Ultra-fast evolution of photonic eigenstates tracked in k-space

Photonic crystals (PhCs) form a powerful new class of materials for miniaturized integrated optical circuitry with PhC waveguides as a key component. The dynamic behavior of such a composite structure, is governed by the photonic eigenstates of each component and the coupling between them. In order to fully understand a composite PhC device, insight in the individual eigenstates and their mutual coupling is essential. Near-field visualization of the light propagation with simultaneous topographical information allows the optical properties to be unraveled and related to geometry. With our time-resolved and phase-sensitive near-field microscope we visualized the optical pulses as they propagate through a composite PhC model structure: a passive filter based on a directional coupler. The real-space measurements are useful to obtain a basic understanding of the dynamics in the structure. However, by transforming our phase-sensitive measurement data into reciprocal space (A:-space), we are able to identify each individual photonic eigenstates by their wavevectors.