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Tunable/selectable-wavelength light sources are beginning to play important roles in dense wavelength-division-multiplexing (DWDM) optical transmission systems. Of the many types of tunable/selectable light sources, we have chosen to develop distributed-feedback (DFB) laser-diode (LD)-array-based "wavelength-selectable" light sources (WSLs) because of their stable and reliable wavelength properties. This paper reviews our recent progress on eight-DFB-LD array WSLs and WSL modules for wide-band DWDM applications. We took full advantage of an advanced form of selective metal-organic-vapor-phase epitaxy (MOVPE), which we call microarray selective epitaxy (MASE), to simultaneously fabricate six types of WSL on two wafers so as to fully cover the S-, C-, and L-bands. These WSLs demonstrated a tunable wavelength range (Δλ) of 15 nm, a high fiber output power of up to about 10 mW, and stable single-mode lasing properties with a side-mode-suppression-ratio greater than 42 dB. We also describe a 94-channel (50-GHz spacing) WSL module that features an integrated multiwavelength locker. A WSL with a band-covering tuning range, i.e., a Δλ of 40 nm in the L-band, was installed with a compact wavelength locker in a 12.7 mm×20.8 mm standard-size 22-pin butterfly package. The WSL module has a stable wavelength locking capability with spectral fluctuations of less than 1 pm and less than +/-5 pm against passage of time and variations in case temperature, respectively.