Photonic crystals (PhCs) have attracted much attention during the last decade as a solution to overcome the low extraction efficiency of as‐grown light‐emitting diodes (LEDs). In this review we describe the underlying physics and summarize recent results obtained with PhC LEDs. Here, the main focus is on diffracting PhC. In order to quantify the benefit from the incorporation of PhCs for diffracting light a comparison by simulations between a PhC LED and a standard state‐of‐the‐art LED is carried out. Finally, the impact of the PhC on the LEDs emission characteristics will be discussed with respect to étendue‐limited applications.

By driving with a microwave pulse the lowest frequency antiferromagnetic resonance of the quasi-1D biaxial antiferromagnet $({\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{NH}}_3{)}_2{\mathrm{CuCl}}_4$ into an unstable region, intrinsic localized spin waves have been generated and detected in the spin wave gap. These findings are consistent with the prediction that nonlinearity plus lattice discreteness can lead to localized excitations with dimensions comparable to the lattice constant.

Optical vortices (nodal lines and phase singularities) are the generic singularities of scalar optics but are unstable in vector optics. We investigate experimentally and theoretically the unfolding of a uniformly polarized optical vortex beam on propagation through a birefringent crystal and characterize the output field in terms of polarization singularities (C lines and points of circular polarization; L surfaces and lines of linear polarization). The field is described both in the 2-dimensional transverse plane, and in three dimensions, where the third is abstract, representing an optical path length propagated through the crystal. Many phenomena of singular optics, such as topological charge conservation and singularity reconnections, occur naturally in the description.

We report what is to our knowledge the first observation of Ince–Gaussian modes directly generated in a stable resonator. By slightly breaking the symmetry of the cavity of a diode-pumped $\mathrm{Nd}:{\mathrm{YVO}}_4$ laser and its pump beam configuration we were able to generate single high-order Ince–Gaussian modes of high quality. The observed transverse modes have an inherent elliptic structure and exhibit remarkable agreement with theoretical predictions.

We investigate the anisotropic optical gain in non-$c$-plane InGaN quantum wells with 20% indium content including band-gap renormalization and the screening of the quantum confined Stark effect. Waveguide modes and their polarizations are determined as TE and TM modes or extraordinary and ordinary modes, depending on the birefringence and the orientation of the laser diode’s ridge waveguide relative to the $c$ axis. The band structures and optical matrix elements along the polarization directions are calculated using a $6\times 6$ $k\cdot p$ Hamiltonian and a self-consistent Schrödinger-Poisson solver. From these calculations the reduced density of states and the optical gain for the different polarizations are determined in the free-carrier picture with an ad hoc inclusion of the band-gap renormalization and compared to a $c$-plane quantum well. It is found that for high indium concentrations the gain can be significantly increased by going from the $c$ plane to a semipolar or a nonpolar crystal orientation. However, due to birefringence and composition of the topmost valence-band wave function, the ridge has to be oriented along the $\left[\overline{1}\overline{1}23\right]$ direction for semipolar and along the [0001] direction for nonpolar laser diodes.