Semiconductor saturable-absorber mirrors (SESAMs) can also be used to mode lock fiber lasers. A major advantage SESAMs have over other saturable absorber techniques is that absorber parameters can be easily tailored to meet the needs of a particular laser design. For example, saturation fluence can be controlled by varying the reflectivity of the top reflector while modulation depth and recovery time can be tailored by changing the low temperature growing conditions for the absorber layers. This freedom of design has further extended the application of SESAMs into modelocking of fiber lasers where a relatively high modulation depth is needed to ensure self-starting and operation stability. Fiber lasers working at 1 µm and 1.5 µm were successfully demonstrated.