The main laser parameters are:
- Amplitude Noise (RIN). Dominates in direct detection scheme particularly in analog systems Frequency or Phase Noise;
- Frequency Stability;
- Output Power;
- Tuning Range (Frequency).
In frequency modulation (FM) formats phase or frequency, fluctuations compete with the signal. Reducing these fluctuations increases a signal to noise ratio. A laser signal may be used to interrogate path length changes in sensors such as a fiber Bragg grating (FBG) or Mach-Zehnder interferometer (MZI). If the frequency or phase of the laser changes it appears as a change of the path length thus degrading the signal to noise ratio.
There are different types of low phase noise lasers:
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