An external cavity in Littrow configuration based on a reflective diffraction grating and a high-power semiconductor laser based on an asymmetric heterostructure with low optical loss was studied. A continuous-wave optical output power of 13 W with a linewidth of 0.15 nm was achieved for an external-cavity laser. It was shown that a decrease in the length of the laser chip to 1500 µm makes it possible to expand the tuning range of the lasing spectrum to 100 nm, while the maximum side-mode suppression reaches 45 dB, and at the edges of the spectral tuning range it is no worse than 30 dB. It was shown that the main factors in reducing the optical power when tuning the laser spectrum are an increase in the threshold current and internal optical loss of the laser chip.