Technical Bulletin N°7

Experts in Next Generation Lightwave Test Equipment

Complex Spectrum Analyzer : The new tool for a complete modulation characterization

Optical Complex Spectrum Analyzer AP2440A application note

Introduction : With the ever increasing channel bit rates, several new modulation formats were established all aimed to reduce performance degradation caused by interaction of dispersion and nonlinearity. DPSK, QPSK, chirp characteristics, return to zero (RZ) are just a few on this list. Channel narrowing and increasing speeds requires comprehensive test instruments to adequately measure overall system performance and is where the Optical Complex Spectrum Analyzer (CSA or OCSA) comes in.

What is an Optical Complex Spectrum Analyzer? An optical complex spectrum analyzer is an optical spectrum analyzer able to characterize the amplitude and relative phase of each individual optical spectral component of a modulated signal giving what we called 'the optical complex spectrum'. After this, a Fourrier transform (FTT) method is applied to convert SPECTRAL DOMAIN <optical complex spectrum> into TIME DOMAIN.   More details on the measurement principle Advantages for high speed system : No speed limit!

Applications (click on the measurement to enlarge and display comments) 40Gb/s RZ pulse and adiabatic chirp 10Gb/s DPSK signal (intensity and phase measurement) 40Gb/s NRZ eye diagram Spectrum comparison between 10Gb/s NRZ and 10Gb/s duobinary 10Gb/s NRZ pulse and transient chirp 40Gb/s Alpha parameter

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