High transmission recovery of slow light in a photonic crystal waveguide using a hetero group velocity waveguide

High transmission of slow-light in a photonic crystal (PC) waveguide (WG) using a hetero group-velocity (Ht-V-g) PC-WG was proposed and experimentally investigated. The Ht-V-g WG, which comprises a low-group- velocity (L-V-g) PC-WG section between two identical high-group-velocity (H-V-g) PC-WGs, is designed to decrease the impedance mismatch of the L-V-g PC-WG. The increase in transmittance of a propagating pulse was confirmed in the Ht-V-g PC-WG even in the vicinity of the band-gap, whereas the homogeneous PC-WG showed a gradual decrease in transmittance with the pulse wavelength approaching the bandgap. The group index (ng) of the L-V-g region in the Ht-V-g PC-WG was measured by the cross-correlation method and attained a value above 20. On the other hand, the transmittance of the Ht-V-g structure recovered approximately 16dB compared to the homogeneous L-V-g WG having same ng, 17. This recovery is mainly dominated by the coupling improvement due to the Ht-V-g structure, around 12dB. These results indicate the effectiveness of the Ht-V-g structure to use slow light in a PC- WG, which leads to various applications in PC-based optical devices. (C) 2007 Optical Society of America