Avalanche photodiodes are the primary choice for photodetection in optical access networks, due to their capacity to meet the current requirements of bandwidth and sensitivity introduced by NG-PON2. This work provides an effective tool for modeling and predicting the operation of an avalanche photodiode, paving the way to making better performing receivers. We employed Lumerical to obtain several steady state and transient parameters for a silicon germanium SACM waveguide avalanche photodiode, where close agreement is illustrated between our findings and measurements reported on fabricated devices. The utility of our work is further demonstrated by implementing and modeling a device, designed to meet certain fabrication specifications, where optimization guidelines are suggested afterwards. By providing an accurate approximation of the avalanche photodiode operation, we offer a cost-effective approach to address the problem of fabricating better devices in optical access networks. The introduced methods can be similarly used for other types of photodiodes, contributing to a vast range of applications. / Graduate