Photonic Crystal Surface Emitting Lasers (PCSELs)

Photonic Crystal Surface Emitting Lasers (PCSELs) are innovative semiconductor lasers consisting of a vertical slab waveguide that includes a photonic crystal (PC) layer. This layer consists of a periodic modulation of dielectric permittivity on the wavelength scale. In our case, these are periodic air holes in an AlN cladding layer, as shown in the figure on the left. Bragg reflections occurring within the PC layer enable both distributed in-plane feedback and the vertical outcoupling of symmetric beams. By utilizing this concept, PCSELs can emit symmetrical, low-divergence beams in the watt-class regime under single-mode operation. In collaboration with Chalmers University of Technology (Gothenburg, Sweden) and Berlin University of Technology, we have demonstrated optically pumped PCSELs lasing at approximately 275 nm in the deep-UV regime. This wavelength range is particularly relevant for disinfection and gas sensing.
Our group specializes in optical mode simulation, which is essential for predicting threshold gains, far-fields, wavelengths, and the stability of lasing modes. Photonic band structure measurements using photoluminescence (PL), as shown in the figure below, reveal features that may enable multi-mode lasing and distort far-fields. Numerical simulations of these band structures (red curves) are therefore critical for tuning device parameters to mitigate such distortions.
A significant challenge in PCSEL modeling is the assessment of undesirable in-plane losses, which requires the consideration of finite-area effects. Modeling a full, finite-sized PCSEL is computationally demanding due to the vast disparity in length scales between the lattice constant and the total mesa size. For example, a device may consist of one million unit cells, rendering standard finite-difference approaches prohibitively inefficient. We are therefore developing tailored multiscale simulation approaches that involve both approximate and first-principles methods based on Guided Mode Expansion and Rigorously Coupled Wave Analysis.

latest theses:
M. Riedel: “Frequency domain simulations of finite-sized Photonic Crystal Surface Emitting Lasers”, Master’s thesis (2025)

latest publicationen:
L. Persson, M. Riedel, et al., Opt. Express 33, 53098-53116 (2025)
D. Apaydın, Hjalmar Andersson, et al., Laser Photonics Rev. 20, e00271 (2025)