Modeling of modulation distortion in semiconductor laser diodes

An analytical model for harmonic and intermodulation distortion resulting from the direct-current modulation of a laser diode has been developed. The model assumes a polynomial approximation for nonlinearities of the device. For a known input impedance of the laser diode and also for the output termination of the photodiode, the P-P characteristics at the fundamental, harmonic, and intermodulation frequencies can be calculated. The experimental characteristics and calculated characteristics obtained using the developed model for a 1.3-μm DFB (distributed feedback) laser diode at various bias conditions are shown. It can be seen that agreement between the model and experiment is good. The significance of the proposed nonlinear model lies in its simplicity and ease of use in subcarrier multiplexing optical system design, where the level of the intermodulation distortion presents a major limitation