Optical Bloch waves in a semiconductor photonic lattice

We have observed multiple optical Bloch waves in a semiconductor photonic lattice. This photonic lattice comprises epitaxial quarter-wave periodic layers surrounding a periodic quantum-well region. After growth, the layers are structured laterally into periodic square unit cells by reactive-ion-beam etching. When photoexcited, the lattice emits a complex angular distribution of photons that reflects its periodic structure. Scattered light is distributed according to the Laue conditions in analogy with x-ray diffraction from a bulk crystal. Optical Bloch waves photostimulated in the lattice are analogous to electron Bloch waves in an atomic lattice. These optical Bloch waves exhibit long-range translational symmetry and local symmetry due to the shape of the unit cell. Interestingly, the far-field pattern of stimulated emission gives a direct mapping of the allowed Bloch wave vectors in the Brillouin zone. The mapping exhibits a wave-vector gap at the Bragg condition and may be associated with a photonic energy gap. In addition to measuring the intensity distribution of these Bloch waves, we directly measure the phase of the wave by polarization shearing interferometry.