We propose a global simulation scheme for studying the output characteristics of quantum cascade lasers subjected to near-infrared optical pulses with a wide range of injection powers. We treat nonresonant excitations where the photon energy of the injected pulse is far from that of QCLs. To maintain consistency even at large injection powers wherein thermal effects become non-negligible, internal parameters, e.g., electron temperatures, scattering times, gains, and waveguide loss, are treated as functions of space and time and evaluated based on the temperature and carrier distribution in the device. The number of photons in the cavity is converted into output power using the time-dependent reflectivity at the cavity facet. This all-in-one scheme well reproduces light output-to-current characteristics observed in a relevant experiment and is able to relate the induced changes in the output powers with the relevant intersubband gain and cavity loss components over a wide range of time scales after the pulse injection.