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| An '''Optical DPSK demodulator''' is a device that provides a method for converting an optical [[differential phase-shift keying]] (DPSK) signal to an intensity-keyed signal at the receiving end in [[fiber-optic communication]] networks. It is also known as [[delay line interferometer]] (DLI), or simply called '''DPSK demodulator'''.<ref>[http://www.optoplex.com/DPSK_Demodulator.htm DPSK demodulation for fiber-optic communications]</ref><ref>[http://216.234.124.74/ITFLabs/Products.php?locale=en&Line_no=13&sub_category_id=155&cat_category_id=138 All-Fiber Delay line interferometer and Optical DPSK demodulator]</ref>
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| [[Image:DPSK-Demodulation.gif|thumb|488px|right|Working principle of optical DPSK demodulation: (a) Incoming DPSK signal with uniform intensity, (b) 1-bit delay of the incoming DPSK signal with uniform intensity, and (c) Demodulated intensity signal after interference between (a)/(a') and (b)/(b').]]
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| The DPSK decoding method is achieved by comparing the [[Phase (waves)|phase]] of two sequential bits. An incoming DPSK optical signal is first split into two beams with equal intensities, in which one beam is delayed in space by an [[optical path difference]] that introduces a [[time delay]] corresponding to ''one bit''. The two beams in the two paths are then coherently recombined to [[Interference (wave propagation)|interfere]] each other constructively or destructively. The interference intensity is measured and becomes the intensity-keyed signal. A typical optical system for such a purpose is [[Mach-Zehnder interferometer]] or [[Michelson interferometer]], forming an optical DPSK Demodulator.
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| Delay time depends on the [[Bit rate|data rate]]. For instance, in a 40 Gbit/s system, one bit corresponds to 25 picoseconds, and light travels 5 mm in a [[fiber optics]] or 7.5 mm in [[free space]] within that period. Thus the optical path difference between the two beams is 5 mm or 7.5 mm depending on the type of interferometer used.
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| [[DQPSK]]<ref>[http://www.optoplex.com/DQPSK_Demodulator.htm DQPSK Demodulators]</ref><ref>[http://www.kylia.com/dpsk.html Tunable DPSK demodulator for DQPSK application]</ref> is the four-level version of DPSK. DQPSK transmits two bits for every symbol (bit combinations being 00, 01, 11 and 10) and has an additional advantage over conventional binary DPSK. DQPSK has a narrower optical spectrum, which tolerates more dispersion (both chromatic and polarization-mode), allows for stronger optical filtering, and enables closer channel spacing. As a result, DQPSK allows processing of 40 Gbit/s data-rate in a 50 GHz channel spacing system. A demodulator for optical DQPSK signals can be constructed using two matched DPSK demodulators with phase off-set at <math>\pm \pi/4</math>.
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| ==References==
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| <references/>
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| {{DEFAULTSORT:DPSK demodulator, optical}}
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| [[Category:Fiber-optic communications]]
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| [[Category:Photonics]]
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Revision as of 06:49, 23 February 2014
Oscar is what my spouse enjoys to call me and I totally dig that title. What I adore doing is performing ceramics but I haven't produced a dime with it. Her family members life in Minnesota. I am a meter reader but I strategy on changing it.
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