We present a cascaded system designed with Er3+-doped,TmS+-doped and Nd3+-doped fibers to realize amplified spontaneous emission (ASE) spectra covering 0.4-2.0 μm.The system is excited with a pump laser emitting 808 nm photons with 500 mW pump power.The emission spectra of the cascaded system covering 0.4-2.0 μm are realized with the Er3+,Tms+ and Nds+ ion doping densities optimized to 8 × 1019,2 × 1020 and 8 × 1020 ion/ms,respectively,and the fiber length optimized to 1 m.Numerical methods reveal that the peak ASE power for the cascaded system can reach 20.9 mW.A minimum ASE power of 4.39 mW is attainable.Using numerical calculations and analytical techniques,we provide a detailed insight into optimized Er3+-doped,Tm3+-doped and Nd3+-doped fiber lengths and their doping concentrations for ASE power spectra covering 0.4-2.0 μm.We believe that the cascaded system can potentially provide significant applications in various optical fields which include but not limited to wavelength-division multiplexing,various optical communications and other salient medical imaging processes.