Characterization of the chirp behavior of integrated laser modulators (ILM) by measurements of its optical spectrum

In this work we present a characterization of the chirp parameters of a commercially available ILM by means of measurements made with a high-resolution optical spectrum analyzer. Particularly, we will use the FM/AM method for the characterization of the transient chirp parameter and will compare results with the standard Fibre Transfer Function method. The FM/AM method will be applied to frequencies down to 100 MHz due to the capabilities of the high-resolution optical spectrum analyzer. We will see that, for the studied ILM, the transient chirp parameter varies in such a way that it changes from positive to negative values when the bias voltage applied to the device changes from 0 to -1,5 volts. Moreover, we will also characterize the adiabatic chirp of the device, which is a parameter difficult to measure due to the small value it has compared with directly modulated lasers. In this case, the possibility of measuring optical frequencies with extremely high resolution will simplify the measurement and will provide accurate values for this parameter.