Time-wavelength reflectance maps of photonic crystal waveguides: A new view on disorder-induced scattering

We investigate the impact of disorder on the propagation of photonic crystal waveguide modes using phase-sensitive optical low-coherence reflectometry. Combined with a suitable numerical processing, this technique reveals a considerable amount of information that we cast as time-wavelength reflectance maps. By comparing measurements on different samples, we easily identify inter-mode scattering and propagation losses mediated by slow leaky modes. We also characterize the dispersive behaviour of point defects. Our results verify previous theoretical predictions about the general group velocity scaling of losses and the dominant role of backscattering.