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Detailed con fi guration of experiments
Coherent detection has been recognized for some time as offering superior
performance to direct detection. Until recently coherent receivers were
prohibitively expensive, and that is why all commercial optical communications
receivers use direct detection. However, a coherent receiver which uses real-time
digital signal processing technology can meet both the performance and cost
needs of future optical communications networks.
Most researchers have not built an actual digital processor that operates at
the relevant data rates, 10 Gb/s and higher, because of the large amount of
resources that task would consume. Instead they have employed a real-time
sampling oscilloscope, and then processed a short measurement burst of
fl ine on a
convenient computing platform. The references listed below all describe this kind
of measurement. Although the approach has been used to date to demonstrate
optical communications systems, it can also be used to record the electric
fi eld
of an optical signal, to study signal distortions, or to characterize active and
passive optical components.
References
M.G. Taylor, "Coherent detection method using DSP for demodulation of signal
and subsequent equalization of propagation impairments," IEEE Phot. Tech.
Lett., vol. 16, no. 2, p. 674-676, 2004.
M.G. Taylor, "Measurement of phase diagrams of optical communication signals
using sampled coherent detection," NIST Tech. Dig.: Symp. Optical Fiber
Measurement, Boulder, CO, vol. 1024, p. 163-166, Sep. 2004.
D.-S. Ly-Gagnon, K. Katoh, K. Kikuchi, "Unrepeatered optical transmission of
20 Gbit/s quadrature phase-shift keying signals over 210km using homodyne
phase-diversity receiver and digital signal processing," IEE Electron. Lett., vol.
41, no. 4, p. 59-60, 2005.
OM4000D Series Coherent Lightwave Signal Analyzer 77