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<title>Arrayed waveguide grating</title>
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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Arrayed waveguide grating</span></span>
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<div id="mw-content-text" class="mw-body-content mw-content-ltr" lang="en" dir="ltr"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><p><b>Arrayed waveguide gratings</b> (<b>AWG</b>) are commonly used as <a href="Optical_add-drop_multiplexer" title="Optical add-drop multiplexer">optical (de)multiplexers</a> in <a href="Wavelength_division_multiplexing" class="mw-redirect" title="Wavelength division multiplexing">wavelength division multiplexed</a> (WDM) systems. These devices are capable of <a href="Multiplexing" title="Multiplexing">multiplexing</a> many <a href="Wavelength" title="Wavelength">wavelengths</a> into a single <a href="Optical_fiber" title="Optical fiber">optical fiber</a>, thereby increasing the <a href="Transmission_(telecommunications)" class="mw-redirect" title="Transmission (telecommunications)">transmission</a> capacity of <a href="Optical_communication" title="Optical communication">optical networks</a> considerably.<sup id="cite_ref-:0_1-0" class="reference"><a href="#cite_note-:0-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>
</p><p>The devices are based on a fundamental principle of <a href="Optics" title="Optics">optics</a>, which states that <a href="Light_wave" class="mw-redirect" title="Light wave">light waves</a> of different wavelengths <a href="Interference_(wave_propagation)" class="mw-redirect" title="Interference (wave propagation)">do not interfere</a> linearly with each other. This means that, if each <a href="Communication_channel" title="Communication channel">channel</a> in an <a href="Optical_communication" title="Optical communication">optical communication</a> network makes use of <a href="Light" title="Light">light</a> of a slightly different wavelength, then the light from many of these channels can be carried by a single optical fiber with negligible <a href="Crosstalk_(electronics)" class="mw-redirect" title="Crosstalk (electronics)">crosstalk</a> 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 <a href="Demultiplexer" class="mw-redirect" title="Demultiplexer">demultiplexers</a> to retrieve individual channels of different wavelengths at the receiving end of an optical communication network.<sup id="cite_ref-:0_1-1" class="reference"><a href="#cite_note-:0-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>
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<div class="mw-heading mw-heading2"><h2 id="Operation_of_AWG_devices">Operation of AWG devices</h2></div>
<p>Conventional <a href="Silica" class="mw-redirect" title="Silica">silica</a>-based AWGs, as illustrated in the figure above, are <a href="Plane_(geometry)" class="mw-redirect" title="Plane (geometry)">planar</a> lightwave circuits fabricated by depositing layers of <a href="Doping_(semiconductor)" title="Doping (semiconductor)">doped and undoped</a> silica on a <a href="Wafer_(electronics)" title="Wafer (electronics)">silicon substrate</a>.
</p><p>The AWGs consist of a number of input <i>(1)</i> and output <i>(5)</i> couplers, a free space <a href="Wave_propagation" class="mw-redirect" title="Wave propagation">propagation</a> region <i>(2)</i> and <i>(4)</i> and the grating <a href="Waveguide" title="Waveguide">waveguides</a> <i>(3)</i>. The grating waveguides consists of many waveguides, each having a constant length increment (ΔL).
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<ul><li>Light is coupled into the device via an optical fiber <i>(1)</i> connected to the input port.</li>
<li>Light <a href="Diffraction" title="Diffraction">diffracting</a> out of the input waveguide at the coupler/slab interface propagates through the free-space region <i>(2)</i> and illuminates the grating with a <a href="Normal_distribution" title="Normal distribution">Gaussian distribution</a>.</li>
<li>Each wavelength of light coupled to the grating waveguides <i>(3)</i> undergoes a constant change of <a href="Phase_(waves)" title="Phase (waves)">phase</a> attributed to the constant length increment in grating waveguides.</li>
<li>The diffracted light from each waveguide within the grating undergoes <a href="Constructive_interference" class="mw-redirect" title="Constructive interference">constructive interference</a>, resulting in a <a href="Focus_(optics)" title="Focus (optics)">refocusing</a> of the light at the output waveguides <i>(5).</i> The spatial position of the output channels is wavelength-dependent, determined by the array <a href="Phase_shift" class="mw-redirect" title="Phase shift">phase shift</a> induced by the constant length increment in the grating waveguides.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup></li></ul>
<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>
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<li id="cite_note-:0-1"><span class="mw-cite-backlink">^ <a href="#cite_ref-:0_1-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-:0_1-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">
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</style><cite id="CITEREFPaschotta2005" class="citation web cs1">Paschotta, Dr Rüdiger (16 April 2005). <a rel="nofollow" class="external text" href="https://www.rp-photonics.com/arrayed_waveguide_gratings.html">"Arrayed waveguide gratings"</a>. <i>RP Photonics AG</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2023-06-15</span></span>.</cite></span>
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<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><cite id="CITEREFHecht2015" class="citation book cs1">Hecht, Jeff (2015). <i>Understanding Fiber Optics</i>.</cite></span>
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