Optical amplifiers are an important component of a fiber optic communication system. The most common use of optical amplifiers is to provide amplification of an optical signal. Noise- and nonlinearity-related properties in amplifiers also make them suitable for a wide variety of specialized applications including wideband optical sources and nonlinearity-induced format and wavelength converters. OptSim has a rich library of different types of optical amplifiers. Broadly speaking, the optical amplifier library in OptSim can be divided into two groups: behavioral models and physical models. Physical models include fiber (Raman and parametric, for example), doped-fiber (Er-, and Yb-, for example) based amplifiers, and semiconductor optical amplifiers (reflective and non-reflective). Behavioral models include fixed-gain, saturable gain and fixed output optical amplifiers.
Here we provide system design tips on two commonly used models: fixed optical output amplifiers and fixed optical gain amplifiers. The most common application of a fixed optical gain amplifier is to compensate for the signal loss in optical fibers. On the other hand, fixed optical power amplifiers help maintain optical power to a desired level by automatically setting its small-signal gain, G. The evaluation of output optical power, Pout, in both cases takes into account internally generated amplified spontaneous emission (ASE) noise, PASE, via the noise figure parameter:
Pout= G Pin+PASE
This has an interesting implication when multiple stages of these amplifiers are used in long-haul transmission systems. Let’s consider a long-haul system with multiple spans of fixed gain optical amplifiers: