[en] Multifrequency lasing in a new class of injection heterolasers, i.e., in an interband two-cascade laser with a tunneling p-n junction separating two active regions of quantum wells located in the same waveguide is obtained and studied. The developed laser structure with pulsed pumping provided the simultaneous emission of two first-order modes with the wavelengths of 1.063 and 0.98 μm and two third-order modes with the wavelengths of 0.951 and 0.894 μm. Due to nonlinear mixing of the modes within the laser cavity, the generation of the second harmonics and sum frequencies was observed