Extended Koch's model for chirp assessment in semiconductor singlemode lasers operating at high currents

Semiconductor singlemode laser chirp models that discriminate the adiabatic and the transient frequency chirp components are very relevant and useful, as they allow evaluating per se the effects of both chirp components on directly modulated (DM) laser communication system performance. For this purpose, Koch's model has been extensively used, showing high accuracy for low and moderate laser current regimes.This paper aims at proposing an extended Koch's (e-Koch's) model that allows its accurate use in high current regimes for an arbitrary functional form of the laser nonlinear gain compression factor. High current regimes are commonly found in high bit-rate optical communication systems, in order to achieve sufficient laser intensity modulation bandwidth. Frequency chirping predictions by the proposed model, assessed by numerical simulation, show good agreement with the ones estimated by the laser rate equations, for both linear and logarithmic carrier density dependent laser gain models. It is also shown that e-Koch's model provides good estimates of the performance of 40 Gbit/s DM laser multi-span system.

► A new model to discriminate the adiabatic and transient chirps in DMLs is proposed.
► The model is valid for an arbitrary functional form of the nonlinear gain compression.
► The model accuracy has been tested for both linear and logarithmic DML gain model.