Optimization of photonics design depends on the computer aided design (CAD)/computer aided engineering (CAE) system intended for the purpose. Photonics simulators include comprehensive numerical models and interconnection with bidirectional interfaces, and must optimize transmission bandwidth and distance as well as active device design. Emphasis is placed on models for semiconductor laser simulation. Multi-wavelength lasers are identified by multimode lasers for long-haul fiber communication models where transmission line laser modelling (TLLM) requires the cavity to be divided into sections each represented by scattering matrices. Beside a laser model for a photonic circuits and systems simulator, an appropriate user interface is also necessary.