12 Important Optical Spectrum Analyzer Glossary Terms

Optical Spectrum Analyzer

An optical spectrum analyzer is a device used to measure optical power as a function of wavelength. This type of technology is used primarily to test the spectral purity and distribution of power in LED (light-emitting diode) and laser light sources. It can also be used to test the quality of transmission in optical devices.


Bandwidth is the unit of measurement used to denote a fiberoptic cable's capacity to carry data. Bandwidth is most frequently measured in hertz.

Double-Pass Monochromator

Double-pass monochromators offer twice the resolution in the refraction and diffraction elements over traditional monochromators. While this device does not result in a narrower band of light waves, it does offer the user the ability to detect lower level signals with ease while preserving the integrity of the light source throughout duration of use.

Dynamic Range

Dynamic range, commonly abbreviated as DR or DNR, refers to the ratio of a designated maximum level of a predetermined parameter (such as sound or light) to the minimum perceptible level of the same parameter. It can also be described as the ratio between the largest and smallest values within a given variable range.

Fresnel reflection

In the realm of optics, Fresnel reflection refers to the reflection of a fraction of light between two media (when these two media possess different indices of refraction). This occurs at both ends of an optical fiber (at the air-glass interfaces).

Graded-Index Fiber

Also known as gradient-index fiber, graded-index fiber is a type of optical fiber with a refractive inner core characterized by concentric rings of glass, silica or another similar material. It is used to increase the bandwidth of optical fiber via the reduction of modal dispersion.


A diffraction grating is an optical component imprinted with a pattern comprised of minute periodic structures or grooves. It is similar to a lens, prism or mirror, as it is used to disperse light in a specific manner conducive to production of a desired image. A reflection grating works in a similar way, dispersing light through wavelength, though the grooved surface of this type of grating is coated with metal to enhance reflection potential.

Michelson Interferometer

A Michelson interferometer is one of the three major types of optical spectrum analyzers. Splitting and recombining multiple beams of light, the device calculates the Fourier transform of a pattern of measured interference. Known for its role in the Michelson-Morley experiment, the interferometer assisted in proving the theory of special relativity. It is most commonly used to measure direct coherence-length waves and in the detection of gravitational waves.


A monochromator is a device that transmits the separated and narrowed portion of a wider range of optical wavelengths. Monochromators are used in a variety of optical measuring tools, including spectrometers and other imaging devices.

Multimode Fiber

With the ability to transmit multiple rays of light or optical modes simultaneously, multimode fiber is a type of optical fiber used to transfer data over relatively short distances. The construction of multimode fiber results in the reflection of light rays in minutely different angles in relation to one another.

Resolution Bandwidth (RBW)

Resolution bandwidth refers to the smallest frequency that can be resolved within a measured spectrum. RBW is a fundamental form of measurement in the realm of spectral analysis, as it delivers the frequency accuracy, or precision, of a given measurement.

Single-Mode Fiber

Single-mode fiber (often called monomode fiber) is one of the most frequently used components of fiberoptic technology. It has a smaller core than multimode, carries only one ray of light at a time and is used to transmit data over longer distances. Due to its ability to maintain the integrity of a light pulse over long distances, single-mode fiber is also able to carry a higher bandwidth than multi-mode fiber.