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Laser Chirp
Definition
Chirp is a measure of the change in transmitter optical frequency as the transmitter is modulated. Chirp is often expressed by the alpha term,
where j is the optical phase of the signal and P is the signal power.
Standards
SONet/SDH specifies a range of allowed a values for transmitters as defined in GR-253-Core.
Test tool
High Resolution Spectrometer 83453A, Lightwave Signal Analyzer 71400C or Time Resolved Chirp measured on an OSA 86146B /DCA 86100B combination.
Measurement Subtleties
Transmitter chirp can combine with chromatic dispersion leading to reduced pulse power, increased jitter and thus higher BER or reduced transmission distance. High levels of chirp can also limit channel spacing in DWDM systems.
Small amounts of chirp however can mitigate non-linear effects caused by high spectral density such as Stimulated Brillouin Scattering and Four Wave Mixing.
Related Measurements:
Transmitter Dispersion Penalty (TDP).
