Theory of lightwave synthetic noise generation

Lightwave synthetic noise generators are instruments for microwave-photonic measurements. They facilitate the measurement of noise and bandwidth in lightwave receivers and electrical amplifiers. When synthetic noise is generated at the input of a lightwave receiver, the equivalent input noise of the receiver can easily be determined by comparing its unknown level with the known level of the synthetic noise. This report demonstrates that elementary properties of synthetic noise can be derived from a simple theoretical model. These properties include: 1) the difference between natural noise and synthetic noise, 2) requirements for reliable operation, and 3) spectral aspects. The lightwave synthetic noise generator discussed here is basically an FM modulated laser, cascaded by an interferometer with unequal arms. Illumination of a p-i-n photodiode results in an (in)coherent mix of lightwave frequencies