To support the design of optoelectronic systems using NIRS (Near-Infrared Spectroscopy), we have enhanced and evaluated an open-source software that uses the Monte-Carlo simulation method to model photon propagation in biological tissues. These enhancements enable accurate estimation of the MOP (Mean Optical Path) and penetration depth of incident light, offering researchers tools to simulate and analyze light behavior in biological tissues. We validated these improvements by applying them to both single-layer and multi-layer tissues. The software now features a crucial function to calculate the transmission and reflection rates based on the area and position of the photodetection zone. Validation results indicated that the relative error between the calculated and theoretical transmis- sion and reflection rates was within acceptable limits. These enhancements significantly enhance the software’s practicality, aiding researchers in better understanding and utilizing NIRS technology. Thus, simulations of human ankle tissue with the upgraded software confirmed the enhancements’ effectiveness through MOP analysis that photons reached the ligament layer.