Efficient material‐gain models for the transmission‐line laser model

Transmission‐line laser models (TLLMs) are time‐domain models suitable for the simulation of complex phenomena in semiconductor lasers. TLLMs include time‐domain filters based on transmission‐line stubs to model the spectral dependence of the material gain. In this paper, numerical simulations are presented which show that the accuracy of these gain models is dependent on the model's iteration timestep. Analytical formulae are derived that relate the accuracy of the filters to the timestep, filter centre frequency, and filter bandwindth. A new wideband stub filter which allows the material gain to be modelled using a larger timestep is presented. This is equivalent to a digital infinite‐impulse‐response filter, which is more computationally efficient than finite‐impulse‐response filters, and is unconditionally stable. The new gain model can improve the computational speed for simulating for multimode Fabry‐Perot lasers by a factor of 10–100.