silicon is not ideal in terms of its optical properties. It only transmits light with losses and has no non-linear optical properties, which are essential for electro-optical applications. In addition, silicon strongly absorbs the wavelengths of visible light, which means that it cannot be used. In contrast, semiconductor crystals made of gallium and indium phosphide, silicon nitride and carbide, and metal oxides such as lithium niobate and barium titanate exhibit new physical properties that modulate and transmit laser light more efficiently. Depending on the material, wavelengths in the visible range can also be used. These materials enable smaller and more efficient photonic chips that transmit light without any loss of quality or intensity, enabling higher transmission speeds with lower energy consumption. 

These requirements are becoming increasingly important, especially with the growing use of AI, because the neural networks used for this require massive parallel computing steps. PICs meet the requirements for speed and efficiency of data transmission within data centres and can thus massively expand the capacities of interconnects. 

By integrating expensive components that were previously only manufactured by machine, such as lasers, optical amplifiers and modulators, on a single chip, PICs enable complex optical components to be built for the mass market. Its high potential for enormous scalability could make a lasting change to photonics production for the first time in 50 years and enable numerous new applications, for example in the automotive industry, in optical sensors, in satellite and medical technology, and in optical communications.  

Switzerland is well positioned to play a leading role in the development of the next generation of integrated photonics. Research groups at universities – particularly at the two ETHs – are at the forefront of the search for new, promising materials for photonic chips that are not yet on the industry’s roadmap. Several start-ups have professional expertise at the highest level and are driving PIC technology forward. In addition to the two ETHs, the Swiss Centre for Electronics and Microtechnology (Centre Suisse d’Électronique et de Microtechnique, CSEM) also plays an important role in the transfer of knowledge from university research to application-oriented start-ups. 

Challenges  

The main obstacle for projects in the field of integrated photonics is the large amount of financing required, especially when it comes to infrastructure. Cleanrooms, i.e. rooms with a very low concentration of airborne particulates, are required for the production of the wafers and the sensitive circuits. Start-ups are generally unable to afford their own cleanrooms owing to the high costs involved. An international comparison shows that innovation is higher in locations where start-ups can make use of university infrastructure.  

The two ETHs, CSEM and a spin-off of the Paul Scherrer Institute (PSI) also provide cleanrooms for local start-ups. However, 20-year-old technologies are still used in Switzerland that are designed for the production of 100-millimetre wafers. Meanwhile, the latest processing techniques are already being established internationally on 150-millimetre or 200-millimetre wafers. In order to remain relevant in the realms of research and development, Switzerland would also have to make this technological leap. 

Conventional project funding in Switzerland does not provide sufficient resources for adequate further development of the technology. There is no national research programme (NRP) to develop integrated photonics, for example by providing the necessary infrastructure. As a result, networking between the relevant actors is also insufficient. 

Focus on industry

PICs offer enormous market potential for Swiss industry. Over the past two years, the importance of this technology has increased rapidly, primarily as a result of the spread of AI applications in many industrial sectors. Within a very short period of time, almost two dozen highly specialised start-ups have emerged that are involved in the production processes crucial to PIC development, such as chip design and manufacturing, packaging and assembly.  

Employees in this area must have excellent knowledge of electrical engineering, physics and materials science, as well as experience in chip manufacturing – particularly in nanofabrication – and working in cleanrooms.  

Owing to the rapid increase in start-ups, there is a growing demand for specialists. Until now, the most important source of highly specialised professionals in the field of PIC technology has been the research groups working in this area. However, only a few research groups are active at the highest level in Switzerland. Given the increasing complexity and breadth of applications, the looming shortage of specialists is endangering the transfer of knowledge between research and real-world use. 

International perspective 

The field has developed rapidly over the past two years – both in the development of PICs and in their industrial use. In Switzerland, there are a few research groups that are well connected and can compete at European and international level.  

Internationally, some clusters around universities in the US, Europe and China play a major role. In many places abroad, the financial opportunities are more advantageous than in Switzerland. There is a lack of national funding programmes (NFPs), which, for example, give research groups and start-ups access to sufficiently developed infrastructure. 

Future applications

Recent advances have shown that integrated photonics, based on hybrid approaches and using new materials, has enormous potential far beyond data transmission. Specially developed PICs that integrate complex and expensive optical components such as lasers or optical amplifiers on a single chip will find new applications. For instance, they can be used in ophthalmic medical devices such as optical coherence tomography (OCT). In the area of autonomous driving, they will be used in LiDAR sensors in assistance systems for information acquisition. Applications in metrology, space travel and military and communications technology are also to be expected. At the same time, photonic integrated circuits are also relevant in basic research – such as quantum research. With this broad usability, PICs will become a basic technology that will lead to groundbreaking developments in numerous industrial sectors. 

This technology opens up great opportunities for the economy. Swiss companies can increase their competitiveness by developing PICs and producing photonic chips, provided that politicians and businesses provide the necessary support to adequately finance the infrastructure. They also open up new markets and can thus create jobs.