Arrayed waveguide grating

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An arrayed waveguide grating (AWG) (in German: "line waveguide grating") is used in optical communications technology to split light into different colors (= wavelengths) or to combine individual colored light signals into one light signal. A division into different frequencies is used to split the signals obtained in this way onto different optical waveguides or glass fibers. The opposite way is used to reunite individual fiber optic strands in one main strand. These two processes are called demultiplexing or multiplexing , depending on their direction .

In modern telecommunications, a frequency spacing of 50 GHz between different light frequencies is common. The state of the art in 2006 is a resolution of 96 frequencies over the entire available spectrum and an insertion loss of less than 4 dB.

Manufacturing

AWGs are on planar substrates - usually silicon - wafer - prepared, on which a layer is applied (for example, glass , silicon, or a polymer can be realized) in which one waveguide.

principle

The light from the input light guide (1) passes through a free beam area (2) and is fed into an arrangement of optical waveguides of different lengths (3) . After exiting these waveguides, the individual partial beams interfere in a further free beam area (4) so that only light of a certain wavelength can enter each output waveguide (5) . The orange lines are only used to illustrate the light path. The light path from (1) to (5) functions as a demultiplexer, from (5) to (1) as a multiplexer.

The functionality of an AWG can be compared to a grating spectrometer : Both serve the wavelength-selective spatial distribution of light.

The AWG consists of one or more input waveguides (1) that shine in a planar free-beam area (2) . At the end of the free beam area there are many waveguides (3) into which the light is coupled. These waveguides serve as diffraction gratings .

Another free radiation area (4) follows , into which the grating waveguides shine, at the end of which the output waveguides (5) are located. Since the light paths in the grating waveguides (3) have graduated lengths, the light interferes on the output waveguides (5) in such a way that each output channel only receives a certain wavelength range.

The entire arrangement is operable in both directions: from (1) to (5) light is split different wavelength to a plurality of fibers, which corresponds to a demultiplexer , from (5) to (1) it is brought together into a fiber, a multiplexer corresponding to .

application areas

AWGs are used in optical communication technology in WDM technology when lasers of different wavelengths are modulated with different data and transmitted to the receiver via just one fiber optic cable. In an optical transport network , these light signals can be split up again by optical cross distributors without being converted into an electrical signal and forwarded to various receivers. The receiver then also divides the light into wavelengths and detects it. This allows the data capacity of an optical fiber to be increased significantly. If only individual optical signals are to be added or removed, add-drop multiplexers are used .

literature

  • Bishnu P. Pal: Guided Wave Optical Components and Devices. Basics - Technology and Applications, Elsevier Academic Press, Amsterdam 2006.

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