Novel optoelectronic simulation strategy of an ultra-fast InP/InGaAsP modulator

In this paper, we detail a new simulation strategy for the accurate prediction of the functionality of InP-based photonic devices. The device under analysis is simulated by means of a commercially available finite-element solver in order to exactly account for the distribution of carriers in the guiding region while another tool calculates the refractive index profile. Due to the semiconductor nature of the multilayer substrate, this is proved to be important in order to consider the effect of carriers in the depleted region that contributes, together with the linear and quadratic electric-field related ones to the overall refractive index change. In order to interface the two FEM solvers, an in-house linking code has been developed. Such a code computes the refractive optical index distribution from the results of the electrical device simulations. Moreover, it makes the grid used by the electrical solver compatible with the software adopted for the optical analysis. The errors related to grid interpolation are then eliminated. As an application, the functionalities of a InP/InGaAsP Mach-Zehnder modulator have been simulated. The presented numerical results, indicating a reverse bias voltage of 5.5 V for a 180° phase shift in a 2-mm-long device, are confirmed by measured data. Transient simulations predict that the analyzed structure is eligible for 40 Gbit/s operation.