Propagation losses in photonic crystal waveguides: Effects of band tail absorption and waveguide dispersion

Propagation losses in GaAs-based photonic crystal (PhC) waveguides are evaluated near the semiconductor band-edge by measuring the finesse of corresponding Ln cavities. This approach yields simultaneously the propagation losses and the mode reflectivity at the terminations of the cavities. We demonstrate that the propagation losses are dominated by band tail absorption for shorter wavelengths and by fabrication disorder related scattering, near the photonic band edge, for longer wavelengths. Strategies for minimizing losses in such elongated cavities and waveguides are discussed, which is important for the monolithic integration of light sources with such optical elements.