Electrical equivalent circuit models for optical components are useful as they allow existing, well-developed circuit simulators to be used in design and analysis of optoelectronic devices. A circuit simulator also allows integration with electrical components (package parasitic, laser driver circuit, etc.). Equivalent circuit models were developed and investigated for some optoelectronic circuit elements, including p-i-n diodes, laser diodes, and waveguide modulators (Bononi et al., 1997; Chen et al., 2000; Desai et al., 1993; Jou et al., 2002; Mortazy & Moravvej-Farshi, 2005; Tsou & Pulfrey, 1997). The features of erbium-doped fiber amplifiers (EDFAs) are continuously investigated because of their great importance in optical communication systems. In order to design and analyze the characteristics of EDFAs, it is essential to have an accurate model. A dynamic model of EDFAs is helpful to understand the transient behavior in networks. The EDFA dynamics can also be used to monitor information in optical networks (Murakami et al., 1996; Shimizu et al., 1993). In this chapter, using a new circuit model for EDFAs, the static and dynamic characteristics of EDFAs can be analyzed conveniently through the aid of a SPICE simulator. The dc gain, amplified spontaneous emission (ASE) spectrum, frequency response and transient analysis of EDFAs can be simulated. Semiconductor optical amplifiers (SOAs) are also important components for optical networks. They are very attractive for their wide gain spectrum, and capability of integration with other devices. In the linear regime, they can be used for both booster and in-line amplifiers (O’Mahony, 1988; Settembre et al., 1997; Simon, 1987). Also, much research activities have been done on all-optical signal processing with SOAs (Danielsen et al., 1998; Durhuus et al., 1996). Laser diodes (LDs) are similar devices to SOAs, and they are also the key components for various applications ranging from high-end and high-speed (i.e. fiber communications, and compact-disc players) to low-end and low-speed (i.e. laser pointers, and laser displays) systems. In this chapter, a new unified equivalent circuit model for SOAs and LDs is also presented.