Optical signal in the presence of noise
Noise in optical measurements

Like any physical measurement, optical measurement involves extracting a signal containing information about the quantity to be evaluated. Experimentally, measurement always involves detecting an intensity (i.e. energy), using a receiver.

These measurements are temporal, when we study variations in a quantity as a function of time. The position of the detector is then fixed. Examples include variations in the intensity emitted by a source, measurements of the absorption of a medium, phase delays in a signal transmitted by an optical fiber as a function of temperature variations, and so on.

Experimentally, the measurement of a quantity is always subject to error.