Editing Spectrum analyzer (section)

== Optical spectrum analyzer ==
{{main|Optical spectrometer}}
An optical spectrum analyzer uses reflective or refractive techniques to separate out the wavelengths of light. An electro-optical detector is used to measure the intensity of the light, which is then normally displayed on a screen in a similar manner to a radio- or audio-frequency spectrum analyzer.

The input to an optical spectrum analyzer may be simply via an aperture in the instrument's case, an optical fiber or an optical connector to which a fiber-optic cable can be attached.

Different techniques exist for separating out the wavelengths. One method is to use a [[monochromator]], for example a Czerny–Turner design, with an optical detector placed at the output slit. As the grating in the monochromator moves, bands of different frequencies (colors) are 'seen' by the detector, and the resulting signal can then be plotted on a display. More precise measurements (down to MHz in the optical spectrum) can be made with a scanning [[Fabry–Pérot interferometer]] along with analog or digital control electronics, which sweep the resonant frequency of an optically resonant cavity using a voltage ramp to [[Piezoelectricity#Piezoelectric motors|piezoelectric motor]] that varies the distance between two highly reflective mirrors. A sensitive [[photodiode]] embedded in the cavity provides an intensity signal, which is plotted against the ramp voltage to produce a visual representation of the optical power spectrum.<ref>Final Report {{cite web |url=http://mason.gmu.edu/~jdilles/capstone/ |title=Team Spectrum |access-date=2015-04-08 |url-status=live |archive-url=https://web.archive.org/web/20160817164232/http://mason.gmu.edu/~jdilles/capstone/ |archive-date=2016-08-17 }}</ref>

The frequency response of optical spectrum analyzers tends to be relatively limited, e.g. {{nowrap|800–1600 nm}} (near-infrared), depending on the intended purpose, although (somewhat) wider-bandwidth general purpose instruments are available.