Dual-beam transformation systems (dual BTSs) are used to obtain a wide wavelength-locking range for high-power large-smile diode-laser arrays. The collimating residual divergence angle can be reduced from 9 mrad to less than 6.5 mrad using a set of two angled BTSs that are located in front of a diode-laser array with about a 2 µm smile. Due to the reduced collimating residual divergence angle, the external cavity with a set of two angled BTSs and a volume Bragg grating achieved a wide wavelength-locking range for temperatures ranging from 20°C to 30°C. In addition, the side-mode suppression ratio exceeds 30 dB.