It is commonly believed that optical amplifiers will play a key role in future telecommunication networks. There are two main types of optical amplifiers. One is an Erbium doped fibre amplifier (EDFA) and the other is a semiconductor laser amplifier (SLA). The advantages of SLA's are their ease of integration with other integrated optical components and their multifunctionality. Among the optical functions that an SLA can perform are amplification, amplitude modulation, phase modulation, detection and wavelength conversion. This paper will concentrate on the modelling and simulation of SLA's used as transparent in-line detectors in optical ring-networks. A software tool will be presented that includes large-signal time-dependent analysis, multiple optical input signals, amplified spontaneous emission, multi-section devices and residual mirror reflection.