Lumerical . Their GPU-FDTD is 10x–50x faster than pure CPU solvers. RSoft’s GPU support is lagging.
For calculating waveguide modes, fiber modes, and propagation constants. rsoft vs lumerical
: Utilizes a diverse "multi-engine" approach. Beyond FDTD, RSoft is well-known for its Beam Propagation Method (BPM) , which is significantly faster and less memory-intensive for long structures like tapered waveguides or fiber couplers where light travels primarily in one direction. User Experience and Programming Lumerical