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Encyclopedia of Laser Physics and Technology

Bandwidth

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Definition: the width of some frequency or wavelength range

In photonics, the term bandwidth occurs with a variety of meanings:

Optical bandwidth values may be specified in terms of frequency or wavelength. Due to the inverse relationship of frequency and wavelength, the conversion factor between gigahertz and nanometers depends on the center wavelength or frequency. For converting a (small) wavelength interval into a frequency interval, the equation

wavelength to frequency interval

can be used. This shows that 1 nm is worth more gigahertz if the center wavelength is shorter.

The term bandwidth is also often used for the data rate (e.g. in Gbit/s) achieved in an optical communication system. Precisely, the data rate is limited by the optical bandwidth, but is not really itself a bandwidth.

The optical bandwidth of a light source is strongly related to the temporal coherence, characterized with the coherence time.

Both for passive resonators (e.g. optical cavities) and for the output of oscillators (e.g. lasers), the Q factor is the oscillation frequency divided by the bandwidth.

See also: time–bandwidth product, gain bandwidth, coherence time, transform limit, Q factor, phase-matching bandwidth

Category: physical foundations


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Since October 2008, the Encyclopedia of Laser Physics and Technology is also available in the form of a two-volume book. Maybe you would enjoy reading it also in that form! The print version has a carefully designed layout and can be considered a must-have for any institute library, laser research group, or laser company.

You may order the print version via Wiley-VCH.

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