NUMERICAL STUDY OF PHYSICAL PARAMETERS INFLUENCING THE PERFORMANCE OF SILICON MZI OPTICAL MODULATOR MADE WITH PLANAR PHOTONIC CRYSTAL WAVEGUIDES

In this article, we studied by numerical simulation, the physical parameters that directly affect the performance of a Mach-Zehnder electro-optic modulator fabricated with silicon on insulator technology. The arms of our modulator are formed by an optimized planar photonic crystal waveguide (PPhCW) in which we have implemented at one arm a PIN diode. The choice of this configuration allows an optimal overlap between the electromagnetic field of the PPhCW guided mode and the optical index modulation induced by the free plasma dispersion effect. In addition, the use of PPhCW in the slow light regime reduces considerably the length of the Mach-Zehnder arms. We carefully studied the limits on the modulation speed for such modulators caused by the slow transit time of injected carriers in the intrinsic region when we applied a forward-bias voltage and the slow recombination process of excess carriers after switching-off the applied forward-bias voltage. We discussed the effect on the transit time provided by increasing the forward-bias voltage value and we observed a high degradation in the spatial uniformity of the optical index modulation at the intrinsic region. We also studied the effect of the surface recombination velocity on improving the transit time and we noticed that for large values of this speed, the optical index modulation becomes highly variable in the intrinsic region. We noticed that it’s possible to reduce significantly the toff by increasing the value of the reverse voltage applied to the anode of th