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<text>
 <s id="1">
    <w id="1.1">2.7</w>
    <w id="1.2">Optical</w>
    <w id="1.3">Multiplexer</w>
    <w id="1.4">and</w>
    <w id="1.5">De‐Multiplexer</w>
</s>
 <s id="2">
    <w id="2.1">A</w>
    <w id="2.2">multiplexer</w>
    <w id="2.3">(</w>
    <w id="2.4">MUX</w>
    <w id="2.5">)</w>
    <w id="2.6">is</w>
    <w id="2.7">used</w>
    <w id="2.8">to</w>
    <w id="2.9">combine</w>
    <w id="2.10">several</w>
    <w id="2.11">WDM</w>
    <w id="2.12">optical</w>
    <w id="2.13">channels</w>
    <w id="2.14">into</w>
    <w id="2.15">a</w>
    <w id="2.16">serial</w>
    <w id="2.17">spectrum</w>
    <w id="2.18">of</w>
    <w id="2.19">closely</w>
    <w id="2.20">spaced</w>
    <w id="2.21">wavelength</w>
    <w id="2.22">signals</w>
    <w id="2.23">and</w>
    <w id="2.24">couple</w>
    <w id="2.25">them</w>
    <w id="2.26">onto</w>
    <w id="2.27">a</w>
    <w id="2.28">single</w>
    <w id="2.29">fiber</w>
    <w id="2.30">.</w>
</s>
 <s id="3">
    <w id="3.1">A</w>
    <w id="3.2">de‐multiplexer</w>
    <w id="3.3">(</w>
    <w id="3.4">DMUX</w>
    <w id="3.5">)</w>
    <w id="3.6">performs</w>
    <w id="3.7">the</w>
    <w id="3.8">complementary</w>
    <w id="3.9">function</w>
    <w id="3.10">to</w>
    <w id="3.11">separate</w>
    <w id="3.12">the</w>
    <w id="3.13">optical</w>
    <w id="3.14">signals</w>
    <w id="3.15">into</w>
    <w id="3.16">appropriate</w>
    <w id="3.17">WDM</w>
    <w id="3.18">wavelength</w>
    <w id="3.19">channels</w>
    <w id="3.20">.</w>
</s>
 <s id="4">
    <w id="4.1">The</w>
    <w id="4.2">multiplexed</w>
    <w id="4.3">optical</w>
    <w id="4.4">signals</w>
    <w id="4.5">at</w>
    <w id="4.6">different</w>
    <w id="4.7">wavelengths</w>
    <w id="4.8">have</w>
    <w id="4.9">no</w>
    <w id="4.10">significant</w>
    <w id="4.11">optical</w>
    <w id="4.12">power</w>
    <w id="4.13">outside</w>
    <w id="4.14">the</w>
    <w id="4.15">designated</w>
    <w id="4.16">channel</w>
    <w id="4.17">spectral</w>
    <w id="4.18">width</w>
    <w id="4.19">;</w>
    <w id="4.20">one</w>
    <w id="4.21">,</w>
    <w id="4.22">due</w>
    <w id="4.23">to</w>
    <w id="4.24">sufficient</w>
    <w id="4.25">separation</w>
    <w id="4.26">between</w>
    <w id="4.27">the</w>
    <w id="4.28">channels</w>
    <w id="4.29">with</w>
    <w id="4.30">the</w>
    <w id="4.31">guard</w>
    <w id="4.32">bands</w>
    <w id="4.33">between</w>
    <w id="4.34">them</w>
    <w id="4.35">,</w>
    <w id="4.36">and</w>