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