Efficient prediction of terahertz quantum cascade laser dynamics from steady-state simulations

Abstract

Terahertz-frequency quantum cascade lasers (THz QCLs) based on bound-to-continuum active regions are difficult to model owing to their large number of quantum states. We present a computationally efficient reduced rate equation (RE) model that reproduces the experimentally observed variation of THz power with respect to drive current and heat-sink temperature. We also present dynamic (time-domain) simulations under a range of drive currents and predict an increase in modulation bandwidth as the current approaches the peak of the light–current curve, as observed experimentally in mid-infrared QCLs. We account for temperature and bias dependence of the carrier lifetimes, gain, and injection efficiency, calculated from a full rate equation model. The temperature dependence of the simulated threshold current, emitted power, and cut-off current are thus all reproduced accurately with only one fitting parameter, the interface roughness, in the full REs. We propose that the model could therefore be used for rapid dynamical simulation of QCL designs.

Model for a pulsed terahertz quantum cascade laser under optical feedback

“…This approach properly reproduces the experimentally-measured light-current characteristics of the free-running QCL over its entire dynamic range of operation [39], when the collection efficiency of the detection system is accounted for. Figure 2 shows the laboratory measured light-current-voltage (L-I-V) characteristics of our exemplar QCL, for a range of cold finger temperatures.…”

“…Using this model, we reproduce all optical feedback-related phenomena, including the compounding effect of re-injected photons on laser electro-optical dynamics, external cavity oscillations [36], altered threshold current [37,38], and modulation bandwidth [39]. In most lasers, changes in temperature or drive current [40] cause a slight perturbation in the emission frequency.…”

“…This initial fitting process allows the RRE model to be solved any number of times for different choices of current-drive excitation, ambient temperature and external cavity characteristics. Reference [39] describes the free-running model.…”

“…However, since they do not account fully for the thermal and electric field (bias) dependence of the RRE parameters, they cannot correctly predict QCL behavior under arbitrary excitation signals such as low duty-cycle pulsing. By contrast, our model accounts for both the bias and temperature dependence of the RRE parameters by using the approach described in [39]. First, the Schrödinger and Poisson equations were solved self-consistently with a full scattering transport-energy balance RE model of the RRE parameters G, η 3 , η 2 , τ 3 , τ 32 , and τ 21 (see Table 1 and Eqs.…”

Terahertz quantum cascade laser bandwidth prediction

“…More information about the structure of the device can be found in [7], and the full set of rate and thermal equations for our model is detailed in [8]. The rate equation parameters comprising gain, carrier lifetimes, and injection efficiencies, were calculated specifically for our exemplar QCL using the structure of the device as input to a S-P solver for the full rate equations.…”