Technical Bulletin N°1

Experts in Next Generation Lightwave Test Equipment

DPSK analysis

Complex Spectrum Analyzer AP1040A application note

Measurement configuration :

We can see two symetric lobes arising and getting closer to the main peak. This is the signature of the relaxation oscillation resonance in energy exchange between electrons and photons inside the cavity of a semiconductor laser. When injection current I decreases, the resonance amplitude increase and its frequency decrease : - The resonance amplitude is inversely proportional to SQRT(I-Io) (Where Io is the treshold current) - The resonance frequency is proportional to SQRT(I-Io) (Where Io is the treshold current) The maximum direct-modulation rate of a laser is directly related to the location of this resonance. This phenomenon can not be seen with a standard optical spectrum analyzer. Only an ultra high resolution OSA like the AP2040A can resolve such fine details.

Comparison between a standard OSA and AP2040A :

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