The Department of Atomic Physics has been taking part in consecutive quantum optical projects starting from the HunQuTech project launched in 2017 for the study and development of quantum optical processes and technologies. This rapidly growing branch of optics-photonics is aimed at realizing devices and methods capable of performing quantum computations, telecommunication as well as cryptography. Our own skills now cover the design, implementation and measurement of photon pair sources and photon-state tomographs. Though all these work fine, our present systems are realized by using free-space bulk optical elements, which hinders subsequent miniaturization.

The urging need for smaller, easily integrable photonic components and systems is already present in the technical world as the numerous relevant journal papers and simple-to-advanced waveguide-based products entering the market testify. Neither the simulation/design nor the fabrication of such photonic integrated circuits (PIC) is a simple task. There are certain waveguide technologies available from companies and research institutes, thanks to which many types of integrated optical components can be realized. The simulation of these require a combined effort by using standard optical design software and wave-optical simulation, such as finite element methods to solve electromagnetic equations. Neither the usage nor the interconnection of such software is a straightforward task.

The applicant must first explore the existing and reproducibly usable technologies by which PICs can be fabricated so that we precisely know what kind of building blocks we may use in our research. Next, they have to identify the key areas, where extensive research takes place, or where there are a lot of questions still open. A most typical example is the efficient and cost-effective coupling of optical fibers to channel waveguides or these latter to optoelectronic components. Other examples are ring resonators, different integrated interferometers/switches, wavelength multiplexers/demultiplexers and so on. The main task is to develop the appropriate simulation techniques necessary for these PICs, and by applying these to devise new, improved photonic structures for quantum-optical systems that can be implemented by existing technologies.