Relative intensity noise (RIN), describes the instability in the

power Power most often refers to: * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power * Power (social and political), the ability to influence people or events ** Abusive power Power may a ...

level of a

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...

. The noise term is important to describe lasers used in

fiber-optic communication Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of infrared light through an optical fiber. The light is a form of carrier wave that is modulated to carry information. Fiber is pref ...

and

LIDAR Lidar (, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranges (variable distance) by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It can also be ...

remote sensing. Relative intensity noise can be generated from

cavity Cavity may refer to: Biology and healthcare *Body cavity, a fluid-filled space in many animals where organs typically develop **Gastrovascular cavity, the primary organ of digestion and circulation in cnidarians and flatworms *Dental cavity or too ...

vibration, fluctuations in the

laser gain medium The active laser medium (also called gain medium or lasing medium) is the source of optical gain within a laser. The gain results from the stimulated emission of photons through electronic or molecular transitions to a lower energy state from a ...

or simply from transferred intensity noise from a pump source. Since intensity noise typically is proportional to the

intensity Intensity may refer to: In colloquial use *Strength (disambiguation) *Amplitude * Level (disambiguation) * Magnitude (disambiguation) In physical sciences Physics *Intensity (physics), power per unit area (W/m2) *Field strength of electric, ma ...

, the ''relative'' intensity noise is typically independent of laser power. Hence, when the signal to noise ratio (SNR) is limited by RIN, it does not depend on laser power. In contrast, when SNR is limited by

shot noise Shot noise or Poisson noise is a type of noise which can be modeled by a Poisson process. In electronics shot noise originates from the discrete nature of electric charge. Shot noise also occurs in photon counting in optical devices, where shot ...

, it improves with increasing laser power. RIN typically peaks at the relaxation oscillation frequency of the laser then falls off at higher frequencies until it converges to the shot noise level. The roll off frequency sets what is specified as the RIN bandwidth. RIN is sometimes referred to as a kind of 1/f noise otherwise known as

pink noise Pink noise or noise is a signal or process with a frequency spectrum such that the power spectral density (power per frequency interval) is inversely proportional to the frequency of the signal. In pink noise, each octave interval (halving ...

. Relative intensity noise is measured by sampling the output current of a

photodetector Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. There is a wide variety of photodetectors which may be classified by mechanism of detection, such as Photoelectric effect, photoelectric or photoc ...

over time and transforming this data set into frequency with a

fast Fourier transform A fast Fourier transform (FFT) is an algorithm that computes the discrete Fourier transform (DFT) of a sequence, or its inverse (IDFT). Fourier analysis converts a signal from its original domain (often time or space) to a representation in th ...

. Alternatively, it can be measured by analyzing the spectrum of the photodetected signal using an electrical spectrum analyzer. Noise observed in the electrical domain is proportional to electric current squared and hence to optical power squared. Therefore, RIN is usually presented as relative fluctuation in the square of the optical power in

decibel The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a po ...

s per

hertz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that on ...

over the RIN bandwidth and at one or several optical intensities. It may also be specified as a percentage, a value that represents the relative fluctuations per Hz multiplied by the RIN bandwidth.

External reference

Intensity noise
in ''Encyclopedia of Laser Physics and Technology''

in ''Encyclopedia of Laser Physics and Technology'' Noise (electronics) Fiber-optic communications Laser science {{optics-stub

See also

External reference