Relative intensity noise

Relative intensity noise (RIN), describes the instability in the power level of a laser. The noise term is important to describe lasers used in fiber-optic communication and LIDAR remote sensing.

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Relative intensity noise can be generated from cavity vibration, fluctuations in the laser gain medium or simply from transferred intensity noise from a pump source. Since intensity noise typically is proportional to the intensity, the relative intensity noise is typically independent of laser power. RIN typically falls off with frequency and is a kind of pink noise.

Relative intensity noise is measured by sampling the output current of a photodetector over time and transforming this data set into frequency with a fast Fourier transform. RIN is usually presented as relative noise power in decibels per hertz at one or several intensities.