An InGaAs/AlGaAs structure with a single InGaAs quantum well emiting at 990 nm in TE polarization ( || QW) is used for laser fabrication. The ridge waveguide is etched to a distance of 150 nm from the GaAs waveguide layer. Electron beam lithography is then used to define a triangular array of holes with lattice constants between 160 and 400 nm in PMMA resist. The pattern is etched in an intermediate metal mask and finally transferred into the semiconductor.
The investigated structures include lasers with a photonic crystal mirror at one end of the waveguide (Fig. 2), the second mirror is formed by a cleaved facet. For these devices, a pronounced dependence of the threshold and output efficiency on lattice period, orientation of the crystal (G-M or G-K) and air filling factor was observed. The output power curves of lasers with different lattice periods for a G-M oriented crystal are shown in Fig. 3. A high reflectivity of the photonic crystal leads to a reduced threshold current and an increased output power on the facet opposite to the photonic crystal.
We also investigated lasers with bend waveguides and splitters. The curved sections of the waveguides are embedded in photonic crystal in order to reduce the radiation losses. For structures with proper lattice period, a clear effect on the guiding properties could be observed. A near field image of the output facet and the corresponding FEM micrograph are displayed in Fig. 4. The light is guided around a bend with a curvature of 5 mm, which is only 2.5 times the width of the waveguide.
