In this paper we are reporting the computation for the Nonlinear Optical Rectification (NOR) and the Second and Third Harmonic Generation (SHG and THG) related with electronic states of asymmetric double Si-d-doped quantum well in a GaAs matrix when this is subjected to an in-plane (x-oriented) constant magnetic field effect. The work is performed in the effective mass and parabolic band approximations in order to compute the electronic structure for the system by a diagonalization procedure. The expressions for the nonlinear optical susceptibilities, chi((2))(0), chi((2))(2 omega), and chi((3))(3 omega), are those arising from the compact matrix density formulation and stand for the NOR, SHG, and THG, respectively. This asymmetric double d-doped quantum well potential profile actually exhibits nonzero NOR, SHG, and THG responses which can be easily controlled by the in-plane (x-direction) externally applied magnetic field. In particular we find that for the chosen configuration the harmonic generation is in the far-infrared/ THz region, thus and becoming suitable building blocks for photodetectors in this range of the electromagnetic spectra.