Simulation of optical communication systems using direct and external modulation

In this work we present an analysis of the performance of optical communication systems using two types of modulation: direct and external. The analysis was based on mathematical models., which was implemented by using of PC SIMFO, a packet of simulation of optical systems developed by Photonic Technology Lab (LTF-UNICAMP). We used a nonlinear dispersive optical fiber and we optimized the optical source for this medium. By using both a Mach-Zehnder optical modulator and electro-absorption modulator we obtained external modulation by using a CW laser. The DFB semiconductor laser was used in the direct modulation. The receiver block used was the same for both types of modulators, and a PIN photodiode with a pre-amplifier circuit and an electrical filter were used to fabricate it. The performance of system was analyzed using the signal-noise ratio (SNR), bit error rate (BER) a and power penalty in the output of a receiver for both, direct and external modulation in a WDM link, considering many systemic parameters like frequency chirping; phase noise and cut-off frequency of 3rd order Butterworth filter.