Separate-confinement InGaAsP/InP heterostructures with highly strained quantum wells are grown by metal-organic vapor-phase epitaxy (MOVPE). The properties of InGaAsP and InGaAs quantum wells are studied, and the influence of the heterostructure parameters on the lasing wavelength is analyzed. The grown structures are used for designing high-intensity multimode and single-mode mesa-stripe laser diodes operating in the range λ=1.7–1.8 µm. The maximum continuous-wave lasing power achieved at room temperature is 1.6 W and 150 mW for multimode and single-mode laser diodes, respectively. Single-mode lasing is retained up to 100 mW.