Measuring complex optical modulation in fiber
Lightwave Magazine Feb 2010
by Daniel van der Weide

As carriers seek to squeeze more spectral efficiency from their fiber plants while managing costs in long-haul DWDM, multilevel modulation formats beyond conventional on-off keying (OOK) become candidates for deployment. These formats include coherent dual-polarization quadrature phase-shift keying (DP-QPSK), quadrature amplitude modulation (QAM), and many variations of orthogonal frequency-division multiplexing (OFDM). All seek to optimize among competing characteristics like reach, robustness, simplicity, and spectral efficiency. Read Full Article

Staying ahead of test requirements a bigger stretch than ever
Lightwave Magazine Dec 2009
by Stephen Hardy

Test, measurement, and management provide the foundation for fiber optics (or any other communications medium, for that matter). Particularly in the lab instrument niche, test and measurement equipment suppliers have to remain at least one step ahead of designers’ requirements. Therefore, as the rapidly developing trends highlighted in our other forecast articles illustrate, test, measurement, and monitoring vendors will have their work cut out for them in 2010. Read Full Article

Optical Constellation Analyzers Tackle Complex Measurements
Lightwave Magazine Dec 2009
by Megan Fuller Hanna

In test applications, typical binary modulation schemes such as on/off keying (OOK), in which only one bit is transmitted per symbol, are amplitude-based and can be directly detected using a high-speed photodiode with a sampling oscilloscope. The measurement results from this digital communications analyzer (DCA) are well understood; high power is a one, no power is a zero. Read Full Article

Automating Bit-Error-Rate Measurements
of Complex Modulated Optical Signals
Daniel van der Weide, Optametra
dan@optametra.com

Introduction: Common to all digital communications systems is the need to characterize bit error rates (BER). In radio or wireline communications, BER is usually plotted vs. signalto‐ noise (SNR) ratio, resulting in “waterfall curves”, log‐log plots usually showing a decline in BER at some critical SNR, which becomes a benchmark of the system. Fiber communications links are also characterized by BER vs. optical signal‐to‐noise ratio (OSNR) or vs. received optical power (ROP)...

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