We successfully demonstrate 20-Gb/s quadrature phase-shift keying (QPSK) signal transmission. The transmission was carried out over endlessly single-mode holey fiber in the waveband of 1276.02-1304.26 nm, whose bandwidth of 5.09- THz is broader than the traditional C-band. A wavelength-tunable quantum dot (QD) laser with broad wavelength tunability helps realize bandwidth availability. A single InAs/InGaAs QD optical gainchip was grown using a sandwiched sub-nanometer separator technique in the wavelength of 1.3-μm band. Using this gain chip, the QD light source has good wavelength stability, compactness and wavelength tunablility. The measured transmission results show bit error rates within a forward error correction limit of 2×10-3 using intradyne coherent detection with offline digital signal processing. In this study, it is expected that abundant frequency resources such as the O-band are coherently enhanced by the use of a large number of wavelength channels by effectively using the QD- laser.