fiber Bragg grating

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fiber Bragg grating

A short length of optical fiber that filters out a particular wavelength. Periodically spaced zones in the fiber core are altered to have different refractive indexes slightly higher than the core. This structure selectively reflects a very narrow range of wavelengths while transmitting others. Fiber Bragg gratings are used to stabilize the output of a laser and to filter out wavelengths in a WDM system.

The name comes from Bragg's Law, which is used to create the spacing of the changes. Sir William Lawrence Bragg, noted British physicist (1890-1971) discovered this in his study of x-rays and crystal structures. See diffraction grating and WDM.

A Fiber Bragg Grating
Fiber Bragg gratings such as this one from JDS Uniphase can be customized for a variety of applications covering a range of wavelength bands from 850 to 1650 nm. (Image courtesy of JDS Uniphase.)

The Gratings Reflect
In this example, the red wavelength matches the grating period and is reflected. The blue wavelength is transmitted because it does not match the grating spacings. (Illustration assistance courtesy of Jeff Hecht.)

Optical Circulators
Since the desired wavelength is reflected back by the grating, another device known as an "optical circulator" detects and switches it. (Illustration courtesy of Jeff Hecht.)
References in periodicals archive ?
The SmartAccel-HF is a single-axis Fibre Bragg Grating (FBG) acceleration sensor.
The temperature and humidity probe, also made in City University's laboratories, is based around the fibre Bragg grating, a type of reflector made of a short length of optical fibre that bounces back specific wavelengths of light and transmits all others.
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King; Fabrication and characterization of fibre Bragg gratings for near 2 [micron]m operation, Meas.
Contract Awarded for Engineering Services for Fibre Bragg Gratings
What is being tested are fibre bragg gratings, developed by the university, which allow researchers to see in real time what strains and stresses the immensely-strong carbon fibre masts undergo as the yacht tacks and turns.