GPU implementation of FSR simulations: performance improvements and limitations

Numerical simulation to calculate the free spectral range scans (FSR scans) of laser resonators is a computationally intensive task. OSCAR is a well-established Matlab toolbox that enables for such simulations based on Fourier optics. Any arbitrary discrete complex electromagnetic input fields as well as misalignment or mismatching of resonators can be considered in the FSR simulation. Unfortunately, it currently only features CPU based calculations on one or more CPU cores. However, the computational cost increases exponentially with increasing lateral resolution of the complex electromagnetic fields. In addition, only a limited number of roundtrips can be carried out in an acceptable computation time, which limits the applicability only to low finesse resonators. Due to good parallelizability of the FSR scan calculation, this numerical computation is very well suited for modern graphics cards, which are outstanding in performing many calculations in parallel. This paper introduces the extension of FSR scan simulations on modern graphics cards (GPUs) within the OSCAR Toolbox. First, a statistical analysis is provided, that presents the massive performance improvement compared to CPU computations. Subsequently, the disadvantages in the form of memory limitations of GPUs are outlined. Therefore, generally valid data is presented, from which a trade-off between lateral resolution of the complex electromagnetic fields and the number of roundtrips to be performed can be derived. In conclusion, the great potentials of new applications are highlighted, which were previously not feasible. Any code of this GPU implementation discussed in this paper has been integrated into the OSCAR Matlab Toolbox and is made available open source on GitHub.