The paper discussed the results of the study of elastically strained InGaAlAs/InGaAs/InP heterostructures grown by molecular beam epitaxy as active region for laser diodes of the spectral range 1510-1580 nm. Structural and optical properties of the heterostructures were studied by transmission electron microscopy and photoluminescence techniques. We obtained the dependence of the critical thickness of multiple elastically strained InGaAs layers separated by InGaAlAs barriers on mole fraction of InAs.