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

Abstract

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 band-gap. The group index (n_g) 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 n_g, 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.