Midinfrared Dispersion Relations in in P -Based Photonic Crystal Slabs Revealed by Fourier-Transform Angle-Resolved Reflection Spectroscopy

Photonic crystals (PCs) offer unique ways to control light-matter interactions. The measurement of dispersion relations is a fundamental prerequisite if we are to create various functionalities in PC devices. Angle-resolved spectroscopic techniques are commonly used for characterizing PCs that work in the visible and near-infrared regions. However, the techniques cannot be applied to the mid- and long-wavelength infrared regions due to the limited sensitivity of infrared detectors. Here, we propose an alternative approach to measuring infrared dispersion relations. We construct a high-precision angle-resolved setup compatible with a Fourier-transform spectrometer with an angle resolution as high as 0.3∘. Hence, the reflection spectra are mapped to the two-dimensional (2D) photonic band structures of In(Ga,Al)As/InP-based PC slabs, which are designed as midinfrared-PC surface-emitting lasers. We identify complex PC modes with the aid of polarization-selection rules derived by group theory. Spectral analysis makes it possible to evaluate the mode quality (Q) factors. Therefore, angle-resolved reflection is a useful way of optimizing 2D PC parameters for midinfrared devices.