Intensity modulation

<p>In <a href="/facts/Optical_communications/gshoNBto">optical communications</a>, intensity modulation (IM) is a form of <a href="/facts/Modulation/aAXPjINv">modulation</a> in which the optical <a href="/facts/Power_(physics)/mkaEyRnn">power</a> output of a source is varied in accordance with some characteristic of the modulating <a href="/facts/Signal_(information_theory)/41YqUJ8c">signal</a>. The envelope of the modulated optical signal is an analog of the modulating signal in the sense that the instantaneous power of the envelope is an analog of the characteristic of interest in the modulating signal. 
</p><p>The recovery of the modulating signal is typically achieved by direct detection, not <a href="/facts/Heterodyne/zf5Ejcey">heterodyning</a>. However, <a href="/facts/Optical_heterodyne_detection/WhGfkWjG">optical heterodyne detection</a> is possible and has been actively studied since 1979. <a href="/facts/Bell_Laboratories/fKP5Gk0H">Bell Laboratories</a> had a working, but impractical, system in 1969. Heterodyne and <a href="/facts/Homodyne/kJIExmpT">homodyne</a> systems are of interest because they are expected to produce an increase in sensitivity of up to 20 dB allowing longer hops between islands for instance. Such systems also have the important advantage of very narrow channel spacing in optical <a href="/facts/Frequency-division_multiplexing/lgj6TMU1">frequency-division multiplexing</a> (OFDM) systems. OFDM is a step beyond <a href="/facts/Wavelength-division_multiplexing/xSkNRxfu">wavelength-division multiplexing</a> (WDM). Normal WDM using direct detection does not achieve anything like the close channel spacing of <a href="/facts/Radio_frequency/aWku7h4R">radio frequency</a> FDM.
</p>

Intensity modulation open-in-new

Intensity modulation