{{Short description|Optical multiplexer component}}'''Arrayed waveguide gratings''' ('''AWG''') are commonly used as [[Optical add-drop multiplexer|optical (de)multiplexer]]s in [[wavelength division multiplexing|wavelength division multiplexed]] (WDM) systems. These devices are capable of [[multiplexing]] many [[wavelength]]s into a single [[optical fiber]], thereby increasing the [[Transmission (telecommunications)|transmission]] capacity of [[optical communication|optical networks]] considerably.<ref name=":0">{{Cite web |last=Paschotta |first=Dr Rüdiger |title=Arrayed waveguide gratings |url=https://www.rp-photonics.com/arrayed_waveguide_gratings.html |access-date=2023-06-15 |website=RP Photonics AG |date=16 April 2005 |language=en}}</ref>
The devices are based on a fundamental principle of [[optics]], which states that [[light wave]]s of different wavelengths [[Interference (wave propagation)|do not interfere]] linearly with each other. This means that, if each [[communication channel|channel]] in an [[optical communication]] network makes use of [[light]] of a slightly different wavelength, then the light from many of these channels can be carried by a single optical fiber with negligible [[crosstalk (electronics)|crosstalk]] between the channels. The AWGs are used to multiplex channels of several wavelengths onto a single optical fiber at the transmission end and are also used as [[demultiplexer]]s to retrieve individual channels of different wavelengths at the receiving end of an optical communication network.<ref name=":0" />
== Operation of AWG devices ==
[[Image:Arrayed-Waveguide-Grating.svg|center|frame|The incoming light '''(1)''' traverses a free space '''(2)''' and enters a bundle of optical fibers or channel waveguides '''(3)'''. The fibers have different length and thus apply a different [[Phase (waves)|phase shift]] at the exit of the fibers. The light then traverses another free space '''(4)''' and interferes at the entries of the output waveguides '''(5)''' in such a way that each output channel receives only light of a certain wavelength. The orange lines only illustrate the light path. The light path from '''(1)''' to '''(5)''' is a demultiplexer, from '''(5)''' to '''(1)''' a multiplexer.]]
Conventional [[silica]]-based AWGs, as illustrated in the figure above, are [[Plane (geometry)|planar]] lightwave circuits fabricated by depositing layers of [[doping (semiconductor)|doped and undoped]] silica on a [[wafer (electronics)|silicon substrate]].
The AWGs consist of a number of input ''(1)'' and output ''(5)'' couplers, a free space [[wave propagation|propagation]] region ''(2)'' and ''(4)'' and the grating [[waveguide]]s ''(3)''. The grating waveguides consists of many waveguides, each having a constant length increment (ΔL).
* Light is coupled into the device via an optical fiber ''(1)'' connected to the input port. * Light [[diffraction|diffracting]] out of the input waveguide at the coupler/slab interface propagates through the free-space region ''(2)'' and illuminates the grating with a [[normal distribution|Gaussian distribution]]. * Each wavelength of light coupled to the grating waveguides ''(3)'' undergoes a constant change of [[phase (waves)|phase]] attributed to the constant length increment in grating waveguides. * The diffracted light from each waveguide within the grating undergoes [[constructive interference]], resulting in a [[Focus (optics)|refocusing]] of the light at the output waveguides ''(5).'' The spatial position of the output channels is wavelength-dependent, determined by the array [[phase shift]] induced by the constant length increment in the grating waveguides.<ref>{{Cite book |last=Hecht |first=Jeff |title=Understanding Fiber Optics |year=2015}}</ref>
== References == {{Reflist}} [[Category:Optical devices]] [[Category:Photonics]] [[Category:Fiber optics]] [[Category:Multiplexing]]