Frequency-dependent and frequency-independent nonlinear characteristics of a high-speed laser diode

It was experimentally demonstrated that a laser diode (LD) can be treated as a memoryless nonlinear device. It was found that for an operating condition with modulation depth below about 60%, the relative time delay (which ranges from zero to several hundred picoseconds) caused by increased modulation depth has a strong effect on the frequency-dependent intermodulation products. In this case, the radiofrequency bandwidth over which the LD can be considered to be effectively memoryless has to be smaller than the inverse of the measured time delay, by two order of magnitude. Increased optical reflections from fiber connectors were observed to cause significant fluctuations of the measured time delay as a function of frequency and thus cause more pronounced frequency-dependent nonlinear behavior. A high speed InGaAsP LD with a threshold current of 15 mA and a 3 dB bandwidth of 6 GHz was used in the experiment.<>